| dc.description.abstract | Swirling flow and gas entrainment induced by vortex formation at pump intakes are possible causes for pump failures and damages. Thus, the avoidance of hollow surface vortices is a safety-related issue for all plants which require a reliable pump operation. The most efficient measure to avoid these problems is a sufficient submergence of the intake. An acceptable submergence can be determined by means of costly experiments, complex CFD calculations or special correlations. When using correlations their applicability for the specific case has to be taken into account carefully, because a universally applicable correlation is not available yet. Hence, there is a present need for improved correlations or numerical methods which are capable to compute the necessary submergence. Within the research alliance SAVE experiments and numerical simulations were performed to investigate the occurrence of surface vortices at industrial scales. Amongst others, the lengths of the gas cores of the surface vortices were measured with varying boundary conditions and the velocity fields were determined by means of PIV (Particle Image Velocimetry) measurements. These experiments were accompanied by CFD simulations, the results were compared with the experimental data. A methodology was developed based on single phase CFD simulations with ANSYS CFX in combination with the Burgers-Rott vortex model which can be used to compute the gas core length with very good accuracy. Additionally, two phase CFD simulations were performed which use a free surface model based on recent developments. In order to develop an improved correlation for the computation of the necessary submergence, which considers in particular the circulation in the approaching flow, several parameter studies were performed. As a result of these studies two new theoretical approaches for the limiting cases of very small and very large circulation were developed which yield new correlations for the computation of the necessary submergence of pump intakes. | nb_NO |
