Development And Validation of a Boundary Layer Control System to Increase Intake Port Steady Permeability 2004-01-0111

Engine permeability, which is commonly known to exert a strong influence on engine performances, is usually experimentally addressed by means of the definition of a global parameter, the steady discharge coefficient. Nevertheless, the use of such a parameter to describe valve-port assembly behaviour appears sometimes to be insufficient to determine port fluidynamic behaviour, due to the simultaneous concurrency of complex mechanisms, such as mean flow distortions and boundary layer detachments. CFD simulation appears therefore to be a fundamental tool to fully understand port fluidynamic behaviour.

In the present paper, two engine intake port assemblies are investigated by using the STAR-CD CFD code, showing a strongly different behaviour from the point of view of secondary detached flows generation across the valve. Flow separation in the valve seat region reveals to be detrimental on engine steady breathing performances, since the subsequent recirculation region strongly limits the valve curtain usage and forces the mean flow to crash against the valve. In order to reduce the growth of secondary detached flows upstream of the valve seat, the detach-favourable port is equipped with a boundary layer control pneumatic device, which proves to be capable of nearly eliminating flow separation in the valve region. This solution is finally compared to the non-detaching design, showing a non negligible benefit in terms of discharge coefficient, and therefore engine permeability. Since the evaluation of the steady-flow discharge coefficient and flow patterns of ICE port assembly is strongly sensitive to the capability of the turbulence sub-models in capturing the boundary layer dynamics, cubic low-Reynolds k-ε model is used for simulations.