A study of three-dimensional, incompressible, turbulent wall jets

Abstract

Abstract : The report presents an experimental investigation of the mean properties of turbulent, three-dimensional, incompressible air jets issuing into a quiescent air ambient from various rectangular orifices parallel to, and at the surface of, a flat plate. An analytical approach to estimate the shear stress distribution at the plate is also presented. The flow field of a three- dimensional wall jet is found to be characterized by three distinct regions in the axis velocity decay. From the results obtained it is concluded that for three-dimensional wall jets the maximum velocity in the flow in the near field exhibits a decay rate dependent on orifice geometry, while far downstream of the jet exit it decays at the same rate as that in a radial wall jet flow field independent of orifice geometry. Furthermore, it is shown that the growth of the mixing layer normal to the plate is apparently independent of orifice shape while the near field spanwise growth is affected by initial geometry. Irregularities in the spanwise distribution of streamwise mean velocity attest to the strong three-dimensionality in the near field of the wall jets studied. These irregularities are manifested as local excesses, or defects, in the velocity profile. Such results indicate that the characterization of the wall jet flow field generated by a finite slot as quasi-two-dimensional may be of questionable validity.