ANALYSIS OF MODERATELY AND STRONGLY SWIRLING FLOWS AT PUMP INTAKES IN ORDER TO DEVELOP EFFICIENT COMPUTATIONAL METHODS FOR THE DETERMINATION OF THE REQUIRED SUBMERGENCE

摘要

The aim of this study is the comparison of characteristic parameters of strongly and moderately swirling surface vortices. Strongly swirling vortices were examined in a test facility at the Hamburg University of Technology. In a previous work it was found that by using a combination of CFD simulations and the analytical vortex model of Burgers and Rott it was possible to compute the length of the gas core of the vortex. The knowledge of the gas core length is required to assess whether the submergence of the pump intake is large enough or not. Based on this approach an approach for strongly swirling flow was developed to compute the gas core length by means of analytical formulas /2/. This theory was also successfully applied to the independent experiment of Moriya /4/. However, this methodology fails for moderately swirling flow like in Jain’s experiment. Thus, in the present work a CFD simulation of Jain’s experiment was compared to CFD results from a simplified cylindrical model in a different length scale in order to identify the parameters which lead to the failure of the theory for strongly swirling flow. Due to the good agreement of the vortices in Jain’s experiment and the simplified model it was concluded that the shape of the surface vortex does not depend on case specific parameters of Jain’s experimental setup. It was observed that the combination of high Froude number and moderate circulation probably leads to tangential velocities which differ in dependency of the vertical coordinate. This is contrary to the basic assumption of the model of Burgers and Rott. This may lead to the deviation between experimental and calculation result for moderately swirling flow.