Self-similarity of nonstationary boundary-layer motions

1976 ◽  
Vol 16 (4) ◽  
pp. 578-581
Author(s):  
E. V. Prozorova
Keyword(s):  
Boundary Layer ◽  
Self Similarity ◽  
Nonstationary Boundary

Nonstationary Boundary Layer of a Fluid with the Ladyzhenskaya Rheological Law

2020 ◽  
Vol 249 (6) ◽  
pp. 850-863
Author(s):  
R. R. Bulatova ◽  
V. N. Samokhin ◽  
G. A. Chechkin
Keyword(s):  
Boundary Layer ◽  
Nonstationary Boundary

Exchange coefficients derived from GPS-sonde and SFMR measurements in hurricane conditions

2020 ◽  
Author(s):  
Olga Ermakova ◽  
Nikita Rusakov ◽  
Evgeny Poplavsky ◽  
Yuliya Troitskaya ◽  
Daniil Sergeev ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Wind Speed ◽  
Atmospheric Boundary Layer ◽  
Moisture Transfer ◽  
Weather Forecasting ◽  
Aerodynamic Drag ◽  
Remote Sensing Data ◽  
Thermodynamic Quantities ◽  
Self Similarity ◽  
Heat And Moisture

<p>Insufficient knowledge of the atmosphere layer momentum, heat and moisture transfer between the wavy water surface and marine atmospheric boundary layer under hurricane conditions lead to the uncertainties while using weather forecasting models and models of climate. In particular, there is a significant lack of data for heat and moisture exchange coefficients. In this regard, it is necessary to analyze and process the vertical profiles of wind speed and thermodynamic quantities. The present study is concerned with the analysis and processing of measurements from the NOAA falling GPS-sondes for hurricanes of categories 4 and 5 of 2003-2017, which represent an array of data on wind speed, temperature, altitude, coordinates, etc.</p><p>The proposed approach for describing a turbulent boundary layer formed in hurricane conditions is based on the use of the self-similarity properties of the velocity and enthalpy profiles in the atmospheric boundary layer, which includes a layer of constant flows, transferring into its “wake” part with height. Based on the proposed approach, the aerodynamic drag coefficients Cd and the enthalpy exchange coefficient Ck for a selected group of hurricanes were restored. As the value of Ck/Cd represents a determining factor in the formation of a hurricane, the dependence of this ratio on the wind speed was constructed.</p><p>This work was supported by the RFBR projects No 19-05-00249, 19-05-00366, 18-35-20068 (remote sensing data analysis) and RSF No 19-17-00209 (GPS-sonde data assimilation and processing).</p>

An Investigation of the Scales in Transitional Boundary Layers Under High Free-Stream Turbulence Conditions

2002 ◽  
Author(s):  
Ralph J. Volino
Keyword(s):  
Boundary Layer ◽  
Free Stream ◽  
Dominant Frequency ◽  
Intermittent Flow ◽  
Self Similarity ◽  
Free Stream Turbulence ◽  
Transitional Boundary Layer ◽  
Streamwise Location ◽  
Transition Models ◽  
Dominant Frequencies

The scales in a transitional boundary layer subject to high (initially 8%) free-stream turbulence and strong acceleration (K as high as 9×10−6) have been investigated using wavelet spectral analysis and conditional sampling of experimental data. The boundary layer shows considerable evolution through transition, with a general shift from the lower frequencies induced by the free-stream unsteadiness to higher frequencies associated with near wall generated turbulence. Within the non-turbulent zone of the intermittent flow, there is considerable self-similarity in the spectra from the beginning of transition to the end, with the dominant frequencies in the boundary layer remaining constant at about the dominant frequency of the free-stream. The frequencies of the energy containing scales in the turbulent zone change with streamwise location and are significantly higher than in the non-turbulent zone. When normalized on the local viscous length scale and velocity, however, the turbulent zone spectra also show good self-similarity throughout transition. Turbulence dissipation occurs almost exclusively in the turbulent zone. The velocity fluctuations associated with dissipation are isotropic, and their normalized spectra at upstream and downstream stations are nearly identical. The distinct differences between the turbulent and non-turbulent zones suggest the potential utility of intermittency based transition models in which these zones are treated separately. The self-similarity noted in both energy containing and dissipation scales in both zones suggests possibilities for simplifying the modeling for each zone.

Development for wind friction velocity retrieval algorithm based on the SFMR and NOAA dropwindsondes measurements in hurricane conditions

2021 ◽  
Author(s):  
Evgeny Poplavsky ◽  
Nikita Rusakov ◽  
Olga Ermakova ◽  
Daniil Sergeev ◽  
Yuliya Troitskaya ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Wind Speed ◽  
Atmospheric Boundary Layer ◽  
Friction Velocity ◽  
Microwave Radiometer ◽  
Field Measurements ◽  
Retrieval Algorithm ◽  
Self Similarity ◽  
Defect Profile ◽  
Stepped Frequency

<p>The work is concerned with the development of a method for the retrieval of tropical cyclones boundary atmospheric layer parameters, namely the wind friction velocity and wind speed at meteorological height. For the analysis, we used the results of field measurements of wind speed profiles from dropwindsondes launched from National Oceanic and Atmospheric Administration (NOAA) aircraft and collocated data from the Stepped-Frequency Microwave Radiometer (SFMR) located onboard of the same aircraft.</p><p>The results of radiometric measurements were used to obtain the emissivity values, which were compared with the field data obtained from the falling dropwindsondes. Using the algorithm taking into account the self-similarity of the velocity defect profile (Ermakova et al., 2019), the parameters of the atmospheric boundary layer were determined from the data measured by dropwindsondes. This algorithm gives an opportunity to obtain the wind speed value at meteorological height and wind friction velocity from the averaged data in the wake part of the profiles of the marine atmospheric boundary layer.</p><p>A comparison of the wind speed U10 dependencies, retrieved from the SFMR data and measurements from dropwindsondes, with the similar dependencies obtained in (Uhlhorn et al., 2007), was made, and their satisfactory agreement was demonstrated. This work was supported by the RFBR projects No. 19-05-00249, 19-05-00366.</p>

scholarly journals Transition to turbulence in the rotating disk boundary layer of a rotor–stator cavity

2018 ◽  
Vol 848 ◽  
pp. 631-647 ◽  
Author(s):  
Eunok Yim ◽  
J.-M. Chomaz ◽  
D. Martinand ◽  
E. Serre
Keyword(s):  
Boundary Layer ◽  
Similarity Solution ◽  
Rotating Disk ◽  
Transition To Turbulence ◽  
Mean Flow ◽  
Self Similarity ◽  
Mean Velocity ◽  
Global Mode ◽  
Spatial Growth ◽  
The Mean

The transition to turbulence in the rotating disk boundary layer is investigated in a closed cylindrical rotor–stator cavity via direct numerical simulation (DNS) and linear stability analysis (LSA). The mean flow in the rotor boundary layer is qualitatively similar to the von Kármán self-similarity solution. The mean velocity profiles, however, slightly depart from theory as the rotor edge is approached. Shear and centrifugal effects lead to a locally more unstable mean flow than the self-similarity solution, which acts as a strong source of perturbations. Fluctuations start rising there, as the Reynolds number is increased, eventually leading to an edge-driven global mode, characterized by spiral arms rotating counter-clockwise with respect to the rotor. At larger Reynolds numbers, fluctuations form a steep front, no longer driven by the edge, and followed downstream by a saturated spiral wave, eventually leading to incipient turbulence. Numerical results show that this front results from the superposition of several elephant front-forming global modes, corresponding to unstable azimuthal wavenumbers $m$, in the range $m\in [32,78]$. The spatial growth along the radial direction of the energy of these fluctuations is quantitatively similar to that observed experimentally. This superposition of elephant modes could thus provide an explanation for the discrepancy observed in the single disk configuration, between the corresponding spatial growth rates values measured by experiments on the one hand, and predicted by LSA and DNS performed in an azimuthal sector, on the other hand.

Magnetohydrodynamic radiative nanofluid flow over a rotating surface with Soret effect

2018 ◽  
Vol 14 (1) ◽  
pp. 168-188 ◽  
Author(s):  
C. Sulochana ◽  
Samrat S.P. ◽  
Sandeep N.
Keyword(s):  
Boundary Layer ◽  
Soret Effect ◽  
Perturbation Technique ◽  
Governing Equations ◽  
Self Similarity ◽  
Nanofluid Flow ◽  
Nonlinear Odes ◽  
Content Type ◽  
Rotating Surface ◽  
Analytical Perturbation

Purpose The purpose of this paper is to theoretically investigate the boundary layer nature of magnetohydrodynamic nanofluid flow past a vertical expanding surface in a rotating geometry with viscous dissipation, thermal radiation, Soret effect and chemical reaction. Design/methodology/approach The self-similarity variables are deliberated to transmute the elementary governing equations. The analytical perturbation technique is used to elaborate the united nonlinear ODEs. Findings To check the disparity on the boundary layer nature, the authors measured two nanofluids, namely, Cu-water and Cu-Kerosene based nanofluids. It is found that the Cu-water is effectively enhancing the thermal conductivity of the flow when compared with the Cu-kerosene. Originality/value Till now no analytical studies are reported on heat transfer enhancement of the rotating nanofluid flow by considering two different base fluids.

Extended self-similarity in boundary layer turbulence

1997 ◽  
Vol 55 (6) ◽  
pp. 6985-6988 ◽  
Author(s):  
G. Amati ◽  
R. Benzi ◽  
S. Succi
Keyword(s):  
Boundary Layer ◽  
Self Similarity ◽  
Extended Self ◽  
Boundary Layer Turbulence

Modeling Heat Transfer From a Vertical Isothermal Plate Using a One-Dimensional Turbulence Stochastic Mixing Model of Turbulence

2005 ◽  
Author(s):  
Harmanjeet Shihn ◽  
Paul E. DesJardin
Keyword(s):  
Boundary Layer ◽  
Similarity Theory ◽  
Local Characteristic ◽  
Convection Boundary Layer ◽  
Self Similarity ◽  
Mixing Processes ◽  
One Dimensional ◽  
Turbulent Natural Convection ◽  
Convection Boundary ◽  
The One

A turbulent natural convection boundary layer along a vertical isothermal flat plate in air is investigated based on the one-dimensional turbulence (ODT) modeling approach of Kerstein. The advantage of this approach is that near-wall conduction process can be treated without approximation. The effects of multi-dimensional turbulent mixing processes are modeled using a stochastic process description via triplet mapping stirring events. Adapting the ODT model to the problem of an isothermal plate includes modifying the local characteristic eddy time scale to account for the effects of buoyancy induced mixing mechanisms. Both a Lagrangian and Eulerian implementations of the ODT model are presented. Profiles of time-averaged and RMS velocity and temperature are compared to experimental data and existing self-similarity theory for thermal boundary layer along with Nusselt number predictions.

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