This paper describes the measurement and data analysis of the turbulence in a two-dimensional water jet discharging from a thin slot into a large body of stationary water having the same width as the slot. Tap water without additives was used as the flow medium. The electromagnetic induction method (commonly known as magnetohydrodynamics, or the MHD method) was used to sense the fluctuation velocities in the diffusion zone of the jet. A DC magnet was placed outside the flow field with the magnetic flux density of 885 Gauss perpendicular to the plane of homogeneity of the two-dimensional flow field. A small probe in the flow field sensed voltage changes due to the turbulent velocities. The induced voltages picked up at the electrodes were fed into a high input 12 impedance (about 10 ohms) differential amplifier. The output from the amplifier was recorded on tape which was later read into a hybrid computer for analyzing the variances, autocorrelation and spectrum of the turbulence signal.
Turbulent velocities induce fluctuating electric potentials everywhere in the flow field whenever a magnetic flux is present, and hence set up fluctuating currents between any two points of different potentials. These currents have an equalizing effect on the induced voltage, thus causing the differential fluctuating voltage sensed by the electrodes in a turbulent flow to be less than the true value. The voltage reduction effect was experimentally determined to be a constant value by comparing the measured variance of turbulence in a water jet by the MHD method with the variance in an air jet using hot-wire anemometry. The constant reduction factor should have no effect on the normalized autocorrelation and spectrum results of the water jet.
Mih, Walter C., "Turbulence Measurements in Submerged Water Jets by Electromagnetic Induction Anemometry" (1973). Symposia on Turbulence in Liquids. 100.
3rd Biennial Symposium on Turbulence in Liquids (1973: Sep., Rolla, MO)
Chemical and Biochemical Engineering
Article - Conference proceedings
Special Methods of Measurement
© 1973 University of Missouri--Rolla, All rights reserved.