The Influence of a Low Reynolds Number on an Impinging Round Jet
An impinging round jet is studied experimentally in a range of nozzle Reynolds number stretching from 5 500 to 44 000, and for an impact distance of 6 diameters. The turbulent structures in the free jet region and in the wall jet region is described by mean of conventional measurements (average, rms and power spectrum of the streamwise turbulent fluctuation), intermittent information and optical visualizations. For the present experimental conditions, the impact proves to have a significant influence on the free jet region; but the main result is the effect of the Reynolds number Re. The upstream and downstream behaviors exhibit the same trends. A decrease of Re provides an increase of the lateral spreading. This is best shown on the mean velocity and intermittency profiles. At low Re the rms of fluctuating velocity increases and we observe two peaks in the spectral distribution which are separated by a factor two in frequency. This fact can be interpreted as the result of successive pairings which is linked to the spreading process.
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