Flows with nodal and saddle attachment and separation

Abstract

The flow field of a bent cylinder with nodal and saddle types of attachment was experimentally investigated at Reynolds numbers of 20,000 and 50,000 based on mean cylinder diameter. Results of flow visualization tests, mean total pressures and hot wire measurements are presented. The bent cylinder's wake was found to be significantly different from the wake of a right circular cylinder and was found to contain structures in addition to the von Karman vortices. It was observed that the wake consisted of streamwise trailing vortices whose orientation and spanwise location depended on the azimuthal angle of the attachment. It was also observed that a change in azimuthal angle from the nodal to the saddle position resulted in a deterioration of the organization and an increase in the complexity of the flow. The above confirmed that the flow field of the bent cylinder was three dimensional. It was also observed that the saddle position of the bent cylinder tended to produce more drag than the nodal position and than that of a right circular cylinder. The bent cylinder's results were compared to results of two dimensional wakes to check the three dimensionality of the flow. It was concluded that the bent cylinder's wake due to three dimensionality was significantly different from the two dimensional wakes. Variations in Strouhal number for the various cylinder configurations were also observed. Power spectra of the wake provided evidence of additional structures in the flow. The differences in StrOLihal number between the right circular cylinder and the bent cylinder again substantiated the differences between them.