I'm not sure if this is the right forum for this question but here goes, I have experimental data from hot films on a circular cylinder & at both separation & stagnation points sinusoidal patterns become clearly evident in the signal, i understand this is due to the attached flow being oscillated on the cylinder surface, but the signal at stagnation is twice the frequency of separation, which one should be used to calculate shedding frequency, and are the positions of both stagnation & separation points moving relative to each other. I would be grateful for any input, Thanks in advance. Ray

I am intrigued by your question because it's really quite vague. If you're interested in the vortex shedding behind the 2-D cylinder, why not place the hot-film or hot-wire several diameter lengths downstream? This is a better estimate of the Strouhal number or shedding frequency. With regard to your findings for the signals at the stagnation and separation points, I am not surprised that they have different frequencies just as long as they're almost identical in form(sinusoidal, I hope...) Just check your data acquisition technique when you acquired your data to be sure that you sampled correctly. Also, there's plenty of literature on cylinder flows. Check out "Experiments in Fluids" and "Journal of Fluid Mechanics" my favorite sources of aerodynamic/fluid dynamics stuff. I hope I helped you out. Go with the Flow, Edward