Channels, Fall 2020

Channels • 2 020 • Volume 5 • Number 1 Page 7 step size of 0.0001 s and 2000 time steps for a total flow time of 0.2 s. The turbulent model used was the Transition SST (Shear Stress Transport) model because of the reliability it holds in regard to external flow over a body [4]. The drag force was calculated using surface integration of the pressure and shear stress on the cylinder surface at each element in the mesh on the boundary. Wang [9] proposes two alternative methods for drag force calculations that were used as the second and third methods in this study. The second method used wake integration to calculate the change in pressure and momentum across the cylinder. = ∫[ ∞ − + ( ∞ − )] (1) The third method is the entropy generation method where = ∞ ∞ ∫̇ Ω Ω (2) and where ̇ = { + } . (3) All three methods were used to ensure an accurate measurement of drag could be found and to attempt to reduce the common overestimation of drag from CFD. However, neither the wake integration and entropy generation method gave consistent results for 2D or 3D CFD. Therefore, the surface integration method was selected for force calculations in the numerical analysis. B. Numerical Study For the 2D simulations, ANSYS ICEM was used to create the meshes that would be run in ANSYS FLUENT. Most meshes for the 2D study numbered about 104 thousand elements over the computational domain. The mesh was refined around the surface of the cylinders to resolve the flow field in boundary layer. Fig. 7 shows the computational domain around the cylinder. Fig. 7 Smooth 2D elliptical cylinder mesh (a) entire computational domain (b) surface of cylinder