Methode zur Berechnung der kavitierenden Stroemung als 2-Phasen Stroemung Abschlussbericht

Abstract

The present report describes a method to predict cavitation inception and development on hydrofoil sections by means of a 2 phase model. Two different concepts for the modelling of cavitation phenomena are shown. The first method -as initially proposed - features a pressure density relation that was integrated in an existing commercial RANSE Solver (Star CD). The limits of this method become clear when examining a typical velocity and pressure range. The sensitivity of the computed pressure is to high in order to predict reasonable results. A second alternative was developed to model the cavitating flow analogous to the prediction of a free surface in a fluid using an inviscid Volume of Fluid (VOF) method. The boundary between a fluid phase (water) and vapour is treated exactly in the same way as a free water surface. Cavitation inception on a body is stimulated when the local pressure falls under the given cavitation pressure described by the cavitation number #sigma#_v. The developing cavitation bubble is modelled by means of an additional source distribution. A transient computation is performed to find a new state of equilibrium. The method was tested using simple geometrical examples, e.g. a step in a canal. Parameters describing the source distribution were determined using this model. A comprehensive study of foil sections was performed and documented. Further, options for the extension of the method are described. Although the second approach using the inviscid VOF method does not comply with the initial idea of modelling cavitating flows by real 2 phase models, results appear to justify this method finally chosen. Extensive development work unfortunately did not allow to cover all aspects initially proposed, e.g. 3 dimensional flows over hydrofoils. The method developed however appears to be a prerequisite for a successful extension into 3 dimensions. (orig.)SIGLEAvailable from TIB Hannover: RN 3150(1627)+a / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekBundesministerium fuer Bildung, Wissenschaft, Forschung und Technologie, Bonn (Germany)DEGerman