LES Simulation of ICE Non-Reactive Flows in Fixed Grids

The increasing of the overall engine performance requires the investigation of the unsteady engine phenomena affecting intake air flow and the air–fuel mixing process. The “standard” RANS methodology often doesn’t allow one to achieve a qualitative and quantitative accurate prediction of these phenomena. The aim of this paper is to show the potential and the limits of LES numerical technique in the simulation of actual IC engine non reactive flows in fixed grids. The paper introduces the use of a merit parameter suggested by Pope for evaluating the quality of the LES turbulence resolution [14]. A basic engine steady flow bench case has been simulated. The CFD code used is Fluent v6.2. The numerical results of a previous LES basic numerical analysis were used for setting up calculations. Large Eddy Simulations using the dynamic one-equation model and a simulation with the WALE sgs model [25] have been performed. In particular, the WALE sgs model has been used with and without wall functions. The numerical results obtained by WALE with wall functions have been compared with those obtained performing a RANS simulation of the same engine test case. The quality of the LES results were checked using the merit parameter when the dynamic one-equation model was used. The quality of the results can be rated as reasonably accurate and useful for engineering investigation. If large scale motion effects must be evaluated in engine flows, encouraging results can be achieved by using the WALE model. The latter allows one to reduce the near wall refinement maintaining a reasonably accuracy in reproducing such large scale flow structures.