Effect of Wall on Mixing of Low Speed Multiple Rectangular Jets

This paper emphasizes on the study of mixing behavior of low speed multiple rectangular jets in the presence of the wall. The experimental studies are carried out at the near field of the jet, as most of the mixing processes of technical interest take place in this region. The practical relevance of this work is generally associated with thrust augmenting ejectors for VTOL / STOL aircraft, gas turbine combustors, furnaces, rocket combustors and noise level reduction in jet flows. The exit velocity of the jet is 40 m/s. The Reynolds number based on the width and exit velocity of the jet is 42900. The number of jets used in the present work is varied from one to four with the help of thin splitter plates of 1 mm thickness. A flat plate is placed at the exit of the orifice, to study the effect of the wall on single and multiple jets. Total pressure measurements are taken along the horizontal plane containing the jet axis and also along the plane perpendicular to the jet axis using a pitot probe arrangement. The local velocity of the flow field is calculated by using atmospheric pressure as reference static pressure. The experimental results show that the presence of the wall (α = 0°) at the exit plane of the orifice results in increased jet centerline velocity. The near field flow velocity at Z/D_e value of 8 is increased by 16.3% due to wall effect, in case of rectangular jet without spacer. Similar arguments hold well in case of rectangular jets with one, two and three spacers respectively Velocities along the transverse direction of the jet are greater due to wall effect. Besides, it has detrimental effects on jet mixing.