Large Eddy Simulation: Flow over a cylinder¶

Overview¶

The purpose of this numerical simulation is to validate the following parameters of incompressible Large Eddy Simulation (LES) of flow over a cylinder:

• Pressure distribution on the surface
• Stream-wise Velocity distribution in the wake

The numerical simulation results of SimScale were compared with the experimental results. The flow regime selected for the study is classified as sub-critical with a flow reynold number of $$Re=3900$$.

Import validation project into workspace

Geometry¶

The geometry of the study is a straight cylindrical body (see Fig.1.). A brief description of the dimensions is provided by the table below.

Fig.1. Geometry of the cylindrical body

Length Diameter
Value [m] $$\pi D$$ 0.1

Domain and Analysis type¶

An O-type domain was selected as the flow domain around the cylinder. The domain was $$15D$$ in the radial direction and $$\pi D$$ in the span-wise direction (see Fig.2.). For this study a structured hexahedral mesh was created with the open source ‘BlockMesh-tool’. The grid nodes are distributed by a geometric grading in the radial direction. Further, the nodes are clustered near the stagnation point and in the wake region along the stream-wise direction. The mesh is based on a y-plus ($$y^+$$) criterion of $$y^+ < 1$$ in the radial direction. The complete details of the mesh are listed in the following table:

Mesh and Element types :

Mesh type Cells in radial Cells in circumferential Cells in spanwise Number of nodes Type
blockMesh 165 204 34 1144440 3D hexahedral

Fig.2. Mesh used for the SimScale case

The numerical analysis performed is detailed as follows:

Tool Type : OPENFOAM®

Analysis Type : Incompressible Large Eddy Simulation

Sub-Grid-Scale Model : Smagorinsky with Cube-Root-Volume delta

Simulation Setup¶

Fluid:

• Air: Dynamic viscosity ($$\nu$$) $$= 1.511^{-5} m^2s$$

Boundary Conditions:

The inlet boundary was set as a non-turbulent fixed velocity condition, while a pressure boundary condition was applied at the outlet. For the spanwise boundaries a symmetry condition was applied. The following table provides the further details.

Boundary type Velocity Pressure
Inlet Fixed Value: $$0.59\ ms^{-1}$$ Zero Gradient
Outlet inletOutlet Fixed Value: $$0\ Pa$$
Wall no-slip Fixed Value: $$0.0\ ms^{-1}$$ Zero Gradient
Symmetry

Results¶

The numerical simulation results of mean pressure distribution and mean stream-wise velocity are compared with experimental data provided by C.Norberg [1] , L.Ong and J.Wallace [2] and L.M.Lourenco and C.Shih [3] . To ensure meaningful results, averaging was carried out over periods of atleast $$100D/U_\infty$$ time units or about 21 vortex shedding cycles.

A comparison of the mean pressure distribution obtained with SimScale and experimental results is given in Fig.3A. The mean stream-wise velocity profile is compared with experimental data as shows by the Fig.3B.

Fig.3. Pressure distribution comparison (left), strea-mwise velocity profile comparison (right)

The instantaneous vorticity component $$w_z$$, and averaged streamlines in the cross-section (x-y plane) are shown by the Fig.4A and Fig.4B respectively.

A visualization of the instantaneous flow field is shown along the cross-sectional and spanwise planes provided by Fig.5A and Fig.5B.

Fig.5. Instantaneous flow field along stream-wise (left), and along span directions (right)

References¶

 [1] Norberg, ‘Effects of Reynolds number and low-intensity free stream turbulence on the flow around a circular cylinder’, Publ. No. 87 /2, Department of Applied Thermoscience and Fluid Mech., Chalmers University of Technology, Gothenburg, Sweden, 1987.
 [2] Ong and J. Wallace, ‘The velocity field of the turbulent very near wake of a circular cylinder’, Exp. Fluids, 20, 441–453, Springer Verlag, Berlin (1996).
 [3] L.M. Lourenco and C. Shih, ‘Characteristics of the plane turbulent near wake of a circular cylinder, a particle image velocimetry study’, Private Communication, 1993.

Disclaimer¶

This offering is not approved or endorsed by OpenCFD Limited, producer and distributor of the OpenFOAM software and owner of the OPENFOAM® and OpenCFD® trade marks. OPENFOAM® is a registered trade mark of OpenCFD Limited, producer and distributor of the OpenFOAM software.