Reynolds Number Effects on Fully Developed Pulsed Jets Impinging on Flat Surfaces

A systematic study of the effect of the Reynolds number on the fluid dynamics and turbulence statistics of pulsed jets impinging on a flat surface is presented. It has been suggested that the influence of the Reynolds number may be somewhat different for a jet subjected to pulsation when compared to an equivalent steady jet. A comparative study of both steady and pulsating jets is presented for a Reynolds number range from Re=4,730Re=4,730 to Re=10,000Re=10,000. All the other factors that affect the flowfield are kept constant, which are H/d=3H/d=3, St=0.25St=0.25, and d=30.5  mmd=30.5  mm. It was found that for the range of the Reynolds numbers tested, pulsation results in a shortening of the jet core, the centerline axial velocity component declines more rapidly, and higher values of the radial velocity component for r/d>0.75r/d>0.75 are observed. As the Reynolds number increases, the jet spreads more rapidly, the turbulent kinetic energy and nondimensional turbulent fluctuations decrease, and the flowfield near the impinging surface changes drastically, which is evident with the development of a turbulent momentum exchange interaction away from the wall for r/d>1.5r/d>1.5.