The cavitation erosion remains an industrial issue for many applications. This paper deals with the cavitation intensity, which can be described as the fluid mechanical loading leading to cavitation damage. The estimation of this quantity is a challenging problem both in terms of modeling the cavitating flow and predicting the erosion due to cavitation. For this purpose, a numerical methodology was proposed to estimate cavitation intensity from 3D unsteady cavitating flow simulations. CFD calculations were carried out using Code_Saturne, which enables U-RANS equations resolution for a homogeneous fluid mixture using the Merkle"s model, coupled to a - turbulence model with the Reboud"s correction. A post-process cavitation intensity prediction model was developed based on pressure and void fraction derivatives. This model is applied on a flow around a hydrofoil using different physical (inlet velocities) and numerical (meshes and time steps) parameters. The article presents the cavitation intensity model as well as the comparison of this model with experimental results. The numerical predictions of cavitation damage are in good agreement with experimental results obtained by pitting test.

methods

https://www.jstage.jst.go.jp/article/ijfms/10/3/10_254/_pdf

First Attempt on Numerical Prediction of Cavitation Damage on a Centrifugal Pump

Numerical Cavitation Intensity on a Hydrofoil for 3D Homogeneous Unsteady Viscous Flows

Lorsqu’un liquide est soumis a de fortes depressions, des bulles de gaz etde vapeur peuvent apparaitre en son sein. Ce phenomene est appele cavitation Ces bulles sont susceptibles d’imploser dans les zones de surpression etd’endommager les parois solides environnantes a travers la creation d’ecoulements violents. Dans les applications industrielles, ce phenomene d’erosionpar cavitation peut reduire la duree de vie des machines hydrauliques. Dans ledomaine biomedical, le phenomene d’erosion par onde de choc est utilise pourl’ablation de tissus mous ou la destruction de calculs renaux.Dans ce travail, a caractere numerique, nous nous interessons a une bulled’air isolee implosant au voisinage d’une paroi deformable sous l’effet d’unesurpression generee par une onde de choc incidente. Le travail de these aconsiste a mettre en place un couplage fluide structure pour simuler le phenomene d’implosion de la bulle dans la partie fluide et la deformation plastiqueengendree dans la partie solide. Pour cela, une strategie en deux etapes a etemise en oeuvre. La premiere etape a consiste a construire un code fluide avecmaillage mobile pour gerer le deplacement de l’interface fluide/solide. Le codedeveloppe est derive du modele numerique developpe par Eric Johnsen et al.a University of Michigan dans lequel nous avons implemente une methodeALE (Arbitrary Lagrangian Eulerian) permettant de passer d’une descriptioneulerienne sur maillage fixe a une description eulerienne sur maillage mobile.La seconde etape a consiste a modeliser la deformation elasto-plastique de lapartie solide au cours de l’implosion de la bulle grâce a un couplage fort ducode fluide avec le logiciel CAST3M. La communication entre les deux codesutilise la bibliotheque MPI.A l’issue du couplage, nous avons ete en mesure de simuler l’implosiond’une bulle d’air a proximite d’une paroi deformable. Nous avons pu calculerle niveau de deformation de la paroi solide ainsi que l’amortissement de la sur-pression en paroi pour plusieurs materiaux. L’outil numerique ainsi developpepermettra a terme d’etudier le comportement de revetements amortissants capables de proteger des structures industrielles de l’erosion de cavitation oud’optimiser les effets benefiques des traitements par onde de choc dans lesapplications biomedicales.

Additional excerpts

Interaction Fluide-Structure et Érosion de Cavitation

A strainer is a device composed of a perforated plate and mesh element designed to remove debris from fluid. Strainers are used in piping systems to protect sensitive equipment such as pumps and compressors against the dirt and particles carried by the fluid, thereby reducing maintenance and downtime. Strainers are available in different types and are generally considered either permanent or temporary strainers. Different parameters such as installation direction (applicable for conical strainers), strainer type selection, strainer flow open area, basket clogging, and filtration affect the strainers’ pressure drop, as discussed in this paper. Comparing different type of strainers, tee-type and conical-type strainers have higher pressure drop values compared to Y-type and basket-type strainers. Capacity or flow open area of a strainer affects the operation characteristics of the strainer in terms of how long the strainer can operate without cleaning and creating a pressure loss. Clogging the strainer using a finer screen or mesh increases the pressure drop. This paper discusses a model of pressure drop calculation for strainers developed based on the screen opening, viscosity of the fluid, component factor, body factor, etc., using the results from a case study of the pressure drop calculation for a 12″ class 300 strainer in 22Cr duplex material. In addition to discussing clean pressure drop for strainers, this article also reviews an example of pressure drop for a strainer in different cases of clogging (dirty pressure drop).

Handling the pressure drop in strainers

The paper presents a new two-phase flow approach to simulate unsteady cavitating flows. The study applied the in-house code neptune_cfd, which allows two-fluid modelling of liquid-vapor flows [1]. The code solves the ensemble-averaged equations of mass, momentum and energy conservation for each phase (liquid and vapour) for a total of six conservation equations. The equations system requires closure laws for the interfacial terms that represent the mass, momentum and energy transfers occurring between the liquid and vapor phases. An original approach is implemented by using an energy-source term based on the difference between the local enthalpy and its saturation value. 2D and 3D simulations are carried out for a NACA 65−012 hydrofoil with an angle of attack of 6°, a cavity length of 40% of the hydrofoil chord and different flow velocities. The methodology to obtain the cavity length and the main frequency of its periodic behavior is presented. Then the numerical results are compared with those previously obtained by a homogeneous approach [2] and with the available experimental data [3]. The quantitative predictions of the hydrodynamic characteristics (i.e. cavitation sigma number, cavity length, shedding frequency and cavity shape) obtained from two-phase flow modeling appear in better accordance with experimental data.

First Attempt on Numerical Prediction of Cavitation Damage on a Centrifugal Pump

Citations

Numerical Cavitation Intensity on a Hydrofoil for 3D Homogeneous Unsteady Viscous Flows

Interaction Fluide-Structure et Érosion de Cavitation

Handling the pressure drop in strainers

Numerical simulation of cavitating flows: comparison between two-fluid and homogeneous approaches

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