Modelling Velocity Spectra in the Lower Part of the Planetary Boundary Layer

DEFF Research Database (Denmark)

Olesen, H.R.; Larsen, Søren Ejling; Højstrup, Jørgen

1984-01-01

of the planetary boundary layer. Knowledge of the variation with stability of the (reduced) frequency f, for the spectral maximum is utilized in this modelling. Stable spectra may be normalized so that they adhere to one curve only, irrespective of stability, and unstable w-spectra may also be normalized to fit...... one curve. The problem of using filtered velocity variances when modelling spectra is discussed. A simplified procedure to provide a first estimate of the filter effect is given. In stable, horizontal velocity spectra, there is often a ‘gap’ at low frequencies. Using dimensional considerations...... and the spectral model previously derived, an expression for the gap frequency is found....

A diagnostic approach to obtaining planetary boundary layer winds using satellite-derived thermal data

Science.gov (United States)

Belt, Carol L.; Fuelberg, Henry E.

1984-01-01

The feasibility of using satellite derived thermal data to generate realistic synoptic scale winds within the planetary boundary layer (PBL) is examined. Diagnostic modified Ekman wind equations from the Air Force Global Weather Central (AFGWC) Boundary Layer Model are used to compute winds at seven levels within the PBL transition layer (50 m to 1600 m AGL). Satellite derived winds based on 62 predawn TIROS-N soundings are compared to similarly derived wind fields based on 39 AVE-SESAME II rawinsonde (RAOB) soundings taken 2 h later. Actual wind fields are also used as a basis for comparison. Qualitative and statistical comparisons show that the Ekman winds from both sources are in very close agreement, with an average vector correlation coefficient of 0.815. Best results are obtained at 300 m AGL. Satellite winds tend to be slightly weaker than their RAOB counterparts and exhibit a greater degree of cross-isobaric flow. The modified Ekman winds show a significant improvement over geostrophic values at levels nearest the surface.

Evaluating Models Of The Neutral, Barotropic Planetary Boundary Layer Using Integral Measures: Part Ii. Modelling Observed Conditions

Science.gov (United States)

Hess, G. D.; Garratt, J. R.

The steady-state, horizontally homogeneous, neutral, barotropiccase forms the foundation of our theoretical understanding of the planetary boundary layer (PBL).While simple analytical models and first-order closure models simulate atmospheric observationsof this case well, more sophisticated models, in general, do not. In this paperwe examine how well three higher-order closure models, E - - l, E - l, and LRR - l,which have been especially modified for PBL applications, perform in predicting the behaviour of thecross-isobaric angle 0, the geostrophic drag coefficient Cg, and the integral of the dissipationrate over the boundary layer, as a function of the surface Rossby number Ro. For comparison we alsoexamine the performance of three first-order closure mixing-length models, two proposed byA. K. Blackadar and one by H. H. Lettau, and the performance of the standard model forsecond-order closure and a modification of it designed to reduce the overprediction of turbulence inthe upper part of the boundary layer.

Studies of planetary boundary layer by infrared thermal imagery

Energy Technology Data Exchange (ETDEWEB)

Albina, Bogdan; Dimitriu, Dan Gheorghe, E-mail: dimitriu@uaic.ro; Gurlui, Silviu Octavian, E-mail: dimitriu@uaic.ro [Alexandru Ioan Cuza University of Iasi, Faculty of Physics, Atmosphere Optics, Spectroscopy and Lasers Laboratory, 11 Carol I Blvd., 700506 Iasi (Romania); Cazacu, Marius Mihai [Alexandru Ioan Cuza University of Iasi, Faculty of Physics, Atmosphere Optics, Spectroscopy and Lasers Laboratory, 11 Carol I Blvd., 700506 Iasi, Romania and Department of Physics, Gheorghe Asachi Technical University of Iasi, 59A Mangeron Blvd., 700 (Romania); Timofte, Adrian [Alexandru Ioan Cuza University of Iasi, Faculty of Physics, Atmosphere Optics, Spectroscopy and Lasers Laboratory, 11 Carol I Blvd., 700506 Iasi, Romania and National Meteorological Administration, Regional Forecast Center Bacau, 1 Cuza Voda Str., 60 (Romania)

2014-11-24

The IR camera is a relatively novel device for remote sensing of atmospheric thermal processes from the Planetary Boundary Layer (PBL) based on measurements of the infrared radiation. Infrared radiation is energy radiated by the motion of atoms and molecules on the surface of aerosols, when their temperature is more than absolute zero. The IR camera measures directly the intensity of radiation emitted by aerosols which is converted by an imaging sensor into an electric signal, resulting a thermal image. Every image pixel that corresponds to a specific radiance is pre-processed to identify the brightness temperature. The thermal infrared imaging radiometer used in this study, NicAir, is a precision radiometer developed by Prata et al. The device was calibrated for the temperature range of 270–320 K and using a calibration table along with image processing software, important information about variations in temperature can be extracted from acquired IR images. The PBL is the lowest layer of the troposphere where the atmosphere interacts with the ground surfaces. The importance of PBL lies in the fact that it provides a finite but varying volume in which pollutants can disperse. The aim of this paper is to analyze the PBL altitude and thickness variations over Iasi region using the IR imaging camera as well as its behavior from day to night and thermal processes occurring in PBL.

Novel lidar algorithms for atmospheric slantrange visibility, planetary boundary layer height, meteorogical phenomena and atmospheric layering measurements

Science.gov (United States)

Pantazis, Alexandros; Papayannis, Alexandros; Georgoussis, Georgios

2018-04-01

In this paper we present a development of novel algorithms and techniques implemented within the Laser Remote Sensing Laboratory (LRSL) of the National Technical University of Athens (NTUA), in collaboration with Raymetrics S.A., in order to incorporate them into a 3-Dimensional (3D) lidar. The lidar is transmitting at 355 nm in the eye safe region and the measurements then are transposed to the visual range at 550 nm, according to the World Meteorological Organization (WMO) and the International Civil Aviation Organization (ICAO) rules of daytime visibility. These algorithms are able to provide horizontal, slant and vertical visibility for tower aircraft controllers, meteorologists, but also from pilot's point of view. Other algorithms are also provided for detection of atmospheric layering in any given direction and vertical angle, along with the detection of the Planetary Boundary Layer Height (PBLH).

Effects of air pollution on thermal structure and dispersion in an urban planetary boundary layer

Science.gov (United States)

Viskanta, R.; Johnson, R. O.; Bergstrom, R. W.

1977-01-01

The short-term effects of urbanization and air pollution on the transport processes in the urban planetary boundary layer (PBL) are studied. The investigation makes use of an unsteady two-dimensional transport model which has been developed by Viskanta et al., (1976). The model predicts pollutant concentrations and temperature in the PBL. The potential effects of urbanization and air pollution on the thermal structure in the urban PBL are considered, taking into account the results of numerical simulations modeling the St. Louis, Missouri metropolitan area.

The surface roughness and planetary boundary layer

Science.gov (United States)

Telford, James W.

1980-03-01

Applications of the entrainment process to layers at the boundary, which meet the self similarity requirements of the logarithmic profile, have been studied. By accepting that turbulence has dominating scales related in scale length to the height above the surface, a layer structure is postulated wherein exchange is rapid enough to keep the layers internally uniform. The diffusion rate is then controlled by entrainment between layers. It has been shown that theoretical relationships derived on the basis of using a single layer of this type give quantitatively correct factors relating the turbulence, wind and shear stress for very rough surface conditions. For less rough surfaces, the surface boundary layer can be divided into several layers interacting by entrainment across each interface. This analysis leads to the following quantitatively correct formula compared to published measurements. 1 24_2004_Article_BF00877766_TeX2GIFE1.gif {σ _w }/{u^* } = ( {2/{9Aa}} )^{{1/4}} ( {1 - 3^{{1/2}{ a/k{d_n }/z{σ _w }/{u^* }z/L} )^{{1/4}} = 1.28(1 - 0.945({{σ _w }/{u^* }}}) {{z/L}})^{{1/4 where u^* = ( {{tau/ρ}}^{{1/2}}, σ w is the standard deviation of the vertical velocity, z is the height and L is the Obukhov scale lenght. The constants a, A, k and d n are the entrainment constant, the turbulence decay constant, Von Karman's constant, and the layer depth derived from the theory. Of these, a and A, are universal constants and not empirically determined for the boundary layer. Thus the turbulence needed for the plume model of convection, which resides above these layers and reaches to the inversion, is determined by the shear stress and the heat flux in the surface layers. This model applies to convection in cool air over a warm sea. The whole field is now determined except for the temperature of the air relative to the water, and the wind, which need a further parameter describing sea surface roughness. As a first stop to describing a surface where roughness elements

The BLLAST field experiment: Boundary-Layer Late Afternoon and Sunset Turbulence

NARCIS (Netherlands)

Lothon, M.; Lohou, F.; Pino, D.; Vilà-Guerau De Arellano, J.; Hartogensis, O.K.; Boer, van de A.; Coster, de O.; Moene, A.F.; Steeneveld, G.J.

2014-01-01

Due to the major role of the sun in heating the earth's surface, the atmospheric planetary boundary layer over land is inherently marked by a diurnal cycle. The afternoon transition, the period of the day that connects the daytime dry convective boundary layer to the night-time stable boundary

Modelization of a large wind farm, considering the modification of the atmospheric boundary layer

Energy Technology Data Exchange (ETDEWEB)

Crespo, A; Gomez-Elvira, R [Univ. Politecnica de Madrid, Mecanica de Fluidos, E.T.S.I. Industriales, Madrid (Spain); Frandsen, S; Larsen, S E [Risoe National Lab., Roskilde (Denmark)

1999-03-01

A method is presented to adapt existing models of wind farms to very large ones that may affect the whole planetary boundary layer. An internal boundary layer is considered that starts developing at the leading edge of the farm until it reaches, sufficiently far downstream, the top of the planetary boundary layer, and a new equilibrium region is reached. The wind farm is simulated by an artificial roughness that is function of the turbine spacing, drag and height. From this model the flow conditions are calculated at a certain reference height and then are used as boundary conditions for a numerical code used to model a wind farm. Three-dimensional effects are considered by applying appropriate conditions at the sides of the farm. Calculations are carried out to estimate the energy production in large wind farms, and it is found that additional losses due to modification of the planetary boundary layer may be of importance for wind farms of size larger than about 100 km. (au)

Relations between overturning length scales at the Spanish planetary boundary layer

Science.gov (United States)

López, Pilar; Cano, José L.

2016-04-01

tides and Thorpe scale in Uchiura Bay, Journal of Oceanography, 59, 845-850, 2003. López P., Cano J. L., Cano D. and Tijera M.: Thorpe method applied to planetary boundary layer data, Il Nuovo Cimento, 31C(5-6), 881-892, 2008. DOI: 10.1393/ncc/i2009-10338-3. Lorke A. and Wüest A.: Probability density of displacement and overturning length scales under diverse stratification, J. Geophys. Res., 107 (C12), 3214-3225, 2002. Piera, J., Roget, E. and Catalan, J.: Turbulent patch identification in microstructure profiles: a method based on wavelet denoising and Thorpe displacement analysis, J. Atmospheric and Oceanic Technology, 19, 1390-1402, 2002. Piera, J.: Signal processing of microstructure profiles: integrating turbulent spatial scales in aquatic ecological modelling, Ph. D. Thesis, Gerona University, Spain, 2004. Smyth, W. D. and Moum, J. N.: Length scales of turbulence in stably stratified mixing layers, Phys. Fluids., 12, 1327-1342, 2000. Thorpe, S.A.: Turbulence and Mixing in a Scottish Loch, Philos. Trans. R. Soc. London (Ser. A), 286(1334), 125-18, 1977.

An investigation of ozone and planetary boundary layer dynamics over the complex topography of Grenoble combining measurements and modeling

OpenAIRE

Couach , O.; Balin , I.; Jiménez , R.; Ristori , P.; Perego , S.; Kirchner , F.; Simeonov , V.; Calpini , B.; Van Den Bergh , H.

2003-01-01

This paper concerns an evaluation of ozone (O3) and planetary boundary layer (PBL) dynamics over the complex topography of the Grenoble region through a combination of measurements and mesoscale model (METPHOMOD) predictions for three days, during July 1999. The measurements of O3 and PBL structure were obtained with a Differential Absorption Lidar (DIAL) system, situated 20 km south of Grenoble at Vif (310 m ASL). The combined lidar observations ...

Modeling dynamic behavior of Radon-222 in the planetary boundary layer

International Nuclear Information System (INIS)

Yuan, Y.C.; Stunder, M.J.

1983-01-01

A model has been used to simulate the dynamic behavior of radon concentration in the lower atmosphere from naturally occurring sources. The model includes prediction of radon exhalation rate from the surface of the ground due to convection and diffusion processes and the radon concentration profile in the planetary boundary layer. A time-dependent radon exhalation rate, variable mixing height, and altitude-dependent diffusivity are incorporated into the diffusion model by transforming the governing equation. The Galerkin finite-element technique and Crank-Nicholson finite different time marching are used in solving the discretized differential equations. The model-simulated time-varying radon concentrations near the ground agree well with measurements made over a period of seven days. It has been demonstrated that the model provides a reasonably good prediction of ambient radon concentration. As a general tool, with the input of actual radon concentration measurements, the model is also capable of estimating average radon exhalation rate from the ground surface. With current techniques, radon flux measurement is still a time-consuming and difficult task

Intercomparison of Martian Lower Atmosphere Simulated Using Different Planetary Boundary Layer Parameterization Schemes

Science.gov (United States)

Natarajan, Murali; Fairlie, T. Duncan; Dwyer Cianciolo, Alicia; Smith, Michael D.

2015-01-01

We use the mesoscale modeling capability of Mars Weather Research and Forecasting (MarsWRF) model to study the sensitivity of the simulated Martian lower atmosphere to differences in the parameterization of the planetary boundary layer (PBL). Characterization of the Martian atmosphere and realistic representation of processes such as mixing of tracers like dust depend on how well the model reproduces the evolution of the PBL structure. MarsWRF is based on the NCAR WRF model and it retains some of the PBL schemes available in the earth version. Published studies have examined the performance of different PBL schemes in NCAR WRF with the help of observations. Currently such assessments are not feasible for Martian atmospheric models due to lack of observations. It is of interest though to study the sensitivity of the model to PBL parameterization. Typically, for standard Martian atmospheric simulations, we have used the Medium Range Forecast (MRF) PBL scheme, which considers a correction term to the vertical gradients to incorporate nonlocal effects. For this study, we have also used two other parameterizations, a non-local closure scheme called Yonsei University (YSU) PBL scheme and a turbulent kinetic energy closure scheme called Mellor- Yamada-Janjic (MYJ) PBL scheme. We will present intercomparisons of the near surface temperature profiles, boundary layer heights, and wind obtained from the different simulations. We plan to use available temperature observations from Mini TES instrument onboard the rovers Spirit and Opportunity in evaluating the model results.

A study of the dilution potential of the planetary boundary layer over India and adjoining oceans using radon measurements

International Nuclear Information System (INIS)

Rangarajan, C; Eapen, C.D.

1990-01-01

A comparison is made of the dilution potential of the Planetary Boundary Layer (PBI) at surface and high altitude locations in India and over the oceans of the Arabian Sea, Bay of Bengal region, using radon as a tracer. The significant difference in the diffusive properties of the PBL at these locations and their variations through the seasons are discussed and the use of these studies for plant siting pointed out. (author)

Characterization of a Planetary Boundary Layer model to evaluate radionuclides releases in nuclear installations

International Nuclear Information System (INIS)

Molnary, Leslie de

1993-01-01

A two layer bulk model is used to simulate numerically the time and spatial evolution of concentration of radionuclides in the Planetary Boundary Layer (PBL) for convective and stable conditions. In this model, the closure hypothesis are based on the integrated version of the Turbulent Kinetics Energy (TKE) equation (Smeda,1979). This type of model was adopted here because it is numerically simple to be applied operationally in routine and emergency support systems of atmospheric releases at nuclear power plants, and the hypothesis of the efficiency of the vertical mixing seems to be physically reasonable to simulated PBL evolution for high wind conditions and stable conditions in Subtropical latitudes regions. In order to validate the model to the nuclear power plants of the Centro Experimental Aramar (CEA), located in Ipero, State of Sao Paulo, Brazil, numerical simulations were carried out with initial and boundary conditions based on vertical profiles of temperature and horizontal wind speed and direction obtained from tethered balloon soundings, synoptic charts at 850 hPa and surface observations. Comparisons between a 24 hour long numerical simulation and observations indicate that the model is capable of reproduce the diurnal evolution of temperature and horizontal wind during the convective regime. During stable conditions, the slab model was able to simulate the intensity of the surface inversion as a difference between the mixed layer and surface temperatures. The simulated mixed layer height matches with observations during the convective and stable regime. A daytime release of radionuclides was simulated for CEA region and the results indicated that the maximum relative concentration reaches a distance about 15 Km in 1 hour, varing from 100 times background at the moment of the release to 15 times the background. For night releases, the maximum concentration reaches the same distance in 45 minutes, varing from 100 to 30 times the background values

Estimating Planetary Boundary Layer Heights from NOAA Profiler Network Wind Profiler Data

Science.gov (United States)

Molod, Andrea M.; Salmun, H.; Dempsey, M

2015-01-01

An algorithm was developed to estimate planetary boundary layer (PBL) heights from hourly archived wind profiler data from the NOAA Profiler Network (NPN) sites located throughout the central United States. Unlike previous studies, the present algorithm has been applied to a long record of publicly available wind profiler signal backscatter data. Under clear conditions, summertime averaged hourly time series of PBL heights compare well with Richardson-number based estimates at the few NPN stations with hourly temperature measurements. Comparisons with clear sky reanalysis based estimates show that the wind profiler PBL heights are lower by approximately 250-500 m. The geographical distribution of daily maximum PBL heights corresponds well with the expected distribution based on patterns of surface temperature and soil moisture. Wind profiler PBL heights were also estimated under mostly cloudy conditions, and are generally higher than both the Richardson number based and reanalysis PBL heights, resulting in a smaller clear-cloudy condition difference. The algorithm presented here was shown to provide a reliable summertime climatology of daytime hourly PBL heights throughout the central United States.

Estimating the planetary boundary layer height from radiosonde and doppler lidar measurements in the city of São Paulo - Brazil

Science.gov (United States)

Marques, Márcia T. A.; Moreira, Gregori de A.; Pinero, Maciel; Oliveira, Amauri P.; Landulfo, Eduardo

2018-04-01

This study aims to compare the planetary boundary layer height (PBLH) values estimated by radiosonde data through the bulk Richardson number (BRN) method and by Doppler lidar measurements through the Carrier to Noise Ratio (CNR) method, which corresponds to the maximum of the variance of CNR profile. The measurement campaign was carried during the summer of 2015/2016 in the city of São Paulo. Despite the conceptual difference between these methods, the results show great agreement between them.

Evaluating winds and vertical wind shear from Weather Research and Forecasting model forecasts using seven planetary boundary layer schemes

DEFF Research Database (Denmark)

Draxl, Caroline; Hahmann, Andrea N.; Pena Diaz, Alfredo

2014-01-01

with different PBL parameterizations at one coastal site over western Denmark. The evaluation focuses on determining which PBL parameterization performs best for wind energy forecasting, and presenting a validation methodology that takes into account wind speed at different heights. Winds speeds at heights...... regarding wind energy at these levels partly depends on the formulation and implementation of planetary boundary layer (PBL) parameterizations in these models. This study evaluates wind speeds and vertical wind shears simulated by theWeather Research and Forecasting model using seven sets of simulations...

Planetary Boundaries: Exploring the Safe Operating Space for Humanity

DEFF Research Database (Denmark)

Richardson, Katherine; Rockström, Johan; Steffen, Will

2009-01-01

boundaries are rough, first estimates only, surrounded by large uncertainties and knowledge gaps. Filling these gaps will require major advancements in Earth System and resilience science. The proposed concept of "planetary boundaries" lays the groundwork for shifting our approach to governance...... and management, away from the essentially sectoral analyses of limits to growth aimed at minimizing negative externalities, toward the estimation of the safe space for human development. Planetary boundaries define, as it were, the boundaries of the "planetary playing field" for humanity if we want to be sure...

Solution of the advection-diffusion equation for a nonhomogeneous and nonstationary Planetary Boundary Layer by GILTT (Generalized Integral Laplace Transform Technique)

International Nuclear Information System (INIS)

Mello, Kelen Berra de

2005-02-01

In this work is shown the solution of the advection-diffusion equation to simulate a pollutant dispersion in the Planetary Boundary Layer. The solution is obtained through of the GILTT (Generalized Integral Laplace Transform Technique) analytic method and of the numerical inversion Gauss Quadrature. The validity of the solution is proved using concentration obtained from the model with concentration obtained for Copenhagen experiment. In this comparison was utilized potential and logarithmic wind profile and eddy diffusivity derived by Degrazia et al (1997) [17] and (2002) [19]. The best results was using the potential wind profile and the eddy diffusivity derived by Degrazia et al (1997). The vertical velocity influence is shown in the plume behavior of the pollutant concentration. Moreover, the vertical and longitudinal velocity provided by Large Eddy Simulation (LES) was stood in the model to simulate the turbulent boundary layer more realistic, the result was satisfactory when compared with contained in the literature. (author)

The climatology of planetary boundary layer height in China derived from radiosonde and reanalysis data

Directory of Open Access Journals (Sweden)

J. Guo

2016-10-01

Full Text Available The important roles of the planetary boundary layer (PBL in climate, weather and air quality have long been recognized, but little is known about the PBL climatology in China. Using the fine-resolution sounding observations made across China and reanalysis data, we conducted a comprehensive investigation of the PBL in China from January 2011 to July 2015. The boundary layer height (BLH is found to be generally higher in spring and summer than that in fall and winter. The comparison of seasonally averaged BLHs derived from observations and reanalysis, on average, shows good agreement, despite the pronounced inconsistence in some regions. The BLH, derived from soundings conducted three or four times daily in summer, tends to peak in the early afternoon, and the diurnal amplitude of BLH is higher in the northern and western subregions of China than other subregions. The meteorological influence on the annual cycle of BLH is investigated as well, showing that BLH at most sounding sites is negatively associated with the surface pressure and lower tropospheric stability, but positively associated with the near-surface wind speed and temperature. In addition, cloud tends to suppress the development of PBL, particularly in the early afternoon. This indicates that meteorology plays a significant role in the PBL processes. Overall, the key findings obtained from this study lay a solid foundation for us to gain a deep insight into the fundamentals of PBL in China, which helps to understand the roles that the PBL plays in the air pollution, weather and climate of China.

HESS Opinions: A planetary boundary on freshwater use is misleading

Science.gov (United States)

Heistermann, Maik

2017-07-01

In 2009, a group of prominent Earth scientists introduced the planetary boundaries (PB) framework: they suggested nine global control variables, and defined corresponding thresholds which, if crossed, could generate unacceptable environmental change. The concept builds on systems theory, and views Earth as a complex adaptive system in which anthropogenic disturbances may trigger non-linear, abrupt, and irreversible changes at the global scale, and push the Earth system outside the stable environmental state of the Holocene. While the idea has been remarkably successful in both science and policy circles, it has also raised fundamental concerns, as the majority of suggested processes and their corresponding planetary boundaries do not operate at the global scale, and thus apparently lack the potential to trigger abrupt planetary changes. This paper picks up the debate with specific regard to the planetary boundary on global freshwater use. While the bio-physical impacts of excessive water consumption are typically confined to the river basin scale, the PB proponents argue that water-induced environmental disasters could build up to planetary-scale feedbacks and system failures. So far, however, no evidence has been presented to corroborate that hypothesis. Furthermore, no coherent approach has been presented to what extent a planetary threshold value could reflect the risk of regional environmental disaster. To be sure, the PB framework was revised in 2015, extending the planetary freshwater boundary with a set of basin-level boundaries inferred from environmental water flow assumptions. Yet, no new evidence was presented, either with respect to the ability of those basin-level boundaries to reflect the risk of regional regime shifts or with respect to a potential mechanism linking river basins to the planetary scale. So while the idea of a planetary boundary on freshwater use appears intriguing, the line of arguments presented so far remains speculative and

Two-wavelength Lidar inversion algorithm for determining planetary boundary layer height

Science.gov (United States)

Liu, Boming; Ma, Yingying; Gong, Wei; Jian, Yang; Ming, Zhang

2018-02-01

This study proposes a two-wavelength Lidar inversion algorithm to determine the boundary layer height (BLH) based on the particles clustering. Color ratio and depolarization ratio are used to analyze the particle distribution, based on which the proposed algorithm can overcome the effects of complex aerosol layers to calculate the BLH. The algorithm is used to determine the top of the boundary layer under different mixing state. Experimental results demonstrate that the proposed algorithm can determine the top of the boundary layer even in a complex case. Moreover, it can better deal with the weak convection conditions. Finally, experimental data from June 2015 to December 2015 were used to verify the reliability of the proposed algorithm. The correlation between the results of the proposed algorithm and the manual method is R2 = 0.89 with a RMSE of 131 m and mean bias of 49 m; the correlation between the results of the ideal profile fitting method and the manual method is R2 = 0.64 with a RMSE of 270 m and a mean bias of 165 m; and the correlation between the results of the wavelet covariance transform method and manual method is R2 = 0.76, with a RMSE of 196 m and mean bias of 23 m. These findings indicate that the proposed algorithm has better reliability and stability than traditional algorithms.

Response of neutral boundary-layers to changes of roughness

DEFF Research Database (Denmark)

Sempreviva, Anna Maria; Larsen, Søren Ejling; Mortensen, Niels Gylling

1990-01-01

boundary layer where again the drag laws can be used to estimate the surface wind. To study this problem, data have been sampled for two years from four 30-m meteorological masts placed from 0 to 30 km inland from the North Sea coast of Jutland in Denmark. The present analysis is limited to neutral......When air blows across a change in surface roughness, an internal boundary layer (IBL) develops within which the wind adapts to the new surface. This process is well described for short fetches, > 1 km. However, few data exist for large fetches on how the IBL grows to become a new equilibrium...... stratification, and the surface roughness is the main parameter. The analysis of wind data and two simple models, a surface layer and a planetary boundary layer (PBL) model, are described. Results from both models are discussed and compared with data analysis. Model parameters have been evaluated and the model...

Assessment of Planetary-Boundary-Layer Schemes in the Weather Research and Forecasting Model Within and Above an Urban Canopy Layer

Science.gov (United States)

Ferrero, Enrico; Alessandrini, Stefano; Vandenberghe, Francois

2018-03-01

We tested several planetary-boundary-layer (PBL) schemes available in the Weather Research and Forecasting (WRF) model against measured wind speed and direction, temperature and turbulent kinetic energy (TKE) at three levels (5, 9, 25 m). The Urban Turbulence Project dataset, gathered from the outskirts of Turin, Italy and used for the comparison, provides measurements made by sonic anemometers for more than 1 year. In contrast to other similar studies, which have mainly focused on short-time periods, we considered 2 months of measurements (January and July) representing both the seasonal and the daily variabilities. To understand how the WRF-model PBL schemes perform in an urban environment, often characterized by low wind-speed conditions, we first compared six PBL schemes against observations taken by the highest anemometer located in the inertial sub-layer. The availability of the TKE measurements allows us to directly evaluate the performances of the model; results of the model evaluation are presented in terms of quantile versus quantile plots and statistical indices. Secondly, we considered WRF-model PBL schemes that can be coupled to the urban-surface exchange parametrizations and compared the simulation results with measurements from the two lower anemometers located inside the canopy layer. We find that the PBL schemes accounting for TKE are more accurate and the model representation of the roughness sub-layer improves when the urban model is coupled to each PBL scheme.

Atmospheric Boundary Layer Modeling for Combined Meteorology and Air Quality Systems

Science.gov (United States)

Atmospheric Eulerian grid models for mesoscale and larger applications require sub-grid models for turbulent vertical exchange processes, particularly within the Planetary Boundary Layer (PSL). In combined meteorology and air quality modeling systems consistent PSL modeling of wi...

An iterative procedure for estimating areally averaged heat flux using planetary boundary layer mixed layer height and locally measured heat flux

Energy Technology Data Exchange (ETDEWEB)

Coulter, R. L.; Gao, W.; Lesht, B. M.

2000-04-04

Measurements at the central facility of the Southern Great Plains (SGP) Cloud and Radiation Testbed (CART) are intended to verify, improve, and develop parameterizations in radiative flux models that are subsequently used in General Circulation Models (GCMs). The reliability of this approach depends upon the representativeness of the local measurements at the central facility for the site as a whole or on how these measurements can be interpreted so as to accurately represent increasingly large scales. The variation of surface energy budget terms over the SGP CART site is extremely large. Surface layer measurements of the sensible heat flux (H) often vary by a factor of 2 or more at the CART site (Coulter et al. 1996). The Planetary Boundary Layer (PBL) effectively integrates the local inputs across large scales; because the mixed layer height (h) is principally driven by H, it can, in principal, be used for estimates of surface heat flux over scales on the order of tens of kilometers. By combining measurements of h from radiosondes or radar wind profiles with a one-dimensional model of mixed layer height, they are investigating the ability of diagnosing large-scale heat fluxes. The authors have developed a procedure using the model described by Boers et al. (1984) to investigate the effect of changes in surface sensible heat flux on the mixed layer height. The objective of the study is to invert the sense of the model.

Exploring the planetary boundary for chemical pollution

DEFF Research Database (Denmark)

Diamond, Miriam L.; de Wit, Cynthia A.; Molander, Sverker

2015-01-01

Rockström et al. (2009a, 2009b) have warned that humanity must reduce anthropogenic impacts defined by nine planetary boundaries if "unacceptable global change" is to be avoided. Chemical pollution was identified as one of those boundaries for which continued impacts could erode the resilience...... of ecosystems and humanity. The central concept of the planetary boundary (or boundaries) for chemical pollution (PBCP or PBCPs) is that the Earth has a finite assimilative capacity for chemical pollution, which includes persistent, as well as readily degradable chemicals released at local to regional scales......, which in aggregate threaten ecosystem and human viability. The PBCP allows humanity to explicitly address the increasingly global aspects of chemical pollution throughout a chemical's life cycle and the need for a global response of internationally coordinated control measures. We submit that sufficient...

Global Distribution of Planetary Boundary Layer Height Derived from CALIPSO

Science.gov (United States)

Huang, J.

2015-12-01

The global distribution of planetary boundary layer (PBL) height, which was estimated from the attenuated back-scatter observations of Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO), is presented. In general, the PBL is capped by a temperature inversion that tends to trap moisture and aerosols. The gradient of back-scatter observed by lidar is almost always associated with this temperature inversion and the simultaneous decrease of moisture content. Thus, the PBL top is defined as the location of the maximum aerosol scattering gradient, which is analogous to the more conventional thermodynamic definition. The maximum standard deviation method, developed by Jordan et al. (2010), is modified and used to derive the global PBL heights. The derived PBL heights are not only consistent with the results of McGrath-Spangler and Denning (2012) but also agree well with the ground-based lidar measurements. It is found that the correlation between CALIPSO and the ground-based lidar was 0.73. The seasonal mean patterns from 4-year mid-day PBL heights over global are demonstrated. Also it is found that the largest PBL heights occur over the Tibetan Plateau and the coastal areas. The smallest PBL heights appear in the Tarim Basin and the northeast of China during the local winter. The comparison of PBL heights from CALIPSO and ECMWF under different land-cover conditions showed that, over ocean and forest surface, the PBL height estimated from the CALIPSO back-scatter climatology is larger than the ones estimated from ECMWF data. However, the PBL heights from ECMWF, over grass land and bare land surface in spring and summer are larger than the ones from CALIPSO.

An ultra-high frequency boundary layer Doppler/interferometric profiler

International Nuclear Information System (INIS)

Van Baelen, J.S.

1994-01-01

The planetary boundary layer (PBL) is that portion of the earth's atmosphere that is directly influenced by the earth's surface. The PBL can be vigorously turbulent and range in depth from a few hundred meters to a few kilometers. Solar energy is primarily absorbed at the earth's surface and transmitted to the free atmosphere through boundary-layer processes. An accurate portrayal of these transfers within the PBL is crucial to understand and predict many atmospheric processes from pollutant dispersion to numerical weather prediction and numerical simulations of climate change. This paper describes and discusses wind profiling techniques, focusing on the newly developed radio acoustic sounding system (RASS), and reviews past efforts to measure flux within the PBL. A new UHF wind profiling radar, the UHF Doppler/Interferometric Boundary Layer Radar, for accurately measuring both mean and flux quantities, as well as wind divergence and acoustic wave propagation, is outlined

Planetary boundaries: exploring the safe operating space for humanity

Science.gov (United States)

Johan Rockström; Will Steffen; Kevin Noone; Asa Persson; F. Stuart Chapin; Eric Lambin; Timothy M. Lenton; Marten Scheffer; Carl Folke; Hans Joachim Schellnhuber; Björn Nykvist; Cynthia A. de Wit; Terry Hughes; Sander van der Leeuw; Henning Rodhe; Sverker Sörlin; Peter K. Snyder; Robert Costanza; Uno Svedin; Malin Falkenmark; Louise Karlberg; Robert W. Corell; Victoria J. Fabry; James Hansen; Brian Walker; Diana Liverman; Katherine Richardson; Paul Crutzen; Jonathan Foley

2009-01-01

Anthropogenic pressures on the Earth System have reached a scale where abrupt global environmental change can no longer be excluded. We propose a new approach to global sustainability in which we define planetary boundaries within which we expect that humanity can operate safely. Transgressing one or more planetary boundaries may be deleterious or even catastrophic due...

A conceptual framework to quantify the influence of convective boundary layer development on carbon dioxide mixing ratios

NARCIS (Netherlands)

Pino, D.; Vilà-Guerau de Arellano, J.; Peters, W.; Schröter, J.; van Heerwaarden, C. C.; Krol, M. C.

2012-01-01

Interpretation of observed diurnal carbon dioxide (CO2) mixing ratios near the surface requires knowledge of the local dynamics of the planetary boundary layer. In this paper, we study the relationship between the boundary layer dynamics and the CO2 budget in convective conditions through a newly

Evolution of the lower planetary boundary layer over strongly contrasting surfaces

International Nuclear Information System (INIS)

Coulter, R.L.; Gao, W.; Martin, T.J.; Shannon, J.D.; Doran, J.C.; Hubbe, J.M.; Shaw, W.M.

1992-01-01

In a multilaboratory field study held near Boardman in northeastern Oregon in June 1991, various properties of the surface and lower atmospheric boundary layer over heavily irrigated cropland and adjacent desert steppe were investigated in the initial campaign of the Atmospheric Radiation Measurement (ARM) program. The locale was selected because its disparate characteristics over various spatial scales stress the ability of general circulation models (GCMS) to describe lower boundary conditions, particularly across the discontinuity between desert (in which turbulent flux of heat must be primarily as sensible heat) and large irrigated tracts (in which turbulent flux of latent heat should be the larger term). This campaign of ARM seeks to increase knowledge in three critical areas: (1) determination of the relationships between surface heat fluxes measured over multiple scales and the controlling surface parameters within each scale, (2) integration of local and nearly local heat flux estimates to produce estimates appropriate for GCM grid cells of 100-200 km horizontal dimension, and (3) characterization of the growth and development of the atmospheric boundary layer near transitions between surfaces with strongly contrasting moisture availabilities

Impacts of synoptic condition and planetary boundary layer structure on the trans-boundary aerosol transport from Beijing-Tianjin-Hebei region to northeast China

Science.gov (United States)

Miao, Yucong; Guo, Jianping; Liu, Shuhua; Zhao, Chun; Li, Xiaolan; Zhang, Gen; Wei, Wei; Ma, Yanjun

2018-05-01

The northeastern China frequently experiences severe aerosol pollution in winter under unfavorable meteorological conditions. How and to what extent the meteorological factors affect the air quality there are not yet clearly understood. Thus, this study investigated the impacts of synoptic patterns on the aerosol transport and planetary boundary layer (PBL) structure in Shenyang from 1 to 3 December 2016, using surface observations, sounding measurements, satellite data, and three-dimensional simulations. Results showed that the aerosol pollution occurred in Shenyang was not only related to the local emissions, but also contributed by trans-boundary transport of aerosols from the Beiijng-Tianjin-Hebei (BTH) region. In the presence of the westerly and southwesterly synoptic winds, the aerosols emitted from BTH could be brought to Shenyang. From December 2 to 3, the aerosols emitted from BTH accounted for ∼20% of near-surface PM2.5 in Shenyang. In addition, the large-scale synoptic forcings could affect the vertical mixing of pollutants through modulating the PBL structure in Shenyang. The westerly and southwesterly synoptic winds not only brought the aerosols but also the warmer air masses from the southwest regions to Shenyang. The strong warm advections above PBL could enhance the already existing thermal inversion layers capping over PBL in Shenyang, leading to the suppressions of PBL. Both the trans-boundary transport of aerosols and the suppressions of PBL caused by the large-scale synoptic forcings should be partly responsible for the poor air quality in Shenyang, in addition to the high pollutant emissions. The present study revealed the physical mechanisms underlying the aerosol pollution in Shenyang, which has important implications for better forecasting and controlling the aerosols pollution.

The effect of baroclinicity on the wind in the planetary boundary layer

DEFF Research Database (Denmark)

Floors, Rogier Ralph; Peña, Alfredo; Gryning, Sven-Erik

2015-01-01

close to zero and a standard deviation of approximately 3ms−1km−1. The geostrophic wind shear had a strong seasonal dependence because of temperature differences between land and sea. The mean wind profile in Hamburg, observed during an intensive campaign using radio sounding and during the whole year...... using the wind lidar, was influenced by baroclinicity. For easterly winds at Høvsøre, the estimated gradient wind decreased rapidly with height, resulting in a mean low-level jet. The turning of the wind in the boundary layer, the boundary-layer height and the empirical constants in the geostrophic drag...

Inter-comparison of lidar and ceilometer retrievals for aerosol and Planetary Boundary Layer profiling over Athens, Greece

Directory of Open Access Journals (Sweden)

G. Tsaknakis

2011-06-01

Full Text Available This study presents an inter-comparison of two active remote sensors (lidar and ceilometer to determine the mixing layer height and structure of the Planetary Boundary Layer (PBL and to retrieve tropospheric aerosol vertical profiles over Athens, Greece. This inter-comparison was performed under various strongly different aerosol loads/types (urban air pollution, biomass burning and Saharan dust event, implementing two different lidar systems (one portable Raymetrics S.A. lidar system running at 355 nm and one multi-wavelength Raman lidar system running at 355 nm, 532 nm and 1064 nm and one CL31 Vaisala S.A. ceilometer (running at 910 nm. Spectral conversions of the ceilometer's data were performed using the Ångström exponent estimated by ultraviolet multi-filter radiometer (UV-MFR measurements. The inter-comparison was based on two parameters: the mixing layer height determined by the presence of the suspended aerosols and the attenuated backscatter coefficient. Additionally, radiosonde data were used to derive the PBL height. In general, a good agreement was found between the ceilometer and the lidar techniques in both inter-compared parameters in the height range from 500 m to 5000 m, while the limitations of each instrument are also examined.

Temperature and Relative Humidity Vertical Profiles within Planetary Boundary Layer in Winter Urban Airshed

Science.gov (United States)

Bendl, Jan; Hovorka, Jan

2017-12-01

The planetary boundary layer is a dynamic system with turbulent flow where horizontal and vertical air mixing depends mainly on the weather conditions and geomorphology. Normally, air temperature from the Earth surface decreases with height but inversion situation may occur, mainly during winter. Pollutant dispersion is poor during inversions so air pollutant concentration can quickly rise, especially in urban closed valleys. Air pollution was evaluated by WHO as a human carcinogen (mostly by polycyclic aromatic hydrocarbons) and health effects are obvious. Knowledge about inversion layer height is important for estimation of the pollution impact and it can give us also information about the air pollution sources. Temperature and relative humidity vertical profiles complement ground measurements. Ground measurements were conducted to characterize comprehensively urban airshed in Svermov, residential district of the city of Kladno, about 30 km NW of Prague, from the 2nd Feb. to the 3rd of March 2016. The Svermov is an air pollution hot-spot for long time benzo[a]pyrene (B[a]P) limit exceedances, reaching the highest B[a]P annual concentration in Bohemia - west part of the Czech Republic. Since the Svermov sits in a shallow valley, frequent vertical temperature inversion in winter and low emission heights of pollution sources prevent pollutant dispersal off the valley. Such orography is common to numerous small settlements in the Czech Republic. Ground measurements at the sports field in the Svermov were complemented by temperature and humidity vertical profiles acquired by a Vaisala radiosonde positioned at tethered He-filled balloon. Total number of 53 series of vertical profiles up to the height of 300 m was conducted. Meteorology parameters were acquired with 4 Hz frequency. The measurements confirmed frequent early-morning and night formation of temperature inversion within boundary layer up to the height of 50 m. This rather shallow inversion had significant

Thorpe method applied to planetary boundary layer data

International Nuclear Information System (INIS)

Gonzalez-Nieto, P.L.; Cano, J.L.; Tijera, M.; Cano, D.

2008-01-01

Turbulence affects the dynamics of atmospheric processes by enhancing the transport of mass, heat, humidity and pollutants. The global objective for our work is to analyze some direct turbulent descriptors which reflect the mixing processes in the atmospheric boundary layer (ABL). In this paper we present results related to the Thorpe displacements d Τ , the maximum Thorpe displacement (d Τ ) max and the Thorpe scale L Τ , the Ozmidov scale and their time evolution in the ABL during a day cycle. A tethered balloon was used to obtain vertical profiles of the atmospheric physical magnitudes up to 1000 m. We discuss the vertical and horizontal variability and how different descriptors are related to atmospheric mixing.

New-particle formation events in a continental boundary layer: first results from the SATURN experiment

Directory of Open Access Journals (Sweden)

F. Stratmann

2003-01-01

Full Text Available During the SATURN experiment, which took place from 27 May to 14 June 2002, new particle formation in the continental boundary layer was investigated. Simultaneous ground-based and tethered-balloon-borne measurements were performed, including meteorological parameters, particle number concentrations and size distributions, gaseous precursor concentrations and SODAR and LIDAR observations. Newly formed particles were observed inside the residual layer, before the break-up process of the nocturnal inversion, and inside the mixing layer throughout the break-up of the nocturnal inversion and during the evolution of the planetary boundary layer.

Turbulent Helicity in the Atmospheric Boundary Layer

Science.gov (United States)

Chkhetiani, Otto G.; Kurgansky, Michael V.; Vazaeva, Natalia V.

2018-05-01

We consider the assumption postulated by Deusebio and Lindborg (J Fluid Mech 755:654-671, 2014) that the helicity injected into the Ekman boundary layer undergoes a cascade, with preservation of its sign (right- or alternatively left-handedness), which is a signature of the system rotation, from large to small scales, down to the Kolmogorov microscale of turbulence. At the same time, recent direct field measurements of turbulent helicity in the steppe region of southern Russia near Tsimlyansk Reservoir show the opposite sign of helicity from that expected. A possible explanation for this phenomenon may be the joint action of different scales of atmospheric flows within the boundary layer, including the sea-breeze circulation over the test site. In this regard, we consider a superposition of the classic Ekman spiral solution and Prandtl's jet-like slope-wind profile to describe the planetary boundary-layer wind structure. The latter solution mimics a hydrostatic shallow breeze circulation over a non-uniformly heated surface. A 180°-wide sector on the hodograph plane exists, within which the relative orientation of the Ekman and Prandtl velocity profiles favours the left rotation with height of the resulting wind velocity vector in the lowermost part of the boundary layer. This explains the negative (left-handed) helicity cascade toward small-scale turbulent motions, which agrees with the direct field measurements of turbulent helicity in Tsimlyansk. A simple turbulent relaxation model is proposed that explains the measured positive values of the relatively minor contribution to turbulent helicity from the vertical components of velocity and vorticity.

Application of Intel Many Integrated Core (MIC) architecture to the Yonsei University planetary boundary layer scheme in Weather Research and Forecasting model

Science.gov (United States)

Huang, Melin; Huang, Bormin; Huang, Allen H.

2014-10-01

The Weather Research and Forecasting (WRF) model provided operational services worldwide in many areas and has linked to our daily activity, in particular during severe weather events. The scheme of Yonsei University (YSU) is one of planetary boundary layer (PBL) models in WRF. The PBL is responsible for vertical sub-grid-scale fluxes due to eddy transports in the whole atmospheric column, determines the flux profiles within the well-mixed boundary layer and the stable layer, and thus provide atmospheric tendencies of temperature, moisture (including clouds), and horizontal momentum in the entire atmospheric column. The YSU scheme is very suitable for massively parallel computation as there are no interactions among horizontal grid points. To accelerate the computation process of the YSU scheme, we employ Intel Many Integrated Core (MIC) Architecture as it is a multiprocessor computer structure with merits of efficient parallelization and vectorization essentials. Our results show that the MIC-based optimization improved the performance of the first version of multi-threaded code on Xeon Phi 5110P by a factor of 2.4x. Furthermore, the same CPU-based optimizations improved the performance on Intel Xeon E5-2603 by a factor of 1.6x as compared to the first version of multi-threaded code.

Evaluation of planetary boundary layer schemes in meso-scale simulations above the North and Baltic Sea

Science.gov (United States)

Wurps, Hauke; Tambke, Jens; Steinfeld, Gerald; von Bremen, Lueder

2014-05-01

The development and design of wind energy converters for offshore wind farms require profound knowledge of the wind profile in the lower atmosphere. Especially an accurate and reliable estimation of turbulence, shear and veer are necessary for the prediction of energy production and loads. Currently existing wind energy turbines in the North Sea have hub heights of around 90 m and upper tip heights around 150 m, which is already higher than the highest measurement masts (e.g. FINO1: 103 m). The next generation of wind turbines will clearly outrange these altitudes, so the interest is to examine the atmosphere's properties above the North Sea up to 300 m. Therefore, besides the Prandtl layer also the Ekman layer has to be taken into account, which implies that changes of the wind direction with height become more relevant. For this investigation we use the Weather Research and Forecasting Model (WRF), a meso-scale numerical weather prediction system. In this study we compare different planetary boundary layer (PBL) schemes (MYJ, MYNN, QNSE) with the same high quality input from ECMWF used as boundary conditions (ERA-Interim). It was found in previous studies that the quality of the boundary conditions is crucially important for the accuracy of comparisons between different PBL schemes. This is due to the fact that the major source of meso-scale simulation errors is introduced by the driving boundary conditions and not by the different schemes of the meso-scale model itself. Hence, small differences in results from different PBL schemes can be distorted arbitrarily by coarse input data. For instance, ERA-Interim data leads to meso-scale RMSE values of 1.4 m/s at 100 m height above sea surface with mean wind speeds around 10 m/s, whereas other Reanalysis products lead to RMSEs larger than 2 m/s. Second, we compare our simulations to operational NWP results from the COSMO model (run by the DWD). In addition to the wind profile, also the turbulent kinetic energy (TKE

Influence of grid aspect ratio on planetary boundary layer turbulence in large-eddy simulations

Directory of Open Access Journals (Sweden)

S. Nishizawa

2015-10-01

Full Text Available We examine the influence of the grid aspect ratio of horizontal to vertical grid spacing on turbulence in the planetary boundary layer (PBL in a large-eddy simulation (LES. In order to clarify and distinguish them from other artificial effects caused by numerical schemes, we used a fully compressible meteorological LES model with a fully explicit scheme of temporal integration. The influences are investigated with a series of sensitivity tests with parameter sweeps of spatial resolution and grid aspect ratio. We confirmed that the mixing length of the eddy viscosity and diffusion due to sub-grid-scale turbulence plays an essential role in reproducing the theoretical −5/3 slope of the energy spectrum. If we define the filter length in LES modeling based on consideration of the numerical scheme, and introduce a corrective factor for the grid aspect ratio into the mixing length, the theoretical slope of the energy spectrum can be obtained; otherwise, spurious energy piling appears at high wave numbers. We also found that the grid aspect ratio has influence on the turbulent statistics, especially the skewness of the vertical velocity near the top of the PBL, which becomes spuriously large with large aspect ratio, even if a reasonable spectrum is obtained.

ESTIMASI KETINGGIAN PLANETARY BOUNDARY LAYER INDONESIA MENGGUNAKAN DATA ECMWF REANALYSIS ERA-INTERM

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Vivi Fitriani

2018-03-01

Full Text Available Planetary Boundary Layer (PBL merupakan bagian dari troposfer yang mendapat pengaruh secara langsung dari permukaan bumi, yang memiliki peranan penting dalam iklim, cuaca dan kualitas udara. PBL dikenal sangat sulit untuk diobservasi dari luar angkasa dikarenakan strukturnya yang sangat kompleks dan berubah-ubah. Salah satu properties yang paling relevan dan fundamental untuk diselidiki adalah ketinggian PBL. Ketinggian PBL dihitung menggunakan tujuh metode berbasis gradien dari kelembaban relatif (RH, temperatur virtual (Tv, temperatur potensial ( , temperatur potensial virtual ( , kelembaban spesifik (q, refraktiviti atmosfer (N, dan Kecepatan angin (V yang diperoleh dari data ECMWF Reanalisis Era Interm selama enam bulan di wilayah 100LU–100LS, 900BT –1500BT dengan resolusi spasial 2.50 x 2.50. Beberapa metode menunjukkan hasil yang indentik untuk ketinggian PBL pada waktu dan tempat tertentu. Metode gradien  dan V konsisten memberikan ketinggian PBL yang tinggi, sementara metode q dan N menghasilkan ketinggian PBL terendah signifikan. Tingginya variasi bulanan dan harian umumnya ditemukan diseluruh wilayah daratan, sedangkan wilayah lautan relatif konstan. Beberapa sumber dari kedua parametrik dan struktur ketidakpastian dari nilai ketinggian PBL diestimasi secara statistik menggunakan lima uji statistik, yaitu uji Student’s t, Uji F, Uji Kormogoorv Sminorv, Uji Korelasi Pearson, dan Uji Korelasi NonParametrik Spearman. Ditemukan adanya perbedaan yang signifikan secara statistik antara ketujuh metode. Rata-rata median ketinggian PBL berbeda ratusan hingga ribuan meter untuk kebanyakan metode yang dibandingkan. Estimasi ketinggian PBL di Indonesia menggunakan metode RH berada di ketinggian 2000 m-4000m pada siang hari dan pada malam hari berada di bawah 2500  m.

Evaluation of the Weather Research and Forecasting mesoscale model for GABLS3: Impact of boundary-layer schemes, boundary conditions and spin-up

NARCIS (Netherlands)

Kleczek, M.A.; Steeneveld, G.J.; Holtslag, A.A.M.

2014-01-01

We evaluated the performance of the three-dimensional Weather Research and Forecasting (WRF) mesoscale model, specifically the performance of the planetary boundary-layer (PBL) parametrizations. For this purpose, Cabauw tower observations were used, with the study extending beyond the third GEWEX

Boundary Layer Depth In Coastal Regions

Science.gov (United States)

Porson, A.; Schayes, G.

The results of earlier studies performed about sea breezes simulations have shown that this is a relevant feature of the Planetary Boundary Layer that still requires effort to be diagnosed properly by atmospheric models. Based on the observations made during the ESCOMPTE campaign, over the Mediterranean Sea, different CBL and SBL height estimation processes have been tested with a meso-scale model, TVM. The aim was to compare the critical points of the BL height determination computed using turbulent kinetic energy profile with some other standard evaluations. Moreover, these results have been analysed with different mixing length formulation. The sensitivity of formulation is also analysed with a simple coastal configuration.

Agriculture production as a major driver of the Earth system exceeding planetary boundaries

Directory of Open Access Journals (Sweden)

Bruce M. Campbell

2017-12-01

Full Text Available We explore the role of agriculture in destabilizing the Earth system at the planetary scale, through examining nine planetary boundaries, or "safe limits": land-system change, freshwater use, biogeochemical flows, biosphere integrity, climate change, ocean acidification, stratospheric ozone depletion, atmospheric aerosol loading, and introduction of novel entities. Two planetary boundaries have been fully transgressed, i.e., are at high risk, biosphere integrity and biogeochemical flows, and agriculture has been the major driver of the transgression. Three are in a zone of uncertainty i.e., at increasing risk, with agriculture the major driver of two of those, land-system change and freshwater use, and a significant contributor to the third, climate change. Agriculture is also a significant or major contributor to change for many of those planetary boundaries still in the safe zone. To reduce the role of agriculture in transgressing planetary boundaries, many interventions will be needed, including those in broader food systems.

Planetary boundary layer and circulation dynamics at Gale Crater, Mars

Science.gov (United States)

Fonseca, Ricardo M.; Zorzano-Mier, María-Paz; Martín-Torres, Javier

2018-03-01

The Mars implementation of the Planet Weather Research and Forecasting (PlanetWRF) model, MarsWRF, is used here to simulate the atmospheric conditions at Gale Crater for different seasons during a period coincident with the Curiosity rover operations. The model is first evaluated with the existing single-point observations from the Rover Environmental Monitoring Station (REMS), and is then used to provide a larger scale interpretation of these unique measurements as well as to give complementary information where there are gaps in the measurements. The variability of the planetary boundary layer depth may be a driver of the changes in the local dust and trace gas content within the crater. Our results show that the average time when the PBL height is deeper than the crater rim increases and decreases with the same rate and pattern as Curiosity's observations of the line-of-sight of dust within the crater and that the season when maximal (minimal) mixing is produced is Ls 225°-315° (Ls 90°-110°). Thus the diurnal and seasonal variability of the PBL depth seems to be the driver of the changes in the local dust content within the crater. A comparison with the available methane measurements suggests that changes in the PBL depth may also be one of the factors that accounts for the observed variability, with the model results pointing towards a local source to the north of the MSL site. The interaction between regional and local flows at Gale Crater is also investigated assuming that the meridional wind, the dynamically important component of the horizontal wind at Gale, anomalies with respect to the daily mean can be approximated by a sinusoidal function as they typically oscillate between positive (south to north) and negative (north to south) values that correspond to upslope/downslope or downslope/upslope regimes along the crater rim and Mount Sharp slopes and the dichotomy boundary. The smallest magnitudes are found in the northern crater floor in a region that

Sensitivity of Turbine-Height Wind Speeds to Parameters in Planetary Boundary-Layer and Surface-Layer Schemes in the Weather Research and Forecasting Model

Science.gov (United States)

Yang, Ben; Qian, Yun; Berg, Larry K.; Ma, Po-Lun; Wharton, Sonia; Bulaevskaya, Vera; Yan, Huiping; Hou, Zhangshuan; Shaw, William J.

2017-01-01

We evaluate the sensitivity of simulated turbine-height wind speeds to 26 parameters within the Mellor-Yamada-Nakanishi-Niino (MYNN) planetary boundary-layer scheme and MM5 surface-layer scheme of the Weather Research and Forecasting model over an area of complex terrain. An efficient sampling algorithm and generalized linear model are used to explore the multiple-dimensional parameter space and quantify the parametric sensitivity of simulated turbine-height wind speeds. The results indicate that most of the variability in the ensemble simulations is due to parameters related to the dissipation of turbulent kinetic energy (TKE), Prandtl number, turbulent length scales, surface roughness, and the von Kármán constant. The parameter associated with the TKE dissipation rate is found to be most important, and a larger dissipation rate produces larger hub-height wind speeds. A larger Prandtl number results in smaller nighttime wind speeds. Increasing surface roughness reduces the frequencies of both extremely weak and strong airflows, implying a reduction in the variability of wind speed. All of the above parameters significantly affect the vertical profiles of wind speed and the magnitude of wind shear. The relative contributions of individual parameters are found to be dependent on both the terrain slope and atmospheric stability.

Depletion of solar wind plasma near a planetary boundary

International Nuclear Information System (INIS)

Zwan, B.J.; Wolf, R.A.

1976-01-01

A mathematical model is presented that describes the squeezing of solar wind plasma out along interplanetary magnetic field lines in the region between the bow shock and the effective planetary boundary (in the case of the earth, the magnetopause). In the absence of local magnetic merging the squeezing process should create a 'depletion layer,' a region of very low plasma density just outside the magnetopause. Numerical solutions are obtained for the dimensionless magnetohydrodynamic equations describing this depletion process for the case where the solar wind magnetic field is perpendicular to the solar wind flow direction. For the case of the earth with a magnetopause standoff distance of 10 R/subE/, the theory predicts that the density should be reduced by a factor > or =2 in a layer about 700--1300 km thick if M/subA/, the Alfven Mach number in the solar wind, is equal to 8. The layer thickness should vary as M/subA/ -2 and should be approximately uniform for a large area of the magnetopause around the subsolar point. Computed layer thicknesses are somewhat smaller than those derived from Lees' axisymmetric model. Depletion layers should develop fully only where magnetic merging is locally unimportant. Scaling of the model calculations to Venus and Mars suggest layer thicknesses about 1/10 and 1/15 those of the earth, respectively, neglecting diffusion and ionospheric effects

An investigation of ozone and planetary boundary layer dynamics over the complex topography of Grenoble combining measurements and modeling

Directory of Open Access Journals (Sweden)

O. Couach

2003-01-01

Full Text Available This paper concerns an evaluation of ozone (O3 and planetary boundary layer (PBL dynamics over the complex topography of the Grenoble region through a combination of measurements and mesoscale model (METPHOMOD predictions for three days, during July 1999. The measurements of O3 and PBL structure were obtained with a Differential Absorption Lidar (DIAL system, situated 20 km south of Grenoble at Vif (310 m ASL. The combined lidar observations and model calculations are in good agreement with atmospheric measurements obtained with an instrumented aircraft (METAIR. Ozone fluxes were calculated using lidar measurements of ozone vertical profiles concentrations and the horizontal wind speeds measured with a Radar Doppler wind profiler (DEGREANE. The ozone flux patterns indicate that the diurnal cycle of ozone production is controlled by local thermal winds. The convective PBL maximum height was some 2700 m above the land surface while the nighttime residual ozone layer was generally found between 1200 and 2200 m. Finally we evaluate the magnitude of the ozone processes at different altitudes in order to estimate the photochemical ozone production due to the primary pollutants emissions of Grenoble city and the regional network of automobile traffic.

Numerical study of the effects of Planetary Boundary Layer structure on the pollutant dispersion within built-up areas.

Science.gov (United States)

Miao, Yucong; Liu, Shuhua; Zheng, Yijia; Wang, Shu; Liu, Zhenxin; Zhang, Bihui

2015-06-01

The effects of different Planetary Boundary Layer (PBL) structures on pollutant dispersion processes within two idealized street canyon configurations and a realistic urban area were numerically examined by a Computational Fluid Dynamics (CFD) model. The boundary conditions of different PBL structures/conditions were provided by simulations of the Weather Researching and Forecasting model. The simulated results of the idealized 2D and 3D street canyon experiments showed that the increment of PBL instability favored the downward transport of momentum from the upper flow above the roof to the pedestrian level within the street canyon. As a result, the flow and turbulent fields within the street canyon under the more unstable PBL condition are stronger. Therefore, more pollutants within the street canyon would be removed by the stronger advection and turbulent diffusion processes under the unstable PBL condition. On the contrary, more pollutants would be concentrated in the street canyon under the stable PBL condition. In addition, the simulations of the realistic building cluster experiments showed that the density of buildings was a crucial factor determining the dynamic effects of the PBL structure on the flow patterns. The momentum field within a denser building configuration was mostly transported from the upper flow, and was more sensitive to the PBL structures than that of the sparser building configuration. Finally, it was recommended to use the Mellor-Yamada-Nakanishi-Niino (MYNN) PBL scheme, which can explicitly output the needed turbulent variables, to provide the boundary conditions to the CFD simulation. Copyright © 2015. Published by Elsevier B.V.

Measurements of atmospheric hydrocarbons and biogenic emission fluxes in the Amazon boundary layer

Science.gov (United States)

Zimmerman, P. R.; Greenberg, J. P.; Westberg, C. E.

1988-01-01

Tropospheric mixing ratios of methane, C2-C10 hydrocarbons, and carbon monoxide were measured over the Amazon tropical forest near Manaus, Amazonas, Brazil, in July and August 1985. The measurements, consisting mostly of altitude profiles of these gases, were all made within the atmospheric boundary layer up to an altitude of 1000 m above ground level. Data characterize the diurnal hydrocarbon composition of the boundary layer. Biogenic emissions of isoprene control hydroxyl radical concentrations over the forest. Biogenic emission fluxes of isoprene and terpenes are estimated to be 25,000 micrograms/sq m per day and 5600 micrograms/sq m per day, respectively. This isoprene emission is equivalent to 2 percent of the net primary productivity of the tropical forest. Atmospheric oxidation of biogenic isoprene and terpenes emissions from the Amazon forest may account for daily increases of 8-13 ppb for carbon monoxide in the planetary boundary layer.

Evaluating Models of The Neutral, Barotropic Planetary Boundary Layer using Integral Measures: Part I. Overview

Science.gov (United States)

Hess, G. D.; Garratt, J. R.

Data for the cross-isobaric angle 0, the geostrophic drag coefficient Cg, and the functions A and B of Rossby number similarity theory, obtained from meteorological field experiments, are used to evaluate a range of models of the neutral, barotropic planetary boundary layer. The data give well-defined relationships for 0, Cg, and the integrated dissipation rate over the boundary layer, as a function of the surface Rossby number. Lettau's first-order closure mixing-length model gives an excellent fit to the data; other simple models give reasonable agreement. However more sophisticated models, e.g., higher-order closure, large-eddy simulation, direct numerical simulation and laboratory models, give poor fits to the data. The simplemodels have (at least) one free parameter in their turbulence closure that is matched toatmospheric observations; the more sophisticated models either base their closure onmore general flows or have no free closure parameters. It is suggested that all of theatmospheric experiments that we could locate violate the strict simplifying assumptionsof steady, homogeneous, neutral, barotropic flow required by the sophisticated models.The angle 0 is more sensitive to violations of the assumptions than is Cg.The behaviour of the data varies in three latitude regimes. In middle and high latitudes the observed values of A and B exhibit little latitudinal dependence; the best estimates are A = 1.3 and B = 4.4. In lower latitudes the neutral, barotropic Rossby number theory breaks down. The value of B increases towards the Equator; the determination of A is ambiguous - the trend can increase or decrease towards the Equator. Between approximately 5° and 30° latitude, the scatter in the data is thought to be primarily due to the inherent presence of baroclinicity. The presence of the trade-wind inversion, thermal instability and the horizontal component of the Earth's rotation ΩH also contribute.Marked changes in the values of A and B occur in the

Sensitivity of WRF-simulated planetary boundary layer height to land cover and soil changes

Directory of Open Access Journals (Sweden)

Ferenc Ács

2014-09-01

Full Text Available Planetary boundary layer (PBL height sensitivity to both so-called single and accumulated land cover and soil changes is investigated in shallow convection under cloud-free conditions to compare the effects. Single land cover type and soil changes are carried out to be able to unequivocally separate the cause and effect relationships. The Yonsei University scheme in the framework of the Weather Research Forecasting (WRF mesoscale modeling system is used as a research tool. The area investigated lies in the Carpathian Basin, where anticyclonic weather type influence dominated on the five summer days chosen for simulations. Observation-based methods applied for validating diurnal PBL height courses manifest great deviations reaching 500–1300 m. The obtained deviations are somewhat smaller around midday and greater at night. They can originate either from the differences in the measuring principles or from the differences in the atmospheric profiles used. Concerning sensitivity analyses, we showed that PBL height differences caused by soil change are comparable with the PBL height differences caused by land cover change. The differences are much greater in the single than in the accumulated tests. Space averaged diurnal course difference around midday reaching a few tens of meters can be presumably treated as strongly significant. PBL height differences obtained in the sensitivity analyses are, at least in our case, smaller than those obtained by applying different observation based methods. The results may be utilized in PBL height diurnal course analyses.

Development of boundary layers

International Nuclear Information System (INIS)

Herbst, R.

1980-01-01

Boundary layers develop along the blade surfaces on both the pressure and the suction side in a non-stationary flow field. This is due to the fact that there is a strongly fluctuating flow on the downstream blade row, especially as a result of the wakes of the upstream blade row. The author investigates the formation of boundary layers under non-stationary flow conditions and tries to establish a model describing the non-stationary boundary layer. For this purpose, plate boundary layers are measured, at constant flow rates but different interferent frequency and variable pressure gradients. By introducing the sample technique, measurements of the non-stationary boundary layer become possible, and the flow rate fluctuation can be divided in its components, i.e. stochastic turbulence and periodical fluctuation. (GL) [de

Challenges in implementing a Planetary Boundaries based Life-Cycle Impact Assessment methodology

DEFF Research Database (Denmark)

Ryberg, Morten; Owsianiak, Mikolaj; Richardson, Katherine

2016-01-01

of resolving the challenges and developing such methodology is discussed. The challenges are related to technical issues, i.e., modelling and including the Earth System processes and their control variables as impact categories in Life-Cycle Impact Assessment and to theoretical considerations with respect...... to the interpretation and use of Life-Cycle Assessment results in accordance with the Planetary Boundary framework. The identified challenges require additional research before a Planetary Boundaries based Life-Cycle Impact Assessment method can be developed. Research on modelling the impacts on Earth System processes......Impacts on the environment from human activities are now threatening to exceed thresholds for central Earth System processes, potentially moving the Earth System out of the Holocene state. To avoid such consequences, the concept of Planetary Boundaries was defined in 2009, and updated in 2015...

An analytical model for dispersion of material in the atmospheric planetary boundary layer in presence of precipitation

International Nuclear Information System (INIS)

Mayhoub, A.B.; Etman, S.M.

1985-05-01

An analytical model for the dispersion of particulates and finely divided material released into the atmosphere near the ground is presented. The possible precipitation when the particles are dense enough and large enough to have deposition velocity, is taken into consideration. The model is derived analytically in the mixing layer or Ekman boundary layer where the mixing process is a direct consequence of turbulent and convective motions generated in the boundary layer. (author)

Assessing planetary and regional nitrogen boundaries related to food security and adverse environmental impacts

NARCIS (Netherlands)

Vries, de W.; Kros, J.; Kroeze, C.; Seitzinger, S.P.

2013-01-01

This paper first describes the concept of, governance interest in, and criticism on planetary boundaries, specifically with respect to the nitrogen (N) cycle. These criticisms are then systematically evaluated. We argue that planetary N boundaries should include both the benefits and adverse impacts

Local and social facets of planetary boundaries: right to nutrients

International Nuclear Information System (INIS)

Kahiluoto, Helena; Kuisma, Miia; Kuokkanen, Anna; Mikkilä, Mirja; Linnanen, Lassi

2015-01-01

Anthropogenic nutrient flows exceed the planetary boundaries. The boundaries and the current excesses vary spatially. Such variations have both an ecological and a social facet. We explored the spatial variation using a bottom-up approach. The local critical boundaries were determined through the current or accumulated flow of the preceding five years before the planetary boundary criteria were met. Finland and Ethiopia served as cases with contrasting ecology and wealth. The variation in excess depends on historical global inequities in the access to nutrients. Globally, the accumulated use per capita is 2300 kg reactive nitrogen (N r ) and 200 kg phosphorus (P). For Finland, the accumulated use per capita is 3400 kg N r and 690 kg P, whereas for Ethiopia, it is 26 kg N r and 12 kg P. The critical N boundary in Finland is currently exceeded by 40 kg cap −1 a −1 and the accumulated excess is 65 kg cap −1 a −1 , while the global current excess is 24 kg cap −1 a −1 and there is space in Ethiopia to increase even the accumulated flow. The critical P boundary is exceeded in Finland and (although less so) in Ethiopia, but for contrary reasons: (1) the excessive past inflow to the agrifood system in Finland and (2) the excessive outflow from the agrifood system triggered by deficits in inflow and waste management in Ethiopia. The critical boundaries set by Finnish marine systems are lower and those set by freshwaters are higher than the planetary boundaries downscaled per capita. The shift to dominance of internal loading in watercourses represents a tipping point. We conclude that food security within the safe boundaries requires global redistribution of nutrients in residues, soils and sediments and of rights to use nutrients. Bottom-up assessments reveal local dynamics that shed new light on the relevant boundary criteria and on estimates and remedies. (letter)

Observations of the Early Evening Boundary-Layer Transition Using a Small Unmanned Aerial System

Science.gov (United States)

Bonin, Timothy; Chilson, Phillip; Zielke, Brett; Fedorovich, Evgeni

2013-01-01

The evolution of the lower portion of the planetary boundary layer is investigated using the Small Multifunction Research and Teaching Sonde (SMARTSonde), an unmanned aerial vehicle developed at the University of Oklahoma. The study focuses on the lowest 200 m of the atmosphere, where the most noticeable thermodynamic changes occur during the day. Between October 2010 and February 2011, a series of flights was conducted during the evening hours on several days to examine the vertical structure of the lower boundary layer. Data from a nearby Oklahoma Mesonet tower was used to supplement the vertical profiles of temperature, humidity, and pressure, which were collected approximately every 30 min, starting 2 h before sunset and continuing until dusk. From the profiles, sensible and latent heat fluxes were estimated. These fluxes were used to diagnose the portion of the boundary layer that was most affected by the early evening transition. During the transition period, a shallow cool and moist layer near the ground was formed, and as the evening progressed the cooling affected an increasingly shallower layer just above the surface.

Analysis of turbulent boundary layers

CERN Document Server

Cebeci, Tuncer

1974-01-01

Analysis of Turbulent Boundary Layers focuses on turbulent flows meeting the requirements for the boundary-layer or thin-shear-layer approximations. Its approach is devising relatively fundamental, and often subtle, empirical engineering correlations, which are then introduced into various forms of describing equations for final solution. After introducing the topic on turbulence, the book examines the conservation equations for compressible turbulent flows, boundary-layer equations, and general behavior of turbulent boundary layers. The latter chapters describe the CS method for calculati

Planetary boundary layer model for estimating the radionuclides concentration in accidental liberations; Modelo de camada limite planetaria para estimar a concentracao de radionuclideos em liberacoes acidentais

Energy Technology Data Exchange (ETDEWEB)

Molnary, Leslie de [Instituto de Pesquisas Energeticas e Nucleares (IPEN), Sao Paulo, SP (Brazil)]. E-mail: molnaryy@net.ipen.br

2002-07-01

A two layer bulk model is used to simulate numerically the time and spatial evolution of concentration of radionuclides in the Planetary Boundary Layer (PBL) for convective and stable conditions. In this model, the closure hypothesis are based on the integrated version of the Turbulent Kinetics Energy equation. This type of model was adopted here because it is numerically simple to be applied operationally in routine and emergency support systems of atmospheric releases at nuclear power plants, and the hypothesis of the efficiency of the vertical mixing seems to be physically reasonable to simulate PBL evolution for high wind conditions and stable conditions in subtropical latitudes regions. In order to validate the model, numerical simulations were carried out with initial and boundary conditions based on vertical profiles of temperatures and horizontal wind speed and direction obtained from tethered balloon soundings, synoptic charts at 850 hPa and surface observations. Comparisons between a 24 hour long numerical simulation and observations indicate that the model is capable of reproduce the diurnal evolution of temperature and horizontal wind during the convective regime. During stable conditions, the slab model was able to simulate the intensity of the surface inversion as a difference between the mixed layer and the surface temperature. The simulated mixed layer height matches with observations during the convective and stable regime. (author)

Comparison of WRF local and nonlocal boundary layer Physics in Greater Kuala Lumpur, Malaysia

Science.gov (United States)

Ooi, M. C. G.; Chan, A.; Kumarenthiran, S.; Morris, K. I.; Oozeer, M. Y.; Islam, M. A.; Salleh, S. A.

2018-02-01

The urban boundary layer (UBL) is the internal advection layer of atmosphere above urban region which determines the exchanges of momentum, water and other atmospheric constituents between the urban land surface and the free troposphere. This paper tested the performance of three planetary boundary layer (PBL) physics schemes of Weather Research and Forecast (WRF) software to ensure the appropriate representation of vertical structure of UBL in Greater Kuala Lumpur (GKL). Comparison was conducted on the performance of respective PBL schemes to generate vertical and near-surface weather profile and rainfall. Mellor-Yamada- Janjíc (MYJ) local PBL scheme coupled with Eta MM5 surface layer scheme was found to predict the near-surface temperature and wind profile and mixing height better than the nonlocal schemes during the intermonsoonal period with least influences of the synoptic background weather.

Stable Boundary Layer Issues

OpenAIRE

Steeneveld, G.J.

2012-01-01

Understanding and prediction of the stable atmospheric boundary layer is a challenging task. Many physical processes are relevant in the stable boundary layer, i.e. turbulence, radiation, land surface coupling, orographic turbulent and gravity wave drag, and land surface heterogeneity. The development of robust stable boundary layer parameterizations for use in NWP and climate models is hampered by the multiplicity of processes and their unknown interactions. As a result, these models suffer ...

The Impact of Microphysics and Planetary Boundary Layer Physics on Model Simulation of U.S. Deep South Summer Convection

Science.gov (United States)

McCaul, Eugene W., Jr.; Case, Jonathan L.; Zavodsky, Bradley T.; Srikishen, Jayanthi; Medlin, Jeffrey M.; Wood, Lance

2014-01-01

Inspection of output from various configurations of high-resolution, explicit convection forecast models such as the Weather Research and Forecasting (WRF) model indicates significant sensitivity to the choices of model physics pararneterizations employed. Some of the largest apparent sensitivities are related to the specifications of the cloud microphysics and planetary boundary layer physics packages. In addition, these sensitivities appear to be especially pronounced for the weakly-sheared, multicell modes of deep convection characteristic of the Deep South of the United States during the boreal summer. Possible ocean-land sensitivities also argue for further examination of the impacts of using unique ocean-land surface initialization datasets provided by the NASA Short-term Prediction Research and Transition (SPoRn Center to select NOAAlNWS weather forecast offices. To obtain better quantitative understanding of these sensitivities and also to determine the utility of the ocean-land initialization data, we have executed matrices of regional WRF forecasts for selected convective events near Mobile, AL (MOB), and Houston, TX (HGX). The matrices consist of identically initialized WRF 24-h forecasts using any of eight microphysics choices and any of three planetary boWldary layer choices. The resulting 24 simulations performed for each event within either the MOB or HGX regions are then compared to identify the sensitivities of various convective storm metrics to the physics choices. Particular emphasis is placed on sensitivities of precipitation timing, intensity, and coverage, as well as amount and coverage oflightuing activity diagnosed from storm kinematics and graupel in the mixed phase layer. The results confirm impressions gleaned from study of the behavior of variously configured WRF runs contained in the ensembles produced each spring at the Center for the Analysis and Prediction of Storms, but with the benefit of more straightforward control of the

AERMOD: A DISPERSION MODEL FOR INDUSTRIAL SOURCE APPLICATIONS PART I: GENERAL MODEL FORMULATION AND BOUNDARY LAYER CHARACTERIZATION

Science.gov (United States)

The formulations of the AMS/EPA Regulatory Model Improvement Committee's applied air dispersion model (AERMOD) as related to the characterization of the planetary boundary layer are described. This is the first in a series of three articles. Part II describes the formulation of...

The BLLAST field experiment: Boundary-Layer Late Afternoon and Sunset Turbulence

Science.gov (United States)

Lothon, M.; Lohou, F.; Pino, D.; Couvreux, F.; Pardyjak, E. R.; Reuder, J.; Vilà-Guerau de Arellano, J.; Durand, P.; Hartogensis, O.; Legain, D.; Augustin, P.; Gioli, B.; Lenschow, D. H.; Faloona, I.; Yagüe, C.; Alexander, D. C.; Angevine, W. M.; Bargain, E.; Barrié, J.; Bazile, E.; Bezombes, Y.; Blay-Carreras, E.; van de Boer, A.; Boichard, J. L.; Bourdon, A.; Butet, A.; Campistron, B.; de Coster, O.; Cuxart, J.; Dabas, A.; Darbieu, C.; Deboudt, K.; Delbarre, H.; Derrien, S.; Flament, P.; Fourmentin, M.; Garai, A.; Gibert, F.; Graf, A.; Groebner, J.; Guichard, F.; Jiménez, M. A.; Jonassen, M.; van den Kroonenberg, A.; Magliulo, V.; Martin, S.; Martinez, D.; Mastrorillo, L.; Moene, A. F.; Molinos, F.; Moulin, E.; Pietersen, H. P.; Piguet, B.; Pique, E.; Román-Cascón, C.; Rufin-Soler, C.; Saïd, F.; Sastre-Marugán, M.; Seity, Y.; Steeneveld, G. J.; Toscano, P.; Traullé, O.; Tzanos, D.; Wacker, S.; Wildmann, N.; Zaldei, A.

2014-10-01

Due to the major role of the sun in heating the earth's surface, the atmospheric planetary boundary layer over land is inherently marked by a diurnal cycle. The afternoon transition, the period of the day that connects the daytime dry convective boundary layer to the night-time stable boundary layer, still has a number of unanswered scientific questions. This phase of the diurnal cycle is challenging from both modelling and observational perspectives: it is transitory, most of the forcings are small or null and the turbulence regime changes from fully convective, close to homogeneous and isotropic, toward a more heterogeneous and intermittent state. These issues motivated the BLLAST (Boundary-Layer Late Afternoon and Sunset Turbulence) field campaign that was conducted from 14 June to 8 July 2011 in southern France, in an area of complex and heterogeneous terrain. A wide range of instrumented platforms including full-size aircraft, remotely piloted aircraft systems, remote-sensing instruments, radiosoundings, tethered balloons, surface flux stations and various meteorological towers were deployed over different surface types. The boundary layer, from the earth's surface to the free troposphere, was probed during the entire day, with a focus and intense observation periods that were conducted from midday until sunset. The BLLAST field campaign also provided an opportunity to test innovative measurement systems, such as new miniaturized sensors, and a new technique for frequent radiosoundings of the low troposphere. Twelve fair weather days displaying various meteorological conditions were extensively documented during the field experiment. The boundary-layer growth varied from one day to another depending on many contributions including stability, advection, subsidence, the state of the previous day's residual layer, as well as local, meso- or synoptic scale conditions. Ground-based measurements combined with tethered-balloon and airborne observations captured the

Evolution of the Planetary Boundary Layer on the northern coast of Brazil during the CHUVA campaign

Science.gov (United States)

Ramos, Diogo Nunes da Silva; Fernandez, Julio Pablo Reyes; Fisch, Gilberto

2018-05-01

This study aims to characterize the wind and thermodynamic structure of the Planetary Boundary Layer (PBL) on the northern coast of Brazil (NCB) via the CHUVA datasets. Three synoptic conditions were present in the NCB region between March 1 and 25, 2010: a dry period, the Upper Tropospheric Cyclonic Vortex (UTCV) and the Intertropical Convergence Zone (ITCZ). Nighttime precipitation accounted for 78% of the total precipitation observed in the month, mainly during the ITCZ. In general, the surface meteorological fields were few changed by intense weather events due to proximity to the ocean and the predominant contribution of the northeasterly trade winds. There was also a weak sea breeze signal that maintained the horizontal moisture flow in the studied area. On dry days, the PBL depth was higher, drier, and warmer, resulting in stronger winds below 500 m. Moreover, trends throughout the period suggest that PBLs are near-neutral below 500 m. However, the wind variability was intensified by up to 20% due to downdrafts and higher wind shears during the deep convection mechanisms derived by UTCV. Furthermore, ITCZ mixed rainfall cooled the PBL at approximately 2 K, making it very stable according to the Richardson number classification adopted. The observed temporal and spatial scale represent challenges to the physical parameterizations used to improve numerical weather prediction models over tropical coastal areas.

Stable Boundary Layer Issues

NARCIS (Netherlands)

Steeneveld, G.J.

2012-01-01

Understanding and prediction of the stable atmospheric boundary layer is a challenging task. Many physical processes are relevant in the stable boundary layer, i.e. turbulence, radiation, land surface coupling, orographic turbulent and gravity wave drag, and land surface heterogeneity. The

The topology of non-linear global carbon dynamics: from tipping points to planetary boundaries

International Nuclear Information System (INIS)

Anderies, J M; Carpenter, S R; Steffen, Will; Rockström, Johan

2013-01-01

We present a minimal model of land use and carbon cycle dynamics and use it to explore the relationship between non-linear dynamics and planetary boundaries. Only the most basic interactions between land cover and terrestrial, atmospheric, and marine carbon stocks are considered in the model. Our goal is not to predict global carbon dynamics as it occurs in the actual Earth System. Rather, we construct a conceptually reasonable heuristic model of a feedback system between different carbon stocks that captures the qualitative features of the actual Earth System and use it to explore the topology of the boundaries of what can be called a ‘safe operating space’ for humans. The model analysis illustrates the existence of dynamic, non-linear tipping points in carbon cycle dynamics and the potential complexity of planetary boundaries. Finally, we use the model to illustrate some challenges associated with navigating planetary boundaries. (letter)

The topology of non-linear global carbon dynamics: from tipping points to planetary boundaries

Science.gov (United States)

Anderies, J. M.; Carpenter, S. R.; Steffen, Will; Rockström, Johan

2013-12-01

We present a minimal model of land use and carbon cycle dynamics and use it to explore the relationship between non-linear dynamics and planetary boundaries. Only the most basic interactions between land cover and terrestrial, atmospheric, and marine carbon stocks are considered in the model. Our goal is not to predict global carbon dynamics as it occurs in the actual Earth System. Rather, we construct a conceptually reasonable heuristic model of a feedback system between different carbon stocks that captures the qualitative features of the actual Earth System and use it to explore the topology of the boundaries of what can be called a ‘safe operating space’ for humans. The model analysis illustrates the existence of dynamic, non-linear tipping points in carbon cycle dynamics and the potential complexity of planetary boundaries. Finally, we use the model to illustrate some challenges associated with navigating planetary boundaries.

Simulation and optimal control of wind-farm boundary layers

Science.gov (United States)

Meyers, Johan; Goit, Jay

2014-05-01

In large wind farms, the effect of turbine wakes, and their interaction leads to a reduction in farm efficiency, with power generated by turbines in a farm being lower than that of a lone-standing turbine by up to 50%. In very large wind farms or `deep arrays', this efficiency loss is related to interaction of the wind farms with the planetary boundary layer, leading to lower wind speeds at turbine level. Moreover, for these cases it has been demonstrated both in simulations and wind-tunnel experiments that the wind-farm energy extraction is dominated by the vertical turbulent transport of kinetic energy from higher regions in the boundary layer towards the turbine level. In the current study, we investigate the use of optimal control techniques combined with Large-Eddy Simulations (LES) of wind-farm boundary layer interaction for the increase of total energy extraction in very large `infinite' wind farms. We consider the individual wind turbines as flow actuators, whose energy extraction can be dynamically regulated in time so as to optimally influence the turbulent flow field, maximizing the wind farm power. For the simulation of wind-farm boundary layers we use large-eddy simulations in combination with actuator-disk and actuator-line representations of wind turbines. Simulations are performed in our in-house pseudo-spectral code SP-Wind that combines Fourier-spectral discretization in horizontal directions with a fourth-order finite-volume approach in the vertical direction. For the optimal control study, we consider the dynamic control of turbine-thrust coefficients in an actuator-disk model. They represent the effect of turbine blades that can actively pitch in time, changing the lift- and drag coefficients of the turbine blades. Optimal model-predictive control (or optimal receding horizon control) is used, where the model simply consists of the full LES equations, and the time horizon is approximately 280 seconds. The optimization is performed using a

Experimental study on effects of inlet boundary layer thickness and boundary layer fence in a turbine cascade

International Nuclear Information System (INIS)

Jun, Y. M.; Chung, J. T.

2000-01-01

The working fluid from the combustor to the turbine stage of a gas turbine makes various boundary layer thickness. Since the inlet boundary layer thickness is one of the important factors that affect the turbine efficiency, It is necessary to investigate secondary flow and loss with various boundary layer thickness conditions. In the present study, the effect of various inlet boundary layer thickness on secondary flow and loss and the proper height of the boundary layer fences for various boundary layer thickness were investigated. Measurements of secondary flow velocity and total pressure loss within and downstream of the passage were taken under 5 boundary layer thickness conditions, 16, 36, 52, 69, 110mm. It was found that total pressure loss and secondary flow areas were increased with increase of thickness but they were maintained almost at the same position. At the following research about the boundary layer fences, 1/6, 1/3, 1/2 of each inlet boundary layer thickness and 12mm were used as the fence heights. As a result, it was observed that the proper height of the fences was generally constant since the passage vortex remained almost at the same position. Therefore once the geometry of a cascade is decided, the location of the passage vortex and the proper fence height are appeared to be determined at the same time. When the inlet boundary layer thickness is relatively small, the loss caused by the proper fence becomes bigger than end wall loss so that it dominates secondary loss. In these cases the proper fence height is decided not by the cascade geometry but by the inlet boundary layer thickness as previous investigations

Large eddy simulation of atmospheric boundary layer over wind farms using a prescribed boundary layer approach

DEFF Research Database (Denmark)

Chivaee, Hamid Sarlak; Sørensen, Jens Nørkær; Mikkelsen, Robert Flemming

2012-01-01

Large eddy simulation (LES) of flow in a wind farm is studied in neutral as well as thermally stratified atmospheric boundary layer (ABL). An approach has been practiced to simulate the flow in a fully developed wind farm boundary layer. The approach is based on the Immersed Boundary Method (IBM......) and involves implementation of an arbitrary prescribed initial boundary layer (See [1]). A prescribed initial boundary layer profile is enforced through the computational domain using body forces to maintain a desired flow field. The body forces are then stored and applied on the domain through the simulation...... and the boundary layer shape will be modified due to the interaction of the turbine wakes and buoyancy contributions. The implemented method is capable of capturing the most important features of wakes of wind farms [1] while having the advantage of resolving the wall layer with a coarser grid than typically...

Agriculture production as a major driver of the earth system exceeding planetary boundaries

DEFF Research Database (Denmark)

Campbell, Bruce Morgan; Beare, Douglas J.; Bennett, Elena M.

2017-01-01

We explore the role of agriculture in destabilizing the Earth system at the planetary scale, through examining nine planetary boundaries, or “safe limits”: land-system change, freshwater use, biogeochemical flows, biosphere integrity, climate change, ocean acidification, stratospheric ozone...

Recent Advances in Modeling of the Atmospheric Boundary Layer and Land Surface in the Coupled WRF-CMAQ Model

Science.gov (United States)

Advances in the land surface model (LSM) and planetary boundary layer (PBL) components of the WRF-CMAQ coupled meteorology and air quality modeling system are described. The aim of these modifications was primarily to improve the modeling of ground level concentrations of trace c...

Impact of Bay-Breeze Circulations on Surface Air Quality and Boundary Layer Export

Science.gov (United States)

Loughner, Christopher P.; Tzortziou, Maria; Follette-Cook, Melanie; Pickering, Kenneth E.; Goldberg, Daniel; Satam, Chinmay; Weinheimer, Andrew; Crawford, James H.; Knapp, David J.; Montzka, Denise D.;

Food supply and bioenergy production within the global cropland planetary boundary.

Science.gov (United States)

Henry, R C; Engström, K; Olin, S; Alexander, P; Arneth, A; Rounsevell, M D A

2018-01-01

Supplying food for the anticipated global population of over 9 billion in 2050 under changing climate conditions is one of the major challenges of the 21st century. Agricultural expansion and intensification contributes to global environmental change and risks the long-term sustainability of the planet. It has been proposed that no more than 15% of the global ice-free land surface should be converted to cropland. Bioenergy production for land-based climate mitigation places additional pressure on limited land resources. Here we test normative targets of food supply and bioenergy production within the cropland planetary boundary using a global land-use model. The results suggest supplying the global population with adequate food is possible without cropland expansion exceeding the planetary boundary. Yet this requires an increase in food production, especially in developing countries, as well as a decrease in global crop yield gaps. However, under current assumptions of future food requirements, it was not possible to also produce significant amounts of first generation bioenergy without cropland expansion. These results suggest that meeting food and bioenergy demands within the planetary boundaries would need a shift away from current trends, for example, requiring major change in the demand-side of the food system or advancing biotechnologies.

Sublayer of Prandtl Boundary Layers

Science.gov (United States)

Grenier, Emmanuel; Nguyen, Toan T.

2018-03-01

The aim of this paper is to investigate the stability of Prandtl boundary layers in the vanishing viscosity limit {ν \\to 0} . In Grenier (Commun Pure Appl Math 53(9):1067-1091, 2000), one of the authors proved that there exists no asymptotic expansion involving one of Prandtl's boundary layer, with thickness of order {√{ν}} , which describes the inviscid limit of Navier-Stokes equations. The instability gives rise to a viscous boundary sublayer whose thickness is of order {ν^{3/4}} . In this paper, we point out how the stability of the classical Prandtl's layer is linked to the stability of this sublayer. In particular, we prove that the two layers cannot both be nonlinearly stable in L^∞. That is, either the Prandtl's layer or the boundary sublayer is nonlinearly unstable in the sup norm.

Zeppelin NT - Measurement Platform for the Exploration of Atmospheric Chemistry and Dynamics in the Planetary Boundary Layer

Science.gov (United States)

Hofzumahaus, Andreas; Holland, Frank; Oebel, Andreas; Rohrer, Franz; Mentel, Thomas; Kiendler-Scharr, Astrid; Wahner, Andreas; Brauchle, Artur; Steinlein, Klaus; Gritzbach, Robert

2014-05-01

The planetary boundary layer (PBL) is the chemically most active and complex part of the atmosphere where freshly emitted reactive trace gases, tropospheric radicals, atmospheric oxidation products and aerosols exhibit a large variability and spatial gradients. In order to investigate the chemical degradation of trace gases and the formation of secondary pollutants in the PBL, a commercial Zeppelin NT was modified to be used as an airborne measurement platform for chemical and physical observations with high spatial resolution. The Zeppelin NT was developed by Zeppelin Luftschifftechnik (ZLT) and is operated by Deutsche Zeppelin Reederei (DZR) in Friedrichshafen, Germany. The modification was performed in cooperation between Forschungszentrum Jülich and ZLT. The airship has a length of 75 m, can lift about 1 ton of scientific payload and can be manoeuvered with high precision by propeller engines. The modified Zeppelin can carry measurement instruments mounted on a platform on top of the Zeppelin, or inside the gondola beneath the airship. Three different instrument packages were developed to investigate a. gas-phase oxidation processes involving free radicals (OH, HO2) b. formation of secondary organic aerosols (SOA) c. new particle formation (nucleation) The presentation will describe the modified airship and provide an overview of its technical performance. Examples of its application during the recent PEGASOS flight campaigns in Europe will be given.

Ensemble using different Planetary Boundary Layer schemes in WRF model for wind speed and direction prediction over Apulia region

Science.gov (United States)

Tateo, Andrea; Marcello Miglietta, Mario; Fedele, Francesca; Menegotto, Micaela; Monaco, Alfonso; Bellotti, Roberto

2017-04-01

The Weather Research and Forecasting mesoscale model (WRF) was used to simulate hourly 10 m wind speed and direction over the city of Taranto, Apulia region (south-eastern Italy). This area is characterized by a large industrial complex including the largest European steel plant and is subject to a Regional Air Quality Recovery Plan. This plan constrains industries in the area to reduce by 10 % the mean daily emissions by diffuse and point sources during specific meteorological conditions named wind days. According to the Recovery Plan, the Regional Environmental Agency ARPA-PUGLIA is responsible for forecasting these specific meteorological conditions with 72 h in advance and possibly issue the early warning. In particular, an accurate wind simulation is required. Unfortunately, numerical weather prediction models suffer from errors, especially for what concerns near-surface fields. These errors depend primarily on uncertainties in the initial and boundary conditions provided by global models and secondly on the model formulation, in particular the physical parametrizations used to represent processes such as turbulence, radiation exchange, cumulus and microphysics. In our work, we tried to compensate for the latter limitation by using different Planetary Boundary Layer (PBL) parameterization schemes. Five combinations of PBL and Surface Layer (SL) schemes were considered. Simulations are implemented in a real-time configuration since our intention is to analyze the same configuration implemented by ARPA-PUGLIA for operational runs; the validation is focused over a time range extending from 49 to 72 h with hourly time resolution. The assessment of the performance was computed by comparing the WRF model output with ground data measured at a weather monitoring station in Taranto, near the steel plant. After the analysis of the simulations performed with different PBL schemes, both simple (e.g. average) and more complex post-processing methods (e.g. weighted average

Experimental investigation of wave boundary layer

DEFF Research Database (Denmark)

Sumer, B. Mutlu

2003-01-01

A review is presented of experimental investigation of wave boundary layer. The review is organized in six main sections. The first section describes the wave boundary layer in a real-life environment and its simulation in the laboratory in an oscillating water tunnel and in a water tank...... with an oscillating seabed. A brief account is given of measured quantities, measurement techniques (LDA, PIV, flow visualization) and limitations/constraints in the experimental investigation of the wave boundary layer in the laboratory. The second section concentrates on uniform oscillating boundary layers...

How to bring absolute sustainability into decision-making: An industry case study using a Planetary Boundary-based methodology

DEFF Research Database (Denmark)

Ryberg, Morten W.; Owsianiak, Mikołaj; Clavreul, Julie

2018-01-01

The Planetary Boundaries concept has emerged as a framework for articulating environmental limits, gaining traction as a basis for considering sustainability in business settings, government policy and international guidelines. There is emerging interest in using the Planetary Boundaries concept...... as part of life cycle assessment (LCA) for gauging absolute environmental sustainability. We tested the applicability of a novel Planetary Boundaries-based life cycle impact assessment methodology on a hypothetical laundry washing case study at the EU level. We express the impacts corresponding...... to the control variables of the individual Planetary Boundaries together with a measure of their respective uncertainties. We tested four sharing principles for assigning a share of the safe operating space (SoSOS) to laundry washing and assessed if the impacts were within the assigned SoSOS. The choice...

Acoustic detection of momentum transfer during the abrupt transition from a laminar to a turbulent atmospheric boundary layer1

International Nuclear Information System (INIS)

Schubert, J.F.

1977-01-01

Acoustic sounder measurements of a vertical profile of the abrupt transition from a laminar to a turbulent atmospheric boundary layer were compared with meteorological measurements made at 10 and 137 m on an instrumented tower. Sounder data show that conditions necessary for the onset of the momentum burst phenomenon exist sometime during a clear afternoon when heat flux changes sign and the planetary surface cools. Under these conditions, the lowest part of the atmospheric boundary layer becomes stable. Prior to this situation, the entire boundary layer is in turbulent motion from surface heating. The boundary layer is then an effective barrier for all fluxes, and as the maximum flux Richardson number is reached at some height close to but above the surface, turbulence is dampened and a laminar layer forms. The profile of this layer is recorded by the sounder. Surface temperature drops, a strong wind shear develops, and the Richardson number decreases below its critical value (Ri/sub cr/<0.25). Subsequently, the laminar layer is eroded by turbulence from above, and with a burst of momentum and heat, it eventually reaches the ground

Exploring the planetary boundary for chemical pollution.

Science.gov (United States)

Diamond, Miriam L; de Wit, Cynthia A; Molander, Sverker; Scheringer, Martin; Backhaus, Thomas; Lohmann, Rainer; Arvidsson, Rickard; Bergman, Åke; Hauschild, Michael; Holoubek, Ivan; Persson, Linn; Suzuki, Noriyuki; Vighi, Marco; Zetzsch, Cornelius

2015-05-01

Rockström et al. (2009a, 2009b) have warned that humanity must reduce anthropogenic impacts defined by nine planetary boundaries if "unacceptable global change" is to be avoided. Chemical pollution was identified as one of those boundaries for which continued impacts could erode the resilience of ecosystems and humanity. The central concept of the planetary boundary (or boundaries) for chemical pollution (PBCP or PBCPs) is that the Earth has a finite assimilative capacity for chemical pollution, which includes persistent, as well as readily degradable chemicals released at local to regional scales, which in aggregate threaten ecosystem and human viability. The PBCP allows humanity to explicitly address the increasingly global aspects of chemical pollution throughout a chemical's life cycle and the need for a global response of internationally coordinated control measures. We submit that sufficient evidence shows stresses on ecosystem and human health at local to global scales, suggesting that conditions are transgressing the safe operating space delimited by a PBCP. As such, current local to global pollution control measures are insufficient. However, while the PBCP is an important conceptual step forward, at this point single or multiple PBCPs are challenging to operationalize due to the extremely large number of commercial chemicals or mixtures of chemicals that cause myriad adverse effects to innumerable species and ecosystems, and the complex linkages between emissions, environmental concentrations, exposures and adverse effects. As well, the normative nature of a PBCP presents challenges of negotiating pollution limits amongst societal groups with differing viewpoints. Thus, a combination of approaches is recommended as follows: develop indicators of chemical pollution, for both control and response variables, that will aid in quantifying a PBCP(s) and gauging progress towards reducing chemical pollution; develop new technologies and technical and social

How to bring absolute sustainability into decision-making: An industry case study using a Planetary Boundary-based methodology.

Science.gov (United States)

Ryberg, Morten W; Owsianiak, Mikołaj; Clavreul, Julie; Mueller, Carina; Sim, Sarah; King, Henry; Hauschild, Michael Z

2018-09-01

The Planetary Boundaries concept has emerged as a framework for articulating environmental limits, gaining traction as a basis for considering sustainability in business settings, government policy and international guidelines. There is emerging interest in using the Planetary Boundaries concept as part of life cycle assessment (LCA) for gauging absolute environmental sustainability. We tested the applicability of a novel Planetary Boundaries-based life cycle impact assessment methodology on a hypothetical laundry washing case study at the EU level. We express the impacts corresponding to the control variables of the individual Planetary Boundaries together with a measure of their respective uncertainties. We tested four sharing principles for assigning a share of the safe operating space (SoSOS) to laundry washing and assessed if the impacts were within the assigned SoSOS. The choice of sharing principle had the greatest influence on the outcome. We therefore highlight the need for more research on the development and choice of sharing principles. Although further work is required to operationalize Planetary Boundaries in LCA, this study shows the potential to relate impacts of human activities to environmental boundaries using LCA, offering company and policy decision-makers information needed to promote environmental sustainability. Copyright © 2018 Elsevier B.V. All rights reserved.

Has land use pushed terrestrial biodiversity beyond the planetary boundary? A global assessment.

Science.gov (United States)

Newbold, Tim; Hudson, Lawrence N; Arnell, Andrew P; Contu, Sara; De Palma, Adriana; Ferrier, Simon; Hill, Samantha L L; Hoskins, Andrew J; Lysenko, Igor; Phillips, Helen R P; Burton, Victoria J; Chng, Charlotte W T; Emerson, Susan; Gao, Di; Pask-Hale, Gwilym; Hutton, Jon; Jung, Martin; Sanchez-Ortiz, Katia; Simmons, Benno I; Whitmee, Sarah; Zhang, Hanbin; Scharlemann, Jörn P W; Purvis, Andy

2016-07-15

Land use and related pressures have reduced local terrestrial biodiversity, but it is unclear how the magnitude of change relates to the recently proposed planetary boundary ("safe limit"). We estimate that land use and related pressures have already reduced local biodiversity intactness--the average proportion of natural biodiversity remaining in local ecosystems--beyond its recently proposed planetary boundary across 58.1% of the world's land surface, where 71.4% of the human population live. Biodiversity intactness within most biomes (especially grassland biomes), most biodiversity hotspots, and even some wilderness areas is inferred to be beyond the boundary. Such widespread transgression of safe limits suggests that biodiversity loss, if unchecked, will undermine efforts toward long-term sustainable development. Copyright © 2016, American Association for the Advancement of Science.

The Bottom Boundary Layer.

Science.gov (United States)

Trowbridge, John H; Lentz, Steven J

2018-01-03

The oceanic bottom boundary layer extracts energy and momentum from the overlying flow, mediates the fate of near-bottom substances, and generates bedforms that retard the flow and affect benthic processes. The bottom boundary layer is forced by winds, waves, tides, and buoyancy and is influenced by surface waves, internal waves, and stratification by heat, salt, and suspended sediments. This review focuses on the coastal ocean. The main points are that (a) classical turbulence concepts and modern turbulence parameterizations provide accurate representations of the structure and turbulent fluxes under conditions in which the underlying assumptions hold, (b) modern sensors and analyses enable high-quality direct or near-direct measurements of the turbulent fluxes and dissipation rates, and (c) the remaining challenges include the interaction of waves and currents with the erodible seabed, the impact of layer-scale two- and three-dimensional instabilities, and the role of the bottom boundary layer in shelf-slope exchange.

The Bottom Boundary Layer

Science.gov (United States)

Trowbridge, John H.; Lentz, Steven J.

2018-01-01

The oceanic bottom boundary layer extracts energy and momentum from the overlying flow, mediates the fate of near-bottom substances, and generates bedforms that retard the flow and affect benthic processes. The bottom boundary layer is forced by winds, waves, tides, and buoyancy and is influenced by surface waves, internal waves, and stratification by heat, salt, and suspended sediments. This review focuses on the coastal ocean. The main points are that (a) classical turbulence concepts and modern turbulence parameterizations provide accurate representations of the structure and turbulent fluxes under conditions in which the underlying assumptions hold, (b) modern sensors and analyses enable high-quality direct or near-direct measurements of the turbulent fluxes and dissipation rates, and (c) the remaining challenges include the interaction of waves and currents with the erodible seabed, the impact of layer-scale two- and three-dimensional instabilities, and the role of the bottom boundary layer in shelf-slope exchange.

The different influence of the residual layer on the development of the summer convective boundary layer in two deserts in northwest China

Science.gov (United States)

Lin, Zhao; Bo, Han; Shihua, Lv; Lijuan, Wen; Xianhong, Meng; Zhaoguo, Li

2018-02-01

The development of the atmospheric boundary layer is closely connected with the exchange of momentum, heat, and mass near the Earth's surface, especially for a convective boundary layer (CBL). Besides being modulated by the buoyancy flux near the Earth's surface, some studies point out that a neutrally stratified residual layer is also crucial for the appearance of a deep CBL. To verify the importance of the residual layer, the CBLs over two deserts in northwest China (Badan Jaran and Taklimakan) were investigated. The summer CBL mean depth over the Taklimakan Desert is shallower than that over the Badan Jaran Desert, even when the sensible heat flux of the former is stronger. Meanwhile, the climatological mean residual layer in the Badan Jaran Desert is much deeper and neutrally stratified in summer. Moreover, we found a significant and negative correlation between the lapse rate of the residual layer and the CBL depth over the Badan Jaran Desert. The different lapse rates of the residual layer in the two regions are partly connected with the advection heating from large-scale atmospheric circulation. The advection heating tends to reduce the temperature difference in the 700 to 500-hPa layer over the Badan Jaran Desert, and it increases the stability in the same atmospheric layer over the Taklimakan Desert. The advection due to climatological mean atmospheric circulation is more effective at modulating the lapse rate of the residual layer than from varied circulation. Also, the interannual variation of planetary boundary layer (PBL) height over two deserts was found to covary with the wave train.

Vertical transport of water in the Martian boundary layer

Science.gov (United States)

Zent, Aaron P.; Haberle, R. M.; Houben, Howard C.

1993-01-01

We are continuing our examination of the transport of H2O through the martian boundary layer, and we have written a one-dimensional numerical model of the exchange of H2O between the atmosphere and subsurface of Mars through the planetary boundary layer (PBL). Our goal is to explore the mechanisms of H2O exchange, and to elucidate the role played by the regolith in the local H2O budget. The atmospheric model includes effects of Coriolis, pressure gradient, and frictional forces for momentum, as well as radiation, sensible heat flux, and advection for heat. The model differs from Flasar and Goody by use of appropriate Viking-based physical constants and inclusion of the radiative effects of atmospheric dust. We specify the pressure gradient force or compute it from a simple slope model. The subsurface model accounts for conduction of heat and diffusion of H2O through a porous adsorbing medium in response to diurnal forcing. The model is initialized with depth-independent H2O concentrations (2 kg M(exp -3)) in the regolith, and a dry atmosphere. The model terminates when the atmospheric H2O column abundance stabilizes at 0.1 percent per sol.

Determination of boundary layer top on the basis of the characteristics of atmospheric particles

Science.gov (United States)

Liu, Boming; Ma, Yingying; Gong, Wei; Zhang, Ming; Yang, Jian

2018-04-01

The planetary boundary layer (PBL) is the lowest layer of the atmosphere that can be directly influenced with the Earth's surface. This layer can also respond to surface forcing. The determination of the PBL is significant to environmental and climate research. PBL can also serve as an input parameter for further data processing with atmospheric models. Traditional detection algorithms are susceptible to errors associated with the vertical distribution of aerosol concentrations. To overcome this limitation, a maximum difference search (MDS) algorithm was proposed to calculate the top of the boundary layer based on differences in particle characteristics. The top positions of the PBL from MDS algorithm under different convection states were compared with those from conventional methods. Experimental results demonstrated that the MDS method can determine the top of the boundary layer precisely. The proposed algorithm can also be used to calculate the top of the PBL accurately under weak convection conditions where the traditional methods cannot be applied. Finally, experimental data from June 2015 to December 2015 were analysed to verify the reliability of the MDS algorithm. The correlation coefficients R2 (RMSE) between the results of MDS algorithm and radiosonde measurements were 0.53 (115 m), 0.79 (141 m) and 0.96 (43 m) under weak, moderate and strong convections, respectively. These findings indicated that the proposed method possessed a good feasibility and stability.

Diffusive boundary layers over varying topography

KAUST Repository

Dell, R. W.

2015-03-25

Diffusive bottom boundary layers can produce upslope flows in a stratified fluid. Accumulating observations suggest that these boundary layers may drive upwelling and mixing in mid-ocean ridge flank canyons. However, most studies of diffusive bottom boundary layers to date have concentrated on constant bottom slopes. We present a study of how diffusive boundary layers interact with various idealized topography, such as changes in bottom slope, slopes with corrugations and isolated sills. We use linear theory and numerical simulations in the regional ocean modeling system (ROMS) model to show changes in bottom slope can cause convergences and divergences within the boundary layer, in turn causing fluid exchanges that reach far into the overlying fluid and alter stratification far from the bottom. We also identify several different regimes of boundary-layer behaviour for topography with oceanographically relevant size and shape, including reversing flows and overflows, and we develop a simple theory that predicts the regime boundaries, including what topographies will generate overflows. As observations also suggest there may be overflows in deep canyons where the flow passes over isolated bumps and sills, this parameter range may be particularly significant for understanding the role of boundary layers in the deep ocean.

Investigation of Kelvin-Helmholtz Instability in the boundary layer using Doppler lidar and radiosonde data

Science.gov (United States)

Das, Subrata Kumar; Das, Siddarth Shankar; Saha, Korak; Murali Krishna, U. V.; Dani, K. K.

2018-04-01

Characteristics of Kelvin Helmholtz Instability (KHI) using Doppler wind lidar observation have rarely been reported during the Indian summer monsoon season. In this paper, we present a case study of KHI near planetary boundary layer using Doppler wind lidar and radiosonde measurements at Mahabubnagar, a tropical Indian station. The data was collected during the Integrated Ground Observation Campaign (June-October 2011) under the Cloud Aerosol Interaction and Precipitation Enhancement EXperiment-2011. The continuous wind lidar observation during 10-16 August 2011 shows there is an increase in carrier-to-noise ratio values near planetary boundary layer from 03:00 to 11:00 LT on 13 August; reveals the formation of KHI. There is a strong power bursts pattern corresponding to high turbulence characteristics in the early half of the day. The KHI temporal evolution from initial to dissipating stage is observed with clear variation in the carrier-to-noise ratio values. The observed KHI billows are in the height between 600 and 1200 m and lasted for about 7.5 h. The vertical velocity from Doppler lidar measurement shows the presence of updrafts after breaking of KHI in the boundary layer. The presence of strong wind shear, high stability parameter, low Richardson number and high relative humidity during the enhanced carrier-to-noise ratio period indicates the ideal condition for the formation and persistence of this dynamic instability. A typical characteristic of trapped humidity above the KHI billows suggest the presence of strong inversion. A wavelet analysis of 3-dimensional wind components show dominant periodicity of 45-65 min and the periodicity in vertical wind is more prominent.

Structure of the low-latitude boundary layer

International Nuclear Information System (INIS)

Sckopke, N.; Paschmann, G.; Haerendel, G.; Sonnerup, B.U.O.; Bame, S.J.; Forbes, T.G.; Hones, E.W. Jr.; Russell, C.T.

1981-01-01

Observations at high temporal resolution of the frontside magnetopause and plasma boundary layer, made with the Los Alamos Scientific Laboratory/Max-Planck-Institut, Institut fuer Extraterrestrische Physik, fast plasma analyzer on board the Isee 1 and 2 spacecraft, have revealed a complex quasi-periodic structure of some of the observed boundary layers: cool tailward streaming boundary layer plasma is seen intermittently, with intervening periods of hot tenuous plasma which has properties similar to the magnetospheric population. While individual encounters with the boundary layer plasma last only a few minutes, the total observation time may extend over 1 hour or more. One such crossing, at 0800 hours local time and 40 0 northern GSM latitude, is examined in detail, including a quantitative comparison of the boundary layer entry and exit times of the two spacecraft. The data are found to be compatible with a boundary layer that is always attached to the magnetopause but where the layer thickness has a large-scale spatial modulation pattern which travels tailward past the spacecraft. Included are periods when the thickness is essentially zero and others when it is of the order of 1 R/sub E/. The duration of these periods is highly variable but is typically in the range of 2--5 min, corresponding to a distance along the magnetopause of the order of 3--8 R/sub E/. The observed boundary layer features include a steep density gradient at the magnetopause, with an approximately constant boundary layer plasma density amounting to about 25% of the magnetosheath density, and a second abrupt density decrease at the inner edge of the layer. It also appears that the purely magnetospheric plasma is ocassionally separated from the boundary layer by a halo region in which the plasma density is somewhat higher, and the temperature somewhat lower, than in the magnetosphere. A tentative model is proposed

Benthic boundary layer modelling studies

International Nuclear Information System (INIS)

Richards, K.J.

1984-01-01

A numerical model has been developed to study the factors which control the height of the benthic boundary layer in the deep ocean and the dispersion of a tracer within and directly above the layer. This report covers tracer clouds of horizontal scales of 10 to 100 km. The dispersion of a tracer has been studied in two ways. Firstly, a number of particles have been introduced into the flow. The trajectories of these particles provide information on dispersion rates. For flow conditions similar to those observed in the abyssal N.E. Atlantic the diffusivity of a tracer was found to be 5 x 10 6 cm 2 s -1 for a tracer within the boundary layer and 8 x 10 6 cm 2 s -1 for a tracer above the boundary layer. The results are in accord with estimates made from current meter measurements. The second method of studying dispersion was to calculate the evolution of individual tracer clouds. Clouds within and above the benthic boundary layer often show quite different behaviour from each other although the general structure of the clouds in the two regions were found to have no significant differences. (author)

Problems of matter-antimatter boundary layers

International Nuclear Information System (INIS)

Lehnert, B.

1975-01-01

This paper outlines the problems of the quasi-steady matter-antimatter boundary layers discussed in Klein-Alfven's cosmological theory, and a crude model of the corresponding ambiplasma balance is presented: (i) at interstellar particle densities, no well-defined boundary layer can exist in presence of neutral gas, nor can such a layer be sustained in an unmagnetized fully ionized ambiplasma. (ii) Within the limits of applicability of the present model, sharply defined boundary layers are under certain conditions found to exist in a magnetized ambiplasma. Thus, at beta values less than unity, a steep pressure drop of the low-energy components of matter and antimatter can be balanced by a magnetic field and the electric currents in the ambiplasma. (iii) The boundary layer thickness is of the order of 2x 0 approximately 10/BT 0 sup(1/4) meters, where B is the magnetic field strength in MKS units and T 0 the characteristic temperature of the low-energy components in the layer. (Auth.)

Linking planetary boundaries and ecosystem accounting, with an illustration for the Colombian Orinoco river basin

NARCIS (Netherlands)

Vargas, Leonardo; Willemen, L.; Hein, Lars

2018-01-01

Economic development has increased pressures on natural resources during the last decades. The concept of planetary boundaries has been developed to propose limits on human activities based on earth processes and ecological thresholds. However, this concept was not developed to downscale planetary

From Planetary Boundaries to national fair shares of the global safe operating space - How can the scales be bridged?

Science.gov (United States)

Häyhä, Tiina; Cornell, Sarah; Lucas, Paul; van Vuuren, Detlef; Hoff, Holger

2016-04-01

The planetary boundaries framework proposes precautionary quantitative global limits to the anthropogenic perturbation of crucial Earth system processes. In this way, it marks out a planetary 'safe operating space' for human activities. However, decisions regarding resource use and emissions are mostly made at much smaller scales, mostly by (sub-)national and regional governments, businesses, and other local actors. To operationalize the planetary boundaries, they need to be translated into and aligned with targets that are relevant at these smaller scales. In this paper, we develop a framework that addresses the three dimension of bridging across scales: biophysical, socio-economic and ethical, to provide a consistent universally applicable approach for translating the planetary boundaries into national level context-specific and fair shares of the safe operating space. We discuss our findings in the context of previous studies and their implications for future analyses and policymaking. In this way, we help link the planetary boundaries framework to widely- applied operational and policy concepts for more robust strong sustainability decision-making.

Boundary-layer effects in droplet splashing

Science.gov (United States)

Riboux, Guillaume; Gordillo, Jose Manuel

2017-11-01

A drop falling onto a solid substrate will disintegrate into smaller parts when its impact velocity exceeds the so called critical velocity for splashing. Under these circumstances, the very thin liquid sheet ejected tangentially to the solid after the drop touches the substrate, lifts off as a consequence of the aerodynamic forces exerted on it and finally breaks into smaller droplets, violently ejected radially outwards, provoking the splash. Here, the tangential deceleration experienced by the fluid entering the thin liquid sheet is investigated making use of boundary layer theory. The velocity component tangent to the solid, computed using potential flow theory provides the far field boundary condition as well as the pressure gradient for the boundary layer equations. The structure of the flow permits to find a self similar solution of the boundary layer equations. This solution is then used to calculate the boundary layer thickness at the root of the lamella as well as the shear stress at the wall. The splash model presented in, which is slightly modified to account for the results obtained from the boundary layer analysis, provides a very good agreement between the measurements and the predicted values of the critical velocity for the splash.

Boundary layers of the earth's outer magnetosphere

Science.gov (United States)

Eastman, T. E.; Frank, L. A.

1984-01-01

The magnetospheric boundary layer and the plasma-sheet boundary layer are the primary boundary layers of the earth's outer magnetosphere. Recent satellite observations indicate that they provide for more than 50 percent of the plasma and energy transport in the outer magnetosphere although they constitute less than 5 percent by volume. Relative to the energy density in the source regions, plasma in the magnetospheric boundary layer is predominantly deenergized whereas plasma in the plasma-sheet boundary layer has been accelerated. The reconnection hypothesis continues to provide a useful framework for comparing data sampled in the highly dynamic magnetospheric environment. Observations of 'flux transfer events' and other detailed features near the boundaries have been recently interpreted in terms of nonsteady-state reconnection. Alternative hypotheses are also being investigated. More work needs to be done, both in theory and observation, to determine whether reconnection actually occurs in the magnetosphere and, if so, whether it is important for overall magnetospheric dynamics.

Boundary layers of the earth's outer magnetosphere

International Nuclear Information System (INIS)

Eastman, T.E.; Frank, L.A.

1984-01-01

The magnetospheric boundary layer and the plasma-sheet boundary layer are the primary boundary layers of the earth's outer magnetosphere. Recent satellite observations indicate that they provide for more than 50 percent of the plasma and energy transport in the outer magnetosphere although they constitute less than 5 percent by volume. Relative to the energy density in the source regions, plasma in the magnetospheric boundary layer is predominantly deenergized whereas plasma in the plasma-sheet boundary layer has been accelerated. The reconnection hypothesis continues to provide a useful framework for comparing data sampled in the highly dynamic magnetospheric environment. Observations of flux transfer events and other detailed features near the boundaries have been recently interpreted in terms of nonsteady-state reconnection. Alternative hypotheses are also being investigated. More work needs to be done, both in theory and observation, to determine whether reconnection actually occurs in the magnetosphere and, if so, whether it is important for overall magnetospheric dynamics. 30 references

Boundary-Layer Characteristics Over a Coastal Megacity

Science.gov (United States)

Melecio-Vazquez, D.; Ramamurthy, P.; Arend, M.; Moshary, F.; Gonzalez, J.

2017-12-01

Boundary-layer characteristics over New York City are analyzed for various local and synoptic conditions over several seasons. An array of vertical profilers, including a Doppler LiDAR, a micro-pulse LiDAR and a microwave radiometer are used to observe the structure and evolution of the boundary-layer. Additionally, an urbanized Weather Research and Forecasting (uWRF) model coupled to a high resolution landcover/land-use database is used to study the spatial variability in boundary layer characteristics. The summer daytime averaged potential temperature profile from the microwave radiometer shows the presence of a thermal internal boundary layer wherein a superadiabatic layer lies underneath a stable layer instead of a mixed-layer. Both the winter daytime and nighttime seasonal averages show that the atmosphere remains unstable near the surface and does not reach stable conditions during the nighttime. The mixing ratio seasonal averages show peaks in humidity near 200-m and 1100-m, above instrument level, which could result from sea breeze and anthropogenic sources. Ceilometer measurements show a high degree of variability in boundary layer height depending on wind direction. Comparison with uWRF results show that the model tends to overestimate convective efficiency for selected summer and winter cases and therefore shows a much deeper thermal boundary layer than the observed profiles. The model estimates a less humid atmosphere than seen in observations.

Validation and Spatiotemporal Distribution of GEOS-5-Based Planetary Boundary Layer Height and Relative Humidity in China

Science.gov (United States)

Si, Yidan; Li, Shenshen; Chen, Liangfu; Yu, Chao; Wang, Zifeng; Wang, Yang; Wang, Hongmei

2018-04-01

Few studies have specifically focused on the validation and spatiotemporal distribution of planetary boundary layer height (PBLH) and relative humidity (RH) data in China. In this analysis, continuous PBLH and surface-level RH data simulated from GEOS-5 between 2004 and 2012, were validated against ground-based observations. Overall, the simulated RH was consistent with the statistical data from meteorological stations, with a correlation coefficient of 0.78 and a slope of 0.9. However, the simulated PBLH was underestimated compared to LIDAR data by a factor of approximately two, which was primarily because of poor simulation in late summer and early autumn. We further examined the spatiotemporal distribution characteristics of two factors in four regions—North China, South China, Northwest China, and the Tibetan Plateau. The results showed that the annual PBLH trends in all regions were fairly moderate but sensitive to solar radiation and precipitation, which explains why the PBLH values were ranked in order from largest to smallest as follows: Tibetan Plateau, Northwest China, North China, and South China. Strong seasonal variation of the PBLH exhibited high values in summer and low values in winter, which was also consistent with the turbulent vertical exchange. Not surprisingly, the highest RH in South China and the lowest RH in desert areas of Northwest China (less than 30%). Seasonally, South China exhibited little variation, whereas Northwest China exhibited its highest humidity in winter and lowest humidity in spring, the maximum values in the other regions were obtained from July to September.

Diamagnetic boundary layers: a kinetic theory

International Nuclear Information System (INIS)

Lemaire, J.; Burlaga, L.F.

1976-01-01

A kinetic theory for boundary layers associated with MHD tangential 'discontinuities' in a collisionless magnetized plasma such as those observed in the solar wind is presented. The theory consists of finding self-consistent solutions of Vlasov's equation and Maxwell's equation for stationary, one-dimensional boundary layers separating two Maxwellian plasma states. Layers in which the current is carried by electrons are found to have a thickness of the order of a few electron gyroradii, but the drift speed of the current-carrying electrons is found to exceed the Alfven speed, and accordingly such layers are not stable. Several types of layers, in which the current is carried by protons are discussed; in particular, cases in which the magnetic field intensity and/or direction changed across the layer were considered. In every case, the thickness was of the order of a few proton gyroradii and the field changed smoothly , although the characteristics depended somewhat on the boundary conditions. The drift speed was always less than the Alfven speed, consistent with stability of such structures. The results are consistent with the observations of boundary layers in the solar wind near 1 AU. (Auth.)

Velocity Spectra in the Unstable Planetary Boundary Layer

DEFF Research Database (Denmark)

Højstrup, Jørgen

1982-01-01

Models for velocity spectra of all three components in the lower half of the unstable PBL are presented. The model spectra are written as a sum of two parts, nS(n) = A(fi, z/zi)w*2 + B(f, z/zi)u*02, a mixed layer part with a stability dependence, and a surface layer part without stability...

Diagnosis of boundary-layer circulations.

Science.gov (United States)

Beare, Robert J; Cullen, Michael J P

2013-05-28

Diagnoses of circulations in the vertical plane provide valuable insights into aspects of the dynamics of the climate system. Dynamical theories based on geostrophic balance have proved useful in deriving diagnostic equations for these circulations. For example, semi-geostrophic theory gives rise to the Sawyer-Eliassen equation (SEE) that predicts, among other things, circulations around mid-latitude fronts. A limitation of the SEE is the absence of a realistic boundary layer. However, the coupling provided by the boundary layer between the atmosphere and the surface is fundamental to the climate system. Here, we use a theory based on Ekman momentum balance to derive an SEE that includes a boundary layer (SEEBL). We consider a case study of a baroclinic low-level jet. The SEEBL solution shows significant benefits over Ekman pumping, including accommodating a boundary-layer depth that varies in space and structure, which accounts for buoyancy and momentum advection. The diagnosed low-level jet is stronger than that determined by Ekman balance. This is due to the inclusion of momentum advection. Momentum advection provides an additional mechanism for enhancement of the low-level jet that is distinct from inertial oscillations.

Characteristics of the magnetospheric boundary layer and magnetopause layer as observed by Imp 6

International Nuclear Information System (INIS)

Eastman, T.E.; Hones, E.W. Jr.

1979-01-01

Imp 6 observations of the low-latitude magnetospheric boundary layer indicate that the plasma within it is supplied primarily by direct entry of magnetosheath plasma across the magnetopause layer. We define the magnetopause layer as the current layer (separating the magnetosheath from the boundary layer) through which the magnetic field shifts in direction. High temporal resolution (3-s average) data reveal that in a majority of Imp 6 magnetopause crossing, no distinct changes in electron density or energry spectra are observed at the magne opause layer. In all Imp 6 crossings, some magnetosheathlike plasma is observed earthward of the magnetopause layer, implying the existence of a boundary layer. Boundary layer electron energy spectra are often virtually indistinguishable from the adjacent magnetosheath spectra. Low-latitude boundary layer bulk plasma flow as observed by Imp 6 almost always has an antisunward component and often has a significant cross-field component. The boundary layer thickness is highly variable and is generally much larger than the magnetopause layer thickness. Energetic electron pitch angle distributions indicate that the low-latitude boundary layers is normally on closed field lines. We conclude that diffusive as well as nondiffusive processes probably contribute to the entry of magnetosheath plasma into the boundary layer

Differences in the efficacy of climate forcings explained by variations in atmospheric boundary layer depth.

Science.gov (United States)

Davy, Richard; Esau, Igor

2016-05-25

The Earth has warmed in the last century and a large component of that warming has been attributed to increased anthropogenic greenhouse gases. There are also numerous processes that introduce strong, regionalized variations to the overall warming trend. However, the ability of a forcing to change the surface air temperature depends on its spatial and temporal distribution. Here we show that the efficacy of a forcing is determined by the effective heat capacity of the atmosphere, which in cold and dry climates is defined by the depth of the planetary boundary layer. This can vary by an order of magnitude on different temporal and spatial scales, and so we get a strongly amplified temperature response in shallow boundary layers. This must be accounted for to assess the efficacy of a climate forcing, and also implies that multiple climate forcings cannot be linearly combined to determine the temperature response.

Suction of MHD boundary layer flows

International Nuclear Information System (INIS)

Rao, B.N.

1985-01-01

The boundary layer growth with tensor electrical conductivity and the transpiration number has been examined using local nonsimilarity solutions method. It is found that suction will cause the increase in wall shearing stress and decrease in thicknesses of the boundary layer. (Auth.)

Horses for courses: analytical tools to explore planetary boundaries

Science.gov (United States)

van Vuuren, Detlef P.; Lucas, Paul L.; Häyhä, Tiina; Cornell, Sarah E.; Stafford-Smith, Mark

2016-03-01

There is a need for more integrated research on sustainable development and global environmental change. In this paper, we focus on the planetary boundaries framework to provide a systematic categorization of key research questions in relation to avoiding severe global environmental degradation. The four categories of key questions are those that relate to (1) the underlying processes and selection of key indicators for planetary boundaries, (2) understanding the impacts of environmental pressure and connections between different types of impacts, (3) better understanding of different response strategies to avoid further degradation, and (4) the available instruments to implement such strategies. Clearly, different categories of scientific disciplines and associated model types exist that can accommodate answering these questions. We identify the strength and weaknesses of different research areas in relation to the question categories, focusing specifically on different types of models. We discuss that more interdisciplinary research is need to increase our understanding by better linking human drivers and social and biophysical impacts. This requires better collaboration between relevant disciplines (associated with the model types), either by exchanging information or by fully linking or integrating them. As fully integrated models can become too complex, the appropriate type of model (the racehorse) should be applied for answering the target research question (the race course).

Effects of leaf area index on the coupling between water table, land surface energy fluxes, and planetary boundary layer at the regional scale

Science.gov (United States)

Lu, Y.; Rihani, J.; Langensiepen, M.; Simmer, C.

2013-12-01

Vegetation plays an important role in the exchange of moisture and energy at the land surface. Previous studies indicate that vegetation increases the complexity of the feedbacks between the atmosphere and subsurface through processes such as interception, root water uptake, leaf surface evaporation, and transpiration. Vegetation cover can affect not only the interaction between water table depth and energy fluxes, but also the development of the planetary boundary layer. Leaf Area Index (LAI) is shown to be a major factor influencing these interactions. In this work, we investigate the sensitivity of water table, surface energy fluxes, and atmospheric boundary layer interactions to LAI as a model input. We particularly focus on the role LAI plays on the location and extent of transition zones of strongest coupling and how this role changes over seasonal timescales for a real catchment. The Terrestrial System Modelling Platform (TerrSysMP), developed within the Transregional Collaborative Research Centre 32 (TR32), is used in this study. TerrSysMP consists of the variably saturated groundwater model ParFlow, the land surface model Community Land Model (CLM), and the regional climate and weather forecast model COSMO (COnsortium for Small-scale Modeling). The sensitivity analysis is performed over a range of LAI values for different vegetation types as extracted from the Moderate Resolution Imaging Spectroradiometer (MODIS) dataset for the Rur catchment in Germany. In the first part of this work, effects of vegetation structure on land surface energy fluxes and their connection to water table dynamics are studied using the stand-alone CLM and the coupled subsurface-surface components of TerrSysMP (ParFlow-CLM), respectively. The interconnection between LAI and transition zones of strongest coupling are investigated and analyzed through a subsequent set of subsurface-surface-atmosphere coupled simulations implementing the full TerrSysMP model system.

Convective Heat Transfer at the Martian Boundary Layer, Measurement and Model

Science.gov (United States)

Tomás Soria-Salinas, Álvaro; Zorzano-Mier, María Paz; Martín-Torres, Javier

2016-04-01

We present a measuring concept to measure the convective heat transfer coefficient h near a spacecraft operating on the surface of Mars. This coefficient can be used to derive the speed of the wind and direction, and to detect its modulations. This measuring concept will be used in the instrument HABIT (HabitAbility: Brines, Irradiance and Temperature) for the Surface Platform of ExoMars 2018 (ESA-Roscosmos). The method is based on the use of 3 Resistance Temperature Thermodetectors (RTD) that measure the temperature at 3 locations along the axial direction of a rod of length L: at the base of the rod, Tb, an intermediate point x = L/n, TLn, and the tip,Ta. This sensing fin is called the Air Temperature Sensor (ATS). HABIT shall incorporate three ATS, oriented in perpendicular directions and thus exposed to wind in a different way. Solving these equations for each ATS, provides three fluid temperatures Tf as well as three m parameters that are used to derive three heat transfer coefficients h. This magnitude is dependent on the local forced convection and therefore is sensitive to the direction, speed and modulations of the wind. The m-parameter has already proven to be useful to investigate the convective activity at the planetary boundary layer on Mars and to determine the height of the planetary boundary layer. This method shall be presented here by: 1) Introducing the mathematical concepts for the retrieval of the m-parameter; 2) performing ANSYS simulations of the fluid dynamics and the thermal environment around the ATS-rods under wind conditions in Mars; and 3) comparing the method by using data measurements from the Rover Environmental Monitoring Station (REMS) at the Curiosity rover of NASA's Mars Science Laboratory project currently operating on Mars. The results shall be compared with the wind sensor measurements of three years of REMS operation on Mars.

Universal dependences between turbulent and mean flow parameters instably and neutrally stratified Planetary Boundary Layers

Directory of Open Access Journals (Sweden)

I. N. Esau

2006-01-01

Full Text Available We consider the resistance law for the planetary boundary layer (PBL from the point of view of the similarity theory. In other words, we select the set of the PBL governing parameters and search for an optimal way to express through these parameters the geostrophic drag coefficient Cg=u* /Ug and the cross isobaric angle α (where u* is the friction velocity and Ug is the geostrophic wind speed. By this example, we demonstrate how to determine the 'parameter space' in the most convenient way, so that make independent the dimensionless numbers representing co-ordinates in the parameter space, and to avoid (or at least minimise artificial self-correlations caused by the appearance of the same factors (such as u* in the examined dimensionless combinations (e.g. in Cg=u* /Ug and in dimensionless numbers composed of the governing parameters. We also discuss the 'completeness' of the parameter space from the point of view of large-eddy simulation (LES modeller creating a database for a specific physical problem. As recognised recently, very large scatter of data in prior empirical dependencies of Cg and α on the surface Rossby number Ro=Ug| fz0|-1 (where z0 is the roughness length and the stratification characterised by µ was to a large extent caused by incompactness of the set of the governing parameters. The most important parameter overlooked in the traditional approach is the typical value of the Brunt-Väisälä frequency N in the free atmosphere (immediately above the PBL, which involves, besides Ro and µ, one more dimensionless number: µN=N/ | f |. Accordingly, we consider Cg and α as dependent on the three (rather then two basic dimensionless numbers (including µN using LES database DATABASE64. By these means we determine the form of the dependencies under consideration in the part of the parameter space representing typical atmospheric PBLs, and provide analytical expressions for Cg and α.

Planetary boundary layer height over the Indian subcontinent: Variability and controls with respect to monsoon

Science.gov (United States)

Sathyanadh, Anusha; Prabhakaran, Thara; Patil, Chetana; Karipot, Anandakumar

2017-10-01

Planetary boundary layer (PBL) height characteristics over the Indian sub-continent at diurnal to seasonal scales and its controlling factors in relation to monsoon are investigated. The reanalysis (Modern Era Retrospective analysis for Research and Applications, MERRA) PBL heights (PBLH) used for the study are validated against those derived from radiosonde observations and radio occultation air temperature and humidity profiles. The radiosonde observations include routine India Meteorological Department observations at two locations (coastal and an inland) for one full year and campaign based early afternoon radiosonde observations at six inland locations over the study region for selected days from May-September 2011. The temperature and humidity profiles from radio occultations spread over the sub-continent at irregular timings during the year 2011. The correlations and root mean square errors are in the range 0.74-0.83 and 407 m-643 m, respectively. Large pre-monsoon, monsoon and post-monsoon variations in PBL maximum height (1000 m-4000 m), time of occurrence of maximum height (11:00 LST-17:00 LST) and growth rate (100 to 400 m h- 1) are noted over the land, depending on geographical location and more significantly on the moisture availability which influences the surface sensible and latent heat fluxes. The PBLH variations associated with active-break intra-seasonal monsoon oscillations are up to 1000 m over central Indian locations. Inter relationship between the PBLH and the controlling factors, i.e. Evaporative Fraction, net radiation, friction velocity, surface Richardson number, and scalar diffusivity fraction, show significant variation between dry and wet PBL regimes, which also varies with geographical location. Evaporative fraction has dominant influence on the PBLH over the region. Enhanced entrainment during monsoon contributes to reduction in PBLH, whereas the opposite effect is noted during dry period. Linear regression, cross wavelet and

Microbubble drag reduction in liquid turbulent boundary layers

International Nuclear Information System (INIS)

Merkle, C.L.; Deutsch, S.

1992-01-01

The interactions between a dense cloud of small bubbles and a liquid turbulent boundary layer are reviewed on the basis of available experimental observations to understand and quantify their capability for reducing skin friction. Gas bubbles are generally introduced into the boundary layer by injection through a porous surface or by electrolysis. After injection, the bubbles stay near the wall in boundary-layer-like fashion giving rise to strong gradients in both velocity and gas concentration. In general, the magnitude of the skin friction reduction increases as the volume of bubbles in the boundary layer is increased until a maximum skin friction reduction of typically 80-90% of the undisturbed skin friction level is reached. The volumetric gas flow required for this maximum is nominally equal to the volume flow of the liquid in the boundary layer. Bubble size estimates indicate that in most microbubble experiments the bubbles have been intermediate in size between the inner and outer scales of the undisturbed boundary layer. Additional studies with other nondimensional bubble sizes would be useful. However, the bubble size is most likely controlled by the injection process, and considerably different conditions would be required to change this ratio appreciably. The trajectories of the bubble clouds are primarily determined by the random effects of turbulence and bubble-bubble interactions. The effects of buoyancy represent a weaker effect. The trajectories are unlike the deterministic trajectory of an individual bubble in a time-averaged boundary layer. Bubbles are most effective in high speed boundary layers and, for the bubble sizes tested to date, produce an effect that persists for some on hundred boundary layer thicknesses. Modeling suggests that microbubbles reduce skin friction by increasing the turbulence Reynolds number in the buffer layer in a manner similar to polymers

On the effectiveness of surface assimilation in probabilistic nowcasts of planetary boundary layer profiles

Science.gov (United States)

Rostkier-Edelstein, Dorita; Hacker, Joshua

2013-04-01

Surface observations comprise a wide, non-expensive and reliable source of information about the state of the near-surface planetary boundary layer (PBL). Operational data assimilation systems have encountered several difficulties in effectively assimilating them, among others due to their local-scale representativeness, the transient coupling between the surface and the atmosphere aloft and the balance constraints usually used. A long-term goal of this work is to find an efficient system for probabilistic PBL nowcasting that can be employed wherever surface observations are present. Earlier work showed that surface observations can be an important source of information with a single column model (SCM) and an ensemble filter (EF). Here we extend that work to quantify the probabilistic skill of ensemble SCM predictions with a model including added complexity. We adopt a factor separation analysis to quantify the contribution of surface assimilation relative to that of selected model components (parameterized radiation and externally imposed horizontal advection) to the probabilistic skill of the system, and of any beneficial or detrimental interactions between them. To assess the real utility of the flow-dependent covariances estimated with the EF and of the SCM of the PBL we compare the skill of the SCM/EF system to that of a reference one based on climatological covariances and a 30-min persistence model. It consists of a dressing technique, whereby a deterministic 3D mesoscale forecast (e.g. from WRF model) is adjusted and dressed with uncertainty using a seasonal sample of mesoscale forecasts and surface forecast errors. Results show that assimilation of surface observations can improve deterministic and probabilistic profile predictions more significantly than major model improvements. Flow-dependent covariances estimated with the SCM/EF show clear advantage over the use of climatological covariances when the flow is characterized by wide variability, when

Beta limitation of matter-antimatter boundary layers

International Nuclear Information System (INIS)

Lehnert, B.

1987-08-01

A model has earlier been proposed for a boundary layer which separates a cloud of matter from one of antimatter in a magnetized ambiplasma. In this model steady pressure equilibrium ceases to exist when a certain beta limit is exceeded. The latter is defined as the ratio between the ambiplasma and magnetic field pressures which balance each other in the boundary layer. Thus, at an increasing density, the high-energy particles created by annihilation within the layer are 'pumped up' to a pressure which cannot be balanced by a given magnetic field. The boundary layer then 'disrupts'. The critical beta limit thus obtained falls within the observed parameter ranges of galaxies and other large cosmical objects. Provided that the considered matter-antimatter balance holds true, this limit is thus expected to impose certain existence conditions on matter-antimatter boundary layers. Such a limitation may apply to certain cosmical objects and cosmological models. The maximum time scale for the corresponding disruption development has been estimated to be in the range from about 10 -4 to 10 2 seconds for boundary layers at ambiplasma particle densities in the range from 10 4 to 10 -2 m -3 , respectively. (author)

Modeling the summertime Arctic cloudy boundary layer

Energy Technology Data Exchange (ETDEWEB)

Curry, J.A.; Pinto, J.O. [Univ. of Colorado, Boulder, CO (United States); McInnes, K.L. [CSIRO Division of Atmospheric Research, Mordialloc (Australia)

1996-04-01

Global climate models have particular difficulty in simulating the low-level clouds during the Arctic summer. Model problems are exacerbated in the polar regions by the complicated vertical structure of the Arctic boundary layer. The presence of multiple cloud layers, a humidity inversion above cloud top, and vertical fluxes in the cloud that are decoupled from the surface fluxes, identified in Curry et al. (1988), suggest that models containing sophisticated physical parameterizations would be required to accurately model this region. Accurate modeling of the vertical structure of multiple cloud layers in climate models is important for determination of the surface radiative fluxes. This study focuses on the problem of modeling the layered structure of the Arctic summertime boundary-layer clouds and in particular, the representation of the more complex boundary layer type consisting of a stable foggy surface layer surmounted by a cloud-topped mixed layer. A hierarchical modeling/diagnosis approach is used. A case study from the summertime Arctic Stratus Experiment is examined. A high-resolution, one-dimensional model of turbulence and radiation is tested against the observations and is then used in sensitivity studies to infer the optimal conditions for maintaining two separate layers in the Arctic summertime boundary layer. A three-dimensional mesoscale atmospheric model is then used to simulate the interaction of this cloud deck with the large-scale atmospheric dynamics. An assessment of the improvements needed to the parameterizations of the boundary layer, cloud microphysics, and radiation in the 3-D model is made.

Removing Boundary Layer by Suction

Science.gov (United States)

Ackeret, J

1927-01-01

Through the utilization of the "Magnus effect" on the Flettner rotor ship, the attention of the public has been directed to the underlying physical principle. It has been found that the Prandtl boundary-layer theory furnishes a satisfactory explanation of the observed phenomena. The present article deals with the prevention of this separation or detachment of the flow by drawing the boundary layer into the inside of a body through a slot or slots in its surface.

Stability of spatially developing boundary layers

Science.gov (United States)

Govindarajan, Rama

1993-07-01

A new formulation of the stability of boundary-layer flows in pressure gradients is presented, taking into account the spatial development of the flow. The formulation assumes that disturbance wavelength and eigenfunction vary downstream no more rapidly than the boundary-layer thickness, and includes all terms of O(1) and O(R(exp -1)) in the boundary-layer Reynolds number R. Although containing the Orr-Sommerfeld operator, the present approach does not yield the Orr-Sommerfeld equation in any rational limit. In Blasius flow, the present stability equation is consistent with that of Bertolotti et al. (1992) to terms of O(R(exp -1)). For the Falkner-Skan similarity solutions neutral boundaries are computed without the necessity of having to march in space. Results show that the effects of spatial growth are striking in flows subjected to adverse pressure gradients.

Tokamak plasma boundary layer model

International Nuclear Information System (INIS)

Volkov, T.F.; Kirillov, V.D.

1983-01-01

A model has been developed for the limiter layer and for the boundary region of the plasma column in a tokamak to facilitate analytic calculations of the thickness of the limiter layers, the profiles and boundary values of the temperature and the density under various conditions, and the difference between the electron and ion temperatures. This model can also be used to analyze the recycling of neutrals, the energy and particle losses to the wall and the limiter, and other characteristics

Diffusive boundary layers over varying topography

KAUST Repository

Dell, R.  W.; Pratt, L.  J.

2015-01-01

Diffusive bottom boundary layers can produce upslope flows in a stratified fluid. Accumulating observations suggest that these boundary layers may drive upwelling and mixing in mid-ocean ridge flank canyons. However, most studies of diffusive bottom

Measurements in a synthetic turbulent boundary layer

Science.gov (United States)

Arakeri, J. H.; Coles, D. E.

Some measurements in a synthetic turbulent boundary layer (SBL) are reported. The main diagnostic tool is an X-wire probe. The velocity of the large eddies is determined to be 0.842 times the freestream velocity. The mean properties of the SBL are reasonably close to those of a natural turbulent boundary layer. The large eddy in the SBL appears to be a pair of counterrotating eddies in the stream direction, inclined at a shallow angle and occupying much of the boundary-layer thickness.

Asymptotic analysis and boundary layers

CERN Document Server

Cousteix, Jean

2007-01-01

This book presents a new method of asymptotic analysis of boundary-layer problems, the Successive Complementary Expansion Method (SCEM). The first part is devoted to a general comprehensive presentation of the tools of asymptotic analysis. It gives the keys to understand a boundary-layer problem and explains the methods to construct an approximation. The second part is devoted to SCEM and its applications in fluid mechanics, including external and internal flows. The advantages of SCEM are discussed in comparison with the standard Method of Matched Asymptotic Expansions. In particular, for the first time, the theory of Interactive Boundary Layer is fully justified. With its chapter summaries, detailed derivations of results, discussed examples and fully worked out problems and solutions, the book is self-contained. It is written on a mathematical level accessible to graduate and post-graduate students of engineering and physics with a good knowledge in fluid mechanics. Researchers and practitioners will estee...

A Coordinate Transformation for Unsteady Boundary Layer Equations

Directory of Open Access Journals (Sweden)

Paul G. A. CIZMAS

2011-12-01

Full Text Available This paper presents a new coordinate transformation for unsteady, incompressible boundary layer equations that applies to both laminar and turbulent flows. A generalization of this coordinate transformation is also proposed. The unsteady boundary layer equations are subsequently derived. In addition, the boundary layer equations are derived using a time linearization approach and assuming harmonically varying small disturbances.

Longitudinal vortices in a transitioning boundary layer

International Nuclear Information System (INIS)

Anders, J.B.; Backwelder, R.F.

1980-01-01

Naturally occurring spanwise variations of the streamwise velocity component, characteristic of longitudinal vortices embedded in a transitioning boundary layer were explored using hot-wire anemometers. A vibrating ribbon introduced stable or unstable Tollmien-Schlichting waves into the laminar boundary layer. These damped or growing disturbances always developed a strong three-dimensional pattern even though no spanwise perturbations were artificially induced. Changing the radius of the leading edge and other modifications to the flat plate, wind tunnel and boundary layer did not alter the spanwise wavelength of the vortices. (orig.)

Characterization of the atmospheric boundary layer from radiosonde ...

Indian Academy of Sciences (India)

In this paper, a comparison of two methods for the calculation of the height of atmospheric boundary layer (ABL) ... Boundary layer; GPS sonde; mixed layer height; turbulent flow depth. J. Earth Syst. ..... for her PhD research work. References.

Sensitivity analysis of WRF model PBL schemes in simulating boundary-layer variables in southern Italy: An experimental campaign

DEFF Research Database (Denmark)

Avolio, E.; Federico, S.; Miglietta, M.

2017-01-01

the surface, where the model uncertainties are, usually, smaller than at the surface. A general anticlockwise rotation of the simulated flow with height is found at all levels. The mixing height is overestimated by all schemes and a possible role of the simulated sensible heat fluxes for this mismatching......The sensitivity of boundary layer variables to five (two non-local and three local) planetary boundary-layer (PBL) parameterization schemes, available in the Weather Research and Forecasting (WRF) mesoscale meteorological model, is evaluated in an experimental site in Calabria region (southern...... is investigated. On a single-case basis, significantly better results are obtained when the atmospheric conditions near the measurement site are dominated by synoptic forcing rather than by local circulations. From this study, it follows that the two first order non-local schemes, ACM2 and YSU, are the schemes...

Superfluid Boundary Layer.

Science.gov (United States)

Stagg, G W; Parker, N G; Barenghi, C F

2017-03-31

We model the superfluid flow of liquid helium over the rough surface of a wire (used to experimentally generate turbulence) profiled by atomic force microscopy. Numerical simulations of the Gross-Pitaevskii equation reveal that the sharpest features in the surface induce vortex nucleation both intrinsically (due to the raised local fluid velocity) and extrinsically (providing pinning sites to vortex lines aligned with the flow). Vortex interactions and reconnections contribute to form a dense turbulent layer of vortices with a nonclassical average velocity profile which continually sheds small vortex rings into the bulk. We characterize this layer for various imposed flows. As boundary layers conventionally arise from viscous forces, this result opens up new insight into the nature of superflows.

The Challenges of Applying Planetary Boundaries as a Basis for Strategic Decision-Making in Companies with Global Supply Chains

DEFF Research Database (Denmark)

Clift, Roland; Sim, Sarah; King, Henry

2017-01-01

The Planetary Boundaries (PB) framework represents a significant advance in specifying the ecological constraints on human development. However, to enable decision-makers in business and public policy to respect these constraints in strategic planning, the PB framework needs to be developed...... in operationalizing the planetary boundaries needs be complemented with progress in addressing the equity and ethical issues in allocating the safe operating space between companies and sectors....

Role of residual layer and large-scale phenomena on the evolution of the boundary layer

NARCIS (Netherlands)

Blay, E.; Pino, D.; Vilà-Guerau de Arellano, J.; Boer, van de A.; Coster, de O.; Faloona, I.; Garrouste, O.; Hartogensis, O.K.

2012-01-01

Mixed-layer theory and large-eddy simulations are used to analyze the dynamics of the boundary layer on two intensive operational periods during the Boundary Layer Late Afternoon and Sunset Turbulence (BLLAST) campaign: 1st and 2nd of July 2011, when convective boundary layers (CBLs) were observed.

Field study of the planetary boundary layer at subtropical regions of Brazil applied to investigate the dispersion conditions in nuclear power plants

International Nuclear Information System (INIS)

Oliveira, A.P. de; Degrazia, G.A.; Moraes, O.L.L. de; Goedert, J.

1993-01-01

In this paper is shown some observational results of four field campaigns carried out in the last two years, three during summer, in March 1991, 92 and 93, and one during the winter in July 1992. The site is located in the country side of State of Sao Paulo, Brazil, (23 0 C 25'S; 47 0 C 35' W), approximately 120 km far from the Atlantic Ocean. Measurements of vertical velocity, temperature and water vapor density at three levels (3,5, and 9.40 m) and horizontal wind velocity components at one level (11.5 m) with a sample rate of 1-10 Hz were made using a 12 m tower. It was also carried out measurements of net radiation and soil heat flux, and tethered balloon and radiosonde system followed the vertical evolution of the local Planetary Boundary Layer (PBL).During daytime in the summer, the vertical evolution of the PBL is strongly dependent upon the cloud activity, that inhibits its vertical evolution. In the winter, cloud activity is reduced but the vertical extent of the PBL is constraint by the small surface heating. During the nighttime, the PBL is characterized by moderate stable conditions and low level jets observed in both seasons. (author)

Planetary and tidal wave-type oscillations in the ionospheric sporadic E layers over Tehran region

Science.gov (United States)

Karami, K.; Ghader, S.; Bidokhti, A. A.; Joghataei, M.; Neyestani, A.; Mohammadabadi, A.

2012-04-01

It is believed that in the lower ionosphere, particularly in the ionospheric sporadic E (Es) layers (90-130 km), the planetary and tidal wave-type oscillations in the ionized component indicate the planetary and tidal waves in the neutral atmosphere. In the present work, the presence of wave-type oscillations, including planetary and tidal waves in the ionospheric sporadic E layers over Tehran region is examined. Data measured by a digital ionosonde at the ionospheric station of the Institute of Geophysics, University of Tehran, from July 2006 to June 2007 are used to investigate seasonal variations of planetary and tidal waves activities. For the purpose of accurate comparison between different seasons, wavelet transform is applied to time series of foEs and h‧Es, namely, the critical frequency and virtual height of Es layers, respectively. The results show that the sporadic E layers over Tehran region are strongly under the influence of upward propagation of waves from below. More specifically, among diverse range of periodicities in the sporadic E layers, we found that diurnal (24 hours) and semidiurnal (12 hours) oscillations in all seasons for both parameters. Moreover, terdiurnal (8 hours) tide-like variation is observed during spring and summer for foEs parameter and summer and winter for h‧Es. Furthermore, the results show that diurnal tidal waves obtain their maximum activities during autumn and winter seasons, and their activities decrease during the late spring and summer. In addition, periods of about 2, 4, 6, 10, 14, and 16 days in our observation verifies the hypothesis of upward propagation of planetary waves from lower atmosphere to the ionosphere. Moreover, planetary waves have their maximum activities during equinox.

Self-similar magnetohydrodynamic boundary layers

Energy Technology Data Exchange (ETDEWEB)

Nunez, Manuel; Lastra, Alberto, E-mail: mnjmhd@am.uva.e [Departamento de Analisis Matematico, Universidad de Valladolid, 47005 Valladolid (Spain)

2010-10-15

The boundary layer created by parallel flow in a magnetized fluid of high conductivity is considered in this paper. Under appropriate boundary conditions, self-similar solutions analogous to the ones studied by Blasius for the hydrodynamic problem may be found. It is proved that for these to be stable, the size of the Alfven velocity at the outer flow must be smaller than the flow velocity, a fact that has a ready physical explanation. The process by which the transverse velocity and the thickness of the layer grow with the size of the Alfven velocity is detailed.

Self-similar magnetohydrodynamic boundary layers

International Nuclear Information System (INIS)

Nunez, Manuel; Lastra, Alberto

2010-01-01

The boundary layer created by parallel flow in a magnetized fluid of high conductivity is considered in this paper. Under appropriate boundary conditions, self-similar solutions analogous to the ones studied by Blasius for the hydrodynamic problem may be found. It is proved that for these to be stable, the size of the Alfven velocity at the outer flow must be smaller than the flow velocity, a fact that has a ready physical explanation. The process by which the transverse velocity and the thickness of the layer grow with the size of the Alfven velocity is detailed.

Boundary Layer Control of Rotating Convection Systems

Science.gov (United States)

King, E. M.; Stellmach, S.; Noir, J.; Hansen, U.; Aurnou, J. M.

2008-12-01

Rotating convection is ubiquitous in the natural universe, and is likely responsible for planetary processes such magnetic field generation. Rapidly rotating convection is typically organized by the Coriolis force into tall, thin, coherent convection columns which are aligned with the axis of rotation. This organizational effect of rotation is thought to be responsible for the strength and structure of magnetic fields generated by convecting planetary interiors. As thermal forcing is increased, the relative influence of rotation weakens, and fully three-dimensional convection can exist. It has long been assumed that rotational effects will dominate convection dynamics when the ratio of buoyancy to the Coriolis force, the convective Rossby number, Roc, is less than unity. We investigate the influence of rotation on turbulent Rayleigh-Benard convection via a suite of coupled laboratory and numerical experiments over a broad parameter range: Rayleigh number, 10310; Ekman number, 10-6≤ E ≤ ∞; and Prandtl number, 1≤ Pr ≤ 100. In particular, we measure heat transfer (as characterized by the Nusselt number, Nu) as a function of the Rayleigh number for several different Ekman and Prandtl numbers. Two distinct heat transfer scaling regimes are identified: non-rotating style heat transfer, Nu ~ Ra2/7, and quasigeostrophic style heat transfer, Nu~ Ra6/5. The transition between the non-rotating regime and the rotationally dominant regime is described as a function of the Ekman number, E. We show that the regime transition depends not on the global force balance Roc, but on the relative thicknesses of the thermal and Ekman boundary layers. The transition scaling provides a predictive criterion for the applicability of convection models to natural systems such as Earth's core.

Modelling stable atmospheric boundary layers over snow

NARCIS (Netherlands)

Sterk, H.A.M.

2015-01-01

Thesis entitled:

Modelling Stable Atmospheric Boundary Layers over Snow

H.A.M. Sterk

Wageningen, 29th of April, 2015

Summary

The emphasis of this thesis is on the understanding and forecasting of the Stable Boundary Layer (SBL) over snow-covered surfaces. SBLs

Characterization of a Planetary Boundary Layer model to evaluate radionuclides releases in nuclear installations; Caracterizacao de um modelo de camada limite planetaria para avaliar liberacoes de radionuclideos em instalacoes nucleares

Energy Technology Data Exchange (ETDEWEB)

Molnary, Leslie de

1993-07-01

A two layer bulk model is used to simulate numerically the time and spatial evolution of concentration of radionuclides in the Planetary Boundary Layer (PBL) for convective and stable conditions. In this model, the closure hypothesis are based on the integrated version of the Turbulent Kinetics Energy (TKE) equation (Smeda,1979). This type of model was adopted here because it is numerically simple to be applied operationally in routine and emergency support systems of atmospheric releases at nuclear power plants, and the hypothesis of the efficiency of the vertical mixing seems to be physically reasonable to simulated PBL evolution for high wind conditions and stable conditions in Subtropical latitudes regions. In order to validate the model to the nuclear power plants of the Centro Experimental Aramar (CEA), located in Ipero, State of Sao Paulo, Brazil, numerical simulations were carried out with initial and boundary conditions based on vertical profiles of temperature and horizontal wind speed and direction obtained from tethered balloon soundings, synoptic charts at 850 hPa and surface observations. Comparisons between a 24 hour long numerical simulation and observations indicate that the model is capable of reproduce the diurnal evolution of temperature and horizontal wind during the convective regime. During stable conditions, the slab model was able to simulate the intensity of the surface inversion as a difference between the mixed layer and surface temperatures. The simulated mixed layer height matches with observations during the convective and stable regime. A daytime release of radionuclides was simulated for CEA region and the results indicated that the maximum relative concentration reaches a distance about 15 Km in 1 hour, varing from 100 times background at the moment of the release to 15 times the background. For night releases, the maximum concentration reaches the same distance in 45 minutes, varing from 100 to 30 times the background values

Development of Prototype Micro-Lidar using Narrow Linewidth Semiconductor Lasers for Mars Boundary Layer Wind and Dust Opacity Profiles

Science.gov (United States)

Menzies, Robert T.; Cardell, Greg; Chiao, Meng; Esproles, Carlos; Forouhar, Siamak; Hemmati, Hamid; Tratt, David

1999-01-01

We have developed a compact Doppler lidar concept which utilizes recent developments in semiconductor diode laser technology in order to be considered suitable for wind and dust opacity profiling in the Mars lower atmosphere from a surface location. The current understanding of the Mars global climate and meteorology is very limited, with only sparse, near-surface data available from the Viking and Mars Pathfinder landers, supplemented by long-range remote sensing of the Martian atmosphere. The in situ measurements from a lander-based Doppler lidar would provide a unique dataset particularly for the boundary layer. The coupling of the radiative properties of the lower atmosphere with the dynamics involves the radiative absorption and scattering effects of the wind-driven dust. Variability in solar irradiance, on diurnal and seasonal time scales, drives vertical mixing and PBL (planetary boundary layer) thickness. The lidar data will also contribute to an understanding of the impact of wind-driven dust on lander and rover operations and lifetime through an improvement in our understanding of Mars climatology. In this paper we discuss the Mars lidar concept, and the development of a laboratory prototype for performance studies, using, local boundary layer and topographic target measurements.

Pitot-probe displacement in a supersonic turbulent boundary layer

Science.gov (United States)

Allen, J. M.

1972-01-01

Eight circular pitot probes ranging in size from 2 to 70 percent of the boundary-layer thickness were tested to provide experimental probe displacement results in a two-dimensional turbulent boundary layer at a nominal free-stream Mach number of 2 and unit Reynolds number of 8 million per meter. The displacement obtained in the study was larger than that reported by previous investigators in either an incompressible turbulent boundary layer or a supersonic laminar boundary layer. The large probes indicated distorted Mach number profiles, probably due to separation. When the probes were small enough to cause no appreciable distortion, the displacement was constant over most of the boundary layer. The displacement in the near-wall region decreased to negative displacement in some cases. This near-wall region was found to extend to about one probe diameter from the test surface.

Diffusion processes in the magnetopause boundary layer

International Nuclear Information System (INIS)

Tsurutani, B.T.; Thorne, R.M.

1982-01-01

Anomalous cross-field diffusion of magnetosheath ions and electrons is a direct consequence of cyclotron-resonant scattering by electrostatic and electromagnetic emissions which are continuously present within the magnetopause boundary layer. Expressions for the rate of cross-field diffusion involving either type of wave are developed and expressed in terms of the absolute upper limit referred to as Bohm diffusion. For the typical average intensity of waves observed in the boundary layer, resonant electron cross-field diffusion is always insignificant. However, magnetosheath ions, resonant with low frequency electrostatic waves, may be transported inward at a rate approaching one tenth the Bohm rate (D/sub perpendiculartsperpendicular/roughly-equal10 3 km 2 /s). While this is not the only mechanism capable of explaining the presence of the low latitude boundary layer it is adequate to account for the typical boundary layer thickness and it should occur at all local times and under all interplanetary conditions. It consequently provides a continuous mechanism for significant mass and momentum transfer across the magnetopause under conditions when field merging is inoperative

Slow Manifolds and Multiple Equilibria in Stratocumulus-Capped Boundary Layers

Directory of Open Access Journals (Sweden)

Junya Uchida

2010-12-01

Full Text Available In marine stratocumulus-capped boundary layers under strong inversions, the timescale for thermodynamic adjustment is roughly a day, much shorter than the multiday timescale for inversion height adjustment. Slow-manifold analysis is introduced to exploit this timescale separation when boundary layer air columns experience only slow changes in their boundary conditions. Its essence is that the thermodynamic structure of the boundary layer remains approximately slaved to its inversion height and the instantaneous boundary conditions; this slaved structure determines the entrainment rate and hence the slow evolution of the inversion height. Slow-manifold analysis is shown to apply to mixed-layer model and large-eddy simulations of an idealized nocturnal stratocumulus- capped boundary layer; simulations with different initial inversion heights collapse onto single relationships of cloud properties with inversion height. Depending on the initial inversion height, the simulations evolve toward a shallow thin-cloud boundary layer or a deep, well-mixed thick cloud boundary layer. In the large-eddy simulations, these evolutions occur on two separate slow manifolds (one of which becomes unstable if cloud droplet concentration is reduced. Applications to analysis of stratocumulus observations and to pockets of open cells and ship tracks are proposed.

Transition to turbulence in the Hartmann boundary layer

Energy Technology Data Exchange (ETDEWEB)

Thess, A.; Krasnov, D.; Boeck, T.; Zienicke, E. [Dept. of Mechanical Engineering, Ilmenau Univ. of Tech. (Germany); Zikanov, O. [Dept. of Mechanical Engineering, Univ. of Michigan, Dearborn, MI (United States); Moresco, P. [School of Physics and Astronomy, The Univ. of Manchester (United Kingdom); Alboussiere, T. [Lab. de Geophysique Interne et Tectonophysique, Observatoire des Science de l' Univers de Grenoble, Univ. Joseph Fourier, Grenoble (France)

2007-07-01

The Hartmann boundary layer is a paradigm of magnetohydrodynamic (MHD) flows. Hartmann boundary layers develop when a liquid metal flows under the influence of a steady magnetic field. The present paper is an overview of recent successful attempts to understand the mechanisms by which the Hartmann layer undergoes a transition from laminar to turbulent flow. (orig.)

Airborne measurements of turbulent trace gas fluxes and analysis of eddy structure in the convective boundary layer over complex terrain

Science.gov (United States)

Hasel, M.; Kottmeier, Ch.; Corsmeier, U.; Wieser, A.

2005-03-01

Using the new high-frequency measurement equipment of the research aircraft DO 128, which is described in detail, turbulent vertical fluxes of ozone and nitric oxide have been calculated from data sampled during the ESCOMPTE program in the south of France. Based on airborne turbulence measurements, radiosonde data and surface energy balance measurements, the convective boundary layer (CBL) is examined under two different aspects. The analysis covers boundary-layer convection with respect to (i) the control of CBL depth by surface heating and synoptic scale influences, and (ii) the structure of convective plumes and their vertical transport of ozone and nitric oxides. The orographic structure of the terrain causes significant differences between planetary boundary layer (PBL) heights, which are found to exceed those of terrain height variations on average. A comparison of boundary-layer flux profiles as well as mean quantities over flat and complex terrain and also under different pollution situations and weather conditions shows relationships between vertical gradients and corresponding turbulent fluxes. Generally, NO x transports are directed upward independent of the terrain, since primary emission sources are located near the ground. For ozone, negative fluxes are common in the lower CBL in accordance with the deposition of O 3 at the surface. The detailed structure of thermals, which largely carry out vertical transports in the boundary layer, are examined with a conditional sampling technique. Updrafts mostly contain warm, moist and NO x loaded air, while the ozone transport by thermals alternates with the background ozone gradient. Evidence for handover processes of trace gases to the free atmosphere can be found in the case of existing gradients across the boundary-layer top. An analysis of the size of eddies suggests the possibility of some influence of the heterogeneous terrain in mountainous area on the length scales of eddies.

Internal and external 2-d boundary layer flows

Science.gov (United States)

Crawford, M. E.; Kays, W. M.

1978-01-01

Computer program computes general two dimensional turbulent boundary-layer flow using finite-difference techniques. Structure allows for user modification to accommodate unique problems. Program should prove useful in many applications where accurate boundary-layer flow calculations are required.

Ground observations of magnetospheric boundary layer phenomena

International Nuclear Information System (INIS)

McHenry, M.A.; Clauer, C.R.; Friis-Christensen, E.; Newell, P.T.; Kelly, J.D.

1990-01-01

Several classes of traveling vortices in the dayside ionospheric convection have been detected and tracked using the Greenland magnetometer chain (Friis-Christensen et al., 1988, McHenry et al., 1989). One class observed during quiet times consists of a continuous series of vortices moving generally anti-sunward for several hours at a time. The vortices strength is seen to be approximately steady and neighboring vortices rotate in opposite directions. Sondrestrom radar observations show that the vortices are located at the ionospheric convection reversal boundary. Low altitude DMSP observations indicate the vortices are on field lines which map to the inner edge of the low latitude boundary layer. Because the vortices are conjugate to the boundary layer, repeat in a regular fashion and travel antisunward, the authors argue that this class of vortices is caused by the Kelvin-Helmholtz instability of the inner edge of the magnetospheric boundary layer

Coupled vs. decoupled boundary layers in VOCALS-REx

Directory of Open Access Journals (Sweden)

C. R. Jones

2011-07-01

Full Text Available We analyze the extent of subtropical stratocumulus-capped boundary layer decoupling and its relation to other boundary-layer characteristics and forcings using aircraft observations from VOCALS-REx along a swath of the subtropical southeast Pacific Ocean running west 1600 km from the coast of Northern Chile. We develop two complementary and consistent measures of decoupling. The first is based on boundary layer moisture and temperature stratification in flight profiles from near the surface to above the capping inversion, and the second is based the difference between the lifted condensation level (LCL and a mean lidar-derived cloud base measured on flight legs at 150 m altitude. Most flights took place during early-mid morning, well before the peak in insolation-induced decoupling.

We find that the boundary layer is typically shallower, drier, and well mixed near the shore, and tends to deepen, decouple, and produce more drizzle further offshore to the west. Decoupling is strongly correlated to the "mixed layer cloud thickness", defined as the difference between the capping inversion height and the LCL; other factors such as wind speed, cloud droplet concentration, and inversion thermodynamic jumps have little additional explanatory power. The results are broadly consistent with the deepening-warming theory of decoupling.

In the deeper boundary layers observed well offshore, there was frequently nearly 100 % boundary-layer cloud cover despite pronounced decoupling. The cloud cover was more strongly correlated to a κ parameter related to the inversion jumps of humidity and temperature, though the exact functional relation is slightly different than found in prior large-eddy simulation studies.

Short climatology of the atmospheric boundary layer using acoustic methods

International Nuclear Information System (INIS)

Schubert, J.F.

1975-06-01

A climatology of the boundary layer of the atmosphere at the Savannah River Laboratory is being compiled using acoustic methods. The atmospheric phenomenon as depicted on the facsimile recorder is classified and then placed into one of sixteen categories. After classification, the height of the boundary layer is measured. From this information, frequency tables of boundary layer height and category are created and then analyzed for the percentage of time that each category was detected by the acoustic sounder. The sounder also accurately depicts the diurnal cycle of the boundary layer and, depending on the sensitivity of the system, shows microstructure that is normally unavailable using other methods of profiling. The acoustic sounder provides a means for continuous, real time measurements of the time rate of change of the depth of the boundary layer. This continuous record of the boundary layer with its convective cells, gravity waves, inversions, and frontal system passages permits the synoptic and complex climatology of the local area to be compiled. (U.S.)

Stability of boundary layer flow based on energy gradient theory

Science.gov (United States)

Dou, Hua-Shu; Xu, Wenqian; Khoo, Boo Cheong

2018-05-01

The flow of the laminar boundary layer on a flat plate is studied with the simulation of Navier-Stokes equations. The mechanisms of flow instability at external edge of the boundary layer and near the wall are analyzed using the energy gradient theory. The simulation results show that there is an overshoot on the velocity profile at the external edge of the boundary layer. At this overshoot, the energy gradient function is very large which results in instability according to the energy gradient theory. It is found that the transverse gradient of the total mechanical energy is responsible for the instability at the external edge of the boundary layer, which induces the entrainment of external flow into the boundary layer. Within the boundary layer, there is a maximum of the energy gradient function near the wall, which leads to intensive flow instability near the wall and contributes to the generation of turbulence.

Turbulent boundary layer in high Rayleigh number convection in air.

Science.gov (United States)

du Puits, Ronald; Li, Ling; Resagk, Christian; Thess, André; Willert, Christian

2014-03-28

Flow visualizations and particle image velocimetry measurements in the boundary layer of a Rayleigh-Bénard experiment are presented for the Rayleigh number Ra=1.4×1010. Our visualizations indicate that the appearance of the flow structures is similar to ordinary (isothermal) turbulent boundary layers. Our particle image velocimetry measurements show that vorticity with both positive and negative sign is generated and that the smallest flow structures are 1 order of magnitude smaller than the boundary layer thickness. Additional local measurements using laser Doppler velocimetry yield turbulence intensities up to I=0.4 as in turbulent atmospheric boundary layers. From our observations, we conclude that the convective boundary layer becomes turbulent locally and temporarily although its Reynolds number Re≈200 is considerably smaller than the value 420 underlying existing phenomenological theories. We think that, in turbulent Rayleigh-Bénard convection, the transition of the boundary layer towards turbulence depends on subtle details of the flow field and is therefore not universal.

Nonlinear Transient Growth and Boundary Layer Transition

Science.gov (United States)

Paredes, Pedro; Choudhari, Meelan M.; Li, Fei

2016-01-01

Parabolized stability equations (PSE) are used in a variational approach to study the optimal, non-modal disturbance growth in a Mach 3 at plate boundary layer and a Mach 6 circular cone boundary layer. As noted in previous works, the optimal initial disturbances correspond to steady counter-rotating streamwise vortices, which subsequently lead to the formation of streamwise-elongated structures, i.e., streaks, via a lift-up effect. The nonlinear evolution of the linearly optimal stationary perturbations is computed using the nonlinear plane-marching PSE for stationary perturbations. A fully implicit marching technique is used to facilitate the computation of nonlinear streaks with large amplitudes. To assess the effect of the finite-amplitude streaks on transition, the linear form of plane- marching PSE is used to investigate the instability of the boundary layer flow modified by spanwise periodic streaks. The onset of bypass transition is estimated by using an N- factor criterion based on the amplification of the streak instabilities. Results show that, for both flow configurations of interest, streaks of sufficiently large amplitude can lead to significantly earlier onset of transition than that in an unperturbed boundary layer without any streaks.

Structure of reconnection boundary layers in incompressible MHD

International Nuclear Information System (INIS)

Sonnerup, B.U.Oe.; Wang, D.J.

1987-01-01

The incompressible MHD equations with nonvanishing viscosity and resistivity are simplified by use of the boundary layer approximation to describe the flow and magnetic field in the exit flow regions of magnetic field reconnection configurations when the reconnection rate is small. The conditions are derived under which self-similar solutions exist of the resulting boundary layer equations. For the case of zero viscosity and resistivity, the equations describing such self-similar layers are then solved in terms of quadratures, and the resulting flow and field configurations are described. Symmetric solutions, relevant, for example, to reconnection in the geomagnetic tail, as well as asymmetric solutions, relevant to reconnection at the earth's magnetopause, are found to exist. The nature of the external solutions to which the boundary layer solutions should be matched is discussed briefly, but the actual matching, which is to occur at Alfven-wave characteristic curves in the boundary layer solutions, is not carried out. Finally, it is argued that the solutions obtained may also be used to describe the structure of the intense vortex layers observed to occur at magnetic separatrices in computer simulations and in certain analytical models of the reconnection process

Accretion disc boundary layers - geometrically and optically thin case

International Nuclear Information System (INIS)

Regev, Oded; Hougerat, A.A.

1988-01-01

The method of matched asymptotic expansions is applied to an optically and geometrically thin boundary layer between an accretion disc and the accreting star. Analytical solutions are presented for a particular viscosity prescription in the boundary layer. For a typical example we find that the disc closely resembles standard steady-disc theory. It is identical to it everywhere save a narrow boundary layer, where the temperature increases rapidly inward (by an order of magnitude), the angular velocity achieves maximum and decreases to its surface value and other variables also undergo rapid changes. This and previous work can now be used to calculate the emission from accretion discs including the boundary layers for a wide range of parameters. (author)

Boundary-layer interactions in the plane-parallel incompressible flows

International Nuclear Information System (INIS)

Nguyen, Toan T; Sueur, Franck

2012-01-01

We study the inviscid limit problem of incompressible flows in the presence of both impermeable regular boundaries and a hypersurface transversal to the boundary across which the inviscid flow has a discontinuity jump. In the former case, boundary layers have been introduced by Prandtl as correctors near the boundary between the inviscid and viscous flows. In the latter case, the viscosity smoothes out the discontinuity jump by creating a transition layer which has the same amplitude and thickness as the Prandtl layer. In the neighbourhood of the intersection of the impermeable boundary and of the hypersurface, interactions between the boundary and the transition layers must then be considered. In this paper, we initiate a mathematical study of this interaction and carry out a strong convergence in the inviscid limit for the case of the plane-parallel flows introduced by Di Perna and Majda (1987 Commun. Math. Phys. 108 667–89). (paper)

Boundary layer flow past a circular cylinder in axial flow

International Nuclear Information System (INIS)

Sawchuk, S.P.; Zamir, M.; Camiletti, S.E.

1985-01-01

This paper discusses a study of the laminar boundary layer on a semi-infinite circular cylinder in axial incompressible flow. Unlike previous studies, the present study investigates a full range of this boundary layer problem to determine skin friction, heat transfer and other integral properties of the boundary layer

Numerical simulation of tsunami-scale wave boundary layers

DEFF Research Database (Denmark)

Williams, Isaac A.; Fuhrman, David R.

2016-01-01

This paper presents a numerical study of the boundary layer flow and properties induced by tsunami-scalewaves. For this purpose, an existing one-dimensional vertical (1DV) boundary layer model, based on the horizontal component of the incompressible Reynolds-averaged Navier–Stokes (RANS) equation...

Boundary-layer theory

CERN Document Server

Schlichting (Deceased), Hermann

2017-01-01

This new edition of the near-legendary textbook by Schlichting and revised by Gersten presents a comprehensive overview of boundary-layer theory and its application to all areas of fluid mechanics, with particular emphasis on the flow past bodies (e.g. aircraft aerodynamics). The new edition features an updated reference list and over 100 additional changes throughout the book, reflecting the latest advances on the subject.

Bristled shark skin: a microgeometry for boundary layer control?

International Nuclear Information System (INIS)

Lang, A W; Hidalgo, P; Westcott, M; Motta, P

2008-01-01

There exists evidence that some fast-swimming shark species may have the ability to bristle their scales during fast swimming. Experimental work using a water tunnel facility has been performed to investigate the flow field over and within a bristled shark skin model submerged within a boundary layer to deduce the possible boundary layer control mechanisms being used by these fast-swimming sharks. Fluorescent dye flow visualization provides evidence of the formation of embedded cavity vortices within the scales. Digital particle image velocimetry (DPIV) data, used to evaluate the cavity vortex formation and boundary layer characteristics close to the surface, indicate increased momentum in the slip layer forming above the scales. This increase in flow velocity close to the shark's skin is indicative of boundary layer control mechanisms leading to separation control and possibly transition delay for the bristled shark skin microgeometry

Analytical solution for the convectively-mixed atmospheric boundary layer

NARCIS (Netherlands)

Ouwersloot, H.G.; Vilà-Guerau de Arellano, J.

2013-01-01

Based on the prognostic equations of mixed-layer theory assuming a zeroth order jump at the entrainment zone, analytical solutions for the boundary-layer height evolution are derived with different degrees of accuracy. First, an exact implicit expression for the boundary-layer height for a situation

Comparison of turbulence in a transitional boundary layer to turbulence in a developed boundary layer*

Science.gov (United States)

Park, G. I.; Wallace, J.; Wu, X.; Moin, P.

2010-11-01

Using a recent DNS of a flat-plate boundary layer, statistics of turbulence in transition at Reθ= 500 where spots merge (distributions of the mean velocity, rms velocity and vorticity fluctuations, Reynolds shear stress, kinetic energy production and dissipation rates and enstrophy) have been compared to these statistics for the developed boundary layer turbulence at Reθ= 1850. When the distributions in the transitional region, determined in narrow planes 0.03 Reθ wide, exclude regions and times when the flow is not turbulent, they closely resemble those in the developed turbulent state at the higher Reynolds number, especially in the buffer and sublayers. The skin friction coefficient, determined in this conditional manner in the transitional flow is, of course, much larger than that obtained by including both turbulent and non-turbulent information there, and is consistent with a value obtained by extrapolating from the developed turbulent region. We are attempting to perform this data analysis even further upstream in the transitioning flow at Reθ= 300 where the turbulent spots are individuated. These results add further evidence to support the view that the structure of a developed turbulent boundary layer is little different from its structure in its embryonic form in turbulent spots. *CTR 2010 Summer Program research.

Analysis and Modeling of Boundary Layer Separation Method (BLSM).

Science.gov (United States)

Pethő, Dóra; Horváth, Géza; Liszi, János; Tóth, Imre; Paor, Dávid

2010-09-01

Nowadays rules of environmental protection strictly regulate pollution material emission into environment. To keep the environmental protection laws recycling is one of the useful methods of waste material treatment. We have developed a new method for the treatment of industrial waste water and named it boundary layer separation method (BLSM). We apply the phenomena that ions can be enriched in the boundary layer of the electrically charged electrode surface compared to the bulk liquid phase. The main point of the method is that the boundary layer at correctly chosen movement velocity can be taken out of the waste water without being damaged, and the ion-enriched boundary layer can be recycled. Electrosorption is a surface phenomenon. It can be used with high efficiency in case of large electrochemically active surface of electrodes. During our research work two high surface area nickel electrodes have been prepared. The value of electrochemically active surface area of electrodes has been estimated. The existence of diffusion part of the double layer has been experimentally approved. The electrical double layer capacity has been determined. Ion transport by boundary layer separation has been introduced. Finally we have tried to estimate the relative significance of physical adsorption and electrosorption.

Prediction of boundary-layer transition caused by crossflow disturbances

OpenAIRE

Nomura, Toshiyuki; 野村　聡幸

1999-01-01

A prediction system for boundary layer transition is developed which consists of the Navier-Stokes code computing a compressible boundary layer, the linear PSE (Parabolized Stability Equations) code computing the spatial growth of a disturbance, and the N-factor code integrating the growth rate. The system is applied to the case that the transition of the compressible boundary layer on a swept cylinder is caused by cross flow disturbances which have the same spanwise wavelength as observed in...

INCOMPRESSIBLE LAMINAR BOUNDARY LAYER CONTROL BY BLOWING AND SUCTION

OpenAIRE

AZZEDINE NAHOUI; LAKHDAR BAHI

2013-01-01

A two-dimensional incompressible laminar boundary layer and its control using blowing and suction over a flat plate and around the NACA 0012 and 661012 profiles, is studied numerically. The study is based on the Prandtl boundary layer model using the finite differences method and the Crank-Nicolson scheme. The velocity distribution, the boundary layer thickness and the friction coefficient, are determined and presented with and without control. The application of the control technique, has de...

Unsteady turbulent boundary layers in swimming rainbow trout.

Science.gov (United States)

Yanase, Kazutaka; Saarenrinne, Pentti

2015-05-01

The boundary layers of rainbow trout, Oncorhynchus mykiss, swimming at 1.02±0.09 L s(-1) (mean±s.d., N=4), were measured by the particle image velocimetry (PIV) technique at a Reynolds number of 4×10(5). The boundary layer profile showed unsteadiness, oscillating above and beneath the classical logarithmic law of the wall with body motion. Across the entire surface regions that were measured, local Reynolds numbers based on momentum thickness, which is the distance that is perpendicular to the fish surface through which the boundary layer momentum flows at free-stream velocity, were greater than the critical value of 320 for the laminar-to-turbulent transition. The skin friction was dampened on the convex surface while the surface was moving towards a free-stream flow and increased on the concave surface while retreating. These observations contradict the result of a previous study using different species swimming by different methods. Boundary layer compression accompanied by an increase in local skin friction was not observed. Thus, the overall results may not support absolutely the Bone-Lighthill boundary layer thinning hypothesis that the undulatory motions of swimming fish cause a large increase in their friction drag because of the compression of the boundary layer. In some cases, marginal flow separation occurred on the convex surface in the relatively anterior surface region, but the separated flow reattached to the fish surface immediately downstream. Therefore, we believe that a severe impact due to induced drag components (i.e. pressure drag) on the swimming performance, an inevitable consequence of flow separation, was avoided. © 2015. Published by The Company of Biologists Ltd.

Comments on Hypersonic Boundary-Layer Transition

Science.gov (United States)

1990-09-01

mechanism by which boundary-layer disturbance growth is generally initiated and establishes the initial distur- banca amplitude at the onset of disturbance...Patankar, S. V., and Spalding, P. B., Heat and Mass Transfer in Boundary Lavers, CRC Press , Cleveland, Ohio, 1968. 87. Neumann, R. D., and Patterson, .J. 1

Vortex sheet approximation of boundary layers

International Nuclear Information System (INIS)

Chorin, A.J.

1978-01-01

a grid free method for approximating incomprssible boundary layers is introduced. The computational elements are segments of vortex sheets. The method is related to the earlier vortex method; simplicity is achieved at the cost of replacing the Navier-Stokes equations by the Prandtl boundary layer equations. A new method for generating vorticity at boundaries is also presented; it can be used with the earlier voartex method. The applications presented include (i) flat plate problems, and (ii) a flow problem in a model cylinder- piston assembly, where the new method is used near walls and an improved version of the random choice method is used in the interior. One of the attractive features of the new method is the ease with which it can be incorporated into hybrid algorithms

Standard deviation of vertical two-point longitudinal velocity differences in the atmospheric boundary layer.

Science.gov (United States)

Fichtl, G. H.

1971-01-01

Statistical estimates of wind shear in the planetary boundary layer are important in the design of V/STOL aircraft, and for the design of the Space Shuttle. The data analyzed in this study consist of eleven sets of longitudinal turbulent velocity fluctuation time histories digitized at 0.2 sec intervals with approximately 18,000 data points per time history. The longitudinal velocity fluctuations were calculated with horizontal wind and direction data collected at the 18-, 30-, 60-, 90-, 120-, and 150-m levels. The data obtained confirm the result that Eulerian time spectra transformed to wave-number spectra with Taylor's frozen eddy hypothesis possess inertial-like behavior at wave-numbers well out of the inertial subrange.

Bristled shark skin: a microgeometry for boundary layer control?

Energy Technology Data Exchange (ETDEWEB)

Lang, A W; Hidalgo, P; Westcott, M [Aerospace Engineering and Mechanics Department, University of Alabama, Box 870280, Tuscaloosa, AL 35487 (United States); Motta, P [Biology Department, University of South Florida, 4202 East Fowler Avenue, Tampa, FL 33620 (United States)], E-mail: alang@eng.ua.edu

2008-12-01

There exists evidence that some fast-swimming shark species may have the ability to bristle their scales during fast swimming. Experimental work using a water tunnel facility has been performed to investigate the flow field over and within a bristled shark skin model submerged within a boundary layer to deduce the possible boundary layer control mechanisms being used by these fast-swimming sharks. Fluorescent dye flow visualization provides evidence of the formation of embedded cavity vortices within the scales. Digital particle image velocimetry (DPIV) data, used to evaluate the cavity vortex formation and boundary layer characteristics close to the surface, indicate increased momentum in the slip layer forming above the scales. This increase in flow velocity close to the shark's skin is indicative of boundary layer control mechanisms leading to separation control and possibly transition delay for the bristled shark skin microgeometry.

Shock-like structures in the tropical cyclone boundary layer

Science.gov (United States)

Williams, Gabriel J.; Taft, Richard K.; McNoldy, Brian D.; Schubert, Wayne H.

2013-06-01

This paper presents high horizontal resolution solutions of an axisymmetric, constant depth, slab boundary layer model designed to simulate the radial inflow and boundary layer pumping of a hurricane. Shock-like structures of increasing intensity appear for category 1-5 hurricanes. For example, in the category 3 case, the u>(∂u/∂r>) term in the radial equation of motion produces a shock-like structure in the radial wind, i.e., near the radius of maximum tangential wind the boundary layer radial inflow decreases from approximately 22 m s-1 to zero over a radial distance of a few kilometers. Associated with this large convergence is a spike in the radial distribution of boundary layer pumping, with updrafts larger than 22 m s-1 at a height of 1000 m. Based on these model results, it is argued that observed hurricane updrafts of this magnitude so close to the ocean surface are attributable to the dry dynamics of the frictional boundary layer rather than moist convective dynamics. The shock-like structure in the boundary layer radial wind also has important consequences for the evolution of the tangential wind and the vertical component of vorticity. On the inner side of the shock the tangential wind tendency is essentially zero, while on the outer side of the shock the tangential wind tendency is large due to the large radial inflow there. The result is the development of a U-shaped tangential wind profile and the development of a thin region of large vorticity. In many respects, the model solutions resemble the remarkable structures observed in the boundary layer of Hurricane Hugo (1989).

Definition of Turbulent Boundary-Layer with Entropy Concept

Directory of Open Access Journals (Sweden)

Zhao Rui

2016-01-01

Full Text Available The relationship between the entropy increment and the viscosity dissipation in turbulent boundary-layer is systematically investigated. Through theoretical analysis and direct numerical simulation (DNS, an entropy function fs is proposed to distinguish the turbulent boundary-layer from the external flow. This approach is proved to be reliable after comparing its performance in the following complex flows, namely, low-speed airfoil flows with different wall temperature, supersonic cavity-ramp flow dominated by the combination of free-shear layer, larger recirculation and shocks, and the hypersonic flow past an aeroplane configuration. Moreover, fs is deduced from the point of energy, independent of any particular turbulent quantities. That is, this entropy concept could be utilized by other engineering applications related with turbulent boundary-layer, such as turbulence modelling transition prediction and engineering thermal protection.

From Planetary Boundaries to national fair shares of the global safe operating space — How can the scales be bridged?

NARCIS (Netherlands)

Häyhä, Tiina; Lucas, Paul L.|info:eu-repo/dai/nl/272607444; van Vuuren, Detlef P.|info:eu-repo/dai/nl/11522016X; Cornell, Sarah E.; Hoff, Holger

2016-01-01

The planetary boundaries framework proposes quantitative global limits to the anthropogenic perturbation of crucial Earth system processes, and thus marks out a planetary safe operating space for human activities. Yet, decisions regarding resource use and emissions are mostly made at less aggregated

Numerical simulations of the stratified oceanic bottom boundary layer

Science.gov (United States)

Taylor, John R.

Numerical simulations are used to consider several problems relevant to the turbulent oceanic bottom boundary layer. In the first study, stratified open channel flow is considered with thermal boundary conditions chosen to approximate a shallow sea. Specifically, a constant heat flux is applied at the free surface and the lower wall is assumed to be adiabatic. When the surface heat flux is strong, turbulent upwellings of low speed fluid from near the lower wall are inhibited by the stable stratification. Subsequent studies consider a stratified bottom Ekman layer over a non-sloping lower wall. The influence of the free surface is removed by using an open boundary condition at the top of the computational domain. Particular attention is paid to the influence of the outer layer stratification on the boundary layer structure. When the density field is initialized with a linear profile, a turbulent mixed layer forms near the wall, which is separated from the outer layer by a strongly stable pycnocline. It is found that the bottom stress is not strongly affected by the outer layer stratification. However, stratification reduces turbulent transport to the outer layer and strongly limits the boundary layer height. The mean shear at the top of the boundary layer is enhanced when the outer layer is stratified, and this shear is strong enough to cause intermittent instabilities above the pycnocline. Turbulence-generated internal gravity waves are observed in the outer layer with a relatively narrow frequency range. An explanation for frequency content of these waves is proposed, starting with an observed broad-banded turbulent spectrum and invoking linear viscous decay to explain the preferential damping of low and high frequency waves. During the course of this work, an open-source computational fluid dynamics code has been developed with a number of advanced features including scalar advection, subgrid-scale models for large-eddy simulation, and distributed memory

The laminar boundary layer equations

CERN Document Server

Curle, N

2017-01-01

Thorough introduction to boundary layer problems offers an ordered, logical presentation accessible to undergraduates. The text's careful expositions of the limitations and accuracy of various methods will also benefit professionals. 1962 edition.

Direct numerical simulation of stable and unstable turbulent thermal boundary layers

International Nuclear Information System (INIS)

Hattori, Hirofumi; Houra, Tomoya; Nagano, Yasutaka

2007-01-01

This paper presents direct numerical simulations (DNS) of stable and unstable turbulent thermal boundary layers. Since a buoyancy-affected boundary layer is often encountered in an urban environmental space where stable and unstable stratifications exist, exploring a buoyancy-affected boundary layer is very important to know the transport phenomena of the flow in an urban space. Although actual observation may qualitatively provide the characteristics of these flows, the relevant quantitative turbulent quantities are very difficult to measure. Thus, in order to quantitatively investigate a buoyancy-affected boundary layer in detail, we have here carried out for the first time time- and space-developing DNS of slightly stable and unstable turbulent thermal boundary layers. The DNS results show the quantitative turbulent statistics and structures of stable and unstable thermal boundary layers, in which the characteristic transport phenomena of thermally stratified boundary layers are demonstrated by indicating the budgets of turbulent shear stress and turbulent heat flux. Even though the input of buoyant force is not large, the influence of buoyancy is clearly revealed in both stable and unstable turbulent boundary layers. In particular, it is found that both stable and unstable thermal stratifications caused by the weak buoyant force remarkably alter the structure of near-wall turbulence

Boundary Layer Control on Airfoils.

Science.gov (United States)

Gerhab, George; Eastlake, Charles

1991-01-01

A phenomena, boundary layer control (BLC), produced when visualizing the fluidlike flow of air is described. The use of BLC in modifying aerodynamic characteristics of airfoils, race cars, and boats is discussed. (KR)

Boundary layer on a flat plate with suction

International Nuclear Information System (INIS)

Favre, A.; Dumas, R.; Verollet, E.

1961-01-01

This research done in wind tunnel concerns the turbulent boundary layer of a porous flat plate with suction. The porous wall is 1 m long and begins 1 m downstream of the leading edge. The Reynolds number based on the boundary layer thickness is of the order of 16.300. The suction rate defined as the ratio of the velocity perpendicular to the wall to the external flow velocity ranges from 0 to 2 per cent. The pressure gradient can be controlled. The mean velocity profiles have been determined for various positions and suction rates by means of total pressure probes together with the intensities of the turbulent velocity fluctuations components, energy spectra and correlations by means of hot wire anemometers, spectral analyser and correlator. The stream lines, the values of the viscous and turbulent shear stresses, of the local wall friction, of the turbulent energy production term, with some information on the dissipation of the energy have been derived from these measurements. For these data the integral of equation of continuity in boundary layer have been drawn. The suction effects on the boundary layer are important. The suction thoroughly alters the mean velocity profiles by increasing the viscous shear stresses near the wall and decreasing them far from the wall, it diminishes the longitudinal and transversal turbulence intensities, the turbulent shear stresses, and the production of energy of turbulence. These effects are much stressed in the inner part of the boundary layer. On the other hand the energy spectra show that the turbulence scale is little modified, the boundary layer thickness being not much diminished by the suction. The suction effects can be appreciated by comparing twice the suction rate to the wall friction coefficient (assumed airtight), quite noticeable as soon as the rate is about unity, they become very important when it reaches ten. (author) [fr

Destiny of earthward streaming plasma in the plasmasheet boundary layer

Science.gov (United States)

Green, J. L.; Horwitz, J. L.

1986-01-01

The dynamics of the earth's magnetotail have been investigated, and it has become clear that the plasmasheet boundary layer field lines map into the Region I Field-Aligned Currents (FAC) of the auroral zone. It is pointed out that the role of earthward streaming ions in the plasmasheet boundary layer may be of fundamental importance in the understanding of magnetotail dynamics, auroral zone physics, and especially for ionospheric-magnetospheric interactions. The present paper has the objective to evaluate propagation characteristics for the earthward streaming ions observed in the plasmasheet boundary layer. An investigation is conducted of the propagation characteristics of protons in the plasmasheet boundary layer using independent single particle dynamics, and conclusions are discussed. The density of earthward streaming ions found in the plasmasheet boundary layer should include the ring current as well as the auroral zone precipitaiton and inner plasmasheet regions of the magnetosphere.

Boundary layer friction of solvate ionic liquids as a function of potential.

Science.gov (United States)

Li, Hua; Rutland, Mark W; Watanabe, Masayoshi; Atkin, Rob

2017-07-01

Atomic force microscopy (AFM) has been used to investigate the potential dependent boundary layer friction at solvate ionic liquid (SIL)-highly ordered pyrolytic graphite (HOPG) and SIL-Au(111) interfaces. Friction trace and retrace loops of lithium tetraglyme bis(trifluoromethylsulfonyl)amide (Li(G4) TFSI) at HOPG present clearer stick-slip events at negative potentials than at positive potentials, indicating that a Li + cation layer adsorbed to the HOPG lattice at negative potentials which enhances stick-slip events. The boundary layer friction data for Li(G4) TFSI shows that at HOPG, friction forces at all potentials are low. The TFSI - anion rich boundary layer at positive potentials is more lubricating than the Li + cation rich boundary layer at negative potentials. These results suggest that boundary layers at all potentials are smooth and energy is predominantly dissipated via stick-slip events. In contrast, friction at Au(111) for Li(G4) TFSI is significantly higher at positive potentials than at negative potentials, which is comparable to that at HOPG at the same potential. The similarity of boundary layer friction at negatively charged HOPG and Au(111) surfaces indicates that the boundary layer compositions are similar and rich in Li + cations for both surfaces at negative potentials. However, at Au(111), the TFSI - rich boundary layer is less lubricating than the Li + rich boundary layer, which implies that anion reorientations rather than stick-slip events are the predominant energy dissipation pathways. This is confirmed by the boundary friction of Li(G4) NO 3 at Au(111), which shows similar friction to Li(G4) TFSI at negative potentials due to the same cation rich boundary layer composition, but even higher friction at positive potentials, due to higher energy dissipation in the NO 3 - rich boundary layer.

Effect of externally generated turbulence on wave boundary layer

DEFF Research Database (Denmark)

Fredsøe, Jørgen; Sumer, B. Mutlu; Kozakiewicz, A.

2003-01-01

This experimental study deals with the effect of externally generated turbulence on the oscillatory boundary layer to simulate the turbulence in the wave boundary layer under broken waves in the swash zone. The subject has been investigated experimentally in a U-shaped, oscillating water tunnel...... results. The mean and turbulence quantities in the outer flow region are increased substantially with the introduction of the grids. It is shown that the externally generated turbulence is able to penetrate the bed boundary layer, resulting in an increase in the bed shear stress, and therefore...

Mean flow structure of non-equilibrium boundary layers with adverse ...

Indian Academy of Sciences (India)

According to them, an equilibrium boundary layer might exist if the pressure ... of adverse pressure gradient on the turbulent boundary layer at the flat plate for ..... of a constant-pressure turbulent layer to the sudden application of an sudden.

Hairpin vortices in turbulent boundary layers

International Nuclear Information System (INIS)

Eitel-Amor, G; Schlatter, P; Flores, O

2014-01-01

The present work addresses the question whether hairpin vortices are a dominant feature of near-wall turbulence and which role they play during transition. First, the parent-offspring mechanism is investigated in temporal simulations of a single hairpin vortex introduced in a mean shear flow corresponding to turbulent channels and boundary layers up to Re τ = 590. Using an eddy viscosity computed from resolved simulations, the effect of a turbulent background is also considered. Tracking the vortical structure downstream, it is found that secondary hairpins are created shortly after initialization. Thereafter, all rotational structures decay, whereas this effect is enforced in the presence of an eddy viscosity. In a second approach, a laminar boundary layer is tripped to transition by insertion of a regular pattern of hairpins by means of defined volumetric forces representing an ejection event. The idea is to create a synthetic turbulent boundary layer dominated by hairpin-like vortices. The flow for Re τ < 250 is analysed with respect to the lifetime of individual hairpin-like vortices. Both the temporal and spatial simulations demonstrate that the regeneration process is rather short-lived and may not sustain once a turbulent background has formed. From the transitional flow simulations, it is conjectured that the forest of hairpins reported in former DNS studies is an outer layer phenomenon not being connected to the onset of near-wall turbulence.

Comments on deriving the equilibrium height of the stable boundary layer

NARCIS (Netherlands)

Steeneveld, G.J.; Wiel, van de B.J.H.; Holtslag, A.A.M.

2007-01-01

Recently, the equilibrium height of the stable boundary layer received much attention in a series of papers by Zilitinkevich and co-workers. In these studies the stable boundary-layer height is derived in terms of inverse interpolation of different boundary-layer height scales, each representing a

Evolution of trace elements in the planetary boundary layer in southern China: Effects of dust storms and aerosol-cloud interactions

Science.gov (United States)

Li, Tao; Wang, Yan; Zhou, Jie; Wang, Tao; Ding, Aijun; Nie, Wei; Xue, Likun; Wang, Xinfeng; Wang, Wenxing

2017-03-01

Aerosols and cloud water were analyzed at a mountaintop in the planetary boundary layer in southern China during March-May 2009, when two Asian dust storms occurred, to investigate the effects of aerosol-cloud interactions (ACIs) on chemical evolution of atmospheric trace elements. Fe, Al, and Zn predominated in both coarse and fine aerosols, followed by high concentrations of toxic Pb, As, and Cd. Most of these aerosol trace elements, which were affected by dust storms, exhibited various increases in concentrations but consistent decreases in solubility. Zn, Fe, Al, and Pb were the most abundant trace elements in cloud water. The trace element concentrations exhibited logarithmic inverse relationships with the cloud liquid water content and were found highly pH dependent with minimum concentrations at the threshold of pH 5.0. The calculation of Visual MINTEQ model showed that 80.7-96.3% of Fe(II), Zn(II), Pb(II), and Cu(II) existed in divalent free ions, while 71.7% of Fe(III) and 71.5% of Al(III) were complexed by oxalate and fluoride, respectively. ACIs could markedly change the speciation distributions of trace elements in cloud water by pH modification. The in-cloud scavenging of aerosol trace elements likely reached a peak after the first 2-3 h of cloud processing, with scavenging ratios between 0.12 for Cr and 0.57 for Pb. The increases of the trace element solubility (4-33%) were determined in both in-cloud aerosols and postcloud aerosols. These results indicated the significant importance of aerosol-cloud interactions to the evolution of trace elements during the first several cloud condensation/evaporation cycles.

Magnetohydrodynamic boundary layer on a wedge

International Nuclear Information System (INIS)

Rao, B.N.; Mittal, M.L.

1981-01-01

The effects of the Hall and ionslip currents on the gas-dynamic boundary layer are investigated in view of the increasing prospects for using the MHD principle in electric power generation. The currents are included in the analysis using the generalized Ohm's law (Sherman and Sutton, 1964), and the resulting two nonlinear coupled equations are solved using a modification in the method suggested by Nachtsheim and Swigert (1965), Dewey and Gross (1967), and Steinheuer (1968). Solutions are presented for the incompressible laminar boundary-layer equations in the absence and the presence of the load parameter, and for the pressure gradient parameter for flow separation

Discussion of boundary-layer characteristics near the casing of an axial-flow compressor

Science.gov (United States)

Mager, Artur; Mahoney, John J; Budinger, Ray E

1951-01-01

Boundary-layer velocity profiles on the casing of an axial-flow compressor behind the guide vanes and rotor were measured and resolved into two components: along the streamline of the flow and perpendicular to it. Boundary-layer thickness and the deflection of the boundary layer at the wall were the generalizing parameters. By use of these results and the momentum-integral equations, the characteristics of boundary on the walls of axial-flow compressor are qualitatively discussed. Important parameters concerning secondary flow in the boundary layer appear to be turning of the flow and the product of boundary-layer thickness and streamline curvature outside the boundary layer. Two types of separation are shown to be possible in three dimensional boundary layer.

Control of Boundary Layers for Aero-optical Applications

Science.gov (United States)

2015-06-23

with some difficulty) from hot-wire velocity measurements, or computed directly from CFD results (e.g. Wang & Wang, 2012). Several different density...of experimental and computational research, especially applied to supersonic and hypersonic boundary layers; see Smits & Dussauge (1996), Spina et...Duan, L., Beekman, I. and Martin, M.P. (2010) Direct Numerical Simulation of Hypersonic Turbulent Boundary Layers. Part 2. Effect of Wall

On hairpin vortices in a transitional boundary layer

Directory of Open Access Journals (Sweden)

Uruba Václav

2012-04-01

Full Text Available In the presented paper the results of experiments on transitional boundary layer are presented. The boundary layer was generated on smooth flat wall with zero pressure gradient forming one side of the channel of rectangular cross section. The hairpin vortices, packets of hairpin vortices, turbulent spots and calmed regions were experimentally investigated using time-resolved PIV technique.

Boundary layer and fundamental problems of hydrodynamics (compatibility of a logarithmic velocity profile in a turbulent boundary layer with the experience values)

Science.gov (United States)

Zaryankin, A. E.

2017-11-01

The compatibility of the semiempirical turbulence theory of L. Prandtl with the actual flow pattern in a turbulent boundary layer is considered in this article, and the final calculation results of the boundary layer is analyzed based on the mentioned theory. It shows that accepted additional conditions and relationships, which integrate the differential equation of L. Prandtl, associating the turbulent stresses in the boundary layer with the transverse velocity gradient, are fulfilled only in the near-wall region where the mentioned equation loses meaning and are inconsistent with the physical meaning on the main part of integration. It is noted that an introduced concept about the presence of a laminar sublayer between the wall and the turbulent boundary layer is the way of making of a physical meaning to the logarithmic velocity profile, and can be defined as adjustment of the actual flow to the formula that is inconsistent with the actual boundary conditions. It shows that coincidence of the experimental data with the actual logarithmic profile is obtained as a result of the use of not particular physical value, as an argument, but function of this value.

Flat Plate Boundary Layer Stimulation Using Trip Wires and Hama Strips

Science.gov (United States)

Peguero, Charles; Henoch, Charles; Hrubes, James; Fredette, Albert; Roberts, Raymond; Huyer, Stephen

2017-11-01

Water tunnel experiments on a flat plate at zero angle of attack were performed to investigate the effect of single roughness elements, i.e., trip wires and Hama strips, on the transition to turbulence. Boundary layer trips are traditionally used in scale model testing to force a boundary layer to transition from laminar to turbulent flow at a single location to aid in scaling of flow characteristics. Several investigations of trip wire effects exist in the literature, but there is a dearth of information regarding the influence of Hama strips on the flat plate boundary layer. The intent of this investigation is to better understand the effects of boundary layer trips, particularly Hama strips, and to investigate the pressure-induced drag of both styles of boundary layer trips. Untripped and tripped boundary layers along a flat plate at a range of flow speeds were characterized with multiple diagnostic measurements in the NUWC/Newport 12-inch water tunnel. A wide range of Hama strip and wire trip thicknesses were used. Measurements included dye flow visualization, direct skin friction and parasitic drag force, boundary layer profiles using LDV, wall shear stress fluctuations using hot film anemometry, and streamwise pressure gradients. Test results will be compared to the CFD and boundary layer model results as well as the existing body of work. Conclusions, resulting in guidance for application of Hama strips in model scale experiments and non-dimensional predictions of pressure drag will be presented.

Coastal boundary layers in ocean modelling: an application to the Adriatic Sea

International Nuclear Information System (INIS)

Malanotte Rizzoli, P.; Dell'Orto, F.

1981-01-01

Boundary layers play an important role in modelling geophysical fluid-dynamical flows, in as much as they constitute regions of ageostrophic dynamics in which the physical balances characterizing the main interior of the water mass break down. A short synopsis is given of important boundary layers in ocean circulation modelling with specific emphasis drawn upon side wall boundary layers, namely those adjacent to the coastlines of the considered basin. Application of boundary layer analysis is thereafter made for one specific phenomenological situation, namely the Northern Adriatic Sea and the problem posed by its wintertime seasonal circulation. The analysis furnishes a mathematical model fo the coastal strip adjacent to the Italian shoreline, treated as a boundary layer in the density field, starting from general model equations valid throughout the interior of the Northern Adriatic. The boundary layer model is consequently used to modify the side wall boundary condition for the interior density field. Related numerical experiments are shown and compared with previous standard experiments in which the boundary layer contribution to the density field has not been considered. (author)

On the modeling of electrical boundary layer (electrode layer) and ...

Indian Academy of Sciences (India)

In the first part of the paper, equations and methodology are discussed and in the second, we discuss results. 2. Methodology. In the atmospheric electricity, the earth's surface is one electrode and electrode layer or electrical boundary layer is a region near the surface of the earth in which profiles of atmospheric electrical.

Large Eddy Simulation of the ventilated wave boundary layer

DEFF Research Database (Denmark)

Lohmann, Iris P.; Fredsøe, Jørgen; Sumer, B. Mutlu

2006-01-01

A Large Eddy Simulation (LES) of (1) a fully developed turbulent wave boundary layer and (2) case 1 subject to ventilation (i.e., suction and injection varying alternately in phase) has been performed, using the Smagorinsky subgrid-scale model to express the subgrid viscosity. The model was found...... slows down the flow in the full vertical extent of the boundary layer, destabilizes the flow and decreases the mean bed shear stress significantly; whereas suction generally speeds up the flow in the full vertical extent of the boundary layer, stabilizes the flow and increases the mean bed shear stress...

Planetary boundary layer height variability over athens, greece, based on the synergy of raman lidar and radiosonde data: Application of the kalman filter and other techniques (2011-2016)

Science.gov (United States)

Alexiou, Dimitrios; Kokkalis, Panagiotis; Papayannis, Alexandros; Rocadenbosch, Francesc; Argyrouli, Athina; Tsaknakis, Georgios; Tzanis, Chris G.

2018-04-01

In this paper we studied the temporal evolution of the Planetary Boundary Layer height (PBLH) over the basin of Athens, Greece during a 5-year period (2011-2016) using data from the EOLE Raman lidar system. The lidar data (range-corrected lidar signals-RCS) were selected around 12:00 UTC and 00:00 UTC for a total of 332 cases: 165 days and 167 nights. Extended Kalman filtering techniques were used for the determination of the PBLH. Moreover, several well established techniques for the PBLH estimation based on lidar data were also tested for a total of 35 cases. Comparisons with the PBLH values derived from radiosonde data were also performed. The mean PBLH over Athens was found to be of the order of 1617±324 m at 12:00 UTC and of 892±130 m at 00:00 UTC, for the period examined. The mean PBLH growth rate was found to be about 170±64 m h-1 and 90±17 m h-1, during daytime and nighttime, respectively.

Exploring the magnetospheric boundary layer

International Nuclear Information System (INIS)

Hapgood, M.A.; Bryant, D.A.

1992-01-01

We show how, for most crossings of the boundary layer, one can construct a 'transition parameter', based on electron density and temperature, which orders independent plasma measurements into well-defined patterns which are consistent from case to case. We conclude that there is a gradual change in the balance of processes which determine the structure of the layer and suggest that there is no advantage in dividing the layer into different regions. We further conclude that the mixing processes in layer act in an organised way to give the consistent patterns revealed by the transition parameter. More active processes must sometimes take to give the extreme values (e.g. in velocity) which are seen in some crossings

Effect of boundary layer thickness on the flow characteristics around a rectangular prism

International Nuclear Information System (INIS)

Ji, Ho Seong; Kim, Kyung Chun

2001-01-01

Effect of boundary layer thickness on the flow characteristics around a rectangular prism has been investigated by using a PIV(Particle Image Velocimetry) technique. Three different boundary layers (thick, medium and thin) were generated in the atmospheric boundary layer wind tunnel at Pusan National University. The thick boundary layer having 670mm thickness was generated by using spires and roughness elements. The medium thickness of boundary layer(δ=270mm) was the natural turbulent boundary layer at the test section with fully long developing length(18m). The thin boundary layer with 36.5mm thickness was generated by on a smooth panel elevated 70cm from the wind tunnel floor. The Reynolds number based on the free stream velocity and the height of the model was 7.9X10 3 . The mean velocity vector fields and turbulent kinetic energy distribution were measured and compared. The effect of boundary layer thickness is clearly observed not only in the length of separation bubble but also in the reattachment points. The thinner boundary layer thickness, the higher turbulent kinetic energy peak around the model roof. It is strongly recommended that the height ratio between model and approaching boundary layer thickness should be a major parameter

The Atmospheric Boundary Layer

Science.gov (United States)

Garratt, J. R.

1994-05-01

A comprehensive and lucid account of the physics and dynamics of the lowest one to two kilometers of the Earth's atmosphere in direct contact with the Earth's surface, known as the atmospheric boundary layer (ABL). Dr. Garratt emphasizes the application of the ABL problems to numerical modeling of the climate, which makes this book unique among recent texts on the subject. He begins with a brief introduction to the ABL before leading to the development of mean and turbulence equations and the many scaling laws and theories that are the cornerstone of any serious ABL treatment. Modeling of the ABL is crucially dependent for its realism on the surface boundary conditions, so chapters four and five deal with aerodynamic and energy considerations, with attention given to both dry and wet land surfaces and the sea. The author next treats the structure of the clear-sky, thermally stratified ABL, including the convective and stable cases over homogeneous land, the marine ABL, and the internal boundary layer at the coastline. Chapter seven then extends this discussion to the cloudy ABL. This is particularly relevant to current research because the extensive stratocumulus regions over the subtropical oceans and stratus regions over the Arctic have been identified as key players in the climate system. In the final chapters, Dr. Garratt summarizes the book's material by discussing appropriate ABL and surface parameterization schemes in general circulation models of the atmosphere that are being used for climate stimulation.

RACORO Extended-Term Aircraft Observations of Boundary-Layer Clouds

Science.gov (United States)

Vogelmann, Andrew M.; McFarquhar, Greg M.; Ogren, John A.; Turner, David D.; Comstock, Jennifer M.; Feingold, Graham; Long, Charles N.; Jonsson, Haflidi H.; Bucholtz, Anthony; Collins, Don R.;

Boundary layers as the primary transport regions of the earth's magnetotail

International Nuclear Information System (INIS)

Eastman, T.E.; Frank, L.A.; Huang, C.Y.

1985-01-01

A comprehensive survey of ISEE and IMP LEPEDEA plasma measurements in the earth's magnetotail reveals that the magnetospheric boundary layer and the plasma sheet boundary layer are the primary transport regions there. These plasma measurements also distinguish various components of the plasma sheet, including the central plasma sheet and plasma sheet boundary layer. A significant new result reported here is the existence of cold-and hot-plasma components that are spatially copresent within the central plasma sheet. Such plasma components cannot be explained merely by temporal variations in spectra involving the entire plasma sheet. Contributions to a low-temperature component of the plasma sheet enter directly from the boundary layer located along the magnetotail flanks. Field-aligned flows predominate within the plasma sheet boundary layer, which is almost always present and is located near the northern and southern border of the plasma sheet. The plasma sheet boundary layer comprises highly anisotropic ion distributions, including counteracting ion beams, that evolve into the hot, isotropic component of the plasma sheet

Rotor blade boundary layer measurement hardware feasibility demonstration

Science.gov (United States)

Clark, D. R.; Lawton, T. D.

1972-01-01

A traverse mechanism which allows the measurement of the three dimensional boundary layers on a helicopter rotor blade has been built and tested on a full scale rotor to full scale conditions producing centrifugal accelerations in excess of 400 g and Mach numbers of 0.6 and above. Boundary layer velocity profiles have been measured over a range of rotor speeds and blade collective pitch angles. A pressure scanning switch and transducer were also tested on the full scale rotor and found to be insensitive to centrifugal effects within the normal main rotor operating range. The demonstration of the capability to measure boundary layer behavior on helicopter rotor blades represents the first step toward obtaining, in the rotating system, data of a quality comparable to that already existing for flows in the fixed system.

Large artificially generated turbulent boundary layers for the study of atmospheric flows

International Nuclear Information System (INIS)

Guimaraes, Joao Henrique D.; Santos Junior, Sergio J.F. dos; Freire, Atila P. Silva; Jian, Su

1999-01-01

The present work discusses in detail the experimental conditions for the establishment of thick artificially generated turbulent boundary layer which can be classified as having the near characteristics of an atmospheric boundary layer. The paper describes the experimental arrangement, including the features of the designed wind tunnel and of the instrumentation. the boundary layer is made to develop over a surface fitted with wedge generators which are used to yield a very thick boundary layer. The flow conditions were validated against the following features: growth, structure, equilibrium and turbulent transport momentum. Results are presented for the following main flow variables: mean velocity, local skin-friction coefficient, boundary layer momentum thickness and the Clauser factor. The velocity boundary layer characteristics were shown to be in good agreement with the expected trend in view of the classical expressions found in literature. (author)

INCOMPRESSIBLE LAMINAR BOUNDARY LAYER CONTROL BY BLOWING AND SUCTION

Directory of Open Access Journals (Sweden)

AZZEDINE NAHOUI

2013-12-01

Full Text Available A two-dimensional incompressible laminar boundary layer and its control using blowing and suction over a flat plate and around the NACA 0012 and 661012 profiles, is studied numerically. The study is based on the Prandtl boundary layer model using the finite differences method and the Crank-Nicolson scheme. The velocity distribution, the boundary layer thickness and the friction coefficient, are determined and presented with and without control. The application of the control technique, has demonstrated its positive effect on the transition point and the friction coefficient. Both control procedures are compared for different lengths, speeds and angles of blowing and suction.

Rough-wall turbulent boundary layers with constant skin friction

KAUST Repository

Sridhar, A.

2017-03-28

A semi-empirical model is presented that describes the development of a fully developed turbulent boundary layer in the presence of surface roughness with length scale ks that varies with streamwise distance x . Interest is centred on flows for which all terms of the von Kármán integral relation, including the ratio of outer velocity to friction velocity U+∞≡U∞/uτ , are streamwise constant. For Rex assumed large, use is made of a simple log-wake model of the local turbulent mean-velocity profile that contains a standard mean-velocity correction for the asymptotic fully rough regime and with assumed constant parameter values. It is then shown that, for a general power-law external velocity variation U∞∼xm , all measures of the boundary-layer thickness must be proportional to x and that the surface sand-grain roughness scale variation must be the linear form ks(x)=αx , where x is the distance from the boundary layer of zero thickness and α is a dimensionless constant. This is shown to give a two-parameter (m,α) family of solutions, for which U+∞ (or equivalently Cf ) and boundary-layer thicknesses can be simply calculated. These correspond to perfectly self-similar boundary-layer growth in the streamwise direction with similarity variable z/(αx) , where z is the wall-normal coordinate. Results from this model over a range of α are discussed for several cases, including the zero-pressure-gradient ( m=0 ) and sink-flow ( m=−1 ) boundary layers. Trends observed in the model are supported by wall-modelled large-eddy simulation of the zero-pressure-gradient case for Rex in the range 108−1010 and for four values of α . Linear streamwise growth of the displacement, momentum and nominal boundary-layer thicknesses is confirmed, while, for each α , the mean-velocity profiles and streamwise turbulent variances are found to collapse reasonably well onto z/(αx) . For given α , calculations of U+∞ obtained from large-eddy simulations are streamwise

Fifty Years of Boundary-Layer Theory and Experiment

Science.gov (United States)

Dryden, Hugh L.

1955-01-01

The year 1954 marked the 50th anniversary of the Prandtl boundary-layer theory from which we may date the beginning of man's understanding of the dynamics of real fluids. A backward look at this aspect of the history of the last 50 years may be instructive. This paper (1) attempts to compress the events of those 50 years into a few thousand words, to tell in this brief space the interesting story of the development of a new concept, its slow acceptance and growth, its spread from group to group within its country of origin, and its diffusion to other countries of the world. The original brief paper of Prandtl (2) was presented at the Third International Mathematical Congress at Heidelberg in 1904 and published in the following year. It was an attempt to explain the d'Alembert paradox, namely, that the neglect of the small friction of air in the theory resulted in the prediction of zero resistance to motion. Prandtl set himself the task of computing the motion of a fluid of small friction, so small that its effect could be neglected everywhere except where large velocity differences were present or a cumulative effect of friction occurred This led to the concept of boundary layer, or transition layer, near the wall of a body immersed in a fluid stream in which the velocity rises from zero to the free-stream value. It is interesting that Prandtl used the term Grenzsehicht (boundary layer) only once and the term Ubergangsschicht (transition layer) seven times in the brief article. Later writers also used Reibungsschicht (friction layer), but most writers today use Grenzschicht (boundary layer).

Receptivity of a high-speed boundary layer to temperature spottiness

OpenAIRE

Fedorov, A. V.; Ryzhov, A. A.; Soudakov, V. G.; Utyuzhnikov, S. V.

2013-01-01

Two-dimensional direct numerical simulation (DNS) of the receptivity of a flat-plate boundary layer to temperature spottiness in the Mach 6 free stream is carried out. The influence of spottiness parameters on the receptivity process is studied. It is shown that the temperature spots propagating near the upper boundary-layer edge generate mode F inside the boundary layer. Further downstream mode F is synchronized with unstable mode S (Mack second mode) and excites the latter via the inter-mod...

Airfoil boundary layer separation and control at low Reynolds numbers

Energy Technology Data Exchange (ETDEWEB)

Yarusevych, S.; Sullivan, P.E. [University of Toronto, Department of Mechanical and Industrial Engineering, Toronto, ON (Canada); Kawall, J.G. [Ryerson University, Department of Mechanical and Industrial Engineering, Toronto, ON (Canada)

2005-04-01

The boundary layer separation on a NACA 0025 airfoil was studied experimentally via hot-wire anemometry and surface pressure measurements. The results provide added insight into periodic boundary layer control, suggesting that matching the excitation frequency with the most amplified disturbance in the separated shear layer is optimal for improving airfoil performance. (orig.)

Interaction of Atmospheric Turbulence with Blade Boundary Layer Dynamics on a 5MW Wind Turbine using Blade-Boundary-Layer-Resolved CFD with hybrid URANS-LES.

Energy Technology Data Exchange (ETDEWEB)

Vijayakumar, Ganesh [National Renewable Energy Lab. (NREL), Golden, CO (United States); Pennsylvania State Univ., University Park, PA (United States); Brasseur, James [Pennsylvania State Univ., University Park, PA (United States); Univ. of Colorado, Boulder, CO (United States); Lavely, Adam; Jayaraman, Balaji; Craven, Brent

2016-01-04

We describe the response of the NREL 5 MW wind turbine blade boundary layer to the passage of atmospheric turbulence using blade-boundary-layer-resolved computational fluid dynamics with hybrid URANS-LES modeling.

Scaling the heterogeneously heated convective boundary layer

Science.gov (United States)

Van Heerwaarden, C.; Mellado, J.; De Lozar, A.

2013-12-01

We have studied the heterogeneously heated convective boundary layer (CBL) by means of large-eddy simulations (LES) and direct numerical simulations (DNS). What makes our study different from previous studies on this subject are our very long simulations in which the system travels through multiple states and that from there we have derived scaling laws. In our setup, a stratified atmosphere is heated from below by square patches with a high surface buoyancy flux, surrounded by regions with no or little flux. By letting a boundary layer grow in time we let the system evolve from the so-called meso-scale to the micro-scale regime. In the former the heterogeneity is large and strong circulations can develop, while in the latter the heterogeneity is small and does no longer influence the boundary layer structure. Within each simulation we can now observe the formation of a peak in kinetic energy, which represents the 'optimal' heterogeneity size in the meso-scale, and the subsequent decay of the peak and the development towards the transition to the micro-scale. We have created a non-dimensional parameter space that describes all properties of this system. By studying the previously described evolution for different combinations of parameters, we have derived three important conclusions. First, there exists a horizontal length scale of the heterogeneity (L) that is a function of the boundary layer height (h) and the Richardson (Ri) number of the inversion at the top of the boundary layer. This relationship has the form L = h Ri^(3/8). Second, this horizontal length scale L allows for expressing the time evolution, and thus the state of the system, as a ratio of this length scale and the distance between two patches Xp. This ratio thus describes to which extent the circulation fills up the space that exists between two patch centers. The timings of the transition from the meso- to the micro-scale collapse under this scaling for all simulations sharing the same flux

Self-consistent model of the low-latitude boundary layer

International Nuclear Information System (INIS)

Phan, T.D.; Sonnerup, B.U.Oe.; Lotko, W.

1989-01-01

A simple two-dimensional, steady state, viscous model of the dawnside and duskside low-latitude boundary layer (LLBL) has been developed. It incorporates coupling to the ionosphere via field-aligned currents and associated field-aligned potential drops, governed by a simple conductance law, and it describes boundary layer currents, magnetic fields, and plasma flow in a self-consistent manner. The magnetic field induced by these currents leads to two effects: (1) a diamagnetic depression of the magnetic field in the equatorial region and (2) bending of the field lines into parabolas in the xz plane with their vertices in the equatorial plane, at z = 0, and pointing in the flow direction, i.e., tailward. Both effects are strongest at the magnetopause edge of the boundary layer and vanish at the magnetospheric edge. The diamagnetic depression corresponds to an excess of plasma pressure in the equatorial boundary layer near the magnetopause. The boundary layer structure is governed by a fourth-order, nonlinear, ordinary differential equation in which one nondimensional parameter, the Hartmann number M, appears. A second parameter, introduced via the boundary conditions, is a nondimensional flow velocity v 0 * at the magnetopause. Numerical results from the model are presented and the possible use of observations to determine the model parameters is discussed. The main new contribution of the study is to provide a better description of the field and plasma configuration in the LLBL itself and to clarify in quantitative terms the circumstances in which induced magnetic fields become important

Boundary-Layer Bypass Transition Over Large-Scale Bodies

Science.gov (United States)

2016-12-16

behaviour of the velocity and pressure changes with the curvature. This work aims to extend the results of the flat-plate boundary layer to a Rankine...example, consume an enormous amount of energy due to friction, many works have been directed to the suppression of transitional boundary layer disturbances...decrease of the enormous amount of energy consumed by airplanes during flight, moreover flight costs and aerodynamic noise could be reduced and number

Modelling the artic stable boundary layer and its coupling to the surface

NARCIS (Netherlands)

Steeneveld, G.J.; Wiel, van de B.J.H.; Holtslag, A.A.M.

2006-01-01

The impact of coupling the atmosphere to the surface energy balance is examined for the stable boundary layer, as an extension of the first GABLS (GEWEX Atmospheric Boundary-Layer Study) one-dimensional model intercomparison. This coupling is of major importance for the stable boundary-layer

Linear segmentation algorithm for detecting layer boundary with lidar.

Science.gov (United States)

Mao, Feiyue; Gong, Wei; Logan, Timothy

2013-11-04

The automatic detection of aerosol- and cloud-layer boundary (base and top) is important in atmospheric lidar data processing, because the boundary information is not only useful for environment and climate studies, but can also be used as input for further data processing. Previous methods have demonstrated limitations in defining the base and top, window-size setting, and have neglected the in-layer attenuation. To overcome these limitations, we present a new layer detection scheme for up-looking lidars based on linear segmentation with a reasonable threshold setting, boundary selecting, and false positive removing strategies. Preliminary results from both real and simulated data show that this algorithm cannot only detect the layer-base as accurate as the simple multi-scale method, but can also detect the layer-top more accurately than that of the simple multi-scale method. Our algorithm can be directly applied to uncalibrated data without requiring any additional measurements or window size selections.

Particle motion in atmospheric boundary layers of Mars and Earth

Science.gov (United States)

White, B. R.; Iversen, J. D.; Greeley, R.; Pollack, J. B.

1975-01-01

To study the eolian mechanics of saltating particles, both an experimental investigation of the flow field around a model crater in an atmospheric boundary layer wind tunnel and numerical solutions of the two- and three-dimensional equations of motion of a single particle under the influence of a turbulent boundary layer were conducted. Two-dimensional particle motion was calculated for flow near the surfaces of both Earth and Mars. For the case of Earth both a turbulent boundary layer with a viscous sublayer and one without were calculated. For the case of Mars it was only necessary to calculate turbulent boundary layer flow with a laminar sublayer because of the low values of friction Reynolds number; however, it was necessary to include the effects of slip flow on a particle caused by the rarefied Martian atmosphere. In the equations of motion the lift force functions were developed to act on a single particle only in the laminar sublayer or a corresponding small region of high shear near the surface for a fully turbulent boundary layer. The lift force functions were developed from the analytical work by Saffman concerning the lift force acting on a particle in simple shear flow.

3D LDV Measurements in Oscillatory Boundary Layers

Science.gov (United States)

Mier, J. M.; Garcia, M. H.

2012-12-01

The oscillatory boundary layer represents a particular case of unsteady wall-bounded flows in which fluid particles follow a periodic sinusoidal motion. Unlike steady boundary layer flows, the oscillatory flow regime and bed roughness character change in time along the period for every cycle, a characteristic that introduces a high degree of complexity in the analysis of these flows. Governing equations can be derived from the general Navier-Stokes equations for the motion of fluids, from which the exact solution for the laminar oscillatory boundary layer is obtained (also known as the 2nd Stokes problem). No exact solution exists for the turbulent case, thus, understanding of the main flow characteristics comes from experimental work. Several researchers have reported experimental work in oscillatory boundary layers since the 1960's; however, larger scale facilities and the development of newer measurement techniques with improved temporal and spatial resolution in recent years provides a unique opportunity to achieve a better understanding about this type of flows. Several experiments were performed in the Large Oscillatory Water and Sediment Tunnel (LOWST) facility at the Ven Te Chow Hydrosystems Laboratory, for a range of Reynolds wave numbers between 6x10^4 3D Laser Doppler Velocimetry (LDV) system was used to measure instantaneous flow velocities with a temporal resolution up to ~ 1,000 Hz. It was mounted on a 3-axis traverse with a spatial resolution of 0.01 mm in all three directions. The closest point to the bottom was measured at z = 0.2 mm (z+ ≈ 4), which allowed to capture boundary layer features with great detail. In order to achieve true 3D measurements, 2 probes were used on a perpendicular configuration, such that u and w components were measured from a probe on the side of the flume and v component was measured from a probe pointing down through and access window on top of the flume. The top probe was submerged in a water container, such that the

Theoretical skin-friction law in a turbulent boundary layer

International Nuclear Information System (INIS)

Cheskidov, A.

2005-01-01

We study transitional and turbulent boundary layers using a turbulent velocity profile equation recently derived from the Navier-Stokes-alpha and Leray-alpha models. From this equation we obtain a theoretical prediction of the skin-friction coefficient in a wide range of Reynolds numbers based on momentum thickness, and deduce the maximal value of c f max =0.0063 for turbulent velocity profiles. A two-parameter family of solutions to the equation matches experimental data in the transitional boundary layers with different free-stream turbulence intensity, while one-parameter family of solutions, obtained using our skin-friction coefficient law, matches experimental data in the turbulent boundary layer for moderately large Reynolds numbers

Turbulence Dissipation Rates in the Planetary Boundary Layer from Wind Profiling Radars and Mesoscale Numerical Weather Prediction Models during WFIP2

Science.gov (United States)

Bianco, L.; McCaffrey, K.; Wilczak, J. M.; Olson, J. B.; Kenyon, J.

2016-12-01

When forecasting winds at a wind plant for energy production, the turbulence parameterizations in the forecast models are crucial for understanding wind plant performance. Recent research shows that the turbulence (eddy) dissipation rate in planetary boundary layer (PBL) parameterization schemes introduces significant uncertainty in the Weather Research and Forecasting (WRF) model. Thus, developing the capability to measure dissipation rates in the PBL will allow for identification of weaknesses in, and improvements to the parameterizations. During a preliminary field study at the Boulder Atmospheric Observatory in spring 2015, a 915-MHz wind profiling radar (WPR) measured dissipation rates concurrently with sonic anemometers mounted on a 300-meter tower. WPR set-up parameters (e.g., spectral resolution), post-processing techniques (e.g., filtering for non-atmospheric signals), and spectral averaging were optimized to capture the most accurate Doppler spectra for measuring spectral widths for use in the computation of the eddy dissipation rates. These encouraging results lead to the implementation of the observing strategy on a 915-MHz WPR in Wasco, OR, operating as part of the Wind Forecasting Improvement Project 2 (WFIP2). These observations are compared to dissipation rates calculated from the High-Resolution Rapid Refresh model, a WRF-based mesoscale numerical weather prediction model run for WFIP2 at 3000 m horizontal grid spacing and with a nest, which has 750-meter horizontal grid spacing, in the complex terrain region of the Columbia River Gorge. The observed profiles of dissipation rates are used to evaluate the PBL parameterization schemes used in the HRRR model, which are based on the modeled turbulent kinetic energy and a tunable length scale.

The atmospheric boundary layer — advances in knowledge and application

Science.gov (United States)

Garratt, J. R.; Hess, G. D.; Physick, W. L.; Bougeault, P.

1996-02-01

We summarise major activities and advances in boundary-layer knowledge in the 25 years since 1970, with emphasis on the application of this knowledge to surface and boundary-layer parametrisation schemes in numerical models of the atmosphere. Progress in three areas is discussed: (i) the mesoscale modelling of selected phenomena; (ii) numerical weather prediction; and (iii) climate simulations. Future trends are identified, including the incorporation into models of advanced cloud schemes and interactive canopy schemes, and the nesting of high resolution boundary-layer schemes in global climate models.

Notes on the Prediction of Shock-induced Boundary-layer Separation

Science.gov (United States)

Lange, Roy H.

1953-01-01

The present status of available information relative to the prediction of shock-induced boundary-layer separation is discussed. Experimental results showing the effects of Reynolds number and Mach number on the separation of both laminar and turbulent boundary layer are given and compared with available methods for predicting separation. The flow phenomena associated with separation caused by forward-facing steps, wedges, and incident shock waves are discussed. Applications of the flat-plate data to problems of separation on spoilers, diffusers, and scoop inlets are indicated for turbulent boundary layers.

Coherent structures in wave boundary layers. Part 2. Solitary motion

DEFF Research Database (Denmark)

Sumer, B. Mutlu; Jensen, Palle Martin; Sørensen, Lone B.

2010-01-01

This study continues the investigation of wave boundary layers reported by Carstensen, Sumer & Fredsøe (J. Fluid Mech., 2010, part 1 of this paper). The present paper summarizes the results of an experimental investigation of turbulent solitary wave boundary layers, simulated by solitary motion...... the boundary-layer flow experiences a regular array of vortex tubes near the bed over a short period of time during the deceleration stage; and (iii) transitional regime characterized with turbulent spots, revealed by single/multiple, or, sometimes, quite dense spikes in the bed shear stress traces...

Structure measurements in a synthetic turbulent boundary layer

Science.gov (United States)

Arakeri, Jaywant H.

1987-09-01

Extensive hot-wire measurements have been made to determine the structure of the large eddy in a synthejc turbulent boundary layer on a flat-plate model. The experiments were carried out in a wind tunnel at a nominal free-stream velocity of 12 m/s. The synthetic turbulent boundary layer had a hexagonal pattern of eddies and a ratio of streamwise scale to spanwise scale of 3.2:1. The measured celerity of the large eddy was 84.2 percent of the free-stream velocity. There was some loss of coherence, but very little distortion, as the eddies moved downstream. Several mean properties of the synthetic boundary layer were found to agree quite well with the mean properties of a natural turbulent boundary layer at the same Reynolds number. The large eddy is composed of a pair of primary counter-rotating vortices about five [...] long in the streamwise direction and about one [...] apart in the spanwise direction, where [...] is the mean boundary-layer thickness. The sense of the primary pair is such as to pump fluid away from the wall in the region between the vortices. A secondary pair of counter-rotating streamwise vortices, having a sense opposite to that of the primary pair, is observed outside of and slightly downstream from the primary vortices. Both pairs of vortices extend across the full thickness of the boundary layer and are inclined at a shallow angle to the surface of the flat plate. The data show that the mean vorticity vectors are not tangential to the large-eddy vortices. In fact, the streamwise and normal vorticity components that signal the presence of the eddy are of the same order of magnitude. Definite signatures are obtained in terms of the mean skin-friction coefficient and the mean wake parameter averaged at constant phase. Velocities induced by the vortices are partly responsible for entrainment of irrotational fluid, for transport of momentum, for generation of Reynolds stresses, and for maintenance of streamwise and normal vorticity in the outer

Experiments in a boundary layer subjected to free stream turbulence. Part 1: Boundary layer structure and receptivity

International Nuclear Information System (INIS)

Westin, K.J.A.; Boiko, A.V.; Klingmann, B.G.B.; Kozlov, V.V.; Alfredsson, P.H.

1993-12-01

The modification of the mean and fluctuating characteristics of a flat plate boundary layer subjected to nearly isotropic free stream turbulence (FST) is studied experimentally using hot-wire anemometry. The study is focussed on the region upstream of the transition onset, where the fluctuations inside the boundary layer are dominated by elongated flow structures which grow downstream both in amplitude and length. Their downstream development and scaling is investigated, and the results are compared to those obtained by previous authors. This allows some conclusions about the parameters which are relevant for the modelling of the transition process. The mechanisms underlying the transition process and the relative importance of the Tollmien-Schlichting wave instability in this flow are treated in an accompanying paper. 25 refs

White dwarf radii and boundary-layer constraints in three dwarf novae

International Nuclear Information System (INIS)

Wood, J.H.

1990-01-01

The structure of the boundary layer between the accretion disc and white dwarf in three quiescent dwarf novae is explored with high signal-to-noise eclipse light curves obtained by phase folding 12-20 eclipses. Models of the eclipse shapes of various white dwarf/boundary layer configurations that might be at the centres of the accretion discs are calculated and compared with observations of the eclipses in Z Cha, OY Car and HT Cas. Possible models for the central objects are found to be a white dwarf with or without its lower hemisphere occulted by the disc, or a white dwarf with an optically thick boundary layer significantly extended in latitude up and down its sides. The most likely of these models for each system is an unocculted white dwarf with no boundary layer contributing significantly to the optical flux, or a white dwarf totally covered by an optically thick boundary layer. (author)

On Hydromagnetic Stresses in Accretion Disk Boundary Layers

DEFF Research Database (Denmark)

Pessah, Martin Elias; Chan, Chi-kwan

2012-01-01

Detailed calculations of the physical structure of accretion disk boundary layers, and thus their inferred observational properties, rely on the assumption that angular momentum transport is opposite to the radial angular frequency gradient of the disk. The standard model for turbulent shear...... of efficient angular momentum transport in the inner disk regions. This suggests that the detailed structure of turbulent MHD accretion disk boundary layers could differ appreciably from those derived within the standard framework of turbulent shear viscosity...

Stability characteristics of compressible boundary layers over thermo-mechanically compliant walls

Science.gov (United States)

Dettenrieder, Fabian; Bodony, Daniel

2017-11-01

Transition prediction at hypersonic flight conditions continues to be a challenge and results in conservative safety factors that increase vehicle weight. The weight and thus cost reduction of the outer skin panels promises significant impact; however, fluid-structure interaction due to unsteady perturbations in the laminar boundary layer regime has not been systematically studied at conditions relevant for reusable, hypersonic flight. In this talk, we develop and apply convective and global stability analyses for compressible boundary layers over thermo-mechanically compliant panels. This compliance is shown to change the convective stability of the boundary layer modes, with both stabilization and destabilization observed. Finite panel lengths are shown to affect the global stability properties of the boundary layer.

The boundary layers as the primary transport regions of the earth's magnetotail

Science.gov (United States)

Eastman, T. E.; Frank, L. A.; Huang, C. Y.

1985-01-01

A comprehensive survey of ISEE and IMP LEPEDEA plasma measurements in the earth's magnetotail reveals that the magnetospheric boundary layer and the plasma sheet boundary layer are the primary transport regions there. These plasma measurements also reveal various components of the plasma sheet, including the central plasma sheet and plasma sheet boundary layer. A significant new result reported here is that of cold- and hot-plasma components that are spatially co-present within the central plasma sheet. Such plasma components cannot be explained merely by temporal variations in spectra involving the entire plasma sheet. Contributions to a low temperature component of the plasma sheet enter directly from the boundary layer located along the magnetotail flanks. Field-aligned flows predominate within the plasma sheet boundary layer which is almost always present and is located near the high- and low-latitude border of the plasma sheet. The plasma sheet boundary layer comprises highly anisotropic ion distributions, including counter-streaming ion beams, that evolve into the hot, isotropic component of the plasma sheet. Tailward acceleration regions generate these ion beams with plasma input from the magnetospheric boundary layer. Antisunward-flowing ion beams, at E/q less than 1 kV and of ionospheric composition, are frequently observed in the plasma sheet boundary layer and in tail lobes. These ion beams are likely accelerated at low altitude over the polar cap and especially along auroral field lines.

Interaction Between Aerothermally Compliant Structures and Boundary-Layer Transition in Hypersonic Flow

Science.gov (United States)

Riley, Zachary Bryce

The use of thin-gauge, light-weight structures in combination with the severe aero-thermodynamic loading makes reusable hypersonic cruise vehicles prone to fluid-thermal-structural interactions. These interactions result in surface perturbations in the form of temperature changes and deformations that alter the stability and eventual transition of the boundary layer. The state of the boundary layer has a significant effect on the aerothermodynamic loads acting on a hypersonic vehicle. The inherent relationship between boundary-layer stability, aerothermodynamic loading, and surface conditions make the interaction between the structural response and boundary-layer transition an important area of study in high-speed flows. The goal of this dissertation is to examine the interaction between boundary layer transition and the response of aerothermally compliant structures. This is carried out by first examining the uncoupled problems of: (1) structural deformation and temperature changes altering boundary-layer stability and (2) the boundary layer state affecting structural response. For the former, the stability of boundary layers developing over geometries that typify the response of surface panels subject to combined aerodynamic and thermal loading is numerically assessed using linear stability theory and the linear parabolized stability equations. Numerous parameters are examined including: deformation direction, deformation location, multiple deformations in series, structural boundary condition, surface temperature, the combined effect of Mach number and altitude, and deformation mode shape. The deformation-induced pressure gradient alters the boundary-layer thickness, which changes the frequency of the most-unstable disturbance. In regions of small boundary-layer growth, the disturbance frequency modulation resulting from a single or multiple panels deformed into the flowfield is found to improve boundary-layer stability and potentially delay transition. For the

Response of a Hypersonic Boundary Layer to Freestream Pulse Acoustic Disturbance

Directory of Open Access Journals (Sweden)

Zhenqing Wang

2014-01-01

Full Text Available The response of hypersonic boundary layer over a blunt wedge to freestream pulse acoustic disturbance was investigated. The stability characteristics of boundary layer for freestream pulse wave and continuous wave were analyzed comparatively. Results show that freestream pulse disturbance changes the thermal conductivity characteristics of boundary layer. For pulse wave, the number of main disturbance clusters decreases and the frequency band narrows along streamwise. There are competition and disturbance energy transfer among different modes in boundary layer. The dominant mode of boundary layer has an inhibitory action on other modes. Under continuous wave, the disturbance modes are mainly distributed near fundamental and harmonic frequencies, while under pulse wave, the disturbance modes are widely distributed in different modes. For both pulse and continuous waves, most of disturbance modes slide into a lower-growth or decay state in downstream, which is tending towards stability. The amplitude of disturbance modes in boundary layer under continuous wave is considerably larger than pulse wave. The growth rate for the former is also considerably larger than the later the disturbance modes with higher growth are mainly distributed near fundamental and harmonic frequencies for the former, while the disturbance modes are widely distributed in different frequencies for the latter.

Response of a hypersonic boundary layer to freestream pulse acoustic disturbance.

Science.gov (United States)

Wang, Zhenqing; Tang, Xiaojun; Lv, Hongqing

2014-01-01

The response of hypersonic boundary layer over a blunt wedge to freestream pulse acoustic disturbance was investigated. The stability characteristics of boundary layer for freestream pulse wave and continuous wave were analyzed comparatively. Results show that freestream pulse disturbance changes the thermal conductivity characteristics of boundary layer. For pulse wave, the number of main disturbance clusters decreases and the frequency band narrows along streamwise. There are competition and disturbance energy transfer among different modes in boundary layer. The dominant mode of boundary layer has an inhibitory action on other modes. Under continuous wave, the disturbance modes are mainly distributed near fundamental and harmonic frequencies, while under pulse wave, the disturbance modes are widely distributed in different modes. For both pulse and continuous waves, most of disturbance modes slide into a lower-growth or decay state in downstream, which is tending towards stability. The amplitude of disturbance modes in boundary layer under continuous wave is considerably larger than pulse wave. The growth rate for the former is also considerably larger than the later the disturbance modes with higher growth are mainly distributed near fundamental and harmonic frequencies for the former, while the disturbance modes are widely distributed in different frequencies for the latter.

High frequency ground temperature fluctuation in a Convective Boundary Layer

NARCIS (Netherlands)

Garai, A.; Kleissl, J.; Lothon, M.; Lohou, F.; Pardyjak, E.; Saïd, F.; Cuxart, J.; Steeneveld, G.J.; Yaguë, C.; Derrien, S.; Alexander, D.; Villagrasa, D.M.

2012-01-01

To study influence of the turbulent structures in the convective boundary layer (CBL) on the ground temperature, during the Boundary Layer Late Afternoon and Sunset Turbulence (BLLAST) observational campaign, high frequency ground temperature was recorded through infra-red imagery from 13 June - 8

Boundary layer control by a fish: Unsteady laminar boundary layers of rainbow trout swimming in turbulent flows.

Science.gov (United States)

Yanase, Kazutaka; Saarenrinne, Pentti

2016-12-15

The boundary layers of rainbow trout, Oncorhynchus mykiss [0.231±0.016 m total body length (L) (mean±s.d.); N=6], swimming at 1.6±0.09 L s -1 (N=6) in an experimental flow channel (Reynolds number, Re=4×10 5 ) with medium turbulence (5.6% intensity) were examined using the particle image velocimetry technique. The tangential flow velocity distributions in the pectoral and pelvic surface regions (arc length from the rostrum, l x =71±8 mm, N=3, and l x =110±13 mm, N=4, respectively) were approximated by a laminar boundary layer model, the Falkner-Skan equation. The flow regime over the pectoral and pelvic surfaces was regarded as a laminar flow, which could create less skin-friction drag than would be the case with turbulent flow. Flow separation was postponed until vortex shedding occurred over the posterior surface (l x =163±22 mm, N=3). The ratio of the body-wave velocity to the swimming speed was in the order of 1.2. This was consistent with the condition of the boundary layer laminarization that had been confirmed earlier using a mechanical model. These findings suggest an energy-efficient swimming strategy for rainbow trout in a turbulent environment. © 2016. Published by The Company of Biologists Ltd.

Convection Cells in the Atmospheric Boundary Layer

Science.gov (United States)

Fodor, Katherine; Mellado, Juan-Pedro

2017-04-01

In dry, shear-free convective boundary layers (CBLs), the turbulent flow of air is known to organise itself on large scales into coherent, cellular patterns, or superstructures, consisting of fast, narrow updraughts and slow, wide downdraughts which together form circulations. Superstructures act as transport mechanisms from the surface to the top of the boundary layer and vice-versa, as opposed to small-scale turbulence, which only modifies conditions locally. This suggests that a thorough investigation into superstructure properties may help us better understand transport across the atmospheric boundary layer as a whole. Whilst their existence has been noted, detailed studies into superstructures in the CBL have been scarce. By applying methods which are known to successfully isolate similar large-scale patterns in turbulent Rayleigh-Bénard convection, we can assess the efficacy of those detection techniques in the CBL. In addition, through non-dimensional analysis, we can systematically compare superstructures in various convective regimes. We use direct numerical simulation of four different cases for intercomparison: Rayleigh-Bénard convection (steady), Rayleigh-Bénard convection with an adiabatic top lid (quasi-steady), a stably-stratified CBL (quasi-steady) and a neutrally-stratified CBL (unsteady). The first two are non-penetrative and the latter two penetrative. We find that although superstructures clearly emerge from the time-mean flow in the non-penetrative cases, they become obscured by temporal averaging in the CBL. This is because a rigid lid acts to direct the flow into counter-rotating circulation cells whose axis of rotation remains stationary, whereas a boundary layer that grows in time and is able to entrain fluid from above causes the circulations to not only grow in vertical extent, but also to move horizontally and merge with neighbouring circulations. Spatial filtering is a useful comparative technique as it can be performed on boundary

Turbulent boundary layer noise : direct radiation at Mach number 0.5

OpenAIRE

Gloerfelt , Xavier; Berland , Julien

2013-01-01

International audience; Boundary layers constitute a fundamental source of aerodynamic noise. A turbulent boundary layer over a plane wall can provide an indirect contribution to the noise by exciting the structure, and a direct noise contribution. The latter part can play a significant role even if its intensity is very low, explaining why it is hardly measured unambiguously. In the present study, the aerodynamic noise generated by a spatially developing turbulent boundary layer is computed ...

Rotor boundary layer development with inlet guide vane (IGV) wake impingement

Science.gov (United States)

Jia, Lichao; Zou, Tengda; Zhu, Yiding; Lee, Cunbiao

2018-04-01

This paper examines the transition process in a boundary layer on a rotor blade under the impingement of an inlet guide vane wake. The effects of wake strengths and the reduced frequency on the unsteady boundary layer development on a low-speed axial compressor were investigated using particle image velocimetry. The measurements were carried out at two reduced frequencies (fr = fIGVS0/U2i, fr = 1.35, and fr = 0.675) with the Reynolds number, based on the blade chord and the isentropic inlet velocity, being 97 500. At fr = 1.35, the flow separated at the trailing edge when the wake strength was weak. However, the separation was almost totally suppressed as the wake strength increased. For the stronger wake, both the wake's high turbulence and the negative jet behavior of the wake dominated the interaction between the unsteady wake and the separated boundary layer on the suction surface of the airfoil. The boundary layer displacement thickened first due to the negative jet effect. Then, as the disturbances developed underneath the wake, the boundary layer thickness reduced gradually. The high disturbance region convected downstream at a fraction of the free-stream velocity and spread in the streamwise direction. The separation on the suction surface was suppressed until the next wake's arrival. Because of the long recovery time at fr = 0.675, the boundary layer thickened gradually as the wake convected further downstream and finally separated due to the adverse pressure gradient. The different boundary layer states in turn affected the development of disturbances.

Boundary Layer Effect on Behavior of Discrete Models.

Science.gov (United States)

Eliáš, Jan

2017-02-10

The paper studies systems of rigid bodies with randomly generated geometry interconnected by normal and tangential bonds. The stiffness of these bonds determines the macroscopic elastic modulus while the macroscopic Poisson's ratio of the system is determined solely by the normal/tangential stiffness ratio. Discrete models with no directional bias have the same probability of element orientation for any direction and therefore the same mechanical properties in a statistical sense at any point and direction. However, the layers of elements in the vicinity of the boundary exhibit biased orientation, preferring elements parallel with the boundary. As a consequence, when strain occurs in this direction, the boundary layer becomes stiffer than the interior for the normal/tangential stiffness ratio larger than one, and vice versa. Nonlinear constitutive laws are typically such that the straining of an element in shear results in higher strength and ductility than straining in tension. Since the boundary layer tends, due to the bias in the elemental orientation, to involve more tension than shear at the contacts, it also becomes weaker and less ductile. The paper documents these observations and compares them to the results of theoretical analysis.

Stabilization of the hypersonic boundary layer by finite-amplitude streaks

Science.gov (United States)

Ren, Jie; Fu, Song; Hanifi, Ardeshir

2016-02-01

Stabilization of two-dimensional disturbances in hypersonic boundary layer flows by finite-amplitude streaks is investigated using nonlinear parabolized stability equations. The boundary-layer flows at Mach numbers 4.5 and 6.0 are studied in which both first and second modes are supported. The streaks considered here are driven either by the so-called optimal perturbations (Klebanoff-type) or the centrifugal instability (Görtler-type). When the streak amplitude is in an appropriate range, i.e., large enough to modulate the laminar boundary layer but low enough to not trigger secondary instability, both first and second modes can effectively be suppressed.

Study of effect of a smooth hump on hypersonic boundary layer instability

Science.gov (United States)

Park, Donghun; Park, Seung O.

2016-12-01

Effect of a two-dimensional smooth hump on linear instability of hypersonic boundary layer is studied by using parabolized stability equations. Linear evolution of mode S over a hump is analyzed for Mach 4.5 and 5.92 flat plate and Mach 7.1 sharp cone boundary layers. Mean flow for stability analysis is obtained by solving the parabolized Navier-Stokes equations. Hump with height smaller than local boundary layer thickness is considered. The case of flat plate and sharp cone without the hump are also studied to provide comparable data. For flat plate boundary layers, destabilization and stabilization effect is confirmed for hump located at upstream and downstream of synchronization point, respectively. Results of parametric studies to examine the effect of hump height, location, etc., are also given. For sharp cone boundary layer, stabilization influence of hump is also identified for a specific range of frequency. Stabilization influence of hump on convective instability of mode S is found to be a possible cause of previous experimental observations of delaying transition in hypersonic boundary layers.

Defects and boundary layers in non-Euclidean plates

International Nuclear Information System (INIS)

Gemmer, J A; Venkataramani, S C

2012-01-01

We investigate the behaviour of non-Euclidean plates with constant negative Gaussian curvature using the Föppl–von Kármán reduced theory of elasticity. Motivated by recent experimental results, we focus on annuli with a periodic profile. We prove rigorous upper and lower bounds for the elastic energy that scales like the thickness squared. In particular we show that are only two types of global minimizers—deformations that remain flat and saddle shaped deformations with isolated regions of stretching near the edge of the annulus. We also show that there exist local minimizers with a periodic profile that have additional boundary layers near their lines of inflection. These additional boundary layers are a new phenomenon in thin elastic sheets and are necessary to regularize jump discontinuities in the azimuthal curvature across lines of inflection. We rigorously derive scaling laws for the width of these boundary layers as a function of the thickness of the sheet. (paper)

Pressure Fluctuations Induced by a Hypersonic Turbulent Boundary Layer

Science.gov (United States)

Duan, Lian; Choudhari, Meelan M.; Zhang, Chao

2016-01-01

Direct numerical simulations (DNS) are used to examine the pressure fluctuations generated by a spatially-developed Mach 5.86 turbulent boundary layer. The unsteady pressure field is analyzed at multiple wall-normal locations, including those at the wall, within the boundary layer (including inner layer, the log layer, and the outer layer), and in the free stream. The statistical and structural variations of pressure fluctuations as a function of wall-normal distance are highlighted. Computational predictions for mean velocity pro les and surface pressure spectrum are in good agreement with experimental measurements, providing a first ever comparison of this type at hypersonic Mach numbers. The simulation shows that the dominant frequency of boundary-layer-induced pressure fluctuations shifts to lower frequencies as the location of interest moves away from the wall. The pressure wave propagates with a speed nearly equal to the local mean velocity within the boundary layer (except in the immediate vicinity of the wall) while the propagation speed deviates from the Taylor's hypothesis in the free stream. Compared with the surface pressure fluctuations, which are primarily vortical, the acoustic pressure fluctuations in the free stream exhibit a significantly lower dominant frequency, a greater spatial extent, and a smaller bulk propagation speed. The freestream pressure structures are found to have similar Lagrangian time and spatial scales as the acoustic sources near the wall. As the Mach number increases, the freestream acoustic fluctuations exhibit increased radiation intensity, enhanced energy content at high frequencies, shallower orientation of wave fronts with respect to the flow direction, and larger propagation velocity.

Pre-LBA Rondonia Boundary Layer Experiment (RBLE) Data

Data.gov (United States)

National Aeronautics and Space Administration — The atmospheric boundary layer (ABL) is the layer of air closest to the ground which is directly influenced on a daily basis by the heating and cooling of the...

Pre-LBA Rondonia Boundary Layer Experiment (RBLE) Data

Data.gov (United States)

National Aeronautics and Space Administration — ABSTRACT: The atmospheric boundary layer (ABL) is the layer of air closest to the ground which is directly influenced on a daily basis by the heating and cooling of...

Temperature boundary layer profiles in turbulent Rayleigh-Benard convection

Science.gov (United States)

Ching, Emily S. C.; Emran, Mohammad S.; Horn, Susanne; Shishkina, Olga

2017-11-01

Classical boundary-layer theory for steady flows cannot adequately describe the boundary layer profiles in turbulent Rayleigh-Benard convection. We have developed a thermal boundary layer equation which takes into account fluctuations in terms of an eddy thermal diffusivity. Based on Prandtl's mixing length ideas, we relate the eddy thermal diffusivity to the stream function. With this proposed relation, we can solve the thermal boundary layer equation and obtain a closed-form expression for the dimensionless mean temperature profile in terms of two independent parameters: θ(ξ) =1/b∫0b ξ [ 1 +3a3/b3(η - arctan(η)) ] - c dη , where ξ is the similarity variable and the parameters a, b, and c are related by the condition θ(∞) = 1 . With a proper choice of the parameters, our predictions of the temperature profile are in excellent agreement with the results of our direct numerical simulations for a wide range of Prandtl numbers (Pr), from Pr=0.01 to Pr=2547.9. OS, ME and SH acknowledge the financial support by the Deutsche Forschungsgemeinschaft (DFG) under Grants Sh405/4-2 (Heisenberg fellowship), Sh405/3-2 and Ho 5890/1-1, respectively.

A class of backward free-convective boundary-layer similarity solutions

NARCIS (Netherlands)

Kuiken, H.K.

1983-01-01

This paper presents a class of backward free-convective boundary-layer similarity solutions. It is shown that these boundary layers can be produced along slender downward-projecting slabs of prescribed thickness variation, which are infinitely long. It is pointed out that these solutions can be used

The time development of the plasma-glass boundary layer in a T-tube

International Nuclear Information System (INIS)

Pavlov, M.; Djurovic, S.

1982-01-01

The refraction of a laser beam by a flat boundary layer between the plasma and the glass plate is analysed. A boundary layer with a constant gradient electron density is assumed. Results of the analysis for plasmas produced in a small T-tube show that the boundary layer thickness increases with time faster than linearly. This means that a relatively fast collapse due to cooling through the boundary layer happens at the second half of the reflected plasma life time, while the boundary layer is negligible thin during the first 2μs after the reflected shock front has passed the point of observation. (author)

Modeling of the heat transfer in bypass transitional boundary-layer flows

Science.gov (United States)

Simon, Frederick F.; Stephens, Craig A.

1991-01-01

A low Reynolds number k-epsilon turbulence model and conditioned momentum, energy and turbulence equations were used to predict bypass transition heat transfer on a flat plate in a high-disturbance environment with zero pressure gradient. The use of conditioned equations was demonstrated to be an improvement over the use of the global-time-averaged equations for the calculation of velocity profiles and turbulence intensity profiles in the transition region of a boundary layer. The approach of conditioned equations is extended to include heat transfer and a modeling of transition events is used to predict transition onset and the extent of transition on a flat plate. The events, which describe the boundary layer at the leading edge, result in boundary-layer regions consisting of: (1) the laminar, (2) pseudolaminar, (3) transitional, and (4) turbulent boundary layers. The modeled transition events were incorporated into the TEXSTAN 2-D boundary-layer code which is used to numerically predict the heat transfer. The numerical predictions in general compared well with the experimental data and revealed areas where additional experimental information is needed.

Unequilibrium kinetic of collisionless boundary layers in binary plasmas

International Nuclear Information System (INIS)

Kotelnikov, V.A.; Nikolaev, F.A.; Cherepanov, V.V.

1985-01-01

Relaxation processes of kinetic nonequilibrium collisionless boundary layers near spherical charged full absorbing surfaces in binary low-temperature plasmas are investigated. The effect of magnetic field on relaxation processes was neglected. The dynamics of components of the ionized gas was treated near the boundary layer. The potential distribution and the space dependence of concentration were calculated numerically. These results agree well with the experimental data. (D.Gy.)

Effects of shock on hypersonic boundary layer stability

Science.gov (United States)

Pinna, F.; Rambaud, P.

2013-06-01

The design of hypersonic vehicles requires the estimate of the laminar to turbulent transition location for an accurate sizing of the thermal protection system. Linear stability theory is a fast scientific way to study the problem. Recent improvements in computational capabilities allow computing the flow around a full vehicle instead of using only simplified boundary layer equations. In this paper, the effect of the shock is studied on a mean flow provided by steady Computational Fluid Dynamics (CFD) computations and simplified boundary layer calculations.

Active Boundary Layer Control on a Highly Loaded Turbine Exit Case Profile

Directory of Open Access Journals (Sweden)

Julia Kurz

2018-03-01

Full Text Available A highly loaded turbine exit guide vane with active boundary layer control was investigated experimentally in the High Speed Cascade Wind Tunnel at the University of the German Federal Armed Forces, Munich. The experiments include profile Mach number distributions, wake traverse measurements as well as boundary layer investigations with a flattened Pitot probe. Active boundary layer control by fluidic oscillators was applied to achieve improved performance in the low Reynolds number regime. Low solidity, which can be applied to reduce the number of blades, increases the risk of flow separation resulting in increased total pressure losses. Active boundary layer control is supposed to overcome these negative effects. The experiments show that active boundary layer control by fluidic oscillators is an appropriate way to suppress massive open separation bubbles in the low Reynolds number regime.

Contrasting the surface ocean distribution of bromoform and methyl iodide; implications for boundary layer physics, chemistry and climate

Energy Technology Data Exchange (ETDEWEB)

Palmer, C J, E-mail: carl.j.palmer@gmail.co [Department of Oceanography, University of Cape Town, 7701 (South Africa)

2010-08-15

Bromoform and methyl iodide are both methane-like hydrocarbons with a halogen atom replacing one or more of the hydrogen atoms. Both of these compounds occur naturally in the environment as a result of their production from seaweed and kelp. They are of interest to climate science as a result of their catalytic destruction of boundary layer ozone (a potent greenhouse gas) and, specifically for methyl iodide, the proposed role in the formation of new cloud condensation nuclei with implications for climate. In this paper, the currently available data on the distribution of bromoform and methyl iodide are analysed and contrasted to show that the concentrations of bromoform and methyl iodide do not correlate, that, in contrast to bromoform, the parameterization of sea surface methyl iodide concentrations demands only the sea surface temperature, and that the pelagic distribution of methyl iodide appears to follow the solar zenith angle. These three observations together suggest that, while the pelagic source of bromoform is mostly biogenic, the source of methyl iodide is photochemical. This has implications for the understanding of planetary boundary layer chemistry and potential organohalogen mediated feedbacks to climate.

Contrasting the surface ocean distribution of bromoform and methyl iodide; implications for boundary layer physics, chemistry and climate

International Nuclear Information System (INIS)

Palmer, C J

2010-01-01

Bromoform and methyl iodide are both methane-like hydrocarbons with a halogen atom replacing one or more of the hydrogen atoms. Both of these compounds occur naturally in the environment as a result of their production from seaweed and kelp. They are of interest to climate science as a result of their catalytic destruction of boundary layer ozone (a potent greenhouse gas) and, specifically for methyl iodide, the proposed role in the formation of new cloud condensation nuclei with implications for climate. In this paper, the currently available data on the distribution of bromoform and methyl iodide are analysed and contrasted to show that the concentrations of bromoform and methyl iodide do not correlate, that, in contrast to bromoform, the parameterization of sea surface methyl iodide concentrations demands only the sea surface temperature, and that the pelagic distribution of methyl iodide appears to follow the solar zenith angle. These three observations together suggest that, while the pelagic source of bromoform is mostly biogenic, the source of methyl iodide is photochemical. This has implications for the understanding of planetary boundary layer chemistry and potential organohalogen mediated feedbacks to climate.

Convective instability in a time-dependent buoyancy driven boundary layer

Energy Technology Data Exchange (ETDEWEB)

Brooker, A.M.H.; Patterson, J.C.; Graham, T.; Schoepf, W. [University of Western Australia, Nedlands (Australia). Centre for Water Research

2000-01-01

The stability of the parallel time-dependent boundary layer adjacent to a suddenly heated vertical wall is described. The flow is investigated through experiments in water, through direct numerical simulation and also through linear stability analysis. The full numerical simulation of the flow shows that small perturbations to the wall boundary conditions, that are also present in the experimental study, are responsible for triggering the instability. As a result, oscillatory behaviour in the boundary layer is observed well before the transition to a steady two-dimensional flow begins. The properties of the observed oscillations are compared with those predicted by a linear stability analysis of the unsteady boundary layer using a quasi-stationary assumption and also using non-stationary assumptions by the formulation of parabolized equations (PSE). (Author)

Towards Adaptive Grids for Atmospheric Boundary-Layer Simulations

Science.gov (United States)

van Hooft, J. Antoon; Popinet, Stéphane; van Heerwaarden, Chiel C.; van der Linden, Steven J. A.; de Roode, Stephan R.; van de Wiel, Bas J. H.

2018-02-01

We present a proof-of-concept for the adaptive mesh refinement method applied to atmospheric boundary-layer simulations. Such a method may form an attractive alternative to static grids for studies on atmospheric flows that have a high degree of scale separation in space and/or time. Examples include the diurnal cycle and a convective boundary layer capped by a strong inversion. For such cases, large-eddy simulations using regular grids often have to rely on a subgrid-scale closure for the most challenging regions in the spatial and/or temporal domain. Here we analyze a flow configuration that describes the growth and subsequent decay of a convective boundary layer using direct numerical simulation (DNS). We validate the obtained results and benchmark the performance of the adaptive solver against two runs using fixed regular grids. It appears that the adaptive-mesh algorithm is able to coarsen and refine the grid dynamically whilst maintaining an accurate solution. In particular, during the initial growth of the convective boundary layer a high resolution is required compared to the subsequent stage of decaying turbulence. More specifically, the number of grid cells varies by two orders of magnitude over the course of the simulation. For this specific DNS case, the adaptive solver was not yet more efficient than the more traditional solver that is dedicated to these types of flows. However, the overall analysis shows that the method has a clear potential for numerical investigations of the most challenging atmospheric cases.

Stability of hypersonic boundary-layer flows with chemistry

Science.gov (United States)

Reed, Helen L.; Stuckert, Gregory K.; Haynes, Timothy S.

1993-01-01

The effects of nonequilibrium chemistry and three dimensionality on the stability characteristics of hypersonic flows are discussed. In two-dimensional (2-D) and axisymmetric flows, the inclusion of chemistry causes a shift of the second mode of Mack to lower frequencies. This is found to be due to the increase in size of the region of relative supersonic flow because of the lower speeds of sound in the relatively cooler boundary layers. Although this shift in frequency is present in both the equilibrium and nonequilibrium air results, the equilibrium approximation predicts modes which are not observed in the nonequilibrium calculations (for the flight conditions considered). These modes are superpositions of incoming and outgoing unstable disturbances which travel supersonically relative to the boundary-layer edge velocity. Such solutions are possible because of the finite shock stand-off distance. Their corresponding wall-normal profiles exhibit an oscillatory behavior in the inviscid region between the boundary-layer edge and the bow shock. For the examination of three-dimensional (3-D) effects, a rotating cone is used as a model of a swept wing. An increase of stagnation temperature is found to be only slightly stabilizing. The correlation of transition location (N = 9) with parameters describing the crossflow profile is discussed. Transition location does not correlate with the traditional crossflow Reynolds number. A new parameter that appears to correlate for boundary-layer flow was found. A verification with experiments on a yawed cone is provided.

Exact solution of nonsteady thermal boundary layer equation

International Nuclear Information System (INIS)

Dorfman, A.S.

1995-01-01

There are only a few exact solutions of the thermal boundary layer equation. Most of them are derived for a specific surface temperature distribution. The first exact solution of the steady-state boundary layer equation was given for a plate with constant surface temperature and free-stream velocity. The same problem for a plate with polynomial surface temperature distribution was solved by Chapmen and Rubesin. Levy gave the exact solution for the case of a power law distribution of both surface temperature and free-stream velocity. The exact solution of the steady-state boundary layer equation for an arbitrary surface temperature and a power law free-stream velocity distribution was given by the author in two forms: of series and of the integral with an influence function of unheated zone. A similar solution of the nonsteady thermal boundary layer equation for an arbitrary surface temperature and a power law free-stream velocity distribution is presented here. In this case, the coefficients of series depend on time, and in the limit t → ∞ they become the constant coefficients of a similar solution published before. This solution, unlike the one presented here, does not satisfy the initial conditions at t = 0, and, hence, can be used only in time after the beginning of the process. The solution in the form of a series becomes a closed-form exact solution for polynomial surface temperature and a power law free-stream velocity distribution. 7 refs., 2 figs

MHD Boundary Layer Slip Flow and Heat Transfer over a Flat Plate

International Nuclear Information System (INIS)

Bhattacharyya, Krishnendu; Mukhopadhyay, Swati; Layek, G. C.

2011-01-01

An analysis of magnetohydrodynamic (MHD) boundary layer flow and heat transfer over a flat plate with slip condition at the boundary is presented. A complete self-similar set of equations are obtained from the governing equations using similarity transformations and are solved by a shooting method. In the boundary slip condition no local similarity occurs. Velocity and temperature distributions within the boundary layer are presented. Our analysis reveals that the increase of magnetic and slip parameters reduce the boundary layer thickness and also enhance the heat transfer from the plate. (fundamental areas of phenomenology(including applications))

Collisional boundary layer analysis for neoclassical toroidal plasma viscosity in tokamaks

International Nuclear Information System (INIS)

Shaing, K. C.; Cahyna, P.; Becoulet, M.; Park, J.-K.; Sabbagh, S. A.; Chu, M. S.

2008-01-01

It is demonstrated that the pitch angle integrals in the transport fluxes in the ν regime calculated in K. C. Shang [Phys. Plasmas 10, 1443 (2003)] are divergent as the trapped-circulating boundary is approached. Here, ν is the collision frequency. The origin of this divergence results from the logarithmic dependence in the bounce averaged radial drift velocity. A collisional boundary layer analysis is developed to remove the singularity. The resultant pitch angle integrals now include not only the original physics of the ν regime but also the boundary layer physics. The transport fluxes, caused by the particles inside the boundary layer, scale as √(ν)

Transonic shock wave. Boundary layer interaction at a convex wall

NARCIS (Netherlands)

Koren, B.; Bannink, W.J.

1984-01-01

A standard finite element procedure has been applied to the problem of transonic shock wave – boundary layer interaction at a convex wall. The method is based on the analytical Bohning-Zierep model, where the boundary layer is perturbed by a weak normal shock wave which shows a singular pressure

The Challenges of Applying Planetary Boundaries as a Basis for Strategic Decision-Making in Companies with Global Supply Chains

Directory of Open Access Journals (Sweden)

Roland Clift

2017-02-01

Full Text Available The Planetary Boundaries (PB framework represents a significant advance in specifying the ecological constraints on human development. However, to enable decision-makers in business and public policy to respect these constraints in strategic planning, the PB framework needs to be developed to generate practical tools. With this objective in mind, we analyse the recent literature and highlight three major scientific and technical challenges in operationalizing the PB approach in decision-making: first, identification of thresholds or boundaries with associated metrics for different geographical scales; second, the need to frame approaches to allocate fair shares in the ‘safe operating space’ bounded by the PBs across the value chain and; third, the need for international bodies to co-ordinate the implementation of the measures needed to respect the Planetary Boundaries. For the first two of these challenges, we consider how they might be addressed for four PBs: climate change, freshwater use, biosphere integrity and chemical pollution and other novel entities. Four key opportunities are identified: (1 development of a common system of metrics that can be applied consistently at and across different scales; (2 setting ‘distance from boundary’ measures that can be applied at different scales; (3 development of global, preferably open-source, databases and models; and (4 advancing understanding of the interactions between the different PBs. Addressing the scientific and technical challenges in operationalizing the planetary boundaries needs be complemented with progress in addressing the equity and ethical issues in allocating the safe operating space between companies and sectors.

Atmospheric boundary layers in storms: advanced theory and modelling applications

Directory of Open Access Journals (Sweden)

S. S. Zilitinkevich

2005-01-01

Full Text Available Turbulent planetary boundary layers (PBLs control the exchange processes between the atmosphere and the ocean/land. The key problems of PBL physics are to determine the PBL height, the momentum, energy and matter fluxes at the surface and the mean wind and scalar profiles throughout the layer in a range of regimes from stable and neutral to convective. Until present, the PBLs typical of stormy weather were always considered as neutrally stratified. Recent works have disclosed that such PBLs are in fact very strongly affected by the static stability of the free atmosphere and must be treated as factually stable (we call this type of the PBL "conventionally neutral" in contract to the "truly neutral" PBLs developed against the neutrally stratified free flow. It is common knowledge that basic features of PBLs exhibit a noticeable dependence on the free-flow static stability and baroclinicity. However, the concern of the traditional theory of neural and stable PBLs was almost without exception the barotropic nocturnal PBL, which develops at mid latitudes during a few hours in the night, on the background of a neutral or slightly stable residual layer. The latter separates this type of the PBL from the free atmosphere. It is not surprising that the nature of turbulence in such regimes is basically local and does not depend on the properties of the free atmosphere. Alternatively, long-lived neutral (in fact only conditionally neutral or stable PBLs, which have much more time to grow up, are placed immediately below the stably stratified free flow. Under these conditions, the turbulent transports of momentum and scalars even in the surface layer - far away from the PBL outer boundary - depend on the free-flow Brunt-Väisälä frequency, N. Furthermore, integral measures of the long-lived PBLs (their depths and the resistance law functions depend on N and also on the baroclinic shear, S. In the traditional PBL models both non-local parameters N and S

BOREAS AFM-6 Boundary Layer Height Data

Science.gov (United States)

Wilczak, James; Hall, Forrest G. (Editor); Newcomer, Jeffrey A. (Editor); Smith, David E. (Technical Monitor)

2000-01-01

The Boreal Ecosystem-Atmosphere Study (BOREAS) Airborne Fluxes and Meteorology (AFM)-6 team from National Oceanic and Atmospheric Adminsitration/Environment Technology Laboratory (NOAA/ETL) operated a 915-MHz wind/Radio Acoustic Sounding System (RASS) profiler system in the Southern Study Area (SSA) near the Old Jack Pine (OJP) site. This data set provides boundary layer height information over the site. The data were collected from 21 May 1994 to 20 Sep 1994 and are stored in tabular ASCII files. The boundary layer height data are available from the Earth Observing System Data and Information System (EOSDIS) Oak Ridge National Laboratory (ORNL) Distributed Active Archive Center (DAAC). The data files are available on a CD-ROM (see document number 20010000884).

Boundary layer heights derived from velocity spectra

Energy Technology Data Exchange (ETDEWEB)

Hoejstrup, J.; Barthelmie, R.J. [Risoe National Lab., Roskilde (Denmark); Kaellstrand, B. [Univ. of Uppsala, Uppsala (Sweden)

1997-10-01

It is a well-known fact that the height of the mixed layer determines the size of the largest and most energetic eddies that can be observed in the unstable boundary layer, and consequently a peak can be observed in the power spectra of the along-wind velocity component at scales comparable to the mixed layer depth. We will now show how the mixed layer depth can be derived from the u-specta and the results will be compared with direct measurements using pibal and tethersonde measurements. (au)

Study of cross-spectra of velocity components and temperature series in a nocturnal boundary layer

Science.gov (United States)

Maqueda, Gregorio; Sastre, Mariano; Viñas, Carmen; Viana, Samuel; Yagüe, Carlos

2010-05-01

The main characteristic of the Planetary Boundary Layer is the turbulent flow that can be understood as the motions of many superimposed eddies with different scales, which are very irregular and produce mixing among the atmospheric properties. Spectral analysis is a widely used statistical tool to know the size of eddies into the flow. The Turbulent Kinetic Energy is split in fractions for each scale of eddy by mean the power spectrum of the wind velocity components. Also, the fluctuation of the other variables as temperature, humidity, gases concentrations or material particles presents in the atmosphere can be divided according to the importance of different scales in a similar way than the wind. A Cross-spectrum between two time series is used in meteorology to know their correlation in frequency space. Specially, coespectrum, or real part of cross-spectrum, amplitud and coherence give us many information about the low or high correlation between two variables in a particular frecuency or scale (Stull, 1988). In this work we have investigated cross-spectra of velocity components and temperature measured along the summer 2009 at the CIBA, Research Centre for the Lower Atmosphere, located in Valladolid province (Spain), which is on a quite flat terrain (Cuxart et al., 2000; Viana et al., 2009). In these experimental dataset, among other instrumentation, two sonic anemometers (20 Hz, sampling rate) at 1.5 m and 10 m height are available. Cross-spectra between variables of the two levels, specially, wind vertical component and sonic temperature, under stable stratification are studied in order to improve the knowledge of the proprieties of the momentum and heat fluxes near the ground in the PBL. Nevertheless, power spectral of horizontal components of the wind, at both levels, have been also analysed. The spectra and cross-spectra were performed by mean the Blackman-Tukey method, widely utilised in the time series studies (Blackman & Tukey, 1958) and, where it is

Diagnostic analysis of turbulent boundary layer data by a trivariate Lagrangian partitioning method

Energy Technology Data Exchange (ETDEWEB)

Welsh, P.T. [Florida State Univ., Tallahassee, FL (United States)

1994-12-31

The rapid scientific and technological advances in meteorological theory and modeling predominantly have occurred on the large (or synoptic) scale flow characterized by the extratropical cyclone. Turbulent boundary layer flows, in contrast, have been slower in developing both theoretically and in accuracy for several reasons. There are many existing problems in boundary layer models, among them are limits to computational power available, the inability to handle countergradient fluxes, poor growth matching to real boundary layers, and inaccuracy in calculating the diffusion of scalar concentrations. Such transport errors exist within the boundary layer as well as into the free atmosphere above. This research uses a new method, which can provide insight into these problems, and ultimately improve boundary layer models. There are several potential applications of the insights provided by this approach, among them are estimation of cloud contamination of satellite remotely sensed surface parameters, improved flux and vertical transport calculations, and better understanding of the diurnal boundary layer growth process and its hysteresis cycle.

Turbulent fluxes in stably stratified boundary layers

International Nuclear Information System (INIS)

L'vov, Victor S; Procaccia, Itamar; Rudenko, Oleksii

2008-01-01

We present here an extended version of an invited talk we gave at the international conference 'Turbulent Mixing and Beyond'. The dynamical and statistical description of stably stratified turbulent boundary layers with the important example of the stable atmospheric boundary layer in mind is addressed. Traditional approaches to this problem, based on the profiles of mean quantities, velocity second-order correlations and dimensional estimates of the turbulent thermal flux, run into a well-known difficulty, predicting the suppression of turbulence at a small critical value of the Richardson number, in contradiction to observations. Phenomenological attempts to overcome this problem suffer from various theoretical inconsistencies. Here, we present an approach taking into full account all the second-order statistics, which allows us to respect the conservation of total mechanical energy. The analysis culminates in an analytic solution of the profiles of all mean quantities and all second-order correlations, removing the unphysical predictions of previous theories. We propose that the approach taken here is sufficient to describe the lower parts of the atmospheric boundary layer, as long as the Richardson number does not exceed an order of unity. For much higher Richardson numbers, the physics may change qualitatively, requiring careful consideration of the potential Kelvin-Helmoholtz waves and their interaction with the vortical turbulence.

Study on turbulent characteristics and transition behavior of combined-convection boundary layer

International Nuclear Information System (INIS)

Hattori, Yasuo

2001-01-01

The stabilizing mechanism of the turbulent combined-convection boundary layer along an isothermally-heated flat plate in air aided by a weak freestream are investigated experimentally and theoretically. The turbulent statistics of the combined-convection boundary layer measured with hot- and cold wires at different Grashof numbers indicates that with an increase in the freestream velocity, a similar change in the turbulent quantities appears independently of local Grashof number. Then based on the such experimental results, it is verified that the laminarization of the boundary layer due to an increase in freestream velocity arises at Grx / Rex 6 . Then, through the experiments with a particle image velocimetry (PIV), the spatio-temporal structure of the turbulent combined-convection boundary layer is investigated. For instantaneous velocity vectors obtained with PIV, large-scale fluid motions, which play a predominant role in the generation of turbulence, are frequently observed in the outer layer, while quasi-coherent structures do not exist in the near-wall region. Thus, it is revealed that increasing freestream restricts large-scale fluid motions in the outer layer, and consequently the generation of turbulence is suppressed and the boundary layer becomes laminar. (author)

A parametric study of adverse pressure gradient turbulent boundary layers

International Nuclear Information System (INIS)

Monty, J.P.; Harun, Z.; Marusic, I.

2011-01-01

There are many open questions regarding the behaviour of turbulent boundary layers subjected to pressure gradients and this is confounded by the large parameter space that may affect these flows. While there have been many valuable investigations conducted within this parameter space, there are still insufficient data to attempt to reduce this parameter space. Here, we consider a parametric study of adverse pressure gradient turbulent boundary layers where we restrict our attention to the pressure gradient parameter, β, the Reynolds number and the acceleration parameter, K. The statistics analyzed are limited to the streamwise fluctuating velocity. The data show that the mean velocity profile in strong pressure gradient boundary layers does not conform to the classical logarithmic law. Moreover, there appears to be no measurable logarithmic region in these cases. It is also found that the large-scale motions scaling with outer variables are energised by the pressure gradient. These increasingly strong large-scale motions are found to be the dominant contributor to the increase in turbulence intensity (scaled with friction velocity) with increasing pressure gradient across the boundary layer.

Exchange Processes in the Atmospheric Boundary Layer Over Mountainous Terrain

Directory of Open Access Journals (Sweden)

Stefano Serafin

2018-03-01

Full Text Available The exchange of heat, momentum, and mass in the atmosphere over mountainous terrain is controlled by synoptic-scale dynamics, thermally driven mesoscale circulations, and turbulence. This article reviews the key challenges relevant to the understanding of exchange processes in the mountain boundary layer and outlines possible research priorities for the future. The review describes the limitations of the experimental study of turbulent exchange over complex terrain, the impact of slope and valley breezes on the structure of the convective boundary layer, and the role of intermittent mixing and wave–turbulence interaction in the stable boundary layer. The interplay between exchange processes at different spatial scales is discussed in depth, emphasizing the role of elevated and ground-based stable layers in controlling multi-scale interactions in the atmosphere over and near mountains. Implications of the current understanding of exchange processes over mountains towards the improvement of numerical weather prediction and climate models are discussed, considering in particular the representation of surface boundary conditions, the parameterization of sub-grid-scale exchange, and the development of stochastic perturbation schemes.

Improved boundary layer height measurement using a fuzzy logic method: Diurnal and seasonal variabilities of the convective boundary layer over a tropical station

Science.gov (United States)

Allabakash, S.; Yasodha, P.; Bianco, L.; Venkatramana Reddy, S.; Srinivasulu, P.; Lim, S.

2017-09-01

This paper presents the efficacy of a "tuned" fuzzy logic method at determining the height of the boundary layer using the measurements from a 1280 MHz lower atmospheric radar wind profiler located in Gadanki (13.5°N, 79°E, 375 mean sea level), India, and discusses the diurnal and seasonal variations of the measured convective boundary layer over this tropical station. The original fuzzy logic (FL) method estimates the height of the atmospheric boundary layer combining the information from the range-corrected signal-to-noise ratio, the Doppler spectral width of the vertical velocity, and the vertical velocity itself, measured by the radar, through a series of thresholds and rules, which did not prove to be optimal for our radar system and geographical location. For this reason the algorithm was tuned to perform better on our data set. Atmospheric boundary layer heights obtained by this tuned FL method, the original FL method, and by a "standard method" (that only uses the information from the range-corrected signal-to-noise ratio) are compared with those obtained from potential temperature profiles measured by collocated Global Positioning System Radio Sonde during years 2011 and 2013. The comparison shows that the tuned FL method is more accurate than the other methods. Maximum convective boundary layer heights are observed between 14:00 and 15:00 local time (LT = UTC + 5:30) for clear-sky days. These daily maxima are found to be lower during winter and postmonsoon seasons and higher during premonsoon and monsoon seasons, due to net surface radiation and convective processes over this region being more intense during premonsoon and monsoon seasons and less intense in winter and postmonsoon seasons.

Coherent structures in wave boundary layers. Part 1. Oscillatory motion

DEFF Research Database (Denmark)

Carstensen, Stefan; Sumer, B. Mutlu; Fredsøe, Jørgen

2010-01-01

This work concerns oscillatory boundary layers over smooth beds. It comprises combined visual and quantitative techniques including bed shear stress measurements. The experiments were carried out in an oscillating water tunnel. The experiments reveal two significant coherent flow structures: (i......) Vortex tubes, essentially two-dimensional vortices close to the bed extending across the width of the boundary-layer flow, caused by an inflectional-point shear layer instability. The imprint of these vortices in the bed shear stress is a series of small, insignificant kinks and dips. (ii) Turbulent...... spots, isolated arrowhead-shaped areas close to the bed in an otherwise laminar boundary layer where the flow ‘bursts’ with violent oscillations. The emergence of the turbulent spots marks the onset of turbulence. Turbulent spots cause single or multiple violent spikes in the bed shear stress signal...

The inland boundary layer at low latitudes

Science.gov (United States)

Garratt, J. R.

1985-08-01

Observations from the Koorin boundary-layer experiment in Australia (latitude 16 °S) were analysed in a study of the nocturnal jet development. For geostrophic winds in the range 10 20 m s-1, ageostrophic wind magnitudes of 5 10m s-1 were common above the surface layer near sunset, with cross-isobar flow angles of about 40 °. The jet that then developed by midnight was probably the result of these large ageostrophic winds, strong surface cooling and favourable baroclinity and sloping terrain. The analysis is supported by numerical model calculations with special emphasis on the role of long-wave radiative cooling on turbulent decay. Decay is rapid in the presence of radiation, although there is little influence on stress divergence levels. Evidence of sea-breeze influences on the jet evolution, and on features of deeply penetrating sea breezes in general, will be presented and discussed in part 2 of this study (submitted to Boundary-Layer Meteorol.).

The turning of the wind in the atmospheric boundary layer

DEFF Research Database (Denmark)

Pena Diaz, Alfredo; Gryning, Sven-Erik; Floors, Rogier Ralph

2014-01-01

Here we use accurate observations of the wind speed vector to analyze the behavior with height of the wind direction. The observations are a combination of tall meteorological mast and long-range wind lidar measurements covering the entire atmospheric boundary layer. The observations were performed...... winds underpredict the turning of the wind and the boundary-layer winds in general....

A global boundary-layer height climatology

Energy Technology Data Exchange (ETDEWEB)

Dop, H. van; Krol, M.; Holtslag, B. [Inst. for Marine and Atmospheric Research Utrecht, IMAU, Utrecht (Netherlands)

1997-10-01

In principle the ABL (atmospheric boundary layer) height can be retrieved from atmospheric global circulation models since they contain algorithms which determine the intensity of the turbulence as a function of height. However, these data are not routinely available, or on a (vertical) resolution which is too crude in view of the application. This justifies the development of a separate algorithm in order to define the ABL. The algorithm should include the generation of turbulence by both shear and buoyancy and should be based on readily available atmospheric parameters. There is obviously a wide application for boundary heights in off-line global and regional chemistry and transport modelling. It is also a much used parameter in air pollution meteorology. In this article we shall present a theory which is based on current insights in ABL dynamics. The theory is applicable over land and sea surfaces in all seasons. The theory is (for various reasons) not valid in mountainous areas. In areas where boundary-layer clouds or deep cumulus convection are present the theory does not apply. However, the same global atmospheric circulation models contain parameterizations for shallow and deep convection from which separate estimates can be obtained for the extent of vertical mixing. (au)

High-energy X-ray production in a boundary layer of an accreting neutron star

International Nuclear Information System (INIS)

Hanawa, Tomoyuki

1991-01-01

It is shown by Monte Carlo simulation that high-energy X-rays are produced through Compton scattering in a boundary layer of an accreting neutron star. The following is the mechanism for the high-energy X-ray production. An accreting neutron star has a boundary layer rotating rapidly on the surface. X-rays radiated from the star's surface are scattered in part in the boundary layer. Since the boundary layer rotates at a semirelativistic speed, the scattered X-ray energy is changed by the Compton effect. Some X-rays are scattered repeatedly between the neutron star and the boundary layer and become high-energy X-rays. This mechanism is a photon analog of the second-order Fermi acceleration of cosmic rays. When the boundary layer is semitransparent, high-energy X-rays are produced efficiently. 17 refs

Representing the atmospheric boundary layer in climate models of intermediate compexity

NARCIS (Netherlands)

Ronda, R.J.; Haarsma, R.J.; Holtslag, A.A.M.

2003-01-01

In this study the role of atmospheric boundary layer schemes in climate models is investigated. Including a boundary layer scheme in an Earth system model of intermediate complexity (EMIC) produces only minor differences in the estimated global distribution of sensible and latent heat fluxes over

A simulation study of the vortex structure in the low-latitude boundary layer

International Nuclear Information System (INIS)

Wei, C.Q.; Lee, L.C.; La Belle-Hamer, A.L.

1990-01-01

Satellite observations indicate that the plasma density and the flow velocity are highly variable in the low-latitude boundary layer. The thickness of the boundary layer is also highly variable and appears to increase with increasing longitudinal distance from the subsolar point. In this paper plasma dynamics in the low-latitude boundary layer region is studied on the basis of a two-dimensional incompressible bydrodynamic numerical model. In the simulation, plasma is driven into the boundary layer region by imposing a diffusion flux along the magnetopause. The vortex motions associated with the Kelvin-Helmholtz instability are observed in the simulation. The resulting vortex structures in the plasma density and the flow velocity may coalesce as they are convected tailward, causing them to grow in size. The boundary layer thickness increases with increasing longitudinal distance from the subsolar point in accord with satellite observations. The plasma density and the flow velocity are positively correlated. A mixing region is formed where magnetosheath plasma and magnetospheric plasma mix due to the vortex motions. In the later stage of development, a density plateau is formed in the central part of the boundary layer. Many features of the satellite observations of the boundary layer can be explained using the numerical model. The simulation results also predict that the vortices generated in the postnoon (prenoon) boundary layer lead to the presence of localized upward (downward) field-aligned currents in both the northern and the southern polar ionospheres. The upward field-aligned currents in turn may lead to the formation of dayside auroral patches observed in the postnoon region

Global stability analysis of axisymmetric boundary layer over a circular cylinder

Science.gov (United States)

Bhoraniya, Ramesh; Vinod, Narayanan

2018-05-01

This paper presents a linear global stability analysis of the incompressible axisymmetric boundary layer on a circular cylinder. The base flow is parallel to the axis of the cylinder at inflow boundary. The pressure gradient is zero in the streamwise direction. The base flow velocity profile is fully non-parallel and non-similar in nature. The boundary layer grows continuously in the spatial directions. Linearized Navier-Stokes (LNS) equations are derived for the disturbance flow quantities in the cylindrical polar coordinates. The LNS equations along with homogeneous boundary conditions forms a generalized eigenvalues problem. Since the base flow is axisymmetric, the disturbances are periodic in azimuthal direction. Chebyshev spectral collocation method and Arnoldi's iterative algorithm is used for the solution of the general eigenvalues problem. The global temporal modes are computed for the range of Reynolds numbers and different azimuthal wave numbers. The largest imaginary part of the computed eigenmodes is negative, and hence, the flow is temporally stable. The spatial structure of the eigenmodes shows that the disturbance amplitudes grow in size and magnitude while they are moving towards downstream. The global modes of axisymmetric boundary layer are more stable than that of 2D flat-plate boundary layer at low Reynolds number. However, at higher Reynolds number they approach 2D flat-plate boundary layer. Thus, the damping effect of transverse curvature is significant at low Reynolds number. The wave-like nature of the disturbance amplitudes is found in the streamwise direction for the least stable eigenmodes.

Interaction of discrete and continuous boundary layer modes to cause transition

International Nuclear Information System (INIS)

Durbin, Paul A.; Zaki, Tamer A.; Liu Yang

2009-01-01

The interaction of discrete and continuous Orr-Sommerfeld modes in a boundary layer is studied by computer simulation. The discrete mode is an unstable Tollmien-Schlichting wave. The continuous modes generate jet-like disturbances inside the boundary layer. Either mode alone does not cause transition to turbulence; however, the interaction between them does. The continuous mode jets distort the discrete modes, producing Λ shaped vortices. Breakdown to turbulence is subsequent. The lateral spacing of the Λ's is sometimes the same as the wavelength of the continuous mode, sometimes it differs, depending on the ratio of wavelength to boundary layer thickness.

Coupled wake boundary layer model of windfarms

Science.gov (United States)

Stevens, Richard; Gayme, Dennice; Meneveau, Charles

2014-11-01

We present a coupled wake boundary layer (CWBL) model that describes the distribution of the power output in a windfarm. The model couples the traditional, industry-standard wake expansion/superposition approach with a top-down model for the overall windfarm boundary layer structure. Wake models capture the effect of turbine positioning, while the top-down approach represents the interaction between the windturbine wakes and the atmospheric boundary layer. Each portion of the CWBL model requires specification of a parameter that is unknown a-priori. The wake model requires the wake expansion rate, whereas the top-down model requires the effective spanwise turbine spacing within which the model's momentum balance is relevant. The wake expansion rate is obtained by matching the mean velocity at the turbine from both approaches, while the effective spanwise turbine spacing is determined from the wake model. Coupling of the constitutive components of the CWBL model is achieved by iterating these parameters until convergence is reached. We show that the CWBL model predictions compare more favorably with large eddy simulation results than those made with either the wake or top-down model in isolation and that the model can be applied successfully to the Horns Rev and Nysted windfarms. The `Fellowships for Young Energy Scientists' (YES!) of the Foundation for Fundamental Research on Matter supported by NWO, and NSF Grant #1243482.

Boundary-layer theory. 9. ed.

Energy Technology Data Exchange (ETDEWEB)

Schlichting, Hermann [Technische Univ. Braunschweig (Germany). Inst. fuer Stroemungsmechanik; Gersten, Klaus [Bochum Univ. (Germany). Lehrstuhl fuer Thermodynamik und Stroemungsmechanik

2017-03-01

This new edition of the near-legendary textbook by Schlichting and revised by Gersten presents a comprehensive overview of boundary-layer theory and its application to all areas of fluid mechanics, with particular emphasis on the flow past bodies (e.g. aircraft aerodynamics). The new edition features an updated reference list and over 100 additional changes throughout the book, reflecting the latest advances on the subject.

Bypass transition in compressible boundary layers

Science.gov (United States)

Vandervegt, J. J.

1992-01-01

Transition to turbulence in aerospace applications usually occurs in a strongly disturbed environment. For instance, the effects of free-stream turbulence, roughness and obstacles in the boundary layer strongly influence transition. Proper understanding of the mechanisms leading to transition is crucial in the design of aircraft wings and gas turbine blades, because lift, drag and heat transfer strongly depend on the state of the boundary layer, laminar or turbulent. Unfortunately, most of the transition research, both theoretical and experimental, has focused on natural transition. Many practical flows, however, defy any theoretical analysis and are extremely difficult to measure. Morkovin introduced in his review paper the concept of bypass transition as those forms of transition which bypass the known mechanisms of linear and non-linear transition theories and are currently not understood by experiments. In an effort to better understand the mechanisms leading to transition in a disturbed environment, experiments are conducted studying simpler cases, viz. the effects of free stream turbulence on transition on a flat plate. It turns out that these experiments are very difficult to conduct, because generation of free stream turbulence with sufficiently high fluctuation levels and reasonable homogeneity is non trivial. For a discussion see Morkovin. Serious problems also appear due to the fact that at high Reynolds numbers the boundary layers are very thin, especially in the nose region of the plate where the transition occurs, which makes the use of very small probes necessary. The effects of free-stream turbulence on transition are the subject of this research and are especially important in a gas turbine environment, where turbulence intensities are measured between 5 and 20 percent, Wang et al. Due to the fact that the Reynolds number for turbine blades is considerably lower than for aircraft wings, generally a larger portion of the blade will be in a laminar

Effects of Boundary Layer Height on the Model of Ground-Level PM2.5 Concentrations from AOD: Comparison of Stable and Convective Boundary Layer Heights from Different Methods

Directory of Open Access Journals (Sweden)

Zengliang Zang

2017-06-01

Full Text Available The aerosol optical depth (AOD from satellites or ground-based sun photometer spectral observations has been widely used to estimate ground-level PM2.5 concentrations by regression methods. The boundary layer height (BLH is a popular factor in the regression model of AOD and PM2.5, but its effect is often uncertain. This may result from the structures between the stable and convective BLHs and from the calculation methods of the BLH. In this study, the boundary layer is divided into two types of stable and convective boundary layer, and the BLH is calculated using different methods from radiosonde data and National Centers for Environmental Prediction (NCEP reanalysis data for the station in Beijing, China during 2014–2015. The BLH values from these methods show significant differences for both the stable and convective boundary layer. Then, these BLHs were introduced into the regression model of AOD-PM2.5 to seek the respective optimal BLH for the two types of boundary layer. It was found that the optimal BLH for the stable boundary layer is determined using the method of surface-based inversion, and the optimal BLH for the convective layer is determined using the method of elevated inversion. Finally, the optimal BLH and other meteorological parameters were combined to predict the PM2.5 concentrations using the stepwise regression method. The results indicate that for the stable boundary layer, the optimal stepwise regression model includes the factors of surface relative humidity, BLH, and surface temperature. These three factors can significantly enhance the prediction accuracy of ground-level PM2.5 concentrations, with an increase of determination coefficient from 0.50 to 0.68. For the convective boundary layer, however, the optimal stepwise regression model includes the factors of BLH and surface wind speed. These two factors improve the determination coefficient, with a relatively low increase from 0.65 to 0.70. It is found that the

The double layers in the plasma sheet boundary layer during magnetic reconnection

Science.gov (United States)

Guo, J.; Yu, B.

2014-11-01

We studied the evolutions of double layers which appear after the magnetic reconnection through two-dimensional electromagnetic particle-in-cell simulation. The simulation results show that the double layers are formed in the plasma sheet boundary layer after magnetic reconnection. At first, the double layers which have unipolar structures are formed. And then the double layers turn into bipolar structures, which will couple with another new weak bipolar structure. Thus a new double layer or tripolar structure comes into being. The double layers found in our work are about several ten Debye lengths, which accords with the observation results. It is suggested that the electron beam formed during the magnetic reconnection is responsible for the production of the double layers.

New Theories on Boundary Layer Transition and Turbulence Formation

Directory of Open Access Journals (Sweden)

Chaoqun Liu

2012-01-01

Full Text Available This paper is a short review of our recent DNS work on physics of late boundary layer transition and turbulence. Based on our DNS observation, we propose a new theory on boundary layer transition, which has five steps, that is, receptivity, linear instability, large vortex structure formation, small length scale generation, loss of symmetry and randomization to turbulence. For turbulence generation and sustenance, the classical theory, described with Richardson's energy cascade and Kolmogorov length scale, is not observed by our DNS. We proposed a new theory on turbulence generation that all small length scales are generated by “shear layer instability” through multiple level ejections and sweeps and consequent multiple level positive and negative spikes, but not by “vortex breakdown.” We believe “shear layer instability” is the “mother of turbulence.” The energy transferring from large vortices to small vortices is carried out by multiple level sweeps, but does not follow Kolmogorov's theory that large vortices pass energy to small ones through vortex stretch and breakdown. The loss of symmetry starts from the second level ring cycle in the middle of the flow field and spreads to the bottom of the boundary layer and then the whole flow field.

Planetary Dynamos: Investigations of Saturn and Ancient Mars

Energy Technology Data Exchange (ETDEWEB)

Stanley, Sabine [University of Toronto

2012-04-18

Magnetic field observations by spacecraft missions have provided vital information on planetary dynamos. The four giant planets as well as Earth, Mercury and Ganymede have observable magnetic fields generated by active dynamos. In contrast, Moon and Mars only have remanent crustal fields from dynamo action in their early histories. A variety of magnetic field morphologies and intensities can be found in the solar system. We have found that some of the differences between planetary magnetic fields can be explained as the result of the presence of boundary thermal variations or stably-stratified layers. In this talk, I will discuss how dynamos are affected by these complications and discuss the implications for Mars’ magnetic dichotomy and Saturn’s extremely axisymmetric magnetic field.

Assessment of boundary layer profiling formulas using tower, sodar and balloon data

Energy Technology Data Exchange (ETDEWEB)

Paine, R.J. [ENSR Consulting and Engineering, Inc., Acton, MA (United States); Kendall, S.B. [Phelps Dodge Corp., Phoenix, AZ (United States)

1994-12-31

The accuracy of an air quality dispersion model is largely dependent upon the availability of representative meteorological data for the simulation of plume rise, transport, and dispersion. In many cases where tall stacks and/or buoyant plumes are involved, the available meteorological measurements do not extend to plume height. Air quality models contend with these situations by either assuming no change of meteorological variables with elevation or by applying a profiling relationship based upon theoretical or empirical relationships. The latter treatment is employed in recently-developed models such as CTDMPLUS, and HPDM, and OML. In the well-mixed convective boundary layer, meteorological variables such as wind direction, wind speed, and turbulence do not vary substantially above the surface layer (about 0.1 z{sub i}, the mixed-layer height). Above the surface layer, behavior on an hourly average basis is fairly well parameterized by boundary-layer formulations. However, models are sensitive to the height of the convective boundary layer, z{sub i}, which affects the magnitude of the convective velocity scale, w., and is important for simulating plume trapping and plume penetration into the stable layer aloft. In the stable boundary layer, plumes are often released at heights above the stable boundary layer, the height of which is often hard to define. Models are sensitive to the manner in which wind direction, wind speed, temperature and turbulence are profiled with height in stable conditions.

Transitional and turbulent flat-plate boundary layers with heat transfer

Science.gov (United States)

Wu, Xiaohua; Moin, Parviz

2010-11-01

We report on our direct numerical simulation of two incompressible, nominally zero-pressure-gradient flat-plate boundary layers from momentum thickness Reynolds number 80 to 1950. Heat transfer between the constant-temperature solid surface and the free-stream is also simulated with molecular Prandtl number=1. Throughout the entire flat-plate, the ratio of Stanton number and skin-friction St/Cfdeviates from the exact Reynolds analogy value of 0.5 by less than 1.5%. Turbulent Prandtl number t peaks at the wall. Preponderance of hairpin vortices is observed in both the transitional and turbulent regions of the boundary layers. In particular, the internal structure of merged turbulent spots is hairpin forest; the internal structure of infant turbulent spots is hairpin packet. Numerous hairpin vortices are readily detected in both the near-wall and outer regions of the boundary layers up to momentum thickness Reynolds number 1950. This suggests that the hairpin vortices in the turbulent region are not simply the aged hairpin forests convected from the upstream transitional region. Temperature iso-surfaces in the companion thermal boundary layers are found to be a useful tracer in identifying hairpin vortex structures.

Boundary layer for non-newtonian fluids on curved surfaces

International Nuclear Information System (INIS)

Stenger, N.

1981-04-01

By using the basic equation of fluid motion (conservation of mass and momentum) the boundary layer parameters for a Non-Newtonian, incompressible and laminar fluid flow, has been evaluated. As a test, the flat plate boundary layer is first analized and afterwards, a case with pressure gradient, allowing separation, is studied. In the case of curved surfaces, the problem is first developed in general and afterwards particularized to a circular cylinder. Finally suction and slip in the flow interface are examined. The power law model is used to represent the stress strain relationship in Non-Newtonian flow. By varying the fluid exponent one can then, have an idea of how the Non-Newtonian behavior of the flow influences the parameters of the boundary layer. Two equations, in an appropriate coordinate system have been obtained after an order of magnitude analysis of the terms in the equations of motion is performed. (Author) [pt

Coupling of magnetopause-boundary layer to the polar ionosphere

International Nuclear Information System (INIS)

Wei, C.Q.; Lee, L.C.

1993-01-01

The authors develop a model which seeks to explain ultraviolet auroral images from the Viking satellite which show periodic bright regions which resemble open-quotes beadsclose quotes or open-quotes pearlsclose quotes aligned along the postnoon auroral oval. ULF geomagnetic pulsations observed in the cusp region are also addressed by this model. The model addresses plasma dynamics in the low-latitude boundary layer and interactions with the polar ionosphere by means of field-aligned current. The Kelvin-Helmholtz instability can develop in the presence of driven plasma flow, which can lead to the formation and growth of plasma vortices in the boundary layer. The finite conductivity of the earth ionosphere causes these vortices to decay. However regions of enhanced field-aligned power density in the postnoon auroral oval can be associated with field-aligned current filaments and boundary layer vortices. These structures may explain the observed bright spots. The authors also discuss the frequency spectrum and the polarization state of the pulsations

RANS Modeling of Benchmark Shockwave / Boundary Layer Interaction Experiments

Science.gov (United States)

Georgiadis, Nick; Vyas, Manan; Yoder, Dennis

2010-01-01

This presentation summarizes the computations of a set of shock wave / turbulent boundary layer interaction (SWTBLI) test cases using the Wind-US code, as part of the 2010 American Institute of Aeronautics and Astronautics (AIAA) shock / boundary layer interaction workshop. The experiments involve supersonic flows in wind tunnels with a shock generator that directs an oblique shock wave toward the boundary layer along one of the walls of the wind tunnel. The Wind-US calculations utilized structured grid computations performed in Reynolds-averaged Navier-Stokes mode. Three turbulence models were investigated: the Spalart-Allmaras one-equation model, the Menter Shear Stress Transport wavenumber-angular frequency two-equation model, and an explicit algebraic stress wavenumber-angular frequency formulation. Effects of grid resolution and upwinding scheme were also considered. The results from the CFD calculations are compared to particle image velocimetry (PIV) data from the experiments. As expected, turbulence model effects dominated the accuracy of the solutions with upwinding scheme selection indicating minimal effects.!

Three-dimensional turbulent boundary layers; Proceedings of the Symposium, Berlin, West Germany, March 29-April 1, 1982

Science.gov (United States)

Fernholz, H. H.; Krause, E.

Papers are presented on recent research concerning three-dimensional turbulent boundary layers. Topics examined include experimental techniques in three-dimensional turbulent boundary layers, turbulence measurements in ship-model flow, measurements of Reynolds-stress profiles in the stern region of a ship model, the effects of crossflow on the vortex-layer-type three-dimensional flow separation, and wind tunnel investigations of some three-dimensional separated turbulent boundary layers. Also examined are three-dimensional boundary layers in turbomachines, the boundary layers on bodies of revolution spinning in axial flows, the effect on a developed turbulent boundary layer of a sudden local wall motion, three-dimensional turbulent boundary layer along a concave wall, the numerical computation of three-dimensional boundary layers, a numerical study of corner flows, three-dimensional boundary calculations in design aerodynamics, and turbulent boundary-layer calculations in design aerodynamics. For individual items see A83-47012 to A83-47036

Acoustic explorations of the upper ocean boundary layer

Science.gov (United States)

Vagle, Svein

2005-04-01

The upper ocean boundary layer is an important but difficult to probe part of the ocean. A better understanding of small scale processes at the air-sea interface, including the vertical transfer of gases, heat, mass and momentum, are crucial to improving our understanding of the coupling between atmosphere and ocean. Also, this part of the ocean contains a significant part of the total biomass at all trophic levels and is therefore of great interest to researchers in a range of different fields. Innovative measurement plays a critical role in developing our understanding of the processes involved in the boundary layer, and the availability of low-cost, compact, digital signal processors and sonar technology in self-contained and cabled configurations has led to a number of exciting developments. This talk summarizes some recent explorations of this dynamic boundary layer using both active and passive acoustics. The resonant behavior of upper ocean bubbles combined with single and multi-frequency broad band active and passive devices are now giving us invaluable information on air-sea gas transfer, estimation of biological production, marine mammal behavior, wind speed and precipitation, surface and internal waves, turbulence, and acoustic communication in the surf zone.

A theory for natural convection turbulent boundary layers next to heated vertical surfaces

International Nuclear Information System (INIS)

George, W.K. Jr.; Capp, S.P.

1979-01-01

The turbulent natural convection boundary layer next to a heated vertical surface is analyzed by classical scaling arguments. It is shown that the fully developed turbulent boundary layer must be treated in two parts: and outer region consisting of most of the boundary layer in which viscous and conduction terms are negligible and an inner region in which the mean convection terms are negligible. The inner layer is identified as a constant heat flux layer. A similarity analysis yields universal profiles for velocity and temperature in the outer and constant heat flux layers. An asymptotic matching of these profiles in an intermediate layer (the buoyant sublayer) yields analytical expressions for the buoyant sublayer profiles. Asymptotic heat transfer and friction laws are obtained for the fully developed boundary layers. Finally, conductive and thermo-viscous sublayers characterized by a linear variation of velocity and temperature are shown to exist at the wall. All predictions are seen to be in excellent agreement with the abundant experimental data. (author)

Flow Visualization in Supersonic Turbulent Boundary Layers.

Science.gov (United States)

Smith, Michael Wayne

This thesis is a collection of novel flow visualizations of two different flat-plate, zero pressure gradient, supersonic, turbulent boundary layers (M = 2.8, Re _theta ~ 82,000, and M = 2.5, Re_ theta ~ 25,000, respectively). The physics of supersonic shear flows has recently drawn increasing attention with the renewed interest in flight at super and hypersonic speeds. This work was driven by the belief that the study of organized, Reynolds -stress producing turbulence structures will lead to improved techniques for the modelling and control of high-speed boundary layers. Although flow-visualization is often thought of as a tool for providing qualitative information about complex flow fields, in this thesis an emphasis is placed on deriving quantitative results from image data whenever possible. Three visualization techniques were applied--'selective cut-off' schlieren, droplet seeding, and Rayleigh scattering. Two experiments employed 'selective cut-off' schlieren. In the first, high-speed movies (40,000 fps) were made of strong density gradient fronts leaning downstream at between 30^circ and 60^ circ and travelling at about 0.9U _infty. In the second experiment, the same fronts were detected with hot-wires and imaged in real time, thus allowing the examination of the density gradient fronts and their associated single-point mass -flux signals. Two experiments employed droplet seeding. In both experiments, the boundary layer was seeded by injecting a stream of acetone through a single point in the wall. The acetone is atomized by the high shear at the wall into a 'fog' of tiny (~3.5mu m) droplets. In the first droplet experiment, the fog was illuminated with copper-vapor laser sheets of various orientations. The copper vapor laser pulses 'froze' the fog motion, revealing a variety of organized turbulence structures, some with characteristic downstream inclinations, others with large-scale roll-up on the scale of delta. In the second droplet experiment, high

Dynamics, thermodynamics, radiation, and cloudiness associated with cumulus-topped marine boundary layers

Energy Technology Data Exchange (ETDEWEB)

Ghate, Virendra P. [Argonne National Lab. (ANL), Argonne, IL (United States); Miller, Mark [Rutgers Univ., New Brunswick, NJ (United States)

2016-11-01

The overall goal of this project was to improve the understanding of marine boundary clouds by using data collected at the Atmospheric Radiation Measurement (ARM) sites, so that they can be better represented in global climate models (GCMs). Marine boundary clouds are observed regularly over the tropical and subtropical oceans. They are an important element of the Earth’s climate system because they have substantial impact on the radiation budget together with the boundary layer moisture, and energy transports. These clouds also have an impact on large-scale precipitation features like the Inter Tropical Convergence Zone (ITCZ). Because these clouds occur at temporal and spatial scales much smaller than those relevant to GCMs, their effects and the associated processes need to be parameterized in GCM simulations aimed at predicting future climate and energy needs. Specifically, this project’s objectives were to (1) characterize the surface turbulent fluxes, boundary layer thermodynamics, radiation field, and cloudiness associated with cumulus-topped marine boundary layers; (2) explore the similarities and differences in cloudiness and boundary layer conditions observed in the tropical and trade-wind regions; and (3) understand similarities and differences by using a simple bulk boundary layer model. In addition to working toward achieving the project’s three objectives, we also worked on understanding the role played by different forcing mechanisms in maintaining turbulence within cloud-topped boundary layers We focused our research on stratocumulus clouds during the first phase of the project, and cumulus clouds during the rest of the project. Below is a brief description of manuscripts published in peer-reviewed journals that describe results from our analyses.

Vortex Formation During Unsteady Boundary-Layer Separation

Science.gov (United States)

Das, Debopam; Arakeri, Jaywant H.

1998-11-01

Unsteady laminar boundary-layer separation is invariably accompanied by the formation of vortices. The aim of the present work is to study the vortex formation mechanism(s). An adverse pressure gradient causing a separation can be decomposed into a spatial component ( spatial variation of the velocity external to the boundary layer ) and a temporal component ( temporal variation of the external velocity ). Experiments were conducted in a piston driven 2-D water channel, where the spatial component could be be contolled by geometry and the temporal component by the piston motion. We present results for three divergent channel geometries. The piston motion consists of three phases: constant acceleration from start, contant velocity, and constant deceleration to stop. Depending on the geometry and piston motion we observe different types of unsteady separation and vortex formation.

Boundary-layer height detection with a ceilometer at a coastal site in western Denmark

DEFF Research Database (Denmark)

Hannesdóttir, Ásta; Hansen, Aksel Walle

in atmospheric transport- and dispersion models. A new method of filtering clouds from the ceilometer data is presented. This allows for the inclusion of more than half of the data in the subsequent analysis, as the presence of clouds would otherwise complicate the boundary-layer height estimations. The boundary....... The boundary-layer height estimates are then used to analyse the daily evolution of the boundary layer and to perform monthly and annual frequency distributions of the boundary-layer height. For westerly winds bi-modal distributions are often found, which may be separated by different criteria, while...

Boundary layer development on turbine airfoil suction surfaces

Science.gov (United States)

Sharma, O. P.; Wells, R. A.; Schlinker, R. H.; Bailey, D. A.

1981-01-01

The results of a study supported by NASA under the Energy Efficient Engine Program, conducted to investigate the development of boundary layers under the influence of velocity distributions that simulate the suction sides of two state-of-the-art turbine airfoils, are presented. One velocity distribution represented a forward loaded airfoil ('squared-off' design), while the other represented an aft loaded airfoil ('aft loaded' design). These velocity distributions were simulated in a low-speed, high-aspect-ratio wind tunnel specifically designed for boundary layer investigations. It is intended that the detailed data presented in this paper be used to develop improved turbulence model suitable for application to turbine airfoil design.

Time-resolved PIV measurements of the atmospheric boundary layer over wind-driven surface waves

Science.gov (United States)

Markfort, Corey; Stegmeir, Matt

2017-11-01

Complex interactions at the air-water interface result in two-way coupling between wind-driven surface waves and the atmospheric boundary layer (ABL). Turbulence generated at the surface plays an important role in aquatic ecology and biogeochemistry, exchange of gases such as oxygen and carbon dioxide, and it is important for the transfer of energy and controlling evaporation. Energy transferred from the ABL promotes the generation and maintenance of waves. A fraction of the energy is transferred to the surface mixed layer through the generation of turbulence. Energy is also transferred back to the ABL by waves. There is a need to quantify the details of the coupled boundary layers of the air-water system to better understand how turbulence plays a role in the interactions. We employ time-resolved PIV to measure the detailed structure of the air and water boundary layers under varying wind and wave conditions in the newly developed IIHR Boundary-Layer Wind-Wave Tunnel. The facility combines a 30-m long recirculating water channel with an open-return boundary layer wind tunnel. A thick turbulent boundary layer is developed in the 1 m high air channel, over the water surface, allowing for the study of boundary layer turbulence interacting with a wind-driven wave field.

Current Challenges in Understanding and Forecasting Stable Boundary Layers over Land and Ice

Directory of Open Access Journals (Sweden)

Gert-Jan eSteeneveld

2014-10-01

Full Text Available Understanding and prediction of the stable atmospheric boundary layer is challenging. Many physical processes come into play in the stable boundary layer, i.e. turbulence, radiation, land surface coupling and heterogeneity, orographic turbulent and gravity wave drag. The development of robust stable boundary-layer parameterizations for weather and climate models is difficult because of the multiplicity of processes and their complex interactions. As a result, these models suffer from biases in key variables, such as the 2-m temperature, boundary-layer depth and wind speed. This short paper briefly summarizes the state-of-the-art of stable boundary layer research, and highlights physical processes that received only limited attention so far, in particular orographically-induced gravity wave drag, longwave radiation divergence, and the land-atmosphere coupling over a snow-covered surface. Finally, a conceptual framework with relevant processes and particularly their interactions is proposed.

Vortex Generator Induced Flow in a High Re Boundary Layer

DEFF Research Database (Denmark)

Velte, Clara Marika; Braud, C.; Coudert, S.

2014-01-01

Stereoscopic Particle Image Velocimetry measurements have been conducted in cross-planes behind three different geometries of Vortex Generators (VGs) in a high Reynolds number boundary layer. The VGs have been mounted in a cascade producing counter-rotating vortices and the downstream flow...... development was examined. Three VG geometries were investigated: rectangular, triangular and cambered. The various VG geometries tested are seen to produce different impacts on the boundary layer flow. Helical symmetry of the generated vortices is confirmed for all investigated VG geometries in this high...... Reynolds number boundary layer. From the parameters resulting from this analysis, it is observed at the most upstream measurement position that the rectangular and triangular VGs produce vortices of similar size, strength and velocity induction whilst the cambered VGs produce smaller and weaker vortices...

Vortex Generator Induced Flow in a High Re Boundary Layer

DEFF Research Database (Denmark)

Velte, Clara Marika; Braud, C.; Coudert, S.

2012-01-01

Stereoscopic Particle Image Velocimetry measurements have been conducted in cross-planes behind three different geometries of Vortex Generators (VGs) in a high Reynolds number boundary layer. The VGs have been mounted in a cascade producing counter-rotating vortices and the downstream flow...... development was examined. Three VG geometries were investigated: rectangular, triangular and cambered. The various VG geometries tested are seen to produce different impacts on the boundary layer flow. Helical symmetry of the generated vortices is confirmed for all investigated VG geometries in this high...... Reynolds number boundary layer. From the parameters resulting from this analysis, it is observed at the most upstream measurement position that the rectangular and triangular VGs produce vortices of similar size, strength and velocity induction whilst the cambered VGs produce smaller and weaker vortices...

Experiments on a smooth wall hypersonic boundary layer at Mach 6

Science.gov (United States)

Neeb, Dominik; Saile, Dominik; Gülhan, Ali

2018-04-01

The turbulent boundary layer along the surface of high-speed vehicles drives shear stress and heat flux. Although essential to the vehicle design, the understanding of compressible turbulent boundary layers at high Mach numbers is limited due to the lack of available data. This is particularly true if the surface is rough, which is typically the case for all technical surfaces. To validate a methodological approach, as initial step, smooth wall experiments were performed. A hypersonic turbulent boundary layer at Ma = 6 (Ma_e=5.4) along a 7{}° sharp cone model at low Reynolds numbers Re_{θ } ≈ 3000 was characterized. The mean velocities in the boundary layer were acquired by means of Pitot pressure and particle image velocimetry (PIV) measurements. Furthermore, the PIV data were used to extract turbulent intensities along the profile. The mean velocities in the boundary layer agree with numerical data, independent of the measurement technique. Based on the profile data, three different approaches to extract the skin friction velocity were applied and show favorable comparison to literature and numerical data. The extracted values were used for inner and outer scaling of the van Driest transformed velocity profiles which are in good agreement to incompressible theoretical data. Morkovin scaled turbulent intensities show ambiguous results compared to literature data which may be influenced by inflow turbulence level, particle lag and other measurement uncertainties.

Development of a life-cycle impact assessment methodology linked to the Planetary Boundaries framework

DEFF Research Database (Denmark)

Ryberg, Morten W.; Owsianiak, Mikolaj; Richardson, Katherine

2018-01-01

to quantify the share of the “safe operating space� that human activities occupy, as was illustrated by calculating indicator scores for about 10,600 products, technologies and services exemplifying several sectors, including materials, energy, transport, and processing. The PB-LCIA can be used...... by companies interested in gauging their activities against the Planetary Boundaries to support decisions that help to reduce the risk of human activities moving the Earth System out of the Holocene state....

Boundary Layer Studies on a Spinning Tangent-Ogive-Cylinder Model

Science.gov (United States)

1975-07-01

ca) An experimental investigation of the Magnus effect on a seven caliber tangent-I ;’ ogive- cylinder model in supersonic flow is reported. The...necessary and Identify by block number) Three-Dimiensional Boundary Layer Compressible Flow Body of Revolution Magnus Effects Boundary Layer...factors have resulted in renewed interest in the study of the Magnus effect . This report describes an experimental study of the effects of spin on

Self-sustained Flow-acoustic Interactions in Airfoil Transitional Boundary Layers

Science.gov (United States)

2015-07-09

AFRL-AFOSR-VA-TR-2015-0235 Self-sustained flow-acoustic interactions in airfoil transitional boundary layers Vladimir Golubev EMBRY-RIDDLE...From - To)      01-04-2012 to 31-03-2015 4.  TITLE AND SUBTITLE Self-sustained flow-acoustic interactions in airfoil transitional boundary layers 5a...complementary experimental and numerical studies of flow-acoustic resonant interactions in transitional airfoils and their impact on airfoil surface

Acoustic Radiation From a Mach 14 Turbulent Boundary Layer

Science.gov (United States)

Zhang, Chao; Duan, Lian; Choudhari, Meelan M.

2016-01-01

Direct numerical simulations (DNS) are used to examine the turbulence statistics and the radiation field generated by a high-speed turbulent boundary layer with a nominal freestream Mach number of 14 and wall temperature of 0:18 times the recovery temperature. The flow conditions fall within the range of nozzle exit conditions of the Arnold Engineering Development Center (AEDC) Hypervelocity Tunnel No. 9 facility. The streamwise domain size is approximately 200 times the boundary-layer thickness at the inlet, with a useful range of Reynolds number corresponding to Re 450 ?? 650. Consistent with previous studies of turbulent boundary layer at high Mach numbers, the weak compressibility hypothesis for turbulent boundary layers remains applicable under this flow condition and the computational results confirm the validity of both the van Driest transformation and Morkovin's scaling. The Reynolds analogy is valid at the surface; the RMS of fluctuations in the surface pressure, wall shear stress, and heat flux is 24%, 53%, and 67% of the surface mean, respectively. The magnitude and dominant frequency of pressure fluctuations are found to vary dramatically within the inner layer (z/delta 0.< or approx. 0.08 or z+ < or approx. 50). The peak of the pre-multiplied frequency spectrum of the pressure fluctuation is f(delta)/U(sub infinity) approx. 2.1 at the surface and shifts to a lower frequency of f(delta)/U(sub infinity) approx. 0.7 in the free stream where the pressure signal is predominantly acoustic. The dominant frequency of the pressure spectrum shows a significant dependence on the freestream Mach number both at the wall and in the free stream.

Boundary layer turbulence in transitional and developed states

Science.gov (United States)

Park, George Ilhwan; Wallace, James M.; Wu, Xiaohua; Moin, Parviz

2012-03-01

Using the recent direct numerical simulations by Wu and Moin ["Transitional and turbulent boundary layer with heat transfer," Phys. Fluids 22, 85 (2010)] of a flat-plate boundary layer with a passively heated wall, statistical properties of the turbulence in transition at Reθ ≈ 300, from individual turbulent spots, and at Reθ ≈ 500, where the spots merge (distributions of the mean velocity, Reynolds stresses, kinetic energy production, and dissipation rates, enstrophy and its components) have been compared to these statistical properties for the developed boundary layer turbulence at Reθ = 1840. When the distributions in the transitional regions are conditionally averaged so as to exclude locations and times when the flow is not turbulent, they closely resemble the distributions in the developed turbulent state at the higher Reynolds number, especially in the buffer layer. Skin friction coefficients, determined in this conditional manner at the two Reynolds numbers in the transitional flow are, of course, much larger than when their values are obtained by including both turbulent and non-turbulent information there, and the conditional averaged values are consistent with the 1/7th power law approximation. An octant analysis based on the combinations of signs of the velocity and temperature fluctuations, u, v, and θ shows that the momentum and heat fluxes are predominantly of the mean gradient type in both the transitional and developed regions. The fluxes appear to be closely associated with vortices that transport momentum and heat toward and away from the wall in both regions of the flow. The results suggest that there may be little fundamental difference between the nonlinear processes involved in the formation of turbulent spots that appear in transition and those that sustain the turbulence when it is developed. They also support the view that the transport processes and the vortical structures that drive them in developed and transitional boundary

Interactive boundary-layer calculations of a transonic wing flow

Science.gov (United States)

Kaups, Kalle; Cebeci, Tuncer; Mehta, Unmeel

1989-01-01

Results obtained from iterative solutions of inviscid and boundary-layer equations are presented and compared with experimental values. The calculated results were obtained with an Euler code and a transonic potential code in order to furnish solutions for the inviscid flow; they were interacted with solutions of two-dimensional boundary-layer equations having a strip-theory approximation. Euler code results are found to be in better agreement with the experimental data than with the full potential code, especially in the presence of shock waves, (with the sole exception of the near-tip region).

An Innovative Flow-Measuring Device: Thermocouple Boundary Layer Rake

Science.gov (United States)

Hwang, Danny P.; Fralick, Gustave C.; Martin, Lisa C.; Wrbanek, John D.; Blaha, Charles A.

2001-01-01

An innovative flow-measuring device, a thermocouple boundary layer rake, was developed. The sensor detects the flow by using a thin-film thermocouple (TC) array to measure the temperature difference across a heater strip. The heater and TC arrays are microfabricated on a constant-thickness quartz strut with low heat conductivity. The device can measure the velocity profile well into the boundary layer, about 65 gm from the surface, which is almost four times closer to the surface than has been possible with the previously used total pressure tube.

Lower Atmospheric Boundary Layer Experiment (LABLE) Final Campaign Report

Energy Technology Data Exchange (ETDEWEB)

Klein, P [University of Oklahoma - School of Meteorology; Bonin, TA; Newman, JF [National Renewable Energy Laboratory; Turner, DD [National Oceanic and Atmospheric Administration; Chilson, P [University of Oklahoma; Blumberg, WG [University of Oklahoma; Mishra, S; Wainwright, CE; Carney, M [University of Oklahoma - School of Meteorology; Jacobsen, EP [University of Oklahoma; Wharton, S [Lawrence Livermore National Laboratory

2015-11-01

The Lower Atmospheric Boundary Layer Experiment (LABLE) included two measurement campaigns conducted at the Atmospheric Radiation Measurement (ARM) Southern Great Plains site in Oklahoma during 2012 and 2013. LABLE was designed as a multi-phase, low-cost collaboration among the University of Oklahoma, the National Severe Storms Laboratory, Lawrence Livermore National Laboratory, and the ARM program. A unique aspect was the role of graduate students in LABLE. They served as principal investigators and took the lead in designing and conducting experiments using different sampling strategies to best resolve boundary-layer phenomena.

Budget of Turbulent Kinetic Energy in a Shock Wave Boundary-Layer Interaction

Science.gov (United States)

Vyas, Manan A.; Waindim, Mbu; Gaitonde, Datta V.

2016-01-01

Implicit large-eddy simulation (ILES) of a shock wave/boundary-layer interaction (SBLI) was performed. Quantities present in the exact equation of the turbulent kinetic energy transport were accumulated and used to calculate terms like production, dissipation, molecular diffusion, and turbulent transport. The present results for a turbulent boundary layer were validated by comparison with direct numerical simulation data. It was found that a longer development domain was necessary for the boundary layer to reach an equilibrium state and a finer mesh resolution would improve the predictions. In spite of these findings, trends of the present budget match closely with that of the direct numerical simulation. Budgets for the SBLI region are presented at key axial stations. These budgets showed interesting dynamics as the incoming boundary layer transforms and the terms of the turbulent kinetic energy budget change behavior within the interaction region.

Numerical Simulations of Hypersonic Boundary Layer Transition

Science.gov (United States)

Bartkowicz, Matthew David

Numerical schemes for supersonic flows tend to use large amounts of artificial viscosity for stability. This tends to damp out the small scale structures in the flow. Recently some low-dissipation methods have been proposed which selectively eliminate the artificial viscosity in regions which do not require it. This work builds upon the low-dissipation method of Subbareddy and Candler which uses the flux vector splitting method of Steger and Warming but identifies the dissipation portion to eliminate it. Computing accurate fluxes typically relies on large grid stencils or coupled linear systems that become computationally expensive to solve. Unstructured grids allow for CFD solutions to be obtained on complex geometries, unfortunately, it then becomes difficult to create a large stencil or the coupled linear system. Accurate solutions require grids that quickly become too large to be feasible. In this thesis a method is proposed to obtain more accurate solutions using relatively local data, making it suitable for unstructured grids composed of hexahedral elements. Fluxes are reconstructed using local gradients to extend the range of data used. The method is then validated on several test problems. Simulations of boundary layer transition are then performed. An elliptic cone at Mach 8 is simulated based on an experiment at the Princeton Gasdynamics Laboratory. A simulated acoustic noise boundary condition is imposed to model the noisy conditions of the wind tunnel and the transitioning boundary layer observed. A computation of an isolated roughness element is done based on an experiment in Purdue's Mach 6 quiet wind tunnel. The mechanism for transition is identified as an instability in the upstream separation region and a comparison is made to experimental data. In the CFD a fully turbulent boundary layer is observed downstream.

The curved kinetic boundary layer of active matter.

Science.gov (United States)

Yan, Wen; Brady, John F

2018-01-03

A body submerged in active matter feels the swim pressure through a kinetic accumulation boundary layer on its surface. The boundary layer results from a balance between translational diffusion and advective swimming and occurs on the microscopic length scale . Here , D T is the Brownian translational diffusivity, τ R is the reorientation time and l = U 0 τ R is the swimmer's run length, with U 0 the swim speed [Yan and Brady, J. Fluid. Mech., 2015, 785, R1]. In this work we analyze the swim pressure on arbitrary shaped bodies by including the effect of local shape curvature in the kinetic boundary layer. When δ ≪ L and l ≪ L, where L is the body size, the leading order effects of curvature on the swim pressure are found analytically to scale as J S λδ 2 /L, where J S is twice the (non-dimensional) mean curvature. Particle-tracking simulations and direct solutions to the Smoluchowski equation governing the probability distribution of the active particles show that λδ 2 /L is a universal scaling parameter not limited to the regime δ, l ≪ L. The net force exerted on the body by the swimmers is found to scale as F net /(n ∞ k s T s L 2 ) = f(λδ 2 /L), where f(x) is a dimensionless function that is quadratic when x ≪ 1 and linear when x ∼ 1. Here, k s T s = ζU 0 2 τ R /6 defines the 'activity' of the swimmers, with ζ the drag coefficient, and n ∞ is the uniform number density of swimmers far from the body. We discuss the connection of this boundary layer to continuum mechanical descriptions of active matter and briefly present how to include hydrodynamics into this purely kinetic study.

Receptivity of Hypersonic Boundary Layers over Straight and Flared Cones

Science.gov (United States)

Balakumar, Ponnampalam; Kegerise, Michael A.

2010-01-01

The effects of adverse pressure gradients on the receptivity and stability of hypersonic boundary layers were numerically investigated. Simulations were performed for boundary layer flows over a straight cone and two flared cones. The steady and the unsteady flow fields were obtained by solving the two-dimensional Navier-Stokes equations in axi-symmetric coordinates using the 5th order accurate weighted essentially non-oscillatory (WENO) scheme for space discretization and using third-order total-variation-diminishing (TVD) Runge-Kutta scheme for time integration. The mean boundary layer profiles were analyzed using local stability and non-local parabolized stability equations (PSE) methods. After the most amplified disturbances were identified, two-dimensional plane acoustic waves were introduced at the outer boundary of the computational domain and time accurate simulations were performed. The adverse pressure gradient was found to affect the boundary layer stability in two important ways. Firstly, the frequency of the most amplified second-mode disturbance was increased relative to the zero pressure gradient case. Secondly, the amplification of first- and second-mode disturbances was increased. Although an adverse pressure gradient enhances instability wave growth rates, small nose-tip bluntness was found to delay transition due to the low receptivity coefficient and the resulting weak initial amplitude of the instability waves. The computed and measured amplitude-frequency spectrums in all three cases agree very well in terms of frequency and the shape except for the amplitude.

Hair receptor sensitivity to changes in laminar boundary layer shape

International Nuclear Information System (INIS)

Dickinson, B T

2010-01-01

Biologists have shown that bat wings contain distributed arrays of flow-sensitive hair receptors. The hair receptors are hypothesized to feedback information on airflows over the bat wing for enhanced stability or maneuverability during flight. Here, we study the geometric specialization of hair-like structures for the detection of changes in boundary layer velocity profiles (shapes). A quasi-steady model that relates the flow velocity profile incident on the longitudinal axis of a hair to the resultant moment and shear force at the hair base is developed. The hair length relative to the boundary layer momentum thickness that maximizes the resultant moment and shear-force sensitivity to changes in boundary layer shape is determined. The sensitivity of the resultant moment and shear force is shown to be highly dependent on hair length. Hairs that linearly taper to a point are shown to provide greater output sensitivity than hairs of uniform cross-section. On an order of magnitude basis, the computed optimal hair lengths are in agreement with the range of hair receptor lengths measured on individual bat species. These results support the hypothesis that bats use hair receptors for detecting changes in boundary layer shape and provide geometric guidelines for artificial hair sensor design and application.

Shooting method for solution of boundary-layer flows with massive blowing

Science.gov (United States)

Liu, T.-M.; Nachtsheim, P. R.

1973-01-01

A modified, bidirectional shooting method is presented for solving boundary-layer equations under conditions of massive blowing. Unlike the conventional shooting method, which is unstable when the blowing rate increases, the proposed method avoids the unstable direction and is capable of solving complex boundary-layer problems involving mass and energy balance on the surface.

A high-latitude, low-latitude boundary layer model of the convection current system

International Nuclear Information System (INIS)

Siscoe, G.L.; Lotko, W.; Sonnerup, B.U.O.

1991-01-01

Observations suggest that both the high- and low-latitude boundary layers contribute to magnetospheric convection, and that their contributions are linked. In the interpretation pursued here, the high-latitude boundary layer (HBL) generates the voltage while the low-latitude boundary layer (LBL) generates the current for the part of the convection electric circuit that closes through the ionosphere. This paper gives a model that joins the high- and low-latitude boundary layers consistently with the ionospheric Ohm's law. It describes an electric circuit linking both boundary layers, the region 1 Birkeland currents, and the ionospheric Pedersen closure currents. The model works by using the convection electric field that the ionosphere receives from the HBL to determine two boundary conditions to the equations that govern viscous LBL-ionosphere coupling. The result provides the needed self-consistent coupling between the two boundary layers and fully specifies the solution for the viscous LBL-ionosphere coupling equations. The solution shows that in providing the current required by the ionospheric Ohm's law, the LBL needs only a tenth of the voltage that spans the HBL. The solution also gives the latitude profiles of the ionospheric electric field, parallel currents, and parallel potential. It predicts that the plasma in the inner part of the LBL moves sunward instead of antisunward and that, as the transpolar potential decreases below about 40 kV, reverse polarity (region 0) currents appear at the poleward border of the region 1 currents. A possible problem with the model is its prediction of a thin boundary layer (∼1000 km), whereas thicknesses inferred from satellite data tend to be greater

Productivity of a coral reef using boundary layer and enclosure methods

Science.gov (United States)

McGillis, W.R.; Langdon, C.; Loose, B.; Yates, K.K.; Corredor, Jorge

2011-01-01

The metabolism of Cayo Enrique Reef, Puerto Rico, was studied using in situ methods during March 2009. Benthic O2 fluxes were used to calculate net community production using both the boundary layer gradient and enclosure techniques. The boundary layer O2 gradient and the drag coefficients were used to calculate productivity ranging from -12.3 to 13.7 mmol O2 m-2 h-1. Productivity measurements from the enclosure method ranged from -11.0 to 12.9 mmol O2 m-2 h-1. During the study, the mean hourly difference between the methods was 0.65 mmol O2 m-2 h-1 (r2 = 0.92), resulting in well-reconciled estimates of net community production between the boundary layer (-33.1 mmol m-2 d-1) and enclosure (-46.3 mmol m-2 d-1) techniques. The results of these independent approaches corroborate quantified rates of metabolism at Cayo Enrique Reef. Close agreement between methods demonstrates that boundary layer measurements can provide near real-time assessments of coral reef health.

Boundary-layer diabatic processes, the virtual effect, and convective self-aggregation

Science.gov (United States)

Yang, D.

2017-12-01

The atmosphere can self-organize into long-lasting large-scale overturning circulations over an ocean surface with uniform temperature. This phenomenon is referred to as convective self-aggregation and has been argued to be important for tropical weather and climate systems. Here we use a 1D shallow water model and a 2D cloud-resolving model (CRM) to show that boundary-layer diabatic processes are essential for convective self-aggregation. We will show that boundary-layer radiative cooling, convective heating, and surface buoyancy flux help convection self-aggregate because they generate available potential energy (APE), which sustains the overturning circulation. We will also show that evaporative cooling in the boundary layer (cold pool) inhibits convective self-aggregation by reducing APE. Both the shallow water model and CRM results suggest that the enhanced virtual effect of water vapor can lead to convective self-aggregation, and this effect is mainly in the boundary layer. This study proposes new dynamical feedbacks for convective self-aggregation and complements current studies that focus on thermodynamic feedbacks.

Observations of the atmospheric boundary layer height over Abu Dhabi, United Arab Emirates: Investigating boundary layer climatology in arid regions

Science.gov (United States)

Marzooqi, Mohamed Al; Basha, Ghouse; Ouarda, Taha B. M. J.; Armstrong, Peter; Molini, Annalisa

2014-05-01

Strong sensible heat fluxes and deep turbulent mixing - together with marked dustiness and a low substrate water content - represent a characteristic signature in the boundary layer over hot deserts, resulting in "thicker" mixing layers and peculiar optical properties. Beside these main features however, desert ABLs present extremely complex local structures that have been scarcely addressed in the literature, and whose understanding is essential in modeling processes such as the transport of dust and pollutants, and turbulent fluxes of momentum, heat and water vapor in hyper-arid regions. In this study, we analyze a continuous record of observations of the atmospheric boundary layer (ABL) height from a single lens LiDAR ceilometer operated at Masdar Institute Field Station (24.4oN, 54.6o E, Abu Dhabi, United Arab Emirates), starting March 2013. We compare different methods for the estimation of the ABL height from Ceilometer data such as, classic variance-, gradient-, log gradient- and second derivation-methods as well as recently developed techniques such as the Bayesian Method and Wavelet covariance transform. Our goal is to select the most suited technique for describing the climatology of the ABL in desert environments. Comparison of our results with radiosonde observations collected at the nearby airport of Abu Dhabi indicate that the WCT and the Bayesian method are the most suitable tools to accurately identify the ABL height in all weather conditions. These two methods are used for the definition of diurnal and seasonal climatologies of the boundary layer conditional to different atmospheric stability classes.

The lobe to plasma sheet boundary layer transition: Theory and observations

International Nuclear Information System (INIS)

Schriver, D.; Ashour-Abdalla, M.; Treumann, R.; Nakamura, M.; Kistler, L.M.

1990-01-01

The lobe and the plasma sheet boundary layer in the Earth's magnetotail are regions of different plasma conditions and share a common interface. The transition from the lobe to the plasma sheet boundary layer is examined here using AMPTE/IRM data. When the satellite crossed from the lobe to the plasma sheet boundary layer, intense narrow banded wave bursts at 1 kHz were observed an d then broadband electrostatic noise (BEN) immediately followed. Simultaneous with the onset of BEN, high energy earthward streaming proton beams at > 40 keV (> 2,700 km/s) were detected. These results are used as input into a numerical simulation to study ion beam instabilities in the PSBL

Hydrodynamic structure of the boundary layers in a rotating cylindrical cavity with radial inflow

International Nuclear Information System (INIS)

Herrmann-Priesnitz, Benjamín; Torres, Diego A.; Calderón-Muñoz, Williams R.; Salas, Eduardo A.; Vargas-Uscategui, Alejandro; Duarte-Mermoud, Manuel A.

2016-01-01

A flow model is formulated to investigate the hydrodynamic structure of the boundary layers of incompressible fluid in a rotating cylindrical cavity with steady radial inflow. The model considers mass and momentum transfer coupled between boundary layers and an inviscid core region. Dimensionless equations of motion are solved using integral methods and a space-marching technique. As the fluid moves radially inward, entraining boundary layers develop which can either meet or become non-entraining. Pressure and wall shear stress distributions, as well as velocity profiles predicted by the model, are compared to numerical simulations using the software OpenFOAM. Hydrodynamic structure of the boundary layers is governed by a Reynolds number, Re, a Rossby number, Ro, and the dimensionless radial velocity component at the periphery of the cavity, U_o. Results show that boundary layers merge for Re > 0.1, and boundary layers become predominantly non-entraining for low Ro, low Re, and high U_o. Results may contribute to improve the design of technology, such as heat exchange devices, and turbomachinery.

Foliar trichomes, boundary layers, and gas exchange in 12 species of epiphytic Tillandsia (Bromeliaceae).

Science.gov (United States)

Benz, Brett W; Martin, Craig E

2006-04-01

We examined the relationships between H2O and CO2 gas exchange parameters and leaf trichome cover in 12 species of Tillandsia that exhibit a wide range in trichome size and trichome cover. Previous investigations have hypothesized that trichomes function to enhance boundary layers around Tillandsioid leaves thereby buffering the evaporative demand of the atmosphere and retarding transpirational water loss. Data presented herein suggest that trichome-enhanced boundary layers have negligible effects on Tillandsia gas exchange, as indicated by the lack of statistically significant relationships in regression analyses of gas exchange parameters and trichome cover. We calculated trichome and leaf boundary layer components, and their associated effects on H2O and CO2 gas exchange. The results further indicate trichome-enhanced boundary layers do not significantly reduce transpirational water loss. We conclude that although the trichomes undoubtedly increase the thickness of the boundary layer, the increase due to Tillandsioid trichomes is inconsequential in terms of whole leaf boundary layers, and any associated reduction in transpirational water loss is also negligible within the whole plant gas exchange pathway.

Hydrodynamic structure of the boundary layers in a rotating cylindrical cavity with radial inflow

Energy Technology Data Exchange (ETDEWEB)

Herrmann-Priesnitz, Benjamín, E-mail: bherrman@ing.uchile.cl; Torres, Diego A. [Department of Mechanical Engineering, Universidad de Chile, Beauchef 851, Santiago (Chile); Advanced Mining Technology Center, Universidad de Chile, Av. Tupper 2007, Santiago (Chile); Calderón-Muñoz, Williams R. [Department of Mechanical Engineering, Universidad de Chile, Beauchef 851, Santiago (Chile); Energy Center, Universidad de Chile, Av. Tupper 2007, Santiago (Chile); Salas, Eduardo A. [CSIRO-Chile International Centre of Excellence, Apoquindo 2827, Floor 12, Santiago (Chile); Vargas-Uscategui, Alejandro [Department of Mechanical Engineering, Universidad de Chile, Beauchef 851, Santiago (Chile); CSIRO-Chile International Centre of Excellence, Apoquindo 2827, Floor 12, Santiago (Chile); Duarte-Mermoud, Manuel A. [Advanced Mining Technology Center, Universidad de Chile, Av. Tupper 2007, Santiago (Chile); Department of Electrical Engineering, Universidad de Chile, Av. Tupper 2007, Santiago (Chile)

2016-03-15

A flow model is formulated to investigate the hydrodynamic structure of the boundary layers of incompressible fluid in a rotating cylindrical cavity with steady radial inflow. The model considers mass and momentum transfer coupled between boundary layers and an inviscid core region. Dimensionless equations of motion are solved using integral methods and a space-marching technique. As the fluid moves radially inward, entraining boundary layers develop which can either meet or become non-entraining. Pressure and wall shear stress distributions, as well as velocity profiles predicted by the model, are compared to numerical simulations using the software OpenFOAM. Hydrodynamic structure of the boundary layers is governed by a Reynolds number, Re, a Rossby number, Ro, and the dimensionless radial velocity component at the periphery of the cavity, U{sub o}. Results show that boundary layers merge for Re < < 10 and Ro > > 0.1, and boundary layers become predominantly non-entraining for low Ro, low Re, and high U{sub o}. Results may contribute to improve the design of technology, such as heat exchange devices, and turbomachinery.

Laminar boundary layer response to rotation of a finite diameter surface patch

International Nuclear Information System (INIS)

Klewicki, J.C.; Hill, R.B.

2003-01-01

The responses of the flat plate laminar boundary layer to perturbations generated by rotating a finite patch of the bounding surface are explored experimentally. The size of the surface patch was of the same order as the boundary layer thickness. The displacement thickness Reynolds number range of the boundary layers explored was 72-527. The rotation rates of the surface patch ranged from 2.14 to 62.8 s-1. Qualitative flow visualizations and quantitative molecular tagging velocimetry measurements revealed that rotation of a finite surface patch generates an asymmetric loop-like vortex. Significant features of this vortex include that, (i) the sign of the vorticity in the vortex head is opposite that of the boundary layer vorticity regardless of the sign of the input rotation, (ii) one leg of the vortex exhibits motion akin to solid body rotation while the other leg is best characterized as a spanwise shear layer, (iii) the vortex leg exhibiting near solid body rotation lifts more rapidly from the surface than the leg more like a shear layer, and (iv) the vortex leg exhibiting near solid body rotation always occurs on the side of the surface patch experiencing downstream motion. These asymmetries switch sides depending on the sign of the input rotation. The present results are interpreted and discussed relative to analytical solutions for infinite geometries. By way of analogy, plausible connections are drawn between the present results and the influences of wall normal vortices in turbulent boundary layer flows

Transitional and turbulent boundary layer with heat transfer

Science.gov (United States)

Wu, Xiaohua; Moin, Parviz

2010-08-01

We report on our direct numerical simulation of an incompressible, nominally zero-pressure-gradient flat-plate boundary layer from momentum thickness Reynolds number 80-1950. Heat transfer between the constant-temperature solid surface and the free-stream is also simulated with molecular Prandtl number Pr=1. Skin-friction coefficient and other boundary layer parameters follow the Blasius solutions prior to the onset of turbulent spots. Throughout the entire flat-plate, the ratio of Stanton number and skin-friction St/Cf deviates from the exact Reynolds analogy value of 0.5 by less than 1.5%. Mean velocity and Reynolds stresses agree with experimental data over an extended turbulent region downstream of transition. Normalized rms wall-pressure fluctuation increases gradually with the streamwise growth of the turbulent boundary layer. Wall shear stress fluctuation, τw,rms'+, on the other hand, remains constant at approximately 0.44 over the range, 800spots are tightly packed with numerous hairpin vortices. With the advection and merging of turbulent spots, these young isolated hairpin forests develop into the downstream turbulent region. Isosurfaces of temperature up to Reθ=1900 are found to display well-resolved signatures of hairpin vortices, which indicates the persistence of the hairpin forests.

Fast Fermi acceleration in the plasma sheet boundary layer

International Nuclear Information System (INIS)

Wu, C.S.; Lui, A.T.Y.

1989-01-01

A longstanding question in the field of magnetospheric physics is the source of the energetic particles which are commonly observed along the plasma sheet boundary layer (PSBL). Several models have been suggested for the acceleration of these particles. We suggest a means by which the fast Fermi acceleration mechanism [Wu, 1984] can accelerate electrons at the plasma sheet and perhaps account for some of the observations. We propose the following: A localized hydromagnetic disturbance propagating through the tail lobe region impinges upon the PSBL deforming it and displacing it in towards the central plasma sheet. The boundary layer can then act like a moving magnetic mirror. If the disturbance is propagating nearly perpendicular to the layer then its velocity projected parallel to the layer (and the magnetic field) can be very large resulting in significant acceleration of reflected particles. copyright American Geophysical Union 1989

Estimates of the height of the boundary layer using SODAR and rawinsoundings in Amazonia

Energy Technology Data Exchange (ETDEWEB)

Fisch, G [Instituto de Aeronautica e Espaco (IAE/CTA), Sao Jose dos Campos, 12228-904 (Brazil); Santos, L A R dos [Instituto Nacional de Meteorologia (INMET), BrasIlia, 70680-900 (Brazil)], E-mail: gfisch@iae.cta.br, E-mail: landre@inmet.gov.br

2008-05-01

During the LBA campaign in Amazonia 2002, simultaneous measurements were made of the boundary layer using different instruments (rawinsoundings and SODAR). The profiles of potential temperature and humidity were used to estimates the height of the boundary layer using 3 different techniques. The SODAR's measurements did not capture the shallow morning boundary layer observed at the profiles.

Dissociation–recombination models in hypersonic boundary layer O2/O flows

International Nuclear Information System (INIS)

Armenise, I.; Esposito, F.

2012-01-01

Graphical abstract: In hypersonic boundary layers, in which the temperature strongly decreases from the edge to the body surface, the coupling of transport phenomena and chemical kinetics causes a strong vibrational non-equilibrium, as demonstrated by the vibrational distributions and the pseudo-first-order dissociation constants. In this work a pure O2/O mixture has been investigated to evaluate the role of new multiquanta atom-molecule collision rate coefficients, calculated by means of a quasiclassical trajectory (QCT) method. Highlights: ► We evaluate the vibrational non-equilibrium in oxygen hypersonic boundary layer flows. ► We adopt a state-to-state vibrational kinetics model. ► We use updated quasicassical trajectory atom–molecule collision rate coefficients. ► Multiquanta transitions and direct dissociation–recombination are important. ► We calculate the heat flux through the boundary layer. - Abstract: A recent complete set of oxygen atom–molecule collision rate coefficients, calculated by means of a quasiclassical trajectory (QCT) method, has been used to evaluate the vibrational non-equilibrium in hypersonic boundary layer flows. The importance of multiquanta transitions has been demonstrated. Moreover a new ‘direct dissociation–recombination’ (DDR) model has been adopted and the corresponding results differ from the ones obtained with the ladder-climbing (LC) model, characterized by the extrapolation of bound-to-bound transitions to the continuum. The heat flux through the boundary layer and at the surface has been calculated too.

A helical magnetic limiter for boundary layer control in large tokamaks

International Nuclear Information System (INIS)

Feneberg, W.; Wolf, G.H.

1981-01-01

In a tokamak configuration, superposition of the magnetic field of resonant helical windings which surround the toroidal plasma current outside the first wall destroys the magnetic surfaces in the boundary layer (ergodization). A transport model is analysed, where convective flow of the plasma from the boundary layer to the first wall permits elevated particle densities in the boundary layer and leads to very high particle and energy transport. The convective flow is driven by the pressure gradient along the field lines which intersect the toroidal wall at an oblique small angle epsilon. The required thickness Δ of the boundary layer is around 10 15 n -1 .cm -2 . As a result, the plasma temperature there can be reduced towards the threshold of critical plasma-wall-interaction processes, the plasma core can be shielded against impurities from the wall and, at the same time, a very short life-time of all particles in the boundary layer can be achieved (use of pumpholes and/or scrape-off-limiters for removing ash). Thus, this model also improves the concepts of edge radiation cooling. An estimate is given of the parameters of INTOR using only a weak helical perturbation field which conserves the magnetic surfaces in the plasma core: one can reach wall temperatures Tsub(w) between 20 and 30 eV in the presence of wall densities nsub(w) approaching 10 14 cm -3 . (author)

More evidence for a planetary wave link with midlatitude E region coherent backscatter and sporadic E layers

Directory of Open Access Journals (Sweden)

K. Schlegel

Full Text Available Measurements of midlatitude E region coherent backscatter obtained during four summers with SESCAT, a 50 MHz Doppler system operating in Crete, Greece, and concurrent ionosonde recordings from the same ionospheric volume obtained with a CADI for one of these summers, are used to analyse the long-term variability in echo and Es occurrence. Echo and Es layer occurrences, computed in percent of time over a 12-h nighttime interval, take the form of time sequences. Linear power spectrum analysis shows that there are dominant spectral peaks in the range of 2–9 days, the most commonly observed periods appearing in two preferential bands, of 2–3 days and 4–7 days. No connection with geomagnetic activity was found. The characteristics of these periodicities compare well with similar properties of planetary waves, which suggests the possibility that planetary waves are responsible for the observed long-term periodicities. These findings indicate also a likely close relation between planetary wave (PW activity and the well known but not well understood seasonal Es dependence. To test the PW postulation, we used simultaneous neutral wind data from the mesopause region around 95 km, measured from Collm, Germany. Direct comparison of the long-term periodicities in echo and Es layer occurrence with those in the neutral wind show some reasonable agreement. This new evidence, although not fully conclusive, is the first direct indication in favour of a planetary wave role on the unstable midlatitude E region ionosphere. Our results suggest that planetary waves observation is a viable option and a new element into the physics of midlatitude Es layers that needs to be considered and investigated.Key words: Ionosphere (ionosphere irregularities; mid-latitude ionosphere – Meteorology and atmospheric dynamics (waves and tides

Towards grid-converged wall-modeled LES of atmospheric boundary layer flows

Science.gov (United States)

Yellapantula, Shashank; Vijayakumar, Ganesh; Henry de Frahan, Marc; Churchfield, Matthew; Sprague, Michael

2017-11-01

Accurate characterization of incoming atmospheric boundary layer (ABL) turbulence is a critical factor in improving accuracy and predictive nature of simulation of wind farm flows. Modern commercial wind turbines operate in the log layer of the ABL that are typically simulated using wall-modeled large-eddy simulation (WMLES). One of the long-standing issues associated with wall modeling for LES and hybrid RANS-LES for atmospheric boundary layers is the over-prediction of the mean-velocity gradient, commonly referred to as log-layer mismatch. Kawai and Larsson in 2012, identified under-resolution of the near-wall region and the incorrect information received by the wall model as potential causes for the log-layer mismatch in WMLES of smooth-wall boundary-layer flows. To solve the log layer mismatch issue, they proposed linking the wall model to the LES solution at a physical of height of ym, instead of the first grid point. In this study, we extend their wall modeling approach to LES of the rough-wall ABL to investigate issues of log-layer mismatch and grid convergence. This work was funded by the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, Wind Energy Technologies Office, under Contract No. DE-AC36-08-GO28308 with the National Renewable Energy Laboratory.

Robust controller with adaptation within the boundary layer: application to nuclear underwater inspection robot

International Nuclear Information System (INIS)

Park, Gee Yong; Yoon, Ji Sup; Hong, Dong Hee; Jeong, Jae Hoo

2002-01-01

In this paper, the robust control scheme with the improved control performance within the boundary layer is proposed. In the control scheme, the robust controller based on the traditional variable structure control method is modified to have the adaptation within the boundary layer. From this controller, the width of the boundary layer where the robust control input is smoothened out can be given by an appropriate value. But the improve control performance within the boundary layer can be achieved without the so-called control chattering because the role of adaptive control is to compensate for the uncovered portions of the robust control occurred from the continuous approximation within the boundary layer. Simulation tests for circular navigation of an underwater wall-ranging robot developed for inspection of wall surfaces in the research reactor, TRIGA MARK III, confirm the performance improvement

Direct simulation of flat-plate boundary layer with mild free-stream turbulence

Science.gov (United States)

Wu, Xiaohua; Moin, Parviz

2014-11-01

Spatially evolving direct numerical simulation of the flat-plate boundary layer has been performed. The momentum thickness Reynolds number develops from 80 to 3000 with a free-stream turbulence intensity decaying from 3 percent to 0.8 percent. Predicted skin-friction is in agreement with the Blasius solution prior to breakdown, follows the well-known T3A bypass transition data during transition, and agrees with the Erm and Joubert Melbourne wind-tunnel data after the completion of transition. We introduce the concept of bypass transition in the narrow sense. Streaks, although present, do not appear to be dynamically important during the present bypass transition as they occur downstream of infant turbulent spots. For the turbulent boundary layer, viscous scaling collapses the rate of dissipation profiles in the logarithmic region at different Reynolds numbers. The ratio of Taylor microscale and the Kolmogorov length scale is nearly constant over a large portion of the outer layer. The ratio of large-eddy characteristic length and the boundary layer thickness scales very well with Reynolds number. The turbulent boundary layer is also statistically analyzed using frequency spectra, conditional-sampling, and two-point correlations. Near momentum thickness Reynolds number of 2900, three layers of coherent vortices are observed: the upper and lower layers are distinct hairpin forests of large and small sizes respectively; the middle layer consists of mostly fragmented hairpin elements.

Boundary Layer Ducting of Low-elevation GNSS Ocean Reflected Signals

DEFF Research Database (Denmark)

Høeg, Per; von Benzon, Hans-Henrik; Durgonics, Tibor

for the data retrievals and the precision and the accuracy, are of interest for assessing the observational data content.Simulations of the low-elevation ocean reflected GNSS signal reveal a ducting of the signalwhen applying a model of the boundary layer. This effect is presented during varying conditions...... of the sea surface roughness, ocean wind and temperature, density and gradient of the water vapor profile in the boundary layer.The model for the sea surface roughness impedance, wind speed, and rms ocean wave-heightshow a stronger signal damping for a smoother ocean surfaces (sea state 0) compared...... to a rough sea (sea state 4). While the real part of the signal shows the reverse effect. At the same time the reflection zone enhances for rough sea states. Simulations, including a standard atmosphere and a boundary layer, give a significant ducting of the received signal, leading to a much larger...

On the Lagrangian description of unsteady boundary-layer separation. I - General theory

Science.gov (United States)

Van Dommelen, Leon L.; Cowley, Stephen J.

1990-01-01

Although unsteady, high-Reynolds number, laminar boundary layers have conventionally been studied in terms of Eulerian coordinates, a Lagrangian approach may have significant analytical and computational advantages. In Lagrangian coordinates the classical boundary layer equations decouple into a momentum equation for the motion parallel to the boundary, and a hyperbolic continuity equation (essentially a conserved Jacobian) for the motion normal to the boundary. The momentum equations, plus the energy equation if the flow is compressible, can be solved independently of the continuity equation. Unsteady separation occurs when the continuity equation becomes singular as a result of touching characteristics, the condition for which can be expressed in terms of the solution of the momentum equations. The solutions to the momentum and energy equations remain regular. Asymptotic structures for a number of unsteady 3-D separating flows follow and depend on the symmetry properties of the flow. In the absence of any symmetry, the singularity structure just prior to separation is found to be quasi 2-D with a displacement thickness in the form of a crescent shaped ridge. Physically the singularities can be understood in terms of the behavior of a fluid element inside the boundary layer which contracts in a direction parallel to the boundary and expands normal to it, thus forcing the fluid above it to be ejected from the boundary layer.

UAV-borne coherent doppler lidar for marine atmospheric boundary layer observations

Science.gov (United States)

Wu, Songhua; Wang, Qichao; Liu, Bingyi; Liu, Jintao; Zhang, Kailin; Song, Xiaoquan

2018-04-01

A compact UAV-borne Coherent Doppler Lidar (UCDL) has been developed at the Ocean University of China for the observation of wind profile and boundary layer structure in Marine Atmospheric Boundary Layer (MABL). The design, specifications and motion-correction methodology of the UCDL are presented. Preliminary results of the first flight campaign in Hailing Island in December 2016 is discussed.

Bandgap tunability at single-layer molybdenum disulphide grain boundaries

KAUST Repository

Huang, Yu Li

2015-02-17

Two-dimensional transition metal dichalcogenides have emerged as a new class of semiconductor materials with novel electronic and optical properties of interest to future nanoelectronics technology. Single-layer molybdenum disulphide, which represents a prototype two-dimensional transition metal dichalcogenide, has an electronic bandgap that increases with decreasing layer thickness. Using high-resolution scanning tunnelling microscopy and spectroscopy, we measure the apparent quasiparticle energy gap to be 2.40±0.05 eV for single-layer, 2.10±0.05 eV for bilayer and 1.75±0.05 eV for trilayer molybdenum disulphide, which were directly grown on a graphite substrate by chemical vapour deposition method. More interestingly, we report an unexpected bandgap tunability (as large as 0.85±0.05 eV) with distance from the grain boundary in single-layer molybdenum disulphide, which also depends on the grain misorientation angle. This work opens up new possibilities for flexible electronic and optoelectronic devices with tunable bandgaps that utilize both the control of two-dimensional layer thickness and the grain boundary engineering.

On the role of acoustic feedback in boundary-layer instability.

Science.gov (United States)

Wu, Xuesong

2014-07-28

In this paper, the classical triple-deck formalism is employed to investigate two instability problems in which an acoustic feedback loop plays an essential role. The first concerns a subsonic boundary layer over a flat plate on which two well-separated roughness elements are present. A spatially amplifying Tollmien-Schlichting (T-S) wave between the roughness elements is scattered by the downstream roughness to emit a sound wave that propagates upstream and impinges on the upstream roughness to regenerate the T-S wave, thereby forming a closed feedback loop in the streamwise direction. Numerical calculations suggest that, at high Reynolds numbers and for moderate roughness heights, the long-range acoustic coupling may lead to absolute instability, which is characterized by self-sustained oscillations at discrete frequencies. The dominant peak frequency may jump from one value to another as the Reynolds number, or the distance between the roughness elements, is varied gradually. The second problem concerns the supersonic 'twin boundary layers' that develop along two well-separated parallel flat plates. The two boundary layers are in mutual interaction through the impinging and reflected acoustic waves. It is found that the interaction leads to a new instability that is absent in the unconfined boundary layer. © 2014 The Author(s) Published by the Royal Society. All rights reserved.

Experimental study of boundary-layer transition on an airfoil induced by periodically passing wake

Energy Technology Data Exchange (ETDEWEB)

Jeon, W.P. [Center for Turbulence and Flow Control Research Institute of Advanced Machinery and Design, Seoul National University (Korea); Park, T.C.; Kang, S.H. [School of Mechanical and Aerospace Engineering, Seoul National University (Korea)

2002-02-01

Hot-wire measurements are performed in boundary-layer flows developing on a NACA 0012 airfoil over which wakes pass periodically. The periodic wakes are generated by rotating circular cylinders clockwise or counterclockwise around the airfoil. The time- and phase-averaged mean streamwise velocities and turbulence fluctuations are measured to investigate the phenomena of wake-induced transition. Especially, the phase-averaged wall shear stresses are evaluated using a computational Preston tube method. The passing wakes significantly change the pressure distribution on the airfoil, which has influence on the transition process of the boundary layer. The orientation of the passing wake alters the pressure distribution in a different manner. Due to the passing wake, the turbulent patches are generated inside the laminar boundary layer on the airfoil, and the boundary layer becomes temporarily transitional. The patches propagate downstream at a speed smaller than the free-stream velocity and merge together further downstream. Relatively high values of phase-averaged turbulence fluctuations in the outer part of the boundary layer indicate the possibility that breakdown occurs in the outer layer away from the wall. It is confirmed that the phase-averaged mean velocity profile has two dips in the outer region of the transitional boundary layer for each passing cycle. (orig.)

Body surface adaptations to boundary-layer dynamics

NARCIS (Netherlands)

Videler, J.J.

1995-01-01

Evolutionary processes have adapted nektonic animals to interact efficiently with the water that surrounds them. Not all these adaptations serve the same purpose. This paper concentrates on reduction of drag due to friction in the boundary layer close to the body surface. Mucus, compliant skins,

Effects of micro-ramps on a shock wave/turbulent boundary layer interaction

NARCIS (Netherlands)

Blinde, P.L.; Humble, R.A.; Van Oudheusden, B.W.; Scarano, F.

2009-01-01

Stereoscopic particle image velocimetry is used to investigate the effects of micro-ramp sub-boundary layer vortex generators, on an incident shock wave/boundary layer interaction at Mach 1.84. Single- and double-row arrangements of micro-ramps are considered. The micro-ramps have a height of 20% of

The effect of small streamwise velocity distortion on the boundary layer flow over a thin flat plate with application to boundary layer stability theory

Science.gov (United States)

Goldstein, M. E.; Leib, S. J.; Cowley, S. J.

1990-01-01

Researchers show how an initially linear spanwise disturbance in the free stream velocity field is amplified by leading edge bluntness effects and ultimately leads to a small amplitude but linear spanwise motion far downstream from the edge. This spanwise motion is imposed on the boundary layer flow and ultimately causes an order-one change in its profile shape. The modified profiles are highly unstable and can support Tollmein-Schlichting wave growth well upstream of the theoretical lower branch of the neutral stability curve for a Blasius boundary layer.

Entropy Generation in Steady Laminar Boundary Layers with Pressure Gradients

Directory of Open Access Journals (Sweden)

Donald M. McEligot

2014-07-01

Full Text Available In an earlier paper in Entropy [1] we hypothesized that the entropy generation rate is the driving force for boundary layer transition from laminar to turbulent flow. Subsequently, with our colleagues we have examined the prediction of entropy generation during such transitions [2,3]. We found that reasonable predictions for engineering purposes could be obtained for flows with negligible streamwise pressure gradients by adapting the linear combination model of Emmons [4]. A question then arises—will the Emmons approach be useful for boundary layer transition with significant streamwise pressure gradients as by Nolan and Zaki [5]. In our implementation the intermittency is calculated by comparison to skin friction correlations for laminar and turbulent boundary layers and is then applied with comparable correlations for the energy dissipation coefficient (i.e., non-dimensional integral entropy generation rate. In the case of negligible pressure gradients the Blasius theory provides the necessary laminar correlations.

Enhanced air pollution via aerosol-boundary layer feedback in China.

Science.gov (United States)

Petäjä, T; Järvi, L; Kerminen, V-M; Ding, A J; Sun, J N; Nie, W; Kujansuu, J; Virkkula, A; Yang, X-Q; Fu, C B; Zilitinkevich, S; Kulmala, M

2016-01-12

Severe air pollution episodes have been frequent in China during the recent years. While high emissions are the primary reason for increasing pollutant concentrations, the ultimate cause for the most severe pollution episodes has remained unclear. Here we show that a high concentration of particulate matter (PM) will enhance the stability of an urban boundary layer, which in turn decreases the boundary layer height and consequently cause further increases in PM concentrations. We estimate the strength of this positive feedback mechanism by combining a new theoretical framework with ambient observations. We show that the feedback remains moderate at fine PM concentrations lower than about 200 μg m(-3), but that it becomes increasingly effective at higher PM loadings resulting from the combined effect of high surface PM emissions and massive secondary PM production within the boundary layer. Our analysis explains why air pollution episodes are particularly serious and severe in megacities and during the days when synoptic weather conditions stay constant.

Boundary-Layer Effects on Acoustic Transmission Through Narrow Slit Cavities.

Science.gov (United States)

Ward, G P; Lovelock, R K; Murray, A R J; Hibbins, A P; Sambles, J R; Smith, J D

2015-07-24

We explore the slit-width dependence of the resonant transmission of sound in air through both a slit array formed of aluminum slats and a single open-ended slit cavity in an aluminum plate. Our experimental results accord well with Lord Rayleigh's theory concerning how thin viscous and thermal boundary layers at a slit's walls affect the acoustic wave across the whole slit cavity. By measuring accurately the frequencies of the Fabry-Perot-like cavity resonances, we find a significant 5% reduction in the effective speed of sound through the slits when an individual viscous boundary layer occupies only 5% of the total slit width. Importantly, this effect is true for any airborne slit cavity, with the reduction being achieved despite the slit width being on a far larger scale than an individual boundary layer's thickness. This work demonstrates that the recent prevalent loss-free treatment of narrow slit cavities within acoustic metamaterials is unrealistic.

Thermocouple Rakes for Measuring Boundary Layer Flows Extremely Close to Surface

Science.gov (United States)

Hwang, Danny P.; Fralick, Gustave C.; Martin, Lisa C.; Blaha, Charles A.

2001-01-01

Of vital interest to aerodynamic researchers is precise knowledge of the flow velocity profile next to the surface. This information is needed for turbulence model development and the calculation of viscous shear force. Though many instruments can determine the flow velocity profile near the surface, none of them can make measurements closer than approximately 0.01 in. from the surface. The thermocouple boundary-layer rake can measure much closer to the surface than conventional instruments can, such as a total pressure boundary layer rake, hot wire, or hot film. By embedding the sensors (thermocouples) in the region where the velocity is equivalent to the velocity ahead of a constant thickness strut, the boundary-layer flow profile can be obtained. The present device fabricated at the NASA Glenn Research Center microsystem clean room has a heater made of platinum and thermocouples made of platinum and gold. Equal numbers of thermocouples are placed both upstream and downstream of the heater, so that the voltage generated by each pair at the same distance from the surface is indicative of the difference in temperature between the upstream and downstream thermocouple locations. This voltage differential is a function of the flow velocity, and like the conventional total pressure rake, it can provide the velocity profile. In order to measure flow extremely close to the surface, the strut is made of fused quartz with extremely low heat conductivity. A large size thermocouple boundary layer rake is shown in the following photo. The latest medium size sensors already provide smooth velocity profiles well into the boundary layer, as close as 0.0025 in. from the surface. This is about 4 times closer to the surface than the previously used total pressure rakes. This device also has the advantage of providing the flow profile of separated flow and also it is possible to measure simultaneous turbulence levels within the boundary layer.

Manipulation of Turbulent Boundary Layers Using Synthetic Jets

Science.gov (United States)

Berger, Zachary; Gomit, Guillaume; Lavoie, Philippe; Ganapathisubramani, Bharath

2015-11-01

This work focuses on the application of active flow control, in the form of synthetic jet actuators, of turbulent boundary layers. An array of 2 synthetic jets are oriented in the spanwise direction and located approximately 2.7 meters downstream from the leading edge of a flat plate. Actuation is applied perpendicular to the surface of the flat plate with varying blowing ratios and reduced frequencies (open-loop). Two-component large window particle image velocimetry (PIV) was performed at the University of Southampton, in the streamwise-wall-normal plane. Complementary stereo PIV measurements were performed at the University of Toronto Institute for Aerospace Studies (UTIAS), in the spanwise-wall-normal plane. The freestream Reynolds number is 3x104, based on the boundary layer thickness. The skin friction Reynolds number is 1,200 based on the skin friction velocity. The experiments at Southampton allow for the observation of the control effects as the flow propagates downstream. The experiments at UTIAS allow for the observation of the streamwise vorticity induced from the actuation. Overall the two experiments provide a 3D representation of the flow field with respect to actuation effects. The current work focuses on the comparison of the two experiments, as well as the effects of varying blowing ratios and reduced frequencies on the turbulent boundary layer. Funded Supported by Airbus.

Receptivity of Hypersonic Boundary Layers to Acoustic and Vortical Disturbances (Invited)

Science.gov (United States)

Balakumar, P.

2015-01-01

Boundary-layer receptivity to two-dimensional acoustic and vortical disturbances for hypersonic flows over two-dimensional and axi-symmetric geometries were numerically investigated. The role of bluntness, wall cooling, and pressure gradients on the receptivity and stability were analyzed and compared with the sharp nose cases. It was found that for flows over sharp nose geometries in adiabatic wall conditions the instability waves are generated in the leading-edge region and that the boundary layer is much more receptive to slow acoustic waves as compared to the fast waves. The computations confirmed the stabilizing effect of nose bluntness and the role of the entropy layer in the delay of boundary layer transition. The receptivity coefficients in flows over blunt bodies are orders of magnitude smaller than that for the sharp cone cases. Wall cooling stabilizes the first mode strongly and destabilizes the second mode. However, the receptivity coefficients are also much smaller compared to the adiabatic case. The adverse pressure gradients increased the unstable second mode regions.

Large Eddy Simulations of a Bottom Boundary Layer Under a Shallow Geostrophic Front

Science.gov (United States)

Bateman, S. P.; Simeonov, J.; Calantoni, J.

2017-12-01

The unstratified surf zone and the stratified shelf waters are often separated by dynamic fronts that can strongly impact the character of the Ekman bottom boundary layer. Here, we use large eddy simulations to study the turbulent bottom boundary layer associated with a geostrophic current on a stratified shelf of uniform depth. The simulations are initialized with a spatially uniform vertical shear that is in geostrophic balance with a pressure gradient due to a linear horizontal temperature variation. Superposed on the temperature front is a stable vertical temperature gradient. As turbulence develops near the bottom, the turbulence-induced mixing gradually erodes the initial uniform temperature stratification and a well-mixed layer grows in height until the turbulence becomes fully developed. The simulations provide the spatial distribution of the turbulent dissipation and the Reynolds stresses in the fully developed boundary layer. We vary the initial linear stratification and investigate its effect on the height of the bottom boundary layer and the turbulence statistics. The results are compared to previous models and simulations of stratified bottom Ekman layers.

Computational Study of Hypersonic Boundary Layer Stability on Cones

Science.gov (United States)

Gronvall, Joel Edwin

Due to the complex nature of boundary layer laminar-turbulent transition in hypersonic flows and the resultant effect on the design of re-entry vehicles, there remains considerable interest in developing a deeper understanding of the underlying physics. To that end, the use of experimental observations and computational analysis in a complementary manner will provide the greatest insights. It is the intent of this work to provide such an analysis for two ongoing experimental investigations. The first focuses on the hypersonic boundary layer transition experiments for a slender cone that are being conducted at JAXA's free-piston shock tunnel HIEST facility. Of particular interest are the measurements of disturbance frequencies associated with transition at high enthalpies. The computational analysis provided for these cases included two-dimensional CFD mean flow solutions for use in boundary layer stability analyses. The disturbances in the boundary layer were calculated using the linear parabolized stability equations. Estimates for transition locations, comparisons of measured disturbance frequencies and computed frequencies, and a determination of the type of disturbances present were made. It was found that for the cases where the disturbances were measured at locations where the flow was still laminar but nearly transitional, that the highly amplified disturbances showed reasonable agreement with the computations. Additionally, an investigation of the effects of finite-rate chemistry and vibrational excitation on flows over cones was conducted for a set of theoretical operational conditions at the HIEST facility. The second study focuses on transition in three-dimensional hypersonic boundary layers, and for this the cone at angle of attack experiments being conducted at the Boeing/AFOSR Mach-6 quiet tunnel at Purdue University were examined. Specifically, the effect of surface roughness on the development of the stationary crossflow instability are investigated

Asymmetric simple exclusion process with position-dependent hopping rates: Phase diagram from boundary-layer analysis.

Science.gov (United States)

Mukherji, Sutapa

2018-03-01

In this paper, we study a one-dimensional totally asymmetric simple exclusion process with position-dependent hopping rates. Under open boundary conditions, this system exhibits boundary-induced phase transitions in the steady state. Similarly to totally asymmetric simple exclusion processes with uniform hopping, the phase diagram consists of low-density, high-density, and maximal-current phases. In various phases, the shape of the average particle density profile across the lattice including its boundary-layer parts changes significantly. Using the tools of boundary-layer analysis, we obtain explicit solutions for the density profile in different phases. A detailed analysis of these solutions under different boundary conditions helps us obtain the equations for various phase boundaries. Next, we show how the shape of the entire density profile including the location of the boundary layers can be predicted from the fixed points of the differential equation describing the boundary layers. We discuss this in detail through several examples of density profiles in various phases. The maximal-current phase appears to be an especially interesting phase where the boundary layer flows to a bifurcation point on the fixed-point diagram.

Provenance of the K/T boundary layers

International Nuclear Information System (INIS)

Hildebrand, A.R.; Boynton, W.V.

1988-01-01

An array of chemical, physical and isotopic evidence indicates that an impact into oceanic crust terminated the Cretaceous Period. Approximately 1500 cu km of debris, dispersed by the impact fireball, fell out globally in marine and nonmarine environments producing a 2 to 4 mm thick layer (fireball layer). In North American locales, the fireball layer overlies a 15 to 25 mm thick layer of similar but distinct composition. This 15 to 25 mm layer (ejecta layer) may represent approximately 1000 cu km of lower energy ejecta from a nearby impact site. Isotopic and chemical evidence supports a mantle provenance for the bulk of the layers. The extraordinary REE pattern of the boundary clays was modelled as a mixture of oceanic crust, mantle, and approximately 10 percent continental material. The results are presented. If the siderophiles of the ejecta layer were derived solely from the mantle, a test may be available to see if the siderophile element anomaly of the fireball layer had an extraterrestrial origin. Radiogenic Os-187 is depleted in the mantle relative to an undifferentiated chondritic source. Os-187/Os-186 ratios of 1.049 and 1.108 were calculated for the ejecta and fireball layers, respectively

Optimal Growth in Hypersonic Boundary Layers

Science.gov (United States)

Paredes, Pedro; Choudhari, Meelan M.; Li, Fei; Chang, Chau-Lyan

2016-01-01

The linear form of the parabolized linear stability equations is used in a variational approach to extend the previous body of results for the optimal, nonmodal disturbance growth in boundary-layer flows. This paper investigates the optimal growth characteristics in the hypersonic Mach number regime without any high-enthalpy effects. The influence of wall cooling is studied, with particular emphasis on the role of the initial disturbance location and the value of the spanwise wave number that leads to the maximum energy growth up to a specified location. Unlike previous predictions that used a basic state obtained from a self-similar solution to the boundary-layer equations, mean flow solutions based on the full Navier-Stokes equations are used in select cases to help account for the viscous- inviscid interaction near the leading edge of the plate and for the weak shock wave emanating from that region. Using the full Navier-Stokes mean flow is shown to result in further reduction with Mach number in the magnitude of optimal growth relative to the predictions based on the self-similar approximation to the base flow.

Boundary layer separation method for recycling of sodium ions from industrial wastewater.

Science.gov (United States)

Petho, Dóra; Horváth, Géza; Liszi, János; Tóth, Imre; Paor, Dávid

2010-12-01

The most effective technological solution for waste treatment is recycling. We have developed a new method for the treatment of industrial wastewaters and have called it the boundary layer separation method (BLSM). We have used the phenomenon that, on the surface of an electrically charged electrode, ions can be enriched in the boundary layer, as compared with the inside of the phase. The essence of the method is that, with an appropriately chosen velocity, the boundary layer can be removed from the wastewater, and the boundary layer, which is rich in ions, can be recycled. The BLSM can be executed as a cyclic procedure. The capacitance of the boundary layer was examined. The best mass transport can be achieved with the use of 1000 and 1200 mV polarization potentials in the examined system, with its value being 1200 mg/m2 per cycle. The necessary operation times were determined by the examination of the velocity of the electrochemical processes. When using 1000 mV polarization potential, the necessary adsorption time is at least 25 seconds, and the desorption time at least 300 seconds. The advantage of the procedure is that it does not use dangerous chemicals, only inert electrodes. The drawback is that it is not selective to ions, the achievable separation in one step is low, and the hydrogen that emerges during the electrolysis might be dangerous.

Prandtl boundary layer expansions of steady Navier-Stokes flows over a moving plate

OpenAIRE

Guo, Yan; Nguyen, Toan T.

2014-01-01

This paper concerns the validity of the Prandtl boundary layer theory in the inviscid limit for steady incompressible Navier-Stokes flows. The stationary flows, with small viscosity, are considered on $[0,L]\\times \\mathbb{R}_{+}$, assuming a no-slip boundary condition over a moving plate at $y=0$. We establish the validity of the Prandtl boundary layer expansion and its error estimates.

Experimental demonstration of the Rayleigh acoustic viscous boundary layer theory.

Science.gov (United States)

Castrejón-Pita, J R; Castrejón-Pita, A A; Huelsz, G; Tovar, R

2006-03-01

Amplitude and phase velocity measurements on the laminar oscillatory viscous boundary layer produced by acoustic waves are presented. The measurements were carried out in acoustic standing waves in air with frequencies of 68.5 and 114.5 Hz using laser Doppler anemometry and particle image velocimetry. The results obtained by these two techniques are in good agreement with the predictions made by the Rayleigh viscous boundary layer theory and confirm the existence of a local maximum of the velocity amplitude and its expected location.

Grain boundary layer behavior in ZnO/Si heterostructure

International Nuclear Information System (INIS)

Liu Bingce; Liu Cihui; Yi Bo

2010-01-01

The grain boundary layer behavior in ZnO/Si heterostucture is investigated. The current-voltage (I-V) curves, deep level transient spectra (DLTS) and capacitance-voltage (C-V) curves are measured. The transport currents of ZnO/Si heterojunction are dominated by grain boundary layer as high densities of interfacial states existed. The interesting phenomenon that the crossing of In I-V curves of ZnO/Si heterojunction at various measurement temperatures and the decrease of its effective barrier height with the decrement of temperature are in contradiction with the ideal heterojunction thermal emission model is observed. The details will be discussed in the following. (semiconductor physics)

A numerical investigation of the impact of surface topology on laminar boundary layers

Science.gov (United States)

Beratlis, Nikolaos; Squires, Kyle; Balaras, Elias

2015-11-01

Surface topology, such as dimples or trip wires, has been utilized in the past for passive separation control over bluff bodies. The majority of the work, however, has focused on the indirect effects on the drag and lift forces, while the details of the impact on the boundary layer evolution are not well understood. Here we report a series of DNS of flow over a single row of spherical and hexagonal dimples, as well as, circular grooves. The Reynolds number and the thickness of the incoming laminar boundary layer is carefully controlled. In all cases transition to turbulence downstream of the elements comes with reorientation of the spanwise vorticity into hairpin like vortices. Although qualitatively the transition mechanism amongst different dimples and grooves is similar, important quantitative differences exist: two-dimensional geometries such as the groove, are more stable than three-dimensional geometries. In addition, it was found that the cavity geometry controls the initial thickness of the boundary layer and practically results in a shift of the virtual origin of the turbulent boundary layer. Important differences in the momentum transport downstream of the dimples exist, but in all cases the boundary layer evolves in a self-similar manner.

Quantifying the relationship between PM2.5 concentration, visibility and planetary boundary layer height for long-lasting haze and fog-haze mixed events in Beijing

Science.gov (United States)

Luan, Tian; Guo, Xueliang; Guo, Lijun; Zhang, Tianhang

2018-01-01

Air quality and visibility are strongly influenced by aerosol loading, which is driven by meteorological conditions. The quantification of their relationships is critical to understanding the physical and chemical processes and forecasting of the polluted events. We investigated and quantified the relationship between PM2.5 (particulate matter with aerodynamic diameter is 2.5 µm and less) mass concentration, visibility and planetary boundary layer (PBL) height in this study based on the data obtained from four long-lasting haze events and seven fog-haze mixed events from January 2014 to March 2015 in Beijing. The statistical results show that there was a negative exponential function between the visibility and the PM2.5 mass concentration for both haze and fog-haze mixed events (with the same R2 of 0.80). However, the fog-haze events caused a more obvious decrease of visibility than that for haze events due to the formation of fog droplets that could induce higher light extinction. The PM2.5 concentration had an inversely linear correlation with PBL height for haze events and a negative exponential correlation for fog-haze mixed events, indicating that the PM2.5 concentration is more sensitive to PBL height in fog-haze mixed events. The visibility had positively linear correlation with the PBL height with an R2 of 0.35 in haze events and positive exponential correlation with an R2 of 0.56 in fog-haze mixed events. We also investigated the physical mechanism responsible for these relationships between visibility, PM2.5 concentration and PBL height through typical haze and fog-haze mixed event and found that a double inversion layer formed in both typical events and played critical roles in maintaining and enhancing the long-lasting polluted events. The variations of the double inversion layers were closely associated with the processes of long-wave radiation cooling in the nighttime and short-wave solar radiation reduction in the daytime. The upper-level stable

Proceedings of the 17th and 18th NAL Workshops on Investigation and Control of Boundary-Layer Transition

OpenAIRE

National Aerospace Laboratory; 航空宇宙技術研究所

1996-01-01

The following topics were discussed: vortex shedding, laminar boundary layer measurement, vortex ring, turbulent flow measurement, high Reynolds number turbulence, pulsed flow, boundary layer instability, Ekman boundary layer, sound receptivity, Tollmien-Schlichting wave in supersonic boundary layer, flow field instability, turbulent flow pattern, vorticity distribution in shear flow, turbulence wedge, streamwise vortex mixing, thermal convection, oblique wave generation in boundary layer, in...

Evaluation of Planetary Boundary Layer Scheme Sensitivities for the Purpose of Parameter Estimation

Science.gov (United States)

Meteorological model errors caused by imperfect parameterizations generally cannot be overcome simply by optimizing initial and boundary conditions. However, advanced data assimilation methods are capable of extracting significant information about parameterization behavior from ...

Derivation of Zagarola-Smits scaling in zero-pressure-gradient turbulent boundary layers

Science.gov (United States)

Wei, Tie; Maciel, Yvan

2018-01-01

This Rapid Communication derives the Zagarola-Smits scaling directly from the governing equations for zero-pressure-gradient turbulent boundary layers (ZPG TBLs). It has long been observed that the scaling of the mean streamwise velocity in turbulent boundary layer flows differs in the near surface region and in the outer layer. In the inner region of small-velocity-defect boundary layers, it is generally accepted that the proper velocity scale is the friction velocity, uτ, and the proper length scale is the viscous length scale, ν /uτ . In the outer region, the most generally used length scale is the boundary layer thickness, δ . However, there is no consensus on velocity scales in the outer layer. Zagarola and Smits [ASME Paper No. FEDSM98-4950 (1998)] proposed a velocity scale, U ZS=(δ1/δ ) U∞ , where δ1 is the displacement thickness and U∞ is the freestream velocity. However, there are some concerns about Zagarola-Smits scaling due to the lack of a theoretical base. In this paper, the Zagarola-Smits scaling is derived directly from a combination of integral, similarity, and order-of-magnitude analysis of the mean continuity equation. The analysis also reveals that V∞, the mean wall-normal velocity at the edge of the boundary layer, is a proper scale for the mean wall-normal velocity V . Extending the analysis to the streamwise mean momentum equation, we find that the Reynolds shear stress in ZPG TBLs scales as U∞V∞ in the outer region. This paper also provides a detailed analysis of the mass and mean momentum balance in the outer region of ZPG TBLs.

The kinetic boundary layer around an absorbing sphere and the growth of small droplets

International Nuclear Information System (INIS)

Widder, M.E.; Titulaer, U.M.

1989-01-01

Deviations from the classical Smoluchowski expression for the growth rate of a droplet in a supersaturated vapor can be expected when the droplet radius is not large compared to the mean free path of a vapor molecule. The growth rate then depends significantly on the structure of the kinetic boundary layer around a sphere. The authors consider this kinetic boundary layer for a dilute system of Brownian particles. For this system a large class of boundary layer problems for a planar wall have been solved. They show how the spherical boundary layer can be treated by a perturbation expansion in the reciprocal droplet radius. In each order one has to solve a finite number of planar boundary layer problems. The first two corrections to the planar problem are calculated explicitly. For radii down to about two velocity persistence lengths (the analog of the mean free path for a Brownian particle) the successive approximations for the growth rate agree to within a few percent. A reasonable estimate of the growth rate for all radii can be obtained by extrapolating toward the exactly known value at zero radius. Kinetic boundary layer effects increase the time needed for growth from 0 to 10 (or 2 1/2) velocity persistence lengths by roughly 35% (or 175%)

The effects of external conditions in turbulent boundary layers

Science.gov (United States)

Brzek, Brian G.

The effects of multiple external conditions on turbulent boundary layers were studied in detail. These external conditions include: surface roughness, upstream turbulence intensity, and pressure gradient. Furthermore, the combined effects of these conditions show the complicated nature of many realistic flow conditions. It was found that the effects of surface roughness are difficult to generalize, given the importance of so many parameters. These parameters include: roughness geometry, roughness regime, roughness height to boundary layer thickness, (k/delta), roughness parameter, ( k+), Reynolds number, and roughness function (Delta B+). A further complication, is the difficulty in computing the wall shear stress, tauw/rho. For the sand grain type roughness, the mean velocity and Reynolds stresses were studied in inner and outer variables, as well as, boundary layer parameters, anisotropy tensor, production term, and viscous stress and form drag contributions. To explore the effects of roughness and Reynolds number dependence in the boundary layer, a new experiment was carefully designed to properly capture the x-dependence of the single-point statistics. It was found that roughness destroys the viscous layer near the wall, thus, reducing the contribution of the viscous stress in the wall region. As a result, the contribution in the skin friction due to form drag increases, while the viscous stress decreases. This yields Reynolds number invariance in the skin friction, near-wall roughness parameters, and inner velocity profiles as k + increases into the fully rough regime. However, in the transitionally rough regime, (i.e., 5 component shows the largest influence of roughness, where the high peak near the wall was decreased and became nearly flat for the fully rough regime profiles. In addition, the Reynolds stresses in outer variables show self-similarity for fixed experimental conditions. However, as the roughness parameter, k +, increases, all Reynolds stress

Factors Influencing Pitot Probe Centerline Displacement in a Turbulent Supersonic Boundary Layer

Science.gov (United States)

Grosser, Wendy I.

1997-01-01

When a total pressure probe is used for measuring flows with transverse total pressure gradients, a displacement of the effective center of the probe is observed (designated Delta). While this phenomenon is well documented in incompressible flow and supersonic laminar flow, there is insufficient information concerning supersonic turbulent flow. In this study, three NASA Lewis Research Center Supersonic Wind Tunnels (SWT's) were used to investigate pitot probe centerline displacement in supersonic turbulent boundary layers. The relationship between test conditions and pitot probe centerline displacement error was to be determined. For this investigation, ten circular probes with diameter-to-boundary layer ratios (D/delta) ranging from 0.015 to 0.256 were tested in the 10 ft x 10 ft SWT, the 15 cm x 15 cm SWT, and the 1 ft x 1 ft SWT. Reynolds numbers of 4.27 x 10(exp 6)/m, 6.00 x 10(exp 6)/in, 10.33 x 10(exp 6)/in, and 16.9 x 10(exp 6)/m were tested at nominal Mach numbers of 2.0 and 2.5. Boundary layer thicknesses for the three tunnels were approximately 200 mm, 13 mm, and 30 mm, respectively. Initial results indicate that boundary layer thickness, delta, and probe diameter, D/delta play a minimal role in pitot probe centerline offset error, Delta/D. It appears that the Mach gradient, dM/dy, is an important factor, though the exact relationship has not yet been determined. More data is needed to fill the map before a conclusion can be drawn with any certainty. This research provides valuable supersonic, turbulent boundary layer data from three supersonic wind tunnels with three very different boundary layers. It will prove a valuable stepping stone for future research into the factors influencing pitot probe centerline offset error.

Air motions accompanying the development of a planetary wave critical layer

Science.gov (United States)

Salby, Murry L.; O'Sullivan, Donal; Callaghan, Patrick; Garcia, Rolando R.

1990-01-01

The horizontal air motions accompanying the development of a planetary wave critical layer are presently investigated on the sphere, in terms of wave amplitude, the characteristics of the zonal flow, and dissipation. While attention is given to adiabatic motions, which should furnish an upper bound on the redistribution of conserved quantities by eddy stirring, nonconservative processes may be important in determining how large a role eddy stirring actually plays in the redistribution of atmospheric constituents. Nonconservative processes may also influence tracer distributions by directly affecting dynamics.

Instability waves and transition in adverse-pressure-gradient boundary layers

Science.gov (United States)

Bose, Rikhi; Zaki, Tamer A.; Durbin, Paul A.

2018-05-01

Transition to turbulence in incompressible adverse-pressure-gradient (APG) boundary layers is investigated by direct numerical simulations. Purely two-dimensional instability waves develop on the inflectional base velocity profile. When the boundary layer is perturbed by isotropic turbulence from the free stream, streamwise elongated streaks form and may interact with the instability waves. Subsequent mechanisms that trigger transition depend on the intensity of the free-stream disturbances. All evidence from the present simulations suggest that the growth rate of instability waves is sufficiently high to couple with the streaks. Under very low levels of free-stream turbulence (˜0.1 % ), transition onset is highly sensitive to the inlet disturbance spectrum and is accelerated if the spectrum contains frequency-wave-number combinations that are commensurate with the instability waves. Transition onset and completion in this regime is characterized by formation and breakdown of Λ vortices, but they are more sporadic than in natural transition. Beneath free-stream turbulence with higher intensity (1-2 % ), bypass transition mechanisms are dominant, but instability waves are still the most dominant disturbances in wall-normal and spanwise perturbation spectra. Most of the breakdowns were by disturbances with critical layers close to the wall, corresponding to inner modes. On the other hand, the propensity of an outer mode to occur increases with the free-stream turbulence level. Higher intensity free-stream disturbances induce strong streaks that favorably distort the boundary layer and suppress the growth of instability waves. But the upward displacement of high amplitude streaks brings them to the outer edge of the boundary layer and exposes them to ambient turbulence. Consequently, high-amplitude streaks exhibit an outer-mode secondary instability.

Evaluation of the Atmospheric Boundary-Layer Electrical Variability

Science.gov (United States)

Anisimov, Sergey V.; Galichenko, Sergey V.; Aphinogenov, Konstantin V.; Prokhorchuk, Aleksandr A.

2017-12-01

Due to the chaotic motion of charged particles carried by turbulent eddies, electrical quantities in the atmospheric boundary layer (ABL) have short-term variability superimposed on long-term variability caused by sources from regional to global scales. In this study the influence of radon exhalation rate, aerosol distribution and turbulent transport efficiency on the variability of fair-weather atmospheric electricity is investigated via Lagrangian stochastic modelling. For the mid-latitude lower atmosphere undisturbed by precipitation, electrified clouds, or thunderstorms, the model is capable of reproducing the diurnal variation in atmospheric electrical parameters detected by ground-based measurements. Based on the analysis of field observations and numerical simulation it is found that the development of the convective boundary layer, accompanied by an increase in turbulent kinetic energy, forms the vertical distribution of radon and its decaying short-lived daughters to be approximately coincident with the barometric law for several eddy turnover times. In the daytime ABL the vertical distribution of atmospheric electrical conductivity tends to be uniform except within the surface layer, due to convective mixing of radon and its radioactive decay products. At the same time, a decrease in the conductivity near the ground is usually observed. This effect leads to an enhanced ground-level atmospheric electric field compared to that normally observed in the nocturnal stably-stratified boundary layer. The simulation showed that the variability of atmospheric electric field in the ABL associated with internal origins is significant in comparison to the variability related to changes in global parameters. It is suggested that vertical profiles of electrical quantities can serve as informative parameters on ABL turbulent dynamics and can even more broadly characterize the state of the environment.

Shear flow beneath oceanic plates: Local nonsimilarity boundary layers for olivine rheology

International Nuclear Information System (INIS)

Yuen, D.A.; Tovish, A.; Schubert, G.

1978-01-01

The principle of local similarity, which has been used to model the two-dimensional boundary layers in the oceanic upper mantle, permits calculation of the temperature, velocity, and stress fields with essentially analytic techniques. Finite difference numerical methods are hard pressed to resolve the detail required by the large variation of viscosity between the lithosphere and the asthenosphere. In this paper the local similarity approximation has been justified by quantitatively evaluating the effect of nonsimilarity due to viscous heating, nonlinear temperature- and pressure-dependent rheology, buoyancy, adiabatic cooling, etc. Nonsimilar effects produce only small modifications of the locally similar boundary layers; important geophysical observables such as surface heat flux and ocean floor topography are given to better than 10% by the locally similar solution. A posteriori evaluations of the term neglected in the boundary layer simplification of the complete equations have been conducted on the locally similar temperature and velocity profiles close to the spreading ridge. The boundary layer models are valid to depths of 100 km at 3 m.y. and 10 km at 0.3 m.y

Transient Growth Analysis of Compressible Boundary Layers with Parabolized Stability Equations

Science.gov (United States)

Paredes, Pedro; Choudhari, Meelan M.; Li, Fei; Chang, Chau-Lyan

2016-01-01

The linear form of parabolized linear stability equations (PSE) is used in a variational approach to extend the previous body of results for the optimal, non-modal disturbance growth in boundary layer flows. This methodology includes the non-parallel effects associated with the spatial development of boundary layer flows. As noted in literature, the optimal initial disturbances correspond to steady counter-rotating stream-wise vortices, which subsequently lead to the formation of stream-wise-elongated structures, i.e., streaks, via a lift-up effect. The parameter space for optimal growth is extended to the hypersonic Mach number regime without any high enthalpy effects, and the effect of wall cooling is studied with particular emphasis on the role of the initial disturbance location and the value of the span-wise wavenumber that leads to the maximum energy growth up to a specified location. Unlike previous predictions that used a basic state obtained from a self-similar solution to the boundary layer equations, mean flow solutions based on the full Navier-Stokes (NS) equations are used in select cases to help account for the viscous-inviscid interaction near the leading edge of the plate and also for the weak shock wave emanating from that region. These differences in the base flow lead to an increasing reduction with Mach number in the magnitude of optimal growth relative to the predictions based on self-similar mean-flow approximation. Finally, the maximum optimal energy gain for the favorable pressure gradient boundary layer near a planar stagnation point is found to be substantially weaker than that in a zero pressure gradient Blasius boundary layer.

Plasma-based actuators for turbulent boundary layer control in transonic flow

Science.gov (United States)

Budovsky, A. D.; Polivanov, P. A.; Vishnyakov, O. I.; Sidorenko, A. A.

2017-10-01

The study is devoted to development of methods for active control of flow structure typical for the aircraft wings in transonic flow with turbulent boundary layer. The control strategy accepted in the study was based on using of the effects of plasma discharges interaction with miniature geometrical obstacles of various shapes. The conceptions were studied computationally using 3D RANS, URANS approaches. The results of the computations have shown that energy deposition can significantly change the flow pattern over the obstacles increasing their influence on the flow in boundary layer region. Namely, one of the most interesting and promising data were obtained for actuators basing on combination of vertical wedge with asymmetrical plasma discharge. The wedge considered is aligned with the local streamlines and protruding in the flow by 0.4-0.8 of local boundary layer thickness. The actuator produces negligible distortion of the flow at the absence of energy deposition. Energy deposition along the one side of the wedge results in longitudinal vortex formation in the wake of the actuator providing momentum exchange in the boundary layer. The actuator was manufactured and tested in wind tunnel experiments at Mach number 1.5 using the model of flat plate. The experimental data obtained by PIV proved the availability of the actuator.

Experimental investigation of a supercritical airfoil boundary layer in pitching motion

Energy Technology Data Exchange (ETDEWEB)

Masdari, Mehran; Tabrizian, Arshia [Faculty of New Science and Technology, University of Tehran, Tehran (Iran, Islamic Republic of); Jahanmiri, Mohsen; Gorji, Mohamamd [Dept. of Mechanical and Aerospace Engineering, Shiraz University of Technology, Shiraz (Iran, Islamic Republic of); Soltani, Mohammad Reza [Dept. of Aerospace Engineering, Sharif University of Technology, Tehran (Iran, Islamic Republic of)

2017-01-15

In this study, the boundary layer velocity profile on the upper surface of a supercritical airfoil in a forced sinusoidal pitching motion was measured and experimentally investigated. Measurements were performed using a boundary layer rake, including total pressure tubes positioned at 25 % of the chord far from the leading edge on the upper surface. For static measurements, the effects of the angle of attack between −3° and 14° and free-stream velocity between 40 m/s and 70 m/s were investigated; for dynamic measurements, the effects of oscillation amplitude variation between ±3° and ±10°, reduced frequency from 0.007 to 0.0313, and mean angle of attack between −3° and 6° were studied during one oscillation cycle. Results indicated that the boundary layer thickness decreased in upstroke motion. Increasing the oscillation frequency led to the extension of hysteresis loops. Fast Fourier transform was used on pressure signals to study the amplitude of the dominant frequency in the velocity profile. Spectral analysis showed that the dominant forced frequency of oscillation in the boundary layer and the amplitude of this frequency were varied by increasing the reduced frequency and other parameters.