The influence of aspect ratio and attack angle on the field structure and dynamic characteristics of the flow around an ellipsoid

The flow of an incompressible viscous fluid around an ellipsoid at a moderate Reynolds number (Re = 300) is numerically investigated, revealing a series of variation laws related to vortex shedding, flow separation, and the lift and drag coefficients as functions of the aspect ratio (AR, defined as the ratio of the vertical axis to the horizontal axis of the ellipsoid) and the angle of attack. The results show that the frequency of vortex shedding decreases, the period of vortex shedding, and the distance between two adjacent hairpin vortices increase with the increase in aspect ratio and attack angle, and the vortex structure in the wake even changes to a double thread wake at 0.5 ≤ AR ≤ 0.6 under an attack angle of 90°. The angle of attack leads to the asymmetric distributions of pressure, velocity, and vorticity on the ellipsoidal surface, and the wake vortex caused by flow separation on the leeward side is dominant. With the increase in the angle of attack, the total drag increases, and the lift first increases and then decreases. The maximum lift is found to exist when the angle of attack is 45°. As the aspect ratio of the ellipsoid approaches 1, the influence of the angle of attack on the flow field structure and the force coefficients acting on the ellipsoid diminishes. Conversely, as the ellipsoid becomes slender, the flow field structure and dynamic characteristics surrounding the ellipsoid become increasingly sensitive to variations in the angle of attack.