scholarly journals ASPECTS OF WAVE CURRENT BOUNDARY LAYER FLOWS

1984 ◽  
Vol 1 (19) ◽  
pp. 150 ◽  
Author(s):  
Felicity C. Coffey ◽  
Peter Nielsen
Keyword(s):  
Boundary Layer ◽  
Eddy Viscosity ◽  
Friction Velocity ◽  
Field Measurements ◽  
Laboratory Measurements ◽  
Boundary Layer Flows ◽  
Steady Current ◽  
Bed Roughness ◽  
Flow Components ◽  
A Current

Field measurements of steady current profiles under the influence of waves are described, including a technique for obtaining an extra independant estimate of the friction velocity. Field and laboratory measurements are analysed for the effect on apparent bed roughness by superimposing waves on a current. Finally the applicability of the eddy viscosity concept to combined flows is examined. The conclusion is that in general, different eddy viscosities must be applied to different flow components.

scholarly journals THB INFLUENCE OF WAVES OH CURRENT PROFILES

1986 ◽  
Vol 1 (20) ◽  
pp. 7 ◽  
Author(s):  
Felicity C. Coffey ◽  
Peter Nielsen
Keyword(s):  
Boundary Layer ◽  
Friction Velocity ◽  
Dimensionless Parameter ◽  
Velocity Amplitude ◽  
Steady Current ◽  
Vertical Scale ◽  
Flow Components ◽  
Current Reduction ◽  
Wave Boundary ◽  
The Waves

A simple model is presented for steady current profiles in the presence of waves. The current reduction and apparent roughness increase caused by the waves are shown to depend mainly on one dimensionless parameter u*/u"*, i.e. the ratio between the friction velocity amplitude due to the waves and the time averaged friction velocity. The model recognises the need to apply different eddy viscosities to different flow components. Also, the thickness of the wave influenced layer near the bed is comceptually separated from the vertical scale of the wave boundary layer.

An Assessment of Three-Dimensional Turbulent Boundary Layer Prediction Methods

1973 ◽  
Vol 95 (3) ◽  
pp. 415-421 ◽  
Author(s):  
A. J. Wheeler ◽  
J. P. Johnston
Keyword(s):  
Boundary Layer ◽  
Eddy Viscosity ◽  
Three Dimensional ◽  
High Sensitivity ◽  
Boundary Layer Flows ◽  
Mean Velocity ◽  
Eddy Viscosity Model ◽  
Separating Flow ◽  
Dimensional Boundary ◽  
Stress Models

Predictions have been made for a variety of experimental three-dimensional boundary layer flows with a single finite difference method which was used with three different turbulent stress models: (i) an eddy viscosity model, (ii) the “Nash” model, and (iii) the “Bradshaw” model. For many purposes, even the simplest stress model (eddy viscosity) was adequate to predict the mean velocity field. On the other hand, the profile of shear stress direction was not correctly predicted in one case by any model tested. The high sensitivity of the predicted results to free stream pressure gradient in separating flow cases is demonstrated.

scholarly journals Estimation of the Friction Velocity in Stably Stratified Boundary-Layer Flows Over Hills

2008 ◽  
Vol 130 (1) ◽  
pp. 15-28 ◽  
Author(s):  
José Luis Argaín ◽  
Pedro M. A. Miranda ◽  
Miguel A. C. Teixeira
Keyword(s):  
Boundary Layer ◽  
Friction Velocity ◽  
Boundary Layer Flows

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>

A Note on a Generalized Eddy-Viscosity Hypothesis

1992 ◽  
Vol 114 (3) ◽  
pp. 463-466 ◽  
Author(s):  
P. Andreasson ◽  
U. Svensson
Keyword(s):  
Boundary Layer ◽  
Shear Stress ◽  
Velocity Gradient ◽  
Eddy Viscosity ◽  
Channel Flows ◽  
Length Scale ◽  
Asymmetric Channel ◽  
Boundary Layer Flows ◽  
Turbulent Length Scale ◽  
Model Predictions

The standard eddy-viscosity concept postulates that zero velocity gradient is accompanied by zero shear stress. This is not true for many boundary layer flows: wall jets, asymmetric channel flows, countercurrent flows, for example. The generalized eddy-viscosity hypothesis presented in this paper, relaxes this limitation by recognizing the influence of gradients in the turbulent length scale and the shear. With this new eddy-viscosity concept, implemented into the standard k–ε model, predictions of some boundary layer flows are made. The modelling results agree well with measurements, where predictions with the standard eddy-viscosity concept are known to fail.

Eddy Viscosity Transport Equations and Their Relation to the k-ε Model

1997 ◽  
Vol 119 (4) ◽  
pp. 876-884 ◽  
Author(s):  
F. R. Menter
Keyword(s):  
Boundary Layer ◽  
Shear Stress ◽  
Eddy Viscosity ◽  
Turbulence Models ◽  
Equation Model ◽  
Turbulent Shear ◽  
Boundary Layer Flows ◽  
Turbulent Layer ◽  
Turbulent Shear Stress ◽  
The One

A formalism will be presented which allows transforming two-equation eddy viscosity turbulence models into one-equation models. The transformation is based on Bradshaw’s assumption that the turbulent shear stress is proportional to the turbulent kinetic energy. This assumption is supported by experimental evidence for a large number of boundary layer flows and has led to improved predictions when incorporated into two-equation models of turbulence. Based on it, a new one-equation turbulence model will be derived from the k-ε model. The model will be tested against the one-equation model of Baldwin and Barth, which is also derived from the k-ε model (plus additional assumptions) and against its parent two-equation model. It will be shown that the assumptions involved in the derivation of the Baldwin-Barth model cause significant problems at the edge of a turbulent layer.

scholarly journals Estimation of Eddy Viscosity Profile in the Bottom Ekman Boundary Layer

2017 ◽  
Vol 34 (10) ◽  
pp. 2163-2175 ◽  
Author(s):  
An-Zhou Cao ◽  
Hui Chen ◽  
Wei Fan ◽  
Hai-Lun He ◽  
Jin-Bao Song ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Turbulent Mixing ◽  
Eddy Viscosity ◽  
Accurate Estimation ◽  
Ekman Boundary Layer ◽  
Steady Current ◽  
Viscosity Profile ◽  
Estimation Scheme ◽  
Tidal Constituents ◽  
Better Than

AbstractPrevious studies have shown that strong tidal currents can cause intense turbulent mixing near the seafloor in continental shelf areas. To quantify the turbulent mixing, the eddy viscosity coefficient is generally used. In this study, an estimation scheme is proposed to evaluate the eddy viscosity profile (EVP) in the bottom Ekman boundary layer based on the adjoint method. The estimation scheme is composed of the bottom Ekman boundary layer model and its adjoint model, and a minimization algorithm. The feasibility and effectiveness of the proposed scheme are validated by a series of twin experiments, where the proposed scheme is compared with three other schemes in previous studies. When large measurement errors exist, the proposed scheme performs better than the three other schemes. When large Ekman balance errors exist, the proposed scheme is better than two of the other schemes. The selection of components of the steady current and tidal constituents also influences the performance of the proposed scheme. Successful estimation of the EVP requires the usage of intense components of the steady current and tidal constituents. With the usage of the intense components, increasing the number of tidal constituents cannot lead to a more accurate estimation of the EVP.

scholarly journals TURBULENT CURRENTS IN THE PRESENCE OF WAVES

1970 ◽  
Vol 1 (12) ◽  
pp. 141
Author(s):  
Helge Lundgren
Keyword(s):  
Boundary Layer ◽  
Wave Propagation ◽  
Velocity Profile ◽  
Current Velocity ◽  
Friction Velocity ◽  
Approximate Theory ◽  
Current Direction ◽  
Constant Depth ◽  
Wave Boundary ◽  
A Current

This paper presents an approximate theory for the reduction of the velocity of a current due to the presence of sinusoidal waves. For a given slope, S, in water of constant depth, d, the current velocity profile is U(z) = U^ (2.5'ln — - A) (1) t zo as a function of the height, z, above the bed. Eq. 1 is valid only above the thin wave boundary layer near the bed, the roughness of which is k = 30 z . Uf is the current friction velocity defined by p Ul = y d S = T (2) f ' cw CW Values of A can be found from: Fig. 2 where Aj applies when the direction of wave propagation is parallel to the current direction, and Fig. 3 where A2 applies when the direction of wave propagation is perpendicular to the current direction, cf. Notation in Sec. 2. The theory is based upon a number of assumptions (see Sec. 4).

Evaluation of Turbulence Models Using Large-Eddy Simulation Data

2010 ◽  
Author(s):  
Hassan Raiesi ◽  
Ugo Piomelli ◽  
Andrew Pollard
Keyword(s):  
Boundary Layer ◽  
Eddy Viscosity ◽  
Predictive Accuracy ◽  
Turbulence Models ◽  
Adverse Pressure Gradient ◽  
Boundary Layer Flows ◽  
Simulation Data ◽  
Critical Effect ◽  
Eddy Simulation ◽  
Large Eddy

The performance of some of the most commonly used eddy viscosity turbulence models to predict separated boundary layer flows in adverse pressure gradient has been evaluated against large eddy simulations. The LES results were used to assess the consistency of the different terms in the k–ε, ζ–f, k–ω and Spalart-Allmaras models. For the separated boundary layer, the eddy-viscosity assumption works well, and anisotropic effects are not significant. However, the near-wall treatment used in k–ε models was found to have a critical effect on the predictive accuracy of the flow (and, in particular, of separation and reattachment points). None of the wall treatments tested resulted in accurate prediction of the flow field.

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