Development and validation of a boundary layer control system to increase intake port steady permeability

Engine permeability, which is commonly knownto exert a strong influence on engine performances, isusually experimentally addressed by means of thedefinition of a global parameter, the steady dischargecoefficient. Nevertheless, the use of such a parameter todescribe valve-port assembly behaviour appearssometimes to be insufficient to determine portfluidynamic behaviour, due to the simultaneousconcurrency of complex mechanisms, such as meanflow distortions and boundary layer detachments. CFDsimulation appears therefore to be a fundamental tool tofully understand port fluidynamic behaviour.In the present paper, two engine intake portassemblies are investigated by using the STAR-CD CFDcode, showing a strongly different behaviour from thepoint of view of secondary detached flows generationacross the valve. Flow separation in the valve seatregion reveals to be detrimental on engine steadybreathing performances, since the subsequentrecirculation region strongly limits the valve curtainusage and forces the mean flow to crash against thevalve. In order to reduce the growth of secondarydetached flows upstream of the valve seat, the detachfavourableport is equipped with a boundary layer controlpneumatic device, which proves to be capable of nearlyeliminating flow separation in the valve region. Thissolution is finally compared to the non-detaching design,showing a non negligible benefit in terms of dischargecoefficient, and therefore engine permeability. Since theevaluation of the steady-flow discharge coefficient andflow patterns of ICE port assembly is strongly sensitiveto the capability of the turbulence sub-models incapturing the boundary layer dynamics, cubic low-Reynolds k-ε model is used for simulations.