APPLICATION OF A NUMERICAL OPTIMIZATION TECHNIQUE TO THE DESIGN OF CAVITATING PROPELLERS IN NONUNIFORM FLOW

High-speed propulsor blades often experience moderate to substantial a mounts of unsteady cavitation, and up to now have been designed via de sign methods for noncavitating blades combined with methods for the an alysis of cavitating flows in a trial-and-error manner. In this paper, a numerical nonlinear optimization algorithm is developed for the aut omated, systematic design of cavitating blades. The method is first ap plied to the design of propeller blades in uniform flow. The blade mea n camber surface is defined via a cubic B-spline polygon net in order to facilitate the handling of the geometry, and to reduce the number o f the design parameters. Noncavitating blade geometries designed by th e present method are directly compared with those designed via an exis ting lifting-line/lifting-surface design approach. Finally, the optimi zation algorithm is applied to the design of cavitating blades in nonu niform flow. The objective of the design is to obtain maximum propelle r efficiency for given conditions by allowing controlled amounts of sh eet cavitation. Several constraints on the unsteady cavity characteris tics, such as the area of cavity planform and the amplitudes of the ca vity volume velocity harmonics, are incorporated in the optimization t echnique. The effect of the constraints on the efficiency of the prope ller design is demonstrated with various test cases.