SHAPE OPTIMIZATION IN HIGH-SPEED HYDRO- AND AERODYNAMICS TO PREVENT SEPARATION AND CAVITATION

The volumetric pressure drag for the standard supercavitating bodies (such as disc or cone) and for the cavitators with curvature was estimated. Analytic formulas for the skinfriction drag of the unseparated slender axisymmetric shapes are presented. It was shown that the main reserve of the drag reduction consists in using shapes providing the unseparated flow pattern. The volumetric drag coefficients for supercavitating and unseparated flow patterns were compared. It was shown that the standard supercavitating flow pattern is preferable for smaller values of the volumetric Reynolds number Re to be close to minimal possible valueσ ≈ 0.01. Some efficiency comparison is also presented for the unsteady movement on inertia. I was shown, for supercavitating flow pattern the maximum range be achieved with the use of special shapes of the bodies located in the cavity. These shapes are different for different isoperimetric conditions, but for large Reynolds numbers the unseparated bodies are preferable. In order to achieve the flow pattern without separation and cavitation the special shaping only was used. The presented unseparated shapes allow reducing the drag and the noise without any additional energy supply, since there is no need in using active boundary-layer control methods (such as suction, blowing or heating). They can be used in water and as well in air. Theoretical and experimental results concerning the axisymmetric unseparated bodies are presented. 2D airfoils with negative pressure gradients over the surface are calculated. Examples of sub- and supersonic axisymmetric shapes without separation are presented. The presented unseparated shapes could be also use to prevent cavitation or to improve the cavitation inception characteristics.