3D numerical simulation of pump cavitating behavior

The quasi-steady cavitating behavior of three pumps was investigated by 3D unsteady viscous computations. The numerical model is based on the commercial code FINE/TURBO™, which was adapted to take into account the cavitation phenomenon. The resolution resorts to a time-marching algorithm initially devoted to compressible flows. A low-speed preconditioner is applied to treat low Mach number flows. The vaporization and condensation processes are controlled by a barotropic state law that links the void ratio evolution to the pressure variations. A radial pump, a centrifugal pump, and a turbopump inducer were calculated and the cavitating behaviors obtained by the computations were compared to experimental measurements and visualizations. A reliable agreement is obtained for the two pumps concerning both the head drop charts and the extension of the vapor structures. A qualitative good agreement with experiments is also observed in the case of the turbopump inducer. The accuracy of the numerical model is discussed for the three geometries. These simulations are a first attempt to simulate the complete 3D cavitating flows in turbomachinery. Results are promising, since the quasi-steady behaviors of the pumps in cavitating condition are found quantitatively close to the experimental ones. A continuing effort is pursued to improve the prediction accuracy, and to simulate unsteady effects observed in experiments, as, for example, rotating cavitation

Numerical simulation of 3D cavitating flows: analysis of cavitation head drop in turbomachinery

International audienceThe numerical simulation of cavitating flows in turbomachinery is studied at the Turbomachinery and Cavitation team of LEGI (Grenoble - France) in collaboration with the French space agency (CNES) and the rocket engine division of SNECMA Moteurs. A barotropic state law is proposed to model the cavitation phenomenon and this model has been integrated in the commercial CFD code Fine/TurboTM, developed and commercialized by Numeca International. The numerical aspects of the work are mainly focused on numerical stability and reliability of the algorithm, when introducing large density variations through the strongly non linear barotropic state law. This research conducted first to changes in the way preconditioning parameters are calculated. Internal flows in turbomachinery have been deeply investigated. A methodology allowing the numerical simulation of the head drop induced by the development of cavitation has been proposed on the basis of computations in inducers and centrifugal pumps. These simulations have allowed the characterization of the mechanisms leading to the head drop and the visualization of the effects of the development of cavitation on internal flows

Numerical analysis of cavitation instabilities in inducer blade cascade

International audienceThe cavitation behavior of a four-blade rocket engine turbopump inducer was simulated by the computational fluid dynamics (CFD) code FINE∕TURBO™. The code was modified to take into account a cavitation model based on a homogeneous approach of cavitation, coupled with a barotropic state law for the liquid∕vapor mixture. In the present study, the numerical model of unsteady cavitation was applied to a four-blade cascade drawn from the inducer geometry. Unsteady behavior of cavitation sheets attached to the inducer blade suction side depends on the flow rate and cavitation number σ⁠. Numerical simulations of the transient evolution of cavitation on the blade cascade were performed for the nominal flow rate and different cavitation numbers, taking into account simultaneously the four blade-to-blade channels. Depending on the flow parameters, steady or unsteady behaviors spontaneously take place. In unsteady cases, subsynchronous or supersynchronous regimes were observed. Some mechanisms responsible for the development of these instabilities are proposed and discussed

Unsteady Cavitating Flows in Turbomachinery: Comparison of Two Numerical Models and Applications

Two numerical models for unsteady cavitating flows in turbomachinery are developed at The Turbomachinery and Cavitation team of LEGI (Grenoble). The first one was entirely developed in the laboratory for 2D unsteady flows, with the support of the French Space Agency CNES. It applies a pressure-correction method derived from the SIMPLE algorithm and a finite volume discretization on structured meshes. The second model for 3D flows has been developed in the FINE/TURBO TM CFD code in collaboration with the Numeca International society. The solver is based on an artificial compressibility method (preconditioning technique) with dual time stepping, adapted to the very large variation of the Mach number. The models are based on a single fluid approach to describe the liquid-vapour mixture. Applications are mainly performed using a barotropic state law to manage the relation between the local static pressure and the mixture density. The alternative consisting in solving a supplementary equation for the void ratio including empirical terms for vaporization and condensation has been tested in the 2D model and some comparative results between both physical approaches are presented. The lecture presents also a comparison between results obtained by the two numerical models on 2D unsteady cavitating flows, making use of the barotropic approach. A discussion about the influence of the numerical and physical parameters is proposed. Finally, examples of applications to 3D cavitating flows in centrifugal pump and turbopump inducer geometry are presented

Numerical simulation of cavitating flow around a 2D hydrofoil: barotropic approach

This paper presents a numerical study of the flow around a 2D hydrofoil, proposed as a test case for the CAV2003 workshop on physical models and CFD tools for computation of cavitating flows. Non-cavitating and cavitating conditions are investigated. The phenomenon of cavitation is modelled through a single fluid model, associated with an arbitrary barotropic state law. The non-cavitating study focuses on the influence of the turbulence model and on the dependence of the results to the mesh used in the computations. The results predicted by three different turbulence models (Baldwin-Lomax, Spalart-Allmaras and k-ε with extended wall function) are compared. The cavitating study first presents an unsteady behaviour of the partial cavity attached to the foil. A quasi-periodic shedding of vapour clouds is observed and in depth analysed. Then, an analysis of a supercavitating condition is performed

Simulation numérique d'un inducteur avec effets thermodynamiques

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Numerical simulation of cryogenic cavitating flows in an inducer

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