IDENTIFICATION OF EDDY VISCOSITY IN THE UNSTEADY MARINE EKMAN LAYER FLOW

2019 ◽  
Author(s):  
P. Fraunié ◽  
C. Aldebert ◽  
J. L. Devenon ◽  
D. Bourras ◽  
A. Sentchev ◽  
...  
Keyword(s):  
Eddy Viscosity ◽  
Ekman Layer ◽  
Layer Flow

A Method for the Calculation of 3D Boundary Layers on Practical Wing Configurations

1981 ◽  
Vol 103 (1) ◽  
pp. 104-111 ◽  
Author(s):  
J. P. F. Lindhout ◽  
G. Moek ◽  
E. De Boer ◽  
B. Van Den Berg
Keyword(s):  
Boundary Layer ◽  
Boundary Layers ◽  
Boundary Layer Flow ◽  
Eddy Viscosity ◽  
Separated Flow ◽  
Laminar Boundary Layers ◽  
Eddy Viscosity Model ◽  
Airplane Wing ◽  
Turbulent Boundary Layer Flow ◽  
Layer Flow

This paper gives a description of a calculation method for 3D turbulent and laminar boundary layers on nondevelopable surfaces. A simple eddy viscosity model is incorporated in the method. Special attention is given to the organization of the computations to circumvent as much as possible stepsize limitations. The method is also able to proceed the computation around separated flow regions. The method has been applied to the laminar boundary layer flow over a flat plate with attached cylinder, and to a turbulent boundary layer flow over an airplane wing.

Separation effects in Ekman layer flow over ridges

1979 ◽  
Vol 105 (443) ◽  
pp. 129-146 ◽  
Author(s):  
P. J. Mason ◽  
R. I. Sykes
Keyword(s):  
Ekman Layer ◽  
Layer Flow

A Four-Equation Eddy-Viscosity Approach for Modeling Bypass Transition

2014 ◽  
Vol 6 (4) ◽  
pp. 523-538
Author(s):  
Guoliang Xu ◽  
Song Fu
Keyword(s):  
Kinetic Energy ◽  
Transport Equation ◽  
Eddy Viscosity ◽  
Turbulent Viscosity ◽  
Transitional Region ◽  
Transition Model ◽  
Bypass Transition ◽  
Turbulence Transition ◽  
Sst Turbulence Model ◽  
Layer Flow

AbstractIt is very important to predict the bypass transition in the simulation of flows through turbomachinery. This paper presents a four-equation eddy-viscosity turbulence transition model for prediction of bypass transition. It is based on the SST turbulence model and the laminar kinetic energy concept. A transport equation for the non-turbulent viscosity is proposed to predict the development of the laminar kinetic energy in the pre-transitional boundary layer flow which has been observed in experiments. The turbulence breakdown process is then captured with an intermittency transport equation in the transitional region. The performance of this new transition model is validated through the experimental cases of T3AM, T3A and T3B. Results in this paper show that the new transition model can reach good agreement in predicting bypass transition, and is compatible with modern CFD software by using local variables.

scholarly journals Explicit Filtering and Reconstruction Turbulence Modeling for Large-Eddy Simulation of Neutral Boundary Layer Flow

2005 ◽  
Vol 62 (7) ◽  
pp. 2058-2077 ◽  
Author(s):  
Fotini Katopodes Chow ◽  
Robert L. Street ◽  
Ming Xue ◽  
Joel H. Ferziger
Keyword(s):  
Boundary Layer ◽  
Boundary Layer Flow ◽  
Eddy Viscosity ◽  
Wall Stress ◽  
Stress Model ◽  
Viscosity Models ◽  
Neutral Boundary Layer ◽  
Large Eddy ◽  
Layer Flow ◽  
Near Wall

Abstract Standard turbulence closures for large-eddy simulations of atmospheric flow based on finite-difference or finite-volume codes use eddy-viscosity models and hence ignore the contribution of the resolved subfilter-scale stresses. These eddy-viscosity closures are unable to produce the expected logarithmic region near the surface in neutral boundary layer flows. Here, explicit filtering and reconstruction are used to improve the representation of the resolvable subfilter-scale (RSFS) stresses, and a dynamic eddy-viscosity model is used for the subgrid-scale (SGS) stresses. Combining reconstruction and eddy-viscosity models yields a sophisticated (and higher order) version of the well-known mixed model of Bardina et al.; the explicit filtering and reconstruction procedures clearly delineate the contribution of the RSFS and SGS motions. A near-wall stress model is implemented to supplement the turbulence models and account for the stress induced by filtering near a solid boundary as well as the effect of the large grid aspect ratio. Results for neutral boundary layer flow over a rough wall using the combined dynamic reconstruction model and the near-wall stress model show excellent agreement with similarity theory logarithmic velocity profiles, a significant improvement over standard eddy-viscosity closures. Stress profiles also exhibit the expected pattern with increased reconstruction level.

An algorithmic approach to the linear stability of the Ekman layer

1983 ◽  
Vol 132 ◽  
pp. 283-293 ◽  
Author(s):  
Mogens V. Melander
Keyword(s):  
Linear Stability ◽  
Maximum Growth ◽  
Ekman Layer ◽  
Plane Boundary ◽  
Neutral Stability ◽  
Nonlinear Stability Analysis ◽  
Algorithmic Approach ◽  
Analytical Formulas ◽  
Boundary Layer Problems ◽  
Layer Flow

The linear stability of the stationary Ekman-layer flow near a plane boundary is considered. Analytical formulas for the eigenfunctions are derived by a spectral analysis. Standard optimization algorithms are used to calculate critical points, maximum growth rates and neutral-stability curves. The near approach provides a better basis for both a linear and a nonlinear stability analysis than the well-known methods have done. The method may also be applied to other boundary-layer problems.

Investigation of a Reattaching Turbulent Shear Layer: Flow Over a Backward-Facing Step

1980 ◽  
Vol 102 (3) ◽  
pp. 302-308 ◽  
Author(s):  
J. Kim ◽  
S. J. Kline ◽  
J. P. Johnston
Keyword(s):  
Boundary Layer ◽  
Shear Layer ◽  
Eddy Viscosity ◽  
Flow Characteristics ◽  
Turbulent Shear ◽  
Turbulence Structure ◽  
Backward Facing Step ◽  
Turbulent Shear Layer ◽  
Separated Shear Layer ◽  
Layer Flow

Incompressible flow over a backward-facing step is studied in order to investigate the flow characteristics in the separated shear-layer, the reattachment zone, and the redeveloping boundary layer after reattachment. Two different step-heights are used: h/δs = 2.2 and h/δs = 3.3. The boundary layer at separation is turbulent for both cases. Turbulent intensities and shear stress reach maxima in the reattachment zone, followed by rapid decay near the surface after reattachment. Downstream of reattachnent, the flow returns very slowly to the structure of an ordinary turbulent boundary layer. In the reattached layer the conventional normalization of outerlayer eddy viscosity by U∞ δ* does not collapse the data. However, it was found that normalization by U∞ (δ − δ*) does collapse the data to within ± 10% of a single curve as far downstream as x/xR ≈ 2, the last data station. This result illustrates the strong downstream persistence of the energetic turbulence structure created in the separated shear layer.

The Improvement of k-ε Model in the Turbulent Wave Boundary Layer

2009 ◽  
Author(s):  
Yuliang Zhu ◽  
Jing Ma ◽  
Peipei Dong
Keyword(s):  
Boundary Layer ◽  
Eddy Viscosity ◽  
Wave Boundary Layer ◽  
Viscosity Models ◽  
Velocity Equation ◽  
Layer Flow ◽  
Wave Boundary ◽  
Advanced Model ◽  
Turbulent Wave ◽  
Empirical Constants

Numerical model is one of the means for investigating turbulent wave boundary layer. Many scholars have used various eddy-viscosity models to simulate wave turbulent boundary layer flow. On the basis of analyzing existing models, the article uses more reasonable boundary condition to establish an advanced model of turbulent wave boundary layer by k-ε model. Past models have two problems. Firstly, the calculation area is not united since one of the calculation areas is all-water depth and another is boundary layer thickness. Aimed at this problem, this model makes a sensitivity analysis of velocity and eddy-viscosity for various calculation area, which turns out that velocity inside the boundary layer is low-sensitive while the eddy-viscosity is high-sensitive to the change of calculation area. Secondly, a new integration adjust coefficient p is presented to solve the five empirical constants which are difficult to adjust in k-ε model. Although these five empirical constants have recommended value, the universality is not good. In order to obtain better eddy-viscosity value, many methods were suggested to get these five empirical constants, however, most are very complicated. In this article, adjust coefficient p is put before the diffusion item in the velocity equation, and p is a little bit smaller than 1. The result indicates that a reasonable eddy-viscosity can be easily adjusted using this method. The modified model has overcome some shortcomings of the previous models, and gets a better simulation effect.

scholarly journals A Method on Estimating Time-Varying Vertical Eddy Viscosity for an Ekman Layer Model with Data Assimilation

2019 ◽  
Vol 36 (9) ◽  
pp. 1789-1812
Author(s):  
Jicai Zhang ◽  
Guoqing Li ◽  
Jiacheng Yi ◽  
Yanqiu Gao ◽  
Anzhou Cao
Keyword(s):  
Present Method ◽  
Eddy Viscosity ◽  
Adjoint Method ◽  
Ekman Layer ◽  
Present Problem ◽  
Layer Model ◽  
Gradient Descent Algorithm ◽  
Vertical Eddy Viscosity ◽  
Vertical Eddy ◽  
Better Than

Temporal vertical eddy viscosity coefficient (VEVC) in an Ekman layer model is estimated using an adjoint method. Twin experiments are carried out to investigate the influences of several factors on inversion results, and the conclusions of twin experiments are 1) the adjoint method is a capable method to estimate different kinds of temporal distributions of VEVCs; 2) the gradient descent algorithm is better than CONMIN and L-BFGS for the present problem, although the posterior two algorithms perform better on convergence efficiency; 3) inversion results are sensitive to initial guesses; 4) the model is applicable to different wind conditions; 5) the inversion result with thick boundary layer depth (BLD) is slightly better than thin BLD; 6) inversion results are more sensitive to observations in upper layers than those in lower layers; 7) inversion results are still acceptable when data noise exists, indicating the method can sustain noise to a certain degree; 8) a regularization method is proved to be useful to improve the results for present problem; and 9) the present method can tolerate the existence of balance errors due to the imperfection of governing equations. The methodology is further validated in practical experiments where Ekman currents are derived from Bermuda Testbed Mooring data and assimilated. Modeled Ekman currents coincide well with observed ones, especially for upper layers. The results demonstrate that the assumptions of depth dependence and time dependence are equally important for VEVCs. The feasibility of the typical Ekman model, the imperfection of Ekman balance equations, and the deficiencies of the present method are discussed. This method provides a potential way to realize the time variations of VEVCs in ocean models.

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