Three-Dimensional Global Linear Stability Analysis of Flow Around a Spheroid

Abstract

Computational study of flowfields around a spheroid at varied angles of attack is done using Chiba's method, which is one of the methods of three-dimensional global linear stability analysis. It is clarified that in the case of a spheroid, nonoscillatory, nonaxisymmetric flow (in the case of zero angle of attack) and nonoscillatory asymmetric flow (in the case of nonzero angle of attack) are observed in a range of the freestream Reynolds number around 4 × 10 3 to 7 × 103, and angle of attack from 0 to 30 deg. The amplification factor of the nonoscillatory asymmetric (or nonaxisymmetric in 0-deg attack angle case) mode is the largest. The transition from nonoscillatory symmetric (or axisymmetric) flow, to nonoscillatory asymmetric (or nonaxisymmetric) flow, occurs when the amplification factor becomes zero. To ascertain the appearance of the nonoscillatory asymmetric flow in an attack angle case, a low-speed wind tunnel experiment was also conducted. The picture of flow visualization shows an asymmetric pattern when the Reynolds number is around 6.5 x 10 3 , whereas the pattern is symmetric at a Reynolds number around 3.5 × 103.