Streamwise and crossflow instabilities on inclined circular cylinders

Observations of streamwise and crossflow instabilities on swept circular cylinders over a range of inclinations are presented. By considering sweep angles through the full range between the two extremes studied in the literature, we relate the streamwise vorticity of the unswept case (Kestin & Wood, J. Fluid Mech. 44) to the more aggressive crossflow instability at high sweep angles (Poll, J. Fluid Mech. 150). Measurements made on the unswept cylinder confirm earlier predictions in the literature, providing a firm basis for referencing the new measurements of vortical behaviour on cylinders with general sweep angle. The study has implications for turbine blading.