Direct numerical simulation of the Ekman layer: A step in Reynolds number, and cautious support for a log law with a shifted origin

Abstract A direct numerical simulation (DNS) at a Reynolds number of 1000 was performed for the neutral atmospheric boundary layer (ABL) using the Ekman layer approximation. The DNS results were used to evaluate several closure approximations that model the turbulent stresses in the Reynolds averaged momentum equations. Two first-order closure equations proposed by O’Brien and by Large, McWilliams, and Doney were tested; both models approximate the eddy diffusivity as a function of height using cubic polynomials. Of these two models, the O’Brien model, which requires data both at the surface layer and at the top of the boundary layer, proved superior. The higher-order k–ɛ model also agreed well with DNS results and more accurately represented the eddy diffusivity in this rotational flow.

Download Full-text

Improved low-Reynolds-number k-epsilon-tilde model based on direct numerical simulation data

AIAA Journal ◽

10.2514/3.13775 ◽

1998 ◽

Vol 36 ◽

pp. 38-43

Author(s):

C. B. Hwang ◽

C. A. Lin

Keyword(s):

Numerical Simulation ◽

Reynolds Number ◽

Direct Numerical Simulation ◽

Low Reynolds Number ◽

Simulation Data ◽

Direct Numerical Simulation Data ◽

Model Based ◽

Low Reynolds

Download Full-text

The Turbulent Flow over the BARC Rectangular Cylinder: A DNS Study

Flow Turbulence and Combustion ◽

10.1007/s10494-021-00254-1 ◽

2021 ◽

Author(s):

Alessandro Chiarini ◽

Maurizio Quadrio

Keyword(s):

Numerical Simulation ◽

Reynolds Number ◽

Direct Numerical Simulation ◽

Finite Differences ◽

Turbulence Models ◽

Fine Tuning ◽

Rectangular Cylinder ◽

Budget Equation ◽

Complete Set ◽

First Time

AbstractA direct numerical simulation (DNS) of the incompressible flow around a rectangular cylinder with chord-to-thickness ratio 5:1 (also known as the BARC benchmark) is presented. The work replicates the first DNS of this kind recently presented by Cimarelli et al. (J Wind Eng Ind Aerodyn 174:39–495, 2018), and intends to contribute to a solid numerical benchmark, albeit at a relatively low value of the Reynolds number. The study differentiates from previous work by using an in-house finite-differences solver instead of the finite-volumes toolbox OpenFOAM, and by employing finer spatial discretization and longer temporal average. The main features of the flow are described, and quantitative differences with the existing results are highlighted. The complete set of terms appearing in the budget equation for the components of the Reynolds stress tensor is provided for the first time. The different regions of the flow where production, redistribution and dissipation of each component take place are identified, and the anisotropic and inhomogeneous nature of the flow is discussed. Such information is valuable for the verification and fine-tuning of turbulence models in this complex separating and reattaching flow.

Download Full-text

Direct numerical simulation of plane Couette flow at the transitional Reynolds number.

TRANSACTIONS OF THE JAPAN SOCIETY OF MECHANICAL ENGINEERS Series B ◽

10.1299/kikaib.52.3460 ◽

1986 ◽

Vol 52 (482) ◽

pp. 3460-3468

Author(s):

Yutaka MIYAKE ◽

Takeo KAJISHIMA ◽

Shigeru OBANA

Keyword(s):

Numerical Simulation ◽

Reynolds Number ◽

Direct Numerical Simulation ◽

Couette Flow ◽

Plane Couette Flow

Download Full-text

Effects of Turbulent Reynolds Number on the Performance of Algebraic Flame Surface Density Models for Large Eddy Simulation in the Thin Reaction Zones Regime: A Direct Numerical Simulation Analysis

Journal of Combustion ◽

10.1155/2012/353257 ◽

2012 ◽

Vol 2012 ◽

pp. 1-13 ◽

Cited By ~ 6

Author(s):

Mohit Katragadda ◽

Nilanjan Chakraborty ◽

R. S. Cant

Keyword(s):

Numerical Simulation ◽

Reynolds Number ◽

Fractal Dimension ◽

Direct Numerical Simulation ◽

Surface Density ◽

Flame Surface ◽

Algebraic Models ◽

Flame Surface Density ◽

Turbulent Reynolds Number ◽

Reaction Zones

A direct numerical simulation (DNS) database of freely propagating statistically planar turbulent premixed flames with a range of different turbulent Reynolds numbers has been used to assess the performance of algebraic flame surface density (FSD) models based on a fractal representation of the flame wrinkling factor. The turbulent Reynolds number Rethas been varied by modifying the Karlovitz number Ka and the Damköhler number Da independently of each other in such a way that the flames remain within the thin reaction zones regime. It has been found that the turbulent Reynolds number and the Karlovitz number both have a significant influence on the fractal dimension, which is found to increase with increasing Retand Ka before reaching an asymptotic value for large values of Retand Ka. A parameterisation of the fractal dimension is presented in which the effects of the Reynolds and the Karlovitz numbers are explicitly taken into account. By contrast, the inner cut-off scale normalised by the Zel’dovich flame thicknessηi/δzdoes not exhibit any significant dependence on Retfor the cases considered here. The performance of several algebraic FSD models has been assessed based on various criteria. Most of the algebraic models show a deterioration in performance with increasing the LES filter width.

Download Full-text