Turbulence Model Selection for Low Reynolds Number Flows.

S. M. A. Aftab,A. S. Mohd Rafie,K. A. Ahmad,N. A. Razak,Xiao-Dong Wang

doi:10.1371/journal.pone.0153755

S. M. A. Aftab, A. S. Mohd Rafie + Show 3 more

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https://doi.org/10.1371/journal.pone.0153755

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Journal: PloS one	Publication Date: Apr 22, 2016
Citations: 64	License type: CC BY 4.0

Affiliation: Universiti Putra Malaysia

Abstract

One of the major flow phenomena associated with low Reynolds number flow is the formation of separation bubbles on an airfoil’s surface. NACA4415 airfoil is commonly used in wind turbines and UAV applications. The stall characteristics are gradual compared to thin airfoils. The primary criterion set for this work is the capture of laminar separation bubble. Flow is simulated for a Reynolds number of 120,000. The numerical analysis carried out shows the advantages and disadvantages of a few turbulence models. The turbulence models tested were: one equation Spallart Allmars (S-A), two equation SST K-ω, three equation Intermittency (γ) SST, k-kl-ω and finally, the four equation transition γ-Reθ SST. However, the variation in flow physics differs between these turbulence models. Procedure to establish the accuracy of the simulation, in accord with previous experimental results, has been discussed in detail.

Highlights

Low Reynolds number flow pose a great challenge in the selection of a Turbulence model for simulation
It is quite clear that Spallart Allmars (S-A) and γ-Reθ SST values are a close and the mesh is quite adequate for the current case
The following conclusions have been drawn from the current CFD study, which was carried out on NACA4415 airfoil at Reynolds no 120,000

Summary

Introduction

Low Reynolds number flow pose a great challenge in the selection of a Turbulence model for simulation. In the case of low Re airfoils, the resistance to separation of the boundary layer is very poor, resulting in a dominant adverse pressure gradient. As flow separates from the point of minimum pressure, due to the increase in adverse pressure at the leading edge, separation takes place. The separated flow is highly unstable, resulting in transition immediately downstream, causing the flow to become turbulent. Thereby turbulent shear stresses energise the flow to counteract the increased adverse pressure, helping the flow to reattach. The separation bubble is dependent on the flow Re, the pressure distribution, the curvature of the airfoil, roughness and various other factors Gad-el-hak [1].

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