Large-eddy simulation of turbulent cavitating flow in a Diesel injector including needle movement, in OpenFOAM®
Konstantinos Kolovos  1@  , Nikolaos Kyriazis  2@  , Phoevos Koukouvinis  2@  , Manolis Gavaises  2@  , Jason Z. Li  3@  , Robert M. Mcdavid  3@  
1 : 1Perkins Engines Company Ltd
Peterborough, PE1 5NA -  United Kingdom
2 : City University London
Northampton Square EC1V 0HB -  United Kingdom
3 : Caterpillar Inc
Mossville, IL 61552 -  United States

In this work the turbulent cavitating flow, inside a five-hole common rail Diesel injector and the effect of cavitation on erosion is investigated for the opening cycle of the injection. An explicit density-based solver of the compressible Navier-Stokes (NS) equations of the Arbitrary Lagrangian–Eulerian (ALE) formulation, suitable for cavitating flows is implemented in the open-source CFD code OpenFOAM®. Numerical fluxes are calculated based on the hybrid approximate Riemann solver. The hybrid scheme provides a Mach number consistent numerical flux, suitable for subsonic up to supersonic flow conditions. Finite Volume (FV) discretization is employed in conjunction with a fourth order Runge-Kutta time integration scheme. The thermodynamic closure is based on a barotropic Equation of State (EoS) for the liquid and vapour phases. The cavitation model is based on a thermodynamic equilibrium assumption and the compressibilities of the liquid and the liquid-vapor mixture are taken into account. The injector needle movement is represented by a cell-based mesh deformation method to ensure mass conservation which accounts for the Space Conservation Law (SCL). This work focuses on potential erosion and on the development vortical structures. First, the potential erosion regions are predicted though three different indexes, the maximum collapse pressures and the erosion damage model. The latter is coupled with the CFD code. The three indexes are compared with experimental results, from CT scans. The structure of the flow is analysed with an emphasis on the interaction between coherent vortical structures and cavitation. The Wall Adapting Local Eddy viscosity (WALE) LES model was used to predict incipient and developed cavitation, while also capturing the shear layer instability, vortex shedding and cavitating vortex formation. The analysis of the turbulent flow field reveals that the opening phase of the injection event consists of four different stages. Initially a negative mass flow rate is observed, followed by a second stage characterized by a complex vortical cavitation in the sac. String cavitation in the orifice is observed during the third stage. At the last stage the cavitation region in the orifice exhibits coherent cavitation structures both in the axial line as sting cavitation and on the orifice surface as shear induced cavitation. Violent collapse events of cavitation structures are detected during the opening phase. Moreover, this work revealed the formation of thin and thick string cavitation in the orifice volume and the effects on the flow pattern in the orifice and at the exit of the orifice.

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