An experimental investigation of laminar axisymmetric submerged jets

Abstract

Detailed measurements of the velocity profiles in a laminar axisymmetric submerged jet of water were taken using a laser-Doppler anemometer. A non-intrusive measurement technique is particularly advantageous in this application owing to the unstable nature of the laminar jet and the destabilizing effect which objects submerged in the jet have. Flow visualization was employed to ensure that all of the measuring points were located within the laminar region of the jet. The variation of centreline velocity, jet half-radius and velocity-profile shape are investigated for various Reynolds numbers and axial distances. Emphasis is placed on the jet-development region; however, data from the fully developed region are also presented. Particular attention is given to determine the proper non-dimensional groups which are required to collapse the data. The predictions of a simple boundary-layer analysis are used as a guide in this regard and found to give an accurate representation of the flow field. Velocity-profile data were taken at sufficiently small radial increments to allow a determination of the jet kinematic momentum using the basic integral definition. Although approximately constant, a slight variation with axial distance is indicated. The momentum initially decreases, and then increases gradually to a value greater than that at the tube exit. An attempt to explain the trend of the variation is made using certain hypotheses regarding the velocity and pressure conditions at the tube exit.