Experimental studies on cavitation inception in a submerged jet

The characteristics, intensity, and spectral distribution of the noise generated at cavitation inception and their variations with the diameter of the jet orifice were studied. In the noncavitating range the rms pressure changes proportionally to root sigma. The inception range is characterized by a sharp increase of rms pressure with reduction in cavitation number. Comparison of statistically counted crossings of the pressure fluctuation signal through zero level, to those expected for a random signal with normal distribution, indicates that in the inception range the pressure fluctuation impulses do not obey the characteristics of random impulses with normal distribution. Investigation of the power spectral density (PSD) functions shows that when PSD curves are presented in log-log scale, they are enclosed by two envelopes. The lower one is a theoretical noncavitating, no-air spectra line. For the noncavitating range the spectrum is the same at lower frequencies as the theoretically predicted one, but increases slightly at higher frequencies.