Turbulence Modelling in CFD Simulation of ICE intake flows

The paper is focused on the influence of the eddy viscosity turbulence models (EVM) in CFD three-dimensional simulations of steady turbulent engine intake flows in order to assess their reliability in predicting the discharge coefficient. Results have been analysed by means of the comparison with experimental measurements at the steady flow bench. High Reynolds linear and non linear and RNG k-ɛ models have been used for simulation, revealing the strong influence of both the constitutive relation and the ɛ-equation formulation on the obtained results, while limits in the applicability of more sophisticated near-wall approaches are briefly discussed in the paper.

Due to the extreme complexity of typical ICE flows and geometries, the analysis of the behaviour of EVM turbulence models has been subsequently applied to a test-case available in literature, i.e. a high-Reynolds compressible flow over a inclined backward facing step (BFS). Different high-Reynolds and low-Reynolds linear and quadratic k-ɛ models, linear and quadratic RNG k-ɛ models and linear and quadratic two-layer models have been used for simulation. The predicted velocity profiles at different locations along the duct have been compared versus experiments available in literature.

The EVM model constitutive relation as well as near-wall treatment were found to be fundamental for accurately predicting the flow characteristics. In the recirculation regions the non-linear EVM models behave much better than the standard linear EVM thanks to their more accurate physical ground, thus determining the best agreement with experimental data. Simulations revealed also limits of the RANS approach and related EVM when faced with typically unsteady and complex phenomena like flow separation as those occurring in engine intake ducts.