Pressure fluctuations in the turbulent boundary layer of a water flow with gas injection

The effect of diffusion injection of 0.1-35 volume percent of air bubbles through pores 150 or 800 microns in diameter in the wall of a rectangular water tunnel on the pressure fluctuation in the turbulent boundary layer of a 3-20-m/s flow is investigated experimentally using pressure sensors and visual observations. The roughness heights of the 200-mm-wide 110-mm-long fine and coarse porous sections are 40 and 10 microns, respectively; the Reynolds-number range of the flow is (2.5-15) x 10 to the 6th; and the absolute hydrostatic pressure is maintained at 1, 2, or 3.8 kgf/sq cm. The results are presented in graphs and discussed. It is found that the spectral density and correlation of the wall-pressure fluctuations are significantly decreased by the injection of air to concentrations of 15 percent or more.