Large Eddy Simulation of a Steady Flow Test Bench Using OpenFOAM®

Stationary flow bench testing is a standard experimental methodology used by the automotive industry to characterize a cylinder head. In order to reduce the development time, the use of a CFD-based virtual test bench is nowadays a standard practice too. The use of a conventional RANS methodology for the simulation of the flow through the ducts of an engine head allows to get only the mean flow variables distributions because the time average of the generic flow variable fluctuation is zero by definition, but the fluid-dynamics of a stationary flow bench is not really stationary due to the flow instability induced by the duct design and the interaction between valve jets in a multi-duct head. In order to obtain an in-depth knowledge of the fluid-dynamics of a stationary flow bench test rig a LES simulation of a heavy duty DI diesel engine head with two intake ducts, for which experimental data was available, has been carried out using OpenFOAM®. The comparison between LES, experimental and conventional RANS results widened the understanding of the test-bench fluid-dynamics and of the swirl generation process. Due to the high computational cost of the LES approach, the outcomes of this latter have been also used to evaluate potential accuracy improvements of the RANS simulation, namely using a model sensible to flow anisotropies and curvatures such as a RSTM model. The simulation with the new turbulence model has been carried out and compared with the previous results demonstrating predictive improvements with an affordable computational cost for industrial routine usage.