3D CFD computations of transitional flows using DES and a correlation based transition model

TLDR: In this article, the correlation based transition model of Menter et al. in combination with the Detached Eddy Simulation (DES) methodology is applied to two cases with large degree of flow separation typically considered difficult to compute.

Abstract: The present article describes the application of the correlation based transition model of Menter et al. in combination with the Detached Eddy Simulation (DES) methodology to two cases with large degree of flow separation typically considered difficult to compute. Firstly, the flow is computed over a circular cylinder from Re = 10 to 1 × 106 reproducing the cylinder drag crisis. The computations show good quantitative and qualitative agreement with the behaviour seen in experiments. This case shows that the methodology performs smoothly from the laminar cases at low Re to the turbulent cases at high Re. Secondly, the flow is computed over a thick airfoil at high angle of attack, in this case the DU-96-W351 is considered. These computations show that a transition model is needed to obtain correct drag predictions at low angle of attack, and that the combination of transition and the DES method improve agreement in the deep stall region. Copyright © 2010 John Wiley & Sons, Ltd.

Figures

Table 1. The Strouhal number ( f ·DU ) number as function of Reynolds number.

Figure 7. Variation of Strouhal number with with Reynolds number.

Figure 12. Comparison between computed lift at various turbulence intensities and measured values from the LM tunnel.

Figure 13. Comparison between computed drag at various turbulence intensities and measured values from the LM tunnel.

Figure 1. Comparison between the four target points from the optimization and different correlation functions.

Figure 5. Comparison of computed drag force for the fully turbulent and the transitional computations with the measurements.

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3D CFD computations of transitional flows using DES and a correlation based
transition model
Sørensen, Niels N.
Publication date:
2009
Document Version
Publisher's PDF, also known as Version of record
Link back to DTU Orbit
Citation (APA):
Sørensen, N. N. (2009). 3D CFD computations of transitional flows using DES and a correlation based transition
model. Danmarks Tekniske Universitet, Risø Nationallaboratoriet for Bæredygtig Energi. Denmark.
Forskningscenter Risoe. Risoe-R No. 1692(EN)

Risø-R-Report
3D CFD computations of transitional flows
using DES and a correlation based transition
model
Niels N. Sørensen
Risø-R-1692(EN)
July 2009
Re = 1.e6

Author: Niels N. Srensen Risø-R-1692(EN)
Title: 3D CFD computations of transitional flows using DES and a correlation based
transition model
Department: Aeroelastic Design – Wind Energy Division
Abstract:
ISSN
The report describes the application of the correlation based tran-
sition model of of Menter et. al. [1, 2] to the cylinder drag crisis
and the stalled flow over an DU-96-W-351 airfoil using the DES
methodology. When predicting the flow over airfoils and rotors, the
laminar-turbulent transition process can be important for the aero-
dynamic performance. Today, the most widespread approach is to
use fully turbulent computations, where the transitional process is
ignored and the entire boundary layer on the wings or airfoils is
handled by the turbulence model. The correlation based transition
model has lately shown promising results, and the present paper de-
scribes the application of the model to predict the drag and shed-
ding frequency for flow around a cylinder from sub to super-critical
Reynolds numbers. Additionally, the model is applied to the flow
around the DU-96 airfoil, at high angles of attack.
ISBN 978-87-550-3749-6
Contract no.:
ENS-33033-0055
Group’s own reg. no.:
Sponsorship:
Danish Energy Agency
Cover:
Separation behind cylinder
Pages: 18
Tables: 17
References: 24
Information Service Department
Risø National Laboratory for Sustain-
able Energy
Technical University of Denmark
P.O.Box 49
DK-4000 Roskilde
Denmark
Telephone +45 4677 4004
bibl@risoe.dk
Fax +45 4677 4013
www.risoe.dk

Contents
1 Abstract 3
2 Introduction 3
3 Code description 3
3.1 Transition Model 4
4 Results 5
4.1 Computational grids 5
4.2 Flow Over a Circular Cylinder 6
4.3 Discussion of Cylinder Results 9
4.4 Flow over a thick airfoil 10
4.5 Discussion of Airfoil Results 15
5 Conclusion 15
6 Acknowledgement 15
2 Risø-R-1692(EN)

1 Abstract
The present report describes the application of the correlation based transition model of of
Menter et al. [1, 2] to the flow over a cylinder and a thick airfoils using the Detached Eddy
Simulation (DES) methodology. When predicting the flow over airfoils and rotors, the laminar-
turbulent transition process can be important for the aerodynamic performance. Today, the most
widespread approach is to use fully turbulent computations, where the transitional process is
ignored and the entire boundary layer on the wings or airfoils is handled by the turbulence
model. In the present work the possibility of combining the DES technique with a transition
model is tested for two flows featuring large separated areas.
2 Introduction
During the last years, Computational Fluid Dynamics has found wide spread use within the
wind energy community, and has been shown to perform well in many cases. Even though
much success has been achieved, important problems still exist where the standard fully tur-
bulent Reynold Averaged Navier-Stokes (RANS) approach fails to give sufficiently accurate
answers. The most obvious problem is the failure to predict the power production and load for
stall controlled turbines at high wind, corresponding to high angle of attack along the blade
span. Attempting to shed some light on some of the fundamental problems connected to the
deep stall physics of wind turbine blades, often equipped with thick airfoil, the present work
firstly addresses the classical problem of predicting the drag crisis of a circular cylinder, sec-
ondly applying the same methodology to the flow over a thick airfoil. The cylinder case is
mainly chosen because a large body of high quality experimental data exists, which for many
other flows can be problematic to obtain for deep stall cases. Additionally, cylindrical or nearly
cylindrical sections exist at the inboard part of most modern wind turbine rotors. To accomplish
the flow simulations, the new correlation based γ− Re
θ
model by Menter et al. [1] and the DES
version of the k − ω SST model by Strelets [3] is applied. It is well known that the movement
of the separation point on the circular cylinder is highly influenced by the laminar to turbulent
transition process. Additionally it is well know that typical RANS are not sufficiently accurate
in massively separated flows, and to help alleviate this problem, the DES technique is applied.
3 Code description
The in-house flow solver EllipSys3D is used in all computations presented in this paper. The
code is developed in co-operation between the Department of Mechanical Engineering at the
Technical University of Denmark and The Department of Wind Energy at Risø National Lab-
oratory, see [4, 5] and [6]. The EllipSys3D code is a multiblock finite volume discretization of
the incompressible Reynolds Averaged Navier-Stokes (RANS) equations in general curvilin-
ear coordinates. The code uses a collocated variable arrangement, and Rhie/Chow interpolation
[7] is used to avoid odd/even pressure decoupling. As the code solves the incompressible flow
equations, no equation of state exists for the pressure, and in the present work the Semi-Implicit
Method for Pressure-Linked Equations (SIMPLE) algorithm of Patankar and Spalding [8, 9] or
the Pressure Implicit with Splitting of Operators (PISO) algorithm of Issa [10, 11] is used to
enforce the pressure/velocity coupling, for steady state and transient computations respectively.
The EllipSys3D code is parallelized with the Message-Passing Interface (MPI) for executions
on distributed memory machines, using a non-overlapping domain decomposition technique.
Both steady state and unsteady computations can be performed. For the unsteady computa-
Risø-R-1692(EN) 3

Frequently asked questions

Q1. What are the contributions mentioned in the paper "3d cfd computations of transitional flows using des and a correlation based transition model" ?

The report describes the application of the correlation based transition model of of Menter et. al. [ 1, 2 ] to the cylinder drag crisis and the stalled flow over an DU-96-W-351 airfoil using the DES methodology. The correlation based transition model has lately shown promising results, and the present paper describes the application of the model to predict the drag and shedding frequency for flow around a cylinder from sub to super-critical Reynolds numbers. 

Q2. What have the authors stated for future works in "3d cfd computations of transitional flows using des and a correlation based transition model" ?

This could be the focus of further work, along with efforts to actually resolve the wind tunnel walls. The problem of the wind tunnel corrections, that do not account for the interaction of the separation and the wall effects would additionally require further studies.