Quantitative Visualization of the Flow Within the Volute of a Centrifugal Pump. Part A: Technique

Abstract

This paper describes a series of quantitative flow visualization experiments within the volute of a centrifugal pump by implementing the “Particle Displacement Velocimetry” method (PDV or PIV). Part A focuses on the measurement procedures and includes an uncertainty analysis. This technique involves illuminating sections of a flow field with pulsed laser sheets while seeding the water with microscopic, neutrally buoyant particles containing imbedded fluorescent dye. By pulsing the laser more than once while recording a single photograph each particle leaves multiple traces on the same film. The analysis procedures consist of dividing the image to a large number of small sections (windows) and computing of the mean shift of all particles within each window. This shift is determined by computing the autocorrelation function of the image within the window. Digital image processing and specially written software are being utilized while analyzing the data. It is demonstrated that by controlling the magnification and particle concentration, the relative error can be maintained at about 1 percent. A sample analyzed image is presented. The rest of the data are included in Part B.