An investigation of the effects of incidence on the flow around a square section cylinder

Measurements of the spectra of pressure and velocity fluctuations are used to describe the changes that take place in the flow around a square section cylinder as the angle of incidence is varied between 0 deg and 45 deg. Measurements of the longitudinal spacing between vortices in the wake and the shedding frequency are presented. These data, together with earlier measurements of mean drag and base pressure, are used in a vortex street model to obtain estimates of vortex strength and vortex street lateral spacing. The Strouhal number based on the cylinder diameter is found to decrease slightly at first and rise rather abruptly to a maximum when the angle of incidence is 13.5 deg. Reattachment of the shear layer may start at this angle. The spectra of the pressure and velocity fluctuations have subharmonic peaks at 5 deg and 10 deg. This may be caused by interaction between a vortex and a trailing edge corner.