Flow around an elliptic cylinder in the critical reynolds number regime

Flow around an elliptic cylinder of axis ratio 1:3 has been investigated experimentally in the critical Reynolds number regime on the basis of mean static pressure measurements along the cylinder surface and of hot-wire velocity measurements in the near wake. The critical Reynold number has been found to vary with the angle of attack α and attains a minimum around α = 5 to 10 deg. At the critical Reynolds number, the drag, lift, and moment coefficients change discontinuously, and the Strouhal number based on the upstream uniform flow velocity and the major axis length of the cylinder reaches a maximum of about 1.0 to 1.5 depending on α. It is found, however, that the universal Strouhal number based on the velocity along the separated shear layer and the wake width is nearly equal to 0.19, on average, even in the critical Reynolds number regime. The pressure distribution along with the surface oil flow pattern revealed the existence of a small separation bubble near the leading edge accompanying a turbulent boundary layer.