Optical Methods for Data Processing in Heat and Fluid Flow

3

An Experimental Investigation of the Flow Produced in a Rectangular Container by a Rotating Disc using LDA

V G Meledin, I V Naumov, and V A Pavlov

Abstract

The swirled flow produced in a rectangular container is investigated experimentally using a laser measuring apparatus. The apparatus consists of the following units: an optoelectronic module of two-dimensional LDA with adaptive temporal selection of the velocity vector, a two-channel ADC for input of a quadrature Doppler signal, a computer with software, a device to generate a stable specialized vortex flow, and a CCD camera for registration of the flow structure. The rectangular container was created from optical quality plexiglas. The swirled flow is generated by a rotating disc (diameter 118 mm) placed in to the top lid of the container. The working fluid was a water-glycerine mixture. The optical module of the two-dimensional LDA was a differential Doppler anemometer. The optoelectronic module of the LDA generated a quadrature pair of the Doppler signals. The measurement algorithm of a Doppler frequency is based on a spectral method of signal processing. This system allows us to carry out noncontact measurements of the swirled flows with velocity range of 10⁻⁴ − 10⁻¹ m/s.

The distribution of the axial velocity component at the axis of the rotating disc was measured for Reynolds numbers in the ranges 1500 ... 6000. It was found that the spiral vortex breakdown occurred at Re > 4000 in confined rotating flow inside the rectangular ...