Investigation of ultrasonic cavitation noise induced near elastic solid boundaries with different elastic modulus

Accompanying with cavitation, cavitation noise generated due to the bubble dynamics is always inevitable, but wholly undesirable, especially for the propeller of marine vehicles which requires high concealment. Nowadays, polymer composite material with good sound absorption capability and high cavitation inception speed due to its elastic deformation characteristics has been used to make propeller blades. Bubble dynamics near elastic boundaries is more complicated and has drawn more and more study interests. Yet, the effect of the elastic modulus on the cavitation noise is lack of attention and still not clear. Here, we show that the total sound pressure level (TSPL) of the measured cavitation noise is nonlinear with the elastic modulus of the solid wall. We adjusted the elastic modulus of polydimethylsiloxane (PDMS) by changing its base-to-agent ratio n and found that TSPL of PDMS3 (n = 20, E = 1.0 MPa) was 8 dB lower than that of PDMS1 (n = 5, E = 3.7 MPa) and 6 dB lower than PDMS2 (n = 10, E = 2.7 MPa). Yet, with further decrease in the elastic modulus (PDMS4, n = 30, E = 0.65 MPa), TSPL bounced back to almost the same value of PDMS1. It is attributed to the influence of the elastic boundary on the bubble dynamics. Only when the bubble collapsed with microjet totally away from the boundary, the lowest TSPL could be achieved. Furthermore, we found that the bubble dynamics of a single laser-induced bubble could be used as a point of reference for the cavitation noise of bubble clusters.