WM-LES-Simulation of a Generic Intake Port Geometry

Fluid mechanical design of the cylinder charge motion is an important part of an engine development. In the present contribution an intake port geometry is proposed that can be used as a test case for intake port flow simulations. The objective is to fill the gap between generic test cases, such as the backward facing step or the sudden expansion, and simulations of proprietary intake ports, which are barely accessible in the community. For the intake geometry measurement data was generated on a flow-through test bench and a wall-modeled LES-simulation using a hybrid RANS/LES approach for near-wall regions was conducted. The objective is to generate and analyze a reference flow case. Since mesh convergence studies are too costly for scale resolving approaches only one simulation was done, but on a very fine and mostly block-structured numerical mesh to achieve minimal numerical dissipation. Also a steady-state RANS was done on the same mesh to identify the significance of the scale-resolving approach. However, to stabilize the RANS on the fine mesh, low-order schemes were required.

The results show that, both, the RANS and the LES predicted the integral values of swirl and mass flow measured on the test bench with decent accuracy. Both methods slightly differ, where the integral swirl coefficient from the WM-LES shows a better agreement with the experimental value. With respect to the turbulence it was found, that the instantaneous swirl number undergoes very significant fluctuations over, both, time and along the cylinder axis, while the time averaged value is nearly constant along the cylinder axis in, both, RANS and LES. The difference in swirl number between RANS and LES is existent already at the cylinder top and at the same time the flow exiting through the intake ports is also quite similar. The details of the flow around the valves reveal that the RANS-results overly damps regions of reversed flow, which seems to be the core reason for the different results.