Abstract

The computation of the characteristic of hydraulic machines, both in pump and turbine mode, needs, when performed over a wide operating range, to take into account turbulence anisotropy. This because highly separated flows largely deviate from isotropic turbulence structures as assumed in RANS eddy viscosity models with the Boussinesq approximation. In this paper CFD computations were performed with anisotropic turbulence models in order to capture the characteristic and investigate flow structures phenomena. Experimental results are compared against the CFD simulations in order to validate the results. Specific occurring phenomena are highlighted and more complex flow structures are evident compared to those computed with standard eddy viscosity models. A in-house pressure based coupled solver was used for the CFD simulations. The code is a finite volume polyhedral CFD solver implemented in a C++ framework with the possibility to implement implicit and coupled algorithms. Second moment closure turbulence model have been successfully implemented with a standard and novel fully coupled algorithm. In the paper the advantage of the novel algorithm is presented for industrial applications. The fully coupled approach for the Reynolds Stress model allows stable simulations of transient and steady state hydraulic machines at any operating point, opening also new opportunities in obtaining high accurate results for anisotropic turbulent flows without the usage of hybrid LES/RANS models and without the model limitation of standard eddy viscosity models.

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