Measurement of cavitation induced wall shear stress

The wall shear stress from cavitation bubbles collapsing close to a rigid boundary is measured with a constant temperature anemometer. The bubble is created with focused laser light, and its dynamics is observed with high-speed photography. By correlating the frames, a hydrophone signal, and the wall shear stress, we find that the highest stresses are created after the impact of the jet, during its radial spreading on the surface. The maximum of the wall shear stress varies with the power of $−2.75$ as a function of the distance from the jet impact and in accordance with the prediction for a steady wall impinging jet. The highest amplitude of the signal of the wall shear stresses is found for bubbles oscillating close to the boundary and reaches more than 3 kPa. Additionally, it contains a slowly decaying weaker component that may be generated by an expanding vortex ring.