Velocity Measurement using Two-Dimensional FFT Concerning with Digital Flow Images

Abstract

Recent development in fluid dynamic have generated and enlarged demand for experimental technique of velocity field measurements. The so-called PIV (Particle Imaging Velocimetry) enables to obtain velocity data of extended spatial region of the flow field simultaneously. This paper describes a method of image processing for obtaining the velocity distribution. Image data of the flow field obtained by flow visualization with tracer is transformed to spatial frequency domain by using two-dimensional Fourier Transform. The velocity vector is determined by dividing of two image data which are taken in a small time difference. Some of the application of 2D-FFT analysis are also shown here. Low-pass and high-pass filter are applied to tracer image data, the so-called speckle photography method is simulated by using computer, and the possibility of turbulence measurement with PIV is examined.