Abstract
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.
Highlights
Significant efforts have been made in the last two decades to develop models able to predict the appearance of cavitation erosion in fuel injection equipment.[1−4] The complexity of the phenomenon, in terms of both geometrical parameters and operation conditions, makes its prediction a nontrivial task
The wide range of numerical models available in the literature is mainly validated against measurements obtained in enlarged injectors or simplified real-size nozzles operating at lower pressures.[5−12] Numerical models based on multiphase computational fluid dynamics (CFD) are able to predict the phase-change process and the hydrodynamic phenomena occurring in cavitating flows and provide useful information with regard to cavitation erosion
The coarse mesh profile is significantly different compared to the other two meshes because the higher numerical diffusion caused by the poorer spatial discretization leads to a change in the flow regime, to what is presented
Summary
Significant efforts have been made in the last two decades to develop models able to predict the appearance of cavitation erosion in fuel injection equipment.[1−4] The complexity of the phenomenon, in terms of both geometrical parameters and operation conditions, makes its prediction a nontrivial task. 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 4, 23, 26, and 27. Turbulence is resolved using LES with the coherent structure model;[37] recent studies from the authors have shown that it is able to capture most of the turbulent scales of the flow, strictly correlated with cavitation phenomena.[38] The contribution of the present work is the investigation of the effect of different diesel viscosity values within the range defined by the European norm[39] for commercial diesel fuels on cavitation erosion phenomena. Because evaporation and condensation processes are the dominant effects on mixture compressibility,[25,46] vapor density was considered constant to reduce the complexity of the model without losing its accuracy
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