The geometry is created based on the simplified aerodynamic body used by Ahmed et al . See Fig.1.a for dimensions and Fig.1.b for the geometry. The slant angle (ψ) is set to 25 degrees. The body is placed in a wind tunnel(6m*5m*13.5m) in order to limit the aerodynamic blockage effect.
Fig.1.a. Dimensions of the Ahmed Body
Fig.1.b. Geometry used in the study
Analysis type and Domain
The snappyHexMesh tool was used to generate the mesh, with refinement near the walls and in the wake region (see Fig.2.).
Fig.2. Mesh used for the SimScale case
A typical property of the generated mesh is the y+(“y-plus”) value, which is defined as the non-dimensionalized distance to the wall; it is given by y+=u∗y/ν. A y+ value of 1 would correspond to the upper limit of the laminar sub-layer.
Full Resolution in the near-wall region: The first cell lies at most at the boundary of the laminar sub-layer and no further. Here, y+ value is 1 or below.
Use of wall-functions to resolve the near-wall region: There is no need to place cells very close to the laminar sub-layer, and typically 30⩽y+⩽300
An average y+ value of 1 was used for the inflation layer. The k−ω SST turbulence model was chosen, with full resolution for near-wall treatment of the flow.
Air with kinematic viscosity of 1.5×10−5kg/ms is assigned as the domain fluid. The boundary conditions for the simulation are shown in Table 3.
Table 2: Boundary Conditions for Ahmed Body simulation¶
63.7 m/s (Moving Wall)
The free stream velocity of the simulation is U=63.7 m/s, so the Reynolds number based on the height of the body H is Re=1.2×106. It is of the same order of magnitude used in the original experiment of Ahmed and Ramm .
The drag coefficient is defined as CD=Fd/0.5×rho×U2×Ax where Ax(0.112 m2) is the projected area of the Ahmed body in streamwise direction and FD the drag force. The time-averaged drag force was determined by integration of surface pressure and shear stress over the entire Ahmed body. The resulting drag coefficient of the Ahmed body was computed to be 0.306 which is within a 2.86% error margin of the measured value of 0.298. .
Wake Flow Patterns
The velocity streamline contour of mean flow obtained with the simulation is reported in Fig. 4 together with experimental results of reference .
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.
Strictly Necessary Cookies
Strictly Necessary Cookie should be enabled at all times so that we can save your preferences for cookie settings.
If you disable this cookie, we will not be able to save your preferences. This means that every time you visit this website you will need to enable or disable cookies again.