CAVITATION INDUCED HULL PRESSURES, SOME RECENT DEVELOPMENTS OF MODEL TESTING TECHNIQUES

The pressure signal induced on the hull by cavities on the propeller is the sum of three contributions due to different physical effects. The most important contribution is the one due to cavity volume variation. In order to get this contribution correctly reproduced for all types of ships by model tests in a cavitation laboratory, it is necessary to test the propeller in a wake distribution where the axial component has been corrected for scale effect. The tangential component is not so important. Cavitation tests have been carried out in both model wake and a wake corrected according to the Sasajima method. The latter test shows best agreement with corresponding full scale measurements. The possibility of wall effects during such measurements in a cavitation tunnel is discussed. A new technique to measure cavity geometry by photogrammetry is briefly described.