A METHOD FOR ANALYSIS OF CAVITATING MARINE PROPELLERS IN NON- UNIFORM FLOW

The article presents a calculation method based on deformable lifting surface theo­ ry. This method enables hydrodynamic analysis of propellers of arbitrary geometry operating in three-dimensional non-uniform velocity field. In the course of analysis the time-dependent pressure distribution on the blades, the resulting unsteady hydrodynamic blade and shaft forces, the extent of unsteady sheet, bubble and tip vortex cavitation are calculated. Apart from description of the method the article includes the results of initial experimental verification based on cavitation tunnel tests with two propeller models. Analysis of different hydrodynamic aspects of marine propeller operation in the non-uniform flow behind ship stern has already become a standard element of the propeller design process. Application of theoretical methods for this purpose in­ stead of cavitation tunnel experiments has an obvious advantage in terms of time and cost, provided that their accuracy is acceptable. The method presented in this article is result of a compromise between as realistic a theoretical model as possible of the physical phenomena and limited computational resources available to the average propeller designer. The method is based on the unsteady lifting surface theory, modified especially to integrate the time-dependent cavitation phenomena into the lifting surface model. This approach is named the deformable lifting sur­ face theory as the dynamically changing cavities deform the initial geometry of the lifting surface. For each analysed blade position in the non-uniform flow the kin­ ematic boundary condition on the blade and dynamic boundary condition on the cavity surface are evaluated and the resulting distribution of velocity of cavity expansion (or contraction) is calculated. This leads to calculation of the cavity geometry for each analysed blade position. The geometry evaluated in the previous