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Title: Influence of the Adverse Pressure Gradient on the Swirling Flow
Published In: Conference on Modelling Fluid Flow (CMFF’15) The 16th International Conference on Fluid Flow Technologies Budapest, Hungary
Description: The flow in the draft tube cone of Francis turbines operated at partial discharge is a complex hydrodynamic phenomenon where an incoming practically steady axi-symmetric swirling flow evolves into a three-dimensional unsteady flow field with precessing helical vortex (also called vortex rope) and associated pressure fluctuations. The paper addresses the influence of the adverse pressure gradient on the swirling flow with vortex breakdown. Consequently, a 2D axi-symmetric model is used to compute the flow. The axi-symmetric swirling flow is computed using available turbulent swirling flow solvers by introducing a stagnant region model (SRM), essentially enforcing a unidirectional circumferentially averaged meridian flow as suggested by the experimental data. Full 3D unsteady flow simulations with same boundary conditions are performed for five cases from a straight pipe up to cone with angle of 25.5°. As a result, the numerical results are compared in order to assess the capabilities of simplified model. The evolution of the quasi-stagnant region is investigated. The vortex sheet angle that separates the quasi-stagnant region and the main flow is evaluated. The energy losses coefficient and kinetic to potential conversion ratio distributions are plotted along to the cone length in order to evaluate the performances. Also, the self-induced instability is quantified based on 3D full unsteady flow simulation.
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Publication year: 2015
Keywords:2D and 3D flow simulation, precessing vortex, swirling flow, self-induced instability, unsteady field analysis
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Authors: MUNTEAN Sebastian , TANASA Constantin , SUSAN-RESIGA Romeo , BOSIOC Ilie Alin ,
Type: International Conference Proceedings
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Laboratory: Numerical Simulation and Parallel Computing Laboratory
Institution: UPT