An Erosion Aggressiveness Index (EAI) Based on Pressure Load Estimation Due to Bubble Collapse in Cavitating Flows Within the RANS Solvers

Bergeles, G.; Li, Jason; Wang, Lifeng; Koukouvinis, Phoevos; Gavaises, Manolis

doi:10.4271/2015-24-2465

Cited by 15 publications

(5 citation statements)

References 12 publications

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“…Moreover, although recent studies [83][84][85] consider temperature effects, for the cases examined here, that refers to pilot injection at a rail pressure of 1600, temperature effects can be ignored. [86][87][88][89][90] The diesel properties employed in the simulations are the ones considered in the aforementioned study. 38 The air properties were computed using the NIST (REFPROP) library.…”

Section: Cavitation In a Diesel Injector With Needle Movementmentioning

confidence: 99%

A direct forcing immersed boundary method for cavitating flows

Stavropoulos-Vasilakis

Rodríguez

Kyriazis

et al. 2021

Numerical Methods in Fluids

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In the current study, an immersed boundary method for simulating cavitating flows with complex or moving boundaries is presented, which follows the discrete direct forcing approach. Although the immersed boundary methods are widely used in various applications of single phase, multiphase, and particulate flows, either incompressible or compressible, and numerous alternative formulations exist, to the best of the authors' knowledge, a handful of computational works employ such methodologies on cavitating flows. The herein proposed method, following previous works of the author's group, tries to fill this gap and to solidify the development of a computational tool of a simple formulation capable to tackle complex numerical problems of cavitation modeling. The method aims to be used in a wide range of applications of industrial interest and treat flows of engineering scales. Therefore, a validation of the method is performed by numerous benchmark test-cases, of progressively increasing complexity, from incompressible low Reynolds number to compressible and highly turbulent cavitating flows. K E Y W O R D Scavitation, diesel injector, direct forcing, immersed boundary method, turbulence modeling INTRODUCTIONWithin the framework of computational fluid dynamics, applications of industrial interest often refer to flows in complex geometries or around moving bodies; their simulation may be numerically challenging and computationally expensive. Many cases of cavitating flows fall into that category. For example, cavitation formation in diesel injector nozzles with moving needle, gear pumps, or propellers mounted under ship hauls, refer to problems with moving geometrical parts and include different geometrical features with wide range of length scales and topological features that impose severe constraints in mesh generation. The conventional strategy of generation of boundary-conforming grids for such problems, may become demanding and time consuming. When the numerical simulation involves moving parts with large displacements, common conformal grid strategies result in remeshing of the entire domain in every time-step, 1 or deforming the grid and adding or removing cell-layers when a desired cell size is reached. 2 In the case of marine propellers, to accommodate their rotational motion, either the entire computational domain would be rotated accordingly, 3 or a multi-region mesh would be used, which lets the part of the grid that conforms with the propeller blades to slide with regards to the global domain. 4 Another approach of over-set grids 5 (also known as Chimera grids), employs multiple overlapping 3092

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Section: Cavitation In a Diesel Injector With Needle Movementmentioning

confidence: 99%

A direct forcing immersed boundary method for cavitating flows

Stavropoulos-Vasilakis

Rodríguez

Kyriazis

et al. 2021

Numerical Methods in Fluids

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“…Various more recent attempts to define the flow aggressiveness and erosion risk have been presented in refs. − A cavitation aggressiveness index was defined by Koukouvinis et al, , considering the Lagrangian derivative of pressure and the collapsing time scales for a single bubble and for the whole vapor cavity. Bergeles et al instead used the acoustic pressure computed from the single bubble collapse to compute an erosion aggressiveness index and validated the model on a real eroded injector geometry. State-of-the-art compressible multiphase CFD simulations are capable to reproduce the interaction between pressure waves and the vapor dynamics, including the peak pressure values at the latest stages of a collapsing cavity.…”

Section: Introductionmentioning

confidence: 99%

“…In ref , the pressure peak values on the walls were recorded during the simulation using a pressure-based solver with a single-fluid LES approach for both, a microchannel flow and a real diesel injector. Additional fluid dynamics simulations relating pressures with locations indicative of erosion as well as quantitative X-ray measurements of the volume cavitation vapor volume fraction in diesel injector orifices were investigated by the authors in refs , , , and .…”

Section: Introductionmentioning

confidence: 99%

Influence of Diesel Fuel Viscosity on Cavitating Throttle Flow Simulations under Erosive Operation Conditions

et al. 2020

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This work investigates the effect of liquid fuel viscosity, as specific by the European Committee for Standardization 2009 (European Norm) for all automotive fuels, on the predicted cavitating flow in micro-orifice flows. The wide range of viscosities allowed leads to a significant variation in orifice nominal Reynolds numbers for the same pressure drop across the orifice. This in turn, is found to affect flow detachment and the formation of large-scale vortices and microscale turbulence. A pressure-based compressible solver is used on the filtered Navier–Stokes equations using the multifluid approach; separate velocity fields are solved for each phase, which share a common pressure. The rates of evaporation and condensation are evaluated with a simplified model based on the Rayleigh–Plesset equation; the coherent structure model is adopted for the subgrid scale modeling in the momentum conservation equation. The test case simulated is a well-reported benchmark throttled flow channel geometry, referred to as “I-channel”; this has allowed for easy optical access for which flow visualization and laser-induced fluorescence measurements allowed for validation of the developed methodology. Despite its simplicity, the I-channel geometry is found to reproduce the most characteristic flow features prevailing in high-speed flows realized in cavitating fuel injectors. Subsequently, the effect of liquid viscosity on integral mass flow, velocity profiles, vapor cavity distribution, and pressure peaks indicating locations prone to cavitation erosion is reported.

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“…In [5], Koukouvinis et al defined a cavitation aggressiveness index based on the Lagrangian derivative of pressure and the time scales of a single bubble and of the whole vapor cavity. Bergeles et al used instead the acoustic pressure of a single bubble collapse to develop an erosion aggressiveness index in [6]. The authors validated it on a real eroded injector geometry, that was also used by Koukouvinis et al in [7] to test the cavitation aggressiveness index.…”

Section: Introductionmentioning

confidence: 99%

Numerical simulation of compressible cavitating two-phase flows with a pressure-based solver

Cristofaro

Edelbauer

Gavaises

et al. 2017

Proceedings ILASS–Europe 2017. 28th Conference on Liquid Atomization and Spray Systems

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This work intends to study the effect of compressibility on throttle flow simulations with a pressure-based solver. The simple micro throttle geometry allows easier access for obtaining experimental data compared to a real injector, but still maintaining the main flow features. For this reasons it represents a meaningful and well reported benchmark for validation of numerical methods developed for cavitating injector flows. An implicit pressure-based compressible solver is used on the filtered Navier-Stokes equations. Thus, no stability limitation is applied on the time step. A common pressure field is computed for all phases, but different velocity fields are solved for each phase, following the multi-fluid approach. The liquid evaporation rate is evaluated with a Rayleigh-Plesset equation based cavitation model and the Coherent Structure Model is adopted as closure for the sub-grid scales in the momentum equation. The aim of this study is to show the capabilities of the pressure-based solver to deal with both vapor and liquid phases considered compressible. A comparison between experimental results and compressible simulations is presented. Time-averaged vapor distribution and velocity profiles are reported and discussed. The distribution of pressure maxima on the surface and the results from a semi-empirical erosion model are in good agreement with the erosion locations observed in the experiments. This test case aims to represent a benchmark for further application of the methodology to industrial relevant cases. Keywords cavitation erosion, compressible pressure-based, multi-fluid LES IntroductionDiesel injectors can suffer from cavitation erosion. Recent regulations in term of emissions forced engine manufacturers to increase the injection pressure to values above 2000 [bar]. The consequent higher velocities in the nozzle lead to the formation of a more diffused spray and, thus, better combustion. This causes higher engine efficiency and less emissions, but, at the same time, higher risk of cavitation. If the pressure reaches locally values below saturation pressure due to the high velocity, the liquid evaporates. Under certain conditions, the repetitive collapse of the generated vapor that is convected further downstream, where pressure is above the saturation pressure, may be an aggressive phenomenon. Fatigue damages can then appear on the nearby surfaces. Many works have been published in the last decades to predict cavitation erosion. Experimental campaigns are of crucial importance to gain a better understanding of the physical phenomena involved and to provide usable data for the validation of new models. Numerical approaches based on multi-phase Computational Fluid Dynamics (CFD) are able to model cavitating flow fields. Useful information can then be obtained to assess the probability of cavitation erosion appearance. A wide range of flow aggressiveness and erosion risk indices were developed in the recent years. A review of some selected cavitation erosion models, together with a descripti...

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An Erosion Aggressiveness Index (EAI) Based on Pressure Load Estimation Due to Bubble Collapse in Cavitating Flows Within the RANS Solvers

Cited by 15 publications

References 12 publications

A direct forcing immersed boundary method for cavitating flows

A direct forcing immersed boundary method for cavitating flows

Influence of Diesel Fuel Viscosity on Cavitating Throttle Flow Simulations under Erosive Operation Conditions

Numerical simulation of compressible cavitating two-phase flows with a pressure-based solver

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