An experimental and computational study was made of a single circular jetimpinging onto a flat ground board. A 1/2" nozzle running at a fixed nozzle pressure ratioof 1.05 was used in the experimental phase (giving an nozzle exit Reynolds number of90xlO'), the nozzle to ground plane separation being varied between 2 and 10 nozzlediameters. Measurements were performed in the free and wall jets using single andcross-wire hot-wire anemometry techniques and pitot pressure probes in order todetemine mean velocity and normal and shear stress distributions. Some analysis is alsopresentedo f earlier measurementso n high pressurer atio impinging jets.Nozzle height was found to effect the initial thickness of the wall jet leaving theimpingement region, increasing nozzle to ground plane separation increasing the wall jetthickness, although this separation distance did not seem to affect the rate at which thewall jet grew. Nozzle height was also found to have a large effect on the peak level ofturbulence found in the wall jet up to a radial distan ce from the jet axial centre line of4.5 nozzle diameters, after which the profiles become self-similar. Lowering the nozzletended to increase the peak level measured in all the turbulent stresses within thisdevelopment region. The production of turbulent kinetic energy in the wall jet, which isan indication of the amount of work done against the mean flow by the turbulent flowwas found to increase dramatically with decreasing nozzle height. This was attributed togreater shearing of the flow at lower nozzle heights due to a thinner wall jet leaving theimpingement region. A moving impingement surface was found to cause separation ofthe wall jet inner boundary layer on the 'approach' side leading to very rapid decay ofpeak velocity. The point of separation was found to occur at radial positions in theregion of 7.0 to 8.0 nozzle diameters, this reducing slightly for lower nozzle heights.A parametric investigation was performed using the k-e turbulence model and thePHOENICS CFD code. It was found that due to inadequacies in the model, it failed topredict accurately the growth of the wall jet, both in terms of its initial thickness and therate of growth. It did, however, predict an increase in wall jet thickness with both increasing nozzle height and exit turbulence intensity and decreasing nozzle pressureratio. Modifications were made to the constants in the model to try and improve thepredictions,w ith a limited degreeo f successT. he low Reynoldsn umber k-F-t urbulencemodel was shown to give a slightly improved non-dimensional wall jet profile, althoughthis did not improve the predicted rate of growth of the wall jet.
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