Vortex shedding, flow separation, and drag coefficient in the flow past an ellipsoid of different aspect ratios at moderate Reynolds number

Abstract

Incompressible viscous flow past an ellipsoid of different aspect ratios ( ARs, the ratio of the vertical to the horizontal axis of the ellipsoid, is ranged from 0.5 to 2) at a Reynolds number of 300 is investigated numerically by a finite volume method with adaptive mesh refinement, and the effects of different aspect ratios on vortex shedding, flow separation, and drag coefficient are analyzed in detail. The accuracy of the present results is ascertained by comparing the present drag coefficient and Strouhal number with other literature studies. The results show that the Strouhal frequency of vortex shedding decreases and the magnitude of vortex shedding becomes weaker with an increase in the aspect ratio. In particular, a secondary frequency will occur within a certain interval of 0.8 ≤ AR ≤ 1.2. The vortex shedding appears as a hairpin vortex at AR ∈ [0.5, 1.6], whereas it becomes a double-line vortex at AR ≥ 1.8. Both the upper flow separation angle and the length of the separation bubble increase with an increase in the aspect ratio. The flow separation is symmetrical about the ( x, z)-plane only at 0.5 ≤ AR ≤ 0.7 and AR ≥ 1.8. Furthermore, the total drag coefficient and the pressure drag coefficient both increase gradually with an increase in the aspect ratio. Due to the trend of the contact area between the fluid and the surface of the ellipsoid, the friction drag coefficient decreases first ( AR ≤ 1) and then increases ( AR ≥1). The pressure drag coefficient reinforces the contribution to the total drag coefficient, and the contribution of the pressure drag coefficient grows with an increase in the aspect ratio.