Dear all,
I was wondering how can we determine the proper laser pulse time separation in tomographic PIV for a jet outflow. It's known that the optimum particle displacement should be around 5 to 7 pixel. But, in jet flow since we have different velocities (high velocity in the vicinity of the jet tip and low velocity downstream). This velocity variation causes different particle displacement. Thanks.
Dear Reza
Your question includes the answer: since there are multiple velocities (from zero to maximum at the centerline), there is no single time separation, i.e. your dynamic range is limited. What I'd do is to set up the maximum velocity to the largest possible pixel displacement, e.g. 16 pixels (for 64 pixel interrogation window) and then you have down to 1-2 pixels displacement for the lowest velocity. You can then try to use multi-pass methods, window-deformation methods to compensate for very different pixel displacements, but all are limited in one way or another. BTW, Lagrangian methods are better in this case, from my personal experience (see our work on jets and 3D-PTV), since they allow for multi-frame tracking using high speed imaging.
Hope it helps, don't hesitate to ask.
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