Velocity Measurements with a New Probe in Inhomogeneous Turbulent Jets

Abstract

A velocity measuring probe, which creates "spots" of heat in a fluid flow by means of a pulsed heated wire and then senses the rate at which they are convected past a sensing wire, has been used to measure velocity profiles in subsonic, inhomogeneous, axisymmetric turbulent jets. In such flows the detected thermal profile of a spot is highly distorted, but reconstruction of a mean profile, by digital computer, from several hundred spots enables calculation of a mean velocity and a turbulence level. The measurements indicate that a jet which is less dense than the quiescent ambient fluid mixes with it more vigorously than a similar ambient density jet with the same nozzle Reynolds number. This is manifested by the higher turbulence levels, more rapid growth, and faster decay of the mean velocity of the less dense jet compared to the homogeneous one. A jet of denser-than-ambient fluid demonstrates the opposite behavior.