Experimental investigation of the effect of endplates and sidewalls on the near field development of a smooth contraction rectangular jet

Abstract

The effects of different boundary conditions on the near field development of a turbulent rectangular jet issuing from a smooth contraction nozzle of aspect ratio 15 have been studied experimentally with x -wire Hot-Wire Anemometry (HWA). Four different configurations resulting from the presence or absence of endplates–configuring a jet out of a wall–and sidewalls, confining the jet at the planes of the short side walls of the exit nozzle, under identical inlet conditions have been considered. The mean streamwise and lateral velocity and associated turbulent characteristics up to an axial distance of 35 nozzle widths, H , have been measured. Results comprise centreline data for three Reynolds numbers, based on mean exit velocity and nozzle width, Re = 10,000 , 20,000 and 30,000 as well as lateral distributions at 13 downstream locations for Re = 20,000 . In the absence of sidewalls the presence or absence of an endplate has little effect on the development of the flow field. Measurements made in the presence of sidewalls indicate that the presence of the endplate results in a jet with higher lateral outward velocities within the jet’s shear layers and smaller inward lateral velocities outside the jet’s edges, followed by higher turbulent intensities of both streamwise and lateral components in the early stages of development. Furthermore, in configurations comprising sidewalls, the presence of an endplate results in a faster spreading and decaying jet whereas a reduction of the momentum flow in the far field is also observed.