On numerical simulation of cavitating flows under thermal regime

International audienceIn this work, we investigate closure laws for the description of interfacial mass transfer in cavitating flowsunder thermal regime. In a first part, we show that, if bubble resident time in the low pressure area of theflow is larger than the inertial/thermal regime transition time, bubble expansion are no longer monitoredby Rayleigh equation, but by heat transfer in the liquid phase at bubbles surfaces. The modelling of inter-facial heat transfer depends thus on a Nusselt number that is a function of the Jakob number and of thebubble thermal Péclet number. This original approach has the advantage to include the kinetic of phasechange in the description of cavitating flow and thus to link interfacial heat flux to interfacial mass fluxduring vapour production. The behaviour of such a model is evaluated for the case of inviscid cavitatingflow in expansion tubes for water and refrigerant R114 using a four equations mixture model. Comparedwith inertial regime (Rayleigh equation), results obtained considering thermal regime seem to predictlower local gas volume fraction maxima as well as lower gradients of velocity and gas volume fraction.It is observed that global vapour production is closely monitored by volumetric interfacial area (bubblesize and gas volume fraction) and mainly by the Jakob number variations. It is found that, in contrast withphase change occurring in common boiling flow, Jakob number variation is influenced by phasic temper-ature difference but also by density ratio variation with pressure and temperature

From Computational Fluid Dynamics (CFD) to Mass Loss Prediction in Cavitation Erosion"

International audienc

28th IAHR symposium on Hydraulic Machinery and Systems (IAHR2016)

International audienc

Cavitation Erosion Mechanism: Numerical Sumulations of the Interaction Between Pressure Waves and Solid Boundaries

To evaluate the aggressiveness power of cavitating flows and to improve prediction methods for cavitation erosion, the pressure waves emitted during bubble collapses were studied and simulated by means of the Keller's and Fujikawa and Akamatsu's physical models. The profile and the energy of the pressure waves emitted during cavity collapse were evaluated by numerical simulation. The dynamic response and the surface deformation (i.e., pit profile and pit volume) of various materials exposed to pressure wave impacts was simulated making use of a 2D axisymmetric numerical code simulating the interaction between pressure wave and an elastoplastic solid. Making use of numerical results, a new parameter b (defined as the ratio between the pressure wave energy and the generated pit volume) was introduced and evaluated for three materials (aluminum, copper and stainless steel). By associating numerical simulations and experimental results concerning pitted samples exposed to cavitating flows (volume damage rate), the pressure wave power density was introduced. This physical property of the flow characterizes the cavitation aggressiveness and can be related to the flow hydrodynamic conditions. Associated to b parameter, the pressure wave power density appeared to be a useful tool to predict the cavitation erosion power

Modélisation des écoulements turbulents instationnaires par une approche moyennée : application à la cavitation

Séminaire Daniel Dautreppe 2008, turbulence : aspects fondamentaux et applications, 20-24 octobre 2008, Grenoble, France

Equation of state for cavitating flows with thermodynamic effects

International audienc

Numerical methodology to predict and analyze cavitating flow in a Kaplan turbine

International audienc

Numerical methodology to predict and analyze cavitating flows in a Kaplan turbine

International audienc

Mécanismes d'interactions fluide/structure et de transfert d'énergie en érosion de cavitation

L'érosion de cavitation se caractérise dans un premier temps par une période de marquage sans perte de masse. Afin d'étudier cette phase, une étude locale a tout d'abord été effectuée : une approche énergétique des ondes de surpressions émises lors du collapsus d'une bulle et de leur interaction avec une paroi solide a été réalisée. Cette approche a mis en évidence un paramètre caractéristique du marquage reliant la déformation finale à l'énergie de l'onde impactante ne dépendant que des propriétés mécanique du matériau. Une comparaison expérimentale a donné une première validation de notre modèle local. Nous avons étendu ce modèle à un aspect global avec l'introduction d'une puissance potentielle liée à l'hydrodynamique de l'écoulement cavitant et d'un rendement d'agressivité caractérisant l'agressivité d'un écoulement vis à vis d'un matériau. Une comparaison avec deux expériences menées à EDF a permis de donner une première validation de notre approche.GRENOBLE1-BU Sciences (384212103) / SudocSudocFranceF

Numerical study of pump-turbines instabilities: prediction and analysis of rotating stall

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