The influence of a low Reynolds number on an impinging round jet

An impinging round jet is studied experimentally in the range of nozzle Reynolds numbers 5,500-44,000, and for an impact distance of 6 diameters. The turbulent structures in the free-jet region and in the wall-jet region are described by the 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 flows exhibit the same trends. A decrease in Re provides an increase in the lateral spreading. This is best shown on the mean velocity and intermittency profiles. At low Re, the rms of fluctuating velocity increases and two peaks are observed in the spectral distribution which are separated by a factor of two in frequency. This fact can be interpreted as the result of successive pairings which are linked to the spreading process.