Computational Study of Unsteady Cavitating Flows and Erosion in a Fuel Nozzle

Shear-driven cavitation plays an important role in many technological applications, including fuel injectors and power generators. Cavitation affects the performance of components and hence it is desirable to understand and predict its behavior since it can have favorable as well as adverse consequences. Although there have been a vast number of studies, a full understanding or theoretical framework describing its behavior has not yet been achieved. This is in part due to the complexities associated with cavitating flows including, internal flow physics, turbulence, two-phase flow and non-equilibrium thermodynamics. Further, experimental techniques are limited in their ability to visualize the phenomena with sufficient resolution for a detailed analysis. In this work, an unstructured, finite volume, computational fluid dynamic (CFD) code coupled to the Eulerian-Eulerian multi-fluid model is utilized to study cavitation phenomena in a nozzle. The well-reported Winkhlofer nozzle at a range of conditions including ΔP = 20, 40, 60, 70, 75, 80, and 85 bar is modeled using n-dodecane reference fuel properties. Three cavitation sub-models were investigated and the results compared with previous experimental and simulation flow data. The flow turbulence was modeled using Reynolds Averaged Navier Stokes Equation (RANS) and Large Eddy Simulation (LES) models and the results evaluated. A mesh sensitivity analysis was conducted with minimum cell sizes of 13.40, 9.48, 7.55, and 6.13 μm were considered to show grid convergence. Further, a novel erosion model was also integrated to identify the potential vulnerability damage zones with respect to the nozzle flow operating conditions. The results were in good agreement with experimental data from optical nozzles as well as previous simulation results. The models capture the cavitation near the solid boundary region and were able to predict the critical cavitation as well as the chocked flow regions. This was consistent with all the models. The results from the erosion model revealed a direct relationship between surface erosion, in terms of Mean Depth of Penetration Rate (MDPR) and incubation time, to higher pressure drops across the nozzle. These findings can be useful to develop future injector nozzle designs that can better mitigate cavitation induced material damage for improved engine endurance.