Measurement of velocity fields in fluids by microparticle image processing

The representation of a fluid velocity field is studied by association of coherent optical analog techniques (optical Fourier transform) to numerical image processing. An axisymmetric air jet and a water jet of a fraction of a m/sec velocity are considered. A double exposed photograph obtained with a double pulse laser beam is treated by optical transform and numerical analysis. A video camera and ultra fast Fourier transform were also tried. The measurement of interference fringes obtained with a continuous emission laser gives the velocity vector in the zone. The resolution of existing video cameras is not sufficient for this technique.