Observation of von K\\'arm\\'an Vortex Street in a Bose-Einstein Condensate
Kwon, Woo Jin; Seo, Sang Won; Shin, Y
2016-01-01
We report on the experimental observation of von K\\'arm\\'an street of quantum vortex clusters generated from a moving obstacle in a highly oblate Bose-Einstein condensate. For a low obstacle velocity $v$ above a critical value, we observe regular shedding of vortex clusters each consisting of two like-sign vortices, and as $v$ is increased, we find that the shedding pattern becomes irregular with many different kinds of vortex clusters. The transition from a von K\\'arm\\'an street regime to turbulence reveals remarkable similarities between a superfluid and a classical viscous fluid. Our work opens a new direction for experimental investigations of the superfluid Reynolds number characterizing universal superfluid hydrodynamics.
Namer, I.
1980-12-01
The interaction of a premixed C2H4-air flame with a Karman vortex street was studied. Laser Doppler anemometry was used for velocity measurements and Rayleigh scattering was used to measure total gas density. A reference hot wire was used to enable phase-locked ensemble averaging to be performed on the data. The velocity measurements for vortex shedding cylinder Reynolds numbers indicated that the vortex street and, hence, the flow field upstream of the flame is deflected by the flame. This is due to the pressure drop across the flame which is necessary to accelerate the flow behind the flame. The vortices were not observed behind the flame. The combination of dilation and increased dissipation consumed the vortices. Density statistics obtained from Rayleigh scattering measurements were compared with predictions by the Bray-Moss-Libby (B-M-L) model which neglects intermediate states. Density fluctuations were overpredicted by the B-M-L model by a small amount.
Real-time visualization of Karman vortex street in water flow field by using digital holography.
Sun, Weiwei; Zhao, Jianlin; Di, Jianglei; Wang, Qian; Wang, Le
2009-10-26
The Karman vortex street generated behind a circular cylinder in water flow field is displayed and analyzed in real time by means of digital holography. Using a modified Mach-Zehnder interferometer, a digital hologram of the flow field in still state and then a video of continuous digital holograms in flowing state are recorded at 14.6 frames per second by a CCD camera, respectively. A series of sequential phase maps of the flow field are numerically reconstructed from the holograms in different states above based on double-exposure holographic interferometry. By seriating these phase maps, the shape and evolution of Karman vortex street can be displayed in real time in the form of a movie. For comparison, numerical simulation of the Karman vortex street under the boundary conditions adopted in the experiment is also presented, and the consistent results indicate that the experimental observation of Karman vortex street by using digital holography is successful and feasible.
Kinematics and forces of a flexible body in Karman vortex street
Institute of Scientific and Technical Information of China (English)
WANG SiYing; JIA LaiBing; YIN XieZhen
2009-01-01
Experiments of a flexible filament in the wake of a cylinder and in free stream were conducted in a ver-tical soap film tunnel. The experiments distinctly visualized the movement of the filament. Based on the experimental kinematic results, a 2-d panel method was used to calculate the forces acting on the filament. The experiment and numerical results revealed that different from that in free stream, the filament in Karman vortex street flapped at the same frequency as the vortex street, and with smaller amplitude and larger curvature. The filament suffered an evident thrust in Karman vortex street, while a drag appeared in the case of free stream. The dependence of the drag coefficient on the phase relation between the movement of the filament and the Karman vortex street was also studied.
Lee, C.; Chung, M. K.; Kim, Y.-H.
1993-06-01
An analytical model is presented for predicting the vortex shedding noise generated from the wake of axial flow fan blades. The downstream wake of a fan blade is assumed to be dominated by the von Karman vortex street, and the strength and the shedding frequency of the wake vortex are determined from the wake structure model. The fluctuating pressure and lift on the blade surface, which are induced from the vortices in the wake, are analyzed by incorporating the wake model for the von Karman vortex street with thin airfoil theory. The predicted vortex shedding frequency and the overall sound pressure level compare favorably with the measured results for the vortex shedding noise from axial flow fans.
Institute of Scientific and Technical Information of China (English)
Su Wanxing; Li Shipeng; Zhang Qiao; Li Junwei; Ye Qingqing; Wang Ningfei
2013-01-01
Vortex-acoustic coupling is one of the most important potential sources of combustion instability in solid rocket motors (SRMs).Based on the Von Karman Institute for Fluid Dynamics (VKI) experimental motor,the influence of the thermal inhibitor position and temperature on vortex-shedding-driven pressure oscillations is numerically studied via the large eddy simulation (LES)method.The simulation results demonstrate that vortex shedding is a periodic process and its accurate frequency can be numerically obtained.Acoustic modes could be easily excited by vortex shedding.The vortex shedding frequency and second acoustic frequency dominate the pressure oscillation characteristics in the chamber.Thermal inhibitor position and gas temperature have little effect on vortex shedding frequency,but have great impact on pressure oscillation amplitude.Pressure amplitude is much higher when the thermal inhibitor locates at the acoustic velocity anti-nodes.The farther the thermal inhibitor is to the nozzle head,the more vortex energy would be dissipated by the turbulence.Therefore,the vortex shedding amplitude at the second acoustic velocity antinode near 3/4L (L is chamber length) is larger than those of others.Besides,the natural acoustic frequencies increase with the gas temperature.As the vortex shedding frequency departs from the natural acoustic frequency,the vortex-acoustic feedback loop is decoupled.Consequently,both the vortex shedding and acoustic amplitudes decrease rapidly.
The “von Karman vortex street” to the west of Big Island
Institute of Scientific and Technical Information of China (English)
LIUWei; LIUQinyu
2004-01-01
Satellite-tracked drifting buoy data and altimetry data are used to study the active vortex field to the west of Big Island. A pair of vortexes were observed at the trajectory of buoy in 1995. The westward propagation of the vortex pair is studied in detail by reproducing the loops of each vortex. The orbital period and radius of the pair of vortex are determined to be 10-11 d and 58-68 km. Two arrays of contra-rotating vortices are displayed in the average sea surface height anomaly (SSHA) field to the west of Big Island. Based on the calculation of the fluid dynamical parameter, the “von Karman vortex street” is proved to be generated to the west of Big Island as the North Equatorial Current impinges upon Big Island from the east. Finally, the analysis of the buoy trajectories in a decade contributes to the conclusion of the pattern of VKVS in a statistical view.
Influence of the Karman Vortex Street on the Broadband Noise Generated from a Multiblade Fan
Institute of Scientific and Technical Information of China (English)
Souichi SASAKI; Yoshio KODAMA; Hidechito HAYASHI; Makoto HATAKEYAMA
2005-01-01
In the prediction theory for the broadband noise generated from a multiblade fan, the vortices in the Karman vortex street was divided into n pieces. The frequency distribution of the noise was estimated so that the Strouhal number could become constant even if the wake is spread by the diffusion. From the results of the measurement of the internal flow of the fan, it was found that the noise was related to the wake characteristics of the specific location in the scroll casing where the relative flow velocity was high. The noise operating in the vicinity of the maximum efficiency point of the fan was distributed over the domain from 500 Hz to 1250 Hz. It was experimentally proved that the influence of the Karman vortex street on the noise in the domains of high and low frequencies did not exist when the distribution of the estimated sound pressure level corresponded to the measured broadband noise.
A Karman-Vortex Generator for passive separation control in a conical diffuser
Institute of Scientific and Technical Information of China (English)
ZHANG YuFei; CHEN HaiXin; FU Song
2012-01-01
Flow separation in a conical diffuser with large divergence angle (29.14°) and large area ratio (3.533) is eliminated by a novel passive flow control device called Karman-Vortex Generator (KVG).The effect of the KVG is verified and investigated by the URANS,DES and DDES methods based on the SST model.CFD results show that the performance coefficient of the diffuser can be doubled by the KVG,and the total pressure recovery coefficient can be improved by about 1.2％.DES and DDES resuits show that the KVG can introduce a Karman-vortex street frequency in the diffuser.This frequency decays rapidly,and could not be detected in the ending plane of the expansion section.Different KVG configurations with different locations and dimensions are numerically simulated and compared.Some suggestions are provided.
Dynamic Optimization for Vortex Shedding Suppression
Directory of Open Access Journals (Sweden)
Bonis Ioannis
2016-01-01
Full Text Available Flows around structures exhibiting vortex shedding induce vibrations that can potentially damage the structure. A way to avoid it is to suppress vortex shedding by controlling the wake. Wake control of laminar flow behind a rotating cylinder is formulated herein as a dynamic optimization problem. Angular cylinder speed is the manipulated variable that is adjusted to suppress vortex shedding by minimizing lift coefficient variation. The optimal angular speed is assumed to be periodic like wake formation. The control problem is solved for different time horizons tH. The impact of tH to control is evaluated and the need for feedback is assessed.
Vortex Shedding From a Flexible Hydrofoil
Dreyer, Matthieu; Farhat, Mohamed
2011-01-01
Video of vortex shedding in the wake of a Naca0009 hydrofoil made of polyoxymethylene type C (POM C). This video was submitted as part of the Gallery of Fluid Motion 2011 which is showcase of fluid dynamics videos.
Vortex shedding by a Savonius rotor
Botrini, M.; Beguier, C.; Chauvin, A.; Brun, R.
1984-05-01
A series of flow visualizations was performed to characterize the wake vortices of a Savonius rotor. The trials were undertaken in an attempt to account for discrepancies between theoretical and experimentally-derived power coefficients. The Savonius examined was two-bladed with a center offset. All tests were made in a water tunnel. Dye injection provided the visualization, and average velocities and velocity fluctuations were measured using a laser Doppler anemometer. A system of three vortices was found to be periodically shed by the rotor. Flow velocity fluctuation intensity peaked as a vortex was shed. The vortex shedding alternated from blade to blade, so that one was shed from a blade moving upstream.
Vortex shedding effects in grid-generated turbulence
Melina, G.; Bruce, P. J. K.; Vassilicos, J. C.
2016-08-01
The flow on the centerline of grid-generated turbulence is characterized via hot-wire anemometry for three grids with different geometry: a regular grid (RG60), a fractal grid (FSG17), and a single-square grid (SSG). Due to a higher value of the thickness t0 of its bars, SSG produces greater values of turbulence intensity Tu than FSG17, despite SSG having a smaller blockage ratio. However, the higher Tu for SSG is mainly due to a more pronounced vortex shedding contribution. The effects of vortex shedding suppression along the streamwise direction x are studied by testing a three-dimensional configuration, formed by SSG and a set of four splitter plates detached from the grid (SSG+SP). When vortex shedding is damped, the centerline location of the peak of turbulence intensity xpeak moves downstream and Tu considerably decreases in the production region. For FSG17 the vortex shedding is less intense and it disappears more quickly, in terms of x /xpeak , when compared to all the other configurations. When vortex shedding is attenuated, the integral length scale Lu grows more slowly in the streamwise direction, this being verified both for FSG17 and for SSG+SP. In the production region, there is a correlation between the vortex shedding energy and the skewness and the flatness of the velocity fluctuations. When vortex shedding is not significant, the skewness is highly negative and the flatness is much larger than 3. On the opposite side, when vortex shedding is prominent, the non-Gaussian behavior of the velocity fluctuations becomes masked.
A Schlieren and Hot-Wire Investigation of Karman Vortex Streets.
1985-12-13
Sons, 1976. 15. Miller, Alan R. BASIC Programs for Scientists and Engineers. Berkeley: Sybex, Inc., 1981, 179-182. 16. Bronson , Richard . Operations...rotational fluid, bounded by irrotational fluid or solid walls" (9:1). Schlichting shows a theoretical vortex as having an approximately linear ... algebraically , and is fully developed in Appendix A. The analysis is based on the assumption that each vortex is of the form (Pu) (cl/r) (l-exp(-c r) (9) 1 2
Suppression of vortex shedding around a square cylinder using blowing
Indian Academy of Sciences (India)
Arun K Saha; Ankit Shrivastava
2015-05-01
Direct numerical simulation (DNS) of flow past a square cylinder at a Reynolds number of 100 has been carried out to explore the effect of blowing in the form of jet(s) on vortex shedding. Higher order spatial as well as temporal discretization has been employed for the discretization of governing equations. The varying number of jets, jet velocity profiles and different blowing velocities are studied to investigate the characteristics of vortex shedding. The parabolic velocity profile has been found to be more effective in suppressing the vortex shedding as compared to the uniform velocity. Complete suppression of vortex shedding along with remarkable reduction in drag coefficient has been achieved for both jet velocity profiles but at different velocities. The corresponding values for uniform and parabolic jet profiles are 0.87 and 0.6, respectively at a mass flux of 0.120. The study also reveals that there is considerable effect of the number of jets on the vortex shedding phenomena.
What information do Karman streets offer to flow sensing?
Energy Technology Data Exchange (ETDEWEB)
Akanyeti, Otar; Venturelli, Roberto; Visentin, Francesco; Fiorini, Paolo [Department of Computer Science, University of Verona, 37134 Verona (Italy); Chambers, Lily; Megill, William M, E-mail: otarakanyeti@yahoo.com [Department of Mechanical Engineering, University of Bath, Bath BA2 7AY (United Kingdom)
2011-09-15
In this work, we focus on biomimetic lateral line sensing in Karman vortex streets. After generating a Karman street in a controlled environment, we examine the hydrodynamic images obtained with digital particle image velocimetry (DPIV). On the grounds that positioning in the flow and interaction with the vortices govern bio-inspired underwater locomotion, we inspect the fluid in the swimming robot frame of reference. We spatially subsample the flow field obtained using DPIV to emulate the local flow around the body. In particular, we look at various sensor configurations in order to reliably identify the vortex shedding frequency, wake wavelength and downstream flow speed. Moreover, we propose methods that differentiate between being in and out of the Karman street with >70% accuracy, distinguish right from left with respect to Karman vortex street centreline (>80%) and highlight when the sensor system enters the vortex formation zone (>75%). Finally, we present a method that estimates the relative position of a sensor array with respect to the vortex formation point within 15% error margin.
How do seal whiskers suppress vortex shedding
Rinehart, Aidan; Flaherty, Justin; Bunjavick, Joseph; Shyam, Vikram; Zhang, Wei
2016-11-01
Certain seal whiskers possess a unique geometry that significantly reduces the vortex-induced vibration; which has attracted great attention to understand how the unique shape re-organizes the wake structure and its potential for passive flow control. The shape of the whiskers can be described as an elliptical cross-section that is lofted along the length of the whisker. Along the entire length of the whisker the ellipse varies in major and minor axis as well as angle of incidence with respect to the axis of the whisker. Of particular interest in this study is to identify what effect the angle of incidence has on the flow structure around the whisker, which has been overlooked in the past. The study will analyze the wake structure behind various scaled-up whisker models using particle image velocimitry (PIV). These whisker models share common geometry dimensions except for the angle of incidence. Flow conditions are created in a water channel and a wind tunnel, covering a wide range of Reynolds number (a few hundreds to thousands), similar to the ambient flow environment of seals and to the targeted aero-propulsion applications. This study will help address knowledge gaps in understanding of how certain geometry features of seal whiskers influence the wake and establish best practices for its application as effective passive flow control strategy.
On aerodynamic noise generation from vortex shedding in rotating blades
Martin, B. T.; Bies, D. A.
1992-06-01
The interaction of the shed wakes of plates in a cascade with each following plate is investigated in a water tunnel and shown to provide an explanation for an observed very powerful aerodynamic noise source. In particular, the noise generation of an idling circular saw may be explained as due to the interaction of the wake shed by an upstream tooth with the leading edge of the following downstream tooth. When a vortex travelling downstream in the gullet between teeth encounters the leading edge of the downstream tooth it is deflected out of the gullet into the main stream. The associated impulses which the teeth encounter give rise to the radiated noise.
Control of Vortex Shedding at Moderate Reynolds Numbers
Institute of Scientific and Technical Information of China (English)
邵传平; 鄂学全; 魏庆鼎; 朱凤荣
2002-01-01
The suppression method of vortex shedding from a circular cylinder has been studied experimentally in the Reynoldsnumber range from 300 to 1600. The test is performed in a water channel. The model cylinder is 1 cm in diameter and 38cm in length. A row of small rods of 0. 18 cm in diameter and 1.5 cm in length are perpendicularly connected to the surfaceof the model cylinder and distributed along the meridian. The distance between the neighboring rods and the angle of attackof the rods can be changed so that the suppression effect on vortex shedding can be adjusted. The results show that vortexshedding can be suppressed effectively if the distance between the neighboring rods is smaller than 3 times and the cylinderdiameter and the angle of attack is in the range of 30°≤β < 90°.
Vortex Shedding from Tapered Cylinders at high Reynolds Numbers
DEFF Research Database (Denmark)
Johansson, Jens; Andersen, Michael Styrk; Christensen, Silas Sverre
2015-01-01
percent for strakes of circular cross section. The present paper argues that this height can be reduced for structures where the critical wind velocity for vortex shedding is in the Supercritical Reynolds number regime. The present investigations are aimed for suppressing VIV on offshore wind turbine......^5 (Supercritical). Results indicate that circular strakes with a diameter corresponding to 3 percent of the structures mean diameter can be used to efficiently reduce VIV in the Supercritical Reynolds number regime....
Laminar vortex shedding behind a cooled circular cylinder
Trávníček, Zdeněk; Wang, An-Bang; Tu, Wen-Yun
2014-02-01
This paper addresses the functional demonstration of a hot air flow generator driven by convective heat transfer and the airflow behind a cooled circular cylinder in cross flow in the low velocity range. The wake flow was investigated experimentally using flow visualization, hot-wire anemometry, and laser Doppler anemometry. An evaluation of the free-stream velocity from the vortex shedding frequency was derived for the isothermal and non-isothermal cases and demonstrated using simple stroboscope measurements. The results confirm that cylinder cooling destabilizes the wake flow in air, i.e., the laminar steady regime can be changed into the vortex shedding regime, and the vortex shedding frequency increases as the cylinder temperature decreases. This thermal effect of cylinder cooling is consistent with its counterpart, the known effect of flow stabilization by cylinder heating. The effective temperature and effective Reynolds number concept have been further quantitatively evaluated, and the extension of their validity to the case of cooled cylinders has been confirmed.
On vortex shedding and prediction of vortex-induced vibrations of circular cylinders
Energy Technology Data Exchange (ETDEWEB)
Halse, Karl Henning
1997-12-31
In offshore installations, many crucial components can be classified as slender marine structures: risers, mooring lines, umbilicals and cables, pipelines. This thesis studies the vortex shedding phenomenon and the problem of predicting vortex-induced vibrations of such structures. As the development of hydrocarbons move to deeper waters, the importance of accurately predicting the vortex-induced response has increased and so the need for proper response prediction methods is large. This work presents an extensive review of existing research publications about vortex shedding from circular cylinders and the vortex-induced vibrations of cylinders and the different numerical approaches to modelling the fluid flow. The response predictions from different methods are found to disagree, both in response shapes and in vibration amplitudes. This work presents a prediction method that uses a fully three-dimensional structural finite element model integrated with a laminar two-dimensional Navier-Stokes solution modelling the fluid flow. This solution is used to study the flow both around a fixed cylinder and in a flexibly mounted one-degree-of-freedom system. It is found that the vortex-shedding process (in the low Reynolds number regime) is well described by the computer program, and that the vortex-induced vibration of the flexibly mounted section do reflect the typical dynamic characteristics of lock-in oscillations. However, the exact behaviour of the experimental results found in the literature was not reproduced. The response of the three-dimensional structural model is larger than the expected difference between a mode shape and a flexibly mounted section. This is due to the use of independent hydrodynamic sections along the cylinder. The predicted response is not unrealistic, and the method is considered a powerful tool. 221 refs., 138 figs., 36 tabs.
Leading-edge vortex shedding from rotating wings
Kolomenskiy, Dmitry; Schneider, Kai
2014-01-01
The paper presents a numerical investigation of the leading-edge vortices generated by rotating triangular wings at Reynolds number $Re=250$. A series of three-dimensional numerical simulations have been carried out using a Fourier pseudo-spectral method with volume penalization. The transition from stable attachment of the leading-edge vortex to periodic vortex shedding is explored, as a function of the wing aspect ratio and the angle of attack. It is found that, in a stable configuration, the spanwise flow in the recirculation bubble past the wing is due to the centrifugal force, incompressibility and viscous stresses. For the flow outside of the bubble, an inviscid model of spanwise flow is presented.
Ancilotto, Francesco; Barranco, Manuel; Eloranta, Jussi; Pi, Martí
2017-08-01
Two-dimensional flow past an infinitely long cylinder of nanoscopic radius in superfluid 4He at zero temperature is studied using time-dependent density-functional theory. The calculations reveal two distinct critical phenomena for the onset of dissipation: (i) vortex-antivortex pair shedding from the periphery of the moving cylinder, and (ii) the appearance of cavitation in the wake, which possesses similar geometry to that observed experimentally for fast-moving micrometer-scale particles in superfluid 4He. The formation of cavitation bubbles behind the cylinder is accompanied by a sudden jump in the drag exerted on the moving cylinder by the fluid. Vortex pairs with the same circulation are occasionally emitted in the form of dimers, which constitute the building blocks for the Benard-von Karman vortex street structure observed in classical turbulent fluids and Bose-Einstein condensates. The cavitation-induced dissipation mechanism should be common to all superfluids that are self-bound and have a finite surface tension, which include the recently discovered self-bound droplets in ultracold Bose gases. These systems would provide an ideal testing ground for further exploration of this mechanism experimentally.
INVESTIGATION OF VORTEX SHEDDING INDUCED HYDRODYNAMIC VIBRATION IN VORTEX STREET FLOWMETER
Institute of Scientific and Technical Information of China (English)
无
2001-01-01
Vortex street flowmeter has been used in steady flo w measurement for about three decades. The benefits of this type of flowmeter i nclude high accuracy,good linearty,wide measuring range,and excellent reliabilit y. However,in unsteady flow measurement,the pressure disturbance as well as the noise from the system or surrounding can reduce the signal-to-noise ra tio of the flowmeter seriously. Aimed to use vortex street flowmeters in unstea dy flow measurement,the characteristics of the vortex shedding induced hydrodyna mic vibration around the prism bluff body in a vortex street flowmeter are inves tigated numerically and by expriments. The results show that the hydrodynamic vibrations with 180° phase shift occur at the axisymmetric points of the channe l around the bluff body. The most intense vibration occurs at the points on the lateral faces close to the base of the prism. The results provide therefore a useful reference for developing an anti-interference vortex flowmeter using the differential sensing technique.
Vortex Shedding in the Wake of a Dual Step Cylinder
Morton, Chris
2012-01-01
A dual-step cylinder is comprised of a large diameter cylinder (D) with low aspect ratio (L/D) attached co-axially to the mid-span of a small diameter cylinder (d). The fluid dynamics video presented in this investigation is used to illustrate the effect of aspect ratio on dual step cylinder wake development for Re = 2100, D/d = 2, and 0.2 < L/D < 3. In addition, the video provides visualization of such flow phenomena as interaction of spanwise vortices, development of streamwise vortex filaments, and formation of Kelvin-Helmholtz rollers. The experiments were performed in a water flume at the University of Waterloo. A hydrogen bubble flow visualization technique was employed to visualize vortical structures downstream of each cylinder model. High-resolution images of the flow were obtained with a high speed Photron camera and post-processed using Adobe Photoshop CS4. The results show a plethora of vortices developing in the wake of the dual step cylinder. For 1 < L/D < 3, spanwise vortex shedding...
Vortex shedding noise of a cylinder with hairy flaps
Kamps, Laura; Geyer, Thomas F.; Sarradj, Ennes; Brücker, Christoph
2017-02-01
This study describes the modification of acoustic noise emitted from cylinders in a stationary subsonic flow for a cylinder equipped with flexible hairy flaps at the aft part as a passive way to manipulate the flow and acoustics. The study was motivated by the results from previous water tunnel measurements, which demonstrated that hairy flaps can modify the shedding cycle behind the cylinder and can reduce the wake deficit. In the present study, wind tunnel experiments were conducted on such a modified cylinder and the results were compared to the reference case of a plain cylinder. The acoustic spectrum was measured using two microphones while simultaneously recording the flap motion. To further examine the flow structures in the downstream vicinity of the cylinder, constant temperature anemometry measurements as well as flow visualizations were also performed. The results show that, above a certain Reynolds number, the hairy flaps lead to a jump in the vortex shedding frequency. This phenomenon is similarly observed in the water flow experiments as a jump in the non-dimensional Strouhal number that is related to the change of the shedding cycle. This jump appears to be coupled to a resonant excitation of the flaps. The specific Reynolds number at which the jump occurs is higher in the present case, which is attributed to the lower added mass in air as compared with the one in water. The flow visualizations confirmed that such action of the flaps lead to a more slender elongated shape of the time-averaged separation bubble. In addition, the hairy flaps induce a noticeable reduction of the tonal noise as well as broadband noise as long as the flaps do not touch each other.
Hot-Wire Calibration at Low Velocities: Revisiting the Vortex Shedding Method
Directory of Open Access Journals (Sweden)
Sohrab S. Sattarzadeh
2013-01-01
Full Text Available The necessity to calibrate hot-wire probes against a known velocity causes problems at low velocities, due to the inherent inaccuracy of pressure transducers at low differential pressures. The vortex shedding calibration method is in this respect a recommended technique to obtain calibration data at low velocities, due to its simplicity and accuracy. However, it has mainly been applied in a low and narrow Reynolds number range known as the laminar vortex shedding regime. Here, on the other hand, we propose to utilize the irregular vortex shedding regime and show where the probe needs to be placed with respect to the cylinder in order to obtain unambiguous calibration data.
Institute of Scientific and Technical Information of China (English)
庞立军; 吕桂萍; 钟苏; 刘晶石
2011-01-01
研究三峡右岸部分机组水轮机固定导叶出水边处的卡门涡街共振问题.根据机组的实际运行情况和产生异常噪声的特点,应用计算流体力学(Computational fluid dynamics,CFD)数值分析技术对固定导叶开展出水边处的涡街振动模拟,建立模拟涡街振动的CFD数值模型,采用Fluent软件实现对卡门涡街振动特性的定量分析；同时采用流固耦合分析方法对固定导叶进行水下动态特性分析,获得结构在水中的固有频率.分析表明,固定导叶的卡门涡街频率与其在水中的固有频率是非常接近的,容易发生耦合并造成局部振动.结合现场振动与噪声测试加以验证,确定产生异常噪声的激振源,找到诱发卡门涡街共振的主要原因.通过对固定导叶不同出水边截面几何形状的对比分析,提出有效预防和消除卡门涡街共振的优化方案.%The Karman vortex shedding resonance at the trailing-edge of stay vanes in some units of right bank of Three Gorges Hydropower station is investigated. According to the actual operation of units and the characteristics of abnormal noise, the Karman vortex shedding resonance at the trailing-edge of stay vanes is simulated by using computational fluid dynamics, CFD numerical technology. Based on the CFD numerical model established, quantitative analysis on the vibration performance of Karman vortex shedding is achieved by using the software FLUENT. Then, dynamic behavior analysis of stay vanes underwater is implemented by using fluid-structure interaction method, and natural frequency of structure underwater is obtained. It is shown that the frequency of Karman vortex shedding is very close to the natural frequency of structure underwater. This phenomenon could cause interaction between them and local vibration easily. By validation with the vibration and noise test on site, vibrating source causing abnormal noise and main reasons inducing the Karman vortex shedding
Numerical Investigation on Vortex Shedding from a Hydrofoil with a Beveled Trailing Edge
Directory of Open Access Journals (Sweden)
Seung-Jae Lee
2015-01-01
study, we numerically investigated vortex shedding from various beveled trailing edges at a Reynolds number of 106. We then compared the numerical results with the experimental data, which show good agreement. We also conducted numerical simulations of wakes behind the hydrofoil at rest in periodically varying flows. Results reveal that vortex shedding is affected by the periodicity of a free-stream flow, as well as the trailing-edge shape.
Hot-Wire Calibration at Low Velocities: Revisiting the Vortex Shedding Method
Sattarzadeh, Sohrab S.; Athanasia Kalpakli; Ramis Örlü
2013-01-01
The necessity to calibrate hot-wire probes against a known velocity causes problems at low velocities, due to the inherent inaccuracy of pressure transducers at low differential pressures. The vortex shedding calibration method is in this respect a recommended technique to obtain calibration data at low velocities, due to its simplicity and accuracy. However, it has mainly been applied in a low and narrow Reynolds number range known as the laminar vortex shedding regime. Here, on the other ha...
Vortex shedding noise control in idling circular saws using air ejection at the teeth
Yanagimoto, K.; Mote, C. D.; Ichimiya, R.
1994-04-01
Aerodynamically induced noise from an idling circular saw can be very intense. The purpose of the present investigation is noise reduction through vortex shedding control in idling circular saws. Reduction of aerodynamic noise in idling circular saws may be possible by controlling the shed vortices and flow structures in the space between teeth, based on the earlier observations.
An Experimental Study of the Effect of Vortex Shedding on Solar Collector Performance
Directory of Open Access Journals (Sweden)
Alaulddin Abdulqader Kadim
2015-07-01
Full Text Available In this work, the effect of vortex shedding on the solar collector performance of the parabolic trough solar collector (PTSC was estimated experimentally. The effect of structure oscillations due to wind vortex shedding on solar collector performance degradation was estimated. The performance of PTSC is evaluated by using the useful heat gain and the thermal instantaneous efficiency. Experimental work to simulate the vortex shedding excitation was done. The useful heat gain and the thermal efficiency of the parabolic trough collector were calculated from experimental measurements with and without vortex loading. The prototype of the collector was fabricated for this purpose. The effect of vortex shedding at different operation conditions was examined. The variation of angles of attack and wind velocity leads to different values of vortex loading coefficients and shedding frequencies. The relation between the dynamic characteristics and solar collector performance was evaluated. The finite element method was used to estimate the dynamic characteristic of the solar collector in addition to experimental work to evaluate the relation between the dynamic behavior of the collector and its performance.
Theoretical Investigation of the Vortex Shedding Noise from the Wake of Airfoil%机翼尾迹脱落涡噪声的理论研究
Institute of Scientific and Technical Information of China (English)
无
2001-01-01
The vortex shedding noise has been revealed as an important wing noise source on some modern commercial aircraft based on the fly-over measurements with a planar microphone array by Michel (1998). In this paper, an analytical model is presented for predicting this vortex shedding noise. The downstream wake of a 2-dimensional airfoil is assumed to be dominated by the von Karman vortex street, and the strength and the shedding frequency of the wake vortex are determined from the wake structure model. An aero-acoustic model is developed based on the Howe's unified theory of trailing edge noise and is incorpo-rated with the wake model to predict the sound pressure level and directivity of vortex shedding noise. The predicted vortex shedding frequencies, sound pressure levels and directivities compare favorably with the measured results for 6 modern commercial aircraft.%Michel等人1998年应用平面传声器阵列对飞机过顶噪声进行的测量研究首次发现，机翼尾迹脱落涡噪声是某些类型飞机重要的噪声源。为发展一种预测这种噪声源的理论预测模型，应用von Karman涡街模型模拟二维机翼下游尾迹脱落涡，尾迹涡的强度和脱落频率应用这个模型进行计算。基于Howe后缘噪声理论，并结合尾迹模型，本文发展了一种预测脱落涡噪声声压级和指向特征的气动声学模型。对6架现代商用飞机的机翼尾迹脱落涡噪声的计算表明，本文理论模型预测的涡脱落频率、声压级以及噪声的指向性等与实验测量结果有较好的一致性。
Vortex shedding experiment with flat and curved bluff plates in water
Reed, D.; Nesman, T.; Howard, P.
1988-01-01
Vortex shedding experiments were conducted in a water flow facility in order to simulate the strong discrete 4000-Hz vibration detected in the Space Shuttle Main Engine (SSME) which is thought to be associated with the SSME LOX inlet tee splitter vanes on the Main Injector. For the case of a flat vane with a blunt trailing edge excited by flow induced vortex shedding, lock-in with the first bending mode of the plate was observed. A curved vane displayed similar behavior, with the lock-in being a more discrete higher amplitude response. Aluminum vanes were employed to decouple the first vane bending mode from the vortex shedding mode. The application of an asymmetric 30-deg trailing edge bevel to both the flat and curved vanes was found to greatly reduce the strength of the shed vortices.
Effect of steady rotation on low Reynolds number vortex shedding behind a circular cylinder
Satish, Paluri; Patwardhan, Saurabh S.; Ramesh, O. N.
2013-08-01
In this paper control of oblique vortex shedding in the wake behind a straight circular cylinder is explored experimentally and computationally. Towards this, steady rotation of the cylinder about its axis is used as a control device. Some limited studies are also performed with a stepped circular cylinder, where at the step the flow is inevitably three-dimensional irrespective of the rotation rate. When there is no rotation, the vortex shedding pattern is three dimensional as described in many previous studies. With a non-zero rotation rate, it is demonstrated experimentally as well as numerically that the shedding pattern becomes more and more two-dimensional. At sufficiently high rotation rates, the vortex shedding is completely suppressed.
Numerical simulation of terrain-induced vortex/wave shedding at the Hong Kong International Airport
Directory of Open Access Journals (Sweden)
Li Lei
2013-07-01
Full Text Available The present study aims at simulating the shedding of vortex/wave from a mountain nearby the Hong Kong International Airport using a computational fluid dynamics model by employing high resolution terrain data without smoothing. The successful simulation of this shedding would have an important application in the short-term forecasting of the chance of occurrence of terrain-induced windshear at an operating airport. Two typical cases of vortex/wave shedding are considered, namely, in neutral atmosphere associated with the passage of a typhoon, and in stably stratified atmosphere in spring-time easterly flow with continental origin. The model is found to successfully capture the salient features of the shedding. The simulated radial velocity fields of weather radar/LIDAR compare well with actual observations. In particular, the creation and the propagation of the vortex/wave through shedding from a mountain nearby the airport are captured well in the model simulation. The shedding periods are also reproduced. From the limited number of cases studied in this paper, it appears that the model has the capability of forecasting the occurrence of vortex/wave shedding by coupling with a mesoscale meteorological model.
Numerical simulation of terrain-induced vortex/wave shedding at the Hong Kong International Airport
Energy Technology Data Exchange (ETDEWEB)
Li, Lei; Zhang, Li-Jie; Mao, Hui [Shenzhen National Climate Observatory, Meteorological Bureau of Shenzhen Municipality (China); Chan, P.W. [Hong Kong Observatory (China)
2013-10-15
The present study aims at simulating the shedding of vortex/wave from a mountain nearby the Hong Kong International Airport using a computational fluid dynamics model by employing high resolution terrain data without smoothing. The successful simulation of this shedding would have an important application in the short-term forecasting of the chance of occurrence of terrain-induced windshear at an operating airport. Two typical cases of vortex/wave shedding are considered, namely, in neutral atmosphere associated with the passage of a typhoon, and in stably stratified atmosphere in spring-time easterly flow with continental origin. The model is found to successfully capture the salient features of the shedding. The simulated radial velocity fields of weather radar/LIDAR compare well with actual observations. In particular, the creation and the propagation of the vortex/wave through shedding from a mountain nearby the airport are captured well in the model simulation. The shedding periods are also reproduced. From the limited number of cases studied in this paper, it appears that the model has the capability of forecasting the occurrence of vortex/wave shedding by coupling with a mesoscale meteorological model. (orig.)
Proper orthogonal decomposition analysis of vortex shedding behind a rotating circular cylinder
Directory of Open Access Journals (Sweden)
Dol Sharul Sham
2016-01-01
Full Text Available Turbulence studies were made in the wake of a rotating circular cylinder in a uniform free stream with the objective of describing the patterns of the vortex shedding up to suppression of the periodic vortex street at high velocity ratios, λ. The results obtained in the present study establish that shedding of Kármán vortices in a rotating circular cylinder-generated wake is modified by rotation of the cylinder. Alternate vortex shedding is highly visible when λ < 2.0 although the strength of the separated shear layers differ due to the rotation of the cylinder. The spectral density in the wakes indicate significant changes at λ = 2.0. The results indicate that the rotation of the cylinder causes significant disruption in the structure of the flow. Alternate vortex shedding is weak, distorted and close to being suppressed at λ = 2.0. It is clear that flow asymmetries will weaken vortex shedding, and when the asymmetries are significant enough, total suppression of a periodic street occurs. Particular attention was paid to the decomposition of the flow using Proper Orthogonal Decomposition (POD. By analyzing this decomposition with the help of Particle Image Velocimetry (PIV data, it was found that large scales contribute to the coherent motion. Vorticity structures in the modes become increasingly irregular with downstream distance, suggesting turbulent interactions are occurring at the more downstream locations, especially when the cylinder rotates.
2012-04-01
a trade-off between static and dynamic stability is evident. 1. Introduction Requirements for rapid increase in thrust for take-off and climb ...injected through spray bars and is atomized by shearing due to the turbine exhaust flow. It then evaporates and mixes with the available oxygen. The mixture...exit through a converging/diverging nozzle with extensive film cooling and a variable throat area located downstream of the afterburner exit. The
On the origins of vortex shedding in two-dimensional incompressible flows
Boghosian, M. E.; Cassel, K. W.
2016-12-01
An exegesis of a novel mechanism leading to vortex splitting and subsequent shedding that is valid for two-dimensional incompressible, inviscid or viscous, and external or internal or wall-bounded flows, is detailed in this research. The mechanism, termed the vortex shedding mechanism (VSM) is simple and intuitive, requiring only two coincident conditions in the flow: (1) the existence of a location with zero momentum and (2) the presence of a net force having a positive divergence. Numerical solutions of several model problems illustrate causality of the VSM. Moreover, the VSM criteria is proved to be a necessary and sufficient condition for a vortex splitting event in any two-dimensional, incompressible flow. The VSM is shown to exist in several canonical problems including the external flow past a circular cylinder. Suppression of the von Kármán vortex street is demonstrated for Reynolds numbers of 100 and 400 by mitigating the VSM.
FORCE CHARACTERISTICS AND VORTEX SHEDDING OF A PITCHING FOIL IN SHEAR FLOWS
Institute of Scientific and Technical Information of China (English)
LI Dan-yong; LIU Nan-sheng; LU Xi-yun; YIN Xie-zhen
2005-01-01
The objective of this study is to deal with unsteady force acting on a pitching foil in shear flow and to study the relation of the force characteristics with vortex shedding near the foil. The two-dimensional incompressible Navier-Stokes equations in the vorticity and stream-function formulation were solved with the fourth-order essentially compact finite difference schemes for the space derivatives and a fourth-order Runge-Kutta scheme for the time advancement. The force characteristics and vortex shedding of the pitching foil in shear flows were investigated. The effects of some typical factors, including the incoming flow shear, the oscillating frequency and amplitude, on the vortex shedding and force behavior were analyzed and discussed.
Vortex Cloud Street during AMTEX 75
DEFF Research Database (Denmark)
Jensen, Niels Otto; Agee, E. M.
1978-01-01
Strong northerly flow across Cheju Island, Korea, during the 1975 Air Mass Transformation Experiment (AMTEX 75) resulted in a pronounced vortex cloud street to the lee of the island on February 17 1975. This pattern has been studied and explained in terms of classical von Karman eddies shed...
Suppression of vortex-shedding noise via derivative-free shape optimization
Marsden, Alison L.; Wang, Meng; Dennis, J. E.; Moin, Parviz
2004-10-01
In this Letter we describe the application of a derivative-free optimization technique, the surrogate management framework (SMF), for designing the shape of an airfoil trailing edge which minimizes the noise of vortex shedding. Constraints on lift and drag are enforced within SMF using a filter. Several optimal shapes have been identified for the case of laminar vortex shedding with reasonable computational cost using several shape parameters, and results show a significant reduction in acoustic power. Physical mechanisms for noise reduction are discussed.
Stochastic oscillations induced by vortex shedding in wind
DEFF Research Database (Denmark)
Christensen, Claus
1997-01-01
As a fluid flows past a circular cylinder,vortices are shed alternately from each side at most values of the Reynolds number. Over a certain range of windspeeds, the periodicity in the wake is synchronized or captured by the mechanical system. The shedding abruptly deviates from the linear Strouhal...... dependence and stays constant at the mechanical natural frequency. This coupling between the velocity field and the motion of the mechanical system is referred to as the lock-in phenomenon. The lock-in phenomenon has importance in structural engineering for slightly damped slender structures exposed to wind...... are supported by experimental wind tunnel investigations. Department of Structural Engineering and Materials, DTUSeries R No 23 1997As a fluid flows past a circular cylinder, vortices are shed alternately from each side at most values of the Reynolds number. Over a certain range of windspeeds, the periodicity...
Vortex shedding noise of a cylinder with hairy flaps
Kamps, L.; Geyer, T. F.; Sarradj, E.; Brücker, C.
2017-01-01
This study describes the modification of acoustic noise emitted from cylinders in a stationary subsonic flow for a cylinder equipped with flexible hairy flaps at the aft part as a passive way to manipulate the flow and acoustics. The study was motivated by the results from previous water tunnel measurements, which demonstrated that hairy flaps can modify the shedding cycle behind the cylinder and can reduce the wake deficit. In the present study, wind tunnel experiments were conducted on such...
Fatigue of threaded rods in cable anchorages due to Vortex shedding
Maljaars, J.; Snijder, H.H.
2013-01-01
The 'Hovenring' is a bicycle roundabout flyover built as a signature bridge with a central steel pylon carrying a circular bridge deck suspended through stay-cables. Shortly after installation of the bridge, the stay-cables turned out to vibrate in the wind due to vortex shedding. These vibrations h
Further validation of the hybrid particle-mesh method for vortex shedding flow simulations
Directory of Open Access Journals (Sweden)
Lee Seung-Jae
2015-11-01
Full Text Available This is the continuation of a numerical study on vortex shedding from a blunt trailing-edge of a hydrofoil. In our previous work (Lee et al., 2015, numerical schemes for efficient computations were successfully implemented; i.e. multiple domains, the approximation of domain boundary conditions using cubic spline functions, and particle-based domain decomposition for better load balancing. In this study, numerical results through a hybrid particle-mesh method which adopts the Vortex-In-Cell (VIC method and the Brinkman penalization model are further rigorously validated through comparison to experimental data at the Reynolds number of 2 × 106. The effects of changes in numerical parameters are also explored herein. We find that the present numerical method enables us to reasonably simulate vortex shedding phenomenon, as well as turbulent wakes of a hydrofoil.
The Transition from Thick to Thin Plate Wake Physics: Whither Vortex Shedding?
Rai, Man Mohan
2016-01-01
The near and very near wake of a flat plate with a circular trailing edge is investigated with data from direct numerical simulations. Computations were performed for six different combinations of the Reynolds numbers based on plate thickness (D) and boundary layer momentum thickness upstream of the trailing edge (theta). Unlike the case of the cylinder, these Reynolds numbers are independent parameters for the flat plate. The separating boundary layers are turbulent in all the cases investigated. One objective of the study is to understand the changes in the wake vortex shedding process as the plate thickness is reduced (increasing theta/D). The value of D varies by a factor of 16 and that of theta by approximately 5 in the computations. Vortex shedding is vigorous in the low theta/D cases with a substantial decrease in shedding intensity in the large theta/D cases. Other shedding characteristics are also significantly altered with increasing theta/D. A visualization of the shedding process in the different cases is provided and discussed. The basic shedding mechanism is explored in depth. The effect of changing theta/D on the time-averaged, near-wake velocity statistics is also discussed. A functional relationship between the shedding frequency and the Reynolds numbers mentioned above is obtained.
Vortex shedding from slender cones at low Reynolds numbers
Papangelou, A.
1992-09-01
Wind-tunnel experiments on the flows created by a number of slightly tapered models of circular cross-section have shown the presence of spanwise cells (regions of constant shedding frequency) at Reynolds numbers of the order of 100. The experiments have also shown a number of other interesting features of these flows: the cellular flow configuration is dependent on the base Reynolds number and independent of the tip Reynolds number, the frequency jump between adjacent cells is a function of flow speed, taper angle and kinematic viscosity, but is constant along a cone's span, and the unsteady hot-wire anemometer signal is both amplitude and phase modulated. A mathematical model is proposed based on the complex Landau-Stuart equation with a spanwise diffusive coupling term. Numerical solutions of this equation have shown many of the qualitative features observed in the experiments.
Interaction between leading and trailing edge vortex shedding: effects of bluff body geometry
Taylor, Zachary; Kopp, Gregory; Gurka, Roi
2011-11-01
Elongated bluff bodies are distinguished from shorter bluff bodies (e.g., circular cylinders) by the fact that they have separating-reattaching flow at the leading edge as well as having vortex shedding at the trailing edge. Engineering examples of these bodies include heat exchanger fins and long-span suspension bridges. We have performed experiments on elongated bluff bodies of varying geometry. These experiments have been performed at Reynolds numbers O(104) based on the thickness of the model. Both surface pressure measurements (using 512 simultaneously sampled pressure taps) and PIV are used to quantify the flow fields of these bodies. The leading edge separation angle is controlled by changing the leading edge geometry. It is observed that the size of the leading edge separation bubble increases with increasing leading edge separation angle. As the size of the leading edge separation bubble increases, it is shown to continually decrease the shedding frequency for a given elongation ratio. It is suggested that the shedding frequency is diminished because the trailing edge vortex shedding is affected by the structures being shed from the leading edge separation bubble. The implications of this competition between leading and trailing edge flows will be explored.
Parametric CFD study of micro-energy harvesting in a flow channel exploiting vortex shedding
Koubogiannis, Dimitrios G.
2016-05-01
Miniature energy harvesting devices are increasingly used in various fields. For example, Wireless Sensor Networks have recently made great progress in many applications. However, their main drawback, i.e. the limited duration of operation, poses the requirement for an effective way to recharge their batteries. In this context, the presentwork focuses on the study of micro-energy harvesting from flow by exploiting vortex shedding behind bluff bodies, in order to cause oscillations to a piezoelectric film and generate the required electrical power. To this end, a Computational Fluid Dynamics (CFD) tool is validated on a particular miniature device configuration proposed in the literature and implemented for the numerical simulations of flow around bluff micro-bodies in a very small channel. Aiming to enhance vortex shedding, parametric studies corresponding to different bluff body shapes and arrangements for a fixed Reynolds number are performed, the main parameters involved in the phenomenon are highlighted and the potential for vortex shedding exploitation is qualitatively assessed.
Preventing noise caused by vortex shedding in gate valves and orifices
Energy Technology Data Exchange (ETDEWEB)
Smith, B.A.W.; Luloff, B.V.; Tromp, J.H. [Atomic Energy of Canada Ltd., Chalk River, Ontario (Canada)
2000-07-01
Gate valves and high-energy orifices can both act as sources of noise. This noise can represent a simple environmental problem or, in severe cases, can cause piping failures within hours. This paper presents the results of two studies, one to eliminate noise in the main steam lines of a new reactor, and, the other, to develop design guidelines for preventing noise in multi-stage, high-energy orifices. Both the valves and orifices were found to have a common noise generation mechanism, namely, an unstable fluid shear layer (e.g., vortex shedding) coupled with a fluid-resonant condition (i.e., an acoustic resonance). The main steam line noise was round to be caused by periodic vortex shedding across the seat cavities of the main steam isolation valves. The orifice noise is thought to be due to vortex shedding within the orifice holes themselves. This paper reviews the findings of both studies and presents measures that can be taken to eliminate noise problems. (author)
Lee, L.; Allen, D.
2010-05-01
In-water vortex-induced vibration (VIV) tests of top-tensioned, flexible cylindrical structures were conducted at Shell Westhollow Technology Center current tank. These tests revealed that the top tension and structural stiffness (both lateral and axial) can have a significant impact on vibration frequencies. During lock-in between the vortex-shedding frequency and the structure's natural frequency, the increase of the vibration frequency with flow speeds is strongly related to the rise of the axial tension. After an initial abrupt rise, the vibration frequency of a bending-stiffness-dominated structure only increased slightly during lock-in. Alternative explanations are provided on why the vibration frequency does not rise significantly but there can still exist a broad lock-in band, and why a more massive structure has a narrower lock-in bandwidth.
Vortex shedding noise reduction by single dielectric barrier discharge plasma actuators
Al-Sadawi, L; Chong, TP
2016-01-01
An experimental study of active control of vortex shedding narrow band tonal noise from both blunt and rounded trailing edge of a profiled body at zero incidences was performed using Single Dielectric Barrier plasma actuators (DBD). Acoustics and flow measurements were carried out in an open jet, aerocoustic wind tunnel at Reynolds numbers ranging from 7x104 to 4x105. The noise results were obtained using single microphone, while both PIV and hot-wire were used for flow measurement in order t...
Model-based control of vortex shedding at low Reynolds numbers
Illingworth, Simon J.
2016-10-01
Model-based feedback control of vortex shedding at low Reynolds numbers is considered. The feedback signal is provided by velocity measurements in the wake, and actuation is achieved using blowing and suction on the cylinder's surface. Using two-dimensional direct numerical simulations and reduced-order modelling techniques, linear models of the wake are formed at Reynolds numbers between 45 and 110. These models are used to design feedback controllers using {H}_∞ loop-shaping. Complete suppression of shedding is demonstrated up to Re = 110—both for a single-sensor arrangement and for a three-sensor arrangement. The robustness of the feedback controllers is also investigated by applying them over a range of off-design Reynolds numbers, and good robustness properties are seen. It is also observed that it becomes increasingly difficult to achieve acceptable control performance—measured in a suitable way—as Reynolds number increases.
Energy Technology Data Exchange (ETDEWEB)
Thomsen, J.R.; Pedersen, B. [LIC Engineering (Denmark); Nielsen, K.G.; Bryndum, M.B. [Dansk Hydraulisk Inst., (Denmark)
1999-07-01
Vortex induced vibrations of pipes generated by high and steep waves in the crest zone have been investigated by full-scale field testing, An instrumented cylinder has been suspended from a platform bridge in the North Sea. Adjacent to it a newly developed acoustic system capable of measuring the three dimensional wave kinematics was placed. The kinematics were measured all the way up to the instantaneous water surface elevation, i.e. it included the wave crest. The paper presents time series of measured water surface elevations and orbital velocities at the instantaneous water surface together with the response of the instrumented pipe in a storm. The sea state was measured to H{sub s} {approx_equal} 6.4 m and T{sub z} = 8.4 sec. It was clearly seen that vortex shedding locking-on takes place in some of the rather high modes at the passage of large waves. Intermittent cross flow vortex induced vibrations of between 0.3 diameters up to 0.8 diameters were found in the 8th and the 4th mode respectively. The Reynolds numbers and KC numbers were up to 5 . 10{sup 5} and KC {approx} 250 respectively. (au)
Multi-frequency response of a cylinder subjected to vortex shedding and support motions
Energy Technology Data Exchange (ETDEWEB)
Vikestad, Kyrre
1998-12-31
This thesis deals with an experimental investigation of vortex induced vibrations of a circular cylinder. The purpose of the experiment was to identify the influence from a controlled disturbance of the cylinder motions on the response caused by vortex shedding. The cylinder investigated is 2 m long and the diameter is 10 cm. The cylinder is elastically mounted in an apparatus using springs, where the foundation of one of the springs can have a harmonic motion. The apparatus is placed on a carriage in a 25 m long towing tank. Towing velocities are varied between 0.140 m/s and 0.655 m/s corresponding to reduced velocity range from 2.8 to 13.2. The still water natural frequency is 0.497 Hz, and the natural frequency in air is 0.634 Hz. The cylinder is only able to oscillate in the cross-flow direction. The support motion frequency was varied between 0.26 Hz and 1.01 Hz, and the force motion amplitude was varied using 2, 4 and 6 cm support amplitudes. Three sets of experiments were carried out: (1) Still water oscillations due to harmonic support motion excitation, support amplitude and frequencies varied, (2) Towing tests with no support motion, the velocity is varied, (3) Combined excitation: Towing tests with support motion. All possible combinations of experiments (1) and (2) are carried out. The two first experiments provide reference values for the combined excitation experiments and for verification purposes. The results reveal the ability of the external disturbance to influence the vortex shedding process both regarding frequency and the resulting response amplitudes. Results for added mass, in-line drag and damping are also obtained. The work may be of use in deep water floating petroleum production. 81 refs., 73 figs., 6 tabs.
1950-01-01
Dr. Theodore von Karman, co-founder of the Jet Propulsion Laboratory (JPL) Pasadena, California was an aeronautical theoretician. His contributions in the fields of aerodynamics and aeronautical engineering are well documented and well known to every aerospace engineer. He was the first winner of the prestigious U.S. Medal of Science presented to him by President John F. Kennedy. As well as being co-founder of JPL, he also was principal founder of a major rocket propulsion firm (Aerojet-General Corp.), the top science advisor to the U.S. Air Force during its transition to jet propulsion aircraft and the top science advisor to NATO. He was, during much of this time, the fountainhead of aerodynamic thought as head of the Guggenheim Aeronautical Laboratory at the California Institute of Technology (GALCIT) in Pasadena, California. In the May 1956 issue of the Journal of Aeronautical Sciences, it was said of him that 'No other man has had so great an impact on the development of aeronautical science in this country. Hundreds of young men became his students and scientific collaborators and were inspired to greater effort.' Dr. William H. Pickering, then director of JPL said in 1960 'We wouldn't have an aeronautical science as we know it today, if it weren't for Dr. Thoedore von Karman.' Under his guidance, Caltech's 10 foot wind tunnel was designed, built and operated. Industry firms such as Douglas, Northrop, Hughes, Lockheed, North American, Vultee and Consolidated all tested new aeronautical designs and concepts in GALCIT's tunnel. Even Boeing's own high-speed wind tunnel was heavily influenced by suggestions from von Karman. The National Advisory Committee for Aeronautics (NACA) became so concerned about GALCIT's growing influence over West coast aviation, it erected the Ames Laboratory in Sunnyvale, California in part to deter an ever widening aeronautical gap that had formed between NACA and GALCIT. From 1936 to 1940, Caltech stood alone as the only university
Control of a coupled map lattice model for vortex shedding in the wake of a cylinder
Indian Academy of Sciences (India)
G Balasubramanian; D J Olinger; M A Demetriou
2002-07-01
The ﬂow behind a vibrating ﬂexible cable at low Reynolds numbers can exhibit complex wake structures such as lace-like patterns, vortex dislocations and frequency cells. These structures have been observed in experiments and numerical simulations, and are predicted by a previously developed low-order coupled map lattice (CML). The discrete (in time and space) CML models consist of a series of diffusively coupled circle map oscillators along the cable span. Motivated by a desire to modify the complex wake patterns behind ﬂexible vibrating cables, we have studied the addition of control terms into the highly efﬁcient CML models and explored the resulting dynamics. Proportional, adaptive proportional and discontinuous non-linear (DNL) control methods were used to derive the control laws. The ﬁrst method employed occasional proportional feedback. The adaptive method used spatio-temporal feedback control. The DNL method used a discontinuous feedback linearization procedure, and the controller was designed for the resulting linearized system using eigenvalue assignment. These techniques were applied to a modeled vortex dislocation structure in the wake of a vibrating cable in uniform freestream ﬂow. Parallel shedding patterns were achieved for a range of forcing frequency-forcing amplitude combinations studied to validate the control theory. The adaptive proportional and DNL methods were found to be more effective than the proportional control method due to the incorporation of a spatially varying feedback gain across the cylinder span. The DNL method was found to be the most efﬁcient controller of the low-order CML model. The required control level across the cable span was correlated to the 1/1 lock-on behavior of the temporal circle map.
Large-scale tests for vortex shedding effects on marine risers
Energy Technology Data Exchange (ETDEWEB)
Hartnup, G.C.; Lyons, G.J.; Patel, M.H.; Sarohia, S.
1983-05-01
The interest increasingly being shown in floating production systems has drawn renewed attention to the problems of riser design. The production riser is clearly a crucial item which requires a design procedure in which a high degree of confidence can be placed. In this respect the requirements of a production riser are more exacting than those of the drilling risers used in the exploratory phase. A reliable prediction of service stress history is essential to the prediction of fatigue life. This is usually obtained from one or more of the computer simulation packages available for riser simulation. Any computer simulation is only as accurate as the mathematical modelling it contains, and in writing such a program assumptions are made as to which effects are significant enough to include, the manner in which to simulate them, and in the choice of various empirical constants involved. Many riser simulations are purely two-dimensional but experimental data, such as that presented here, shows that a uni-directional wave input does not result in a uni-directional response. Vortex shedding effects are a significant result of wave loading on a marine riser.
A self-learning coupled map lattice for vortex shedding in cable and cylinder wakes.
Balasubramanian, G; Olinger, D J; Demetriou, M A
2004-06-01
A coupled map lattice (CML) with self-learning features is developed to model flow over freely vibrating cables and stationary cylinders at low Reynolds numbers. Coupled map lattices that combine a series of low-dimensional circle maps with a diffusion model have been used previously to predict qualitative features of these flows. However, the simple nature of these CML models implies that there will be unmodeled wake features if a detailed, quantitative comparison is made with laboratory or simulated wake flows. Motivated by a desire to develop an improved CML model, we incorporate self-learning features into a new CML that is first trained to precisely estimate wake patterns from a target numerical simulation. A new convective-diffusive map that includes additional wake dynamics is developed. The new self-learning CML uses an adaptive estimation scheme (multivariable least-squares algorithm). Studies of this approach are conducted using wake patterns from a Navier-Stokes solution (spectral element-based NEKTAR simulation) of freely vibrating cable wakes at Reynolds numbers Re=100. It is shown that the self-learning model accurately and efficiently estimates the simulated wake patterns. The self-learning scheme is then successfully applied to vortex shedding patterns obtained from experiments on stationary cylinders. This constitutes a first step toward the use of the self-learning CML as a wake model in flow control studies of laboratory wake flows.
The boundary element method applied to viscous and vortex shedding flows around cylinders
Farrant, Tim
Studies are presented to further extend the use of the boundary element method (BEM) for the solution of viscous flows around bluff bodies, governed by the incompressible Navier-Stokes equations. Two distinct formulations are applied to various flows around cylindrical geometries for Reynolds numbers Tan (1994) and known herein as the global BEM, was coded to execute in parallel on multi-processor computers. Reductions in execution time were achieved and the method was employed to solve an oscillating cylinder problem. In this study, the displacement undergone by the body was very large but the Reynolds number was always Tan et al (1998). A validation for isolated and double circular cylinders in a uniform stream was performed against experimental evidence to demonstrate the method's stability and accuracy for laminar vortex shedding with geometries involving multiply connected domains. Finally, computational results for flows around four equispaced circular cylinders of equal diameter and two cylinders, one circular the other elliptical, are reported. Many of the concepts established for the flow around two cylinders of equal diameter were found to be useful in interpretation of these more complicated arrangements.
Choi, H.; You, D.; Choi, M.-R.; Kang, S.-H.
1996-11-01
Laminar vortex sheddings behind a circular cylinder with and without splitter plates attached to the cylinder at low Reynolds numbers are simulated by solving the unsteady incompressible Navier-Stokes equations. The Strouhal number, lift and drag rapidly change with the length of the splitter plate. Far-field noise from the vortex shedding behind the cylinder is computed using the Curle's formulation of the Lighthill acoustic analogy. The acoustic source functions are obtained from the computed near-field velocity and pressure. Numerical results show that the volume quadrupole noise is small at a low Mach number, compared to the surface dipole noise from the cylinder. Variations of the far-field noise characteristics with respect to the splitter plate are being investigated and will be shown in the final presentation. ^* Supported by KOSEF under Contract No. 961-1009-075-2
Mantič-Lugo, Vladislav; Arratia, Cristóbal; Gallaire, François
2014-08-22
The Bénard-von Kármán vortex shedding instability in the wake of a cylinder is perhaps the best known example of a supercritical Hopf bifurcation in fluid dynamics. However, a simplified physical description that accurately accounts for the saturation amplitude of the instability is still missing. Here, we present a simple self-consistent model that provides a clear description of the saturation mechanism and quantitatively predicts the saturated amplitude and flow fields. The model is formally constructed by a set of coupled equations governing the mean flow together with its most unstable eigenmode with finite size. The saturation amplitude is determined by requiring the mean flow to be neutrally stable. Without requiring any input from numerical or experimental data, the resolution of the model provides a good prediction of the amplitude and frequency of the vortex shedding as well as the spatial structure of the mean flow and the Reynolds stress.
Institute of Scientific and Technical Information of China (English)
魏中磊; 张子强; H.E.Fiedler
1995-01-01
The behavior of synchronization in an open flow dynamical system, especially in an excited wake flow behind a 2-D oscillating circular cylinder with Reynolds number Re ranging from 45 to 200 is presented. The experiment reveals that only under certain conditions can the competition between frequencies of oscillating cylinder and the vortex shedding in the wake flow result in "window of chaos" with the mixed RTN and Feigenbaum scenario in the range of Re<185.
Sevilla, A.; Martínez-Bazán, C.
2004-09-01
In the present work we study the large-scale helical vortex shedding regime in the wake of an axisymmetric body with a blunt trailing edge at high Reynolds numbers, both experimentally and by means of local, linear, and spatiotemporal stability analysis. In the instability analysis we take into account the detailed downstream evolution of the basic flow behind the body base. The study confirms the existence of a finite region of absolute instability for the first azimuthal number in the near field of the wake. Such instability is believed to trigger the large-scale helical vortex shedding downstream of the recirculating zone. Inhibition of vortex shedding is examined by blowing a given flow rate of fluid through the base of the slender body. The extent of the locally absolute region of the flow is calculated as a function of the bleed coefficient, Cb=qb/(πR2u∞), where qb is the bleed flow rate, R is the radius of the base, and u∞ is the incident free-stream velocity. It is shown that the basic flow becomes convectively unstable everywhere for a critical value of the bleed coefficient of Cb*˜0.13, such that no self-excited regime is expected for Cb>Cb*. In addition, we report experimental results of flow visualizations and hot-wire measurements for increasing values of the bleed coefficient. When a sufficient amount of base bleed is applied, flow visualizations indicate that vortex shedding is suppressed and that the mean flow becomes axisymmetric. The critical bleed coefficient predicted by linear instability analysis is shown to fall within the experimental values in the range of Reynolds numbers analyzed here.
Energy Technology Data Exchange (ETDEWEB)
Kawamura, T.; Nakao, T.; Takahashi, M.; Hayashi, M.; Goto, N. [Hitachi, Ltd., Tokyo (Japan)
1999-07-25
Vortex-induced vibrations were measured for a circular cylinder subjected to a water cross flow at supercritical Reynolds numbers for a wide range of reduced velocities. Turbulence intensities were changed from 1% to 13% in order to investigate the effect of the Strouhal number on the region of synchronization by symmetrical and Karman vortex shedding. The reduced damping of the test cylinder was about 0.1 in water. The surface roughness of the cylinder was a mirror-polished surface. Strouhal number decreased from about 0.48 to 0.29 with increasing turbulence intensity. Synchronized vibrations were observed even at supercritical Reynolds numbers where fluctuating fluid force was small. Reduced velocities at which drag and lift direction lock-in by Karman vortex shedding were initiated decreased with increasing Strouhal number. When Strouhal number was about 0.29, the self-excited vibration in drag direction by symmetrical vortex shedding began at which the frequency ratio of Karman vortex shedding frequency to the natural frequency of cylinder was 0.32. (author)
Energy Technology Data Exchange (ETDEWEB)
Bovand, M. [Department of Mechanical Engineering, Ferdowsi University of Mashhad, P.O. Box 91775-1111, Mashhad (Iran, Islamic Republic of); Rashidi, S., E-mail: samanrashidi3983@gmail.com [Department of Mechanical Engineering, Ferdowsi University of Mashhad, P.O. Box 91775-1111, Mashhad (Iran, Islamic Republic of); Dehghan, M. [Faculty of Mechanical Engineering, Semnan University, P.O. 35131-19111, Semnan (Iran, Islamic Republic of); Esfahani, J.A. [Department of Mechanical Engineering, Ferdowsi University of Mashhad, P.O. Box 91775-1111, Mashhad (Iran, Islamic Republic of); Valipour, M.S. [Faculty of Mechanical Engineering, Semnan University, P.O. 35131-19111, Semnan (Iran, Islamic Republic of)
2015-07-01
In this article the finite volume method (FVM) is carried out to simulate the flow around and through a two-dimensional porous cylinder. An external magnetic field is used to control the wake behind the bluff body and also to suppress the vortex shedding phenomena. The Darcy–Brinkman–Forchheimer model has been used for modeling the flow in the porous medium. Effects of Stuart (N), Reynolds (Re) and Darcy (Da) numbers on the flow behavior have been investigated. The results show that the critical Stuart number for suppress vortex shedding decreases with increasing the Darcy numbers. Also, the Stuart number for disappearance the re-circulating wake increases with increased Reynolds number for both porous and solid cylinders. - Highlights: • The formation and shedding of wakes behind a porous bluff-body are investigated. • Effects of a magnetic field on controlling the wake formation is explored. • Roles of Darcy, Reynolds and Stuart numbers on the flow behavior are analyzed. • Flow patterns change with Reynolds number and Darcy numbers. • The critical Stuart number decreases with increased Darcy numbers.
Vortex wakes of a flapping foil
DEFF Research Database (Denmark)
Schnipper, Teis; Andersen, Anders Peter; Bohr, Tomas
2009-01-01
and the shedding process at the sharp trailing edge in detail. This allows us to identify the origins of the vortices in the 2P wake, to understand that two distinct 2P regions are present in the phase diagram due to the timing of the vortex shedding at the leading edge and the trailing edge and to propose......We present an experimental study of a symmetric foil performing pitching oscillations in a vertically flowing soap film. By varying the frequency and amplitude of the oscillation we visualize a variety of wakes with up to 46 vortices per oscillation period, including von Karman vortex street......, inverted von Karman vortex street, 2P wake, 2P+2S wake and novel wakes ranging from 4P to 8P. We map out the wake types in a phase diagram spanned by the width-based Strouhal number and the dimensionless amplitude. We follow the time evolution of the vortex formation near the round leading edge...
Ford, C. L.; Winroth, M.; Alfredsson, P. H.
2016-08-01
An entirely pressure-based vortex-shedding meter has been designed for use in practical time-dependent flows. The meter is capable of measuring mass-flow rate in variable density gases in spite of the fact that fluid temperature is not directly measured. Unlike other vortex meters, a pressure based meter is incredibly robust and may be used in industrial type flows; an environment wholly unsuitable for hot-wires for example. The meter has been tested in a number of static and dynamic flow cases, across a range of mass-flow rates and pressures. The accuracy of the meter is typically better than about 3% in a static flow and resolves the fluctuating mass-flow with an accuracy that is better than or equivalent to a hot-wire method.
Rai, Man Mohan
2017-01-01
The near wake of a flat plate is investigated via direct numerical simulations (DNS). Many earlier experimental investigations have used thin plates with sharp trailing edges and turbulent boundary layers to create the wake. This results in large theta divided by D (sub TE) values (theta is the boundary layer momentum thickness towards the end of the plate and D (sub TE) is the trailing edge thickness). In the present study the emphasis is on relatively thick plates with circular trailing edges (CTE) resulting in theta divided by D values less than one (D is the plate thickness and the diameter of the CTE), and vigorous vortex shedding. The Reynolds numbers based on the plate length and D are 1.255 x 10 (sup 6) and 10,000, respectively. Two cases are computed; one with turbulent boundary layers on both the upper and lower surfaces of the plate (statistically the same, symmetric wake, Case TT) and, a second with turbulent and laminar boundary layers on the upper and lower surfaces, respectively (asymmetric case, Case TL). The data and understanding obtained is of considerable engineering interest, particularly in turbomachinery where the pressure side of an airfoil can remain laminar or transitional because of a favorable pressure gradient and the suction side is turbulent. Shed-vortex structure and phase-averaged velocity statistics obtained in the two cases are compared here. The upper negative shed vortices in Case TL (turbulent separating boundary layer) are weaker than the lower positive ones (laminar separating boundary layer) at inception (a factor 1.27 weaker in terms of peak phase-averaged spanwise vorticity at first appearance of a peak). The upper vortices weaken rapidly as they travel downstream. A second feature of interest in Case TL is a considerable increase in the peak phase-averaged, streamwise normal intensity (random component) with increasing streamwise distance (x divided by D) that occurs nears the positive vortex cores. This behavior is
Vortex Formation, Shedding and Energy Harvesting from a Cyber-Physical Pitching Flat Plate
Onoue, Kyohei; Breuer, Kenneth
2014-11-01
We examine the dynamics and energy harvesting capabilities of an elastically mounted flat plate undergoing large amplitude limit cycle oscillations in a uniform flow. All experiments are performed using a cyber-physical system, wherein the structural inertia, stiffness and damping are numerically simulated using a position-following feedback algorithm. The cyber-physical system also allows for implementation of nonlinear spring and damping coefficients, which control the plate dynamics and subsequent energy harvesting characteristics. Analysis of the plate kinematics and the fluid flow over the plate and in the wake (measured using PIV) are used to understand the interplay between structural motion and vortex formation at the sharp leading and trailing edges of the plate. By varying the structural properties of the system we systematically analyze the formation, strength, stability and separation of the leading edge vortex, as well as the dependence on kinematic parameters and Reynolds number. Connections to previous results on vortex formation time and bluff body aerodynamics are discussed. This research is funded by the Air Force Office of Scientific Research (AFOSR).
Low-frequency unsteadiness of vortex wakes over slender bodies at high angle of attack
Directory of Open Access Journals (Sweden)
Ma Baofeng
2014-08-01
Full Text Available A type of flow unsteadiness with low frequencies and large amplitude was investigated experimentally for vortex wakes around an ogive-tangent cylinder. The experiments were carried out at angles of attack of 60–80° and subcritical Reynolds numbers of 0.6–1.8 × 105. The reduced frequencies of the unsteadiness are between 0.038 and 0.072, much less than the frequency of Karman vortex shedding. The unsteady flow induces large fluctuations of sectional side forces. The results of pressure measurements and particle image velocimetry indicate that the flow unsteadiness comes from periodic oscillation of the vortex wakes over the slender body. The time-averaged vortex patterns over the slender body are asymmetric, whose orientation is dependent on azimuthal locations of tip perturbations. Therefore, the vortex oscillation is a type of unsteady oscillation around a time-averaged asymmetric vortex structure.
Autonomous Sensors Powered by Energy Harvesting from von Karman Vortices in Airflow.
Demori, Marco; Ferrari, Marco; Bonzanini, Arianna; Poesio, Pietro; Ferrari, Vittorio
2017-09-13
In this paper an energy harvesting system based on a piezoelectric converter to extract energy from airflow and use it to power battery-less sensors is presented. The converter is embedded as a part of a flexure beam that is put into vibrations by von Karman vortices detached from a bluff body placed upstream. The vortex street has been investigated by Computational Fluid Dynamics (CFD) simulations, aiming at assessing the vortex shedding frequency as a function of the flow velocity. From the simulation results the preferred positioning of the beam behind the bluff body has been derived. In the experimental characterization the electrical output from the converter has been measured for different flow velocities and beam orientations. Highest conversion effectiveness is obtained by an optimal orientation of the beam, to exploit the maximum forcing, and for flow velocities where the repetition frequency of the vortices allows to excite the beam resonant frequency at its first flexural mode. The possibility to power battery-less sensors and make them autonomous has been shown by developing an energy management and signal conditioning electronic circuit plus two sensors for measuring temperature and flow velocity and transmitting their values over a RF signal. A harvested power of about 650 μW with retransmission intervals below 2 min have been obtained for the optimal flow velocity of 4 m/s.
Autonomous Sensors Powered by Energy Harvesting from von Karman Vortices in Airflow
Directory of Open Access Journals (Sweden)
Marco Demori
2017-09-01
Full Text Available In this paper an energy harvesting system based on a piezoelectric converter to extract energy from airflow and use it to power battery-less sensors is presented. The converter is embedded as a part of a flexure beam that is put into vibrations by von Karman vortices detached from a bluff body placed upstream. The vortex street has been investigated by Computational Fluid Dynamics (CFD simulations, aiming at assessing the vortex shedding frequency as a function of the flow velocity. From the simulation results the preferred positioning of the beam behind the bluff body has been derived. In the experimental characterization the electrical output from the converter has been measured for different flow velocities and beam orientations. Highest conversion effectiveness is obtained by an optimal orientation of the beam, to exploit the maximum forcing, and for flow velocities where the repetition frequency of the vortices allows to excite the beam resonant frequency at its first flexural mode. The possibility to power battery-less sensors and make them autonomous has been shown by developing an energy management and signal conditioning electronic circuit plus two sensors for measuring temperature and flow velocity and transmitting their values over a RF signal. A harvested power of about 650 μW with retransmission intervals below 2 min have been obtained for the optimal flow velocity of 4 m/s.
Institute of Scientific and Technical Information of China (English)
Zhang Ning; Li Guang-zheng; Huang Jian-chun
2003-01-01
The influence of buoyancy on vortex shedding from a heated square cylinder and its effects on the heat transfer of mixed convection were simulated.The flow equations, based on the velocity and the pressure, were solved along with the energy equation by a modified SIMPLER algorithm-the Quick Scheme and small Control Volume (QSCV) algorithm developed by the authors of the present paper.A set of optimized computational domain and artificial lateral boundary conditions were used along with the QSCV algorithm.Several cases were simulated for the Grashof numbers up to 1.8×105, the Reynolds numbers up to 500, and a range of angles between free stream velocity and gravity from 0 to 1.5π.In opposing flow, the results distinguish two different flow patterns: periodic flow for Gr＜Grc and steady flow with attached twin vortices for Gr＞Grc, and a precise correlation between Grc and Re expressed as Grc=0.00166(Re)2.97795 for Re up to 500 was firstly obtained.In cross flow, it could be seen that the Ri=Gr/Re2 plays a great role in the wake vortex patterns and the temperature fields.In aiding flow, it is found that the main flow currents cause a large expansion of the streamlines and isotherms in the direction normal to the free stream velocity.These changes in the wake vortex patterns and the temperature fields greatly modify the heat flux along the surface of the square cylinder and consequently, the heat transfer rate is strongly dependent upon the Reynolds numbers, the Grashof numbers, and the gravity direction.
Drop impact into a deep pool: Vortex shedding and jet formation
Agbaglah, Gilou
2015-01-02
One of the simplest splashing scenarios results from the impact of a single drop on a deep pool. The traditional understanding of this process is that the impact generates an axisymmetric sheet-like jet that later breaks up into secondary droplets. Recently it was shown that even this simplest of scenarios is more complicated than expected because multiple jets can be generated from a single impact event and there are transitions in the multiplicity of jets as the experimental parameters are varied. Here, we use experiments and numerical simulations of a single drop impacting on a deep pool to examine the transition from impacts that produce a single jet to those that produce two jets. Using high-speed X-ray imaging methods we show that vortex separation within the drop leads to the formation of a second jet long after the formation of the ejecta sheet. Using numerical simulations we develop a phase diagram for this transition and show that the capillary number is the most appropriate order parameter for the transition. © 2014 Cambridge University Press.
Directory of Open Access Journals (Sweden)
Adrian Klein
2011-06-01
Full Text Available The lateral line system of fish consists of superficial neuromasts, and neuromasts embedded in lateral line canals. Lateral line neuromasts allow fish to sense both minute water motions and pressure gradients, thereby enabling them to detect predators and prey or to recognize and discriminate stationary objects while passing them. With the aid of the lateral line, fish can also sense vortices caused by an upstream object or by undulatory swimming movements of fish. We show here that artificial lateral line canals equipped with optical flow sensors can be used to detect the water motions generated by a stationary vibrating sphere, the vortices caused by an upstream cylinder or the water (air movements caused by a passing object. The hydrodynamic information retrieved from optical flow sensors can be used to calculate bulk flow velocity and thus the size of the cylinder that shed the vortices. Even a bilateral sensor platform equipped with only one artificial lateral line canal on each side is sufficient to determine the position of an upstream cylinder.
Energy Technology Data Exchange (ETDEWEB)
Octavianty, Ressa, E-mail: ressa-octavianty@ed.tmu.ac.jp; Asai, Masahito, E-mail: masai@tmu.ac.jp [Department of Aerospace Engineering, Tokyo Metropolitan University, 6-6 Asahigaoka, Hino, Tokyo 191-0065 (Japan)
2015-10-15
Synchronized vortex shedding from two side-by-side cylinders and the associated sound radiation were examined experimentally at Reynolds numbers of the order of 10{sup 4} in low-Mach-number flows. In addition to a pair of square cylinders, a pair of rectangular cylinders, one with a square cross section (d × d) and the other with a rectangular cross section (d × c) having a cross-sectional aspect ratio (c/d) of 1.2–1.5, was considered. The center-to-center distance between the two cylinders L/d was 3.6, 4.5, and 6.0; these settings were within the non-biased flow regime for side-by-side square cylinders. In case of a square cylinder pair, anti-phase synchronized vortex shedding occurring for L/d = 3.6 and 4.5 generated a quadrupole-like sound source which radiated in-phase, planar-symmetric sound in the far field. Synchronized vortex shedding from the two rectangular cylinders with different c/d also occurred with almost the same frequency as the characteristic frequency of the square-cylinder wake in the case of the small center-to-center distance, L/d = 3.6, for all the cylinder pairs examined. The synchronized sound field was anti-phase and asymmetric in amplitude, unlike the case of a square cylinder pair. For larger spacing L/d = 4.5, synchronized vortex shedding and anti-phase sound still occurred, but only for close cross-sectional aspect ratios (c/d = 1.0 and 1.2), and highly modulated sound was radiated with two different frequencies due to non-synchronized vortex shedding from the two cylinders for larger differences in c/d. It was also found that when synchronized vortex shedding occurred, near-wake velocity fluctuations exhibited high spanwise-coherency, with a very sharp spectral peak compared with the single-cylinder case.
Akhtar, Imran; Nayfeh, Ali H.; Ribbens, Calvin J.
2009-07-01
Proper orthogonal decomposition (POD) has been used to develop a reduced-order model of the hydrodynamic forces acting on a circular cylinder. Direct numerical simulations of the incompressible Navier-Stokes equations have been performed using a parallel computational fluid dynamics (CFD) code to simulate the flow past a circular cylinder. Snapshots of the velocity and pressure fields are used to calculate the divergence-free velocity and pressure modes, respectively. We use the dominant of these velocity POD modes (a small number of eigenfunctions or modes) in a Galerkin procedure to project the Navier-Stokes equations onto a low-dimensional space, thereby reducing the distributed-parameter problem into a finite-dimensional nonlinear dynamical system in time. The solution of the reduced dynamical system is a limit cycle corresponding to vortex shedding. We investigate the stability of the limit cycle by using long-time integration and propose to use a shooting technique to home on the system limit cycle. We obtain the pressure-Poisson equation by taking the divergence of the Navier-Stokes equation and then projecting it onto the pressure POD modes. The pressure is then decomposed into lift and drag components and compared with the CFD results.
Energy Technology Data Exchange (ETDEWEB)
Akhtar, Imran [Virginia Tech, Department of Engineering Science and Mechanics, MC 0219, Blacksburg, VA (United States); Virginia Tech, Interdisciplinary Center for Applied Mathematics, MC 0531, Blacksburg, VA (United States); Nayfeh, Ali H. [Virginia Tech, Department of Engineering Science and Mechanics, MC 0219, Blacksburg, VA (United States); Ribbens, Calvin J. [Virginia Tech, Department of Computer Science, Blacksburg, VA (United States)
2009-07-15
Proper orthogonal decomposition (POD) has been used to develop a reduced-order model of the hydrodynamic forces acting on a circular cylinder. Direct numerical simulations of the incompressible Navier-Stokes equations have been performed using a parallel computational fluid dynamics (CFD) code to simulate the flow past a circular cylinder. Snapshots of the velocity and pressure fields are used to calculate the divergence-free velocity and pressure modes, respectively. We use the dominant of these velocity POD modes (a small number of eigenfunctions or modes) in a Galerkin procedure to project the Navier-Stokes equations onto a low-dimensional space, thereby reducing the distributed-parameter problem into a finite-dimensional nonlinear dynamical system in time. The solution of the reduced dynamical system is a limit cycle corresponding to vortex shedding. We investigate the stability of the limit cycle by using long-time integration and propose to use a shooting technique to home on the system limit cycle. We obtain the pressure-Poisson equation by taking the divergence of the Navier-Stokes equation and then projecting it onto the pressure POD modes. The pressure is then decomposed into lift and drag components and compared with the CFD results. (orig.)
Effect of span length and temperature on the 3-D confined flow around a vortex promoter
Energy Technology Data Exchange (ETDEWEB)
Martin, E. [Fluid Mechanics Area, School of Industrial Engineering, Universidad de Vigo, Campus Lagoas-Marcosende, 36310 Vigo (Spain); Velazquez, A., E-mail: angel.velazquez@upm.es [Aerospace Propulsion and Fluid Mechanics Department, School of Aeronautics, Universidad Politecnica de Madrid, Plaza del Cardenal Cisneros 3, 28040 Madrid (Spain)
2011-12-15
Highlights: Black-Right-Pointing-Pointer The article deals with study of vortex promoter flow in a 3-D micro-channel. Black-Right-Pointing-Pointer Aspects studied are: channel aspect ratio and prism surface temperature. Black-Right-Pointing-Pointer Flow is classified into three different regimes depending on different parameters. Black-Right-Pointing-Pointer Results could be used for practical engineering design purposes. - Abstract: This article presents a numerical study on the influence of span length and wall temperature on the 3-D flow pattern around a square section vortex promoter located inside a micro-channel in the low Reynolds number regime. The first objective of the work is to quantify the critical Reynolds number that defines the onset of vortex shedding and to identify the different regimes that appear as a function of the channel aspect ratio (span to height ratio). We found that the critical Reynolds number for the onset of the Karman street regime increases as the aspect ratio decreases. In particular, for the aspect ratio of 1/2 the critical Reynolds number is nearly six times the critical Reynolds number of the 2-D problem. An intermediate oscillating regime between the steady and the Karman street solutions was also found to exist within a rather wide range of Reynolds numbers for small channel aspect ratios. The second objective was to investigate the influence of the vortex promoter wall temperature on both vortex shedding and flow pattern. This has practical engineering implications because the working fluid considered in the article is water that has a viscosity that depends significantly on temperature and promotes a strong coupling between the momentum and energy equations that influences the system behaviour. Results indicate that high surface temperature on the prism promotes the onset of the Karman street, suggesting design guidelines for micro-channel based heat sinks that make use of vortex promoters.
Institute of Scientific and Technical Information of China (English)
AHMED N A
2006-01-01
A comprehensive hot wire investigation of the flow around a circular cylinder is carried out in an 18" × 18" wind tunnel to look into the dominant frequencies at the stagnation, separation and separated shear layers in the transition Reynolds number range. The majority of the experiments are carried out at Reynolds number of 4.5 × 104, with additional transition frequency tests at Reynolds numbers of 2.9 × 104, 3.3 × 104 and 9.7 × 104 respectively. The results are analysed in terms of power spectral density. While the frequency associated with stagnation is found to be essentially due to vortex shedding, frequency doubling of vortex shedding is also evident in the separated shear layers.Two peaks associated with transition frequencies are detected and their possible implications are presented.
Study on Hydrodynamic Vibration in Dual Bluff Body Vortex Flowmeter
Institute of Scientific and Technical Information of China (English)
无
2001-01-01
The characteristics of the dual bluff body vortex shedding is investigated, and the possibility to use dual bluff body combinations to strengthen the hydrodynamic vibration around the bluff body objects is explored. The numerical and experimental approaches were utilized to examine the time dependent flow field and the pressure oscillation around the bluff bodies. The numerical data were obtained by the advanced large eddy simulation model. The experiment was conducted on a laboratory scale of Karman vortex flowmeter with 40 mm diameter. It is revealed that the optimized dual bluff body combinations strengthened the hydrodynamic vibration. It was also found that the hydrodynamic vibration with 180° phase difference occurred at the axisymmetric points of circular pipe on the lateral faces of the equilateral triangle-section bluff bodies. Using the dual bluff body configuration and the differential sensing technique, a novel prototype of vortex flowmeter with excellent noise immunity and improved sensibility was developed.
Hydrogen Bubbles as a Visualization Tool for Cylinder Shedding
Sigurdson, Lorenz; Gilbert, Stuart
2004-11-01
We examine the behavior of hydrogen bubbles formed by electrolysis of water on a 2.54 mm cylindrical electrode in a water tunnel. The Reynolds Number based on cylinder diameter varies from 400 to 1100, and tunnel velocities range from 17 to 50 cm/s. At the lowest velocity buoyancy is a strong effect which inhibits accurate flow tracking by the bubbles. This effect largely disappears by 25 cm/s. As the tunnel velocity increases, bubble size decreases, reflected light for photography is reduced, and bubbles begin to track the von Karman vortex street vortex cores near the cylinder. The vortex cores have a sufficiently low pressure to capture the bubbles. Vortex street wavelength is seen to discretely increase as vortices proceed downstream. The location of this scale-change becomes nearer the cylinder as Re increases. Voids of bubbles occur in continuous linear downstream segments originating near the cylinder. They seem to be due to vortex modification in the wake similar to what other cylinder shedding researchers have found.
Schoepe, W.
2016-08-01
Vortex shedding from a microsphere oscillating in superfluid ^4{He} at mK temperatures is compared with that from a laser beam moving in a Bose-Einstein condensate as observed by other authors. In particular, in either case a linear dependence of the shedding frequency f_v on Δ v = v - v_c is observed, where v is the velocity amplitude of the sphere or the constant velocity of the laser beam above a critical velocity v_c for the onset of turbulent flow: f_v = a Δ v , where the coefficient a is proportional to the oscillation frequency ω above some characteristic frequency ω _k and assumes a finite value for steady motion ω → 0.
Measurement and Discovery of Shedding Vortex Noise%基于麦克风阵列测量的机翼脱落涡噪声研究
Institute of Scientific and Technical Information of China (English)
乔渭阳; UlfMichel
2001-01-01
During Qiao Weiyang′s 18 month stay at DLR working on a CAE (Chinese Aeronautical Establishment)/DLR Cooperation project, we measured and discovered shedding vortex noise. Using DLR's large planar microphone array consisting of 111 microphones, we studied the two dimensional mapping of sound sources on landing aircraft. We first discovered a new noise source, shedding vortex noise source, located on the wing somewhat near to wing tip than to wing root (Fig.4b). The spectrum of this noise is typically tone spectral. The frequency of this noise source increases with increasing aircraft airspeed. With this noise source as center we imagine a circle touching the ground; the noise sound pressure level becomes higher and higher as we move along the circle in the direction of flight; when the emission angle changes from 60° to 120°, the noise sound pressure level increases by about 5～8 dB.%应用由111个麦克风组成的平面麦克风阵列对当前流行的民用客机进场着陆过程中的飞机噪声源进行了测量分析，在国际上首次发现了机翼脱落涡单音噪声源，并且得到了这种噪声源的频谱特性、指向特性和声级变化特征。
Zhou, Y. L.; Deng, D.
2010-03-01
Considering the turbulence deduced by shearing stress and air bubble, and based on two-fluid model, gas-liquid two-phase flow around two square cylinders in side-by-side arrangement in vertical tube with different void fraction different spacing ratio is numerically simulated by using the finite volume method in this paper. It is found that the gap flow with the spacing ratio smaller than 2.0 is not only biased to one side, resulting in the formation of a narrower wake behind one cylinder and a wider wake behind the other, but also not-biased to neither of them; vortex shedding from the two cylinders with the spacing ratio larger than or equal to 2.0 is synchronized. But when the spacing ratio is equal to 2.0, In-phase mode is the predominant mode while anti-phase mode predominates when the spacing ratio is 2.5, 3.0, 5.0. In bias pattern, the cylinder with wide wake has smaller resistance, the cylinder with narrow wake has larger resistance, and the cylinders with middle wake have equality resistance. Meanwhile the spacing ratio has tremendous influence on pulsating lift, amplitude spectrum and so on. The volume of void fraction in the incident flow influence the vortex production, falling off & development heavily. When the volume of void fraction increases to 0.12, the stable vortex street does not produce.
Liu, C. H.
1975-01-01
The construction of a theoretical flow field due to shedding of vortex rings, the identification of the controlling parameters, and the determination of whether the theoretical model successfully simulated the unsteady pressure field near jet (and consequently the far field noise) was studied. The basic parameters contained in the analytic solutions were the epoch at which a vortex ring was shed near the jet exit and the eddy viscosity coefficient. These parameters were identified from the experimental data for the real-time pressure and from the spread of the mixing layer of the jet. Results of the theoretical analysis show good qualitative agreement with the experimental data.
Eret, Petr; Kennedy, John; Bennett, Gareth J.
2015-10-01
using a simple vortex shedding oscillator acting on the strut. The stability boundary was found to remain unaltered by vortex shedding. Significantly however, the addition of freeplay in the torque link was found to cause shimmy over the more typical operating conditions studied here. Unlike the no-freeplay case, there was a suppressed stabilising effect of increased torsional stiffness of the strut caused by the presence of fairing. No interaction between the vortex shedding and the freeplay on the stability threshold was observed.
基于双共振的涡街信号检测方法%A method based on dual-resonance to detect vortex shedding signals
Institute of Scientific and Technical Information of China (English)
郑俊; 林敏
2014-01-01
A coupled bistable system was composed of a controlled system and a control system by means of nonlinear coupling.The dual-resonance characteristics of the coupled bistable system under a controlling signal action were analyzed.A method based on dual-resonance to enhance stochastic resonance was proposed,and the method was applied to detect vortex shedding signals.Numerical simulations and experimental results showed that with a controlling signal added to the control system,adjusting signal frequency can excite resonances of the system to enhance stochastic resonance of the controlled system substantially;the output power spectral values of the system at the eigen-frequencies increase obviously,and weak signals of vortex shedding submerged in noise can be detected effectively.%耦合双稳系统由控制系统和被控系统经非线性方式耦合而成。分析了控制信号作用下耦合双稳系统的双共振特性，提出了基于双共振的随机共振增强方法，并将该方法应用于涡街流量信号的检测。数值仿真和实验结果表明，改变控制信号的频率可在控制系统中产生共振，进而增强被控系统中的随机共振，系统输出功率谱在特征频率处的谱值显著提高，从而准确检测出噪声背景中的微弱涡街信号。
Evolution equations of von Karman type
Cherrier, Pascal
2015-01-01
In these notes we consider two kinds of nonlinear evolution problems of von Karman type on Euclidean spaces of arbitrary even dimension. Each of these problems consists of a system that results from the coupling of two highly nonlinear partial differential equations, one hyperbolic or parabolic and the other elliptic. These systems take their name from a formal analogy with the von Karman equations in the theory of elasticity in two dimensional space. We establish local (respectively global) results for strong (resp., weak) solutions of these problems and corresponding well-posedness results in the Hadamard sense. Results are found by obtaining regularity estimates on solutions which are limits of a suitable Galerkin approximation scheme. The book is intended as a pedagogical introduction to a number of meaningful application of classical methods in nonlinear Partial Differential Equations of Evolution. The material is self-contained and most proofs are given in full detail. The interested reader will gain a ...
The vortex street as a statistical-mechanical phenomenon
Montgomery, D.
1974-01-01
An explanation of the Karman vortex street is presented on the basis of the two-temperature canonical distribution for inviscid two-dimensional flows in Navier-Stokes fluids or guiding-center plasmas.
Institute of Scientific and Technical Information of China (English)
AHMED N A
2006-01-01
An attempt has been made to explore whether the power relation can be obtained from theoretical considerations. The classical laminar and turbulent boundary layer concepts have been employed to determine appropriate values of the scaling lengths associated with vortex shedding and shear layer frequencies to predict the power law relationship with Reynolds number. The predicted results are in good agreement with experimental results. The findings will provide a greater insight into the overall phenomenon involved.
Vortex wakes of a flapping foil
DEFF Research Database (Denmark)
Schnipper, Teis; Andersen, Anders Peter; Bohr, Tomas
2009-01-01
We present an experimental study of a symmetric foil performing pitching oscillations in a vertically flowing soap film. By varying the frequency and amplitude of the oscillation we visualize a variety of wakes with up to 46 vortices per oscillation period, including von Karman vortex street...
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Dupays, J.; Prevost, M.; Tarrin, P.; Vuillot, F.
1998-07-01
Two campaigns of tests based on a small bench test installation, naturally instable and using various propellants with or without calibrated particles, were carried out at the Onera. The numerous pressure measurements performed along the engine have permitted to explain the wave system that takes place inside the combustion chamber as the sum of two acoustic waves and a convective wave with the same frequency, and linked with the evolution of vortices. This result shows that a coupling exists between the acoustic properties of the chamber and the vortex shedding whatever is the propellant used. (J.S.)
Numerical study of impeller-driven von Karman flows via a volume penalization method
Kreuzahler, Sebastian; Homann, Holger; Ponty, Yannick; Grauer, Rainer
2013-01-01
Simulations of impeller-driven flows in cylindrical geometry are performed via direct numerical simulations (DNS) and compared to flows obtained in the von Karman flow experiments. The geometry of rotating impellers assembled of several basic geometric objects is modeled via a penalization method and implemented in a massive parallel pseudo-spectral Navier-Stokes solver. We performed simulations of impellers with different curvature of blades, especially one resembling the so-called TM28 configuration used in water experiments. The decomposition into poloidal, toroidal components and the mean velocity fields from our simulations are quantitatively in agreement with experimental results. We analyzed the flow structure close to the impeller blades and found different vortex topologies.
Institute of Scientific and Technical Information of China (English)
甘晓松; 何国强; 杨尚荣; 岳赟
2011-01-01
采用冷流试验系统研究了不同主流速度对压强振荡的影响,并通过在流场中加入示踪粒子,且运用连续片光流动显示技术和高速数字摄像技术获得了试验器中流场的旋涡运动情况.实验结果表明,随着主流速度的增加,旋涡脱落的频率相应升高.同时,对比压强测试结果与高速摄影结果,发现当旋涡脱落的频率接近实验器声场的某一阶固有频率时,就可能引起压强振荡,且两者频率的差值越小,压强振荡的振幅就越大.%A cold flow experimental system was built to study the influence of mean flow velocities on pressure oscillation. By putting trace particles into the flow field, its vortex movement in tester was obtained with continuous laser sheet displaying of flow and high speed digital camera. Hie results show that vortex shedding frequency rises with the increasing of mean flow velocity. By comparing the pressure oscillation data and the high speed visualization image sequence, it can be concluded that when the vortex shedding frequency is close to the frequency of one of resonant acoustic modes of the experimental facility, pressure oscillation occurs. The closer the two frequencies are, the higher the amplitude is.
On the vortex dynamics in the wake of a finite surface-mounted square cylinder
Energy Technology Data Exchange (ETDEWEB)
Sattari, P.; Bourgeois, J.A.; Martinuzzi, R.J. [University of Calgary, Department of Mechanical and Manufacturing Engineering, Calgary, AB (Canada)
2012-05-15
The shedding process in the near wake of a surface-mounted, square cross-section cylinder of height-to-width aspect ratio 4 at a Reynolds number of 12,000 based on free-stream velocity and the obstacle width was investigated. The boundary layer thickness was 0.18 obstacle heights based on 99% free-stream velocity. The study is performed using planar high frame-rate particle image velocimetry synchronized with pressure measurements and hot-wire anemometry. Spatial cross-correlation, instantaneous phase relationships, and phase-averaged velocity data are reported. Two dominant vortex-shedding regimes are observed. During intervals of high-amplitude pressure fluctuations on the obstacle side faces, alternate formation and shedding of vortices is observed (regime A) similar to the von Karman process. Regime B is characterized by two co-existing vortices in the obstacle lee throughout the shedding cycle and is observed within low-amplitude pressure fluctuation intervals. Despite the coexisting vortices in the base region, opposite sign vorticity is still shed out-of-phase downstream of this vortex pair giving rise to a staggered arrangement of counter-rotating vortices downstream. While the probability of occurrence of Regime B increases toward the free end, the amplitude modulation remains coherent along the obstacle height. Conditionally phase-averaged reconstructions of the flow field are consistent with the spatial distribution of the phase relationships and their probability density function. Earlier observations are reconciled showing that the symmetric shedding of vortices is a rare occurrence. (orig.)
Institute of Scientific and Technical Information of China (English)
苏新军; 王祺; 林宗虎
2001-01-01
通过试验，对气液两相流中相同直径的3排错列圆柱表面上旋涡的脱落与节径比、含气率的关系进行了研究.研究发现：旋涡的周期性脱落仅在含气率α小于等于0.14的范围内发生；对于横向节径比s1／d小于等于2.0的错列圆柱，隙缝流呈现双稳态的偏斜流，而横向节径比s1／d大于2.0时，双稳态的偏斜流消失；两相流斯特拉赫数随含气率的增加而减小.%The relationship between the vortex shedding from the surface ofthree row circular cylinders of the same diameter in staggered arrangement and the ratio of pitch to diameter or void friction is experimentally investigated.The results show that periodical vortex shedding happens when the void fraction is no more than 0.14.As the ratio of transverse pitch to diameter is no more than 2.0,gap-flow is bistable deflective flow.But bistable deflective flow disappears as the ratio more than 2.0.Strouhal number in two-phase flow reduces with the increase of the void friction.
Bifurcation and instability problems in vortex wakes
Energy Technology Data Exchange (ETDEWEB)
Aref, H [Center for Fluid Dynamics and Department of Physics, Technical University of Denmark, Kgs. Lyngby, DK-2800 (Denmark); Broens, M [Center for Fluid Dynamics and Department of Mathematics, Technical University of Denmark, Kgs. Lyngby, DK-2800 (Denmark); Stremler, M A [Department of Engineering Science and Mechanics, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061 (United States)
2007-04-15
A number of instability and bifurcation problems related to the dynamics of vortex wake flows are addressed using various analytical tools and approaches. We discuss the bifurcations of the streamline pattern behind a bluff body as a vortex wake is produced, a theory of the universal Strouhal-Reynolds number relation for vortex wakes, the bifurcation diagram for 'exotic' wake patterns behind an oscillating cylinder first determined experimentally by Williamson and Roshko, and the bifurcations in topology of the streamlines pattern in point vortex streets. The Hamiltonian dynamics of point vortices in a periodic strip is considered. The classical results of von Karman concerning the structure of the vortex street follow from the two-vortices-in-a-strip problem, while the stability results follow largely from a four-vortices-in-a-strip analysis. The three-vortices-in-a-strip problem is argued to be relevant to the wake behind an oscillating body.
Multiply-interacting Vortex Streets
Oskouei, Babak G; Newton, Paul K
2010-01-01
We investigate the behavior of an infinite array of (reverse) von K'arm'an streets. Our primary motivation is to model the wake dynamics in large fish schools. We ignore the fish and focus on the dynamic interaction of multiple wakes where each wake is modeled as a reverse von K'arm'an street. There exist configurations where the infinite array of vortex streets is in relative equilibrium, that is, the streets move together with the same translational velocity. We examine the topology of the streamline patterns in a frame moving with the same translational velocity as the streets which lends insight into fluid transport through the mid-wake region. Fluid is advected along different paths depending on the distance separating two adjacent streets. Generally, when the distance between the streets is large enough, each street behaves as a single von K'arm'an street and fluid moves globally between two adjacent streets. When the streets get closer to each other, the number of streets that enter into partnership in...
New Numerical Solution of von Karman Equation of Lengthwise Rolling
Directory of Open Access Journals (Sweden)
Rudolf Pernis
2015-01-01
Full Text Available The calculation of average material contact pressure to rolls base on mathematical theory of rolling process given by Karman equation was solved by many authors. The solutions reported by authors are used simplifications for solution of Karman equation. The simplifications are based on two cases for approximation of the circular arch: (a by polygonal curve and (b by parabola. The contribution of the present paper for solution of two-dimensional differential equation of rolling is based on description of the circular arch by equation of a circle. The new term relative stress as nondimensional variable was defined. The result from derived mathematical models can be calculated following variables: normal contact stress distribution, front and back tensions, angle of neutral point, coefficient of the arm of rolling force, rolling force, and rolling torque during rolling process. Laboratory cold rolled experiment of CuZn30 brass material was performed. Work hardening during brass processing was calculated. Comparison of theoretical values of normal contact stress with values of normal contact stress obtained from cold rolling experiment was performed. The calculations were not concluded with roll flattening.
A Powerful Friendship: Theodore von Karman and Hugh L. Dryden
Gorn, Michael
2003-01-01
During their long personal friendship and professional association, Theodore von Karman (1882-1963) and Hugh L. Dryden (1898-1965) exercised a pivotal if somewhat elusive influence over American aeronautics and spaceflight. Both decisive figures in organizing scientists and engineers at home and abroad, both men of undisputed eminence in their technical fields, their range of contacts in government, academia, the armed forces, industry, and professional societies spanned the globe to an extent unparalleled then as now. Moreover, because they coordinated their activities closely, their combined influence far exceeded the sum of each one s individual contributions. This paper illustrates their personal origins as well as the foundations of their friendship, how their relationship became a professional alliance, and their joint impact on the world of aeronautics and astronautics during the twentieth century.
Dynamics of Diffusion Flames in von Karman Swirling Flows Studied
Nayagam, Vedha; Williams, Forman A.
2002-01-01
Von Karman swirling flow is generated by the viscous pumping action of a solid disk spinning in a quiescent fluid media. When this spinning disk is ignited in an oxidizing environment, a flat diffusion flame is established adjacent to the disk, embedded in the boundary layer (see the preceding illustration). For this geometry, the conservation equations reduce to a system of ordinary differential equations, enabling researchers to carry out detailed theoretical models to study the effects of varying strain on the dynamics of diffusion flames. Experimentally, the spinning disk burner provides an ideal configuration to precisely control the strain rates over a wide range. Our original motivation at the NASA Glenn Research Center to study these flames arose from a need to understand the flammability characteristics of solid fuels in microgravity where slow, subbuoyant flows can exist, producing very small strain rates. In a recent work (ref. 1), we showed that the flammability boundaries are wider and the minimum oxygen index (below which flames cannot be sustained) is lower for the von Karman flow configuration in comparison to a stagnation-point flow. Adding a small forced convection to the swirling flow pushes the flame into regions of higher strain and, thereby, decreases the range of flammable strain rates. Experiments using downward facing, polymethylmethacrylate (PMMA) disks spinning in air revealed that, close to the extinction boundaries, the flat diffusion flame breaks up into rotating spiral flames (refs. 2 and 3). Remarkably, the dynamics of these spiral flame edges exhibit a number of similarities to spirals observed in biological systems, such as the electric pulses in cardiac muscles and the aggregation of slime-mold amoeba. The tail of the spiral rotates rigidly while the tip executes a compound, meandering motion sometimes observed in Belousov-Zhabotinskii reactions.
Influence of polymer additives on turbulence in von Karman swirling flow between two disks. II
Burnishev, Yuri; Steinberg, Victor
2016-03-01
We present the experimental studies of the influence of polymer additives on the statistical and scaling properties of the fully developed turbulent regime in a von Karman swirling flow driven either by the smooth or bladed disks using only the global measurements of torque Γ and pressure p fluctuations in water- and water-sugar-based solutions of different viscosities, or elasticity El, and different polymer concentrations ϕ as a function of Re in the same apparatus. There are three highlights achieved and reported in the paper: (i) An observation of turbulent drag reduction (TDR) at both the inertial and viscous flow forcing, in a contradiction to a currently accepted opinion that only the viscous forcing leads to TDR, and the unexpected drastic difference in the transition to the fully developed turbulent and TDR regimes in von Karman swirling flow of water-based polymer solutions depending on the way of the forcing; (ii) a continuous transition to TDR in both the normalized torque drop and the rms pressure fluctuations drop and universality in scaling behavior of Cf in an agreement with theoretical predictions; and (iii) the dramatic differences in the appearance of the frequency power spectra of Γ and in particular p due to the different ways of the forcing are also observed. We discuss and summarize further the results in accordance with these three main achievements. The main message of these studies is that both the inertial forcing and viscous forcing of von Karman swirling flow between two counter-rotating disks lead to TDR in the sharp contrast to the currently accepted opinion [O. Cadot et al., "Turbulent drag reduction in a closed flow system: Boundary layer versus bulk effects," Phys. Fluids 10, 426 (1998); D. Bonn et al., "From scale scales to large scales in three-dimensional turbulence: The effect of diluted polymers," Phys. Rev. E 47, R28 (1993); and D. Bonn et al., "Turbulent drag reduction by polymers," J. Phys.: Condens. Matter 17, S1195
Holm, Darryl D
2015-01-01
Vortex blob methods are typically characterized by a regularization length scale, below which the the dynamics are trivial for isolated blobs. In this article we will find that the dynamics need not be trivial if one is willing to consider distributional derivatives of Dirac delta functionals as valid vorticity distributions. More specifically, a new singular vortex theory is presented for regularised Euler fluid equations of ideal incompressible flow in the plane. We determine the conditions under which such regularised Euler fluid equations may admit vorticity singularities which are stronger than delta functions, e.g., derivatives of delta functions. We also characterise the Hamiltonian dynamics of the higher-order singular vortices. Applications to the design of numerical meth- ods similar to vortex blob methods are also discussed. Such findings shed light onto the rich dynamics which occur below the regularization length scale and enlighten our perspective on the multiscale aspects of regularized fluid m...
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Akhmetov, D.G. [Lavrentiev Institute of Hydrodynamics, Novosibirsk (Russian Federation)
2009-07-01
This book presents a comprehensive coverage of the wide field of vortex rings. The book presents the results of systematic experimental investigations, theoretical foundation, as well as the practical applications of vortex rings, such as the extinction of fires at gushing gas and oil wells. All the basic properties of vortex rings as well as their hydrodynamic structures are presented. Special attention is paid to the formation and motion of turbulent vortex rings. (orig.)
Cho, Inyong
2008-01-01
We investigate vortex configurations with the "vulcanization" term introduced for renormalization of $\\phi_\\star^4$ theory in canonical $\\theta$-deformed noncommutativity. In the small-$\\theta$ limit, we perform numerical calculations and find that nontopological vortex solutions exist as well as Q-ball type solutions, but topological vortex solutions are not admitted.
Numerical Solutions of the von Karman Equations for a Thin Plate
da Silva, Pedro Patricio; Krauth, Werner
1996-01-01
In this paper, we present an algorithm for the solution of the von Karman equations of elasticity theory and related problems. Our method of successive reconditioning is able to avoid convergence problems at any ratio of the nonlinear streching and the pure bending energies. We illustrate the power of the method by numerical calculations of pinched or compressed plates subject to fixed boundaries.
Lift enhancement by trapped vortex
Rossow, Vernon J.
1992-01-01
The viewgraphs and discussion of lift enhancement by trapped vortex are provided. Efforts are continuously being made to find simple ways to convert wings of aircraft from an efficient cruise configuration to one that develops the high lift needed during landing and takeoff. The high-lift configurations studied here consist of conventional airfoils with a trapped vortex over the upper surface. The vortex is trapped by one or two vertical fences that serve as barriers to the oncoming stream and as reflection planes for the vortex and the sink that form a separation bubble on top of the airfoil. Since the full three-dimensional unsteady flow problem over the wing of an aircraft is so complicated that it is hard to get an understanding of the principles that govern the vortex trapping process, the analysis is restricted here to the flow field illustrated in the first slide. It is assumed that the flow field between the two end plates approximates a streamwise strip of the flow over a wing. The flow between the endplates and about the airfoil consists of a spanwise vortex located between the suction orifices in the endplates. The spanwise fence or spoiler located near the nose of the airfoil serves to form a separated flow region and a shear layer. The vorticity in the shear layer is concentrated into the vortex by withdrawal of fluid at the suction orifices. As the strength of the vortex increases with time, it eventually dominates the flow in the separated region so that a shear or vertical layer is no longer shed from the tip of the fence. At that point, the vortex strength is fixed and its location is such that all of the velocity contributions at its center sum to zero thereby making it an equilibrium point for the vortex. The results of a theoretical analysis of such an idealized flow field are described.
Space gravity spectroscopy: the benefits of Taylor-Karman structured criterion matrices
Directory of Open Access Journals (Sweden)
P. Marinkovice
2003-01-01
Full Text Available As soon as a space gravity spectroscopy was successfully performed, for instance by means of semicontinuous ephemeris of LEO - GPS tracked satellites, the problem of data validation appeared. It is for this purpose that a stochastic model for the homogeneous and isotropic analysis of measurements, obtained as “directly" measured values in LEO satellite missions (CHAMP, GRACE, GOCE, is studied. An isotropic analysis is represented by the homogeneous distribution of measured values and the statistical properties of the model are calculated. In particular, a correlation structure function is defined by the third order tensor (Taylor-Karman tensor for the ensemble average of a set of incremental differences in measured components. Specifically, Taylor-Karman correlation tensor is calculated with the assumption that the analyzed random function is of a “potential type". The special class of homogeneous and isotropic correlation functions is introduced. Finally, a successful application of the concept is presented in the case study CHAMP and a comparison between modeled and estimated correlations is performed.Key words. data validation, 3D correlation tensor, homogeneous and isotropic correlation functions, Taylor-Karman structure, CHAMP
Vortex noise from nonrotating cylinders and airfoils
Schlinker, R. H.; Amiet, R. K.; Fink, M. R.
1976-01-01
An experimental study of vortex-shedding noise was conducted in an acoustic research tunnel over a Reynolds-number range applicable to full-scale helicopter tail-rotor blades. Two-dimensional tapered-chord nonrotating models were tested to simulate the effect of spanwise frequency variation on the vortex-shedding mechanism. Both a tapered circular cylinder and tapered airfoils were investigated. The results were compared with data for constant-diameter cylinder and constant-chord airfoil models also tested during this study. Far-field noise, surface pressure fluctuations, and spanwise correlation lengths were measured for each configuration. Vortex-shedding noise for tapered cylinders and airfoils was found to contain many narrowband-random peaks which occurred within a range of frequencies corresponding to a predictable Strouhal number referenced to the maximum and minimum chord. The noise was observed to depend on surface roughness and Reynolds number.
Interaction of a Vortex Ring with a Thin Porous Surface
Hrynuk, John; Bohl, Doug
2012-11-01
The interaction of vortex rings with thin porous screens was investigated using Molecular Tagging Velocimetry (MTV). The surface porosity, defined as the ratio of the open area to total area of the screen, was held constant at ϕ = 65% while the diameter of screen wires was varied. The three screens of varying wire diameter tested were: a fine wire (Dwire = 0.0178 cm), a medium wire (Dwire = 0.104 cm) and coarse wire (Dwire = 0.204 cm). When the vortex interacted with the fine wire screen a secondary vortex formed on the upstream face of the screen that orbited the primary vortex and then convected back up stream. The primary vortex reformed immediately downstream of the screen with significantly lower strength. For medium and large wire screens additional vorticity was generated and shed from individual wires, changing the downstream vortex behavior. Secondary vortices were observed for these larger screens but they were weaker and remained in proximity to the screen. Vortex shedding from the screen wires was observed for the medium screen which delayed the reformation of the vortex ring downstream of the screen. Shed vortex pairs, from individual wires, were observed to dominate the downstream flow for the large wire screen and no vortex ring reformation was observed. Vorticity and circulation will be used to further understand the interaction process for each of these screens.
Cheng, J Y; Chahine, G L
2001-12-01
The slender body theory, lifting surface theories, and more recently panel methods and Navier-Stokes solvers have been used to study the hydrodynamics of fish swimming. This paper presents progress on swimming hydrodynamics using a boundary integral equation method (or boundary element method) based on potential flow model. The unsteady three-dimensional BEM code 3DynaFS that we developed and used is able to model realistic body geometries, arbitrary movements, and resulting wake evolution. Pressure distribution over the body surface, vorticity in the wake, and the velocity field around the body can be computed. The structure and dynamic behavior of the vortex wakes generated by the swimming body are responsible for the underlying fluid dynamic mechanisms to realize the high-efficiency propulsion and high-agility maneuvering. Three-dimensional vortex wake structures are not well known, although two-dimensional structures termed 'reverse Karman Vortex Street' have been observed and studied. In this paper, simulations about a swimming saithe (Pollachius virens) using our BEM code have demonstrated that undulatory swimming reduces three-dimensional effects due to substantially weakened tail tip vortex, resulting in a reverse Karman Vortex Street as the major flow pattern in the three-dimensional wake of an undulating swimming fish.
Energy Technology Data Exchange (ETDEWEB)
Ravelet, F
2005-09-15
We report experimental studies of the turbulent von Karman flow, inertially stirred between counter-rotating impellers. We first study the flow and its transition from laminar to turbulent regime. We highlight the role of slowly varying large scales, due to the presence of an azimuthal mixing layer. The large scales of this flow can be unstable in turbulent regime. We study the statistics of the transitions between the different mean states. The second part is dedicated to an experiment in liquid sodium, called VKS2. We optimize the time-averaged flow in order to allow kinematic dynamo action. We report the very first results of the experiment, and discuss the role of the large scales temporal non-stationariness. (author)
The Interaction Vortex Flow Around Two Bluff Cylinders
Directory of Open Access Journals (Sweden)
Hirao K.
2013-04-01
Full Text Available In this study, the interaction vortex flow features around a pair of parallel arranged bluff cylinders were observed by visualizing water flow experiment at the range of the gap ratio G/d=0~3. It was obtained that the result of established wind tunnel test and the result of this water tank test agreed about the characteristics of vortex shedding when varying the distance of circular cylinder gap. The flow pattern and vortex shedding frequency of another type bluff cylinder (triangular and square cylinder were also investigated. As a result of the experiment, it was shown that the flow pattern of wake flow was divided into three kinds (coupled vortex streets, biased gap flow and single vortex street regardless of the cylinder section shape and cylinder size. Then, the region of the appearance of flow pattern was shown about each case. In the case where two each other independent vortex streets were formed, three typical flow patterns of vortex formation (in-phase coupled vortex streets, out-of-phase coupled vortex streets and complication coupled vortex streets were observed. It was known that three configuration of vortex formation appear intermittently and alternatively.
The Interaction Vortex Flow Around Two Bluff Cylinders
Yokoi, Y.; Hirao, K.
2013-04-01
In this study, the interaction vortex flow features around a pair of parallel arranged bluff cylinders were observed by visualizing water flow experiment at the range of the gap ratio G/d=0~3. It was obtained that the result of established wind tunnel test and the result of this water tank test agreed about the characteristics of vortex shedding when varying the distance of circular cylinder gap. The flow pattern and vortex shedding frequency of another type bluff cylinder (triangular and square cylinder) were also investigated. As a result of the experiment, it was shown that the flow pattern of wake flow was divided into three kinds (coupled vortex streets, biased gap flow and single vortex street) regardless of the cylinder section shape and cylinder size. Then, the region of the appearance of flow pattern was shown about each case. In the case where two each other independent vortex streets were formed, three typical flow patterns of vortex formation (in-phase coupled vortex streets, out-of-phase coupled vortex streets and complication coupled vortex streets) were observed. It was known that three configuration of vortex formation appear intermittently and alternatively.
The method to control the submarine horseshoe vortex by breaking the vortex core
Institute of Scientific and Technical Information of China (English)
LIU Zhi-hua; XIONG Ying; TU Cheng-xu
2014-01-01
The quality of the inflow across the propeller is closely related with the hydrodynamic performance and the noise characteristics of the propeller. For a submarine, with a horseshoe vortex generated at the junction of the main body and the appendages, the submarine wake is dominated by a kind of highly non-uniform flow field, which has an adverse effect on the performance of the submarine propeller. In order to control the horseshoe vortex and improve the quality of the submarine wake, the flow field around a submarine model is simulated by the detached eddies simulation (DES) method, and the vortex configuration is displayed using the second invariant of the velocity derivative tensor. The state and the transition process of the horseshoe vortex are analyzed, then a modified method to break the vortex core by a vortex baffle is proposed. The flow numerical simulation is carried out to study the effect of this method. Numerical simulations show that, with the breakdown of the vortex core, many unstable vortices are shed and the energy of the horseshoe vortex is dissipated quickly, and the uniformity of the submarine wake is improved. The submarine wake test in a wind tunnel has verified the effect of the method to control the horseshoe vortex. The vortex baffle can improve the wake uniformity in cases of high Reynolds numbers as well, and it does not have adverse effects on the maneuverability and the speed ability of the submarine.
Energy Technology Data Exchange (ETDEWEB)
Chorin, A.J. [California Univ., Berkeley, CA (United States). Dept. of Mathematics]|[Lawrence Berkeley Lab., CA (United States)
1993-06-01
Vortex methods originated from the observation that in incompressible inviscid flow vorticity (or, more accurately, circulation) is a conserved quantity, as can be readily deduced from the absence of tangential stresses. Thus, if the vorticity is known at time t=0, one can find the flow at a later time by simply following the vorticity. In this narrow context, a vortex method is a numerical method that follows vorticity. The author restricts himself in these lectures to a special class of numerical vortex methods, those that are based on a Lagrangian transport of vorticity in hydrodynamics by smoothed particles (blobs) and those whose analysis contributes to the understanding of blob methods. Blob methods started in the 1930`s.
Visualization and computation of hovering mode vortex dynamics
Freymuth, Peter; Gustafson, Karl E.; Leben, Robert
Results from experimental and numerical simulations of the unsteady hovering flight of small birds or insects are presented in extensive photographs and computer graphics and discussed in detail. In the flow-visualization experiments, an airfoil in combined pitching and plunging motion is used to generate a thrusting jet in still air, producing in addition a vortex street with rotation opposite to that of a Karman street. The numerical studies are based on an extension of the robust multigrid method of Gustafson and Leben (1986 and 1988) to hovering-mode vortex dynamics. The derivation of the governing equations is outlined, and it is shown that the numerical and experimental results are in good qualitative agreement.
Xu, Jinglei; Li, Meng; Zhang, Yang; Chen, Longfei
2016-12-01
The von Karman length scale is able to reflect the size of the local turbulence structure. However, it is not suitable for the near wall region of wall-bounded flows, for its value is almost infinite there. In the present study, a simple and novel length scale combining the wall distance and the von Karman length scale is proposed by introducing a structural function. The new length scale becomes the von Karman length scale once local unsteady structures are detected. The proposed method is adopted in a series of turbulent channel flows at different Reynolds numbers. The results show that the proposed length scale with the structural function can precisely simulate turbulence at high Reynolds numbers, even with a coarse grid resolution.
The Interaction Vortex Flow Around Two Bluff Cylinders
Hirao K.; Yokoi Y.
2013-01-01
In this study, the interaction vortex flow features around a pair of parallel arranged bluff cylinders were observed by visualizing water flow experiment at the range of the gap ratio G/d=0~3. It was obtained that the result of established wind tunnel test and the result of this water tank test agreed about the characteristics of vortex shedding when varying the distance of circular cylinder gap. The flow pattern and vortex shedding frequency of another type bluff cylinder (triangular and squ...
Nonlocal modeling and buckling features of cracked nanobeams with von Karman nonlinearity
Akbarzadeh Khorshidi, Majid; Shaat, Mohamed; Abdelkefi, Abdessattar; Shariati, Mahmoud
2017-01-01
Buckling and postbuckling behaviors of cracked nanobeams made of single-crystalline nanomaterials are investigated. The nonlocal elasticity theory is used to model the nonlocal interatomic effects on the beam's performance accounting for the beam's axial stretching via von Karman nonlinear theory. The crack is then represented as torsional spring where the crack severity factor is derived accounting for the nonlocal features of the beam. By converting the beam into an equivalent infinite long plate with an edge crack subjected to a tensile stress at the far field, the crack energy release rate, intensity factor, and severity factor are derived according to the nonlocal elasticity theory. An analytical solution for the buckling and the postbuckling responses of cracked nonlocal nanobeams accounting for the beam axial stretching according to von Karman nonlinear theory of kinematics is derived. The impacts of the nonlocal parameter on the critical buckling loads and the static nonlinear postbuckling responses of cracked nonlocal nanobeams are studied. The results indicate that the buckling and postbuckling behaviors of cracked nanobeams are strongly affected by the crack location, crack depth, nonlocal parameter, and length-to-thickness ratio.
Vortex dynamics in the wake of a mechanical fish
Energy Technology Data Exchange (ETDEWEB)
Bruecker, Christoph [TU Bergakademie Freiberg, Lehrstuhl fuer Stroemungslehre und Stroemungsmaschinen, Freiberg (Germany); Bleckmann, Horst [Poppelsdorfer Schloss, Zoologisches Institut Bonn, Bonn (Germany)
2007-11-15
This study focuses on the three-dimensional flow around a mechanical fish model, which reproduces the typical undulatory body and fin motion of a carangiform swimmer. The mechanical model consists of a flexible skeleton embedded in a soft transparent silicone body, which is connected with two cams to a flapping and bending hinge generating a traveling wave motion with increasing amplitude from anterior to posterior, extending to a combined heaving and pitching motion at the fin. The model is submerged in a water tank and towed at the characteristic swimming speed for the neutral swimming mode at U/V = 1. The method of Scanning Particle Image Velocimetry was used to analyze the three-dimensional time-dependent flow field in the axial and saggital planes. The results confirm the earlier observations that the wake develops into a chain of vortex rings which travel sidewards perpendicular to the swimming direction. However, instead of one single vortex shed at each tail beat half-cycle we observed a pair of two vortex rings being shed. Each pair consists of a larger main vortex ring corresponding to the tail beat start-stop vortex, while the second vortex ring is due to the body bending motion. The existence of the second vortex reflects the role of the body in undulatory swimming. A simplified model of the fish body comparing it to a plate with a hinged flap demonstrates the link between the sequence of kinematics and vortex shedding. (orig.)
Sun, Bo; Lin, Jiayi; Darby, Ellis; Grosberg, Alexander Y.; Grier, David G.
2009-07-01
Mechanical equilibrium at zero temperature does not necessarily imply thermodynamic equilibrium at finite temperature for a particle confined by a static but nonconservative force field. Instead, the diffusing particle can enter into a steady state characterized by toroidal circulation in the probability flux, which we call a Brownian vortex. The circulatory bias in the particle’s thermally driven trajectory is not simply a deterministic response to the solenoidal component of the force but rather reflects interplay between advection and diffusion in which thermal fluctuations extract work from the nonconservative force field. As an example of this previously unrecognized class of stochastic heat engines, we consider a colloidal sphere diffusing in a conventional optical tweezer. We demonstrate both theoretically and experimentally that nonconservative optical forces bias the particle’s fluctuations into toroidal vortexes whose circulation can reverse direction with temperature or laser power.
Ferrando, Albert; Zacarés, Mario; García-March, Miguel-Angel; Monsoriu, Juan A; de Córdoba, Pedro Fernández
2005-09-16
Using group theory arguments and numerical simulations, we demonstrate the possibility of changing the vorticity or topological charge of an individual vortex by means of the action of a system possessing a discrete rotational symmetry of finite order. We establish on theoretical grounds a "transmutation pass" determining the conditions for this phenomenon to occur and numerically analyze it in the context of two-dimensional optical lattices. An analogous approach is applicable to the problems of Bose-Einstein condensates in periodic potentials.
Influence of Reynolds number and forcing type in a turbulent von K\\'arm\\'an flow
Saint-Michel, Brice; Marié, Louis; Ravelet, Florent; Daviaud, François
2014-01-01
We present a detailed study of of a global bifurcation occuring in a turbulent von K\\'arm\\'an swirling flow. In this system, the statistically steady states progressively display hysteretic behaviour when the Reynolds number is increased above the transition to turbulence. We examine in detail this hysteresis using asymmetric forcing conditions --- rotating the impellers at different speeds. For very high Reynolds numbers, we study the sensitivity of the hysteresis cycle --- using complementary Particle Image Velocimetry (PIV) and global mechanical measurements --- to the forcing nature, imposing either the torque or the speed of the impellers. New mean states, displaying multiple quasi-steady states and negative differential responses, are experimentally observed in torque control. A simple analogy with electrical circuits is performed to understand the link between multi-stability and negative responses. The system is compared to other, similar "bulk" systems, to understand some relevant ingredients of nega...
Flow dynamics and magnetic induction in the von-Karman plasma experiment
Plihon, Nicolas; Palermo, Francesco; Morales, Jorge A; Bos, Wouter; Godeferd, Fabien S; Bourgoin, Mickaël; Pinton, Jean-François; Moulin, M; Aanesland, Ane
2014-01-01
The von-Karman plasma experiment is a novel versatile experimental device designed to explore the dynamics of basic magnetic induction processes and the dynamics of flows driven in weakly magnetized plasmas. A high-density plasma column (10^16 - 10^19 particles.m^-3) is created by two radio-frequency plasma sources located at each end of a 1 m long linear device. Flows are driven through JxB azimuthal torques created from independently controlled emissive cathodes. The device has been designed such that magnetic induction processes and turbulent plasma dynamics can be studied from a variety of time-averaged axisymmetric flows in a cylinder. MHD simulations implementing volume-penalization support the experimental development to design the most efficient flow-driving schemes and understand the flow dynamics. Preliminary experimental results show that a rotating motion of up to nearly 1 km/s is controlled by the JxB azimuthal torque.
Kinematic dynamo simulations of von K\\'arm\\'an flows: application to the VKS experiment
Pinter, A; Daviaud, F; Leorat, J
2011-01-01
The VKS experiment has evidenced dynamo action in a highly turbulent liquid sodium von K\\'arm\\'an flow [R. Monchaux et al., Phys. Rev. Lett. {\\bf 98}, 044502 (2007)]. However, the existence and the onset of a dynamo happen to depend on the exact experimental configuration. By performing kinematic dynamo simulations on real flows, we study their influence on dynamo action, in particular the sense of rotation and the presence of an annulus in the shear layer plane. The 3 components of the mean velocity fields are measured in a water prototype for different VKS configurations through Stereoscopic Particle Imaging Velocimetry. Experimental data are then processed in order to use them in a periodic cylindrical kinematic code. Even if the kinematic predicted mode appears to be different from the experimental saturated one, the results concerning the existence of a dynamo and the thresholds are in qualitative agreement, showing the importance of the flow characteristics.
Unsteady interaction of a viscous fluid with an elastic shell modeled by full von Karman equations
Chueshov, Igor; Ryzhkova, Iryna
We study well-posedness and asymptotic dynamics of a coupled system consisting of linearized 3D Navier-Stokes equations in a bounded domain and a classical (nonlinear) full von Karman shallow shell equation that accounts for both transversal and lateral displacements on a flexible part of the boundary. We also take into account rotational inertia of filaments of the shell. Our main result shows that the problem generates a semiflow in an appropriate phase space. The regularity provided by viscous dissipation in the fluid allows us to consider simultaneously both cases of presence inertia in the lateral displacements and its absence. Our second result states the existence of a compact global attractor for this semiflow in the case of presence of (rotational) damping in the transversal component and a particular structure of external forces.
Unsteady interaction of a viscous fluid with an elastic shell modeled by full von Karman equations
Chueshov, Igor
2011-01-01
We study well-posedness and asymptotic dynamics of a coupled system consisting of linearized 3D Navier--Stokes equations in a bounded domain and a classical (nonlinear) full von Karman shallow shell equations that accounts for both transversal and lateral displacements on a flexible part of the boundary. We also take into account rotational inertia of filaments of the shell. Out main result shows that the problem generates a semiflow in an appropriate phase space. The regularity provided by viscous dissipation in the fluid allows us to consider simultaneously both cases of presence inertia in the lateral displacements and its absence. Our second result states the existence of a compact global attractor for this semiflow in the case of presence of (rotational) damping in the transversal component and a particular structure of external forces.
On point vortex models of exotic bluff body wakes
Energy Technology Data Exchange (ETDEWEB)
Stremler, Mark A; Basu, Saikat, E-mail: stremler@vt.edu [Department of Engineering Science and Mechanics, Virginia Tech, Blacksburg, VA 24061 (United States)
2014-12-01
Exotic vortex wakes, in which three or more vortices are generated during each shedding cycle, are frequently found in the wake of an oscillating bluff body. Two common examples are P+S wakes (with 3 vortices) and 2P wakes (with 4 vortices). We consider mathematical models of these wakes consisting of N = 3 or 4 point vortices with constant strengths in an inviscid fluid that is otherwise at rest in a singly-periodic domain. By enforcing constraints on the vortex strengths and, in the case of N = 4, on the symmetry of the vortex locations, the mathematical models reduce to integrable Hamiltonian systems. We compare the point vortex trajectories with two exotic wake patterns reported in the literature. Results support the use of point vortex modeling to investigate vortex dynamics in exotic wakes and suggest the need for additional classification of experimental wake patterns. (paper)
Vortex oscillations around a hemisphere-cylinder body with a high fineness ratio
Ma, Bao-Feng
2016-01-01
The vortex unsteadiness around a hemisphere-cylinder body at AOAs of 10 to 80 deg was studied using Large Eddy Simulation (LES) and Dynamic Mode Decomposition (DMD). The Reynolds number (Re) based on the cylinder diameter of the body is 22000. The results show that vortex oscillations exist over the forebody at the whole range of AOAs. The oscillation is characterized by alternate oscillations of a forebody leeward vortex pair up and down and in-phase swings from side to side. The vortex shedding can be found at the afterbody as AOAs more than 20o, and the shedding region moves forwards gradually with AOAs increasing, and accordingly the region of vortex oscillations contracts and eventually only exists near the nose as AOAs sufficiently high. The vortex oscillation and shedding all induce fluctuating side forces along the body, but the ones from vortex oscillations are larger. The frequencies of vortex oscillations are similar to the ones of vortex shedding at the AOAs of 10o-40o with St=0.085-0.12, in which...
Oscillating pendulum decay by emission of vortex rings
Bolster, Diogo; Hershberger, Robert E.; Donnelly, Russell J.
2010-04-01
We have studied oscillation of a pendulum in water using spherical bobs. By measuring the loss in potential energy, we estimate the drag coefficient on the sphere and compare to data from liquid-helium experiments. The drag coefficients compare very favorably illustrating the true scaling behavior of this phenomenon. We also studied the decay of amplitude of the pendulum over time. As observed previously, at small amplitudes, the drag on the bob is given by the linear Stokes drag and the decay is exponential. For larger amplitudes, the pendulum bob sheds vortex rings as it reverses direction. The momentum imparted to these vortex rings results in an additional discrete drag on the bob. We present experiments and a theoretical estimate of this vortex-ring-induced drag. We analytically derive an estimate for a critical amplitude beyond which vortex ring shedding will occur as well as an estimate of the radius of the ring as a function of amplitude.
Vortex Interaction on Low Aspect Ratio Membrane Wings
Waldman, Rye M.; Breuer, Kenneth S.
2013-11-01
Inspired by the flight of bats and by recent interest in Micro Air Vehicles, we present measurements on the steady and unsteady behavior of low aspect ratio membrane wings. We conduct wind tunnel experiments with coupled force, kinematic, and flow field measurements, both on the wing and in the near wake. Membrane wings interact strongly with the vortices shed from the leading- and trailing-edges and the wing tips, and the details of the membrane support play an important role in the fluid-structure interaction. Membranes that are supported at the wing tip exhibit less membrane flutter, more coherent tip vortices, and enhanced lift. The interior wake can exhibit organized spanwise vortex shedding, and shows little influence from the tip vortex. In contrast, membranes with an unsupported wing tip show exaggerated static deformation, significant membrane fluttering and a diffuse, unsteady tip vortex. The unsteady tip vortex modifies the behavior of the interior wake, disrupting the wake coherence.
Approaches for Reduced Order Modeling of Electrically Actuated von Karman Microplates
Saghir, Shahid
2016-07-25
This article presents and compares different approaches to develop reduced order models for the nonlinear von Karman rectangular microplates actuated by nonlinear electrostatic forces. The reduced-order models aim to investigate the static and dynamic behavior of the plate under small and large actuation forces. A fully clamped microplate is considered. Different types of basis functions are used in conjunction with the Galerkin method to discretize the governing equations. First we investigate the convergence with the number of modes retained in the model. Then for validation purpose, a comparison of the static results is made with the results calculated by a nonlinear finite element model. The linear eigenvalue problem for the plate under the electrostatic force is solved for a wide range of voltages up to pull-in. Results among the various reduced-order modes are compared and are also validated by comparing to results of the finite-element model. Further, the reduced order models are employed to capture the forced dynamic response of the microplate under small and large vibration amplitudes. Comparison of the different approaches are made for this case. Keywords: electrically actuated microplates, static analysis, dynamics of microplates, diaphragm vibration, large amplitude vibrations, nonlinear dynamics
Downstream Thermal Evolution of Vortex Cores
Gómez-Barea, A.; Herrada, M. A.; Pérez-Saborid, M.; Barrero, A.
1999-11-01
The downstream evolution of the total temperature field in a quasi-incompressible axisymmetric vortex core has been computed. Starting at an initial station (z=0) with velocity profiles of the Burgers type and given temperature distributions, the numerical results of the evolution show that, according to experimental results, the total temperature in the near-axis region decreases substantially due to the work done by pressure and viscous forces together with the effect of both convection and conduction of heat. Depending on the values of the parameters characterizing the initial profiles and on the value of the Prandtl number, the vortex either breaks down or eventually reaches a self-similar regime. The results obtained shed light on the basic physics involved in the thermal separation phenomenon which appears inside Ranque-Hilsch vortex tubes.
Cyclone–anticyclone vortex asymmetry mechanism and linear Ekman friction
Energy Technology Data Exchange (ETDEWEB)
Chefranov, S. G., E-mail: schefranov@mail.ru [Russian Academy of Sciences, Obukhov Institute of Atmospheric Physics (Russian Federation)
2016-04-15
Allowance for the linear Ekman friction has been found to ensure a threshold (in rotation frequency) realization of the linear dissipative–centrifugal instability and the related chiral symmetry breaking in the dynamics of Lagrangian particles, which leads to the cyclone–anticyclone vortex asymmetry. An excess of the fluid rotation rate ω{sub 0} over some threshold value determined by the fluid eigenfrequency ω (i.e., ω{sub 0} > ω) is shown to be a condition for the realization of such an instability. A new generalization of the solution of the Karman problem to determine the steady-state velocity field in a viscous incompressible fluid above a rotating solid disk of large radius, in which the linear Ekman friction was additionally taken into account, has been obtained. A correspondence of this solution and the conditions for the realization of the dissipative–centrifugal instability of a chiral-symmetric vortex state and the corresponding cyclone–anticyclone vortex asymmetry has been shown. A generalization of the well-known spiral velocity distribution in an “Ekman layer” near a solid surface has been established for the case where the fluid rotation frequency far from the disk ω differs from the disk rotation frequency ω{sub 0}.
U-shaped Vortex Structures in Large Scale Cloud Cavitation
Cao, Yantao; Peng, Xiaoxing; Xu, Lianghao; Hong, Fangwen
2015-12-01
The control of cloud cavitation, especially large scale cloud cavitation(LSCC), is always a hot issue in the field of cavitation research. However, there has been little knowledge on the evolution of cloud cavitation since it is associated with turbulence and vortex flow. In this article, the structure of cloud cavitation shed by sheet cavitation around different hydrofoils and a wedge were observed in detail with high speed camera (HSC). It was found that the U-shaped vortex structures always existed in the development process of LSCC. The results indicated that LSCC evolution was related to this kind of vortex structures, and it may be a universal character for LSCC. Then vortex strength of U-shaped vortex structures in a cycle was analyzed with numerical results.
Fractional vortex Hilbert's Hotel
Gbur, Greg
2015-01-01
We demonstrate how the unusual mathematics of transfinite numbers, in particular a nearly perfect realization of Hilbert's famous hotel paradox, manifests in the propagation of light through fractional vortex plates. It is shown how a fractional vortex plate can be used, in principle, to create any number of "open rooms," i.e. topological charges, simultaneously. Fractional vortex plates are therefore demonstrated to create a singularity of topological charge, in which the vortex state is completely undefined and in fact arbitrary.
Freilich, Daniel; Llewellyn Smith, Stefan
2014-11-01
A Sadovskii vortex is a patch of fluid with uniform vorticity surrounded by a vortex sheet. Using a boundary element type method, we investigate the steady states of this flow in an incompressible, inviscid straining flow. Outside the vortex, the fluid is irrotational. In the limiting case where the entire circulation is due to the vortex patch, this is a patch vortex (Moore & Saffman, Aircraft wake turbulence and its detection 1971). In the other limiting case, where all the circulation is due to the vortex sheet, this is a hollow vortex (Llewellyn Smith and Crowdy, J. Fluid Mech. 691, 2012). This flow has two governing nondimensional parameters, relating the strengths of the straining field, vortex sheet, and patch vorticity. We study the relationship between these two parameters, and examine the shape of the resulting vortices. We also work towards a bifurcation diagram of the steady states of the Sadovskii vortex in an attempt to understand the connection between vortex sheet and vortex patch desingularizations of the point vortex. Support from NSF-CMMI-0970113.
Streamwise Vortex Interaction with a Horseshoe Vortex
Institute of Scientific and Technical Information of China (English)
Piotr Doerffer; Pawel Flaszynski; Franco Magagnato
2003-01-01
Flow control in turbomachinery is very difficult because of the complexity of its fully 3-D flow structure. The authors propose to introduce streamwise vortices into the control of internal flows. A simple configuration of vortices was investigated in order to better understand the flow control methods by means of streamwise vortices.The research presented here concerns streamwise vortex interaction with a horseshoe vortex. The effects of such an interaction are significantly dependent on the relative location of the streamwise vortex in respect to the leading edge of the profile. The streamwise vortex is induced by an air jet. The horseshoe vortex is generated by the leading edge of a symmetric profile. Such a configuration gives possibility to investigate the interaction of these two vortices alone. The presented analysis is based on numerical simulations by means of N-S compressible solver with a two-equation turbulence model.
Vortex mechanism in hydrocyclones
Institute of Scientific and Technical Information of China (English)
徐继润; 刘正宁; 邢军; 李新跃; 黄慧; 徐海燕; 罗茜
2001-01-01
On the basis of analyzing the vortex characteristics, a new mechanism of the vortex formation in hydrocyclones is developed. The main concept of the mechanism is that the vortex flow in a hydrocyclone is resulted from the overlapping of container rotation and hole leakage. The model is then used to explain the compound distribution of free vortex and forced vortex, predict the similarity of tangential velocity at different input pressures, and make count of the principle of small hydrocyclone with lower cut-size than large one. Meanwhile a new possible approach to a large hydro-cyclone with lower cut-size by minimizing or eliminating the air core is discussed briefly.
Integrability and chaos in body-vortex interactions
DEFF Research Database (Denmark)
Pedersen, Johan Rønby; Aref, Hassan
2009-01-01
have fixed strengths and are intended to model vortices that have been shed by the body or elsewhere in the flow field. The flow at any given time and position is determined by the instantaneous vortex and body positions together with the instantaneous linear and angular velocity of the body...
Depicting Vortex Stretching and Vortex Relaxing Mechanisms
Institute of Scientific and Technical Information of China (English)
符松; 李启兵; 王明皓
2003-01-01
Different from many existing studies on the paranetrization of vortices, we investigate the effectiveness of two new parameters for identifying the vortex stretching and vortex relaxing mechanisms. These parameters are invariants and identify three-dimensional flow structures only, i.e. they diminish in two-dimensional flows. This is also unlike the existing vortex identification approaches which deliver information in two-dimensional flows. The present proposals have been successfully applied to identify the stretching and relaxing vortices in compressible mixing layers and natural convection flows.
Vortex-Based Aero- and Hydrodynamic Estimation
Hemati, Maziar Sam
Flow control strategies often require knowledge of unmeasurable quantities, thus presenting a need to reconstruct flow states from measurable ones. In this thesis, the modeling, simulation, and estimator design aspects of flow reconstruction are considered. First, a vortex-based aero- and hydrodynamic estimation paradigm is developed to design a wake sensing algorithm for aircraft formation flight missions. The method assimilates wing distributed pressure measurements with a vortex-based wake model to better predict the state of the flow. The study compares Kalman-type algorithms with particle filtering algorithms, demonstrating that the vortex nonlinearities require particle filters to yield adequate performance. Furthermore, the observability structure of the wake is shown to have a negative impact on filter performance regardless of the algorithm applied. It is demonstrated that relative motions can alleviate the filter divergence issues associated with this observability structure. In addition to estimator development, the dissertation addresses the need for an efficient unsteady multi-body aerodynamics testbed for estimator and controller validation studies. A pure vortex particle implementation of a vortex panel-particle method is developed to satisfy this need. The numerical method is demonstrated on the impulsive startup of a flat plate as well as the impulsive startup of a multi-wing formation. It is clear, from these validation studies, that the method is able to accommodate the unsteady wake effects that arise in formation flight missions. Lastly, successful vortex-based estimation is highly dependent on the reliability of the low-order vortex model used in representing the flow of interest. The present treatise establishes a systematic framework for vortex model improvement, grounded in optimal control theory and the calculus of variations. By minimizing model predicted errors with respect to empirical data, the shortcomings of the baseline vortex model
Steady vortex force theory and slender-wing flow diagnosis
Institute of Scientific and Technical Information of China (English)
Y.T.Yang; R.K.Zhang; Y.R.An; J.Z.Wu
2007-01-01
The concept vortex force in aerodynamics is sys-tematically examined based on a new steady vortex-force theory (Wu et al., Vorticity and vortex dynamics, Springer, 2006) which expresses the aerodynamic force (and moment) by the volume and boundary integrals of the Lamb vector.In this paper, the underlying physics of this theory is explo-red, including the general role of the Lamb vector in non-linear aerodynamics, its initial formation, and its relevance to the total-pressure non-uniformity. As a typical example, the theory is applied to the flow over a slender delta wing at a large angle of attack. The highly localized flow structures with high Lamb-vector peaks are identified in terms of their net contribution to various constituents of the total aerody-namic force. This vortex-force diagnosis sheds new light on the flow control and configuration optimization.
Manipulation of Leading-Edge Vortex Evolution by Applied Suction
Buchholz, James; Akkala, James
2016-11-01
The generation and shedding of vortices from unsteady maneuvering bodies can be characterized within a framework of vorticity transport, accounting for the effects of multiple sources and sinks of vorticity on the overall circulation of the vortex system. On a maneuvering wing, the diffusive flux of secondary vorticity from the surface is a critical contributor to the strength and dynamics of the leading-edge vortex, suggesting that flow control strategies targeting the manipulation of the secondary vorticity flux and the secondary vortex may provide an effective means of manipulating vortex development. Suction has been applied in the vicinity of the secondary vortex during the downstroke of a periodically-plunging flat-plate airfoil, and the flow evolution and aerodynamic loads are compared to the baseline case in which suction is not applied. Observation of the resulting surface pressure distribution and flow evolution suggest that the secondary flux of vorticity and the evolution of the flow field can be altered subject to appropriate position of the suction ports relative to the developing vortex structures, and at a specific temporal window in the development of the vortex. This work was supported by the Air Force Office of Scientific Research, Grant Number FA9550-16-1-0107 and NSF EPSCoR Grant Number EPS1101284.
Vortex Anemometer Using MEMS Cantilever Sensor
Zylka, P; Zylka, Pawel; Modrzynski, Pawel
2010-01-01
This paper presents construction and performance of a novel hybrid microelectromechanical system (MEMS) vortex flowmeter. A miniature cantilever MEMS displacement sensor was used to detect frequency of vortices development. 3-mm-long silicon cantilever, protruding directly out of a trailing edge of a trapezoidal glass-epoxy composite bluff body was put into oscillatory motion by vortices shed alternately from side surfaces of the obstacle. Verified linearmeasurement range of the device extended from 5 to 22 m/s; however, it could be broadened in absence of external 50-Hz mains electrical interfering signal which required bandpass frequency-domain digital sensor signal processing. The MEMS vortex sensor proved its effectiveness in detection of semilaminar airflow velocity distribution in a 40-mm-diameter tubular pipe.
Experimental Investigation on Cavitating Flow Shedding over an Axisymmetric Blunt Body
Institute of Scientific and Technical Information of China (English)
HU Changli; WANG Guoyu; HUANG Biao
2015-01-01
Nowadays, most researchers focus on the cavity shedding mechanisms of unsteady cavitating flows over different objects, such as 2D/3D hydrofoils, venturi-type section, axisymmetric bodies with different headforms, and so on. But few of them pay attention to the differences of cavity shedding modality under different cavitation numbers in unsteady cavitating flows over the same object. In the present study, two kinds of shedding patterns are investigated experimentally. A high speed camera system is used to observe the cavitating flows over an axisymmetric blunt body and the velocity fields are measured by a particle image velocimetry (PIV) technique in a water tunnel for different cavitation conditions. The U-type cavitating vortex shedding is observed in unsteady cavitating flows. When the cavitation number is 0.7, there is a large scale cavity rolling up and shedding, which cause the instability and dramatic fluctuation of the flows, while at cavitation number of 0.6, the detached cavities can be conjunct with the attached part to induce the break-off behavior again at the tail of the attached cavity, as a result, the final shedding is in the form of small scale cavity and keeps a relatively steady flow field. It is also found that the interaction between the re-entrant flow and the attached cavity plays an important role in the unsteady cavity shedding modality. When the attached cavity scale is insufficient to overcome the re-entrant flow, it deserves the large cavity rolling up and shedding just as that at cavitation number of 0.7. Otherwise, the re-entrant flow is defeated by large enough cavity to induce the cavity-combined process and small scale cavity vortexes shedding just as that of the cavitation number of 0.6. This research shows the details of two different cavity shedding modalities which is worthful and meaningful for the further study of unsteady cavitation.
DEFF Research Database (Denmark)
Aumasson, Jean-Philippe; Dunkelman, Orr; Mendel, Florian;
2009-01-01
Vortex is a hash function that was first presented at ISC'2008, then submitted to the NIST SHA-3 competition after some modifications. This paper describes several attacks on both versions of Vortex, including collisions, second preimages, preimages, and distinguishers. Our attacks exploit flaws ...
Aerodynamically shaped vortex generators
DEFF Research Database (Denmark)
Hansen, Martin Otto Laver; Velte, Clara Marika; Øye, Stig;
2016-01-01
An aerodynamically shaped vortex generator has been proposed, manufactured and tested in a wind tunnel. The effect on the overall performance when applied on a thick airfoil is an increased lift to drag ratio compared with standard vortex generators. Copyright © 2015 John Wiley & Sons, Ltd....
U.S. Environmental Protection Agency — Inputs and outputs for SHEDS-HT runs of DiNP, DEHP, DBP. This dataset is associated with the following publication: Moreau, M., J. Leonard, K. Phillips, J. Campbell,...
Vortex cutting in superconductors
Glatz, A.; Vlasko-Vlasov, V. K.; Kwok, W. K.; Crabtree, G. W.
2016-08-01
Vortex cutting and reconnection is an intriguing and still-unsolved problem central to many areas of classical and quantum physics, including hydrodynamics, astrophysics, and superconductivity. Here, we describe a comprehensive investigation of the crossing of magnetic vortices in superconductors using time dependent Ginsburg-Landau modeling. Within a macroscopic volume, we simulate initial magnetization of an anisotropic high temperature superconductor followed by subsequent remagnetization with perpendicular magnetic fields, creating the crossing of the initial and newly generated vortices. The time resolved evolution of vortex lines as they approach each other, contort, locally conjoin, and detach, elucidates the fine details of the vortex-crossing scenario under practical situations with many interacting vortices in the presence of weak pinning. Our simulations also reveal left-handed helical vortex instabilities that accompany the remagnetization process and participate in the vortex crossing events.
Optimal load shedding and restoration
Xu, Ding
Load shedding is an emergency control action in power systems that can save systems from a wide-area blackout. Underfrequency load shedding, steady state load shedding, and voltage load shedding are widely used in power systems. These methods utilize either the steady state model or a simplified dynamic model to represent a power systems. In this dissertation, a general optimal load shedding method that considers both the dynamic process and load distribution is proposed. The unfavorable load shedding is then formulated as an optimization problem with the objective function of cost minimization. This objective function is subjected to system, security, and operation constraints. The entire problem becomes a question of optimization with differential and nonlinear equations as constraints. To solve this problem, discretization is used to change the differential equations into algebraic equations. The original problem is thus reformulated as an optimization problem and can be solved by a standard mathematical program. The general idea is then applied to traditional power systems, deregulated power systems, power systems with distributed generation, and load restoration. In the traditional power system, the method shows that governor action, generation dynamic, disturbance location, and economic factors can be taken into consideration. In the deregulated power system, two power market models are developed and incorporated into the load shedding scheme. In power systems with multiple distributed generations, the different cases of disturbances are analyzed and models of different distributed generation developed. The general idea is then applied. Finally, the load restoration problem is studied, and it is proposed that an optimization method be applied to it. This dissertation provides a comprehensive solution for load shedding problem in power systems. The models developed in this research can also be used to study other power system problems.
von K\\'arm\\'an energy decay and heating of protons and electrons in a kinetic plasma
Wu, P; Matthaeus, W H; Shay, M A; Swisdak, M
2013-01-01
Decay in time of undriven weakly collisional kinetic plasma turbulence in systems large compared to the ion kinetic scales is investigated using fully electromagnetic particle-in-cell simulations initiated with transverse flow and magnetic disturbances, constant density, and a strong guide field. The observed energy decay is consistent with the von K\\'arm\\'an hypothesis of similarity decay, in a formulation adapted to magnetohydrodyamics (MHD). Kinetic dissipation occurs at small scales, but the overall rate is apparently controlled by large scale dynamics. At small turbulence amplitude the electrons are preferentially heated. At larger amplitudes proton heating is the dominant effect. In the solar wind and corona the protons are typically hotter, suggesting that these natural systems are in large amplitude turbulence regime.
Topology of vortex creation in the cylinder wake
DEFF Research Database (Denmark)
Brøns, Morten; Bisgaard, Anders Villefrance
2010-01-01
We analyze the topology of the two-dimensional flow around a circular cylinder at moderate Reynolds numbers in the regime where the vortex wake is created. A normal form for the stream function close to the cylinder is presented and used to predict the streamline pattern both in the steady...... and the periodic regime, where two different vortex shedding scenarios are identified. The theoretical predictions are verified numerically. For the vorticity, a very different topology occurs with infinite nested sequences of iso-curves moving downstream. General equations of motion for critical points...
Wake-Vortex Hazards During Cruise
Rossow, Vernon J.; James, Kevin D.; Nixon, David (Technical Monitor)
1998-01-01
Even though the hazard posed by lift-generated wakes of subsonic transport aircraft has been studied extensively for approach and departure at airports, only a small amount of effort has gone into the potential hazard at cruise altitude. This paper reports on a studio of the wake-vortex hazard during cruise because encounters may become more prevalent when free-flight becomes available and each aircraft, is free to choose its own route between destinations. In order to address the problem, the various fluid-dynamic stages that vortex wakes usually go through as they age will be described along with estimates of the potential hazard that each stage poses. It appears that a rolling-moment hazard can be just as severe at cruise as for approach at airports, but it only persists for several minutes. However, the hazard posed by the downwash in the wake due to the lift on the generator aircraft persists for tens of minutes in a long narrow region behind the generating aircraft. The hazard consists of severe vertical loads when an encountering aircraft crosses the wake. A technique for avoiding vortex wakes at cruise altitude will be described. To date the hazard posed by lift-generated vortex wakes and their persistence at cruise altitudes has been identified and subdivided into several tasks. Analyses of the loads to be encounter and are underway and should be completed shortly. A review of published literature on the subject has been nearly completed (see text) and photographs of vortex wakes at cruise altitudes have been taken and the various stages of decay have been identified. It remains to study and sort the photographs for those that best illustrate the various stages of decay after they are shed by subsonic transport aircraft at cruise altitudes. The present status of the analysis and the paper are described.
Palacios, David M.
2005-08-01
An optical vortex may be characterized as a dark core of destructive interference in a beam of spatially coherent light. This dark core may be used as a filter to attenuate a coherent beam of light so an incoherent background signal may be detected. Applications of such a filter include: eye and sensor protection, forward-scattered light measurement, and the detection of extra-solar planets. Optical vortices may be created by passing a beam of light through a vortex diffractive optical element, which is a plate of glass etched with a spiral pattern, such that the thickness of the glass increases in the azimuthal direction. An optical vortex coronagraph may be constructed by placing a vortex diffractive optical element near the image plane of a telescope. An optical vortex coronagraph opens a dark window in the glare of a distant star so nearby terrestrial sized planets and exo-zodiacal dust may be detected. An optical vortex coronagraph may hold several advantages over other techniques presently being developed for high contrast imaging, such as lower aberration sensitivity and multi-wavelength operation. In this manuscript, I will discuss the aberration sensitivity of an optical vortex coronagraph and the key advantages it may hold over other coronagraph architectures. I will also provide numerical simulations demonstrating high contrast imaging in the presence of low-order static aberrations.
STABILITY OF VORTEX STREET IN GAS-LIQUID TWO-PHASE FLOW
Institute of Scientific and Technical Information of China (English)
Li Yong-guang; Lin Zong-hu
2003-01-01
The stability of the Karmen vortex street in gas-liquid two-phase flow was studied experimentally and theoretically. The values of the parameter h/l characterizing the vortex street structure (I.e., the ratio of the vortex street width to the distance between two vortexes) for a stable vortex street in gas-liquid two-phase flow were obtained for the first time. The parameter h/l was proved to be a variable, not a constant as in single-phase flow. H/l is related to the upstream fluid void fraction. In gas-liquid two-phase fluid flow to form a steady vortex street is more difficult than in a single-phase fluid flow. Because in the unsteady vortex shedding the vortex shedding band frequency is broader than the one in the single phase fluid flow, so it is easier to induce the cross-cylinder resonance than in the single phase fluid flow, and this case should give rise to the attention of engineers.
Energy Technology Data Exchange (ETDEWEB)
Malishevskii, A.S.; Silin, V.P.; Uryupin, S.A
2002-12-30
For the magnetically coupled waveguide and long Josephson junction we gave the analytic description of two separate velocity domains where the free motion of traveling vortex (2{pi}-kink) exists. The role of the mutual influence of waveguide and long Josephson junction is discussed. It is shown the possibility of the fast vortex motion with the velocity much larger than Swihart velocity of Josephson junction and close to the speed of light in the waveguide. The excitation of motion of such fast Josephson vortex is described.
Development of a perturbation generator for vortex stability studies
Riester, J. E.; Ash, Robert L.
1991-01-01
Theory predicts vortex instability when subjected to certain types of disturbances. It was desired to build a device which could introduce controlled velocity perturbations into a trailing line vortex in order to study the effects on stability. A perturbation generator was designed and manufactured which can be attached to the centerbody of an airfoil type vortex generator. Details of design tests and manufacturing of the perturbation generator are presented. The device produced controlled perturbation with frequencies in excess of 250 Hz. Preliminary testing and evaluation of the perturbation generator performance was conducted in a 4 inch cylindrical pipe. Observations of vortex shedding frequencies from a centerbody were measured. Further evaluation with the perturbation generator attached to the vortex generator in a 2 x 3 foot wind tunnel were also conducted. Hot-wire anemometry was used to confirm the perturbation generator's ability to introduce controlled frequency fluctuations. Comparison of the energy levels of the disturbances in the vortex core was made between locations 42 chord lengths and 15 chord lengths downstream.
Cunningham, A. M., Jr.
1986-01-01
An experimental study was conducted to quantify the hysteresis associated with various vortex flow transition points and to determine the effect of planform geometry. The transition points observed consisted of the appearance (or disappearance) of trailing edge vortex burst and the transition to (or from) flat plate or totally separated flows. Flow visualization with smoke injected into the vortices was used to identify the transitions on a series of semi-span models tested in a low speed tunnel. The planforms tested included simple deltas (55 deg to 80 deg sweep), cranked wings with varying tip panel sweep and dihedral, and a straked wing. High speed movies at 1000 frames per second were made of the vortex flow visualization in order to better understand the dynamics of vortex flow, burst and transition.
Modeling gasodynamic vortex cooling
Allahverdyan, A. E.; Fauve, S.
2017-08-01
We aim at studying gasodynamic vortex cooling in an analytically solvable, thermodynamically consistent model that can explain limitations on the cooling efficiency. To this end, we study an angular plus radial flow between two (coaxial) rotating permeable cylinders. Full account is taken of compressibility, viscosity, and heat conductivity. For a weak inward radial flow the model qualitatively describes the vortex cooling effect, in terms of both temperature and the decrease of the stagnation enthalpy, seen in short uniflow vortex (Ranque) tubes. The cooling does not result from external work and its efficiency is defined as the ratio of the lowest temperature reached adiabatically (for the given pressure gradient) to the lowest temperature actually reached. We show that for the vortex cooling the efficiency is strictly smaller than 1, but in another configuration with an outward radial flow, we find that the efficiency can be larger than 1. This is related to both the geometry and the finite heat conductivity.
Vector Lattice Vortex Solitons
Institute of Scientific and Technical Information of China (English)
WANG Jian-Dong; YE Fang-Wei; DONG Liang-Wei; LI Yong-Ping
2005-01-01
@@ Two-dimensional vector vortex solitons in harmonic optical lattices are investigated. The stability properties of such solitons are closely connected to the lattice depth Vo. For small Vo, vector vortex solitons with the total zero-angular momentum are more stable than those with the total nonzero-angular momentum, while for large Vo, this case is inversed. If Vo is large enough, both the types of such solitons are stable.
Buoyant Norbury's vortex rings
Blyth, Mark; Rodriguez-Rodriguez, Javier; Salman, Hayder
2014-11-01
Norbury's vortices are a one-parameter family of axisymmetric vortex rings that are exact solutions to the Euler equations. Due to their relative simplicity, they are extensively used to model the behavior of real vortex rings found in experiments and in Nature. In this work, we extend the original formulation of the problem to include buoyancy effects for the case where the fluid that lies within the vortex has a different density to that of the ambient. In this modified formulation, buoyancy effects enter the problem through the baroclinic term of the vorticity equation. This permits an efficient numerical solution of the governing equation of motion in terms of a vortex contour method that tracks the evolution of the boundary of the vortex. Finally, we compare our numerical results with the theoretical analysis of the short-time evolution of a buoyant vortex. Funded by the Spanish Ministry of Economy and Competitiveness through grant DPI2011-28356-C03-02 and by the London Mathematical Society.
1997-01-01
There are as many ways to build and arrange crab shedding setups as there are people who make them. The following drawings are suggestions based on the experiencesof successful shedders. You may find changes that suit your operation better. (8pp.)
Controlling vortex motion and vortex kinetic friction
Nori, Franco; Savel'ev, Sergey
2006-05-01
We summarize some recent results of vortex motion control and vortex kinetic friction. (1) We describe a device [J.E. Villegas, S. Savel'ev, F. Nori, E.M. Gonzalez, J.V. Anguita, R. Garcìa, J.L. Vicent, Science 302 (2003) 1188] that can easily control the motion of flux quanta in a Niobium superconducting film on an array of nanoscale triangular magnets. Even though the input ac current has zero average, the resulting net motion of the vortices can be directed along either one direction, the opposite direction, or producing zero net motion. We also consider layered strongly anisotropic superconductors, with no fixed spatial asymmetry, and show [S. Savel'ev, F. Nori, Nature Materials 1 (2002) 179] how, with asymmetric drives, the ac motion of Josephson and/or pancake vortices can provide a net dc vortex current. (2) In analogy with the standard macroscopic friction, we present [A. Maeda, Y. Inoue, H. Kitano, S. Savel'ev, S. Okayasu, I. Tsukada, F. Nori , Phys. Rev. Lett. 94 (2005) 077001] a comparative study of the friction force felt by vortices in superconductors and charge density waves.
Kim, Ildoo; Wu, X. L.
2015-10-01
A structure-based Strouhal-Reynolds number relationship, St =1 /(A +B /Re ) , has been recently proposed based on observations of laminar vortex shedding from circular cylinders in a flowing soap film. Since the new St -Re relation was derived from a general physical consideration, it raises the possibility that it may be applicable to vortex shedding from bodies other than circular ones. The work presented herein provides experimental evidence that this is the case. Our measurements also show that, in the asymptotic limit (Re →∞ ), St∞=1 /A ≃0.21 is constant independent of rod shapes, leaving B the only parameter that is shape dependent.
Thalabard, Simon; Herbert, Éric; Daviaud, Francois; Dubrulle, Bérengère
2015-01-01
In the present paper, recent experimental results on large scale coherent steady states observed in experimental von K{\\'a}rm{\\'a}n flows are revisited from a statistical mechanics perspective. The latter is rooted on two levels of description. We first argue that the coherent steady states may be described as the equilibrium states of well-chosen lattice models, that can be used to define global properties of von K{\\'a}rm{\\'a}n flows, such as their temperatures. The equilibrium description is then enlarged, in order to reinterpret a series of results about the stability of those steady states, their susceptibility to symmetry breaking, in the light of a deep analogy with the statistical theory of Ferromagnetism. We call this analogy "Ferro-Turbulence".
Kármán vortex street detection by the lateral line.
Chagnaud, Boris P; Bleckmann, Horst; Hofmann, Michael H
2007-07-01
Fish use the lateral line system for prey detection, predator avoidance, schooling behavior, intraspecific communication and spatial orientation. In addition the lateral line may be important for station holding and for the detection of the hydrodynamic trails (vortex streets) generated by swimming fish. We investigated the responses of anterior lateral line nerve fibers of goldfish, Carassius auratus, to unidirectional water flow (10 cm s(-1)) and to running water that contained a Kármán vortex street. Compared to still water conditions, both unidirectional water flow and Kármán vortex streets caused a similar increase in the discharge rate of anterior lateral line nerve fibers. If exposed to a Kármán vortex street, the amplitude of spike train frequency spectra increased at the vortex shedding frequency. This increase was especially pronounced if the fish intercepted the edge of a Kármán vortex street. Our data show that the vortex shedding frequency can be retrieved from the responses of anterior lateral line nerve fibers.
Opazo, A; Bustamante, G; Labbé, R
2015-01-01
We report experimental results for fluctuations of injected power in confined von K\\'arm\\'an swirling flows with constant external torque applied to the stirrers. Two experiments were performed at nearly equal Reynolds numbers in geometrically similar experimental setups, using air in one of them and water in the other. We found that the probability density function of power fluctuations is strongly asymmetric in air, while in water it is closer to a Gaussian, showing that the effect that a big change on the fluid density has on the flow-stirrer interaction is not reflected merely by a change in the amplitude of stirrers' response. In the case of water, with a density roughly 830 times greater than air density, the forcing exerted by the flow on the stirrers is stronger, so that they follow more closely the locally averaged rotation of the flow. When the fluid is air, the forcing is much weaker, resulting not only in a smaller stirrer response to the torque exerted by the flow, but also in power fluctuations ...
Global vs local energy dissipation: the energy cycle of the turbulent Von K\\'arm\\'an flow
Kuzzay, Denis; Dubrulle, Bérengère
2015-01-01
In this paper, we investigate the relations between global and local energy transfers in a turbulent Von K\\'arm\\'an flow. The goal is to understand how and where energy is dissipated in such a flow and to reconstruct the energy cycle in an experimental device where local as well as global quantities can be measured. We use PIV measurements and we model the Reynolds stress tensor to take subgrid scales into account. This procedure involves a free parameter that is calibrated using angular momentum balance. We then estimate the local and global mean injected and dissipated power for several types of impellers, for various Reynolds numbers and for various flow topologies. These PIV-estimates are then compared with direct injected power estimates provided by torque measurements at the impellers. The agreement between PIV-estimates and direct measurements depends on the flow topology. In symmetric situations, we are able to capture up to 90% of the actual global energy dissipation rate. However, our results become...
Reconnection of superfluid vortex bundles.
Alamri, Sultan Z; Youd, Anthony J; Barenghi, Carlo F
2008-11-21
Using the vortex filament model and the Gross-Pitaevskii nonlinear Schroedinger equation, we show that bundles of quantized vortex lines in He II are structurally robust and can reconnect with each other maintaining their identity. We discuss vortex stretching in superfluid turbulence and show that, during the bundle reconnection process, kelvin waves of large amplitude are generated, in agreement with the finding that helicity is produced by nearly singular vortex interactions in classical Euler flows.
Nano magnetic vortex wall guide
Directory of Open Access Journals (Sweden)
H. Y. Yuan
2015-11-01
Full Text Available A concept of nano magnetic vortex wall guide is introduced. Two architectures are proposed. The first one is properly designed superlattices while the other one is bilayer nanostrips. The concept is verified by micromagnetic simulations. Both guides can prevent the vortex core in a magnetic vortex wall from colliding with sample surface so that the information stored in the vortex core can be preserved during its transportation from one location to another one through the guides.
Vortex Characterization for Engineering Applications
Energy Technology Data Exchange (ETDEWEB)
Jankun-Kelly, M; Thompson, D S; Jiang, M; Shannahan, B; Machiraju, R
2008-01-30
Realistic engineering simulation data often have features that are not optimally resolved due to practical limitations on mesh resolution. To be useful to application engineers, vortex characterization techniques must be sufficiently robust to handle realistic data with complex vortex topologies. In this paper, we present enhancements to the vortex topology identification component of an existing vortex characterization algorithm. The modified techniques are demonstrated by application to three realistic data sets that illustrate the strengths and weaknesses of our approach.
Vortex tube optimization theory
Energy Technology Data Exchange (ETDEWEB)
Lewins, Jeffery [Cambridge Univ., Magdalene Coll., Cambridge (United Kingdom); Bejan, Adrian [Duke Univ., Dept. of Mechanical Engineering and Materials Science, Durham, NC (United States)
1999-11-01
The Ranque-Hilsch vortex tube splits a single high pressure stream of gas into cold and warm streams. Simple models for the vortex tube combined with regenerative precooling are given from which an optimisation can be undertaken. Two such optimisations are needed: the first shows that at any given cut or fraction of the cold stream, the best refrigerative load, allowing for the temperature lift, is nearly half the maximum loading that would result in no lift. The second optimisation shows that the optimum cut is an equal division of the vortex streams between hot and cold. Bounds are obtainable within this theory for the performance of the system for a given gas and pressure ratio. (Author)
Magnetic vortex racetrack memory
Geng, Liwei D.; Jin, Yongmei M.
2017-02-01
We report a new type of racetrack memory based on current-controlled movement of magnetic vortices in magnetic nanowires with rectangular cross-section and weak perpendicular anisotropy. Data are stored through the core polarity of vortices and each vortex carries a data bit. Besides high density, non-volatility, fast data access, and low power as offered by domain wall racetrack memory, magnetic vortex racetrack memory has additional advantages of no need for constrictions to define data bits, changeable information density, adjustable current magnitude for data propagation, and versatile means of ultrafast vortex core switching. By using micromagnetic simulations, current-controlled motion of magnetic vortices in cobalt nanowire is demonstrated for racetrack memory applications.
Ji, B.; Peng, X. X.; Long, X. P.; Luo, X. W.; Wu, Y. L.
2015-12-01
Results of cavitating turbulent flow simulation around a twisted hydrofoil were presented in the paper using the Partially-Averaged Navier-Stokes (PANS) method (Ji et al. 2013a), Large-Eddy Simulation (LES) (Ji et al. 2013b) and Reynolds-Averaged Navier-Stokes (RANS). The results are compared with available experimental data (Foeth 2008). The PANS and LES reasonably reproduce the cavitation shedding patterns around the twisted hydrofoil with primary and secondary shedding, while the RANS model fails to simulate the unsteady cavitation shedding phenomenon and yields an almost steady flow with a constant cavity shape and vapor volume. Besides, it is noted that the predicted shedding vapor cavity by PANS is more turbulent and the shedding vortex is stronger than that by LES, which is more consistent with experimental photos.
Shock-vortex interactions in a soap film
Wen, C. Y.; Wu, W. J.; Chen, H.
2008-08-01
This work experimentally visualizes the interaction of a quasi-one-dimensional moving shock wave with a two-dimensional vortex in a soap film for the first time. A vertical soap film shock tube was used to generate a quasi-one-dimensional moving shock wave and a NACA-0012 airfoil intruded into the soap film was towed to shed the starting vortex. The interesting interaction phenomena were then visualized using a traditional high-speed flash photography. The concentration of sodium dodecyl sulfate (SDS) used was 0.5 CMC (critical micelle concentration) to keep the surfactant molecules behave as two-dimensional gases. A sequence of pictures shows that the shock is distorted non-symmetrically as it passes through the spiral vortex flow field and the vortex structure is compressed in the direction normal to the shock. These flow features observed in soap films are qualitatively similar to their counterparts in gases. In addition, the visualization of the interactions of a quasi-one-dimensional moving shock wave with a K árm án vortex street are presented.
Vortex structure analysis of unsteady cloud cavitating flows around a hydrofoil
Zhao, Yu; Wang, Guoyu; Huang, Biao
2016-01-01
In this paper, time dependent vortex structures are numerically analyzed for both noncavitating and cloud cavitating flows around a Clark-Y hydrofoil with angle of attack α = 8∘ at a moderate Reynolds number, Re = 7 × 105. The numerical simulations are performed using a transport equation-based cavitation model and the large eddy simulation (LES) approach with a classical eddy viscosity subgrid scale (SGS) model. Compared with experimental results, present numerical predictions are capable of capturing the initiation of cavity, growth toward the trailing edge and subsequent shedding process. Results indicate that in noncavitating conditions, the trailing edge vortex and induced positive vortex shed periodically into the wake region to form the vortex street. In cloud cavitating conditions, interrelations between cavity and vortex induce different vortex dynamics at different cavity developing stages. (i) As attached cavity grows, vorticity production is greatly enhanced by the favorable pressure gradient at the leading edge. The trailing edge flow does not have a direct impact on the attached cavity expansion process. Furthermore, the liquid-vapor interface that moves toward the trailing edge enhances the vorticity in the attached cavity closure region. (ii) When the stable attached sheet cavity grows to its maximum length, the accumulation process of vorticity is eventually interrupted by the formation of the re-entrant jet. Re-entrant jet’s moving upstream leads to a higher spreading rate of the attached cavity and the formation of a large coherent structure inside the attached cavity. Moreover, the wavy/bubbly cavity interface enhances the vorticity near the trailing edge. (iii) As the attached sheet cavity breaks up, this large vortex structure converts toward the trailing edge region, which will eventually couple with a trailing edge vortex shedding from the lower surface to form the cloud cavity. The breakup of the stable attached cavity is the main
Pennings, P.C.
2016-01-01
This thesis describes the mechanisms with which tip vortex cavitation is responsible for broadband pressure fluctuations on ship propellers. Hypotheses for these are described in detail by Bosschers (2009). Validation is provided by three main cavitation-tunnel experiments, one on a model propeller
Energy Technology Data Exchange (ETDEWEB)
Ortega, J M
2001-10-18
The collapse of the Soviet Union and ending of the Cold War brought about many significant changes in military submarine operations. The enemies that the US Navy faces today and in the future will not likely be superpowers armed with nuclear submarines, but rather smaller, rogue nations employing cheaper diesel/electric submarines with advanced air-independent propulsion systems. Unlike Cold War submarine operations, which occurred in deep-water environments, future submarine conflicts are anticipated to occur in shallow, littoral regions that are complex and noisy. Consequently, non-acoustic signatures will become increasingly important and the submarine stealth technology designed for deep-water operations may not be effective in these environments. One such non-acoustic signature is the surface detection of a submarine's trailing vortex wake. If a submarine runs in a slightly buoyant condition, its diving planes must be inclined at a negative angle of attack to generate sufficient downforce, which keeps the submarine from rising to the surface. As a result, the diving planes produce a pair of counter-rotating trailing vortices that propagate to the water surface. In previous deep-water operations, this was not an issue since the submarines could dive deep enough so that the vortex pair became incoherent before it reached the water surface. However, in shallow, littoral environments, submarines do not have the option of diving deep and, hence, the vortex pair can rise to the surface and leave a distinct signature that might be detectable by synthetic aperture radar. Such detection would jeopardize not only the mission of the submarine, but also the lives of military personnel on board. There has been another attempt to solve this problem and reduce the intensity of trailing vortices in the wakes of military submarines. The research of Quackenbush et al. over the past few years has been directed towards an idea called ''vortex leveraging
Three-dimensional vortex wake structure of flapping wings in hovering flight.
Cheng, Bo; Roll, Jesse; Liu, Yun; Troolin, Daniel R; Deng, Xinyan
2014-02-06
Flapping wings continuously create and send vortices into their wake, while imparting downward momentum into the surrounding fluid. However, experimental studies concerning the details of the three-dimensional vorticity distribution and evolution in the far wake are limited. In this study, the three-dimensional vortex wake structure in both the near and far field of a dynamically scaled flapping wing was investigated experimentally, using volumetric three-component velocimetry. A single wing, with shape and kinematics similar to those of a fruitfly, was examined. The overall result of the wing action is to create an integrated vortex structure consisting of a tip vortex (TV), trailing-edge shear layer (TESL) and leading-edge vortex. The TESL rolls up into a root vortex (RV) as it is shed from the wing, and together with the TV, contracts radially and stretches tangentially in the downstream wake. The downwash is distributed in an arc-shaped region enclosed by the stretched tangential vorticity of the TVs and the RVs. A closed vortex ring structure is not observed in the current study owing to the lack of well-established starting and stopping vortex structures that smoothly connect the TV and RV. An evaluation of the vorticity transport equation shows that both the TV and the RV undergo vortex stretching while convecting downwards: a three-dimensional phenomenon in rotating flows. It also confirms that convection and secondary tilting and stretching effects dominate the evolution of vorticity.
High amplitude vortex-induced pulsations in a gas transport system
Kriesels, P.C.; Peters, M.C.A.M.; Hirschberg, A.; Wijnands, A.P.J.; Iafrati, A.; Riccardi, G.; Piva, R.; Bruggeman, J.C.
1995-01-01
High Reynolds number, low Mach number gas flows in pipe systems with closed side branches exhibit spectacular low frequency self-sustained pulsations driven by periodic vortex shedding at specific values of the Strouhal number. A detailed study is presented of the behaviour of the flow in a system w
Shedding of immature germ cells.
Ariagno, J; Curi, S; Mendeluk, G; Grinspon, D; Repetto, H; Chenlo, P; Pugliese, N; Sardi, M; Blanco, A M
2002-01-01
The immature germ cells (IGC) constitute the highest percentage (90%) of nonsperm cells (NSpC) in ejaculates from fertile or infertile men. The objective of this study was to evaluate IGC concentration and the IGC/(IGC + Sp) ratio, in normozoospermia and dispermia. Normozoospermia from men with proven fertility (NPF). nonproven fertility (NNPF). dispermia (D) and semen samples with excessive shedding of immature germ cells (GI 1.7 x 10(6) to 5 x 10(6) IGC/mL and GII > 5.0 x 10(6) IGC/mL) were used in this study. The mean value +2 SD for the NNPF (1.7 x 10(6)/mL) and the value proposed by WHO (5 x 10(6)/mL) were employed to define GI and GII groups. IGC concentration is statistically different in the studied groups. The IGC/Sp ratio showed a significant difference only between the NNPF and the D. When comparing semen parameters (Sp/ejaculate. grade (a) motility and morphology) there was a highly significant difference between NNPF and GI and GII: no difference was found between GI and GII. While studying 200 cases of dispermias 83% showed a high shedding of immature germ cells. The cytological study of nonsperm cells and the count and identification of the immature germ cells could be used to evaluate the dispermic disorders.
The shock-vortex interaction patterns affected by vortex flow regime and vortex models
Chang, Keun-Shik; Barik, Hrushikesh; Chang, Se-Myong
2009-08-01
We have used a third-order essentially non-oscillatory method to obtain numerical shadowgraphs for investigation of shock-vortex interaction patterns. To search different interaction patterns, we have tested two vortex models (the composite vortex model and the Taylor vortex model) and as many as 47 parametric data sets. By shock-vortex interaction, the impinging shock is deformed to a S-shape with leading and lagging parts of the shock. The vortex flow is locally accelerated by the leading shock and locally decelerated by the lagging shock, having a severely elongated vortex core with two vertices. When the leading shock escapes the vortex, implosion effect creates a high pressure in the vertex area where the flow had been most expanded. This compressed region spreads in time with two frontal waves, an induced expansion wave and an induced compression wave. They are subsonic waves when the shock-vortex interaction is weak but become supersonic waves for strong interactions. Under a intermediate interaction, however, an induced shock wave is first developed where flow speed is supersonic but is dissipated where the incoming flow is subsonic. We have identified three different interaction patterns that depend on the vortex flow regime characterized by the shock-vortex interaction.
Vortex sound in confined flows
Hofmans, Gerardus Carolus Johannus
of a simple quasi-steady theoretical model. At higher frequencies the acoustic source is calculated as a function of the Strouhal number for nine flow configurations in a T-joint. We have restricted ourselves to configurations that have one side branch closed. For the simple case of a single-side-branch system the numerical results have been used to set up an energy balance of the system in order to predict pulsation levels. These results have been compared with the results of experiments. It was found that for low-amplitude pulsations the results agree within 10%, while for high- amplitude pulsations the predictions appeared to be 35% too high. These deviations can partially be explained by our model considering only vortex shedding at the upstream edge of the T-joint. The present study indicates that quantitative predictions of vortex-sound interaction in internal flows is possible with relatively simple numerical tools as long as the flow is approximately two-dimensional and flow separation occurs at sharp edges. In our study of the flow through the glottis also a first step has been taken towards the use of simplified boundary-layer models in the prediction of flow separation from curved walls. (Abstract shortened by UMI.)
Simulations of vortex generators
Koumoutsakos, P.
1995-01-01
We are interested in the study, via direct numerical simulations, of active vortex generators. Vortex generators may be used to modify the inner part of the boundary layer or to control separation thus enhancing the performance and maneuverability of aerodynamic configurations. We consider generators that consist of a surface cavity elongated in the stream direction and partially covered with a moving lid that at rest lies flush with the boundary. Streamwise vorticity is generated and ejected due to the oscillatory motion of the lid. The present simulations complement relevant experimental investigations of active vortex generators at NASA Ames and Stanford University (Saddoughi, 1994, and Jacobson and Reynolds, 1993). Jacobson and Reynolds (1993) used a piezoelectric device in water, allowing for small amplitude high frequency oscillations. They placed the lid asymmetrically on the cavity and observed a strong outward velocity at the small gap of the cavity. Saddoughi used a larger mechanically driven device in air to investigate this flow and he observed a jet emerging from the wide gap of the configuration, contrary to the findings of Jacobson and Reynolds. Our task is to simulate the flows generated by these devices and to conduct a parametric study that would help us elucidate the physical mechanisms present in the flow. Conventional computational schemes encounter difficulties when simulating flows around complex configurations undergoing arbitrary motions. Here we present a formulation that achieves this task on a purely Lagrangian frame by extending the formulation presented by Koumoutsakos, Leonard and Pepin (1994). The viscous effects are taken into account by modifying the strength of the particles, whereas fast multipole schemes employing hundreds of thousands of particles allow for high resolution simulations. The results of the present simulations would help us assess some of the effects of three-dimensionality in experiments and investigate the role
Multiply Phased Traveling BPS Vortex
Kimm, Kyoungtae; Cho, Y M
2016-01-01
We present the multiply phased current carrying vortex solutions in the U(1) gauge theory coupled to an $(N+1)$-component SU(N+1) scalar multiplet in the Bogomolny limit. Our vortex solutions correspond to the static vortex dressed with traveling waves along the axis of symmetry. What is notable in our vortex solutions is that the frequencies of traveling waves in each component of the scalar field can have different values. The energy of the static vortex is proportional to the topological charge of $CP^N$ model in the BPS limit, and the multiple phase of the vortex supplies additional energy contribution which is proportional to the Noether charge associated to the remaining symmetry.
Vortex cores and vortex motion in superconductors with anisotropic Fermi surfaces
Galvis, J. A.; Herrera, E.; Guillamón, I.; Vieira, S.; Suderow, H.
2017-02-01
Explaning static and dynamic properties of the vortex lattice in anisotropic superconductors requires a careful characterization of vortex cores. The vortex core contains Andreev bound states whose spatial extension depends on the anisotropy of the electronic band-structure and superconducting gap. This might have an impact on the anisotropy of the superconducting properties and on vortex dynamics. Here we briefly summarize basic concepts to understand anisotropic vortex cores and review vortex core imaging experiments. We further discuss moving vortex lattices and the influence of vortex core shape in vortex motion. We find vortex motion in highly tilted magnetic fields. We associate vortex motion to the vortex entry barrier and the screening currents at the surface. We find preferential vortex motion along the main axis of the vortex lattice. After travelling integers of the intervortex distance, we find that vortices move more slowly due to the washboard potential of the vortex lattice.
A generalization of vortex lines
Fecko, Marian
2016-01-01
Helmholtz theorem states that, in ideal fluid, vortex lines move with the fluid. Another Helmholtz theorem adds that strength of a vortex tube is constant along the tube. The lines may be regarded as integral surfaces of an 1-dimensional integrable distribution (given by the vorticity 2-form). In general setting of theory of integral invariants, due to Poincare and Cartan, one can find $d$-dimensional integrable distribution whose integral surfaces show both properties of vortex lines: they move with (abstract) fluid and, for appropriate generalization of vortex tube, strength of the latter is constant along the tube.
Aircraft Wake Vortex Deformation in Turbulent Atmosphere
Hennemann, Ingo; Holzaepfel, Frank
2007-01-01
Large-scale distortion of aircraft wake vortices appears to play a crucial role for aircraft safety during approach and landing. Vortex distortion is investigated based on large eddy simulations of wake vortex evolution in a turbulent atmosphere. A vortex identification method is developed that can be adapted to the vortex scales of interest. Based on the identified vortex center tracks, a statistics of vortex curvature radii is established. This statistics constitutes the basis for understan...
Large-eddy simulations and vortex structures of turbulent jets in crossflow
Institute of Scientific and Technical Information of China (English)
2007-01-01
Using the method of large-eddy simulation, the 3-dimensional turbulent jets in crossflow with stream-wise and transverse arrangements of nozzle are simulated, emphasizing on the dynamical process of generation and evolution of vortex structures in these flows. The results show that the basic vortex structures in literatures, such as the counter-rotating vortex pair, leading-edge vortices, lee-side vortices, hanging vortices, kidney vortices and anti-kidney vortices, are not independent physical substances, but local structures of the basic vortex structure of turbulent jets in crossflow-the 3-D stretching vortex rings originating from the orifice of the nozzle, which is discovered in this study. Therefore, the most important large-scale structures of turbulent jets in crossflow are unified to the 3-D vortex rings which stretch and twist in stream-wise and swing in transverse directions. We also found that the shedding frequencies of vortex rings are much lower than the one corresponding to the appearance of leading-edge and lee-side vortices in the turbulent jets.
Large-eddy simulations and vortex structures of turbulent jets in crossflow
Institute of Scientific and Technical Information of China (English)
GUAN Hui; WU ChuiJie
2007-01-01
Using the method of large-eddy simulation,the 3-dimensional turbulent jets in crossflow with stream-wise and transverse arrangements of nozzle are simulated,emphasizing on the dynamical process of generation and evolution of vortex structures in these flows.The results show that the basic vortex structures in literatures,such as the counter-rotating vortex pair,leading-edge vortices,lee-side vortices,hanging vortices,kidney vortices and anti-kidney vortices,are not independent physical substances,but local structures of the basic vortex structure of turbulent jets in crossflow-the 3-D stretching vortex rings originating from the orifice of the nozzle,which is discovered in this study.Therefore,the most important large-scale structures of turbulent jets in crossflow are unified to the 3-D vortex rings which stretch and twist in stream-wise and swing in transverse directions.We also found that the shedding frequencies of vortex rings are much lower than the one corresponding to the appearance of leading-edge and lee-side vortices in the turbulent jets.
Vortex-Surface Interactions: Vortex Dynamics and Instabilities
2015-10-16
a) Main vortex structures developing on a typical submarine hull; (b) Schematic illustrating a horseshoe vortex at a wing-body junction of a " Rood ...secondary vortices. Firstly, looking at Figure 7, showing only the secondary vortices being visualized by our technique , we see that a tongue of secondary
Evolution of optical vortex distributions in stochastic vortex fields
CSIR Research Space (South Africa)
Roux, FS
2011-01-01
Full Text Available dipole,? Opt. Commun. 236, 433?440 (2004). [23] Dana, I. and Freund, I., ?Vortex-lattice wave fields,? Opt. Commun. . [24] Jenkins, R., Banerji, J., and Davies, A., ?The generation of optical vortices and shape preserving vortex arrays in hollow...
A Nonlinear Vortex Induced Vibration Model of Marine Risers
Institute of Scientific and Technical Information of China (English)
LIU Juan; HUANG Weiping
2013-01-01
With the exploitation of oil and gas in deep water,the traditional vortex induced vibration (VIV) theory is challenged by the unprecedented flexibility of risers.A nonlinear time-dependent VIV model is developed in this paper based on a VIV lift force model and the Morison equation.Both the inline vibration induced by the flow due to vortex shedding and the fluid-structure interaction in the transverse direction are included in the model.One of the characteristics of the model is the response-dependent lift force with nonlinear damping,which is different from other VIV models.The calculations show that the model can well describe the VIV of deepwater risers with the results agreeing with those calculated by other models.
Solve Von-Karman equation with perturbation-complexity function%Von-Karman板方程的摄动—复变函数解法
Institute of Scientific and Technical Information of China (English)
刘平; 付功义
2015-01-01
板的大挠度方程由Von-Karman于1909年推导出来,这便是著名的Von-Karman大挠度方程组. 但是,由于Von-Karman方程为八阶非线性耦合方程,求解十分困难,至今尚无精确解. 为求解Von-Karman方程,一般采用瑞利 李兹法、能量法、迦辽金法及摄动法以求得近似解. 复变函数最初由原苏联科学家柯索洛夫引入解弹性平面问题,而后由穆什维海尔院士集大成,解决弹性平面问题及一系列孔洞及复杂边界问题,后由萨文、卢尔瓦兹等一批原苏联科学家引入到求解板的小挠度方程问题中. 本文进一步将复变函数推广到板的大挠度方程中,得出Von-Karman方程在复变函数下的表达式;另外,给出了求解大挠度板复变函数方法的一般步骤,并求解出固支边界圆板的渐近解.%A large deflection plate equation was derived by Von-Karman in 1909 which is the famous Von-Karman large deflection equation. Because Von-Karman equation for eight-order nonlinear coupled equation, which is very difficult to solve, there is no exact solution so far. The general methods to solve Von-Karman equation are Rayleigh-Ritz, Energy method, Galerkin and the perturbation method,which can achieve an approximate solution. Complex function was originally introduced by the former Soviet Scientists Kesuoluofu to deal with elastic plane problems,then by the comprehensive expression of Мусхелишвили of Sciences to address a series of holes of elastic plane problems. And then Savimbi,Luerwazi such a grantof former Soviet Union scientists had introduced into the method into small deflection plate equation. Complex function was extended into large deflection plate equations, then obtained Von-Karman equation in the complex variable expression. In addition, addressing an example of solving the large deflection plate with complex function of the general steps. At last,solving a clamped circular plate of the asymptotic solution to make a
Solitary vortexes in magnetohydrodynamics
Energy Technology Data Exchange (ETDEWEB)
Vainshtein, S.I.
1985-12-01
Stationary configurations in magnetohydrodynamics are investigated for the following two particular cases: (1) there is no motion, which corresponds to a state of magnetostatic equilibrium; and (2) the magnetic field intensity becomes zero, i.e., hydrodynamic vortexes are involved. It is shown that in certain cases the line-of-force topology must be sufficiently simple in order before a stationary or equilibrium state can be achieved. It is also shown that in the two-dimensional case, the magnetic surfaces of an equilibrium configuration represent coaxial cylindrical surfaces. 12 references.
1981-01-01
j . 1978. 93. Grabowski , W.J.; "Solutions of the Navier-Stokes Equations for Vortex Breakdown," NASA CR...including foreign nations. This technical report has been reviewed and is approved for publication. LAWRENCE W. ROGERS Q LOWELL C. KEEL, Major, USAF Project...or’ a w U - a LU LU U- LU C - J ’di 2 2 C LU I- 4 S Ua * - w x 2 40 20 I- 2 LU W S ~ 00 * U. 4 I- LU a 4 U 4 2 C C LU 4 a 4a 2 I- 4 a 3 9
Structure of the vortex wake in hovering Anna's hummingbirds (Calypte anna).
Wolf, M; Ortega-Jimenez, V M; Dudley, R
2013-12-22
Hummingbirds are specialized hoverers for which the vortex wake has been described as a series of single vortex rings shed primarily during the downstroke. Recent findings in bats and birds, as well as in a recent study on Anna's hummingbirds, suggest that each wing may shed a discrete vortex ring, yielding a bilaterally paired wake. Here, we describe the presence of two discrete rings in the wake of hovering Anna's hummingbirds, and also infer force production through a wingbeat with contributions to weight support. Using flow visualization, we found separate vortices at the tip and root of each wing, with 15% stronger circulation at the wingtip than at the root during the downstroke. The upstroke wake is more complex, with near-continuous shedding of vorticity, and circulation of approximately equal magnitude at tip and root. Force estimates suggest that the downstroke contributes 66% of required weight support, whereas the upstroke generates 35%. We also identified a secondary vortex structure yielding 8-26% of weight support. Lift production in Anna's hummingbirds is more evenly distributed between the stroke phases than previously estimated for Rufous hummingbirds, in accordance with the generally symmetric down- and upstrokes that characterize hovering in these birds.
Robustness of a coherence vortex.
Alves, Cleberson R; Jesus-Silva, Alcenisio J; Fonseca, Eduardo J S
2016-09-20
We study, experimentally and theoretically, the behavior of a coherence vortex after its transmission through obstacles. Notably, we find that such a vortex survives and preserves its effective topological charge. Despite suffering changes on the modulus of the coherence function, these changes disappear during propagation.
Vortex duality in higher dimensions
Beekman, Aron Jonathan
2011-01-01
A dynamic vortex line traces out a world sheet in spacetime. This thesis shows that the information of all its dynamic behaviour is completely contained in the world sheet. Furthermore a mathematical framework for order–disorder phase transitions in terms of the proliferation of such vortex world sh
DEFF Research Database (Denmark)
Pico Geerdsen, Lars; Koch-Nielsen, Inger; Vinther, Henrik
Hjemløshed er ofte forbundet med en række problemer som misbrug, psykisk sygdom, vold i parforholdet, ringe arbejdsmarkedstilknytning og levevilkår, kriminalitet, gæld og manglende sociale netværk. Det er alle problemer, der kan udløse hjemløshed og potentielt fastholde personer i en hjemløshedst...
Shedding of cell membrane-bound proteoglycans.
Nam, Eon Jeong; Park, Pyong Woo
2012-01-01
Membrane-bound proteoglycans function primarily as coreceptors for many glycosaminoglycan (GAG)-binding ligands at the cell surface. The majority of membrane-bound proteoglycans can also function as soluble autocrine or paracrine effectors as their extracellular domains, replete with all GAG chains, are enzymatically cleaved and released from the cell surface by ectodomain shedding. In particular, the ectodomain shedding of syndecans, a major family of cell surface heparan sulfate proteoglycans, is an important posttranslational mechanism that modulates diverse pathophysiological processes. Syndecan shedding is a tightly controlled process that regulates the onset, progression, and resolution of various infectious and noninfectious inflammatory diseases. This review describes methods to induce and measure the shedding of cell membrane-bound proteoglycans, focusing on syndecan shedding as a prototypic example.
Tanaeva, I. A.; Lindemann, U.; Jiang, N.; de Waele, A. T. A. M.; Thummes, G.
2004-06-01
A superfluid vortex cooler (SVC) is a combination of a fountain pump and a vortex cooler. The working fluid in the SVC is 4He at a temperature below the lambda line. The cooler has no moving parts, is gravity independent, and hardly requires any additional infrastructure. At saturated vapour pressure the SVC is capable of reaching a temperature as low as 0.75 K. At pressures close to the melting pressure the temperature can be brought down to 0.65 K. As the SVC operates only below the lambda line, it has to be precooled e.g. by a liquid-helium bath or a cryocooler. As a first step of our research we have carried out a number of experiments, using a liquid-helium bath as a precooler for the SVC. In this arrangement we have reached temperatures below 1 K with 3.5 mW heating power supplied to the fountain part of the SVC at 1.4 K. The next step was combining the SVC with a pulse tube refrigerator (PTR), developed at the University of Giessen. It is a two-stage G-M type refrigerator with 3He as a working fluid that reached a lowest temperature of 1.27 K. In this contribution we report on the results of the SVC tests in liquid helium and the progress in the integration of the SVC with the PTR.
von Kármán Vortex Street within an Impacting Drop
Thoraval, Marie-Jean
2012-06-29
The splashing of a drop impacting onto a liquid pool produces a range of different sized microdroplets. At high impact velocities, the most significant source of these droplets is a thin liquid jet emerging at the start of the impact from the neck that connects the drop to the pool. We use ultrahigh-speed video imaging in combination with high-resolution numerical simulations to show how this ejecta gives way to irregular splashing. At higher Reynolds numbers, its base becomes unstable, shedding vortex rings into the liquid from the free surface in an axisymmetric von Kármán vortex street, thus breaking the ejecta sheet as it forms.
Regimes of flow past a vortex generator
DEFF Research Database (Denmark)
Velte, Clara Marika; Okulov, V.L.; Naumov, I.V.
2012-01-01
A complete parametric investigation of the development of multi-vortex regimes in a wake past simple vortex generator has been carried out. It is established that the vortex structure in the wake is much more complicated than a simple monopole tip vortex. The vortices were studied by stereoscopic...
Some discussions on Arctic vortex
Institute of Scientific and Technical Information of China (English)
Li Hai; Sun Lantao; Wu Huiding; Li Xiang
2006-01-01
The Arctic vortex is a persistent large-scale cyclonic circulation in the middle and upper troposphere and the stratosphere. Its activity and variation control the semi-permanent active centers of Pan-Arctic and the short-time cyclone activity in the subarctic areas. Its strength variation, which directly relates to the atmosphere, ocean, sea ice and ecosystem of the Arctic, can affect the lower atmospheric circulation, the weather of subarctic area and even the weather of middle latitude areas. The 2003 Chinese Second Arctic Research Expedition experienced the transition of the stratosphereic circulation from a warm anticyclone to a cold cyclone during the ending period of Arctic summertime, a typical establishing process of the polar vortex circulation. The impact of the polar vortex variation on the low-level circulation has been investigated by some scientists through studying the coupling mechanisms of the stratosphere and troposphere. The impact of the Stratospheric Sudden Warming (SFW) events on the polar vortex variation was drawing people's great attention in the fifties of the last century. The Arctic Oscillation (AO) , relating to the variation of the Arctic vortex, has been used to study the impact of the Arctic vortex on climate change. The recent Arctic vortex studies are simply reviewed and some discussions on the Arctic vertex are given in the paper. Some different views and questions are also discussed.
Fuentes, Oscar Velasco
2015-01-01
We study the motion of a single helical vortex in an unbounded, inviscid, incompressible fluid. The vortex is an infinite tube whose centerline is a helix and whose cross section is a circle of small radius (compared to the radius of curvature) where the vorticity is uniform and parallel to the centerline. Ever since Joukowsky (1912) deduced that this vortex translates and rotates steadily without change of form, numerous attempts have been made to compute these self-induced velocities. Here we use Hardin's (1982) solution for the velocity field to find new expressions for the vortex's linear and angular velocities. Our results, verified by numerically computing the Helmholtz integral and the Rosenhead-Moore approximation to the Biot-Savart law, are more accurate than previous results over the whole range of values of the vortex pitch and cross-section. We then use the new formulas to study the advection of passive particles near the vortex; we find that the vortex's motion and capacity to transport fluid dep...
Bathtub vortex induced by instability
Mizushima, Jiro; Abe, Kazuki; Yokoyama, Naoto
2014-10-01
The driving mechanism and the swirl direction of the bathtub vortex are investigated by the linear stability analysis of the no-vortex flow as well as numerical simulations. We find that only systems having plane symmetries with respect to vertical planes deserve research for the swirl direction. The bathtub vortex appearing in a vessel with a rectangular cross section having a drain hole at the center of the bottom is proved to be induced by instability when the flow rate exceeds a threshold. The Coriolis force is capable of determining the swirl direction to be cyclonic.
Dynamic signatures of driven vortex motion.
Energy Technology Data Exchange (ETDEWEB)
Crabtree, G. W.; Kwok, W. K.; Lopez, D.; Olsson, R. J.; Paulius, L. M.; Petrean, A. M.; Safar, H.
1999-09-16
We probe the dynamic nature of driven vortex motion in superconductors with a new type of transport experiment. An inhomogeneous Lorentz driving force is applied to the sample, inducing vortex velocity gradients that distinguish the hydrodynamic motion of the vortex liquid from the elastic and-plastic motion of the vortex solid. We observe elastic depinning of the vortex lattice at the critical current, and shear induced plastic slip of the lattice at high Lorentz force gradients.
2003-01-01
Understanding the nature of vortices in high-Tc superconductors is a crucial subject for research on superconductive electronics, especially for superconducting interference devices (SQUIDs), it is also a fundamental problem in condensed-matter physics. Recent technological progress in methods for both direct and indirect observation of vortices, e.g. scanning SQUID, terahertz imaging, and microwave excitation, has led to new insights into vortex physics, the dynamic behavior of vortices in junctions and related questions of noise. This book presents the current status of research activity and provides new information on the applications of SQUIDs, including magnetocardiography, immunoassays, and laser-SQUID microscopes, all of which are close to being commercially available.
D'Ambrosio, Vincenzo; Carvacho, Gonzalo; Graffitti, Francesco; Vitelli, Chiara; Piccirillo, Bruno; Marrucci, Lorenzo; Sciarrino, Fabio
2016-09-01
Light beams having a vectorial field structure, or polarization, that varies over the transverse profile and a central optical singularity are called vector vortex (VV) beams and may exhibit specific properties such as focusing into "light needles" or rotation invariance. VV beams have already found applications in areas ranging from microscopy to metrology, optical trapping, nano-optics, and quantum communication. Individual photons in such beams exhibit a form of single-particle quantum entanglement between different degrees of freedom. On the other hand, the quantum states of two photons can be also entangled with each other. Here, we combine these two concepts and demonstrate the generation of quantum entanglement between two photons that are both in VV states: a form of entanglement between two complex vectorial fields. This result may lead to quantum-enhanced applications of VV beams as well as to quantum information protocols fully exploiting the vectorial features of light.
Energy Technology Data Exchange (ETDEWEB)
Chesi, Stefano [Department of Physics, McGill University, Montreal, Quebec H3A 2T8 (Canada); CEMS, RIKEN, Wako, Saitama 351-0198 (Japan); Jaffe, Arthur [Harvard University, Cambridge, Massachusetts 02138 (United States); Department of Physics, University of Basel, Basel (Switzerland); Institute for Theoretical Physics, ETH Zürich, Zürich (Switzerland); Loss, Daniel [CEMS, RIKEN, Wako, Saitama 351-0198 (Japan); Department of Physics, University of Basel, Basel (Switzerland); Pedrocchi, Fabio L. [Department of Physics, University of Basel, Basel (Switzerland)
2013-11-15
We investigate the role that vortex loops play in characterizing eigenstates of interacting Majoranas. We give some general results and then focus on ladder Hamiltonian examples as a test of further ideas. Two methods yield exact results: (i) A mapping of certain spin Hamiltonians to quartic interactions of Majoranas shows that the spectra of these two examples coincide. (ii) In cases with reflection-symmetric Hamiltonians, we use reflection positivity for Majoranas to characterize vortices in the ground states. Two additional methods suggest wider applicability of these results: (iii) Numerical evidence suggests similar behavior for certain systems without reflection symmetry. (iv) A perturbative analysis also suggests similar behavior without the assumption of reflection symmetry.
Vortex cores and vortex motion in superconductors with anisotropic Fermi surfaces
Energy Technology Data Exchange (ETDEWEB)
Galvis, J.A. [Laboratorio de Bajas Temperaturas, Departamento de Física de la Materia Condensada, Instituto de Ciencia de Materiales Nicolás Cabrera, Condensed Matter Physics Center (IFIMAC), Facultad de Ciencias, Universidad Autónoma de Madrid, E-28049 Madrid (Spain); Departamento de Ciencias Naturales, Facultad de ingeniería y Ciencias Básicas, Universidad Central, Bogotá (Colombia); National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida 32310 (United States); Herrera, E.; Guillamón, I.; Vieira, S. [Laboratorio de Bajas Temperaturas, Departamento de Física de la Materia Condensada, Instituto de Ciencia de Materiales Nicolás Cabrera, Condensed Matter Physics Center (IFIMAC), Facultad de Ciencias, Universidad Autónoma de Madrid, E-28049 Madrid (Spain); Unidad Asociada de Altos Campos Magnéticos y Bajas Temperaturas, UAM, CSIC, Madrid (Spain); Suderow, H., E-mail: hermann.suderow@uam.es [Laboratorio de Bajas Temperaturas, Departamento de Física de la Materia Condensada, Instituto de Ciencia de Materiales Nicolás Cabrera, Condensed Matter Physics Center (IFIMAC), Facultad de Ciencias, Universidad Autónoma de Madrid, E-28049 Madrid (Spain); Unidad Asociada de Altos Campos Magnéticos y Bajas Temperaturas, UAM, CSIC, Madrid (Spain)
2017-02-15
Highlights: • The observation of vortex cores is reviewed, with emphasis in new experiments. • Vortex cores are follow superconducting gap and Fermi surface shapes. • The vortex core shape influences vortex dynamics. - Abstract: Explaning static and dynamic properties of the vortex lattice in anisotropic superconductors requires a careful characterization of vortex cores. The vortex core contains Andreev bound states whose spatial extension depends on the anisotropy of the electronic band-structure and superconducting gap. This might have an impact on the anisotropy of the superconducting properties and on vortex dynamics. Here we briefly summarize basic concepts to understand anisotropic vortex cores and review vortex core imaging experiments. We further discuss moving vortex lattices and the influence of vortex core shape in vortex motion. We find vortex motion in highly tilted magnetic fields. We associate vortex motion to the vortex entry barrier and the screening currents at the surface. We find preferential vortex motion along the main axis of the vortex lattice. After travelling integers of the intervortex distance, we find that vortices move more slowly due to the washboard potential of the vortex lattice.
Vortex-induced vibrations of a DU96-W-180 airfoil at 90° angle of attack
DEFF Research Database (Denmark)
Skrzypinski, Witold Robert; Gaunaa, Mac; Sørensen, Niels N.;
2014-01-01
This work presents an analysis of vortex-induced vibrations of a DU96-W-180 airfoil in deep stall at a 90 degrees angle of attack, based on 2D and 3D Reynolds Averaged Navier Stokes and 3D Detached Eddy Simulation unsteady Computational Fluid Dynamics computations with non-moving, prescribed motion...... and elastically mounted airfoil suspensions. Stationary vortex-shedding frequencies computed in 2D and 3D Computational Fluid Dynamics differed. In the prescribed motion computations, the airfoil oscillated in the direction of the chord line. Negative aerodynamic damping, found in both 2D and 3D Computational...... Fluid Dynamics computations with moving airfoil, showed in the vicinity of the stationary vortex-shedding frequency computed by 2D Computational Fluid Dynamics. A shorter time series was sufficient to verify the sign of the aerodynamic damping in the case of the elastic computations than the prescribed...
Experimental Study of Tip Vortex Flow from a Periodically Pitched Airfoil Section
Zaman, KBMQ; Fagan, A. F.; Mankbadi, M. R.
2016-01-01
An experimental investigation of a tip vortex from a NACA0012 airfoil is conducted in a low-speed wind tunnel at a chord Reynolds number of 4x10(exp 4). Initially, data for a stationary airfoil held at various angles-of-attack (alpha) are gathered. Detailed surveys are done for two cases: alpha=10 deg with attached flow and alpha=25 deg with massive flow separation on the upper surface. Distributions of various properties are obtained using hot-wire anemometry. Data include mean velocity, streamwise vorticity and turbulent stresses at various streamwise locations. For all cases, the vortex core is seen to involve a mean velocity deficit. The deficit apparently traces to the airfoil wake, part of which gets wrapped by the tip vortex. At small alpha, the vortex is laminar within the measurement domain. The strength of the vortex increases with increasing alpha but undergoes a sudden drop around alpha (is) greater than 16 deg. The drop in peak vorticity level is accompanied by transition and a sharp rise in turbulence within the core. Data are also acquired with the airfoil pitched sinusoidally. All oscillation cases pertain to a mean alpha=15 deg while the amplitude and frequency are varied. An example of phase-averaged data for an amplitude of +/-10 deg and a reduced frequency of k=0.2 is discussed. All results are compared with available data from the literature shedding further light on the complex dynamics of the tip vortex.
Institute of Scientific and Technical Information of China (English)
张辉; 范宝春; 李鸿志
2012-01-01
The flow of the weak electrolyte solution can be controlled by Lorentz force achieved with the suitable magnetic and electric fields, and it has the advantages of vortex street suppression, drag reduction, lift enhancement and oscillatory suppression for the flow over a bluff body. The electro-magnetic control of vortex-induced vibration (VIV) of a circular cyl- inder in the shear flow was investigated numerically in the exponential-polar coordinates attached on the moving cylinder for Re = 150. With the effect of background vorticity, the vortex street of VIV cylinder was composed of two parallel rows with an opposite sign of the vortices which inclines toward the lower side and the strength of upper vortex is larger than that of lower vortex. The lift force vibrated periodically with the effect of vortex shedding and the mean value was negative due to the background vorticity. The Lorentz force for controlling the VIV cylinder was classified into the field Lorentz force and the wall Lorentz force. The field Lorentz force suppresses the lift oscillation, and in turn, suppresses the VIV, whereas the wall Loreutz force increases the lift.
Measurements and modeling of flow structure in the wake of a low profile wishbone vortex generator
Wendt, B. J.; Hingst, W. R.
1994-01-01
The results of an experimental examination of the vortex structures shed from a low profile 'wishbone' generator are presented. The vortex generator height relative to the turbulent boundary layer was varied by testing two differently sized models. Measurements of the mean three-dimensional velocity field were conducted in cross-stream planes downstream of the vortex generators. In all cases, a counter-rotating vortex pair was observed. Individual vortices were characterized by three descriptors derived from the velocity data; circulation, peak vorticity, and cross-stream location of peak vorticity. Measurements in the cross plane at two axial locations behind the smaller wishbone characterize the downstream development of the vortex pairs. A single region of stream wise velocity deficit is shared by both vortex cores. This is in contrast to conventional generators, where each core coincides with a region of velocity deficit. The measured cross-stream velocities for each case are compared to an Oseen model with matching descriptors. The best comparison occurs with the data from the larger wishbone.
Prediction of Vortex Shedding from Circular and Noncircular Bodies in Subsonic Flow
1987-01-01
IIETETT ITTTTD IDRPNDI VV NN ICBC I IOTKD IU DE IL RAA IAAAVX IXAE I EE STI TL L I INR M TI RP I S25 1678 I T SI LL NR IYED EX.EIM I REFERENCES IIIIIIIII...IRCCMAE OAX IE I PHPYP BFOQI IN SCI IETETT ITTTT IDRPNDI VV .NN ICBC IIOTKDIU DE IL RAAIAAAVXIXAE IJEE STITLL I I NR HTI RP I S25 1678 1 1T SI LL NR IYED...DOPI PNNLLI LLLL01D EHKO ORURC ILTT SWROWIt AUADAI HNPEH ID PRS IVPVO0 OOO R IRPAIR IRCMAE IOAX NNE IPHPYP BFOQI IN SCI IETET TTTTD DRPNDI VV NN ICBC I
Magneto-hydrodynamic detection of vortex shedding for molten salt flow sensing.
Energy Technology Data Exchange (ETDEWEB)
Kruizenga, Alan Michael; Crocker, Robert W.
2012-09-01
High temperature flow sensors must be developed for use with molten salts systems at temperatures in excess of 600ÀC. A novel magneto-hydrodynamic sensing approach was investigated. A prototype sensor was developed and tested in an aqueous sodium chloride solution as a surrogate for molten salt. Despite that the electrical conductivity was a factor of three less than molten salts, it was found that the electrical conductivity of an electrolyte was too low to adequately resolve the signal amidst surrounding noise. This sensor concept is expected to work well with any liquid metal application, as the generated magnetic field scales proportionately with electrical conductivity.
Optimal wavy surface to suppress vortex shedding using second-order sensitivity to shape changes
Tammisola, Outi
2016-01-01
A method to find optimal 2nd-order perturbations is presented, and applied to find the optimal spanwise-wavy surface for suppression of cylinder wake instability. Second-order perturbations are required to capture the stabilizing effect of spanwise waviness, which is ignored by standard adjoint-based sensitivity analyses. Here, previous methods are extended so that (i) 2nd-order sensitivity is formulated for base flow changes satisfying linearised Navier-Stokes, and (ii) the resulting method is applicable to a 2D global instability problem. This makes it possible to formulate 2nd-order sensitivity to shape modifications. Using this formulation, we find the optimal shape to suppress the a cylinder wake instability. The optimal shape is then perturbed by random distributions in full 3D stability analysis to confirm that it is a local optimal at the given amplitude and wavelength. Furthermore, it is shown that none of the 10 random wavy shapes alone stabilize the wake flow at Re=50, while the optimal shape does....
Chatterjee, Monish R.; Mohamed, Fathi H. A.
2014-10-01
In recent research, propagation of plane electromagnetic (EM) waves through a turbulent medium with modified von Karman phase characteristics was modeled and numerically simulated using transverse planar apertures representing narrow phase turbulence along the propagation path. The case for extended turbulence was also studied by repeating the planar phase screens multiple times over the propagation path and incorporating diffractive effects via a split-step algorithm. The goal of the research reported here is to examine two random phenomena: (a) atmospheric turbulence due to von Karman-type phase fluctuations, and (b) chaos generated in an acousto-optic (A-O) Bragg cell under hybrid feedback. The latter problem has been thoroughly examined for its nonlinear dynamics and applications in secure communications. However, the statistical characteristics (such as the power spectral density (PSD)) of the chaos have not been estimated in recent work. To that end, treating the chaos phenomena as a random process, the time waveforms of the chaos intensity and their spectra are numerically evaluated over a (large) number of time iterations. These spectra are then averaged to derive the equivalent PSD of the A-O chaos. For the turbulence problem, an optical beam passing through an input pinhole is propagated through a random phase screen (placed at different locations) to a desired distance (typically near-field) under different levels of turbulence strength. The resulting spatial intensity profile is then averaged and the process repeated over a (large) number of pre-specified time intervals. From this data, once again, the turbulence PSD is calculated via the Fourier spectra of the average intensity snapshots. The results for the two systems are compared.
Adaptive load shedding and regional protection
Energy Technology Data Exchange (ETDEWEB)
Ford, J.J.; Ledwich, G. [School of Engineering Systems, Queensland University of Technology, Brisbane, Qld 4001 (Australia); Bevrani, H. [Department of Electrical and Computer Engineering, University of Kurdistan Sanandaj, Kurdistan (Iran)
2009-11-15
The requirement for improved efficiency whilst maintaining system security necessitates the development of improved system analysis approaches and the development of advanced emergency control technologies. Load shedding is a type of emergency control that is designed to ensure system stability by curtailing system load to match generation supply. This paper presents a new adaptive load shedding scheme that provides emergency protection against excess frequency decline, whilst minimizing the risk of line overloading. The proposed load shedding scheme uses the local frequency rate information to adapt the load shedding behaviour to suit the size and location of the experienced disturbance. The proposed scheme is tested in simulation on a 3-region, 10-generator sample system and shows good performance. (author)
Vortex state in ferromagnetic nanoparticles
Betto, Davide; Coey, J. M. D.
2014-05-01
The evolution of the magnetic state of a soft ferromagnetic nanoparticle with its size is usually thought to be from superparamagnetic single domain to blocked single domain to a blocked multidomain structure. Néel pointed out that a vortex configuration produces practically no stray field at the cost of an increase in the exchange energy, of the order of RJS2lnR /c, where JS2 is the bond energy, R is the particle radius, and c is of the order of the exchange length. A vortex structure is energetically cheaper than single domain when the radius is greater than a certain value. The correct sequence should include a vortex configuration between the single domain and the multidomain states. The critical size is calculated for spherical particles of four important materials (nickel, magnetite, permalloy, and iron) both numerically and analytically. A vortex state is favored in materials with high magnetisation.
Particle-vortex symmetric liquid
Mulligan, Michael
2016-01-01
We introduce an effective theory with manifest particle-vortex symmetry for disordered thin films undergoing a magnetic field-tuned superconductor-insulator transition. The theory may enable one to access both the critical properties of the strong-disorder limit, which has recently been confirmed [Breznay et al., PNAS 113, 280 (2016)] to exhibit particle-vortex symmetric electrical response, and the metallic phase discovered earlier [Mason and Kapitulnik, Phys. Rev. Lett. 82, 5341 (1999)] in less disordered samples. Within the effective theory, the Cooper-pair and field-induced vortex degrees of freedom are simultaneously incorporated into an electrically-neutral Dirac fermion minimally coupled to an (emergent) Chern-Simons gauge field. A derivation of the theory follows upon mapping the superconductor-insulator transition to the integer quantum Hall plateau transition and the subsequent use of Son's particle-hole symmetric composite Fermi liquid. Remarkably, particle-vortex symmetric response does not requir...
Vortex migration in protoplanetary discs
Directory of Open Access Journals (Sweden)
Papaloizou John C. B.
2013-04-01
Full Text Available Vortices embedded in protoplanetary discs can act as obstacles to the unperturbed disc flow. The resulting velocity perturbations propagate away from the vortex in the form of density waves that transport angular momentum. Any asymmetry between the inner and the outer density wave means that the region around the vortex has to change its angular momentum. We find that this leads to orbital migration of the vortex. Asymmetric waves always arise except in the case of a disc with constant pressure, for isothermal as well as non-isothermal discs. Depending on the size and strength of the vortex, the resulting migration time scales can be as short as a few thousand orbits.
New omega vortex identification method
Liu, ChaoQun; Wang, YiQian; Yang, Yong; Duan, ZhiWei
2016-08-01
A new vortex identification criterion called Ω-method is proposed based on the ideas that vorticity overtakes deformation in vortex. The comparison with other vortex identification methods like Q-criterion and λ 2-method is conducted and the advantages of the new method can be summarized as follows: (1) the method is able to capture vortex well and very easy to perform; (2) the physical meaning of Ω is clear while the interpretations of iso-surface values of Q and λ 2 chosen to visualize vortices are obscure; (3) being different from Q and λ 2 iso-surface visualization which requires wildly various thresholds to capture the vortex structure properly, Ω is pretty universal and does not need much adjustment in different cases and the iso-surfaces of Ω=0.52 can always capture the vortices properly in all the cases at different time steps, which we investigated; (4) both strong and weak vortices can be captured well simultaneously while improper Q and λ 2 threshold may lead to strong vortex capture while weak vortices are lost or weak vortices are captured but strong vortices are smeared; (5) Ω=0.52 is a quantity to approximately define the vortex boundary. Note that, to calculate Ω, the length and velocity must be used in the non-dimensional form. From our direct numerical simulation, it is found that the vorticity direction is very different from the vortex rotation direction in general 3-D vortical flow, the Helmholtz velocity decomposition is reviewed and vorticity is proposed to be further decomposed to vortical vorticity and non-vortical vorticity.
Formation number for vortex dipoles
Sadri, Vahid; Krueger, Paul S.
2016-11-01
This investigation considers the axisymmetric formation of two opposite sign concentric vortex rings from jet ejection between concentric cylinders. This arrangement is similar to planar flow in that the vortex rings will travel together when the gap between the cylinders is small, similar to a vortex dipole, but it has the advantage that the vortex motion is less constrained than the planar case (vortex stretching and vortex line curvature is allowed). The flow was simulated numerically at a jet Reynolds number of 1,000 (based on ΔR and the jet velocity), jet pulse length-to-gap ratio (L / ΔR) in the range 10-20, and gap-to-outer radius ratio (ΔR /Ro) in the range 0.01-0.1. Small gap ratios were chosen for comparison with 2D results. In contrast with 2D results, the closely paired vortices in this study exhibited pinch-off from the generating flow and finite formation numbers. The more complex flow evolution afforded by the axisymmetric model and its influence on the pinch-off process will be discussed. This material is based on work supported by the National Science Foundation under Grant No. 1133876 and SMU. This supports are gratefully acknowledged.
Vortex migration in protoplanetary disks
Paardekooper, S -J; Papaloizou, J C B
2010-01-01
We consider the radial migration of vortices in two-dimensional isothermal gaseous disks. We find that a vortex core, orbiting at the local gas velocity, induces velocity perturbations that propagate away from the vortex as density waves. The resulting spiral wave pattern is reminiscent of an embedded planet. There are two main causes for asymmetries in these wakes: geometrical effects tend to favor the outer wave, while a radial vortensity gradient leads to an asymmetric vortex core, which favors the wave at the side that has the lowest density. In the case of asymmetric waves, which we always find except for a disk of constant pressure, there is a net exchange of angular momentum between the vortex and the surrounding disk, which leads to orbital migration of the vortex. Numerical hydrodynamical simulations show that this migration can be very rapid, on a time scale of a few thousand orbits, for vortices with a size comparable to the scale height of the disk. We discuss the possible effects of vortex migrat...
Optical Vortex Solitons in Parametric Wave Mixing
Alexander, T J; Buryak, A V; Sammut, R A; Alexander, Tristram J.; Kivshar, Yuri S.; Buryak, Alexander V.; Sammut, Rowland A.
2000-01-01
We analyze two-component spatial optical vortex solitons supported by degenerate three- or four-wave mixing in a nonlinear bulk medium. We study two distinct cases of such solitons, namely, parametric vortex solitons due to phase-matched second-harmonic generation in a optical medium with competing quadratic and cubic nonlinear response, and vortex solitons in the presence of third-harmonic generation in a cubic medium. We find, analytically and numerically, the structure of two-component vortex solitons, and also investigate modulational instability of their plane-wave background. In particular, we predict and analyze in detail novel types of vortex solitons, a `halo-vortex', consisting of a two-component vortex core surrounded by a bright ring of its harmonic field, and a `ring-vortex' soliton which is a vortex in a harmonic field that guides a bright localized ring-like mode of a fundamental frequency field.
Instabilities of interacting vortex rings generated by an oscillating disk
Deng, Jian; Teng, Lubao; Caulfield, C. P.; Mao, Xuerui
2016-09-01
We propose a natural model to probe in a controlled fashion the instability of interacting vortex rings shed from the edge of an oblate spheroid disk of major diameter c , undergoing oscillations of frequency f0 and amplitude A . We perform a Floquet stability analysis to determine the characteristics of the instability modes, which depend strongly on the azimuthal (integer) wave number m . We vary two key control parameters, the Keulegan-Carpenter number KC=2 π A /c and the Stokes number β =f0c2/ν , where ν is the kinematic viscosity of the fluid. We observe two distinct flow regimes. First, for sufficiently small β , and hence low frequency of oscillation corresponding to relatively weak interaction between sequentially shedding vortex rings, symmetry breaking occurs directly to a single unstable mode with m =1 . Second, for sufficiently large yet fixed values of β , corresponding to a higher oscillation frequency and hence stronger ring-ring interaction, the onset of asymmetry is predicted to occur due to two branches of high m instabilities as the amplitude is increased, with m =1 structures being dominant only for sufficiently large values of KC. These two branches can be distinguished by the phase properties of the vortical structures above and below the disk. The region in (KC,β ) parameter space where these two high m instability branches arise can be described accurately in terms of naturally defined Reynolds numbers, using appropriately chosen characteristic length scales. We subsequently carry out direct numerical simulations of the fully three-dimensional flow to verify the principal characteristics of the Floquet analysis, in particular demonstrating that high wave-number symmetry-breaking generically occurs when vortex rings sequentially interact sufficiently strongly.
Water tunnel visualization of the vortex flows of the F-15
Lorincz, D. J.; Friend, E. L.
1979-01-01
Flow visualization studies were conducted in a diagnostic water tunnel to provide details of the wing, glove, and forebody vortex flow fields of the F-15 aircraft over a range of angles of attack and sideslip. Both the formation and breakdown of the vortex flow as a function of angle of attack and sideslip are detailed for the basic aircraft configuration. Additional tests showed that the wing upper surface vortex flows were sensitive to variations in an inlet mass flow ratio and an inlet cowl deflection angle. Two lengthened forebodies, one with a modified cross-sectional shape, were tested in addition to the basic forebody. Asymmetric forebody vortices were observed at zero sideslip and high angles of attack on each forebody. A large nose boom was added to each of the three forebodies, and it was observed that the turbulent wake shed from the boom disrupted the forebody vortices.
Wu, C M; Chen, W J; Zheng, Yue; Ma, D C; Wang, B; Liu, J Y; Woo, C H
2014-02-04
Ferroelectric vortex domain structure which exists in low-dimensional ferroelectrics is being intensively researched for future applications in functional nanodevices. Here we demonstrate that adjusting surface charge screening in combination with temperature can provide an efficient way to gain control of vortex domain structure in ferroelectric nanodot. Systematical simulating experiments have been conducted to reveal the stability and evolution mechanisms of domain structure in ferroelectric nanodot under various conditions, including processes of cooling-down/heating-up under different surface charge screening conditions, and increasing/decreasing surface charge screening at different temperatures. Fruitful phase diagrams as functions of surface screening and temperature are presented, together with evolution paths of various domain patterns. Calculations discover up to 25 different kinds of domain patterns and 22 typical evolution paths of phase transitions. The fruitful controllability of vortex domain structure by surface charge screening in combination with temperature should shed light on prospective nanodevice applications of low-dimensional ferroelectric nanostructures.
Secondary vortex street in the wake of two tandem circular cylinders at low Reynolds number.
Wang, Si-ying; Tian, Fang-bao; Jia, Lai-bing; Lu, Xi-yun; Yin, Xie-zhen
2010-03-01
The experiments on two tandem circular cylinders were conducted in a horizontal soap film tunnel for the Reynolds number Re=60 , 80, and 100 and the nondimensional center-to-center spacing Gamma ranging in 1 approximately 12. The flow patterns were recorded by a high-speed camera and the vortex shedding frequency was obtained by a spatiotemporal evolution method. The secondary vortex formation (SVF) mode characterized by the formation of a secondary vortex street in the wake of the downstream cylinder was found at large gamma. Moreover, some typical modes predicted by previous investigations, including the single bluff-body, shear layer reattachment, and synchronization of vortex shedding modes, were also revisited in our experiments. Further, numerical simulations were carried out using a space-time finite-element method and the results confirmed the existence of the SVF mode. The mechanism of SVF mode was analyzed in terms of the numerical results. The dependence of the Strouhal number Sr on Gamma was given and the flow characteristics relevant to the critical spacing values and the hysteretic mode transitions were investigated.
Cheung, M. C. M.; Moreno-Insertis, F.; Schüssler, M.
2006-05-01
Aims.We study the buoyant rise of magnetic flux tubes in a stratified layer over a range of Reynolds numbers (25 ⪉ Re ⪉ 2600) by means of numerical simulations. Special emphasis is placed on studying the fragmentation of the rising tube, its trailing wake and the formation of a vortex street in the high-Reynolds number regime. Furthermore, we evaluate the relevance of the thin flux tube approximation with regard to describing the evolution of magnetic flux tubes in the simulations. Methods: .We used the FLASH code, which has an adaptive mesh refinement (AMR) algorithm, thus allowing the simulations to be carried out at high Reynolds numbers. Results: .The evolution of the magnetic flux tube and its wake depends on the Reynolds number. At Re up to a few hundred, the wake consists of two counter-rotating vortex rolls. At higher Re, the vortex rolls break up and the shedding of flux into the wake occurs in a more intermittent fashion. The amount of flux retained by the central portion of the tube increases with the field line twist (in agreement with previous literature) and with Re. The time evolution of the twist is compatible with a homologous expansion of the tube. The motion of the central portion of the tube in the simulations is very well described by the thin flux tube model whenever the effects of flux loss or vortex forces can be neglected. If the flux tube has an initial net vorticity, it undergoes asymmetric vortex shedding. In this case, the lift force accelerates the tube in such a way that an oscillatory horizontal motion is super-imposed on the vertical rise of the tube, which leaves behind a vortex street. This last result is in accordance with previous simulations reported in the literature, which were carried out at lower Reynolds number.
Energy Technology Data Exchange (ETDEWEB)
Murakami, Satoshi [Customer System Co. Ltd. (Japan); Muramatsu, Toshiharu [Japan Nuclear Cycle Development Inst., Oarai, Ibaraki (Japan). Oarai Engineering Center
2002-05-01
Numerical analyses for turbulence thermal mixing, the aim of which is to evaluate relationship between hydrodynamics and temperature distribution of an arched-vortex, were carried out using the direct numerical simulation code DINUS-3. From the analyses, the following results have been obtained: (1) Transportation period of the arched-vortex and distance between the arched-vortices were kept constant in isothermal and non-isothermal conditions. (2) The transportation period of arched-vortex was decreased with increasing Reynolds number under the condition of the constant flow velocity ratio between both coolant pipes. (3) One of the main reasons for this behavior was considered that the motion of the cold fluid flowing out of the branch pipe was restricted by the difference of fluid density between the branch and the main pipes. The amplitudes of the cross flow velocity fluctuation in the leg region of the arched-vortex were larger than those under isothermal condition. (4) It was confirmed that the arched-vortex consists of two kinds of vortexes, i.e., a longitudinal vortex generated by a shear motion at the top of the arched-vortex, and a horizontal vortex by shedding motion at both sides of the branch jet flow. (author)
Martinuzzi, Robert
2016-11-01
Quasi-periodic vortex shedding in the turbulent wake of a thin-flat plate placed normal to a uniform stream at Reynolds number of 6700 is investigated based on Particle Image Velocimetry experiments. The wake structure and vortex formation are characterized using a generalized phase average (GPA), a refinement of the triple decomposition of Reynolds and Hussain (1970) incorporating elements of mean-field theory (Stuart, 1958). The resulting analysis highlights the importance of cycle-to-cycle variations in characterizing vortex formation, wake topology and the residual turbulent Reynolds Stresses. For example, it is shown that during high-amplitude cycles vorticity is strongly concentrated within the well-organized shed vortices, whereas during low-amplitude cycles the shed vortices are highly distorted resulting in significant modulation of the shedding frequency. It is found that high-amplitude cycles contribute more to the coherent Reynolds stress field while the low-amplitude cycles contribute to the residual stress field. It is further shown that traditional phase-averaging techniques lead to an over-estimation of the residual stress field. Natural Sciences and Engineering Research Council of Canada.
Vortex Laser at Exceptional Point
Wang, Xing-Yuan; Li, Ying; Li, Bo; Ma, Ren-Min
2016-01-01
The optical vortices carrying orbital angular momentum (OAM) are commonly generated by modulating the available conventional light beam. This article shows that a micro-laser operates at the exceptional point (EP) of the non-Hermitian quantum system can directly emit vortex laser with well-defined OAM at will. Two gratings (the refractive index modulation and along azimuthal direction and the grating protruding from the micro-ring cavity) modulate the eigenmode of a micro-ring cavity to be a vortex laser mode. The phase-matching condition ensures that we can tune the OAM of the vortex beam to be arbitrary orders by changing the grating protruding from the micro-ring cavity while the system is kept at EP. The results are obtained by analytical analysis and confirmed by 3D full wave simulations.
A Experimental Study of Viscous Vortex Rings.
Dziedzic, Mauricio
Motivated by the role played by vortex rings in the process of turbulent mixing, the work is focused on the problem of stability and viscous decay of a single vortex ring. A new classification is proposed for vortex rings which is based on extensive hot-wire measurements of velocity in the ring core and wake and flow visualization. Vortex rings can be classified as laminar, wavy, turbulence-producing, and turbulent. Prediction of vortex ring type is shown to be possible based on the vortex ring Reynolds number. Linear growth rates of ring diameter with time are observed for all types of vortex rings, with different growth rates occurring for laminar and turbulent vortex rings. Data on the viscous decay of vortex rings are used to provide experimental confirmation of the accuracy of Saffman's equation for the velocity of propagation of a vortex ring. Experimental data indicate that instability of the vortex ring strongly depends on the mode of generation and can be delayed by properly adjusting the generation parameters. A systematic review of the literature on vortex-ring interactions is presented in the form of an appendix, which helps identify areas in which further research may be fruitful.
Fractional vortex dipole phase filter
Sharma, Manoj Kumar; Joseph, Joby; Senthilkumaran, Paramasivam
2014-10-01
In spatial filtering experiments, the use of vortex phase filters plays an important role in realizing isotropic edge enhancement. In this paper, we report the use of a vortex dipole phase filter in spatial filtering. A dipole made of fractional vortices is used, and its filtering characteristics are studied. It is observed that the filter performance can be tuned by varying the distance of separation between the vortices of the dipole to achieve better contrast and output noise suppression, and when this distance tends to infinity, the filter performs like a 1-D Hilbert mask. Experimental and simulation results are presented.
Vortex ice in nanostructured superconductors
Energy Technology Data Exchange (ETDEWEB)
Reichhardt, Charles [Los Alamos National Laboratory; Reichhardt, Cynthia J [Los Alamos National Laboratory; Libal, Andras J [Los Alamos National Laboratory
2008-01-01
We demonstrate using numerical simulations of nanostructured superconductors that it is possible to realize vortex ice states that are analogous to square and kagome ice. The system can be brought into a state that obeys either global or local ice rules by applying an external current according to an annealing protocol. We explore the breakdown of the ice rules due to disorder in the nanostructure array and show that in square ice, topological defects appear along grain boundaries, while in kagome ice, individual defects appear. We argue that the vortex system offers significant advantages over other artificial ice systems.
Generation of nonlinear vortex precursors
Chen, Yue-Yue; Liu, Chengpu
2016-01-01
We numerically study the propagation of a few-cycle pulse carrying orbital angular momentum (OAM) through a dense atomic system. Nonlinear precursors consisting of high-order vortex har- monics are generated in the transmitted field due to ultrafast Bloch oscillation. The nonlinear precursors survive to propagation effects and are well separated with the main pulse, which provide a straightforward way of measuring precursors. By the virtue of carrying high-order OAM, the obtained vortex precursors as information carriers have potential applications in optical informa- tion and communication fields where controllable loss, large information-carrying capacity and high speed communication are required.
Experimental study on vortex induced vibration (VIV of a wide-D-section cylinder in a cross flow
Directory of Open Access Journals (Sweden)
Qingyang Wang
2015-01-01
Full Text Available Wake structures and vortex induced vibration (VIV of a spring-supported wide-D-section cylinder were experimentally investigated using an X-wire, a novel phase-locked particle image velocimetry (PIV, and an acceleration sensor at a low speed wind tunnel. Compared with the fixed case, the 2P (two pair vortex mode as defined by Govardhan and Williamson (2000 rather than S (single vortex mode exists in the wake. The velocity deficit behind the cylinder is much larger than that of fixed case. The mean drag coefficient increases from 1.42 for the fixed case to 1.64 for the vibrating case. The Reynolds stress presents even distribution and small with increased distance of X/D=−2 to X/D=−10. The power spectra density based on accelerator and hot wire data presents a highlight identical. It shows that after a strong interaction the cylinder vibration and the vortex shedding come to a stable state. The vortex shedding is totally locked on and controlled by the cylinder vibration.
Vortex rings and jets recent developments in near-field dynamics
Yu, Simon
2015-01-01
In this book, recent developments in our understanding of fundamental vortex ring and jet dynamics will be discussed, with a view to shed light upon their near-field behaviour which underpins much of their far-field characteristics. The chapters provide up-to-date research findings by their respective experts and seek to link near-field flow physics of vortex ring and jet flows with end-applications in mind. Over the past decade, our knowledge on vortex ring and jet flows has grown by leaps and bounds, thanks to increasing use of high-fidelity, high-accuracy experimental techniques and numerical simulations. As such, we now have a much better appreciation and understanding on the initiation and near-field developments of vortex ring and jet flows under many varied initial and boundary conditions. Chapter 1 outlines the vortex ring pinch-off phenomenon and how it relates to the initial stages of jet formations and subsequent jet behaviour, while Chapter 2 takes a closer look at the behaviour resulting from vor...
Vortex dynamics and surface pressure fluctuations on a normal flat plate
Hemmati, Arman; Wood, David H.; Martinuzzi, Robert J.; Ferrari, Simon W.; Hu, Yaoping
2016-11-01
The effect of vortex formation and interactions on surface pressure fluctuations is examined in the wake of a normal flat plate by analyzing Direct Numerical Simulations at Re =1200. A novel local maximum score-based 3D method is used to track vortex development in the region close to the plate where the major contributions to the surface pressure are generated. Three distinct vortex shedding regimes are identified by changes in the lift and drag fluctuations. The instances of maximum drag coincide with impingement of newly formed vortices on the plate. This results in large and concentrated areas of rotational and strain contributions to generation of pressure fluctuations. Streamwise vortex straining and chordwise stretching are correlated with the large ratios of streamwise to chordwise normal stresses and regions of significant rotational contribution to the pressure. In contrast at the minimum drag, the vorticity field close to the plate is disorganized, and vortex roll-up occurs farther downstream. This leads to a uniform distribution of pressure. This study was supported by Alberta Innovates Technology Futures (AITF) and Natural Sciences and Engineering Research Council of Canada (NSERC).
1998-01-01
I8. detsembrist Rüütelkonna hoones näitus "Itaalia maalikooli shedöövreid Eesti Kunstimuuseumi kogust" sarjast "Kadrioru lossi aarded", mis kajastab ka teoste restaureerimist ja uurimistööd. Maali "Püha Joosepi surm" ümberatribueerimisest XVII sajandi Veneetsia meistrile Giovanni Battista Piazzettale
Shedding further light on late globalization
DEFF Research Database (Denmark)
Turcan, Romeo V.
2016-01-01
In his opening essay on ‘What and/or Who is Late’, Nikhilesh Dholakia delineated inter alia “stage-setting contexts” or levels of analysis which could shed light on the phenomenon of late globalization, including its causes and effects. Indeed, these, especially the effects in contemporary contex...
Control of vortex-induced vibration using a pair of synthetic jets: Influence of active lock-on
Wang, Chenglei; Tang, Hui; Yu, Simon C. M.; Duan, Fei
2017-08-01
While conventional vortex-induced vibration (VIV) of bluff bodies is suppressed through reducing the strength of asymmetric vortex shedding, it can also be mitigated by shifting the vortex shedding frequency away from the natural frequency of the body structures using active lock-on. Recently Du and Sun ["Suppression of vortex-induced vibration using the rotary oscillation of a cylinder," Phys. Fluids 27, 023603 (2015)] utilized periodical rotation to induce the lock-on of the frequency of vortex shedding from a transversely vibrating cylinder to the rotation frequency and demonstrated successful VIV suppression. However, questions were raised from this investigation: Does the occurrence of active lock-on always suppress VIV? If not, how to ensure the appropriate usage of active lock-on for VIV suppression? To address these research questions, a numerical investigation is conducted on the active VIV control of a circular cylinder using a pair of synthetic jets (SJs) at a low Reynolds number of 100. The SJ pair operates with various phase differences over a wide frequency range so that the influence of various lock-on can be investigated. It is found that the VIV control can be affected not only by the occurrence of the primary lock-on but also by the occurrence of other lock-on such as secondary and tertiary lock-on. The occurrence of lock-on does not always result in successful VIV suppression. Sometimes it even causes the augmentation of VIV. Compared to the VIV suppression using the conventional vortex-strength-reduction method, the control by the means of active lock-on seems less effective.
Melting of heterogeneous vortex matter: The vortex `nanoliquid'
Indian Academy of Sciences (India)
S S Banerjee; S Goldberg; Y Myasoedov; M Rappaport; E Zeldov; A Soibel; F de la Cruz; C J van der Beek; M Konczykowski; T Tamegai; V Vinokur
2006-01-01
Disorder and porosity are parameters that strongly influence the physical behavior of materials, including their mechanical, electrical, magnetic and optical properties. Vortices in superconductors can provide important insight into the effects of disorder because their size is comparable to characteristic sizes of nanofabricated structures. Here we present experimental evidence for a novel form of vortex matter that consists of inter-connected nanodroplets of vortex liquid caged in the pores of a solid vortex structure, like a liquid permeated into a nanoporous solid skeleton. Our nanoporous skeleton is formed by vortices pinned by correlated disorder created by high-energy heavy ion irradiation. By sweeping the applied magnetic field, the number of vortices in the nanodroplets is varied continuously from a few to several hundred. Upon cooling, the caged nanodroplets freeze into ordered nanocrystals through either a first-order or a continuous transition, whereas at high temperatures a uniform liquid phase is formed upon delocalization-induced melt- ing of the solid skeleton. This new vortex nanoliquid displays unique properties and symmetries that are distinct from both solid and liquid phases.
Backreaction of excitations on a vortex
Arodz, H; Arodz, Henryk; Hadasz, Leszek
1997-01-01
Excitations of a vortex are usually considered in a linear approximation neglecting their backreaction on the vortex. In the present paper we investigate backreaction of Proca type excitations on a straightlinear vortex in the Abelian Higgs model. We propose exact Ansatz for fields of the excited vortex. From initial set of six nonlinear field equations we obtain (in a limit of weak excitations) two linear wave equations for the backreaction corrections. Their approximate solutions are found in the cases of plane wave and wave packet type excitations. We find that the excited vortex radiates vector field and that the Higgs field has a very broad oscillating component.
Particle-vortex symmetric liquid
Mulligan, Michael
2017-01-01
We introduce an effective theory with manifest particle-vortex symmetry for disordered thin films undergoing a magnetic field-tuned superconductor-insulator transition. The theory may enable one to access both the critical properties of the strong-disorder limit, which has recently been confirmed by Breznay et al. [Proc. Natl. Acad. Sci. USA 113, 280 (2016), 10.1073/pnas.1522435113] to exhibit particle-vortex symmetric electrical response, and the nearby metallic phase discovered earlier by Mason and Kapitulnik [Phys. Rev. Lett. 82, 5341 (1999), 10.1103/PhysRevLett.82.5341] in less disordered samples. Within the effective theory, the Cooper-pair and field-induced vortex degrees of freedom are simultaneously incorporated into an electrically neutral Dirac fermion minimally coupled to a (emergent) Chern-Simons gauge field. A derivation of the theory follows upon mapping the superconductor-insulator transition to the integer quantum Hall plateau transition and the subsequent use of Son's particle-hole symmetric composite Fermi liquid. Remarkably, particle-vortex symmetric response does not require the introduction of disorder; rather, it results when the Dirac fermions exhibit vanishing Hall effect. The theory predicts approximately equal (diagonal) thermopower and Nernst signal with a deviation parameterized by the measured electrical Hall response at the symmetric point.
DEFF Research Database (Denmark)
Andersen, Anders Peter; Bohr, Tomas; Stenum, Bjarne
2003-01-01
We present experiments and theory for the "bathtub vortex," which forms when a fluid drains out of a rotating cylindrical container through a small drain hole. The fast down-flow is found to be confined to a narrow and rapidly rotating "drainpipe" from the free surface down to the drain hole. Sur...
Merger of Long Vortex Filaments
Khandekar, Akshay
2012-01-01
This fluid dynamics video demonstrates the merger of long vortex filaments is shown experimentally. Two counter-rotating vortices are generated using in a tank with very high aspect ratio. PIV demonstrates the merger of the vortices within a single orbit.
Thermal inhomogeneities in vortex tubes
Lemesh, N. I.; Senchuk, L. A.
An experimental study of the effect of the temperature of the inlet gas on the temperature difference between the hot and cold streams discharged from a Ranque-Hilsch vortex tube is described. The experimental results are presented in graphical form. It is that the temperature difference increases with the temperature of the entering gas.
Instability of vortex pair leapfrogging
DEFF Research Database (Denmark)
Tophøj, Laust; Aref, Hassan
2013-01-01
pairs fly off to infinity, and a "walkabout" mode, where the vortices depart from leapfrogging but still remain within a finite distance of one another. We show numerically that this transition is more gradual, a result that we relate to earlier investigations of chaotic scattering of vortex pairs [L...
DEFF Research Database (Denmark)
Aref, Hassan
2010-01-01
An IUTAM symposium with the title of this paper was held on October 12-16, 2008, in Lyngby and Copenhagen, Denmark, to mark the sesquicentennial of publication of Helmholtz's seminal paper on vortex dynamics. This volume contains the proceedings of the Symposium. The present paper provides...
Chaos in body-vortex interactions
DEFF Research Database (Denmark)
Pedersen, Johan Rønby; Aref, Hassan
2010-01-01
The model of body–vortex interactions, where the fluid flow is planar, ideal and unbounded, and the vortex is a point vortex, is studied. The body may have a constant circulation around it. The governing equations for the general case of a freely moving body of arbitrary shape and mass density...... of a circle is integrable. As the body is made slightly elliptic, a chaotic region grows from an unstable relative equilibrium of the circle-vortex case. The case of a cylindrical body of any shape moving in fluid otherwise at rest is also integrable. A second transition to chaos arises from the limit between...... and an arbitrary number of point vortices are presented. The case of a body and a single vortex is then investigated numerically in detail. In this paper, the body is a homogeneous, elliptical cylinder. For large body–vortex separations, the system behaves much like a vortex pair regardless of body shape. The case...
Vortex-wake interactions of a flapping foil that models animal swimming and flight.
Lentink, David; Muijres, Florian T; Donker-Duyvis, Frits J; van Leeuwen, Johan L
2008-01-01
The fluid dynamics of many swimming and flying animals involves the generation and shedding of vortices into the wake. Here we studied the dynamics of similar vortices shed by a simple two-dimensional flapping foil in a soap-film tunnel. The flapping foil models an animal wing, fin or tail in forward locomotion. The vortical flow induced by the foil is correlated to (the resulting) thickness variations in the soap film. We visualized these thickness variations through light diffraction and recorded it with a digital high speed camera. This set-up enabled us to study the influence of foil kinematics on vortex-wake interactions. We varied the dimensionless wavelength of the foil (lambda*=4-24) at a constant dimensionless flapping amplitude (A*=1.5) and geometric angle of attack amplitude (A(alpha,geo)=15 degrees ). The corresponding Reynolds number was of the order of 1000. Such values are relevant for animal swimming and flight. We found that a significant leading edge vortex (LEV) was generated by the foil at low dimensionless wavelengths (lambda*wake dynamics evolved from a wavy von Kármán-like vortex wake shed along the sinusoidal path of the foil into a wake densely packed with large interacting vortices. We found that strongly interacting vortices could change the wake topology abruptly. This occurred when vortices were close enough to merge or tear each other apart. Our experiments show that relatively small changes in the kinematics of a flapping foil can alter the topology of the vortex wake drastically.
76 FR 66220 - Automatic Underfrequency Load Shedding and Load Shedding Plans Reliability Standards
2011-10-26
... differentiation in requirements based on entity size, though it provides the opportunity for planning coordinators... type of load shedding (i.e., automatic and manual) should not overlap. 49. There are no requirements in...
Superhydrophobic porous networks for enhanced droplet shedding
Liu, Yahua; Wang, Zuankai
2016-09-01
Recent research has shown that the use of submillimeter-scale tapered post arrays could generate the so-called pancake bouncing, which is characterized by the fast shedding of impinging drops from the surface in a pancake shape without undergoing the retraction stage as observed on conventional superhydrophobic surfaces. Despite this exciting discovery, the fabrication of this unique superhydrophobic surface with tapered post arrays involves complex processes, hindering its wide applications in practical sectors. Here, we report on the facile strategy to prepare a new hierarchical multilayered superhydrophobic surface directly from commercially available porous matrix that allows for efficient drop shedding. Further study shows that the enhanced drop mobility observed on such a surface is attributed to the synergistic cooperation of hierarchical structures endowing an adequate energy storage and effective energy release. The facile fabrication of superhydrophobic surface with enhanced drop mobility may find many practical applications including anti-icing, dropwise condensation and self-cleaning.
On Load Shedding in Complex Event Processing
2013-01-01
Complex Event Processing (CEP) is a stream processing model that focuses on detecting event patterns in continuous event streams. While the CEP model has gained popularity in the research communities and commercial technologies, the problem of gracefully degrading performance under heavy load in the presence of resource constraints, or load shedding, has been largely overlooked. CEP is similar to "classical" stream data management, but addresses a substantially different class of queries. Thi...
CAD Instructor Designs Eco-Friendly Shed
Schwendau, Mark
2013-01-01
Dissatisfied with the options offered by big box stores--and wanting to save some money and go as green as possible--the author puts his design and construction skills to good use. In this article, he shares how he designed and built an eco-friendly shed. He says he is very pleased with the results of working with his own design, reducing waste,…
CAD Instructor Designs Eco-Friendly Shed
Schwendau, Mark
2013-01-01
Dissatisfied with the options offered by big box stores--and wanting to save some money and go as green as possible--the author puts his design and construction skills to good use. In this article, he shares how he designed and built an eco-friendly shed. He says he is very pleased with the results of working with his own design, reducing waste,…
Biology and biogenesis of shed microvesicles.
Tricarico, Christopher; Clancy, James; D'Souza-Schorey, Crislyn
2016-08-05
The ability of cells to transmit bioactive molecules to recipient cells and the extracellular environment is a fundamental requirement for both normal physiology and disease pathogenesis. It has traditionally been thought that soluble factors released from cells were responsible for this cellular signaling but recent research has revealed a fundamental role for microvesicles in this process. Microvesicles are heterogeneous membrane-bound sacs that are shed from the surface of cells into the extracellular environment in a highly regulated process. They are shed following the selective incorporation of a host of molecular cargo including multiple types of proteins and nucleic acids. In addition to providing new insight into the etiology of complex human diseases, microvesicles also show great promise as a tool for advanced diagnosis and therapy as we move forward into a new age of personalized medicine. Here we review current status of the rapidly evolving field of microvesicle biology, highlighting critical regulatory roles for several small GTPases in the biology and biogenesis of shed microvesicles.
Institute of Scientific and Technical Information of China (English)
QI E-rong; LI Guo-ya; LI Wei; WU Jian; ZHANG Xin
2006-01-01
In the gap-ratio range of 0.0≤G≤7.0, a particle image velocimetry PIV is applied to conduct a systematic experimental research of the flow around a horizontal circular cylinder in the cross-flow of shallow water. The velocity distribution of transient flow field at various gap-ratios is obtained. Based on these data, the phenomena and rules of the vortex and its course of generation, development and evolvement at various gap-ratios are analyzed, and it is found that there are similar unshedding vortex structures at G = 0.0 and G = 7.0, and others are structures of shedding vortex. The figures of typical vortex movements are given. Based on this, the differences between the transient flow field and the time-averaged flow field and the characteristics of the vortex structures are analyzed. In addition when the Strouhal number keeps constant (about 0.2) concerning vortex shedding have been discussed. The findings of this paper are of guiding significance for engineering issues with similar flowing features.
Experiments on the vortex wake of a swimming knifefish
Taylor, Zachary J; Gurka, Roi; Holzman, Roi; Reesbeck, Thomas; Diez, F Javier
2012-01-01
The knifefish species propels itself by generating a reverse Karman street from an anal fin and without significantly moving its body. This unique feature makes this species' propulsion method highly efficient (Blake, 1983). It has been suggested that there is an optimal swimming range for fish based on the amplitude and frequency of the reverse K\\'arm\\'an street. Experiments have been performed to measure the ratio between the amplitude and wavelength of vortices in the wake of a knifefish. It is suggested that by optimizing the thrust created by the reverse Karman street the wave efficiency can be estimated for a given spacing ratio, and present observations have an average value of 0.89. The relationship established between spacing ratio and wave efficiency, in addition to the measured parameters, will be invaluable for bio-inspired designs based on the knifefish.
Two vortex-blob regularization models for vortex sheet motion
Sohn, Sung-Ik
2014-04-01
Evolving vortex sheets generally form singularities in finite time. The vortex blob model is an approach to regularize the vortex sheet motion and evolve past singularity formation. In this paper, we thoroughly compare two such regularizations: the Krasny-type model and the Beale-Majda model. It is found from a linear stability analysis that both models have exponentially decaying growth rates for high wavenumbers, but the Beale-Majda model has a faster decaying rate than the Krasny model. The Beale-Majda model thus gives a stronger regularization to the solution. We apply the blob models to the two example problems: a periodic vortex sheet and an elliptically loaded wing. The numerical results show that the solutions of the two models are similar in large and small scales, but are fairly different in intermediate scales. The sheet of the Beale-Majda model has more spiral turns than the Krasny-type model for the same value of the regularization parameter δ. We give numerical evidences that the solutions of the two models agree for an increasing amount of spiral turns and tend to converge to the same limit as δ is decreased. The inner spiral turns of the blob models behave differently with the outer turns and satisfy a self-similar form. We also examine irregular motions of the sheet at late times and find that the irregular motions shrink as δ is decreased. This fact suggests a convergence of the blob solution to the weak solution of infinite regular spiral turns.
Vortex tube reconnection at Re = 104
van Rees, Wim M.; Hussain, Fazle; Koumoutsakos, Petros
2012-07-01
We present simulations of the long-time dynamics of two anti-parallel vortex tubes with and without initial axial flow, at Reynolds number Re = Γ/ν = 104. Simulations were performed in a periodic domain with a remeshed vortex method using 785 × 106 particles. We quantify the vortex dynamics of the primary vortex reconnection that leads to the formation of elliptical rings with axial flow and report for the first time a subsequent collision of these rings. In the absence of initial axial flow, a -5/3 slope of the energy spectrum is observed during the first reconnection of the tubes. The resulting elliptical vortex rings experience a coiling of their vortex lines imparting an axial flow inside their cores. These rings eventually collide, exhibiting a -7/3 slope of the energy spectrum. Studies of vortex reconnection with an initial axial flow exhibit also the -7/3 slope during the initial collision as well as in the subsequent collision of the ensuing elliptical vortex rings. We quantify the detailed vortex dynamics of these collisions and examine the role of axial flow in the breakup of vortex structures.
Influence of mesoscale topography on vortex intensity
Institute of Scientific and Technical Information of China (English)
无
2008-01-01
The effect of mesoscale topography on multi-vortex self-organization is investigated numerically in this paper using a barotropic primitive equation model with topographic term. In the initial field there are one DeMaria major vortex with the maximum wind radius rm of 80 km at the center of the computational domain, and four meso-β vortices in the vicinity of rm to the east of the major vortex center.When there is no topography present, the initial vortices self-organize into a quasi-final state flow pattern, I.e. A quasi-axisymmetric vortex whose intensity is close to that of the initial major vortex. However, when a mesoscale topography is incorporated, the spatial scale of the quasi-final state vortex reduces, and the relative vorticity at the center of the vortex and the local maximum wind speed remarkably increase. The possible mechanism for the enhancement of the quasi-final state vortex might be that the negative relative vorticity lump,generated above the mesoscale topography because of the constraint of absolute vorticity conservation, squeezes the center of positive vorticity towards the mountain slope area, and thus reduces the spatial range of the major vortex. Meanwhile, because the total kinetic energy is basically conservative, the squeezing directly leads to the concentration of the energy in a smaller area, I.e. The strengthening of the vortex.
Single Cavity Trapped Vortex Combustor Dynamics – Part-1: Experiments
Directory of Open Access Journals (Sweden)
Atul Singhal
2011-03-01
Full Text Available In the present work, a water-cooled, modular, atmospheric pressure Trapped Vortex Combustor (TVC test rig is designed and fabricated for reacting and non-reacting flow experiments. The unique features of this rig consist of a continuously variable length-to-depth ratio (L/D of the cavity and optical access through quartz plates provided on three sides for visualization. Flame stabilization in the single cavity TVC was successfully achieved with methane as fuel and the range of flow conditions for stable operation were identified. From these, a few cases were selected for detailed experimentation. Reacting flow experiments for the selected cases indicated that reducing L/D ratio and increasing cavity-air velocity favour stable combustion. The pressure drop across the single cavity TVC is observed to be lower as compared to conventional combustors. Temperatures are measured at the exit using thermocouples and corrected for radiative losses. Species concentrations are measured at the exit using an exhaust gas analyzer. The combustion efficiency is observed to be around 97-99 % and the pattern factor is observed to be in the range of 0.08 to 0.13. High-speed imaging made possible by the optical access indicates that the overall combustion is fairly steady, and there is no vortex shedding downstream.
Start-up vortex flow past an accelerated flat plate
Xu, Ling
2014-01-01
Viscous flow past a finite flat plate moving in direction normal to itself is studied numerically.The plate moves with velocity $at^p$, where $p=0,0.5,1,2$. We present the evolution of vorticity profiles, streaklines and streamlines, and study the dependence on the acceleration parameter $p$. Four stages in the vortex evolution, as proposed by Luchini & Tognaccini (2002), are clearly identified. The initial stage, in which the vorticity consists solely of a Rayleigh boundary layer, is shown to last for a time-interval whose length shrinks to zero like $p^3$, as $p \\to 0$. In the second stage, a center of rotation develops near the tip of the plate, well before a vorticity maximum within the vortex core develops. Once the vorticity maximum develops, its position oscillates and differs from the center of rotation. The difference between the two increases with increasing $p$, and decreases in time. In the third stage, the center of rotation and the shed circulation closely satisfy self-similar scaling laws f...
Roughness Effects on the Formation of a Leading Edge Vortex
Elliott, Cassidy; Lang, Amy; Wahidi, Redha; Wilroy, Jacob
2016-11-01
Microscopic scales cover the wings of Monarch butterflies, creating a patterned surface. This patterning is an important natural flow control mechanism that is thought to delay the growth of the leading edge vortex (LEV) produced by the flapping motion of a wing. The increased skin friction caused by the scales leads to a weaker LEV being shed into the butterfly's wake, lessening drag and increasing flight efficiency. To test this theory, a plate of random roughness was designed in SolidWorks and printed on the Objet 30 Pro 3D printer. A 2x3x5 cubic foot tow tank was used to test the rough plate at Reynold's numbers of 1500, 3000, and 6000 (velocities of 8, 16, and 32 mm/s) at an angle of attack of 45 degrees. Particle Image Velocimetry (PIV) captured images of the LEV generated by the plate when towed upwards through the particle-seeded flow. Codes written in MatLab were used to automatically track and determine the strength of the LEV. Circulation values for the randomly-rough plate were then compared to the same values generated in a previous experiment that used a smooth plate and a grooved plate to determine the effect of the patterning on vortex development. Funding provided by NSF REU site Grant EEC 1358991 and CBET 1628600.
Vortex-induced vibrations of a flexible cylinder at large inclination angle.
Bourguet, Rémi; Triantafyllou, Michael S
2015-01-28
The free vibrations of a flexible circular cylinder inclined at 80° within a uniform current are investigated by means of direct numerical simulation, at Reynolds number 500 based on the body diameter and inflow velocity. In spite of the large inclination angle, the cylinder exhibits regular in-line and cross-flow vibrations excited by the flow through the lock-in mechanism, i.e. synchronization of body motion and vortex formation. A profound reconfiguration of the wake is observed compared with the stationary body case. The vortex-induced vibrations are found to occur under parallel, but also oblique vortex shedding where the spanwise wavenumbers of the wake and structural response coincide. The shedding angle and frequency increase with the spanwise wavenumber. The cylinder vibrations and fluid forces present a persistent spanwise asymmetry which relates to the asymmetry of the local current relative to the body axis, owing to its in-line bending. In particular, the asymmetrical trend of flow-body energy transfer results in a monotonic orientation of the structural waves. Clockwise and counter-clockwise figure eight orbits of the body alternate along the span, but the latter are found to be more favourable to structure excitation. Additional simulations at normal incidence highlight a dramatic deviation from the independence principle, which states that the system behaviour is essentially driven by the normal component of the inflow velocity.
Control of a Backward-Facing Step flow through vortex pairing and phase locking
Duriez, Thomas; Wesfreid, Jose Eduardo; Artana, Guillermo
2014-01-01
Many experimental and numerical studies report a large reduction of the recirculation bubble in Backward-Facing Step flows or airfoils in stall situation when excited at the natural shedding frequency $f_0$. Through a simple experiment using Dielectric Barrier Discharge actuator, we find a different result. For a given Reynolds number, the frequency of the perturbation is varied for a fixed duty-cycle dc = 27%. Through phase-averaging of Particle Image Velocimetry measurements, we show that the actuation creates a forced vortex which interacts with the natural shedding with a different phase velocity than the unforced one. The largest reduction of the recirculation bubble (-35%) is obtained in a very narrow frequency range around $0.73 f_0$ where early vortex pairing occurs between forced and unforced vortices. Phase averaging shows that in this case, the actuation clearly forces the vortex pairing in the shear layer. On the contrary, when the forcing frequency is higher, the shear layer behaves like an ampli...
Vortex scattering by step topography
Hinds, A. K.; Johnson, E. R.; McDonald, N. R.
The scattering at a rectilinear step change in depth of a shallow-water vortex pair consisting of two patches of equal but opposite-signed vorticity is studied. Using the constants of motion, an explicit relationship is derived relating the angle of incidence to the refracted angle after crossing. A pair colliding with a step from deep water crosses the escarpment and subsequently propagates in shallow water refracted towards the normal to the escarpment. A pair colliding with a step from shallow water either crosses and propagates in deep water refracted away from the normal or, does not cross the step and is instead totally internally reflected by the escarpment. For large depth changes, numerical computations show that the coherence of the vortex pair is lost on encountering the escarpment.
Perturbations of vortex ring pairs
Gubser, Steven S; Parikh, Sarthak
2015-01-01
We study pairs of co-axial vortex rings starting from the action for a classical bosonic string in a three-form background. We complete earlier work on the phase diagram of classical orbits by explicitly considering the case where the circulations of the two vortex rings are equal and opposite. We then go on to study perturbations, focusing on cases where the relevant four-dimensional transfer matrix splits into two-dimensional blocks. When the circulations of the rings have the same sign, instabilities are mostly limited to wavelengths smaller than a dynamically generated length scale at which single-ring instabilities occur. When the circulations have the opposite sign, larger wavelength instabilities can occur.
Collisions of Vortex Filament Pairs
Banica, Valeria; Faou, Erwan; Miot, Evelyne
2014-12-01
We consider the problem of collisions of vortex filaments for a model introduced by Klein et al. (J Fluid Mech 288:201-248, 1995) and Zakharov (Sov Phys Usp 31(7):672-674, 1988, Lect. Notes Phys 536:369-385, 1999) to describe the interaction of almost parallel vortex filaments in three-dimensional fluids. Since the results of Crow (AIAA J 8:2172-2179, 1970) examples of collisions are searched as perturbations of antiparallel translating pairs of filaments, with initial perturbations related to the unstable mode of the linearized problem; most results are numerical calculations. In this article, we first consider a related model for the evolution of pairs of filaments, and we display another type of initial perturbation leading to collision in finite time. Moreover, we give numerical evidence that it also leads to collision through the initial model. We finally study the self-similar solutions of the model.
Divergence of optical vortex beams
Reddy, Salla Gangi; Prabhakar, Shashi; Anwar, Ali; Banerji, J; Singh, R P
2015-01-01
We show, both theoretically and experimentally, that the propagation of optical vortices in free space can be analysed by using the width ($w(z)$) of the host Gaussian beam and the inner and outer radii of the vortex beam at the source plane ($z=0$) as defined in \\textit{Optics Letters \\textbf{39,} 4364-4367 (2014)}. We also studied the divergence of vortex beams, considered as the rate of change of inner or outer radius with the propagation distance, and found that it varies with the order in the same way as that of the inner and outer radii at zero propagation distance. These results may be useful in designing optical fibers for orbital angular momentum modes that play a crucial role in quantum communication.
Energy Technology Data Exchange (ETDEWEB)
Shukla, P.K
2002-12-30
Coherent nonlinear structures in the form of dust vortex flows have been observed in unmagnetized laboratory dusty plasmas. Our objective here is show that the dynamics of such dust vortices is governed by a modified Navier-Stokes equation (MNSE) and that the stationary solutions of the MNSE can be represented as monopolar as well as a row of identical Stuart and a row of counter-rotating vortices.
Experimental characteristics of vortex heaters
Piralishvili, Sh. A.; Novikov, N. N.
The performance of a Ranque-Hilsch vortex tube is investigated experimentally for the case where the tube operates as a heater, with the mass of the heated gas remaining constant. The results obtained indicate that energy separation zones with sufficiently high (50 percent) relative heating effects can be achieved for a gas flow ratio of unity. A nomogram is presented for calculating the relative and absolute heating effects as a function of the tube geometry.
Prediction and Control of Vortex Dominated and Vortex-wake Flows
Kandil, Osama
1996-01-01
This report describes the activities and accomplishments under this research grant, including a list of publications and dissertations, produced in the field of prediction and control of vortex dominated and vortex wake flows.
Birth and evolution of an optical vortex
Vallone, Giuseppe; D'Ambrosio, Vincenzo; Marrucci, Lorenzo; Sciarrino, Fabio; Villoresi, Paolo
2016-01-01
When a phase singularity is suddenly imprinted on the axis of an ordinary Gaussian beam, an optical vortex appears and starts to grow radially, by effect of diffraction. This radial growth and the subsequent evolution of the optical vortex under focusing or imaging can be well described in general within the recently introduced theory of circular beams, which generalize the hypergeometric-Gaussian beams and which obey novel kinds of ABCD rules. Here, we investigate experimentally these vortex propagation phenomena and test the validity of circular-beam theory. Moreover, we analyze the difference in radial structure between the newly generated optical vortex and the vortex obtained in the image plane, where perfect imaging would lead to complete closure of the vortex core.
Topology of Vortex-Wing Interaction
McKenna, Chris; Rockwell, Donald
2016-11-01
Aircraft flying together in an echelon or V formation experience aerodynamic advantages. Impingement of the tip vortex from the leader (upstream) wing on the follower wing can yield an increase of lift to drag ratio. This enhancement is known to depend on the location of vortex impingement on the follower wing. Particle image velocimetry is employed to determine streamline topology in successive crossflow planes, which characterize the streamwise evolution of the vortex structure along the chord of the follower wing and into its wake. Different modes of vortex-follower wing interaction are created by varying both the spanwise and vertical locations of the leader wing. These modes are defined by differences in the number and locations of critical points of the flow topology, and involve bifurcation, attenuation, and mutual induction. The bifurcation and attenuation modes decrease the strength of the tip vortex from the follower wing. In contrast, the mutual induction mode increases the strength of the follower tip vortex. AFOSR.
Vortex rings impinging on permeable boundaries
Mujal-Colilles, Anna; Dalziel, Stuart B.; Bateman, Allen
2015-01-01
Experiments with vortex rings impinging permeable and solid boundaries are presented in order to investigate the influence of permeability. Utilizing Particle Image Velocimetry, we compared the behaviour of a vortex ring impinging four different reticulated foams (with permeability k ˜ 26 - 85 × 10-8 m2) and a solid boundary. Results show how permeability affects the stretching phenomena of the vortex ring and the formation and evolution of the secondary vortex ring with opposite sign. Moreover, permeability also affects the macroscopic no-slip boundary condition found on the solid boundary, turning it into an apparent slip boundary condition for the most permeable boundary. The apparent slip-boundary condition and the flux exchange between the ambient fluid and the foam are jointly responsible for both the modified formation of the secondary vortex and changes on the vortex ring diameter increase.
Vortex dynamics in nonrelativistic Abelian Higgs model
Directory of Open Access Journals (Sweden)
A.A. Kozhevnikov
2015-11-01
Full Text Available The dynamics of the gauge vortex with arbitrary form of a contour is considered in the framework of the nonrelativistic Abelian Higgs model, including the possibility of the gauge field interaction with the fermion asymmetric background. The equations for the time derivatives of the curvature and the torsion of the vortex contour generalizing the Betchov–Da Rios equations in hydrodynamics, are obtained. They are applied to study the conservation of helicity of the gauge field forming the vortex, twist, and writhe numbers of the vortex contour. It is shown that the conservation of helicity is broken when both terms in the equation of the vortex motion are present, the first due to the exchange of excitations of the phase and modulus of the scalar field and the second one due to the coupling of the gauge field forming the vortex, with the fermion asymmetric background.
An axisymmetric steady state vortex ring model
Wang, Ruo-Qian
2016-01-01
Based on the solution of Atanasiu et al. (2004), a theoretical model for axisymmetric vortex flows is derived in the present study by solving the vorticity transport equation for an inviscid, incompressible fluid in cylindrical coordinates. The model can describe a variety of axisymmetric flows with particular boundary conditions at a moderately high Reynolds number. This paper shows one example: a high Reynolds number laminar vortex ring. The model can represent a family of vortex rings by specifying the modulus function using a Rayleigh distribution function. The characteristics of this vortex ring family are illustrated by numerical methods. For verification, the model results compare well with the recent direct numerical simulations (DNS) in terms of the vorticity distribution and streamline patterns, cross-sectional areas of the vortex core and bubble, and radial vorticity distribution through the vortex center. Most importantly, the asymmetry and elliptical outline of the vorticity profile are well capt...
Control of rod shedding in the frog retina.
Basinger, S F; Hollyfield, J G
1980-01-01
In all vertebrate species examined thus far, rod outer segment shedding follows a cyclic pattern in which the outer segment tips are shed shortly after the onset of light. Work in the rat retina suggests that rod shedding may follow a circadian rhythm which is controlled by one or more circadian oscillators. Our results in the frog retina are significantly different in that: rod shedding can be driven by the onset of light or other environmental cues; shedding does not persist in constant darkness; shedding is unaffected in frogs with chronic unilateral or bilateral optic nerve section; and shedding will rapidly phase shift to the time of light onset on a wide variety of diurnal cycles. Thus, rod shedding in the frog retina does not appear to be a classical circadian rhythm.
Magnetism near Vortex Cores of Cuprate Superconductors
Lee, J. C.; Prudchenko, K.; Launspach, B.; Ruiz, E. J.; Boekema, C.
2005-03-01
We examined muon-spin-resonance (μSR) vortex data of Bi2212, Tl2223, and YBCO to search for antiferromagnetism (AF) near the vortex cores. [1] Field distributions were obtained from μSR data using Maximum-Entropy analysis. The grainboundary and vortex signals were fitted by Gaussian and Lorentzian curves, the latter suggestive of extra AF ordering. Narrow Gaussians fit the grainboundary signals well, independent of temperature. For T B17 (2003) 3436.
Astronomical demonstration of an optical vortex coronagraph.
Swartzlander, Grover A; Ford, Erin L; Abdul-Malik, Rukiah S; Close, Laird M; Peters, Mary A; Palacios, David M; Wilson, Daniel W
2008-07-07
Using an optical vortex coronagraph and simple adaptive optics techniques, we have made the first convincing demonstration of an optical vortex coronagraph that is coupled to a star gazing telescope. We suppressed by 97% the primary star of a resolvable binary system, Cor Caroli. The stars had an angular separation of 1.9lambda/D at our imaging camera. The secondary star suffered no suppression from the vortex lens.
DEFF Research Database (Denmark)
Spietz, Henrik Juul; Hejlesen, Mads Mølholm; Walther, Jens Honore
in the oncoming flow. This may lead to structural instability e.g. when the shedding frequency aligns with the natural frequency of the structure. Fluid structure interaction must especially be considered when designing long span bridges. A three dimensional vortex-in-cell method is applied for the direct....... This we combine with an iterative penalization method, that allows the simulation of external flows past arbitrary geometries in arbitrary motions such as bridge decks in forced heave and pitch motion...
The quasi-vortex-lattice method for wings with edge vortex separation
Pao, J. L.; Lan, E.
1980-01-01
The aerodynamic characteristics of wings with leading-edge vortex separation were predicted using a method based on a flow model with free vortex elements which are allowed to merge into a concentrated core. The calculated pressure distribution is more accurate than that predicted by methods with discrete vortex filaments alone. In addition, the computer time is reduced approximately by half.
Recent Advances in Study of Oceanic Vortex
Institute of Scientific and Technical Information of China (English)
FU Gang; LI Li; LIU Qinyu
2002-01-01
In this paper, the recent advances in the study of oceanic vortex are outlined. Firstly, the previous studies on oceanic vortex are reviewed. Secondly, some prominent features of oceanic vortex in the Gulf Stream, the Kuroshio, the South China Sea and the Japan Sea regions are depicted based upon the observations and numerical modeling results. Generally, the lifetime of these oceanic vortices ranges from several weeks to several months, and their horizontal scales vary from tens of kilometers to hundreds of kilometers. Their vertical scales are on the order of thousands of meters. Finally, some theoretical studies, mainly on the splitting of a cyclonic vortex and the merging of anticyclonic vortices, are introduced.
Modeling and simulation of vortex induced vibration on the subsea riser/pipeline (GRP pipe)
Raja Adli, Raja Nor Fauziah bt; Ibrahim, Idris
2012-06-01
This paper presents the research work conducted to investigate the dynamics characteristics of the offshore riser pipeline due to vortex flow and to develop a model that could predict its vortex induced responses. Glass-fiber reinforced plastic (GRP) pipe is used for this study which has smaller density from the steel. A two-dimensional finite element computational method is implemented to describe the dynamic behavior of the riser. The governing equation of motion was based on Hamilton's principle, consists of the strain energy due to bending and axial deformation, kinetic energy due to both riser and internal fluid movement and also external force from currents and waves. A direct integration method namely Newmark integration scheme is proposed to solve the equation of motion. A MATLAB program code was developed to obtain the simulation results. The natural frequency and damping ratio are presented for each mode. Dynamic response of riser is shown in time-domain and the numerical results are discussed. Several parameter effects are used to investigate dynamic responses and the results show an agreement with the theory. Vortex shedding phenomenon also has been discussed in this paper. As a conclusion, the simulation results have successfully shown the vortex induced vibration responses for GRP pipeline.
Raghu Gowda, Belagumba Venkatachalaiah
This dissertation examines how simple structural compliance impacts a specific transient vortex phenomenon that occurs on high angle of attack lifting surfaces termed dynamic stall. In many Fluid structure interaction (FSI) research efforts, a purely physical or purely computational approach is taken. In this work a low cost cyber-physical (CPFD) system is designed and developed for representing the FSI in the leading edge vortex (LEV) development problem. The leading edge compliance appears to be favorable in a specific spring constant range for a given wing. When the leading edge compliance prescribed via CPFD system is too low compared with the moment due to dynamic pressure or fluid unsteady effect, the LEV behavior is similar to that of a rigid wing system. When the leading edge compliance is too high, excessive compliance is introduced into the wing system and the leading edge vortex evolution is affected by the large change in wing angle. At moderate leading edge compliance, a balance appears to be achieved in which the leading edge vorticity shedding rate supports the long term evolution of the leading edge vortex. Further investigation is required to determine specific parameters governing these leading edge compliance ranges.
Experimental study of the turbulent field behind a perforated vortex generator
Habchi, C.; Lemenand, T.; Della Valle, D.; Al Shaer, A.; Peerhossaini, H.
2015-07-01
The influence of the wake vortex arising behind a perforated tab on the mixing process in heat exchangers and chemical reactors is analyzed. The preliminary step of this study, i.e., investigation of the turbulent field generated by a single perforated tab, is presented here. For this aim, laser Doppler velocimetry measurements are conducted downstream from a perforated trapezoidal vortex generator placed in a wind tunnel. It is shown that two shear layers are generated by the tab. The first shear layer is located at the upper edge of the tab, and the other is ejected from the perforation edges. These shear layers are characterized by high turbulent kinetic energy levels, which are profitable for meso-mixing enhancement. Finally, a spectral study shows that the turbulent macro-scale is nearly the same for typical locations in the shear layers shed from the tab and perforation edges.
Energy Technology Data Exchange (ETDEWEB)
Barpanda, Prabeer, E-mail: prabeer.barpanda@u-picardie.f [Laboratoire de Reactivite et Chimie des Solides, Universite de Picardie Jules Verne, 33 rue Saint Leu, Amiens Cedex 80039 (France); Department of Chemistry, Dalhousie University, Halifax, Nova Scotia, B3H 3J5 (Canada)
2011-03-15
A three-dimensional, Fast-Fourier-Transformed (3D-FFT) micromagnetic simulation was employed to study the magnetization reversal mechanisms in cylindrical nickel nanobars possessing magnetic vortices. Individual Ni nanobars of height 150-250 nm with aspect ratio varying from 2.1 to 2.5 were considered, all of them supporting magnetic vortices domains. Magnetization reversal in these nanobars involves the vortex-creation-annihilation (VCA) mechanism with an inversion symmetry feature observed mid-way during reversal process. The effect of incidence angle of externally applied field on overall magnetization reversal process is examined in detail. The corresponding variations in coercivity, squareness, exchange energy and vortex parameters are described by the micromagnetic study that can shed insights for building practical Ni nanobars magnetic nanostructures/devices.
The Effect of Internal Fluid on the Response of Vortex-Induced Vibration of Marine Risers
Institute of Scientific and Technical Information of China (English)
郭海燕; 王元斌; 傅强
2004-01-01
Based on Iwan′s wake oscillator model developed with the classical van der Pol equation, the differential equation for the response of the vortex-induced vibration (VIV) of the riser considering the effect of the internal flowing fluid and the external marine environmental condition is derived. The effect of the internal flowing fluid on the response of VIV of the riser is studied by means of the Finite Element Method. The results show that the effect of the internal fluid velocity on the VIV of the riser is strong when the natural frequency of the riser is close to the vortex shedding frequency. In addition, the increase of the top tension can decrease the sensitivity of the riser to the internal fluid velocity.
Investigation of vortical flows over oscillating body using fast Lagrangian vortex method
Institute of Scientific and Technical Information of China (English)
Baoshan ZHU
2009-01-01
A computational method facilitating long-time and high-resolution unsteady vortical flows is developed with the advantages of the discrete vortex methods. Both the velocity and pressure distribution of the flow field are calculated by integral formulations in combination with a fast summation algorithm. The vorticity field is described by Lagrangian representation, which is well suited to the moving boundary. Viscosity diffusion of the vorticity is considered with the core spreading model corrected by an adaptive splitting and merging algorithm. The effective-ness of the present method is examined by comparing the numerical results of unsteady separated flows which pass a cylinder and a thin cambered blade undergoing rotational oscillations with available experimental results. Interesting results about vortex shedding patterns and lock-in characteristics are provided for the thin cambered blade.
Strouhal number effect on synchronized vibration range of a circular cylinder in cross flow
Energy Technology Data Exchange (ETDEWEB)
Kawamura, Tsutomu; Nakao, Toshitsugu; Hayashi, Masaaki; Murayama, Kouichi [Hitachi Ltd., Tokyo (Japan)
2001-11-01
Synchronized vibrations were measured for a circular cylinder in a water cross flow at subcritical Reynolds numbers to compare the synchronization range between the subcritical and supercritical regions and clarify the effect of the Strouhal number on the range. A small vibration in the lift direction was found in only the subcritical region when the Karman vortex shedding frequency was about 1/5 of the cylinder natural frequency. The ratio of the Karman vortex shedding frequency to the natural frequency where the self-excited vibration in the drag direction by the symmetrical vortex shedding began was about 1/4 in the subcritical region, and increased to 0.32 at the Strouhal number of 0.29 in the supercritical region. The frequency ratio at the beginning of the lock-in vibration in the drag direction by the Karman vortex shedding was about 1/2, and that in the lift direction decreased from 1 to 0.8 with decreasing Strouhal number. (author)
Rotating hot-wire investigation of the vortex responsible for blade-vortex interaction noise
Fontana, Richard Remo
1988-01-01
This distribution of the circumferential velocity of the vortex responsible for blade-vortex interaction noise was measured using a rotating hot-wire rake synchronously meshed with a model helicopter rotor at the blade passage frequency. Simultaneous far-field acoustic data and blade differential pressure measurements were obtained. Results show that the shape of the measured far-field acoustic blade-vortex interaction signature depends on the blade-vortex interaction geometry. The experimental results are compared with the Widnall-Wolf model for blade-vortex interaction noise.
Vortex diffusion and vortex-line hysteresis in radial quantum turbulence
Energy Technology Data Exchange (ETDEWEB)
Saluto, L., E-mail: lidia.saluto@unipa.it [DEIM, Università degli Studi di Palermo, Viale delle Scienze, 90128 Palermo (Italy); Jou, D., E-mail: david.jou@uab.es [Departament de Física, Universitat Autònoma de Barcelona, 08193 Bellaterra, Catalonia (Spain); Mongiovi, M.S., E-mail: m.stella.mongiovi@unipa.it [DEIM, Università degli Studi di Palermo, Viale delle Scienze, 90128 Palermo (Italy)
2014-05-01
We study the influence of vortex diffusion on the evolution of inhomogeneous quantized vortex tangles. A simple hydrodynamical model to describe inhomogeneous counterflow superfluid turbulence is used. As an illustration, we obtain solutions for these effects in radial counterflow of helium II between two concentric cylinders at different temperatures. The vortex diffusion from the inner hotter cylinder to the outer colder cylinder increases the vortex length density everywhere as compared with the non-diffusive situation. The possibility of hysteresis in the vortex line density under cyclical variations of the heat flow is explored.
Pinch-off of axisymmetric vortex pairs in the limit of vanishing vortex line curvature
Sadri, V.; Krueger, P. S.
2016-07-01
Pinch-off of axisymmetric vortex pairs generated by flow between concentric cylinders with radial separation ΔR was studied numerically and compared with planar vortex dipole behavior. The axisymmetric case approaches planar vortex dipole behavior in the limit of vanishing ΔR. The flow was simulated at a jet Reynolds number of 1000 (based on ΔR and the jet velocity), jet pulse length-to-gap ratio ( /L Δ R ) in the range 10-20, and gap-to-outer radius ratio ( /Δ R R o ) in the range 0.01-0.1. Contrary to investigations of strictly planar flows, vortex pinch-off was observed for all gap sizes investigated. This difference was attributed to the less constrained geometry considered, suggesting that even very small amounts of vortex line curvature and/or vortex stretching may disrupt the absence of pinch-off observed in strictly planar vortex dipoles.
Simulations of Active Vortex Generators
Mansour, N. N.; Koumoutsakos, P.; Merriam, Marshal (Technical Monitor)
1996-01-01
We are interested in the study, via numerical simulations, of active vortex generators. Vortex generators may be used to modify the inner part of the boundary layer or to control separation thus enhancing the performance and maneuverability of aerodynamic configurations. We consider generators that consist of a surface cavity elongated in the streamwise direction and partially covered with a moving lid that at rest lies flush with the boundary. Streamwise voracity is generated and ejected due to the oscillatory motion of the lid. The present simulations c Implement relevant experimental investigations of active vortex generators that have been conducted at NASA Ames Research Center and Stanford University. Jacobson and Reynolds used a piezoelectric device in water, allowing for small amplitude high frequency oscillations. They placed the lid asymmetrically on the cavity and observed a strong outward velocity at the small gap of the cavity. Saddoughi used a larger mechanically driven device in air to investigate this flow and observed a jet emerging from the wide gap of the configuration, contrary to the findings of Jacobson and Reynolds. More recently, Lachowiez and Wlezien are investigating the flow generated by an electro-mechanically driven lid to be used for assertion control in aerodynamic applications. We are simulating the flows generated by these devices and we are conducting a parametric study that would help us elucidate the physical mechanisms present in the flow. Conventional computational schemes encounter difficulties when simulating flows around complex configurations undergoing arbitrary motions. Here we present a formulation that achieves this task on a purely Lagrangian frame by extending the formulation presented by Koumoutsakos, Leonard and Pepin. The viscous effects are taken into account by modifying the strength of the particles, whereas fast multipole schemes employing hundreds of thousands ol'particle's allow for high resolution simulations
Vortex metrology using Fourier analysis techniques: vortex networks correlation fringes.
Angel-Toro, Luciano; Sierra-Sosa, Daniel; Tebaldi, Myrian; Bolognini, Néstor
2012-10-20
In this work, we introduce an alternative method of analysis in vortex metrology based on the application of the Fourier optics techniques. The first part of the procedure is conducted as is usual in vortex metrology for uniform in-plane displacement determination. On the basis of two recorded intensity speckled distributions, corresponding to two states of a diffuser coherently illuminated, we numerically generate an analytical signal from each recorded intensity pattern by using a version of the Riesz integral transform. Then, from each analytical signal, a two-dimensional pseudophase map is generated in which the vortices are located and characterized in terms of their topological charges and their core's structural properties. The second part of the procedure allows obtaining Young's interference fringes when Fourier transforming the light passing through a diffracting mask with multiple apertures at the locations of the homologous vortices. In fact, we use the Fourier transform as a mathematical operation to compute the far-field diffraction intensity pattern corresponding to the multiaperture set. Each aperture from the set is associated with a rectangular hole that coincides both in shape and size with a pixel from recorded images. We show that the fringe analysis can be conducted as in speckle photography in an extended range of displacement measurements. Effects related with speckled decorrelation are also considered. Our experimental results agree with those of speckle photography in the range in which both techniques are applicable.
Delaying vortex breakdown by waves
Yao, M. F.; Jiang, L. B.; Wu, J. Z.; Ma, H. Y.; Pan, J. Y.
1989-03-01
The effect of spiral waves on delaying vortex breakdown in a tube is studied experimentally and theoretically. When a harmonic oscillation was imposed on one of guiding vanes in the tube, the breakdown was observed to be postponed appreciately. According to the generalized Lagrangian mean theory, proper forcing spiral waves may produce an additional streaming momentum, of which the effect is favorable and similar to an axial suction at downstream end. The delayed breakdown position is further predicted by using nonlinear wave theory. Qualitative agreement between theory and experiment is obtained, and experimental comparison of the effects due to forcing spiral wave and axial suction is made.
Andersen, A; Bohr, T; Stenum, B; Rasmussen, J Juul; Lautrup, B
2003-09-05
We present experiments and theory for the "bathtub vortex," which forms when a fluid drains out of a rotating cylindrical container through a small drain hole. The fast down-flow is found to be confined to a narrow and rapidly rotating "drainpipe" from the free surface down to the drain hole. Surrounding this drainpipe is a region with slow upward flow generated by the Ekman layer at the bottom of the container. This flow structure leads us to a theoretical model similar to one obtained earlier by Lundgren [J. Fluid Mech. 155, 381 (1985)
Formation of Ion Phase-Space Vortexes
DEFF Research Database (Denmark)
Pécseli, Hans; Trulsen, J.; Armstrong, R. J.
1984-01-01
The formation of ion phase space vortexes in the ion two stream region behind electrostatic ion acoustic shocks are observed in a laboratory experiment. A detailed analysis demonstrates that the evolution of such vortexes is associated with ion-ion beam instabilities and a nonlinear equation for ...
Tight Focusing of Partially Coherent Vortex Beams
Directory of Open Access Journals (Sweden)
Rakesh Kumar Singh
2012-01-01
Full Text Available Tight focusing of partially polarized vortex beams has been studied. Compact form of the coherence matrix has been derived for polarized vortex beams. Effects of topological charge and polarization distribution of the incident beam on intensity distribution, degree of polarization, and coherence have been investigated.
The linear stability of swirling vortex rings
Gargan-Shingles, C.; Rudman, M.; Ryan, K.
2016-11-01
The stability of vortex rings with an azimuthal component of velocity is investigated numerically for various combinations of ring wavenumber and swirl magnitude. The vortex rings are equilibrated from an initially Gaussian distribution of azimuthal vorticity and azimuthal velocity, at a circulation-based Reynolds number of 10 000, to a state in which the vortex core is qualitatively identical to that of the piston generated vortex rings. The instability modes of these rings can be characterised as Kelvin instability modes, analogous to instability modes observed for Gaussian and Batchelor vortex pairs. The shape of an amplified mode typically depends only on the azimuthal wavenumber at the centre of the vortex core and the magnitude of the corresponding velocity component. The wavenumber of a particular sinuous instability varies with radius from the vortex ring centre for rings of finite aspect ratio. Thicker rings spread the amplification over a wider range of wavenumbers for a particular resonant mode pair, while the growth rate and the azimuthal wavenumber corresponding to the peak growth both vary as a function of the wavenumber variation. Normalisation of the wavenumber and the growth rate by a measure of the wavenumber variation allows a coherent description of stability modes to be proposed, across the parameter space. These results provide a framework for predicting the development of resonant Kelvin instabilities on vortex rings with an induced component of swirling velocity.
Ring vortex solitons in nonlocal nonlinear media
DEFF Research Database (Denmark)
Briedis, D.; Petersen, D.E.; Edmundson, D.;
2005-01-01
or higher charge fundamental vortices as well as higher order (multiple ring) vortex solitons. Our results pave the way for experimental observation of stable vortex rings in other nonlocal nonlinear systems including Bose-Einstein condensates with pronounced long-range interparticle interaction....
An investigation of the vortex method
Energy Technology Data Exchange (ETDEWEB)
Pryor, Jr., Duaine Wright [Univ. of California, Berkeley, CA (United States)
1994-05-01
The vortex method is a numerical scheme for solving the vorticity transport equation. Chorin introduced modern vortex methods. The vortex method is a Lagrangian, grid free method which has less intrinsic diffusion than many grid schemes. It is adaptive in the sense that elements are needed only where the vorticity is non-zero. Our description of vortex methods begins with the point vortex method of Rosenhead for two dimensional inviscid flow, and builds upon it to eventually cover the case of three dimensional slightly viscous flow with boundaries. This section gives an introduction to the fundamentals of the vortex method. This is done in order to give a basic impression of the previous work and its line of development, as well as develop some notation and concepts which will be used later. The purpose here is not to give a full review of vortex methods or the contributions made by all the researchers in the field. Please refer to the excellent review papers in Sethian and Gustafson, chapters 1 Sethian, 2 Hald, 3 Sethian, 8 Chorin provide a solid introduction to vortex methods, including convergence theory, application in two dimensions and connection to statistical mechanics and polymers. Much of the information in this review is taken from those chapters, Chorin and Marsden and Batchelor, the chapters are also useful for their extensive bibliographies.
Vortex attraction and the formation of sunspots
Parker, E. N.
1992-01-01
A downdraft vortex ring in a stratified atmosphere exhibits universal attraction for nearby vertical magnetic flux bundles. It is speculated that the magnetic fields emerging through the surface of the sun are individually encircled by one or more subsurface vortex rings, providing an important part of the observed clustering of magnetic fibrils to form pores and sunspots.
Investigation of Wake-Vortex Aircraft Encounters
Smith, Sonya T.
1999-01-01
The National Aeronautics and Space Administration is addressing airport capacity enhancements during instrument meteorological conditions though the Terminal Area Productivity (TAP) program. The major goal of the TAP program is to develop the technology that will allow air traffic levels during instrument meteorological condition to approach those achieved during visual operations. The Reduced Spacing Operations (RSO) subelement of TAP at the NASA Langley Research Center (LaRC) will develop the Aircraft Vortex Spacing System (AVOSS). The purpose of the AVOSS is to integrate current and predicted weather conditions, wake vortex transport and decay knowledge, wake vortex sensor data, and operational definitions of acceptable strengths for vortex encounters to produce dynamic wake vortex separation criteria. The proposed research is in support of the wake vortex hazard definition component of the LaRC AVOSS development research. The research program described in the next section provided an analysis of the static test data and uses this data to evaluate the accuracy vortex/wake-encounter models. The accuracy of these models has not before been evaluated using experimental data. The research results also presented the first analysis of the forces and moments imparted on an airplane during a wake vortex encounter using actual flight test data.
On a few Aspects of Vortex Motion
Directory of Open Access Journals (Sweden)
Prantik Sinha
2013-08-01
Full Text Available Intricacies of vortex motion have been drawing the attention of scientists for many years. A number of works both experimental and numerical have been conducted to understand the various features of vortex motion and its effects on drag, etc. In the present experimental work we have made an attempt to visualize the patterns of both Forced and Free vortex motion. Here colored die has been used to understand the profiles and an arrow shaped strip marks the difference between irrotational and rotational flow. In the Forced vortex motion it has been observed that the parabolic profile remains invariant with the flow rate (speed of paddle, height of the lowest point of the profile decreases with the increase in flow rate (paddle speed. In the Free Vortex motion observations, the hyperbolic profile doesn’t change with the change in flow rate. In this case, suction is created towards the centre where as in the case of Force vortex no such suction arises. With the reduction in the size of the orifice diameter, the profile becomes less steep for Free vortex. In this case the velocity profile in the core region is straight, as the radius increases the profile becomes rectangular hyperbola where as in the case of Forced vortex the velocity profile maintains its linear nature for the entire range of radii.
The bathtub vortex in a rotating container
DEFF Research Database (Denmark)
Andersen, Anders Peter; Bohr, Tomas; Stenum, B.
2006-01-01
We study the time-independent free-surface flow which forms when a fluid drains out of a container, a so-called bathtub vortex. We focus on the bathtub vortex in a rotating container and describe the free-surface shape and the complex flow structure using photographs of the free surface, flow...
Numerical simulation of icing, deicing, and shedding
Wright, W. B.; Dewitt, K. J.; Keith, T. G., Jr.
1991-01-01
An algorithm has been developed to numerically model the concurrent phenomena of two-dimensional transient heat transfer, ice accretion, ice shedding and ice trajectory which arise from the use of electrothermal pad. The Alternating Direction Implicit method is used to simultaneously solve the heat transfer and accretion equations occurring in the multilayered body covered with ice. In order to model the phase change between ice and water, a technique was used which assumes a phase for each node. This allows the equations to be linearized such that a direct solution is possible. This technique requires an iterative procedure to find the correct phase at each node. The computer program developed to find this solution has been integrated with the NASA-Lewis flow/trajectory code LEWICE.
EXPERIMENTAL AND NUMERICAL INVESTIGATION OF FREE SURFACE VORTEX
Institute of Scientific and Technical Information of China (English)
LI Hai-feng; CHEN Hong-xun; MA Zheng; ZHOU Yi
2008-01-01
An experimental model was set up to investigate the formation and evolution of the free surface vortex. A Particle Image Velocimetry (PIV) was used to measure the free surface vortex flow field at different development stages. Flow visualization was used to locate the vortex position and find its structure. Empirical formulas about the critical submergence and the whole field structure were obtained. It is found that the tangential velocity distribution is similar to that of the Rankine vortex and the radial velocity changes little in the vortex functional scope. Vortex starts from the free surface and gradually intensifies to air entrainment vortex. The vortex core moves during the formation and evolution of the free surface vortex. Based on the experimental model, the vortex position and structure were predicted by numerical simulation combined with a vortex model and compared with that of the experiments, which shows satisfactory agreement.
Bifurcation and instability problems in vortex wakes
DEFF Research Database (Denmark)
Aref, Hassan; Brøns, Morten; Stremler, Mark A.
2007-01-01
A number of instability and bifurcation problems related to the dynamics of vortex wake flows are addressed using various analytical tools and approaches. We discuss the bifurcations of the streamline pattern behind a bluff body as a vortex wake is produced, a theory of the universal Strouhal......-Reynolds number relation for vortex wakes, the bifurcation diagram for "exotic" wake patterns behind an oscillating cylinder first determined experimentally by Williamson & Roshko, and the bifurcations in topology of the streamlines pattern in point vortex streets. The Hamiltonian dynamics of point vortices...... in a periodic strip is considered. The classical results of von Kármán concerning the structure of the vortex street follow from the two-vortices-in-a-strip problem, while the stability results follow largely from a four-vortices-in-a-strip analysis. The three-vortices-in-a-strip problem is argued...
Experimental investigation of wing fin configurations for alleviation of vortex wakes of aircraft
Rossow, V. J.
1978-01-01
A variety of fin configurations were tested on a model of the Boeing B747 in 40 by 80 foot wind tunnels. The test results confirmed that a reduction in wake rolling moment was brought about by the vortex shed by the fins so that a wide range of designs can be used to achieve wake alleviation. It was also found that the reduction in wake-induced rolling moments was especially sensitive to the location of the smaller fins on the wing and that the penalties in lift and drag can probably be made negligible by proper fin design.
Long, J.; New, T. H.
2016-07-01
Vortical structures and dynamics of a Re h = 2100 elliptic jet impinging upon a flat plate were studied at H/ d h = 1, 2 and 4 jet-to-plate separation distances. Flow investigations were conducted along both its major and minor planes using laser-induced fluorescence and digital particle image velocimetry techniques. Results show that the impingement process along the major plane largely consists of primary jet ring-vortex and wall-separated secondary vortex formations, where they subsequently separate from the flat plate at smaller H/ d h = 1 and 2 separation distances. Key vortex formation locations occur closer to the impingement point as the separation distance increases. Interestingly, braid vortices and rib structures begin to take part in the impingement process at H/ d h = 4 and wave instabilities dominate the flow field. In contrast, significantly more coherent primary and secondary vortices with physically larger vortex core sizes and higher vortex strengths are observed along the minor plane, with no signs of braid vortices and rib structures. Lastly, influences of these different flow dynamics on the major and minor plane instantaneous and mean skin friction coefficient levels are investigated to shed light on the effects of separation distance on the wall shear stress distributions.
Introduction to Vortex Lattice Theory
Directory of Open Access Journals (Sweden)
Santiago Pinzón
2015-10-01
Full Text Available Panel methods have been widely used in industry and are well established since the 1970s for aerodynamic analysis and computation. The Vortex Lattice Panel Method presented in this study comes across a sophisticated method that provides a quick solution time, allows rapid changes in geometry and suits well for aerodynamic analysis. The aerospace industry is highly competitive in design efficiency, and perhaps one of the most important factors on airplane design and engineering today is multidisciplinary optimization. Any cost reduction method in the design cycle of a product becomes vital in the success of its outcome. The subsequent sections of this article will further explain in depth the theory behind the vortex lattice method, and the reason behind its selection as the method for aerodynamic analysis during preliminary design work and computation within the aerospace industry. This article is analytic in nature, and its main objective is to present a mathematical summary of this widely used computational method in aerodynamics.
The VORTEX coronagraphic test bench
Jolivet, Aissa; Huby, Elsa; Absil, Olivier; Delacroix, Christian; Mawet, Dimitri; Surdej, Jean; Habraken, Serge
2016-01-01
In this paper, we present the infrared coronagraphic test bench of the University of Li\\`ege named VODCA (Vortex Optical Demonstrator for Coronagraphic Applications). The goal of the bench is to assess the performances of the Annular Groove Phase Masks (AGPMs) at near- to mid-infrared wavelengths. The AGPM is a subwavelength grating vortex coronagraph of charge two (SGVC2) made out of diamond. The bench is designed to be completely achromatic and will be composed of a super continuum laser source emitting in the near to mid-infrared, several parabolas, diaphragms and an infrared camera. This way, we will be able to test the different AGPMs in the M, L, K and H bands. Eventually, the bench will also allow the computation of the incident wavefront aberrations on the coronagraph. A reflective Lyot stop will send most of the stellar light to a second camera to perform low-order wavefront sensing. This second system coupled with a deformable mirror will allow the correction of the wavefront aberrations. We also ai...
Shashikanth, Banavara N
2011-01-01
The vortex dynamics of Euler's equations for a constant density fluid flow in $R^4$ is studied. Most of the paper focuses on singular Dirac delta distributions of the vorticity two-form $\\omega$ in $R^4$. These distributions are supported on two-dimensional surfaces termed {\\it membranes} and are the analogs of vortex filaments in $R^3$ and point vortices in $R^2$. The self-induced velocity field of a membrane is shown to be unbounded and is regularized using a local induction approximation (LIA). The regularized self-induced velocity field is then shown to be proportional to the mean curvature vector field of the membrane but rotated by 90 degrees in the plane of normals. Next, the Hamiltonian membrane model is presented. The symplectic structure for this model is derived from a general formula for vorticity distributions due to Marsden and Weinstein (1983). Finally, the dynamics of the four-form $\\omega \\wedge \\omega$ is examined. It is shown that Ertel's vorticity theorem in $R^3$, for the constant density...
Vortex bursting and tracer transport of a counter-rotating vortex pair
Misaka, T.; Holzäpfel, F.; Hennemann, I.; Gerz, T.; Manhart, M.; Schwertfirm, F.
2012-02-01
Large-eddy simulations of a coherent counter-rotating vortex pair in different environments are performed. The environmental background is characterized by varying turbulence intensities and stable temperature stratifications. Turbulent exchange processes between the vortices, the vortex oval, and the environment, as well as the material redistribution processes along the vortex tubes are investigated employing passive tracers that are superimposed to the initial vortex flow field. It is revealed that the vortex bursting phenomenon, known from photos of aircraft contrails or smoke visualization, is caused by collisions of secondary vortical structures traveling along the vortex tube which expel material from the vortex but do not result in a sudden decay of circulation or an abrupt change of vortex core structure. In neutrally stratified and weakly turbulent conditions, vortex reconnection triggers traveling helical vorticity structures which is followed by their collision. A long-lived vortex ring links once again establishing stable double rings. Key phenomena observed in the simulations are supported by photographs of contrails. The vertical and lateral extents of the detrained passive tracer strongly depend on environmental conditions where the sensitivity of detrainment rates on initial tracer distributions appears to be low.
Rotor Wake Vortex Definition Using 3C-PIV Measurements: Corrected for Vortex Orientation
Burley, Casey L.; Brooks, Thomas F.; vanderWall, Berend; Richard, Hughues Richard; Raffel, Markus; Beaumier, Philippe; Delrieux, Yves; Lim, Joon W.; Yu, Yung H.; Tung, Chee
2003-01-01
Three-component (3-C) particle image velocimetry (PIV) measurements, within the wake across a rotor disk plane, are used to determine wake vortex definitions important for BVI (Blade Vortex Interaction) and broadband noise prediction. This study is part of the HART II test program conducted using a 40 percent scale BO-105 helicopter main rotor in the German-Dutch Wind Tunnel (DNW). In this paper, measurements are presented of the wake vortex field over the advancing side of the rotor operating at a typical descent landing condition. The orientations of the vortex (tube) axes are found to have non-zero tilt angles with respect to the chosen PIV measurement cut planes, often on the order of 45 degrees. Methods for determining the orientation of the vortex axis and reorienting the measured PIV velocity maps (by rotation/projection) are presented. One method utilizes the vortex core axial velocity component, the other utilizes the swirl velocity components. Key vortex parameters such as vortex core size, strength, and core velocity distribution characteristics are determined from the reoriented PIV velocity maps. The results are compared with those determined from velocity maps that are not corrected for orientation. Knowledge of magnitudes and directions of the vortex axial and swirl velocity components as a function of streamwise location provide a basis for insight into the vortex evolution.
A numerical study of viscous vortex rings using a spectral method
Stanaway, S. K.; Cantwell, B. J.; Spalart, Philippe R.
1988-01-01
Viscous, axisymmetric vortex rings are investigated numerically by solving the incompressible Navier-Stokes equations using a spectral method designed for this type of flow. The results presented are axisymmetric, but the method is developed to be naturally extended to three dimensions. The spectral method relies on divergence-free basis functions. The basis functions are formed in spherical coordinates using Vector Spherical Harmonics in the angular directions, and Jacobi polynomials together with a mapping in the radial direction. Simulations are performed of a single ring over a wide range of Reynolds numbers (Re approximately equal gamma/nu), 0.001 less than or equal to 1000, and of two interacting rings. At large times, regardless of the early history of the vortex ring, it is observed that the flow approaches a Stokes solution that depends only on the total hydrodynamic impulse, which is conserved for all time. At small times, from an infinitely thin ring, the propagation speeds of vortex rings of varying Re are computed and comparisons are made with the asymptotic theory by Saffman. The results are in agreement with the theory; furthermore, the error is found to be smaller than Saffman's own estimate by a factor square root ((nu x t)/R squared) (at least for Re=0). The error also decreases with increasing Re at fixed core-to-ring radius ratio, and appears to be independent of Re as Re approaches infinity). Following a single ring, with Re=500, the vorticity contours indicate shedding of vorticity into the wake and a settling of an initially circular core to a more elliptical shape, similar to Norbury's steady inviscid vortices. Finally, we consider the case of leapfrogging vortex rings with Re=1000. The results show severe straining of the inner vortex core in the first pass and merging of the two cores during the second pass.
Microscale vortex laser with controlled topological charge
Wang, Xing-Yuan; Chen, Hua-Zhou; Li, Ying; Li, Bo; Ma, Ren-Min
2016-12-01
A microscale vortex laser is a new type of coherent light source with small footprint that can directly generate vector vortex beams. However, a microscale laser with controlled topological charge, which is crucial for virtually any of its application, is still unrevealed. Here we present a microscale vortex laser with controlled topological charge. The vortex laser eigenmode was synthesized in a metamaterial engineered non-Hermitian micro-ring cavity system at exceptional point. We also show that the vortex laser cavity can operate at exceptional point stably to lase under optical pumping. The microscale vortex laser with controlled topological charge can serve as a unique and general building block for next-generation photonic integrated circuits and coherent vortex beam sources. The method we used here can be employed to generate lasing eigenmode with other complex functionalities. Project supported by the “Youth 1000 Talent Plan” Fund, Ministry of Education of China (Grant No. 201421) and the National Natural Science Foundation of China (Grant Nos. 11574012 and 61521004).
Nonlinear ion acoustic waves scattered by vortexes
Ohno, Yuji; Yoshida, Zensho
2016-09-01
The Kadomtsev-Petviashvili (KP) hierarchy is the archetype of infinite-dimensional integrable systems, which describes nonlinear ion acoustic waves in two-dimensional space. This remarkably ordered system resides on a singular submanifold (leaf) embedded in a larger phase space of more general ion acoustic waves (low-frequency electrostatic perturbations). The KP hierarchy is characterized not only by small amplitudes but also by irrotational (zero-vorticity) velocity fields. In fact, the KP equation is derived by eliminating vorticity at every order of the reductive perturbation. Here, we modify the scaling of the velocity field so as to introduce a vortex term. The newly derived system of equations consists of a generalized three-dimensional KP equation and a two-dimensional vortex equation. The former describes 'scattering' of vortex-free waves by ambient vortexes that are determined by the latter. We say that the vortexes are 'ambient' because they do not receive reciprocal reactions from the waves (i.e., the vortex equation is independent of the wave fields). This model describes a minimal departure from the integrable KP system. By the Painlevé test, we delineate how the vorticity term violates integrability, bringing about an essential three-dimensionality to the solutions. By numerical simulation, we show how the solitons are scattered by vortexes and become chaotic.
A VORTEX MODEL OF A HELICOPTER ROTOR
Directory of Open Access Journals (Sweden)
Valentin BUTOESCU
2009-06-01
Full Text Available A vortex model of a helicopter rotor is presented. Each blade of the rotor has three degrees of freedom: flapping, lagging and feathering. The motions after each degree of freedom are also known for all blades. The blade is modelled as a thin vortex surface. The wakes are free fluid surfaces. A system of five equations are obtained: the first one is the integral equation of the lifting surface (rotor, the next three describe the wakes motion, and the last one relates the vortex strength on the wakes and the variation of vorticity on the rotor. A numerical solution of this system is presented. To avoid the singularities that can occur due to the complexity of vortex system, a desingularized model of the vortex core was adopted. A Mathcad worksheet containing the method has been written.The original contribution of the work. The calculation method of the motion of the wakes free vortex system, the development of the vortex cores in time and a new method to approximate the aerodynamic influence of remoted wake regions.
Han, Dong-Soo; Jeong, Han-Byeol; Kim, Sang-Koog
2013-09-01
We performed micromagnetic numerical and analytical calculations in studying the effects of change in the primitive unit cells of one-dimensional (1D) vortex arrays on collective vortex-gyration dispersion. As the primitive basis, we consider alternating constituent materials (NiMnSb vs. Permalloy) and alternating dimensions including constituent disk diameter and thickness. In the simplest case, that of one vortex-state disk of given dimensions and single material in the primitive cell, only a single branch of collective vortex-gyration dispersion appears. By contrast, two constituent disks' different alternating materials, thicknesses, and diameters yield characteristic two-branch dispersions, the band widths and gaps of which differ in each case. This work offers not only an efficient means of manipulating collective vortex-gyration band structures but also a foundation for the development of a rich variety of 1D or 2D magnonic crystals and their band structures based on dipolar-coupled-vortex arrays.
Evaluation of travelling vortex speed by means of vortex tracking and dynamic mode decomposition
Hyhlík, Tomáš
2016-06-01
The article deals with the analysis of unsteady periodic flow field related to synthetic jet creation. The analyses are based on the data obtained using ANSYS Fluent solver. Numerical results are validated by hot wire anemometry data measured along the jet centerline. The speed of travelling vortex ring is evaluated by using vortex tracking method and by using dynamic mode decomposition method. Vortex identification is based on residual vorticity which allows identifying regions in the flow field where fluid particles perform the rotational motion. The regime of the synthetic jet with Re = 329 and S = 19.7 is chosen. Both the vortex tracking and the dynamic mode decomposition based vortex speed evaluation indicate an increase in the vortex speed close to the orifice and then decrease with maximum reaching almost one and half of orifice centerline velocity. The article contains extended version the article presented at the conference AEaNMiFMaE 2016.
Meng, Qingyou; Varney, Christopher N.; Fangohr, Hans; Babaev, Egor
2017-01-01
It was recently proposed to use the stray magnetic fields of superconducting vortex lattices to trap ultracold atoms for building quantum emulators. This calls for new methods for engineering and manipulating of the vortex states. One of the possible routes utilizes type-1.5 superconducting layered systems with multi-scale inter-vortex interactions. In order to explore the possible vortex states that can be engineered, we present two phase diagrams of phenomenological vortex matter models with multi-scale inter-vortex interactions featuring several attractive and repulsive length scales. The phase diagrams exhibit a plethora of phases, including conventional 2D lattice phases, five stripe phases, dimer, trimer, and tetramer phases, void phases, and stable low-temperature disordered phases. The transitions between these states can be controlled by the value of an applied external field.
Symmetry-constrained electron vortex propagation
Clark, L; Béché, A; Lubk, A; Verbeeck, J
2016-01-01
Electron vortex beams hold great promise for development in transmission electron microscopy, but have yet to be widely adopted. This is partly due to the complex set of interactions that occur between a beam carrying orbital angular momentum (OAM) and a sample. Herein, the system is simplified to focus on the interaction between geometrical symmetries, OAM and topology. We present multiple simulations, alongside experimental data to study the behaviour of a variety of electron vortex beams after interacting with apertures of different symmetries, and investigate the effect on their OAM and vortex structure, both in the far-field and under free-space propagation.
Vortex dynamics in ferromagnetic/superconducting bilayers
Energy Technology Data Exchange (ETDEWEB)
Cieplak, M.Z.; Adamus, Z. [Polish Acad Sci, Inst Phys, PL-02668 Warsaw, (Poland); Konczykowski, M. [CEA, DSM, DRECAM, Lab Solides Irradies, Ecole Polytechnique, CNRS-UMR 7642, F-91128 Palaiseau (France); Zhu, L.Y.; Chien, C.L. [Johns Hopkins Univ, Dept Phys and Astron, Baltimore, MD 21218 (United States)
2008-07-01
The dependence of vortex dynamics on the geometry of magnetic domain pattern is studied in the superconducting/ferromagnetic bilayers, in which niobium is a superconductor, and Co/Pt multilayer with perpendicular magnetic anisotropy serves as a ferromagnetic layer. Magnetic domain patterns with different density of domains per surface area and different domain size, w, are obtained for Co/Pt with different thickness of Pt. The dense patterns of domains with the size comparable to the magnetic penetration depth (w {>=} {lambda}) produce large vortex pinning and smooth vortex penetration, while less dense patterns with larger domains (w {>=}{>=} {lambda}) enhance pinning less effectively and result in flux jumps during flux motion. (authors)
Superconducting Josephson vortex flow transistors
Tavares, P A C
2002-01-01
The work reported in this thesis focuses on the development of high-temperature superconducting Josephson vortex-flow transistors (JVFTs). The JVFT is a particular type of superconducting transistor, i.e. an electromagnetic device capable of delivering gain while keeping the control and output circuits electrically isolated. Devices were fabricated from (100) YBa sub 2 Cu sub 3 O sub 7 sub - subdelta thin films grown by Pulsed Laser Deposition on 24 deg magnesium oxide and strontium titanate bicrystals. The design of the JVFTs was guided by numerical simulations and the devices were optimised for current gain. Improvements were made to the fabrication process in order to accurately pattern the small structures required. The devices exhibited current gains higher than 60 in liquid nitrogen. Gains measured at lower temperatures were significantly higher. As part of the work a data acquisition suite was developed for the characterisation of three-terminal devices and, in particular, of JVFTs.
Vortex disruption by magnetohydrodynamic feedback
Mak, Julian; Hughes, D W
2016-01-01
In an electrically conducting fluid, vortices stretch out a weak, large-scale magnetic field to form strong current sheets on their edges. Associated with these current sheets are magnetic stresses, which are subsequently released through reconnection, leading to vortex disruption, and possibly even destruction. This disruption phenomenon is investigated here in the context of two-dimensional, homogeneous, incompressible magnetohydrodynamics. We derive a simple order of magnitude estimate for the magnetic stresses --- and thus the degree of disruption --- that depends on the strength of the background magnetic field (measured by the parameter $M$, a ratio between the Alfv\\'en speed and a typical flow speed) and on the magnetic diffusivity (measured by the magnetic Reynolds number $\\mbox{Rm}$). The resulting estimate suggests that significant disruption occurs when $M^{2}\\mbox{Rm} = O(1)$. To test our prediction, we analyse direct numerical simulations of vortices generated by the breakup of unstable shear flo...
Institute of Scientific and Technical Information of China (English)
孙志强; 陈延平
2013-01-01
The Burg algorithm based AR model spectral estimation was used to analyze the output signals of a vortex flowmeter within water flow rates from 3 to 35 m3/h, to extract the vortex shedding frequency from noisy signals accurately and effectively. The effect of the AR model's order on the estimation of vortex shedding frequency was discussed. A fitting correlation was established between the minimum AR model's order and the vortex shedding frequency with an error of 3%. The results show that the accuracy of the vortex shedding frequency extracted is high by the Burg algorithm based AR model spectral estimation. The AR model's order has a marked influence on the spectral estimation accuracy and the computation efficiency of Burg algorithm, which suggests that an appropriate order be selected to estimate the vortex shedding frequency from vortex flowmeter output signals. The minimum AR model's order decreases with the increase of vortex shedding frequency.%为了从含噪信号中准确高效地提取出旋涡脱落频率,采用基于Burg算法的AR模型谱估计对测量介质为水、流量范围为3～35 m3/h的涡街流量计输出信号进行分析,讨论AR模型阶次对旋涡脱落频率估计性能的影响,建立频率相对误差小于3％的AR模型最小阶次与旋涡脱落频率的拟合关系式.结果表明,基于Burg算法的AR模型谱估计对涡街流量计旋涡脱落频率的提取精度较高；AR模型的阶次对Burg算法的谱估计精度和计算效率有重要影响,应选用匹配的AR模型阶次对涡街流量计输出信号进行估计；AR模型最小阶次随旋涡脱落频率的增大而减小.
Vortex Dynamics in Anisotropic Superconductors
Steel, David Gordon
Measurements of the ac screening response and resistance of superconducting Bi_2Sr _2CaCu_2O _8 (BSCCO) crystals have been used to probe the dynamics of the magnetic flux lines within the mixed state as a function of frequency, temperature, and applied dc field. For the particular range of temperature and magnetic field in which measurements were made, the systematic behavior of the observed dissipation peak in the screening response is consistent with electromagnetic skin size effects rather than a phase transition. According to microscopic theories of the interaction between the flux lines and a driving ac field, such a skin size effect is expected for the case when the vortex motion is diffusive in nature. However, diffusive motion is inconsistent with simple activation models that use a single value for the pinning energy (derived from direct measurement of the dc resistance). This contradiction suggests a distribution of pinning energies within the sample. Interlayer vortex decoupling has been directly observed as a function of temperature and applied magnetic field using electronic transport perpendicular to the layers in synthetic amorphous MoGe/Ge multilayer samples. Perpendicular transport has been shown to be a far more sensitive measure of the phase coupling between layers than in-plane properties. Below the decoupling temperature T_{D} the resistivity anisotropy collapses and striking nonlinearities appear in the perpendicular current-voltage behavior, which are not observed in parallel transport. A crossover in behavior is also observed at a field H _{x}, in accordance with theory. The data suggest the presence of a phase transition into a state with finite in-plane resistivity. (Copies available exclusively from MIT Libraries, Rm. 14-0551, Cambridge, MA 02139-4307. Ph. 617-253-5668; Fax 617-253-1690.).
Prediction and control of vortex-dominated and vortex-wake flows
Kandil, Osama
1993-01-01
This progress report documents the accomplishments achieved in the period from December 1, 1992 until November 30, 1993. These accomplishments include publications, national and international presentations, NASA presentations, and the research group supported under this grant. Topics covered by documents incorporated into this progress report include: active control of asymmetric conical flow using spinning and rotary oscillation; supersonic vortex breakdown over a delta wing in transonic flow; shock-vortex interaction over a 65-degree delta wing in transonic flow; three dimensional supersonic vortex breakdown; numerical simulation and physical aspects of supersonic vortex breakdown; and prediction of asymmetric vortical flows around slender bodies using Navier-Stokes equations.
Scattering of a vortex pair by a single quantum vortex in a Bose-Einstein condensate
Smirnov, L. A.; Smirnov, A. I.; Mironov, V. A.
2016-01-01
We analyze the scattering of vortex pairs (the particular case of 2D dark solitons) by a single quantum vortex in a Bose-Einstein condensate with repulsive interaction between atoms. For this purpose, an asymptotic theory describing the dynamics of such 2D soliton-like formations in an arbitrary smoothly nonuniform flow of a ultracold Bose gas is developed. Disregarding the radiation loss associated with acoustic wave emission, we demonstrate that vortex-antivortex pairs can be put in correspondence with quasiparticles, and their behavior can be described by canonical Hamilton equations. For these equations, we determine the integrals of motion that can be used to classify various regimes of scattering of vortex pairs by a single quantum vortex. Theoretical constructions are confirmed by numerical calculations performed directly in terms of the Gross-Pitaevskii equation. We propose a method for estimating the radiation loss in a collision of a soliton-like formation with a phase singularity. It is shown by direct numerical simulation that under certain conditions, the interaction of vortex pairs with a core of a single quantum vortex is accompanied by quite intense acoustic wave emission; as a result, the conditions for applicability of the asymptotic theory developed here are violated. In particular, it is visually demonstrated by a specific example how radiation losses lead to a transformation of a vortex-antivortex pair into a vortex-free 2D dark soliton (i.e., to the annihilation of phase singularities).
Kleckner, Dustin; Irvine, William T M
2013-01-01
The idea that the knottedness (hydrodynamic Helicity) of a fluid flow is conserved has a long history in fluid mechanics. The quintessential example of a knotted flow is a knotted vortex filament, however, owing to experimental difficulties, it has not been possible until recently to directly generate knotted vortices in real fluids. Using 3D printed hydrofoils and high-speed laser scanning tomography, we generate vortex knots and links and measure their subsequent evolution. In both cases, we find that the vortices deform and stretch until a series of vortex reconnections occurs, eventually resulting several disjoint vortex rings. This article accompanies a fluid dynamics video entered into the Gallery of Fluid Motion at the 66th Annual Meeting of the APS Division of Fluid Dynamics.
Advanced Vortex Hybrid Rocket Engine (AVHRE) Project
National Aeronautics and Space Administration — Orbital Technologies Corporation (ORBITEC) proposes to develop a unique Advanced Vortex Hybrid Rocket Engine (AVHRE) to achieve a highly-reliable, low-cost and...
Advanced Vortex Hybrid Rocket Engine (AVHRE) Project
National Aeronautics and Space Administration — ORBITEC proposes to develop a unique Advanced Vortex Hybrid Rocket Engine (AVHRE) to achieve a safe, highly-reliable, low-cost and uniquely versatile propulsion...
Free wake models for vortex methods
Energy Technology Data Exchange (ETDEWEB)
Kaiser, K. [Technical Univ. Berlin, Aerospace Inst. (Germany)
1997-08-01
The blade element method works fast and good. For some problems (rotor shapes or flow conditions) it could be better to use vortex methods. Different methods for calculating a wake geometry will be presented. (au)
'Optimal' vortex rings and aquatic propulsion mechanisms
Linden, Paul; Turner, Stewart
2004-11-01
Fish swim by flapping their tail and other fins. Other sea creatures, such as squid and salps, eject fluid intermittently as a jet. We discuss the fluid mechanics behind these propulsion mechanisms, and show that these animals produce optimal vortex rings, which give the maximum thrust for a given energy input. We show fish optimise both their steady swimming and their ability to accelerate and turn by producing an individual optimal ring with each flap of the tail or fin. Salps produce vortex rings directly by ejecting a volume of fluid through a rear orifice, and these are also optimal. An important implication of this paper is that the repetition of vortex production is not necessary for an individual vortex to have the `optimal' characteristics.
Experiments with vortex rings in air
Hernández, R. H.; Cibert, B.; Béchet, C.
2006-09-01
We report quantitative experimental measurements of the instability of vortex rings generated in air. Vortex rings are created by pushing air through the circular orifice of a cylindrical cavity with a flat piston driven by a loudspeaker. Hot-wire anemometry provides accurate measurements of the velocity profile at all stages of the ring formation including stable and unstable rings. Flow visualization using a laser light sheet shows that the initially undisturbed vortex ring is progressively deformed in the azimuthal direction giving rise to a wavy azimuthal and periodic pattern in the circumference of the ring. The wavy pattern is steady, i.e., it does not rotate or translate during the ring's motion. However as the vortex motion progresses in the axial direction, the displaced portions of the ring are convected away from the initial undisturbed position and the wavy pattern grows with local Reynolds number.
Cockpit-based Wake Vortex Visualization Project
National Aeronautics and Space Administration — To prevent aircraft accidents due to wake vortex hazards, FAA procedures specify the minimum separation required between different categories of aircraft. However, a...
Development of gas pressure vortex regulator
Uss, A. Yu.; Chernyshyov, A. V.; Krylov, V. I.
2017-08-01
The present paper describes the applications of vortex regulators and the current state of the issue on the use and development of such devices. A patent review has been carried out. Automatic control systems using a vortex regulator are considered. Based on the analysis and preliminary numerical calculation of gas flow in the working cavity of the regulator, a new design of a vortex gas pressure regulator has been developed. An experimental sample of the device was made using additive technologies and a number of tests were carried out. The results of experimental studies confirmed the adequacy of the created mathematical model. Based on further numerical studies a new design of a vortex regulator with a distributed feed of the process control flow as well as with the regulated swirl of the supply and control process flows has been developed.
Investigation of aircraft vortex wake structure
Baranov, N. A.; Turchak, L. I.
2014-11-01
In this work we analyze the mechanisms of formation of the vortex wake structure of aircraft with different wing shape in the plan flying close to or away from the underlying surface cleaned or released mechanization wing.
Interaction and merging of vortex filaments
Liu, C. H.; Weston, R. P.; Ishii, K.; Ting, L.; Visintainer, J. A.
1988-01-01
The asymptotic solutions of Navier-Stokes equations for vortex filaments of finite strength with small effective vortical cores are summarized with special emphasis placed on the physical meaning and the practical limit to the applicability of the asymptotic solution. Finite-difference solutions of Navier-Stokes equations for the marging of the filament(s) are described with a focus on the development of the approximate boundary conditions for the computational domain. An efficiency study employing a model problem is used to assess the advantages of the present approximate boundary condition method over previously used techniques. Applications of the present method are presented for the motion and decay of a 3:1 elliptic vortex ring, and for the merging process of a pair of coaxial vortex rings. A numerical procedure for the problem of local merging of vortex filaments, which requires the asymptotic analysis as well as the numerical Navier-Stokes solver, is also presented.
Applications of 2D helical vortex dynamics
DEFF Research Database (Denmark)
Okulov, Valery; Sørensen, Jens Nørkær
2010-01-01
In the paper, we show how the assumption of helical symmetry in the context of 2D helical vortices can be exploited to analyse and to model various cases of rotating flows. From theory, examples of three basic applications of 2D dynamics of helical vortices embedded in flows with helical symmetry...... of the vorticity field are addressed. These included some of the problems related to vortex breakdown, instability of far wakes behind rotors and vortex theory of ideal rotors....
Bourguet, Remi; Triantafyllou, Michael
2016-11-01
Slender flexible cylinders immersed in flow are common in nature (e.g. plants and trees in wind) and in engineering applications, for example in the domain of offshore engineering, where risers and mooring lines are exposed to ocean currents. Vortex-induced vibrations (VIV) naturally develop when the cylinder is placed at normal incidence but they also appear when the body is inclined in the current, including at large angles. In a previous work concerning a flexible cylinder inclined at 80 degrees, we found that the occurrence of VIV is associated with a profound alteration of the flow dynamics: the wake exhibits a slanted vortex shedding pattern in the absence of vibration, while the vortices are shed parallel to the body once the large-amplitude VIV regime is reached. The present study aims at bridging the gap between these two extreme configurations. On the basis of direct numerical simulations, we explore the intermediate states of the flow-structure system. We identify two dominant components of the flow: a high-frequency component that relates to the stationary body wake and a low-frequency component synchronized with body motion. We show that the scenario of flow reconfiguration is driven by the opposite trends of these two component contributions.
Effects of tapes with double-sided delta-winglets on heat and vortex characteristics
Energy Technology Data Exchange (ETDEWEB)
Yakut, K.; Sahin, B.; Alemdaroglu, N.; Kurnuc, A. [University of Ataturk, Erzurum (Turkey). Department of Mechanical Engineering; Celik, C. [University of Ataturk, Erzurum (Turkey). Department of Industrial Engineering
2005-01-01
An experimental study was carried out for tapes with double-sided delta-winglets under different geometrical and flow parameters, including angles of attack (90{sup o}, 60{sup o} and 30{sup o}), winglet heights (8, 12 and 16 mm), pitch arrangements (25, 50 and 75 mm) and Reynolds numbers (3690, 10493 and 16906). By using the Taguchi experimental-design method, the optimum parameters of the turbulator were determined by obtaining the Nusselt number, friction factor, amplitude of fluctuation pressure of the vortices and the vortex-shedding frequency. First of all, each goal was optimized, separately. Then, all the goals were optimized together, considering the priority of the goals, and the optimum results were obtained at a Reynolds number of 16906, 25 mm pitch, 8 mm height of winglet and 30{sup o} angle of attack, so that vortex-shedding frequencies are maximised. For lower frequencies, optimum conditions occurred at a Reynolds number of 16906 for 75 mm pitch, 8 mm height of winglet and 60{sup o} angle of attack. (author)
Structure of a Steady Bathtub Vortex
Andersen, Anders; Bøhling, Lasse; Fabre, David
2010-11-01
Bathtub vortex flows constitute an important class of concentrated vortex flows which are characterised by intense axial down-flow and stress free surface. We use direct numerical simulations to explore the flow structure of a steady bathtub vortex in a cylindrical tank with a central drain-hole. We find that the qualitative structure of the meridional flow does not depend on the radial Reynolds number, whereas we observe a weak overall rotation at low radial Reynolds number and a concentrated vortex above the drain-hole at high radial Reynolds number. We present a simple analytical model which shows the same qualitative dependence on the radial Reynolds number as the simulations and which compares favourably with the results for the radial velocity and the azimuthal velocity at the surface. Finally, we describe the height dependence of the radius of the vortex core and the maximum of the azimuthal velocity at high radial Reynolds number, and we show that the data on the radius of the vortex core and the maximum of the azimuthal velocity as functions of height collapse on single curves by appropriate scaling.
Application of vortex method; Uzuho no tekiyo
Energy Technology Data Exchange (ETDEWEB)
Tsukiji, T. [Ashikaga Inst. of Technology, Tochigi (Japan); Shimizu, S. [Hiroshima Univ., Hiroshima (Japan). Faculty of Engineering
1995-07-15
Basic jets such as two dimensional free jet, impact jet, axisymmetric circular free jet, and jet flowing out from a nozzle equipped with a collar at the outlet, as well as flow in such valves as disc valves, spool valves, and poppet valves are taken up to discuss their applications using the vortex method, and the results of studies made using vortex method on the analysis of jet and conditions inside valves are reported. The state of the development of large scale vortex structure in the shear layer can be simulated comparatively simply by using the vortex method. The effects of the radius and the lift of a valve on the fluid outlet angle of jet and on the discharge coefficient of orifice are analyzed. Although the shape of the spool valve near the throttle is very complicated, simplified models are used for numerical analysis. An example of calculated result in the case where the spool reciprocates is introduced. Actual vibrating phenomena can be simulated well by the vortex method for minute vibration of the poppet caused by the discharge of lump vortex. 17 refs., 16 figs., 1 tab.
Boundary Layers in Laminar Vortex Flows.
Baker, Glenn Leslie
A detailed experimental study of the flow in an intense, laminar, axisymmetric vortex has been conducted in the Purdue Tornado Vortex Simulator. The complicated nature of the flow in the boundary layer of laboratory vortices and presumably on that encountered in full-scale tornadoes has been examined. After completing a number of modifications to the existing facility to improve the quality of the flow in the simulator, hot-film anemometry was employed for making velocity-component and turbulence-intensity measurements of both the free-stream and boundary layer portions of the flow. The measurements represent the first experimental boundary layer investigation of a well-defined vortex flow to appear in the literature. These results were compared with recent theoretical work by Burggraf, Stewartson and Belcher (1971) and with an exact similarity solution for line-sink boundary layers developed by the author. A comparison is also made with the numerical simulation of Wilson (1981) in which the boundary conditions were matched to those of the present experimental investigation. Expressions for the vortex core radius, the maximum tangential velocity and the maximum pressure drop are given in terms of dimensionless modeling parameters. References. Burggraf, O. R., K. Stewartson and R. Belcher, Boundary layer. induced by a potential vortex. Phys. Fluids 14, 1821-1833 (1971). Wilson, T., M. S. thesis, Vortex Boundary Layer Dynamics, Univ. Calif. Davis (1981).
Methods to describe barotropic vortices by global fields and vortex characteristics
Directory of Open Access Journals (Sweden)
W.-G. Früh
2002-01-01
Full Text Available Results from an experimental study of vortices in a rotating shear layer are presented. The data are in the form of maps of the instantaneous horizontal velocity field obtained by a particle tracking technique. Two fundamentally different methods to analyse time series of these velocity fields are presented and compared. One technique is the empirical orthogonal function (EOF analysis, and the other method describes the flow field in terms of a few individual localised vortices. The flows discussed here are time-dependent two-vortex flows, which could either be described as a global mode 2 or as a collection of four unequal vortices. The results show that, while EOF analysis is a very powerful tool to detect fairly regular travelling modes or stationary features, it cannot detect local dynamics. The vortex identification technique is very good at detecting local structures and events but cannot put them into the context of a global flow structure. The comparison of the techniques shows indications that the time-dependence found in the system for low mode numbers could arise from an interaction of the large scale, global-mode flow with a local mechanism of vortex generation and shedding at a solid boundary.
Numerical Study of Mechanism of U-shaped Vortex Formation
Lu, Ping; Liu, Chaoqun
2014-01-01
This paper illustrates the mechanism of U-shaped vortex formation which is found both by experiment and DNS. The main goal of this paper is to explain how the U-shaped vortex is formed and further develops. According to the results obtained by our direct numerical simulation with high order accuracy, the U-shaped vortex is part of the coherent vortex structure and is actually the tertiary streamwise vortices induced by the secondary vortices. The new finding is quite different from existing theories which describe that the U-shaped vortex is newly formed as the head of young turbulence spot and finally break down to small pieces. In addition, we find that the U-shaped vortex has the same vorticity sign as the original {\\lambda}-shaped vortex tube legs and serves as a second neck to supply vorticity to the ringlike vortex when the original vortex tube is stretched and multiple rings are generated.
Experimental Investigation of wing-tip vortex evolution in turbulence
Bailey, Sean; Ghimire, Hari
2016-11-01
Towing tank experiments were conducted to examine the evolution of a wing-tip vortex in grid-generated turbulence. Measurements using particle image velocimetry (PIV) were conducted of the velocity field generated by towing a semi-span symmetric wing oriented at 8 degree angle of attack. Turbulence of different kinetic energy and length scales was produced by simultaneously towing grids of different mesh sizes upstream of the wing. Results showed that wing-tip vortex wandering increased with the increase in turbulence kinetic energy, ultimately leading to spontaneous collapse of the vortex. During this process, a measurable diffusion of overall vortex circulation was observed, with the rate of diffusion leading to the collapse of the vortex dependent on the turbulence intensity. Interestingly, the radius of the vortex core remained largely unchanged during the diffusion process, Evidence suggests that the breakdown of vortex was enhanced by entrainment of fluid inside vortex core due to vortex stripping in presence of turbulence.
DEFF Research Database (Denmark)
Bhattacharyya, S.; Singh, Ashok
2010-01-01
vorticity on the wake formation is addressed in the present study. The variation of Strouhal number and Nusselt number with the 'effective Reynolds number', is analyzed for different values of cylinder to free stream temperature ratio. Both Strouhal number and the rate of heat transfer increases...... the effective Reynolds number and the computed data for Strouhal number and Nusselt number do not collapse for the range of temperature ratio considered here. The flow field is found to be asymmetric and the cylinder experiences a negative lift. The drag coefficient increases steadily with the rise of surface...... temperature. © 2010 Elsevier Ltd. All rights reserved....
Laurent Egli (visit)
2013-01-01
13 September 2013 - Chairman of the Board of Directors of the von Karman Institute Kingdom of Belgium J.-P. Contzen visiting the ATLAS experimental cavern with ATLAS Former Spokesperson P. Jenni; visiting the LHC tunnel at Point 1 with Technology Department N. Delruelle and signing the guest book with Technology Department Head F. Bordry. International Relations Adviser T. Kurtyka present.
Numerical study of wingtip shed vorticity reduction by wing Boundary Layer Control
Posada, Jose Alejandro
Wingtip vortex reductions have been obtained by Boundary Layer Control application to an AR=1.5 rectangular wing using a NACA 0012 airfoil. If wingtip shed vorticity could be reduced significantly, then so would induced drag resulting in improved cruise fuel economy. Power savings would be even more impressive at low flight speed or in climb. A two dimensional wing produces lift without wingtip vorticity. Its bound vorticity, Gamma, equals the contour integral of the boundary layer vorticity gamma or Gamma = ∮gamma · dl. Where the upper and lower boundary layers meet at the cusped TE, their local static pressure pu=pl then the boundary layer outer edge inviscid velocity Vupper=Vlower and gammalower=-gamma upper. This explains the 2-D wing self cancellation of the upper and lower surface boundary layer vorticity when they meet upon shedding at the trailing edge. In finite wings, the presence of spanwise pressure gradients near the wing tips misaligns gammalower and gammaupper at the wingtip TE preventing the upper and lower surface boundary layers from completely canceling each other. To prevent them from generating wing tip vortices, the local boundary layers need to be captured in suction slots. Once vorticity is captured, it can be eliminated by viscous mixing prior to venting over board. The objective of this dissertation was to use a commercial Computational Fluid Dynamics code (Fluent) to search for the best configuration to locate BLC suction slots to capture non-parallel boundary layer vorticity prior to shedding near the wingtips. The configuration selected for running the simulations was tested by trying to duplicate a 3D wing for which sufficient experimental and computational models by others are available. The practical case selected was done by Chow et al in the 32 x 48 in. low speed wind tunnel at the Fluid Mechanics Laboratory of NASA Ames Research Center, and computationally analyzed by Dacles-Mariani et al, and Khim and Rhee. The present
Effects of surface anisotropy on magnetic vortex core
Energy Technology Data Exchange (ETDEWEB)
Pylypovskyi, Oleksandr V., E-mail: engraver@univ.net.ua [Taras Shevchenko National University of Kiev, 01601 Kiev (Ukraine); Sheka, Denis D. [Taras Shevchenko National University of Kiev, 01601 Kiev (Ukraine); Kravchuk, Volodymyr P.; Gaididei, Yuri [Institute for Theoretical Physics, 03143 Kiev (Ukraine)
2014-06-01
The vortex core shape in the three dimensional Heisenberg magnet is essentially influenced by a surface anisotropy. We predict that depending of the surface anisotropy type there appears barrel- or pillow-shaped deformation of the vortex core along the magnet thickness. Our theoretical study is well confirmed by spin–lattice simulations. - Highlights: • The shape of magnetic vortex core is essentially influenced by SA (surface anisotropy). • We predict barrel- or pillow-shaped deformation of the vortex depending on SA. • The variational approach fully describes the vortex core deformation. • We performed spin–lattice simulations to detect SA influence on the vortex core.
Effect of Dzyaloshinskii–Moriya interaction on magnetic vortex
Directory of Open Access Journals (Sweden)
Y. M. Luo
2014-04-01
Full Text Available The effect of the Dzyaloshinskii–Moriya (DM interaction on the vortex in magnetic microdisk was investigated by micro-magnetic simulation based on the Landau–Lifshitz–Gilbert equation. Our results show that the DM interaction modifies the size of the vortex core, and also induces an out-of-plane magnetization component at the edge and inside the disk. The DM interaction can destabilizes one vortex handedness, generate a bias field to the vortex core and couple the vortex polarity and chirality. This DM-interaction-induced coupling can therefore provide a new way to control vortex polarity and chirality.
Sculptured 3D twister superlattices embedded with tunable vortex spirals.
Xavier, Jolly; Vyas, Sunil; Senthilkumaran, Paramasivam; Denz, Cornelia; Joseph, Joby
2011-09-01
We present diverse reconfigurable complex 3D twister vortex superlattice structures in a large area embedded with tunable vortex spirals as well as dark rings, threaded by vortex helices. We demonstrate these tunable complex chiral vortex superlattices by the superposition of relatively phase engineered plane waves. The generated complex 3D twister lattice vortex structures are computationally as well as experimentally analyzed using various tools to verify the presence of phase singularities. Our observation indicates the application-specific flexibility of our approach to tailor the transverse superlattice spatial irradiance profile of these longitudinally whirling vortex-cluster units and dark rings.
Vortex loops entry into type-II superconductors
Samokhvalov, A V
1996-01-01
The magnetic field distribution, the magnetic flux, and the free energy of an Abrikosov vortex loop near a flat surface of type--II superconductors are calculated in the London approximation. The shape of such a vortex line is a semicircle of arbitrary radius. The interaction of the vortex half--ring and an external homogeneous magnetic field applied along the surface is studied. The magnitude of the energy barrier against the vortex expansion into superconductor is found. The possibilities of formation of an equilibrium vortex line determined by the structure of the applied magnetic field by creating the expanding vortex loops near the surface of type--II superconductor are discussed.
Institute of Scientific and Technical Information of China (English)
徐万海; 杜杰; 余建星; 李敬成
2011-01-01
A wake oscillator model is presented for the stream-wise vortex-induced vibration of a circular cylinder in the second excitation region. The near wake dynamics related to the fluctuating nature of alternate vortex shedding is modeled based on the classical van der Pol equation. An appropriate approach used in cross-Sow VIV is developed to estimate the model empirical parameters. The comparison between our calculations and experiments is carried out to validate the proposed model. It is found that the present model results agree fairly well with the experimental data.%A wake oscillator model is presented for the stream-wise vortex-induced vibration of a circular cylinder in the second excitation region.The near wake dynamics related to the fluctuating nature of alternate vortex shedding is modeled based on the classical van der Pol equation.An appropriate approach used in cross-flow VIV is developed to estimate the nodel empirical parameters.The comparison between our calculations and experiments is carried out to validate the proposed model.It is found that the present model results agree fairly well with the experimental data.
Hub vortex helical instability as the origin of wake meandering in the lee of a model wind-turbine
Viola, Francesco; Iungo, Giacomo Valerio; Camarri, Simone; Porte-Agel, Fernando; Gallaire, Francois
2012-11-01
Wind tunnel measurements were performed for the wake produced by a three-bladed wind turbine immersed in uniform flow. These tests show the presence of a vorticity structure in the near wake region mainly oriented along the streamwise direction, which is denoted as hub vortex. The hub vortex is characterized by oscillations with frequencies lower than the one connected to the rotational velocity of the rotor, which are ascribed to wake meandering by previous works. This phenomenon consists in transversal oscillations of the wind turbine wake, which are excited by the shedding of vorticity structures from the rotor disc acting as a bluff body. In this work temporal and spatial linear stability analyses of a wind turbine wake are performed on a base flow obtained through time-averaged wind tunnel velocity measurements. This study shows that the low frequency spectral component detected experimentally is the result of a convective instability of the hub vortex, which is characterized by a counter-winding single-helix structure. Simultaneous hot-wire measurements confirm the presence of a helicoidal unstable mode of the hub vortex with a streamwise wavenumber roughly equal to the one predicted from the linear instability analysis.
Analysis of Vortex Line Cutting and Reconnection by a Blade
Saunders, Curtis; Marshall, Jeffrey
2015-11-01
The essence of vortex reconnection involves the cutting of vortex lines originating from one region and reconnecting to vortex lines originating from another region via the diffusion-regulated annihilation of vorticity. Vortex cutting by a blade is a special case of the more general class of vortex reconnection problems, with an important difference being that vorticity is generated at the reconnection site. In this study, a series of Navier-Stokes simulations of orthogonal vortex cutting by a blade with different values of vortex strength are reported. The three phases of vortex reconnection identified in the literature are found to have counterparts for the vortex cutting problem. However numerous differences between the mechanics of vortex cutting and reconnection within each phase are discussed. In addition, comparisons are made between the temporal changes of the maximum and minimum components of vorticity for vortices of differing strength but still within the vortex cutting regime. The vortex cutting results are also compared with predictions of a simple analytical model that incorporates the key elements of a stretched vorticity field interacting with a solid surface, which is representative of the vortex cutting mechanism near the blade leading edge. Funded by National Science Foundation project DGE-1144388.
Beardsell, Guillaume; Dufresne, Louis; Dumas, Guy
2016-09-01
This paper aims to shed further light on the viscous reconnection phenomenon. To this end, we propose a robust and efficient method in order to quantify the degree of reconnection of two vortex tubes. This method is used to compare the evolutions of two simple initial vortex configurations: orthogonal and antiparallel. For the antiparallel configuration, the proposed method is compared with alternative estimators and it is found to improve accuracy since it can account properly for the formation of looping structures inside the domain. This observation being new, the physical mechanism for the formation of those looping structures is discussed. For the orthogonal configuration, we report results from simulations that were performed at a much higher vortex Reynolds number (ReΓ ≡ circulation/viscosity = 104) and finer resolution (N3 = 10243) than previously presented in the literature. The incompressible Navier-stokes equations are solved directly (Direct Numerical Simulation or DNS) using a Fourier pseudospectral algorithm with triply periodic boundary conditions. The associated zero-circulation constraint is circumvented by solving the governing equations in a proper rotating frame of reference. Using ideas similar to those behind our method to compute the degree of reconnection, we split the vorticity field into its reconnected and non-reconnected parts, which allows to create insightful visualizations of the evolving vortex topology. It also allows to detect regions in the vorticity field that are neither reconnected nor non-reconnected and thus must be associated to internal looping structures. Finally, the Reynolds number dependence of the reconnection time scale Trec is investigated in the range 500 ≤ ReΓ ≤ 10 000. For both initial configurations, the scaling is generally found to vary continuously as ReΓ is increased from T rec ˜ R eΓ - 1 to T rec ˜ R eΓ - 1 / 2 , thus providing quantitative support for previous claims that the reconnection
Experimental Study on Coupled Cross-Flow and in-Line Vortex-Induced Vibration of Flexible Risers
Institute of Scientific and Technical Information of China (English)
GUO Hai-yan; LOU Min
2008-01-01
In this work, we study the coupled cross-flow and in-line vortex-induced vibration (VIV) of a fixedly mounted flexible pipe, which is free to move in cross-flow (Y-) and in-line (X-) direction in a fluid flow where the mass and natural frequencies are precisely the same in both X- and Y-direction. The fluid speed varies from low to high with the corresponding vortex shedding frequency varying from below the first natural frequency to above the second natural frequency of the flexible pipe. Particular emphasis was placed on the investigation of the relationship between in-line and cross-flow vibration. The experimental results analyzed by using these measurements exhibits several valuable features.
Borazjani, Iman; Sotiropoulos, Fotis
2009-01-01
We investigate numerically vortex-induced vibrations (VIV) of two identical two-dimensional elastically mounted cylinders in tandem in the proximity-wake interference regime at Reynolds number Re = 200 for systems having both one (transverse vibrations) and two (transverse and in-line) degrees of freedom (1-DOF and 2-DOF, respectively). For the 1-DOF system the computed results are in good qualitative agreement with available experiments at higher Reynolds numbers. Similar to these experiments our simulations reveal: (1) larger amplitudes of motion and a wider lock-in region for the tandem arrangement when compared with an isolated cylinder; (2) that at low reduced velocities the vibration amplitude of the front cylinder exceeds that of the rear cylinder; and (3) that above a threshold reduced velocity, large-amplitude VIV are excited for the rear cylinder with amplitudes significantly larger than those of the front cylinder. By analysing the simulated flow patterns we identify the VIV excitation mechanisms that lead to such complex responses and elucidate the near-wake vorticity dynamics and vortex-shedding modes excited in each case. We show that at low reduced velocities vortex shedding provides the initial excitation mechanism, which gives rise to a vertical separation between the two cylinders. When this vertical separation exceeds one cylinder diameter, however, a significant portion of the incoming flow is able to pass through the gap between the two cylinders and the gap-flow mechanism starts to dominate the VIV dynamics. The gap flow is able to periodically force either the top or the bottom shear layer of the front cylinder into the gap region, setting off a series of very complex vortex-to-vortex and vortex-to-cylinder interactions, which induces pressure gradients that result in a large oscillatory force in phase with the vortex shedding and lead to the experimentally observed larger vibration amplitudes. When the vortex shedding is the dominant
BORAZJANI, IMAN; SOTIROPOULOS, FOTIS
2009-01-01
We investigate numerically vortex-induced vibrations (VIV) of two identical two-dimensional elastically mounted cylinders in tandem in the proximity–wake interference regime at Reynolds number Re = 200 for systems having both one (transverse vibrations) and two (transverse and in-line) degrees of freedom (1-DOF and 2-DOF, respectively). For the 1-DOF system the computed results are in good qualitative agreement with available experiments at higher Reynolds numbers. Similar to these experiments our simulations reveal: (1) larger amplitudes of motion and a wider lock-in region for the tandem arrangement when compared with an isolated cylinder; (2) that at low reduced velocities the vibration amplitude of the front cylinder exceeds that of the rear cylinder; and (3) that above a threshold reduced velocity, large-amplitude VIV are excited for the rear cylinder with amplitudes significantly larger than those of the front cylinder. By analysing the simulated flow patterns we identify the VIV excitation mechanisms that lead to such complex responses and elucidate the near-wake vorticity dynamics and vortex-shedding modes excited in each case. We show that at low reduced velocities vortex shedding provides the initial excitation mechanism, which gives rise to a vertical separation between the two cylinders. When this vertical separation exceeds one cylinder diameter, however, a significant portion of the incoming flow is able to pass through the gap between the two cylinders and the gap-flow mechanism starts to dominate the VIV dynamics. The gap flow is able to periodically force either the top or the bottom shear layer of the front cylinder into the gap region, setting off a series of very complex vortex-to-vortex and vortex-to-cylinder interactions, which induces pressure gradients that result in a large oscillatory force in phase with the vortex shedding and lead to the experimentally observed larger vibration amplitudes. When the vortex shedding is the dominant
Vortex-based line beam optical tweezers
Cheng, Shubo; Tao, Shaohua
2016-10-01
A vortex-based line beam, which has a straight-line shape of intensity and possesses phase gradient along the line trajectory is developed and applied for optical manipulation in this paper. The intensity and phase distributions of the beam in the imaging plane of the Fourier transform are analytically studied. Simulation results show that the length of the line and phase gradient possessed by a vortex-based line beam are dependent on the topological charge and the azimuthal proportional constant. A superposition of multiple phase-only holograms with elliptical azimuthal phases can be used to generate an array of vortex-based line beams. Optical trapping with the vortex-based line beams has been implemented. Furthermore, the automatic transportation of microparticles along the line trajectory perpendicular to the optical axis is realized with an array of the beams. The generation method for the vortex-based line beam is simple. The beam would have potential applications in fields such as optical trapping, laser machining, and so on.
Vortices and vortex lattices in quantum ferrofluids
Martin, A. M.; Marchant, N. G.; O’Dell, D. H. J.; Parker, N. G.
2017-03-01
The experimental realization of quantum-degenerate Bose gases made of atoms with sizeable magnetic dipole moments has created a new type of fluid, known as a quantum ferrofluid, which combines the extraordinary properties of superfluidity and ferrofluidity. A hallmark of superfluids is that they are constrained to rotate through vortices with quantized circulation. In quantum ferrofluids the long-range dipolar interactions add new ingredients by inducing magnetostriction and instabilities, and also affect the structural properties of vortices and vortex lattices. Here we give a review of the theory of vortices in dipolar Bose–Einstein condensates, exploring the interplay of magnetism with vorticity and contrasting this with the established behaviour in non-dipolar condensates. We cover single vortex solutions, including structure, energy and stability, vortex pairs, including interactions and dynamics, and also vortex lattices. Our discussion is founded on the mean-field theory provided by the dipolar Gross–Pitaevskii equation, ranging from analytic treatments based on the Thomas–Fermi (hydrodynamic) and variational approaches to full numerical simulations. Routes for generating vortices in dipolar condensates are discussed, with particular attention paid to rotating condensates, where surface instabilities drive the nucleation of vortices, and lead to the emergence of rich and varied vortex lattice structures. We also present an outlook, including potential extensions to degenerate Fermi gases, quantum Hall physics, toroidal systems and the Berezinskii–Kosterlitz–Thouless transition.
Nonlinear ion acoustic waves scattered by vortexes
Ohno, Yuji
2015-01-01
The Kadomtsev--Petviashvili (KP) hierarchy is the archetype of infinite-dimensional integrable systems, which describes nonlinear ion acoustic waves in two-dimensional space. This remarkably ordered system resides on a singular submanifold (leaf) embedded in a larger phase space of more general ion acoustic waves (low-frequency electrostatic perturbations). The KP hierarchy is characterized not only by small amplitudes but also by irrotational (zero-vorticity) velocity fields. In fact, the KP equation is derived by eliminating vorticity at every order of the reductive perturbation. Here we modify the scaling of the velocity field so as to introduce a vortex term. The newly derived system of equations consists of a generalized three-dimensional KP equation and a two-dimensional vortex equation. The former describes `scattering' of vortex-free waves by ambient vortexes that are determined by the latter. We say that the vortexes are `ambient' because they do not receive reciprocal reactions from the waves (i.e.,...
Insulation Characteristics of Bushing Shed at Cryogenic Temperature
Kim, W. J.; Kim, Y. J.; Kim, S. H.
2014-05-01
In the development of high-Tc superconducting(HTS) devices, the bushing for HTS devices (HTS bushing) is the core technology, the need to because of supply high voltage to the cable or the winding of the transformer. The lower part of the bushing is exposed to the liquid nitrogen (LN2), and it has many sheds. In particular, the insulation body with sheds and electrical insulation at cryogenic temperature have attracted a great deal of interest from the view point of the size, weight and efficiency of bushing. This study has mainly investigated the shed and insulation body by comparing glass fiber reinforced plastics (GFRP) in LN2. We investigated the surface discharge characteristics according to insulating materials, width and height of the shed.
Study Sheds Light on Safety of Driving with Epilepsy
... Study Sheds Light on Safety of Driving With Epilepsy Those who had longer seizures during driving tests ... SUNDAY, Dec. 4, 2016 (HealthDay News) -- People with epilepsy who experienced longer seizures during a simulated driving ...
Oral shedding of herpes simplex virus type 2
Wald, A; Ericsson, M.; Krantz, E; Selke, S; Corey, L
2004-01-01
Objectives: Herpes simplex virus (HSV) 1 and HSV-2 reactivate preferentially in the oral and genital area, respectively. We aimed to define frequency and characteristics associated with oral shedding of HSV-2.
Asymptomatic Herpes Simplex Virus Shedding in STI Patients
Institute of Scientific and Technical Information of China (English)
叶兴东; 颜景兰; 朱慧兰; 张莉; 佟菊贞
2002-01-01
Objective: This study examined Herpes Simplex Virus(HSV) subclinical shedding in the genital tract of patients withgenital herpes (GH) or non-gonoccal urethritis (NGU). Method: Swabs were collected after exposure to rash andgenital tract during GH relapse or remission on a weekly basisfor four to six weeks. NGU patients with negative chlamydiaand mycoplasma tests were also swabbed for a similarduration. All swabs underwent HSV DNA detection withquantitative PCR. Result: There was a significant difference in the rate ofasymptomatic HSV shedding in urinary tracts comparing GHand the control group and comparing NGU and the controlgroup (P<0.05). The rate of HSV shedding was 22%, 9.8%and 3.3% for GH, NGU and control groups respectively. Therate of HSV shedding was 21.7% (20/92) for patients withactive GH and 23% for those in remission. The HSV positiverate was significantly higher in the group with patients whohad more than six relapses within one year compared to thegroup of patients with less than six GH relapses. Conclusion: There is HSV subclinical shedding in theirgenital tract during active GH and remission. SubclinicalHSV shedding is more common in patients with more than sixGH relapses per year compared to GH patients with fewerrelapses. Approximately 9.9% of NGU patients with negativechlamydia, mycoplasma testing was found to have subclinicalHSV infection.
Capacity building in indigenous men's groups and sheds across Australia.
Southcombe, Amie; Cavanagh, Jillian; Bartram, Timothy
2015-09-01
This article presents an investigation into capacity building, at the community level, in Aboriginal and Torres Strait Islander Men's Groups and Sheds. As safe men's spaces, Men's Groups and Sheds represent an ever-growing social, and health and well-being community service across Australia. The study is qualitative and employs 'yarning circles' (focus groups), semi-structured interviews and observations to gather data from 15 Groups/Sheds involving 45 men from urban, regional and remote communities. We found that capacity building is primarily about securing relationships between Group Leaders/Shed Co-ordinators and Government services. Capacity building establishes links to services such as Centrelink, Medicare, Department of Housing, Probation and Control, and positive outcomes such as Indigenous men securing housing and Centrelink payments. Capacity building results in better health outcomes and, educates and empowers men to improve their social, cultural, emotional and economic well-being. It helps men to better connect with family and community. The current research paves the way for countries worldwide to explore the conceptual and empirical approach of capacity building applicable to other Indigenous [and non-Indigenous] Men's Groups/Sheds. We recommend feasibilities studies, on approaches to capacity building in Indigenous Groups/Sheds, be carried out within urban, regional and remote regions across the country. © The Author (2014). Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.
Optical vortex array in spatially varying lattice
Kapoor, Amit; Senthilkumaran, P; Joseph, Joby
2015-01-01
We present an experimental method based on a modified multiple beam interference approach to generate an optical vortex array arranged in a spatially varying lattice. This method involves two steps which are: numerical synthesis of a consistent phase mask by using two-dimensional integrated phase gradient calculations and experimental implementation of produced phase mask by utilizing a phase only spatial light modulator in an optical 4f Fourier filtering setup. This method enables an independent variation of the orientation and period of the vortex lattice. As working examples, we provide the experimental demonstration of various spatially variant optical vortex lattices. We further confirm the existence of optical vortices by formation of fork fringes. Such lattices may find applications in size dependent trapping, sorting, manipulation and photonic crystals.
Scattering by a draining bathtub vortex
Dolan, Sam R.; Oliveira, Ednilton S.
2013-06-01
We present an analysis of scattering by a fluid-mechanical “black hole analogue,” known as the draining bathtub vortex: a two-dimensional flow that possesses both a sonic horizon and an ergoregion. We consider the scattering of a plane wave of fixed frequency impinging upon the vortex. At low frequency, we encounter a modified Aharonov-Bohm effect. At high frequencies, we observe regular “orbiting” oscillations in the scattering length, due to interference between contra-orbiting rays. We present approximate formulas for both effects and a selection of numerical results obtained by summing partial-wave series. Finally, we examine interference patterns in the vicinity of the vortex and highlight the prospects for experimental investigation.
Scattering by a draining bathtub vortex
Dolan, Sam R
2013-01-01
We present an analysis of scattering by a fluid-mechanical `black hole analogue', known as the draining bathtub (DBT) vortex: a two-dimensional flow which possesses both a sonic horizon and an ergoregion. We consider the scattering of a plane wave of fixed frequency impinging upon the vortex. At low frequency, we encounter a modified Aharonov-Bohm effect. At high frequencies, we observe regular `orbiting' oscillations in the scattering length, due to interference between contra-orbiting rays. We present approximate formulae for both effects, and a selection of numerical results obtained by summing partial-wave series. Finally, we examine interference patterns in the vicinity of the vortex, and highlight the prospects for experimental investigation.
Alternate powers in Serrin's swirling vortex solutions
Bělík, Pavel; Scholz, Kurt; Shvartsman, Mikhail M
2012-01-01
We consider a modification of the fluid flow model for a swirling vortex developed by J. Serrin, where velocity decreases as the reciprocal of the distance from the vortex axis. Recent studies, based on radar data of selected severe weather events, indicate that the angular momentum in a tornado may not be constant with the radius, and thus suggest a different scaling of the velocity/radial distance dependence. Motivated by this suggestion, we consider Serrin's approach with the assumption that the velocity decreases as the reciprocal of the distance from the vortex axis to the power b with a general b>0. This leads to a boundary-value problem for a system of nonlinear differential equations. We analyze this problem for particular cases, both with nonzero and zero viscosity, discuss the question of existence of solutions, and use numerical techniques to describe those solutions that we cannot obtain analytically.
Holographic Vortex Pair Annihilation in Superfluid Turbulence
Du, Yiqiang; Tian, Yu; Zhang, Hongbao
2014-01-01
We make a first principles investigation of the dynamical evolution of vortex number in a two-dimensional (2D) turbulent superfluid by holography through numerically solving its highly non-trivial gravity dual. With the randomly placed vortices and antivortices prepared as initial states, we find that the temporal evolution of the vortex number can be well fit statistically by two-body decay due to the vortex pair annihilation featured relaxation process remarkably from a very early time on. In particular, subtracted by the universal offset, the power law fit indicates that our holographic turbulent superfluid exhibits an apparently different decay pattern from the superfluid recently experimented in highly oblate Bose-Einstein condensates.
Vortex knots in tangled quantum eigenfunctions
Taylor, Alexander J
2016-01-01
Tangles of string typically become knotted, from macroscopic twine down to long-chain macromolecules such as DNA. Here we demonstrate that knotting also occurs in quantum wavefunctions, where the tangled filaments are vortices (nodal lines/phase singularities). The probability that a vortex loop is knotted is found to increase with its length, and a wide gamut of knots from standard tabulations occur. The results follow from computer simulations of random superpositions of degenerate eigenstates of three simple quantum systems: a cube with periodic boundaries, the isotropic 3-dimensional harmonic oscillator and the 3-sphere. In the latter two cases, vortex knots occur frequently, even in random eigenfunctions at relatively low energy, and are constrained by the spatial symmetries of the modes. The results suggest that knotted vortex structures are generic in complex 3-dimensional wave systems, establishing a topological commonality between wave chaos, polymers and turbulent Bose-Einstein condensates.
Convectively driven vortex flows in the Sun
Bonet, J A; Almeida, J Sanchez; Cabello, I; Domingo, V
2008-01-01
We have discovered small whirlpools in the Sun, with a size similar to the terrestrial hurricanes (<~0.5 Mm). The theory of solar convection predicts them, but they had remained elusive so far. The vortex flows are created at the downdrafts where the plasma returns to the solar interior after cooling down, and we detect them because some magnetic bright points (BPs) follow a logarithmic spiral in their way to be engulfed by a downdraft. Our disk center observations show 0.009 vortexes per Mm^2, with a lifetime of the order of 5 min, and with no preferred sense of rotation. They are not evenly spread out over the surface, but they seem to trace the supergranulation and the mesogranulation. These observed properties are strongly biased by our type of measurement, unable to detect vortexes except when they are engulfing magnetic BPs.
Chiral specific electron vortex beam spectroscopy
Yuan, J; Babiker, M
2013-01-01
Electron vortex beams carry well-defined orbital angular momentum (OAM) about the propagation axis. Such beams are thus characterised by chirality features which make them potentially useful as probes of magnetic and other chiral materials. An analysis of the inelastic processes in which electron vortex beams interact with atoms and which involve OAM exchange is outlined, leading to the multipolar selection rules governing this chiral specific electron vortex beam spectroscopy. Our results show clearly that the selection rules are dependent on the dynamical state and location of the atoms involved. In the most favorable scenario, this form of electron spectroscopy can induce magnetic sublevel transitions which are commonly probed using circularly polarized photon beams.
Introduction to vortex filaments in equilibrium
Andersen, Timothy D
2014-01-01
This book presents fundamental concepts and seminal results to the study of vortex filaments in equilibrium. It also presents new discoveries in quasi-2D vortex structures with applications to geophysical fluid dynamics and magnetohydrodynamics in plasmas. It fills a gap in the vortex statistics literature by simplifying the mathematical introduction to this complex topic, covering numerical methods, and exploring a wide range of applications with numerous examples. The authors have produced an introduction that is clear and easy to read, leading the reader step-by-step into this topical area. Alongside the theoretical concepts and mathematical formulations, interesting applications are discussed. This combination makes the text useful for students and researchers in mathematics and physics.
Vortex ventilation in the laboratory environment.
Meisenzahl, Lawrence R
2014-01-01
Assured containment at low airflow has long eluded the users of ventilated enclosures including chemical fume hoods used throughout industry. It is proposed that containment will be enhanced in a hood that has a particular interior shape that causes a natural vortex to occur. The sustained vortex improves the containment of contaminants within the enclosure at low airflow. This hypothesis was tested using the ASHRAE 110 tracer gas test. A known volume of tracer gas was emitted in the hood. A MIRAN SapphIRe infrared spectrometer was used to measure the concentration of tracer gas that escapes the enclosure. The design of the experiment included a written operating procedure, data collection plan, and statistical analysis of the data. A chemical fume hood of traditional design was tested. The hood interior was then reconstructed to enhance the development of a vortex inside the enclosure. The hood was retested using the same method to compare the performance of the traditional interior shape with the enhanced vortex shape. In every aspect, the vortex hood showed significant improvement over the traditional hood design. Use of the Hood Index characterizing the dilution of gas in an air stream as a logarithmic function indicates a causal relationship between containment and volumetric airflow through an enclosure. Use of the vortex effect for ventilated enclosures can provide better protection for the user and lower operating cost for the owner. [Supplementary materials are available for this article. Go to the publisher's online edition of Journal of Occupational and Environmental Hygiene for the following free supplemental resource: a data collection spreadsheet, data analysis, and data collection procedure.].
Vortex lattice theory: A linear algebra approach
Chamoun, George C.
Vortex lattices are prevalent in a large class of physical settings that are characterized by different mathematical models. We present a coherent and generalized Hamiltonian fluid mechanics-based formulation that reduces all vortex lattices into a classic problem in linear algebra for a non-normal matrix A. Via Singular Value Decomposition (SVD), the solution lies in the null space of the matrix (i.e., we require nullity( A) > 0) as well as the distribution of its singular values. We demonstrate that this approach provides a good model for various types of vortex lattices, and makes it possible to extract a rich amount of information on them. The contributions of this thesis can be classified into four main points. The first is asymmetric equilibria. A 'Brownian ratchet' construct was used which converged to asymmetric equilibria via a random walk scheme that utilized the smallest singular value of A. Distances between configurations and equilibria were measured using the Frobenius norm ||·||F and 2-norm ||·||2, and conclusions were made on the density of equilibria within the general configuration space. The second contribution used Shannon Entropy, which we interpret as a scalar measure of the robustness, or likelihood of lattices to occur in a physical setting. Third, an analytic model was produced for vortex street patterns on the sphere by using SVD in conjunction with expressions for the center of vorticity vector and angular velocity. Equilibrium curves within the configuration space were presented as a function of the geometry, and pole vortices were shown to have a critical role in the formation and destruction of vortex streets. The fourth contribution entailed a more complete perspective of the streamline topology of vortex streets, linking the bifurcations to critical points on the equilibrium curves.
Reactive Flow Control of Delta Wing Vortex (Postprint)
2006-08-01
Passive vortex control devices such as vortex generators and winglets attach to the wing and require no energy input. Passive vortex control...width. The dynamic test parameters are summarized in Table 2. The composite duty cycle input signal is denoted ( ) ( )ou t u u tδ= + in which ou
Acoustics of finite-aperture vortex beams
Mitri, F G
2014-01-01
A method based on the Rayleigh-Sommerfeld surface integral is provided, which makes it feasible to rigorously model, evaluate and compute the acoustic scattering and other mechanical effects of finite-aperture vortex beams such as the acoustic radiation force and torque on a viscoelastic sphere in various applications in acoustic tweezers and microfluidics, particle entrapment, manipulation and rotation. Partial-wave series expansions are derived for the incident field of acoustic spiraling (vortex) beams, comprising high-order Bessel and Bessel-Gauss beams.
Characterization of Vortex Generator Induced Flow
DEFF Research Database (Denmark)
Velte, Clara Marika
The aim of this thesis is the characterization and modeling of the longitudinal structures actuated by vortex generators. Results from generic studies performed at low Reynolds numbers have shown that the device induced vortices possess helical structure of the vortex core. Further, their ability...... to control separation and downstream evolution across the chord of a circular sector have been studied. Similar flow structures to the ones found in the generic experiments have been found in a higher Reynolds number setting, more applicable to realistic cases common to, e.g., aeronautical applications...
Paramagnetic excited vortex states in superconductors
Gomes, Rodolpho Ribeiro; Doria, Mauro M.; Romaguera, Antonio R. de C.
2016-06-01
We consider excited vortex states, which are vortex states left inside a superconductor once the external applied magnetic field is switched off and whose energy is lower than of the normal state. We show that this state is paramagnetic and develop here a general method to obtain its Gibbs free energy through conformal mapping. The solution for any number of vortices in any cross-section geometry can be read off from the Schwarz-Christoffel mapping. The method is based on the first-order equations used by Abrikosov to discover vortices.
Center-vortex loops with one selfintersection
Moosmann, Julain
2008-01-01
We investigate the 2D behavior of one-fold selfintersecting, topologically stabilized center-vortex loops in the confining phase of an SU(2) Yang-Mills theory. This coarse-graining is described by curve-shrinking evolution of center-vortex loops immersed in a flat 2D plane driving the renormalization-group flow of an effective `action'. We observe that the system evolves into a highly ordered state at finite noise level, and we speculate that this feature is connected with 2D planar high $T_c$ superconductivity in $FeAs$ systems.
On Stratified Vortex Motions under Gravity.
2014-09-26
AD-A156 930 ON STRATIFIED VORTEX MOTIONS UNDER GRAVITY (U) NAVAL i/i RESEARCH LAB WASHINGTON DC Y T FUNG 20 JUN 85 NRL-MIR-5564 UNCLASSIFIED F/G 20/4...Under Gravity LCn * Y. T. Fung Fluid Dynamics Branch - Marine Technologyv Division June 20, 1985 SO Cyk. NAVAL RESEARCH LABORATORY Washington, D.C...DN880-019 TITLE (Include Security Classification) On Stratified Vortex Motions Under Gravity 12 PERSONAL AUTHOR(S) Funa, Y.T. 13a. TYPE OF REPORT 13b
Intra-cavity vortex beam generation
CSIR Research Space (South Africa)
Naidoo, Darryl
2011-08-01
Full Text Available ? per photon, and may be found as beams expressed in several basis functions, including Laguerre-Gaussian (LGpl) beams1, Bessel-Gaussian beams3 and Airy beams4 to name but a few. LG0l are otherwise known as vortex beams and LG0l beams are routinely... are represented by ?petals? and we show that through a full modal decomposition, the ?petal? fields are a superposition of two LG0l modes. Keywords: Vortex beams, SLM, Laguerre-Gaussian beams, Porro-prism resonator, Petals. 1. INTRODUCTION It is well...
Vortex gyroscope imaging of planar superfluids.
Powis, A T; Sammut, S J; Simula, T P
2014-10-17
We propose a robust imaging technique that makes it possible to distinguish vortices from antivortices in quasi-two-dimensional Bose-Einstein condensates from a single image of the density of the atoms. Tilting the planar condensate prior to standard absorption imaging excites a generalized gyroscopic mode of the condensate, revealing the sign and location of each vortex. This technique is anticipated to enable experimental measurement of the incompressible kinetic energy spectrum of the condensate and the observation of a negative-temperature phase transition of the vortex gas, driven by two-dimensional superfluid turbulence.
Coupled dynamics of vortex-induced vibration and stationary wall at low Reynolds number
Li, Zhong; Jaiman, Rajeev K.; Khoo, Boo Cheong
2017-09-01
The flow past an elastically mounted circular cylinder placed in proximity to a plane wall is numerically studied in both two dimensions (2D) and three dimensions (3D). This paper aims to explain the mechanism of the cylinder bottom shear layer roll-up suppression in the context of laminar vortex-induced vibration (VIV) of a cylinder placed in the vicinity of a plane stationary wall. In 2D simulations, VIV of a near-wall cylinder with structure-to-displaced fluid mass ratios of m* = 2 and 10 is investigated at the Reynolds number of Re = 100 at a representative gap ratio of e/D = 0.90, where e denotes the gap distance between the cylinder surface and the plane wall. First, the cylinder is placed at five different upstream distances, LU, to study the effects of the normalized wall boundary layer thickness, δ /D , on the hydrodynamic quantities involved in the VIV of a near-wall cylinder. It is found that the lock-in range shifts towards the direction of the higher reduced velocity Ur as δ /D increases and that the lock-in range widens as m* reduces. Second, via visualization of the vortex shedding patterns, four different modes are classified and the regime maps are provided for both m* = 2 and 10. Third, the proper orthogonal decomposition analysis is employed to assess the cylinder bottom shear layer roll-up suppression mechanism. For 3D simulations at Re = 200, the circular cylinder of a mass ratio of m* = 10 with a spanwise length of 4D is placed at a gap ratio of e/D = 0.90 and an upstream distance of LU = 10D. The 3D vortex patterns are investigated to re-affirm the vortex shedding suppression mechanism. The pressure distributions around the cylinder are identified within one oscillation cycle of VIV. The pressure and the shear stress distributions on the bottom wall are examined to demonstrate the effects of near-wall VIV on the force distributions along the plane wall. It is found that both the suction pressure and the shear stress right below the cylinder
Experimental Study on the Vortex-Induced Vibration of Towed Pipes
HONG, S.; CHOI, Y. R.; PARK, J.-B.; PARK, Y.-K.; KIM, Y.-H.
2002-01-01
We experimentally attempted to understand the vibration characteristics of a flexible pipe excited by vortex shedding. This has been extensively studied in the previous decades (for example, see Sarpkaya 1979 Journal of Applied Mechanics46, 241-258; Price et al. 1989 Eighth International Conference on Offshore Mechanics and Arctic Engineering, The Hague-March 19 -23, 447-454; Yoerger et al. 1991 Journal of Offshore Mechanics and Arctic Engineering, Transaction of Engineers113, 117-127; Grosenbaugh et al. 1991Journal of Offshore Mechanics and Arctic Engineering, Transaction of Engineers113 , 199-204; Brika and Laneville 1992 Journal of Fluid Mechanics250, 481-508; Chakrabarti et al. 1993 Ocean Engineering20, 135-162; Jong 1983 Ph.D. Dissertation, Department of Ocean Engineering, M. I. T.; Kimet al. 1986 Journal of Energy Resources Technology, Transactions of American Society of Mechanical Engineers108, 77-83). However, there are still areas that need more study. One of them is the relation between spatial characteristics of a flow-induced vibrating pipe, such as its length, the distribution of wave number, and frequency responses. A non-linear mechanism between the responses of in-line and cross-flow directions is also an area of interest, if the pipe is relatively long so that structural modal density is reasonably high. In order to investigate such areas, two kinds of instrumented pipe were designed. The instrumented pipes, of which the lengths are equally 6 m, are wound with rubber and silicon tape in different ways, having different vortex-shedding conditions. One has uniform cross-section of diameter of 26·7 mm, and the other has equally spaced four sub-sections, which are composed of different diameters of 75·9, 61·1, 45·6 and 26·7 mm. Both pipes are towed in a water tank (200 m×16 m×7 m) so that they experienced different vortex-shedding excitations. Various measures were obtained from the towing experiment, including frequency responses, the time
Some interactions of a vortex with a seamount
Energy Technology Data Exchange (ETDEWEB)
McDonald, N.R.; Dunn, D.C. [London University College, London (United Kingdom). Dept. of Mathematics
1999-12-01
The initial value problem for the motion of an equivalent-barotropic vortex which is initially circular and of uniform potential vorticity near a circular seamount of constant dynamics. Counter surgery experiments are used to investigate qualitative changes in behaviour of the vortex-seamount system as these parameters are varied. Of particular note is the generation of additional vortex features by the original vortex as it sweeps fluid from the seamount. Moreover, when the origin vortex is an anticyclone, dipoles are frequently formed over a wide range of parameter values, which subsequently propagate away from the seamount.
A mathematical consideration of vortex thinning in 2D turbulence
Yoneda, Tsuyoshi
2016-01-01
In two dimensional turbulence, vortex thinning process is one of the attractive mechanism to explain inverse energy cascade in terms of vortex dynamics. By direct numerical simulation to the two-dimensional Navier-Stokes equations with small-scale forcing and large-scale damping, Xiao-Wan-Chen-Eyink (2009) found an evidence that inverse energy cascade may proceed with the vortex thinning mechanism. The aim of this paper is to analyze the vortex-thinning mechanism mathematically (using the incompressible Euler equations), and give a mathematical evidence that large-scale vorticity gains energy from small-scale vorticity due to the vortex-thinning process.
Hybrid Vortex Method for the Aerodynamic Analysis of Wind Turbine
Directory of Open Access Journals (Sweden)
Hao Hu
2015-01-01
Full Text Available The hybrid vortex method, in which vortex panel method is combined with the viscous-vortex particle method (HPVP, was established to model the wind turbine aerodynamic and relevant numerical procedure program was developed to solve flow equations. The panel method was used to calculate the blade surface vortex sheets and the vortex particle method was employed to simulate the blade wake vortices. As a result of numerical calculations on the flow over a wind turbine, the HPVP method shows significant advantages in accuracy and less computation resource consuming. The validation of the aerodynamic parameters against Phase VI wind turbine experimental data is performed, which shows reasonable agreement.
Pourmahmoud, Nader; Azar, Farid Sepehrian; Hassanzadeh, Amir
2014-09-01
A vortex tube with additional chamber is investigated by computational fluid mechanics techniques to realize the effects of additional chamber in Ranque-Hilsch vortex tube and to understand optimal length for placing the second chamber in order to have maximum cooling effect. Results show that by increasing the distance between two chambers, both minimum cold and maximum hot temperatures increase and maximum cooling effect occurs at Z/ L = 0.047 (dimensionless distance).
Analysis of Axial Flow Ventilation Fans by Vortex - Method.
Hardin, Richard Anthony
A steady vortex-lattice method is used to solve the lifting surface equation for an axial flow fan. The type of fan studied is designed for industrial and ventilation applications and in thermofluid systems such as cooling towers. The fan blades are thin cambered surfaces manufactured from metal sheets. The numerical approach is inviscid and results in a boundary value problem with viscous effects partially accounted for by application of drag coefficient data. A non-linear wake alignment procedure is used to account for the effects of vorticity shedding in the wake and variation in wake geometry with operating conditions. The wake alignment procedure is semi-free with wake input parameters required for accurate use of the technique. A study of the wake parameters was conducted and gave trends in the variation of their values with flow rate. At "free-air" conditions, flow visualization estimates of these parameters were found to agree with those from the computations. Comparisons are made between the measured and predicted fan performance with and without a surrounding duct. The comparison of the results were especially good at the "free-air" condition using wake parameters determined from flow visualization and an inlet velocity profile measured using hot-wire anemometry. To enable better understanding of basic flow phenomena and to provide data for verification of numerical analyses, a method for measuring unsteady surface pressure on a rotating axial-flow fan blade was devised. Unsteadiness of pressure on the blade surfaces is due to the effects of upstream fan motor supports and other installation features. A pressure transducer and signal amplification circuit were mounted on a circuit board at the rotating hub with signals taken off the rotating shaft through copper disk-mercury slip rings. The pressure difference across the blade was determined and the data were corrected for time lag and distortion caused by the length of tubing. The pressure difference
Flow regimes in a trapped vortex cell
Lasagna, D.; Iuso, G.
2016-03-01
This paper presents results of an experimental investigation on the flow in a trapped vortex cell, embedded into a flat plate, and interacting with a zero-pressure-gradient boundary layer. The objective of the work is to describe the flow features and elucidate some of the governing physical mechanisms, in the light of recent investigations on flow separation control using vortex cells. Hot-wire velocity measurements of the shear layer bounding the cell and of the boundary layers upstream and downstream are reported, together with spectral and correlation analyses of wall-pressure fluctuation measurements. Smoke flow visualisations provide qualitative insight into some relevant features of the internal flow, namely a large-scale flow unsteadiness and possible mechanisms driving the rotation of the vortex core. Results are presented for two very different regimes: a low-Reynolds-number case where the incoming boundary layer is laminar and its momentum thickness is small compared to the cell opening, and a moderately high-Reynolds-number case, where the incoming boundary layer is turbulent and the ratio between the momentum thickness and the opening length is significantly larger than in the first case. Implications of the present findings to flow control applications of trapped vortex cells are also discussed.
Vortex ring breakdown induced by topographic forcing
Energy Technology Data Exchange (ETDEWEB)
Geiser, J; Kiger, K T, E-mail: kkiger@umd.edu [Department of Mechanical Engineering, University of Maryland, College Park, MD 20910 (United States)
2011-12-22
Detailed measurements of the vortex breakdown within a strongly forced impinging jet are presented, with the goal of studying the effects of a small topographic disturbance on the breakdown and turbulence structure. This work is related to an ongoing effort to understand the dynamics of sediment suspension within a landing rotorcraft where a mobile boundary is subject to rapid erosion and deposition. The current work compares the results of a uniform surface to that of a small radial fence placed upstream of the vortex impingement location. The result is a dramatic increase in the coherence of the three-dimensional looping exhibited by the secondary vortex, leading to a more organized and strongly perturbed mean flow. Specifically, a triple decomposition of the velocity fluctuations indicates a very intense periodic stress in the vicinity of the impingement site, followed by a significant decay. Conversely, the random component of the fluctuating stresses gradually increases to modest levels as the coherent contributions decrease, eventually becoming greater than the coherent stress. The fence produces a bifurcation in the flow through the perturbation of the secondary vortex, which in turn creates a high-and low-speed streak on either side of the fence. The subsequent dynamics leads to increased fluctuating stress in the high-speed region, and a dramatically lower stress in the low-speed region, favoring preferential erosion on either side of the topographic disturbance.
Iterative Brinkman penalization for remeshed vortex methods
DEFF Research Database (Denmark)
Hejlesen, Mads Mølholm; Koumoutsakos, Petros; Leonard, Anthony;
2015-01-01
We introduce an iterative Brinkman penalization method for the enforcement of the no-slip boundary condition in remeshed vortex methods. In the proposed method, the Brinkman penalization is applied iteratively only in the neighborhood of the body. This allows for using significantly larger time s...
Chemical Observations of a Polar Vortex Intrusion
Schoeberl, M. R.; Kawa, S. R.; Douglass, A. R.; McGee, T. J.; Browell, E.; Waters, J.; Livesey, N.; Read, W.; Froidevaux, L.
2006-01-01
An intrusion of vortex edge air in D the interior of the Arctic polar vortex was observed on the January 31,2005 flight of the NASA DC-8 aircraft. This intrusion was identified as anomalously high values of ozone by the AROTAL and DIAL lidars. Our analysis shows that this intrusion formed when a blocking feature near Iceland collapsed, allowing edge air to sweep into the vortex interior. along the DC-8 flight track also shows the intrusion in both ozone and HNO3. Polar Stratospheric Clouds (PSCs) were observed by the DIAL lidar on the DC-8. The spatial variability of the PSCs can be explained using MLS HNO3 and H2O observations and meteorological analysis temperatures. We also estimate vortex denitrification using the relationship between N2O and HNO3. Reverse domain fill back trajectory calculations are used to focus on the features in the MLS data. The trajectory results improve the agreement between lidar measured ozone and MLS ozone and also improve the agreement between the HNO3 measurements PSC locations. The back trajectory calculations allow us to compute the local denitrification rate and reduction of HCl within the filament. We estimate a denitrification rate of about lO%/day after exposure to below PSC formation temperature. Analysis of Aura MLS observations made
Soliton algebra by vortex-beam splitting.
Minardi, S; Molina-Terriza, G; Di Trapani, P; Torres, J P; Torner, L
2001-07-01
We experimentally demonstrate the possibility of breaking up intense vortex light beams into stable and controllable sets of parametric solitons. We report observations performed in seeded second-harmonic generation, but the scheme can be extended to all parametric processes. The number of generated solitons is shown to be determined by a robust arithmetic rule.
Superconducting vortex pinning with artificial magnetic nanostructures.
Energy Technology Data Exchange (ETDEWEB)
Velez, M.; Martin, J. I.; Villegas, J. E.; Hoffmann, A.; Gonzalez, E. M.; Vicent, J. L.; Schuller, I. K.; Univ. de Oviedo-CINN; Unite Mixte de Physique CNRS/Thales; Univ. Paris-Sud; Univ.Complutense de Madrid; Univ. California at San Diego
2008-11-01
This review is dedicated to summarizing the recent research on vortex dynamics and pinning effects in superconducting films with artificial magnetic structures. The fabrication of hybrid superconducting/magnetic systems is presented together with the wide variety of properties that arise from the interaction between the superconducting vortex lattice and the artificial magnetic nanostructures. Specifically, we review the role that the most important parameters in the vortex dynamics of films with regular array of dots play. In particular, we discuss the phenomena that appear when the symmetry of a regular dot array is distorted from regularity towards complete disorder including rectangular, asymmetric, and aperiodic arrays. The interesting phenomena that appear include vortex-lattice reconfigurations, anisotropic dynamics, channeling, and guided motion as well as ratchet effects. The different regimes are summarized in a phase diagram indicating the transitions that take place as the characteristic distances of the array are modified respect to the superconducting coherence length. Future directions are sketched out indicating the vast open area of research in this field.
Vortex formation with a snapping shrimp claw.
Directory of Open Access Journals (Sweden)
David Hess
Full Text Available Snapping shrimp use one oversized claw to generate a cavitating high speed water jet for hunting, defence and communication. This work is an experimental investigation about the jet generation. Snapping shrimp (Alpheus-bellulus were investigated by using an enlarged transparent model reproducing the closure of the snapper claw. Flow inside the model was studied using both High-Speed Particle Image Velocimetry (HS-PIV and flow visualization. During claw closure a channel-like cavity was formed between the plunger and the socket featuring a nozzle-type contour at the orifice. Closing the mechanism led to the formation of a leading vortex ring with a dimensionless formation number of approximate ΔT*≈4. This indicates that the claw might work at maximum efficiency, i.e. maximum vortex strength was achieved by a minimum of fluid volume ejected. The subsequent vortex cavitation with the formation of an axial reentrant jet is a reasonable explanation for the large penetration depth of the water jet. That snapping shrimp can reach with their claw-induced flow. Within such a cavitation process, an axial reentrant jet is generated in the hollow cylindrical core of the cavitated vortex that pushes the front further downstream and whose length can exceed the initial jet penetration depth by several times.
Axisymmetric Vortex Simulations with Various Turbulence Models
Directory of Open Access Journals (Sweden)
Brian Howard Fiedler
2010-10-01
Full Text Available The CFD code FLUENT^{TM} has been applied to a vortex within an updraft above a frictional lower boundary. The sensitivity of vortex intensity and structure to the choice of turbulent model is explored. A high Reynolds number of 10^{8} is employed to make the investigation relevant to the atmospheric vortex known as a tornado. The simulations are axisymmetric and are integrated forward in time to equilibrium. In a variety of turbulence models tested, the Reynolds Stress Model allows for the greatest intensification of the vortex, with the azimuthal wind speed near the surface being 2.4 times the speed of the updraft, consistent with the destructive nature of tornadoes. The Standard k-e Model, which is simpler than the Reynolds Stress Model but still more detailed than what is commonly available in numerical weather prediction models, produces an azimuthal wind speed near the surface of at most 0.6 times the updraft speed.
Vortex properties of mesoscopic superconducting samples
Energy Technology Data Exchange (ETDEWEB)
Cabral, Leonardo R.E. [Laboratorio de Supercondutividade e Materiais Avancados, Departamento de Fisica, Universidade Federal de Pernambuco, Recife 50670-901 (Brazil); Barba-Ortega, J. [Grupo de Fi' sica de Nuevos Materiales, Departamento de Fisica, Universidad Nacional de Colombia, Bogota (Colombia); Souza Silva, C.C. de [Laboratorio de Supercondutividade e Materiais Avancados, Departamento de Fisica, Universidade Federal de Pernambuco, Recife 50670-901 (Brazil); Albino Aguiar, J., E-mail: albino@df.ufpe.b [Laboratorio de Supercondutividade e Materiais Avancados, Departamento de Fisica, Universidade Federal de Pernambuco, Recife 50670-901 (Brazil)
2010-10-01
In this work we investigated theoretically the vortex properties of mesoscopic samples of different geometries, submitted to an external magnetic field. We use both London and Ginzburg-Landau theories and also solve the non-linear Time Dependent Ginzburg-Landau equations to obtain vortex configurations, equilibrium states and the spatial distribution of the superconducting electron density in a mesoscopic superconducting triangle and long prisms with square cross-section. For a mesoscopic triangle with the magnetic field applied perpendicularly to sample plane the vortex configurations were obtained by using Langevin dynamics simulations. In most of the configurations the vortices sit close to the corners, presenting twofold or three-fold symmetry. A study of different meta-stable configurations with same number of vortices is also presented. Next, by taking into account de Gennes boundary conditions via the extrapolation length, b, we study the properties of a mesoscopic superconducting square surrounded by different metallic materials and in the presence of an external magnetic field applied perpendicularly to the square surface. It is determined the b-limit for the occurrence of a single vortex in a mesoscopic square of area d{sup 2}, for 4{xi}(0){<=}d{<=}10{xi}(0).
Coherent Vortex Evolution in Drift Wave Turbulence
Gatto, R.; Terry, P. W.
1998-11-01
Localized structures in turbulence are subject to loss of coherence by mixing. Phase space structures, such as drift-hole, (P. W. Terry, P. H. Diamond, T. S. Hahm, Phys. Fluids B) 2 9 2048 (1990) possess a self-electric field, which if sufficiently large maintains particle trapping against the tidal deformations of ambient turbulence. We show here that intense vortices in fluid drift wave turbulence avoid mixing by suppressing ambient turbulence with the strong flow shear of the vortex edge. Analysis of turbulence evolution in the vortex edge recovers Rapid Distortion Theory (G. K. Batchelor and I. Proudman, Q. J. Mech. Appl. Math.) 7 83 (1954) as the short time limit and the shear suppression scaling theory (H. Biglari, P. H. Diamond and P. W. Terry, Phys. Fluids B) 2 1 (1990) as the long time limit. Shear suppression leads to an amplitude condition for coherence and delineates the Gaussian core from the non Gaussian tail of the probability distribution function. The amplitude condition of shear suppression is compared with the trapping condition for phase space holes. The possibility of nonlinear vortex growth will be examined by considering electron dynamics in the vortex evolution.
Wake Vortex Transport and Decay in Ground Effect: Vortex Linking with the Ground
Proctor, Fred H.; Hamilton, David W.; Han, Jongil
2000-01-01
Numerical simulations are carried out with a three-dimensional Large-Eddy Simulation (LES) model to explore the sensitivity of vortex decay and transport in ground effect (IGE). The vortex decay rates are found to be strongly enhanced following maximum descent into ground effect. The nondimensional decay rate is found to be insensitive to the initial values of circulation, height, and vortex separation. The information gained from these simulations is used to construct a simple decay relationship. This relationship compares well with observed data from an IGE case study. Similarly, a relationship for lateral drift due to ground effect is constructed from the LES data. In the second part of this paper, vortex linking with the ground is investigated. Our numerical simulations of wake vortices for IGE show that a vortex may link with its image beneath the ground, if the intensity of the ambient turbulence is moderate to high. This linking with the ground (which is observed in real cases)gives the appearance of a vortex tube that bends to become vertically oriented and which terminates at the ground. From the simulations conducted, the linking time for vortices in the free atmosphere; i.e., a function of ambient turbulence intensity.
Planet-vortex interaction:How a vortex can shepherd a planetary embryo
Kley, W; Meheut, H
2014-01-01
Context: Anticyclonic vortices are considered as a favourable places for trapping dust and forming planetary embryos. On the other hand, they are massive blobs that can interact gravitationally with the planets in the disc. Aims: We aim to study how a vortex interacts gravitationally with a planet which migrates toward it or a planet which is created inside the vortex. Methods: We performed hydrodynamical simulations of a viscous locally isothermal disc using GFARGO and FARGO-ADSG. We set a stationary Gaussian pressure bump in the disc in a way that RWI is triggered. After a large vortex is established, we implanted a low mass planet in the outer disc or inside the vortex and allowed it to migrate. We also examined the effect of vortex strength on the planet migration and checked the validity of the final result in the presence of self-gravity. Results: We noticed regardless of the planet's initial position, the planet is finally locked to the vortex or its migration is stopped in a farther orbital distance i...
Flow visualization of a vortex ring interaction with porous surfaces
Hrynuk, John T.; Van Luipen, Jason; Bohl, Douglas
2012-03-01
The interaction of vortex rings of constant Reynolds number with porous surfaces composed of wire meshes of constant open area, i.e., surface porosity, but variable wire diameter is studied using flow visualization. The results indicate that several regimes of flow behavior exist in the parameter space investigated. The vortex ring passes through and immediately reforms downstream of the surface for porous surfaces with small wire mesh diameters. The transmitted vortex ring has the same diameter, but lower convection speed and circulation than the pre-interaction vortex ring. For these cases, secondary vortex rings are formed on the upstream side of the porous surface that convect upstream away from the screen. As the wire diameter of the porous surface is increased, smaller sub-scale vortical structures are formed on the transmitted vortex ring as it passes through the surface. The spatial scale of these structures is dependent on the diameter of the mesh wire. The vortex ring is disrupted but is able to reform downstream when these structures are small compared to the scale of the vortex ring. When these structures are large enough the transmitted vortex ring is disrupted and does not reform. The results indicate that the dynamics governing the vortex ring/mesh surface interaction are dependent not only on the strength of the vortex ring and the porosity of the surface, as previously thought, but also on the length scales (i.e., the diameter and spacing of the wire mesh) of the porous surface.
Surface Roughness Effects on Vortex Torque of Air Supported Gyroscope
Institute of Scientific and Technical Information of China (English)
LIANG Yingchun; LIU Jingshi; SUN Yazhou; LU Lihua
2011-01-01
In order to improve the drift precision of air supported gyroscope, effects of surface roughness magnitude and direction on vortex torque of air supported gyroscope are studied. Based on Christensen's rough surface stochastic model and consistency transformation method, Reynolds equation of air supported gyroscope containing surface roughness information is established.Also effects of mathematical models of main machining errors on vortex torque are established. By using finite element method,the Reynolds equation is solved numerically and the vortex torque in the presence of machining errors and surface roughness is calculated. The results show that surface roughness of slit has a significant effect on vortex torque. Transverse surface roughness makes vortex torque greater, while longitudinal surface roughness makes vortex torque smaller. The maximal difference approaches 11.4％ during the range analyzed in this article. However surface roughness of journal influences vortex torque insignificantly. The research is of great significance for designing and manufacturing air supported gyroscope and predicting its performance.
Topological Aspect of Knotted Vortex Filaments in Excitable Media
Institute of Scientific and Technical Information of China (English)
REN Ji-Rong; ZHU Tao; DUAN Yi-Shi
2008-01-01
Scroll waves exist ubiquitously in three-dimensional excitable media.The rotation centre can be regarded as a topological object called the vortex filament.In three-dimensional space,the vortex filaments usually form closed loops,and can be even linked and knotted.We give a rigorous topological description of knotted vortex filaments.By using the Φ-mapping topological current theory,we rewrite the topological current form of the charge density of vortex filaments,and using this topological current we reveal that the Hopf invariant of vortex filaments is just the sum of the linking and self-linking numbers of the knotted vortex filaments.We think that the precise expression of the Hopf invariant may imply a new topological constraint on knotted vortex filaments.
Borneo vortex and mesoscale convective rainfall
Koseki, S.; Koh, T.-Y.; Teo, C.-K.
2014-05-01
We have investigated how the Borneo vortex develops over the equatorial South China Sea under cold surge conditions in December during the Asian winter monsoon. Composite analysis using reanalysis and satellite data sets has revealed that absolute vorticity and water vapour are transported by strong cold surges from upstream of the South China Sea to around the Equator. Rainfall is correspondingly enhanced over the equatorial South China Sea. A semi-idealized experiment reproduced the Borneo vortex over the equatorial South China Sea during a "perpetual" cold surge. The Borneo vortex is manifested as a meso-α cyclone with a comma-shaped rainband in the northeast sector of the cyclone. Vorticity budget analysis showed that the growth/maintenance of the meso-α cyclone was achieved mainly by the vortex stretching. This vortex stretching is due to the upward motion forced by the latent heat release around the cyclone centre. The comma-shaped rainband consists of clusters of meso-β-scale rainfall cells. The intense rainfall in the comma head (comma tail) is generated by the confluence of the warmer and wetter cyclonic easterly flow (cyclonic southeasterly flow) and the cooler and drier northeasterly surge in the northwestern (northeastern) sector of the cyclone. Intense upward motion and heavy rainfall resulted due to the low-level convergence and the favourable thermodynamic profile at the confluence zone. In particular, the convergence in the northwestern sector is responsible for maintenance of the meso-α cyclone system. At both meso-α and meso-β scales, the convergence is ultimately caused by the deviatoric strain in the confluence wind pattern but is significantly self-enhanced by the nonlinear dynamics.
Persistence of Metastable Vortex Lattice Domains in MgB2 in the Presence of Vortex Motion
Energy Technology Data Exchange (ETDEWEB)
Rastovski, Catherine [University of Notre Dame, IN; Schlesinger, Kimberly [University of Notre Dame, IN; Gannon, William J [Northwestern University, Evanston; Dewhurst, Charles [Institut Laue-Langevin (ILL); Debeer-Schmitt, Lisa M [ORNL; Zhigadlo, Nikolai [ETH Zurich, Switzerland; Karpinski, Janusz [ETH Zurich, Switzerland; Eskildsen, Morten [University of Notre Dame, IN
2013-01-01
Recently, extensive vortex lattice metastability was reported in MgB2 in connection with a second-order rotational phase transition. However, the mechanism responsible for these well-ordered metastable vortex lattice phases is not well understood. Using small-angle neutron scattering, we studied the vortex lattice in MgB2 as it was driven from a metastable to the ground state through a series of small changes in the applied magnetic field. Our results show that metastable vortex lattice domains persist in the presence of substantial vortex motion and directly demonstrate that the metastability is not due to vortex pinning. Instead, we propose that it is due to the jamming of counterrotated vortex lattice domains which prevents a rotation to the ground state orientation.
Persistence of metastable vortex lattice domains in MgB2 in the presence of vortex motion.
Rastovski, C; Schlesinger, K J; Gannon, W J; Dewhurst, C D; DeBeer-Schmitt, L; Zhigadlo, N D; Karpinski, J; Eskildsen, M R
2013-09-01
Recently, extensive vortex lattice metastability was reported in MgB2 in connection with a second-order rotational phase transition. However, the mechanism responsible for these well-ordered metastable vortex lattice phases is not well understood. Using small-angle neutron scattering, we studied the vortex lattice in MgB2 as it was driven from a metastable to the ground state through a series of small changes in the applied magnetic field. Our results show that metastable vortex lattice domains persist in the presence of substantial vortex motion and directly demonstrate that the metastability is not due to vortex pinning. Instead, we propose that it is due to the jamming of counterrotated vortex lattice domains which prevents a rotation to the ground state orientation.
Automatic load shedding in multiarea elastic power systems
Energy Technology Data Exchange (ETDEWEB)
Di Caprio, U.; Marconato, R.
1979-04-01
A procedure for the design of automatic load shedding in an elastic multiarea power system is proposed. Assuming that the power-frequency transfer functions of the various areas are similar, and that the interconnection network can be approximated by a purely reactive network, separate specifications can be given with regard to the control of the mean-frequency transient and that of the interarea electromechanical oscillations. While the first determines the total load to be shed, the second determines its optimal subdivision in order to maximize the stability margin in the large.
Distributed Load Shedding over Directed Communication Networks with Time Delays
Energy Technology Data Exchange (ETDEWEB)
Yang, Tao; Wu, Di
2016-07-25
When generation is insufficient to support all loads under emergencies, effective and efficient load shedding needs to be deployed in order to maintain the supply-demand balance. This paper presents a distributed load shedding algorithm, which makes efficient decision based on the discovered global information. In the global information discovery process, each load only communicates with its neighboring load via directed communication links possibly with arbitrarily large but bounded time varying communication delays. We propose a novel distributed information discovery algorithm based on ratio consensus. Simulation results are used to validate the proposed method.
Experimental observation of the collision of three vortex rings
Hernández, R. H.; Monsalve, E.
2015-06-01
We investigate for the first time the motion, interaction and simultaneous collision between three initially stable vortex rings arranged symmetrically, making an angle of 120 degrees between their straight path lines. We report results with laminar vortex rings in air and water obtained through measurements of the ring velocity field with a hot-wire anemometer, both in free flight and during the entire collision. In the air experiment, our flow visualizations allowed us to identify two main collision stages. A first ring-dominated stage where the rings slowdown progressively, increasing their diameter rapidly, followed by secondary vortex structures resulting after the rings make contact. Local portions of the vortex tubes of opposite circulation are coupled together thus creating local arm-like vortex structures moving radially in outward directions, rapidly dissipating kinetic energy. From a similar water experiment, we provide detailed shadowgraph visualizations of both the ring bubble and the full size collision, showing clearly the final expanding vortex structure. It is accurately resolved that the physical contact between vortex ring tubes gives rise to three symmetric expanding vortex arms but also the vortex reconnection of the top and lower vortex tubes. The central collision zone was found to have the lowest kinetic energy during the entire collision and therefore it can be identified as a safe zone. The preserved collision symmetries leading to the weak kinematic activity in the safe zone is the first step into the development of an intermittent hydrodynamic trap for small and lightweight particles.
Computational investigation of the temperature separation in vortex chamber
Energy Technology Data Exchange (ETDEWEB)
Anish, S. [National Institute of Technology Karnataka, Mangalore (India); Setoguchi, T. [Institute of Ocean Energy, Saga University (Japan); Kim, H. D. [Andong National University, Andong (Korea, Republic of)
2014-06-15
The vortex chamber is a mechanical device, without any moving parts that separates compressed gas into a high temperature region and a low temperature region. Functionally vortex chamber is similar to a Ranque-Hilsch vortex tube (RVHT), but it is a simpler and compact structure. The objective of the present study is to investigate computationally the physical reasoning behind the energy separation mechanism inside a vortex chamber. A computational analysis has been performed using three-dimensional compressible Navier Stokes equations. A fully implicit finite volume scheme was used to solve the governing equations. A commercial software ANSYS CFX is used for this purpose. The computational predictions were validated with existing experimental data. The results obtained show that the vortex chamber contains a large free vortex zone and a comparatively smaller forced vortex region. The physical mechanism that causes the heating towards periphery of the vortex chamber is identified as the work done by the viscous force. The cooling at the center may be due to expansion of the flow. The extent of temperature separation greatly depends on the outer diameter of the vortex chamber. A small amount of compression is observed towards the periphery of the vortex chamber when the outer diameter is reduced.
Dynamically controlled energy dissipation for fast magnetic vortex switching
Badea, R.; Berezovsky, J.
2017-09-01
Manipulation of vortex states in magnetic media provides new routes towards information storage and processing technology. The typical slow relaxation times (˜100 ns) of magnetic vortex dynamics may present an obstacle to the realization of these applications. Here, we investigate how a vortex state in a ferromagnetic microdisk can be manipulated in a way that translates the vortex core while enhancing energy dissipation to rapidly damp the vortex dynamics. We use time-resolved differential magneto-optical Kerr effect microscopy to measure the motion of the vortex core in response to applied magnetic fields. We first map out how the vortex core becomes sequentially trapped by pinning sites as it translates across the disk. After applying a fast magnetic field step to translate the vortex from one pinning site to another, we observe long-lived dynamics of the vortex as it settles to the new equilibrium. We then demonstrate how the addition of a short (magnetic field pulse can induce additional energy dissipation, strongly damping the long-lived dynamics. A model of the vortex dynamics using the Thiele equation of motion explains the mechanism behind this effect.
Institute of Scientific and Technical Information of China (English)
Akira OGAWA; Tutomu OONO; Hayato OKABE; Noriaki AKIBA; Taketo OOYAGI
2005-01-01
@@ Vortex flow is applied to a cyclone dust collector, a vortex combustion chamber, and a vortex diode for vortex control. In order to apply the vortex flow to the industries, it is necessary to keep the stable flow condition and to estimate the response time of the transient flow process and also the intensity of the vortex flow. For control vortex flow, two types of vortex chamber with two inlet pipes were designed. One of them is to promote the vortex flow named as Co-Rotating Flow System and another one is to hinder the vortex flow named as Counter-Rotating Flow System. The pressure drops and the velocity distributions were measured for these vortex chambers. The estimation of the tangential velocity by the application of the angular momentum flux is compared with the measured velocity by a cylindrical Pitot-tube. The characteristics of the total pressure drop could be explained by introducing the circulation.
Heritage Conservation in the "Back Shed" of the Learning City.
Boshier, Roger
2003-01-01
Describes Back Shed, a group of New Zealand heritage conservationists who center their work in lifelong learning. Situates their activities in the context of the learning city, a community development concept that mobilizes learning resources across many sectors. Discusses heritage conservation as a process of meaning making. (Contains 29…
The transmembrane domain of TACE regulates protein ectodomain shedding
Institute of Scientific and Technical Information of China (English)
Xiaojin Li; Liliana Pérez; Zui Pan; Huizhou Fan
2007-01-01
Numerous membrane proteins are cleaved by tumor necrosis factor-α converting enzyme (TACE), which causes the release of their ectodomains. An ADAM (a disintegrin and metalloprotease domain) family member, TACE contains several noncatalytic domains whose roles in ectodomain shedding have yet to be fully resolved. Here, we have explored the function of the transmembrane domain (TM) of TACE by coupling molecular engineering and functional analysis. A TM-free TACE construct that is anchored to the plasma membrane by a glycosylphosphatidylino-sitol (GPI)-binding polypeptide failed to restore shedding of transforming growth factor-α (TGF-α), tumor necrosis factor-α (TNF-α) and L-selectin in cells lacking endogenous TACE activity. Substitution of the TACE TM with that of the prolactin receptor or platelet-derived growth factor receptor (PDGFR) also resulted in severe loss of TGF-α shedding, but had no effects on the cleavage of TNF-α and L-selectin. Replacement of the TM in TGF-a with that of L-selectin enabled TGF-a shedding by the TACE mutants carrying the TM of prolactin receptor and PDGFR. Taken together, our observations suggest that anchorage of TACE to the lipid bilayer through a TM is required for efficient cleavage of a broad spectrum of substrates, and that the amino-acid sequence of TACE TM may play a role in regulatory specificity among TACE substrates.
Weight-Loss Surgery Sheds Pounds Long Term
... page: https://medlineplus.gov/news/fullstory_160719.html Weight-Loss Surgery Sheds Pounds Long Term 10-year follow- ... 31, 2016 WEDNESDAY, Aug. 31, 2016 (HealthDay News) -- Weight-loss surgery helps people drop a significant amount of ...
Shedding Phenomenon of Ventilated Partial Cavitation around an Underwater Projectile
Institute of Scientific and Technical Information of China (English)
WANG Yi-Wei; HUANG Chen-Guang; DU Te-Zhuan; WU Xian-Qian; FANG Xin; LIANG Nai-Gang; WEI Yan-Peng
2012-01-01
A new shedding phenomenon of ventilated partial cavitations is observed around an axisymmetric projectile in a horizontal launching experiment. The experiment system is established based on SHPB launching and high speed photography. A numerical simulation is carried out based on the homogeneous mixture approach, and its predicted evolutions of cavities are compared with the experimental results. The cavity breaks off by the interaction between the gas injection and the re-entry jet at the middle location of the projectile, which is obviously different from natural cavitation. The mechanism of cavity breaking and shedding is investigated, and the influences of important factors are also discussed.%A new shedding phenomenon of ventilated partial cavitations is observed around an axisymmetric projectile in a horizontal launching experiment.The experiment system is established based on SHPB launching and high speed photography.A numerical simulation is carried out based on the homogeneous mixture approach,and its predicted evolutions of cavities are compared with the experimental results.The cavity breaks off by the interaction between the gas injection and the re-entry jet at the middle location of the projectile,which is obviously different from natural cavitation.The mechanism of cavity breaking and shedding is investigated,and the influences of important factors are also discussed.
Developing of the EV charging and parking shed of BIPV
Institute of Scientific and Technical Information of China (English)
Wu Shaobo; Wei Chuanchuan; Yu Jiang
2013-01-01
Building-integrated photovoltaic (BIPV) is an important application way of solar photovoltaic power. The electric vehicle (EV) charging and parking shed of BIPV is the regeneration energy intellectual integration demonstration application system collection of photovoltaic (PV) grid power,PV off-grid power,EV charging and parking shed,and any part of the functions and their combination will be engaged in practical application on demand. The paper describes the PV shed system structure and design in detail with the present of its actual photos. The shed is 50 m long and 5.5 m wide and capable of parking 18 cars. Under the control of system intellectual con-troller,the power produced by PV from sunlight will charge the parking EV car prior to charging the storage bat-tery,charging the storage battery prior to grid power,grid power at last,and charge the EV by utility grid when it is a cloudy or rainy day.
Older Men as Learners: Irish Men's Sheds as an Intervention
Carragher, Lucia; Golding, Barry
2015-01-01
To date, little attention has been placed on older men (aged 50+ years) as learners, with much of the literature on adult learning concerned with younger age-groups and issues around gender equity directed mainly at women. This article examines the impact of community-based men's sheds on informal and nonformal learning by older men in Ireland. It…
USEPA SHEDS MODEL: METHODOLOGY FOR EXPOSURE ASSESSMENT FOR WOOD PRESERVATIVES
A physically-based, Monte Carlo probabilistic model (SHEDS-Wood: Stochastic Human Exposure and Dose Simulation model for wood preservatives) has been applied to assess the exposure and dose of children to arsenic (As) and chromium (Cr) from contact with chromated copper arsenat...
A Robust Load Shedding Strategy for Microgrid Islanding Transition
Energy Technology Data Exchange (ETDEWEB)
Liu, Guodong [ORNL; Xiao, Bailu [ORNL; Starke, Michael R [ORNL; Ceylan, Oguzhan [ORNL; Tomsovic, Kevin [University of Tennessee, Knoxville (UTK)
2016-01-01
A microgrid is a group of interconnected loads and distributed energy resources. It can operate in either gridconnected mode to exchange energy with the main grid or run autonomously as an island in emergency mode. However, the transition of microgrid from grid-connected mode to islanded mode is usually associated with excessive load (or generation), which should be shed (or spilled). Under this condition, this paper proposes an robust load shedding strategy for microgrid islanding transition, which takes into account the uncertainties of renewable generation in the microgrid and guarantees the balance between load and generation after islanding. A robust optimization model is formulated to minimize the total operation cost, including fuel cost and penalty for load shedding. The proposed robust load shedding strategy works as a backup plan and updates at a prescribed interval. It assures a feasible operating point after islanding given the uncertainty of renewable generation. The proposed algorithm is demonstrated on a simulated microgrid consisting of a wind turbine, a PV panel, a battery, two distributed generators (DGs), a critical load and a interruptible load. Numerical simulation results validate the proposed algorithm.
Vortex wake interactions and energy harvesting from tandem pitching and heaving hydrofoils
Su, Yunxing; Cardona, Jennifer; Miller, Michael; Mandre, Shreyas; Breuer, Kenneth
2016-11-01
Measurements of flow structure and power extraction by tandem pitching and heaving hydrofoils are conducted in a flume. The leading and trailing hydrofoils are synchronized and aligned parallel to the oncoming flow. Force measurements and time-resolved PIV are used to characterize the system. The system efficiency of tandem foils with the same kinematics is quantified as a function of the phase difference between the foils and there exist favorable and unfavorable phase angles and that system efficiencies can be as large as 0.45. For unfavorable phase angles, PIV indicates that the leading edge vortex generated by the trailing foil, which is critical to good energy harvesting, is weakened by the oncoming wake from the leading foil. Conversely, at a favorable phase, the vortex shed from the leading foil enhances the performance of the trailing foil, compensating for the otherwise negative aspects of operating in the wake. A model, combining frequency, separation distance and a characteristic convection velocity, is introduced to predict the optimal phase region and is validated over a range of parameters. By changing the pitching amplitude and phase angle in trailing foil we show that relatively larger pitching amplitudes can further improve the system efficiency. ARPA-e.
Dynamic characteristics of an inclined flexible cylinder undergoing vortex-induced vibrations
Han, Qinghua; Ma, Yexuan; Xu, Wanhai; Lu, Yan; Cheng, Ankang
2017-04-01
A series of experimental tests were conducted on vortex-induced vibrations (VIV) of a flexible inclined cylinder with a yaw angle equals 45° for investigating the response characteristics in a towing tank. The flexible cylinder model was 5.6 m in length and 16 mm in diameter with an aspect ratio of 350 and a mass ratio of 1.9. The Reynolds numbers ranged from about 800 to 16,000.The strain responses were measured directly in both cross-flow (CF) and in-line (IL) directions and corresponding displacements were obtained using a modal approach. The dynamic response characteristics of the inclined flexible cylinder excited by vortex shedding was examined from the aspect of strain response, displacement amplitudes, dominant modes, response frequencies and drag force coefficients. The experimental results indicated that the CF response amplitude could be up to a value of 3.0D and the IL one more than 1.1D. The dominant modes were from 1 to 3 in CF direction and 1 to 5 in IL direction. And it was found that dominant frequencies increased linearly with the reduced velocity. The multi-modal response of the flexible inclined cylinder model excited by VIV was observed and analyzed. Moreover, the values of drag coefficients were in the range of 0.9-2.6.
Vortex and structural dynamics of a flexible cylinder in cross-flow
Energy Technology Data Exchange (ETDEWEB)
Shang, Jessica K., E-mail: jshang@princeton.edu; Stone, Howard A. [Department of Mechanical and Aerospace Engineering, Princeton University, Princeton, New Jersey 08544 (United States); Smits, Alexander J. [Department of Mechanical and Aerospace Engineering, Princeton University, Princeton, New Jersey 08544 (United States); Monash University, VIC 3800 (Australia)
2014-05-15
A low-density, flexible cantilevered cylinder was permitted to vibrate freely under the influence of vortex shedding in the laminar flow regime. We find that the vortex-induced vibrations (VIV) of a flexible cantilever depart from those of a flexible cylinder that is fixed at both ends. In particular, we find discontinuous regions of VIV behavior – here called states – as a function of the reduced velocity U{sup *}. These states are demarcated by discrete changes in the dominant eigenmodes of the structural response as the cylinder vibrates in progressively higher structural modes with increasing U{sup *}. The contribution of structural modes can be identified readily by a modal projection of the cylinder oscillation onto known cantilever beam modes. Oscillation frequencies do not monotonically increase with U{sup *}. The wake response between different states is also found to have distinct characteristics; of particular note is the occurrence of a P+S wake over one of these regions, which is associated with a high-amplitude vibration of the cylinder that is due to the constructive interference of contributing eigenmodes.
Vortex-breakdown and wall-separation states in swirling flows in a straight pipe
Zhang, Yuxin; Rusak, Zvi; Wang, Shixiao
2016-11-01
The appearance of vortex-breakdown and wall-separation states in various incoming swirling flows to a straight circular pipe is investigated. Fixed-in-time profiles of the axial and circumferential velocities and of the azimuthal vorticity are prescribed at the pipe inlet. A parallel flow state is set at the pipe outlet. Following the theory of Wang & Rusak (1997), the outlet state of the steady flow problem is determined for a long pipe by solutions of the columnar (axially-independent) Squire-Long equation. For each of the incoming flows studied, these solutions include the base columnar flow state, a decelerated flow along the centerline, an accelerated flow along the centerline, a vortex-breakdown state and a wall-separation state. These theoretical predictions are numerically realized by flow simulations based on the unsteady flow equations. The simulations shed light on the base flow stability and the dynamics of initial perturbations to the various states. The present study extends all the six bifurcation diagrams of solutions studied in Leclaire & Sipp (2010), who stopped the development of branches of steady states once breakdown and wall-separation states first appear.
Vortex-Induced Vibration of a Circular Cylinder Fitted with a Single Spanwise Tripwire
Vaziri, Ehsan; Ekmekci, Alis
2016-11-01
A spanwise tripwire can be used to alter the coherence and strength of the vortex shedding from cylindrical structures. While this has been well-documented for cylinders in stationary state, there exists a lack of understanding regarding the control induced by spanwise tripwires for cylinders undergoing vortex-induced vibration (VIV). The current experimental research investigates the consequences of spanwise tripping on VIV of a cylinder. Experiments are conducted in a recirculating water tunnel at a Reynolds number of 10,000. The test setup allows the rigid test cylinder to have one-degree-of-freedom vibration in the cross-flow direction as a result of fluid forcing. To measure the cylinder motion, a high-resolution laser displacement sensor is used. The tripwire diameter to cylinder diameter ratio is fixed at 6.1%. Various angular positions of tripwire are studied ranging from 40 to 90 degrees. It is shown that the tripwire location controls the pattern, amplitude, frequency, and mid-position of oscillations significantly. Different oscillation modes are classified based on the observed oscillation pattern, amplitude and frequency. Oscillation amplitude can be reduced by 61% with respect to the amplitude of a clean cylinder undergoing VIV under the same flow condition.
Engineering diagnostics for vortex-induced stay vanes cracks in a Francis turbine
D'Agostini Neto, Alexandre; Gissoni, Humberto, Dr.; Gonçalves, Manuel, Dr.; Cardoso, Rogério; Jung, Alexander, Dr.; Meneghini, Julio, Prof.
2016-11-01
Despite the fact that vortex-induced vibration (VIV) in hydraulic turbines components (especially in stay vanes) is a well-known phenomenon, it still remains challenging for operation and maintenance teams in several power plants around the world. Since the first publication of a similar problem in 1967, literature shows that at least 27 other turbines witnessed strong stay vane vibrations associated with vortex shedding. Recurrent stay vane cracks in a 250 MW Francis turbine in Brazil motivated an engineering study involving prototype measurements, structural and Computational Fluid Dynamics (CFD) analysis in order to determine a proper geometry modification that could eliminate the periodic vortex wake generated at the stay vanes trailing edge. First cracks appeared in 1978 just after the machine was put into operation. A study published in 1982 associated these cracks with dynamic excitations caused by the water flow at high flow conditions. New stay vane profiles were proposed and executed as well as improved welding recommendations. Cracks however, continued to appear requiring welding repairs roughly every two years. Although Voith Hydro was not the original equipment manufacturer for these units, the necessary information was available to study the issue and propose and execute new stay vane profiles. This paper details the approach taken for the study. First, indirect vibration measurements were used to determine vibration frequencies to help to characterize the affected mode shapes. These results were compared to finite element (FE) calculations. Strain gage measurements performed afterwards confirmed the conclusions of this analysis. Next, transient CFD calculations were run to reproduce the measured phenomenon and to serve as a basis for a new stay vane geometry. This modification was then implemented in the actual turbine stay vanes. A new set of indirect vibration measurements indicated the effectiveness of the proposed solution. Final confirmation
Fungal recognition enhances mannose receptor shedding through dectin-1 engagement.
Gazi, Umut; Rosas, Marcela; Singh, Sonali; Heinsbroek, Sigrid; Haq, Imran; Johnson, Simon; Brown, Gordon D; Williams, David L; Taylor, Philip R; Martinez-Pomares, Luisa
2011-03-11
The mannose receptor (MR) is an endocytic type I membrane molecule with a broad ligand specificity that is involved in both hemostasis and pathogen recognition. Membrane-anchored MR is cleaved by a metalloproteinase into functional soluble MR (sMR) composed of the extracellular domains of intact MR. Although sMR production was initially considered a constitutive process, enhanced MR shedding has been observed in response to the fungal pathogen Pneumocystis carinii. In this work, we have investigated the mechanism mediating enhanced MR shedding in response to fungi. We show that other fungal species, including Candida albicans and Aspergillus fumigatus, together with zymosan, a preparation of the cell wall of Saccharomyces cerevisiae, mimic the effect of P. carinii on sMR production and that this effect takes place mainly through β-glucan recognition. Additionally, we demonstrate that MR cleavage in response to C. albicans and bioactive particulate β-glucan requires expression of dectin-1. Our data, obtained using specific inhibitors, are consistent with the canonical Syk-mediated pathway triggered by dectin-1 being mainly responsible for inducing MR shedding, with Raf-1 being partially involved. As in the case of steady-state conditions, MR shedding in response to C. albicans and β-glucan particles requires metalloprotease activity. The induction of MR shedding by dectin-1 has clear implications for the role of MR in fungal recognition, as sMR was previously shown to retain the ability to bind fungal pathogens and can interact with numerous host molecules, including lysosomal hydrolases. Thus, MR cleavage could also impact on the magnitude of inflammation during fungal infection.
Topological fluid mechanics of point vortex motions
Boyland, P; Aref, H; Boyland, Philip; Stremler, Mark; Aref, Hassan
1999-01-01
Topological techniques are used to study the motions of systems of point vortices in the infinite plane, in singly-periodic arrays, and in doubly-periodic lattices. The reduction of each system using its symmetries is described in detail. Restricting to three vortices with zero net circulation, each reduced system is described by a one degree of freedom Hamiltonian. The phase portrait of this reduced system is subdivided into regimes using the separatrix motions, and a braid representing the topology of all vortex motions in each regime is computed. This braid also describes the isotopy class of the advection homeomorphism induced by the vortex motion. The Thurston-Nielsen theory is then used to analyse these isotopy classes, and in certain cases strong conclusions about the dynamics of the advection can be made.
Vortex Generators to Control Boundary Layer Interactions
Babinsky, Holger (Inventor); Loth, Eric (Inventor); Lee, Sang (Inventor)
2014-01-01
Devices for generating streamwise vorticity in a boundary includes various forms of vortex generators. One form of a split-ramp vortex generator includes a first ramp element and a second ramp element with front ends and back ends, ramp surfaces extending between the front ends and the back ends, and vertical surfaces extending between the front ends and the back ends adjacent the ramp surfaces. A flow channel is between the first ramp element and the second ramp element. The back ends of the ramp elements have a height greater than a height of the front ends, and the front ends of the ramp elements have a width greater than a width of the back ends.
Vortex structures in exponentially shaped Josephson junctions
Shukrinov, Yu. M.; Semerdjieva, E. G.; Boyadjiev, T. L.
2005-04-01
We report the numerical calculations of the static vortex structure and critical curves in exponentially shaped long Josephson junctions for in-line and overlap geometries. Stability of the static solutions is investigated by checking the sign of the smallest eigenvalue of the associated Sturm-Liouville problem. The change in the junction width leads to the renormalization of the magnetic flux in comparison with the case of a linear one-dimensional model. We study the influence of the model's parameters, and particularly, the shape parameter on the stability of the states of the magnetic flux. We compare the vortex structure and critical curves for the in-line and overlap geometries. Our numerically constructed critical curve of the Josephson junction matches well with the experimental one.
Simulations Of On Demand Vortex Generators
Koumoutsakos, P.; Mansour, N. N.; Rai, Man Mohan (Technical Monitor)
1995-01-01
The development of a two-dimensional viscous incompressible flow generated by an off center thin oscillating bd on top of a cavity is studied computationally as a prototype of vortex generators. The lid is placed asymmetrically over the cavity so that the gap size is different on either side of the cavity. An adaptive numerical scheme, based on high resolution viscous vortex methods, is used to integrate the vorticity/velocity formulation of the Navier-Stokes equations with the no-slip boun.lary condition enforced on the lid and cavity walls. Depending on the a amplitude and frequency of the oscillation as well as the the gap size, vorticity is ejected in the fluid above the cavity either from the large and/or the small gap. The results of the computations complement ongoing experimental work.
Helicity of the toroidal vortex with swirl
Bannikova, Elena Yu; Poslavsky, Sergey A
2016-01-01
On the basis of solutions of the Bragg-Hawthorne equations we discuss the helicity of thin toroidal vortices with the swirl - the orbital motion along the torus diretrix. It is shown that relationship of the helicity with circulations along the small and large linked circles - directrix and generatrix of the torus - depends on distribution of the azimuthal velocity in the core of the swirling vortex ring. In the case of non-homogeneous swirl this relationship differs from the well-known Moffat relationship - the doubled product of such circulations multiplied by the number of links. The results can be applied to vortices in planetary atmospheres and to vortex movements in the vicinity of active galactic nuclei.
Vortices and vortex lattices in quantum ferrofluids
Martin, A M; O'Dell, D H J; Parker, N G
2016-01-01
The achievement of quantum-degenerate Bose gases composed of atoms with sizeable magnetic dipole moments has realized quantum ferrofluids, a form of fluid which combines the extraordinary properties of superfluidity and ferrofluidity. A hallmark of superfluids is that they are constrained to circulate through vortices with quantized circulation. These excitations underpin a variety of rich phenomena, including vortex lattices, quantum turbulence, the Berenzinksii-Kosterlitz-Thouless transition and Kibble-Zurek defect formation. Here we provide a comprehensive review of the theory of vortices and vortex lattices in quantum ferrofluids created from dipolar Bose-Einstein condensates, exploring the interplay of magnetism with vorticity and contrasting this with the established behaviour in non-dipolar condensates. Our discussion is based on the mean-field theory provided by the dipolar Gross-Pitaevskii equation, from analytic treatments based on the Thomas-Fermi and variational approaches to full numerical simula...
Numerical Study of Tip Vortex Flows
Dacles-Mariani, Jennifer; Hafez, Mohamed
1998-01-01
This paper presents an overview and summary of the many different research work related to tip vortex flows and wake/trailing vortices as applied to practical engineering problems. As a literature survey paper, it outlines relevant analytical, theoretical, experimental and computational study found in literature. It also discusses in brief some of the fundamental aspects of the physics and its complexities. An appendix is also included. The topics included in this paper are: 1) Analytical Vortices; 2) Experimental Studies; 3) Computational Studies; 4) Wake Vortex Control and Management; 5) Wake Modeling; 6) High-Lift Systems; 7) Issues in Numerical Studies; 8) Instabilities; 9) Related Topics; 10) Visualization Tools for Vertical Flows; 11) Further Work Needed; 12) Acknowledgements; 13) References; and 14) Appendix.
Coherent vortex structures in fluids and plasmas
Tur, Anatoli
2017-01-01
This monograph introduces readers to the hydrodynamics of vortex formation, and reviews the last decade of active research in the field, offering a unique focus on research topics at the crossroads of traditional fluids and plasmas. Vortices are responsible for the process of macroscopic transport of momentum, energy and mass, and are formed as the result of spontaneous self-organization. Playing an important role in nature and technology, localized, coherent vortices are regularly observed in shear flows, submerged jets, afterbody flows and in atmospheric boundary layers, sometimes taking on the form of vortex streets. In addition, the book addresses a number of open issues, including but not limited to: which singularities are permitted in a 2D Euler equation besides point vortices? Which other, even more complex, localized vortices could be contained in the Euler equation? How do point vortices interact with potential waves?
Solitary vortex couples in viscoelastic Couette flow
Groisman, A; Groisman, Alexander; Steinberg, Victor
1996-01-01
We report experimental observation of a localized structure, which is of a new type for dissipative systems. It appears as a solitary vortex couple ("diwhirl") in Couette flow with highly elastic polymer solutions. A unique property of the diwhirls is that they are stationary, in contrast to the usual localized wave structures in both Hamiltonian and dissipative systems which are stabilized by wave dispersion. It is also a new object in fluid dynamics - a couple of vortices that build a single entity somewhat similar to a magnetic dipole. The diwhirls arise as a result of a purely elastic instability through a hysteretic transition at negligible Reynolds numbers. It is suggested that the vortex flow is driven by the same forces that cause the Weissenberg effect. The diwhirls have a striking asymmetry between the inflow and outflow, which is also an essential feature of the suggested elastic instability mechanism.
Particle Image Velocimetry Measurment of Flow Across Tube Bundle in Waste Heat Boiler
Institute of Scientific and Technical Information of China (English)
无
2000-01-01
In the present paper the experimental investigations of flow across staggered tube bundles in waste heat boiler are conducted by mans of PIV (Particle Image Velocimetry)system,Flow visualization and velocity distribution of the wake between different cylinders are measured in detail.It is concluded that there are still Von Karman vortices in the wake and the phenomenas of vortex shedding,pairing,merging are observed in the flow.The Von Karman vortices can't fully developed because of the existence of the downstream cylinder.There is interaction between main streams and vortices,and the development of the vortex is enhanced by this interaction.Meanwhile some statistical results are performed.The distribution of correlated variables of the velocity fluctuations μ′μ′，μ′ν′，ν′ν′ and the space correlation coefficients are obtained.
A nonabelian particle–vortex duality
Directory of Open Access Journals (Sweden)
Jeff Murugan
2016-02-01
Full Text Available We define a nonabelian particle–vortex duality as a 3-dimensional analogue of the usual 2-dimensional worldsheet nonabelian T-duality. The transformation is defined in the presence of a global SU(2 symmetry and, although derived from a string theoretic setting, we formulate it generally. We then apply it to so-called “semilocal strings” in an SU(2G×U(1L gauge theory, originally discovered in the context of cosmic string physics.
HYDRAULIC CHARACTERISTICS OF VERTICAL VORTEX AT HYDRAULIC INTAKES
Institute of Scientific and Technical Information of China (English)
CHEN Yun-liang; WU Chao; YE Mao; JU Xiao-ming
2007-01-01
The trace of vertical vortex flow at hydraulic intakes is of the shape of spiral lines, which was observed in the presented experiments with the tracer technique. It represents the fluid particles flow spirally from the water surface to the underwater and rotate around the vortex-axis multi-cycle. This process is similar to the movement of screw. To describe the multi-circle spiral characteristics under the axisymmetric condition, the vertical vortex would change not only in the radial direction but also in the axial direction. The improved formulae for three velocity components for the vertical vortex flow were deduced by using the method of separation of variables in this article. In the improved formulae, the velocity components are the functions of the radial and axial coordinates, so the multi-circle spiral flow of vertical vortex could be simulated. The calculated and measured results for the vertical vortex flow were compared and the causes of errors were analyzed.
GENERALIZED ENERGY CONSERVATION AND UNSTABLE PERTURBATION PROPERTY IN BAROTROPIC VORTEX
Institute of Scientific and Technical Information of China (English)
HUANG Hong; ZHANG Ming
2006-01-01
Based on a barotropic vortex model, generalized energy-conserving equation was derived and two necessary conditions of basic flow destabilization are gained. These conditions correspond to generalized barotropic instability and super speed instability. They are instabilities of vortex and gravity inertial wave respectively. In order to relate to practical situation, a barotropic vortex was analyzed, the basic flow of which is similar to lower level basic wind field of tropical cyclones and the maximum wind radius of which is 500 km.The results show that generalized barotropic instability depending upon the radial gradient of relative vorticity can appear in this vortex. It can be concluded that unstable vortex Rossby wave may appear in barotropic vortex.
Comparison of four different models of vortex generators
DEFF Research Database (Denmark)
Fernandez, U.; Réthoré, Pierre-Elouan; Sørensen, Niels N.
2012-01-01
A detailed comparison between four different models of vortex generators is presented in this paper. To that end, a single Vortex Generator on a flat plate test case has been designed and solved by the following models. The first one is the traditional mesh-resolved VG and the second one, called...... Actuator Vortex Generator Model (AcVG), is based on the lifting force theory of Bender, Anderson and Yagle, the BAY Model, which provides an efficient method for computational fluid dynamic (CFD) simulations of flow with VGs, and the forces are applied into the computational domain using the actuator shape...... model. This AcVG Model enables to simulate the effects of the Vortex Generators without defining the geometry of the vortex generator in the mesh and makes it easier for researchers the investigations of different vortex generator lay outs. Both models have been archived by the in house EllipSys CFD...
Robust and adjustable C-shaped vortex beams
Mousley, M; Babiker, M; Yuan, J
2016-01-01
Wavefront engineering is an important quantum technology. Here, we demonstrate the design and production of a robust C-shaped and orbital angular momentum (OAM) carrying beam in which the doughnut shaped structure contains an adjustable gap. We find that the presence of the vortex line in the core of the beam is crucial for the robustness of the C-shape against beam propagation. The topological charge of the vortex core controls mainly the size of the C, while its opening angle is controlled by the presence of vortex-anti-vortex loops. We demonstrate the generation and characterisation of C-shaped electron vortex beams, although the result is equally applicable to other quantum waves. Applications of C-shaped vortex beams include lithography, dynamical atom sorting and atomtronics.
COMPARATIVE ANALYSIS OF PERFORMANCE CHARACTERISTICS OF JET VORTEX TYPE SUPERCHAGES
Directory of Open Access Journals (Sweden)
A. Rogovyi
2016-06-01
Full Text Available On the basis of mathematical modeling there was carried out a comparative analysis of characteristics of jet vortex type superchargers. Dependences of the energy performance of vortex ejector on the geometry parameters and the largest values in terms of efficiency as well as the coefficient of ejection are analyzed. There were built combined characteristics of vortex chamber pumps and vortex ejectors. Vortex chamber pump has advantage pressure in an exit channel over the vortex ejector, consequently there is a more effective power transmission from a working medium, besides the withdrawal of pumping medium in a tangential channel allows to avoid energy losses owing to rotation of a stream in an exit channel.
Distinct magnetic signatures of fractional vortex configurations in multiband superconductors
Energy Technology Data Exchange (ETDEWEB)
Silva, R. M. da [Programa de Pós-Graduação em Ciência dos Materiais, Universidade Federal de Pernambuco, Av. Prof. Luiz Freire, s/n, 50670-901 Recife-PE (Brazil); Milošević, M. V.; Peeters, F. M. [Departement Fysica, Universiteit Antwerpen, Groenenborgerlaan 171, B-2020 Antwerpen (Belgium); Domínguez, D. [Centro Atómico Bariloche, 8400 San Carlos de Bariloche, Río Negro (Argentina); Aguiar, J. Albino, E-mail: albino@df.ufpe.br [Departamento de Física, Universidade Federal de Pernambuco, Av. Prof. Luiz Freire, s/n, 50670-901 Recife-PE (Brazil); Programa de Pós-Graduação em Ciência dos Materiais, Universidade Federal de Pernambuco, Av. Prof. Luiz Freire, s/n, 50670-901 Recife-PE (Brazil)
2014-12-08
Vortices carrying fractions of a flux quantum are predicted to exist in multiband superconductors, where vortex core can split between multiple band-specific components of the superconducting condensate. Using the two-component Ginzburg-Landau model, we examine such vortex configurations in a two-band superconducting slab in parallel magnetic field. The fractional vortices appear due to the band-selective vortex penetration caused by different thresholds for vortex entry within each band-condensate, and stabilize near the edges of the sample. We show that the resulting fractional vortex configurations leave distinct fingerprints in the static measurements of the magnetization, as well as in ac dynamic measurements of the magnetic susceptibility, both of which can be readily used for the detection of these fascinating vortex states in several existing multiband superconductors.
Competing stability modes in vortex structure formation
Garrett, Stephen; Gostelow, J. Paul; Rona, Aldo; McMullan, W. Andrew
2015-11-01
Nose cones and turbine blades have rotating components and represent very practical geometries for which the behavior of vortex structures is not completely understood. These two different physical cases demonstrate a common theme of competition between mode and vortex types. The literature concerning boundary-layer transition over rotating cones presents clear evidence of an alternative instability mode leading to counter-rotating vortex pairs, consistent with a centrifugal instability. This is in contrast to co-rotating vortices present over rotating disks that arise from crossflow effects. It is demonstrated analytically that this mode competes with the crossflow mode and is dominant only over slender cones. Predictions are aligned with experimental measurements over slender cones. Concurrent experimental work on the flow over swept cylinders shows that organized fine-scale streamwise vorticity occurs more frequently on convex surfaces than is appreciated. The conventional view of purely two-dimensional laminar boundary layers following blunt leading edges is not realistic and such boundary layers need to be treated three-dimensionally, particularly when sweep is present. The vortical structures are counter-rotating for normal cylinders and co-rotating under high sweep conditions. Crossflow instabilities may have a major role to play in the transition process but the streamline curvature mode is still present, and seemingly unchanged, when the boundary layer becomes turbulent.
Optical vortex beam generator at nanoscale level
Garoli, Denis; Zilio, Pierfrancesco; Gorodetski, Yuri; Tantussi, Francesco; De Angelis, Francesco
2016-01-01
Optical beams carrying orbital angular momentum (OAM) can find tremendous applications in several fields. In order to apply these particular beams in photonic integrated devices innovative optical elements have been proposed. Here we are interested in the generation of OAM-carrying beams at the nanoscale level. We design and experimentally demonstrate a plasmonic optical vortex emitter, based on a metal-insulator-metal holey plasmonic vortex lens. Our plasmonic element is shown to convert impinging circularly polarized light to an orbital angular momentum state capable of propagating to the far-field. Moreover, the emerging OAM can be externally adjusted by switching the handedness of the incident light polarization. The device has a radius of few micrometers and the OAM beam is generated from subwavelength aperture. The fabrication of integrated arrays of PVLs and the possible simultaneous emission of multiple optical vortices provide an easy way to the large-scale integration of optical vortex emitters for wide-ranging applications. PMID:27404659
Plasma spectroscopy using optical vortex laser
Yoshimura, Shinji; Aramaki, Mitsutoshi; Terasaka, Kenichiro; Toda, Yasunori; Czarnetzki, Uwe; Shikano, Yutaka
2014-10-01
Laser spectroscopy is a useful tool for nonintrusive plasma diagnostics; it can provide many important quantities in a plasma such as temperature, density, and flow velocity of ions and neutrals from the spectrum obtained by scanning the frequency of narrow bandwidth laser. Obtainable information is, however, limited in principle to the direction parallel to the laser path. The aim of this study is to introduce a Laguerre-Gaussian beam, which is called as optical vortex, in place of a widely used Hermite-Gaussian beam. One of the remarkable properties of the Laguerre-Gaussian beam is that it carries an angular momentum in contrast to the Hermite-Gaussian beam. It follows that particles in the laser beam feel the Doppler effect even in the transverse direction of the laser path. Therefore it is expected that the limitation imposed by the laser path can be overcome by using an optical vortex laser. The concept of optical vortex spectroscopy, the development of the laser system, and some preliminary results of a proof-of-principle experiment will be presented. This work is performed with the support and under the auspices of NINS young scientists collaboration program for cross-disciplinary study, NIFS collaboration research program (NIFS13KOAP026), and JSPS KAKENHI Grant Number 25287152.
Monopole-Antimonopole and Vortex Rings
Teh, R; Teh, Rosy; Wong, Khai-Ming
2004-01-01
The SU(2) Yang-Mills-Higgs theory supports the existence of monopoles, antimonopoles, and vortex rings. In this paper, we would like to present new exact static antimonopole-monopole-antimonopole (A-M-A) configurations. The net magnetic charge of these configurations is always negative one, whilst the net magnetic charge at the origin is always positive one for all positive integer values of the solution parameter $m$. However, when $m$ increases beyond one, vortex rings appear coexisting with these A-M-A configurations. The number of vortex rings increases proportionally with the value of $m$. They are magnetically neutral and are located in space where the Higgs field vanishes. We also show that a single point singularity in the Higgs field need not corresponds to a structureless 1-monopole at the origin but to a zero size monopole-antimonopole-monopole (MAM) structure. These exact solutions are a different kind of BPS solutions as they satisfy the first order Bogomol'nyi equation but possess infinite energ...
Monopole-antimonopole and vortex rings
Teh, Rosy; Wong, Khai-Ming
2005-08-01
The SU(2) Yang-Mills-Higgs theory supports the existence of monopoles, antimonopoles, and vortex rings. In this paper, we would like to present new exact static antimonopole-monopole-antimonopole (A-M-A) configurations. The net magnetic charge of these configurations is always -1, while the net magnetic charge at the origin is always +1 for all positive integer values of the solution's parameter m. However, when m increases beyond 1, vortex rings appear coexisting with these AMA configurations. The number of vortex rings increases proportionally with the value of m. They are located in space where the Higgs field vanishes along rings. We also show that a single-point singularity in the Higgs field does not necessarily correspond to a structureless 1-monopole at the origin but to a zero-size monopole-antimonopole-monopole (MAM) structure when the solution's parameter m is odd. This monopole is the Wu-Yang-type monopole and it possesses the Dirac string potential in the Abelian gauge. These exact solutions are a different kind of Bogomol'nyi-Prasad-Sommerfield (BPS) solutions as they satisfy the first-order Bogomol'nyi equation but possess infinite energy due to a point singularity at the origin of the coordinate axes. They are all axially symmetrical about the z-axis.
Lagrangian analysis of fluid transport in empirical vortex ring flows
Shadden, Shawn C.; Dabiri, John O.; Marsden, Jerrold E.
2006-01-01
In this paper we apply dynamical systems analyses and computational tools to fluid transport in empirically measured vortex ring flows. Measurements of quasisteadily propagating vortex rings generated by a mechanical piston-cylinder apparatus reveal lobe dynamics during entrainment and detrainment that are consistent with previous theoretical and numerical studies. In addition, the vortex ring wake of a free-swimming Aurelia aurita jellyfish is measured and analyzed in the framework of dynami...
Experimental demonstration of vortex pancake in high temperature superconductor
Institute of Scientific and Technical Information of China (English)
WANG Wei-xian; ZHANG Yu-heng
2006-01-01
In order to demonstrate the existence of the vortex pancake in high temperature superconductor experimentally,a configuration in which the current and voltage electrodes lies separately on the top and bottom surface is used.The E-j relation obtained with this electrodes spatial configuration is different from the expected E-j behavior of the stiff vortex line model.Thus,the current results support the existence of the vortex pancake in high temperature superconductor.
Dynamic Evolution Equations for Isolated Smoke Vortexes in Rational Mechanics
2011-01-01
Smoke circle vortexes are a typical dynamic phenomenon in nature. The similar circle vortexes phenomenon appears in hurricane, turbulence, and many others. A semi-empirical method is constructed to get some intrinsic understanding about such circle vortex structures. Firstly, the geometrical motion equations for smoke circle is formulated based on empirical observations. Based on them, the mechanic dynamic motion equations are established. Finally, the general dynamic evolution equations for ...
Wake Vortex Inverse Model User's Guide
Lai, David; Delisi, Donald
2008-01-01
NorthWest Research Associates (NWRA) has developed an inverse model for inverting landing aircraft vortex data. The data used for the inversion are the time evolution of the lateral transport position and vertical position of both the port and starboard vortices. The inverse model performs iterative forward model runs using various estimates of vortex parameters, vertical crosswind profiles, and vortex circulation as a function of wake age. Forward model predictions of lateral transport and altitude are then compared with the observed data. Differences between the data and model predictions guide the choice of vortex parameter values, crosswind profile and circulation evolution in the next iteration. Iterations are performed until a user-defined criterion is satisfied. Currently, the inverse model is set to stop when the improvement in the rms deviation between the data and model predictions is less than 1 percent for two consecutive iterations. The forward model used in this inverse model is a modified version of the Shear-APA model. A detailed description of this forward model, the inverse model, and its validation are presented in a different report (Lai, Mellman, Robins, and Delisi, 2007). This document is a User's Guide for the Wake Vortex Inverse Model. Section 2 presents an overview of the inverse model program. Execution of the inverse model is described in Section 3. When executing the inverse model, a user is requested to provide the name of an input file which contains the inverse model parameters, the various datasets, and directories needed for the inversion. A detailed description of the list of parameters in the inversion input file is presented in Section 4. A user has an option to save the inversion results of each lidar track in a mat-file (a condensed data file in Matlab format). These saved mat-files can be used for post-inversion analysis. A description of the contents of the saved files is given in Section 5. An example of an inversion input
Incidence of Latent Virus Shedding during Space Flight
Mehta, Satish K.; Cohrs, Randall J.; Gilden, Donald H.; Tyring, Stephen K.; Ott, C. Mark; Pierson, Duane L.
2008-01-01
Measurements of immune parameters of both cellular and innate immunity indicate alterations in immune function in astronauts. Immune changes are due to stress and perhaps other factors associated with launch, flight, and landing phases. Medical relevance of observed changes is not known. The reactivation of latent viruses has been identified as an important in vivo indicator of clinically relevant immune changes. The polymerase chain reaction (PCR) was used to detect the presence of specific viral DNA in body fluids. Initial studies demonstrated Epstein-Barr virus (EBV) reactivation during all 3 mission phases. EBV is shed in saliva following reactivation from B-cells. Incidence of EBV in saliva was higher than control subjects during all 3 mission phases. However, quantitative PCR revealed 10-fold higher levels of EBV DNA present in saliva collected during flight than found in pre- and post flight specimens. To determine if other latent viruses showed similar effects, cytomegalovirus (CMV), another herpes virus, shed in urine following reactivation was studied. A very low incidence (less than 2%) of CMV in urine is found in healthy, lowstressed individuals. However, 25-50% of astronauts shed CMV in their urine before, during, or after flight. Our studies are now focused on varicella-zoster virus (VZV), the etiological agent of chicken-pox during childhood and shingles later in life. We demonstrated reactivation of VZV and shedding of the virus during and after spaceflight in saliva of astronauts with no sign of active infection or symptoms. The maximum shedding of VZV occurred during the flight phase and diminishes rapidly during the first five days after landing. We have utilized the same PCR assay for VZV in a clinical study of shingles patients. Generally, shingles patients shed much more VZV in saliva than astronauts. However, the VZV levels in astronauts overlap with the lower range of VZV numbers in shingles patients. Saliva from shingles patients and
Observation of Vortex Patterns in a Magnetized Dusty Plasma System
Institute of Scientific and Technical Information of China (English)
HUANG Feng; YE Maofu; WANG Long; LIU Yanhong
2007-01-01
Vortex patterns of dust particles have been observed in a magnetized dusty plasma system. The formation mechanism of two-dimensional (2D) vortex patterns has been investigated by analysing the forces acting on dust particles and molecular dynamics (MD) simulations in a 2D confined magnetized dusty plasma. It has been found that with a weak confining electric field and a strong magnetic field, the particles' trajectories will form a vortex shape. The simulation results agree with our experimental observations. In our experiments, vortex patterns can be induced via circular rotation of particles by changing the rf (radio-frequency) power in a magnetized dusty plasma.
Dynamic Evolution Equations for Isolated Smoke Vortexes in Rational Mechanics
Jianhua, Xiao
2011-01-01
Smoke circle vortexes are a typical dynamic phenomenon in nature. The similar circle vortexes phenomenon appears in hurricane, turbulence, and many others. A semi-empirical method is constructed to get some intrinsic understanding about such circle vortex structures. Firstly, the geometrical motion equations for smoke circle is formulated based on empirical observations. Based on them, the mechanic dynamic motion equations are established. Finally, the general dynamic evolution equations for smoke vortex are formulated. They are dynamic evolution equations for exact stress field and dynamic evolution equations for average stress field. For industrial application and experimental data processing, their corresponding approximation equations for viscous fluid are given. Some simple discussions are made.
Vortex Strings and Nonabelian sine-Gordon Theories
Park, Q H
1999-01-01
We generalize the Lund-Regge model for vortex string dynamics in 4-dimensional Minkowski space to the arbitrary n-dimensional case. The n-dimensional vortex equation is identified with a nonabelian sine-Gordon equation and its integrability is proven by finding the associated linear equations of the inverse scattering. An explicit expression of vortex coordinates in terms of the variables of the nonabelian sine-Gordon system is derived. In particular, we obtain the n-dimensional vortex soliton solution of the Hasimoto-type from the one soliton solution of the nonabelian sine-Gordon equation.
Two possible mechanisms for vortex self-organization
Institute of Scientific and Technical Information of China (English)
无
2006-01-01
The vortex self-organization is investigated in this paper by four groups of numerical experiments within the framework of quasi-geostrophic model, and based on the experimental results two types of possible mechanisms for vortex self-organization are suggested. The meso-scale topography may enable separated vortices to merge into a larger scale vortex; and the interaction of meso-γand meso-β scale systems may make separated vortices to self organize a typhoon-like vortex circulation.
Wake Vortex Field Measurement Program at Memphis, Tennessee: Data Guide
Campbell, S. D.; Dasey, T. J.; Freehart, R. E.; Heinrichs, R. M.; Mathews, M. P.; Perras, G. H.; Rowe, G. S.
1997-01-01
Eliminating or reducing current restrictions in the air traffic control system due to wake vortex considerations would yield increased capacity, decreased delays, and cost savings. Current wake vortex separation standards are widely viewed as very conservative under most conditions. However, scientific uncertainty about wake vortex behavior under different atmospheric conditions remains a barrier to development of an adaptive vortex spacing system. The objective of the wake vortex field measurement efforts during December, 1994 and August, 1995 at Memphis, TN were to record wake vortex behavior for varying atmospheric conditions and types of aircraft. This effort is part of a larger effort by the NASA Langley Research Center to develop an Aircraft Vortex Spacing System (AVOSS) as an element of the Terminal Area Productivity (TAP) program. The TAP program is being performed in concert with the FAA Terminal Air Traffic Control Automation (TATCA) program and ATC Automation. Wake vortex behavior was observed using a mobile continuous-wave (CW) coherent laser Doppler radar (lidar) developed at Lincoln Laboratory. This lidar features a number of improvements over previous systems, including the first-ever demonstration of an automatic wake vortex detection and tracking algorithm.
Alteration of helical vortex core without change in flow topology
DEFF Research Database (Denmark)
Velte, Clara Marika; Okulov, Valery; Hansen, Martin Otto Laver
2011-01-01
The abrupt expansion of the slender vortex core with changes in flow topology is commonly known as vortex breakdown. We present new experimental observations of an alteration of the helical vortex core in wall bounded turbulent flow with abrupt growth in core size, but without change in flow...... topology. The helical symmetry as such is preserved, although the characteristic parameters of helical symmetry of the vortex core transfer from a smooth linear variation to a different trend under the influence of a non-uniform pressure gradient, causing an increase in helical pitch without changing its...
Helicity conservation under quantum reconnection of vortex rings
Zuccher, Simone
2016-01-01
Here we show that under quantum reconnection, simulated by using the three-dimensional Gross- Pitaevskii equation, self-helicity of a system of two interacting vortex rings remains conserved. By resolving the fine structure of the vortex cores, we demonstrate that total length of the vortex system reaches a maximum at the reconnection time, while both writhe helicity and twist helicity remain separately unchanged throughout the process. Self-helicity is computed by two independent methods, and topological information is based on the extraction and analysis of geometric quantities such as writhe, total torsion and intrinsic twist of the reconnecting vortex rings.
Boson-Vortex Duality in 3+1 Dimensions for Open Vortex Lines Ending on Dark Solitons
Mateo, A Muñoz; Nian, Jun
2016-01-01
We propose a boson-vortex duality in 3+1 dimensions for open vortex lines together with planar dark solitons to which the endpoints of vortex lines are attached. Combining the one-form gauge field living on the soliton plane which couples to the endpoints of vortex lines and the two-form gauge field which couples to vortex lines, we obtain a gauge-invariant dual action of open vortex lines with their endpoints attached to dark solitons. We demonstrate numerically the existence of such stationary composite topological excitations in scalar Bose-Einstein condensates. Dynamically stable states of this type are found at low values of the chemical potential in channeled condensates, where the long-wavelength instability of dark solitons is prevented. Our results are reported for parameters typical of current experiments, and open up a way to explore the interplay of different topological structures in scalar Bose-Einstein condensations.
Kovalev, A S
2003-01-01
A plaquette spin system in a vortex configuration is considered analytically and numerically to treat theoretically the vortex switching in magnetic nanodots due to the action of external circular magnetic field. The initial (linear) stage of the switching is analyzed. The analytical results obtained confirm the numerical data on the plaquette dynamics. Both the numerical analysis and the analytical consideration of the initial activation stage show the importance of taking into account the system azimuthal modes. At the frequencies of these modes the most rapid amplification of the vortex energy and the total out-of-plane magnetization occurs. The growth of the modes amplitudes gives rise to a parametrical activation of the low-frequency symmetric mode, and in turn causes the vortex switching. The results obtained provide a qualitative explanation of the numerical data on vortex switching in large-sized magnetic systems and may be used in experiments on guided effect on vortex polarization in magnetic nanodo...
Syndecan-4 shedding impairs macrovascular angiogenesis in diabetes mellitus
Energy Technology Data Exchange (ETDEWEB)
Li, Ran; Xie, Jun; Wu, Han; Li, Guannan; Chen, Jianzhou; Chen, Qinhua; Wang, Lian; Xu, Biao, E-mail: xubiao@medmail.com.cn
2016-05-20
Purpose: Syndecan-4 (synd4) is a ubiquitous heparan sulfate proteoglycan cell surface receptor that modulates cell proliferation, migration, mechanotransduction, and endocytosis. The extracellular domain of synd4 sheds heavily in acute inflammation, but the shedding of synd4 in chronic inflammation, such as diabetes mellitus (DM), is still undefined. We investigated the alterations of synd4 endothelial expression in DM and the influence of impaired synd4 signaling on angiogenesis in human umbilical vein endothelial cells (HUVECs), diabetic rats, synd4 null mice, and db/db mice. Material and methods: HUVECs were incubated with advanced glycation end products (AGEs). Western blot analysis was used to determine synd4 protein expression and ELISA was used to detect soluble synd4 fragments. The concentration of synd4 in the aortic endothelia of diabetic rats was detected by immunohistochemical staining. Aortic ring assays were performed to study the process of angiogenesis in the diabetic rats and in synd4 null and db/db mice. Recombinant adenoviruses containing the synd4 gene or null were constructed to enhance synd4 aortic expression in db/db mice. Results: Western blot analysis showed decreased expression of the synd4 extracellular domain in HUVECs, and ELISA detected increased soluble fragments of synd4 in the media. Synd4 endothelial expression in the aortas of diabetic rats was decreased. Aortic ring assay indicated impaired angiogenesis in synd4 null and db/db mice, which was partially reversed by synd4 overexpression in db/db mice. Conclusion: Synd4 shedding from vascular endothelial cells played an important role in the diabetes-related impairment of angiogenesis. -- Highlights: •Synd4 shedding from endothelial cells is accelerated under the stimulation of AGEs. •Extracellular domain of synd4 is diminished in the endothelium of DM rats. •Aortic rings of synd4 null mice showed impaired angiogenesis. •Overexpression of synd4 partly rescues macrovascular
Birds shed RNA-viruses according to the pareto principle.
Directory of Open Access Journals (Sweden)
Mark D Jankowski
Full Text Available A major challenge in disease ecology is to understand the role of individual variation of infection load on disease transmission dynamics and how this influences the evolution of resistance or tolerance mechanisms. Such information will improve our capacity to understand, predict, and mitigate pathogen-associated disease in all organisms. In many host-pathogen systems, particularly macroparasites and sexually transmitted diseases, it has been found that approximately 20% of the population is responsible for approximately 80% of the transmission events. Although host contact rates can account for some of this pattern, pathogen transmission dynamics also depend upon host infectiousness, an area that has received relatively little attention. Therefore, we conducted a meta-analysis of pathogen shedding rates of 24 host (avian - pathogen (RNA-virus studies, including 17 bird species and five important zoonotic viruses. We determined that viral count data followed the Weibull distribution, the mean Gini coefficient (an index of inequality was 0.687 (0.036 SEM, and that 22.0% (0.90 SEM of the birds shed 80% of the virus across all studies, suggesting an adherence of viral shedding counts to the Pareto Principle. The relative position of a bird in a distribution of viral counts was affected by factors extrinsic to the host, such as exposure to corticosterone and to a lesser extent reduced food availability, but not to intrinsic host factors including age, sex, and migratory status. These data provide a quantitative view of heterogeneous virus shedding in birds that may be used to better parameterize epidemiological models and understand transmission dynamics.
Birds shed RNA-viruses according to the pareto principle.
Jankowski, Mark D; Williams, Christopher J; Fair, Jeanne M; Owen, Jennifer C
2013-01-01
A major challenge in disease ecology is to understand the role of individual variation of infection load on disease transmission dynamics and how this influences the evolution of resistance or tolerance mechanisms. Such information will improve our capacity to understand, predict, and mitigate pathogen-associated disease in all organisms. In many host-pathogen systems, particularly macroparasites and sexually transmitted diseases, it has been found that approximately 20% of the population is responsible for approximately 80% of the transmission events. Although host contact rates can account for some of this pattern, pathogen transmission dynamics also depend upon host infectiousness, an area that has received relatively little attention. Therefore, we conducted a meta-analysis of pathogen shedding rates of 24 host (avian) - pathogen (RNA-virus) studies, including 17 bird species and five important zoonotic viruses. We determined that viral count data followed the Weibull distribution, the mean Gini coefficient (an index of inequality) was 0.687 (0.036 SEM), and that 22.0% (0.90 SEM) of the birds shed 80% of the virus across all studies, suggesting an adherence of viral shedding counts to the Pareto Principle. The relative position of a bird in a distribution of viral counts was affected by factors extrinsic to the host, such as exposure to corticosterone and to a lesser extent reduced food availability, but not to intrinsic host factors including age, sex, and migratory status. These data provide a quantitative view of heterogeneous virus shedding in birds that may be used to better parameterize epidemiological models and understand transmission dynamics.
Shear driven droplet shedding and coalescence on a superhydrophobic surface
Moghtadernejad, S.; Tembely, M.; Jadidi, M.; Esmail, N.; Dolatabadi, A.
2015-03-01
The interest on shedding and coalescence of sessile droplets arises from the importance of these phenomena in various scientific problems and industrial applications such as ice formation on wind turbine blades, power lines, nacelles, and aircraft wings. It is shown recently that one of the ways to reduce the probability of ice accretion on industrial components is using superhydrophobic coatings due to their low adhesion to water droplets. In this study, a combined experimental and numerical approach is used to investigate droplet shedding and coalescence phenomena under the influence of air shear flow on a superhydrophobic surface. Droplets with a size of 2 mm are subjected to various air speeds ranging from 5 to 90 m/s. A numerical simulation based on the Volume of Fluid method coupled with the Large Eddy Simulation turbulent model is carried out in conjunction with the validating experiments to shed more light on the coalescence of droplets and detachment phenomena through a detailed analysis of the aerodynamics forces and velocity vectors on the droplet and the streamlines around it. The results indicate a contrast in the mechanism of two-droplet coalescence and subsequent detachment with those related to the case of a single droplet shedding. At lower speeds, the two droplets coalesce by attracting each other with successive rebounds of the merged droplet on the substrate, while at higher speeds, the detachment occurs almost instantly after coalescence, with a detachment time decreasing exponentially with the air speed. It is shown that coalescence phenomenon assists droplet detachment from the superhydrophobic substrate at lower air speeds.
A corrective load shedding scheme to mitigate voltage collapse
Energy Technology Data Exchange (ETDEWEB)
Echavarren, F.M.; Lobato, E.; Rouco, L. [School of Engineering, Universidad Pontificia Comillas, C/Alberto Aguilera, 23, 28015 Madrid (Spain)
2006-01-15
Voltage stability is concerned with the ability of a power system to maintain acceptable voltages at all buses. A measure of the power system voltage stability is the distance to the saddle node bifurcation of the power flow equations, which is called the load margin. When the power system load is very high, and/or there exists a large generation-demand imbalance in the power system areas the load margin to the saddle node bifurcation may be too low, and the power system may become close to voltage collapse. In case that active and reactive power generation resources in the importing areas are exhausted, corrective load shedding may become the last option. This paper presents a LP-based optimization load shedding algorithm to improve the load margin. The objective function consists of minimizing the total system demand decrease. First order sensitivities of the load margin with respect to the load to be shed are considered. The performance of the method is illustrated with a scenario of the Spanish power system. (author)
HSV oropharyngeal shedding among HIV-infected children in Tanzania.
Zuckerman, Richard; Manji, Karim; Matee, Mecky; Naburi, Helga; Bisimba, Jema; Martinez, Raquel; Wieland-Alter, Wendy; Kim, Faith; von Reyn, C Fordham; Palumbo, Paul
2015-06-01
Herpes simplex virus (HSV) oral shedding has not been studied among HIV-positive children in Africa. We sought to evaluate longitudinal oral HSV reactivation in HIV-positive and -negative children. Twenty HIV-positive antiretroviral-naive and 10 HIV-negative children aged 3-12 years in Tanzania were followed prospectively for 14 days. Oral swabs were collected daily and submitted for HSV DNA PCR analysis. Clinical data were collected via chart review and daily diaries. HSV DNA was detected in 10 (50%) of HIV-positive and 4 (40%) of HIV-negative children. Children who shed HSV had virus detected in a median of 21.4% of samples; shedding was intermittent. Median CD4 count among HIV-infected children was 667 cells/µL in those with positive HSV DNA and 886 cells/µL in those who were negative (p = 0.6). Of the HIV-positive children reporting prior sores, five (83%) had positive HSV swabs, whereas the one HIV-negative child with prior sores did not have a PCR-positive swab. HSV is detected frequently in children with and without HIV. HIV-infected children reporting oral sores have a high rate of HSV detection. Given the proven strong interactions between HIV and HSV, further study of co-infection with these viruses is warranted in children.
Autotransfusion of shed mediastinal blood after open heart surgery
Institute of Scientific and Technical Information of China (English)
赵康丽; 许建屏; 胡盛寿; 吴清玉; 魏以桢; 刘迎龙
2003-01-01
Objective To determine the safety and effectiveness of autotransfusion of shed mediastinal blood after open heart surgery. Methods Sixty patients undergoing coronary artery bypass grafting (CABG) were selected randomly to receive either nonwashed shed mediastinal blood (Group 1, n=30) or banked blood (Group 2, n=30). Drainage and transfusion volume were determined after the operation. Hb, RBC, HCT and PLT were detected immediately before and after the operation, as well as 24 hours and 7 days after the operation. Data were analyzed using Fisher's exact test. A P0.05). In the two groups, no significant difference in the mean blood loss was observed during 24 hours after the operation (660±300 ml in Group 1 and 655±280 ml in Group 2, P>0.05). In Group 1, the mean volume autotransfused was 280±160 ml, and the patients required 360±80 ml banked blood compared with 660±120 ml in Group 2. In other words, the banked blood requirement in Group 1 was 40% lower. Conclusions Autotransfusion of shed mediastinal blood after an open heart operation is safe and effective.
Guiding-center dynamics of vortex dipoles in Bose-Einstein condensates
Energy Technology Data Exchange (ETDEWEB)
Middelkamp, S.; Schmelcher, P. [Zentrum fuer Optische Quantentechnologien, Universitaet Hamburg, Luruper Chaussee 149, DE-22761 Hamburg (Germany); Torres, P. J. [Departamento de Matematica Aplicada, Universidad de Granada, ES-18071 Granada (Spain); Kevrekidis, P. G. [Department of Mathematics and Statistics, University of Massachusetts, Amherst, Massachusetts 01003-4515 (United States); Frantzeskakis, D. J. [Department of Physics, University of Athens, Panepistimiopolis, Zografos, Athens 157 84 (Greece); Carretero-Gonzalez, R. [Nonlinear Dynamical System Group, Computational Science Research Center and Department of Mathematics and Statistics, San Diego State University, San Diego, California 92182-7720 (United States); Freilich, D. V.; Hall, D. S. [Department of Physics, Amherst College, Amherst, Massachusetts 01002-5000 (United States)
2011-07-15
A quantized vortex dipole is the simplest vortex molecule, comprising two countercirculating vortex lines in a superfluid. Although vortex dipoles are endemic in two-dimensional superfluids, the precise details of their dynamics have remained largely unexplored. We present here several striking observations of vortex dipoles in dilute-gas Bose-Einstein condensates, and develop a vortex-particle model that generates vortex line trajectories that are in good agreement with the experimental data. Interestingly, these diverse trajectories exhibit essentially identical quasiperiodic behavior, in which the vortex lines undergo stable epicyclic orbits.
Institute of Scientific and Technical Information of China (English)
赵锐霞; 尹亮; 潘玲英
2012-01-01
对PMI泡沫夹层结构整流罩冯卡门锥段成型技术进行了研究,通过对玻璃钢面板及其泡沫夹层结构性能、面板成型、泡沫热成形、泡沫拼接、玻璃钢泡沫夹层结构成型及无损检测等技术研究,确定了玻璃钢外面板、预先固化,然后与泡沫等复合组装,最后铺覆内面板,整体进罐固化的成型工艺.结果表明,玻璃钢面板纵、横向拉伸强度为602、593MPa,模量为26.0、27.2 GPa,满足设计强度≥350MPa、模量≥25GPa的要求；玻璃钢/PMI泡沫夹层结构泡沫密度为(110±10)kg/m3,厚度28mm,纵、横向侧压强度为32.9、30.5MPa、模量为2.31、2.38GPa,满足设计指标侧压强度≥25MPa、模量≥2.0GPa的要求,采用玻璃钢/PMI 泡沫夹层结构分步固化成型工艺研制的首件新型号整流罩冯卡门锥段,满足设计使用要求.%The processing technology of Von Karman Fairing Fabricated by PMI Foam Sandwich Structure was investigated. The processing method was determined by the investigation on the properties of glass fiber reinforced composite and foam structure, the thermoforming and splicing of foam, the processing of composite and sandwich structure, and the nondestructive testing technology. The results show that the lognitudinal and transverse strength of glass reinforced composite panel are respectively 602 MPa and 593 MPa. The lognitudinal and transverse modulus of panel are respectively 26. 0 GPa and 27. 2 GPa. The lognitudinal and transverse edgewise compression strength of foam sandwich structure with density of (110±10) kg/m3 and thickness of 8mm are respectively 32. 9 MPa and 30. 5 MPa. The lognitudinal and transverse edgewise compression modulus of foam sandwich structure are respectively 2.31 GPa and 2. 38 GPa. The mechanical properties of panel and foam sandwich can meet the design requirements. In addition , the lest Von Karman Fairing fabricated with the PMI foam sandwich structure with glass fiber reinforced composite
Vortex erosion in a shallow water model of the polar vortex
Beaumont, Robin; Kwasniok, Frank; Thuburn, John
2017-06-01
The erosion of a model stratospheric polar vortex in response to bottom boundary forcing is investigated numerically. Stripping of filaments of air from the polar vortex has been implicated in the occurrence of stratospheric sudden warmings (SSWs) but it is not understood in detail what factors determine the rate and amount of stripping. Here a shallow water vortex forced by topography is used to investigate the factors initiating stripping and whether this leads the vortex to undergo an SSW. It is found that the amplitude of topographic forcing must exceed some threshold (of order 200-450 m) in order for significant stripping to occur. For larger forcing amplitudes significant stripping occurs, but not as an instantaneous response to the forcing; rather, the forcing appears to initiate a process that ultimately results in stripping several tens of days later. There appears to be no simple quantitative relationship between the amount of mass stripped and the topography amplitude. However, at least over the early stages of the experiments, there is a good correlation between the amount of mass stripped and the global integral of wave activity, which may be interpreted as a measure of the accumulated topographic forcing. Finally there does not appear to be a simple correspondence between amount of mass stripped and the occurrence of an SSW.
A Hybrid Vortex Sheet / Point Vortex Model for Unsteady Separated Flows
Darakananda, Darwin; Eldredge, Jeff D.; Colonius, Tim; Williams, David R.
2015-11-01
The control of separated flow over an airfoil is essential for obtaining lift enhancement, drag reduction, and the overall ability to perform high agility maneuvers. In order to develop reliable flight control systems capable of realizing agile maneuvers, we need a low-order aerodynamics model that can accurately predict the force response of an airfoil to arbitrary disturbances and/or actuation. In the present work, we integrate vortex sheets and variable strength point vortices into a method that is able to capture the formation of coherent vortex structures while remaining computationally tractable for control purposes. The role of the vortex sheet is limited to tracking the dynamics of the shear layer immediately behind the airfoil. When parts of the sheet develop into large scale structures, those sections are replaced by variable strength point vortices. We prevent the vortex sheets from growing indefinitely by truncating the tips of the sheets and transfering their circulation into nearby point vortices whenever the length of sheet exceeds a threshold. We demonstrate the model on a variety of canonical problems, including pitch-up and impulse translation of an airfoil at various angles of attack. Support by the U.S. Air Force Office of Scientific Research (FA9550-14-1-0328) with program manager Dr. Douglas Smith is gratefully acknowledged.
Observational Facts of Sustained Departure Plateau Vortexes
Institute of Scientific and Technical Information of China (English)
YU Shuhua; GAO Wenliang; PENG Jun; XIAO Yuhua
2014-01-01
By using the twice-daily atmospheric observation data from 1998 to 2012, station rainfall data, Tropical Rainfall Measure Mission (TRMM) data, as well as the plateau vortex and shear line year book, charac-teristics of the sustained departure plateau vortexes (SDPVs) are analyzed. Some new useful observational facts and understanding are obtained about the SDPV activities. The following results are obtained. (1) The active period of SDPVs is from June to August, most in July, unlike that of the unsustained depar-ture plateau vortexes (UDPVs), which have same occurrence frequencies in the three summer months. (2) The SDPVs, generated mainly in the Qumalai neighborhood and situated in a sheared surrounding, move eastward or northeastward, while the UDPVs are mainly led by the upper-level trough, and move eastward or southeastward. (3) The SDPVs influence wide areas of China, even far to the Korean Peninsula, Japan, and Vietnam. (4) The SDPVs change their intensities and properties on the way to the east. Most of them become stronger and produce downpour or sustained regional rainstorms to the south of Yellow River. (5) The longer the SDPV sustains, the more baroclinity it has. (6) When an SDPV moves into the sea, its central pressure descends and rainfall increases in all probability. (7) An SDPV might spin over the bend of the Yellow River when there exists a tropical cyclone in the East China Sea. It could also move oppositely to a landed tropical low pressure originated from the sea to the east of Taiwan or from the South China Sea.
Frequency response of Lamb-Oseen vortex
Blanco-Rodríguez, F. J.; Parras, L.; del Pino, C.
2016-12-01
In this numerical study we present the frequency response of the Lamb-Oseen (Gaussian) vortex for two synthetic jet configurations. The first one consists of an annular axial jet that is superimposed on the Gaussian vortex. The other configuration deals with an off-axis, single-point, axial jet (SPI). We detect that the system responds to the forcing for a given axial wavenumber, k, exciting natural modes of the vortex by a resonance mechanism. We propose an explanation for the physical mechanism responsible for the maximum energy gain obtained by comparing our results with the different branches found theoretically by Fabre et al (2006 J. Fluid Mech. 551 235-74). We find high energy gains in both cases ({G}∞ ≃ {10}3 for the annular jet and {G}∞ ≃ {10}4 for the SPI jet), so these types of forcing are able to produce responses of the system strong enough to reach a non-linear state. Axisymmetric modes, with azimuthal wavenumber m = 0, produce the highest energy gain while applying an annular forcing. However, other modes, such as the helical one m = 1 and also double helix modes with m = 2, contribute in the SPI configuration. We find that the best region to be tested experimentally in both cases is the region that corresponds to the L2 branch described by Fabre and his collaborators. Furthermore, and whenever using these L2 branch frequencies, the response of the system is always axisymmetric, independently of the type of excitation. Finally, we conclude that the energy gain with the SPI jet is one order of magnitude greater than for the annular jet, so that the single-point off-axis jet is a feasible candidate to design a control device.