WAVE REFLECTION ON POROUS WALLS: NUMERICAL MODELLING AND APPLICATION TO TRANSONIC WIND TUNNELS

Transonic wind tunnel tests are often affected by wave reflections stemming from the edge of the test section that may be attenuated by using perforated end walls. In this work, a numerical model is presented that includes a novel boundary condition for thick walls, that can be used to enhance perforated wind tunnel test section designs. An in-house finite volume scheme for compressible inviscid flows is enhanced by the addition of a new perforated wall boundary condition. This wall condition is based on the assumption that the wall thickness is larger than the perforation size or diameter, which is common of transonic wind tunnels with single leaf walls. The model was validated against a simple oblique shock reflection test case. The model predictions were shown to be an improvement with respect to those from a benchmark perforated wall boundary condition that assumes a small wall thickness in relation to the perforation size. A numerical and experimental study was conducted of the end wall effects in a chocked nozzle turbine linear cascade, discharging at Mach 1.27. Without a perforated wall, the cascade displays strong end wall trailing edge shock reflections, giving a pitchwise non-periodic discharge. A numerical model flow with a 50% void ratio tailboard indicated some regain in flow periodicity, as verified by experiment. The thick wall model better reproduced the flow features documented in the flow visualisations than the benchmark model, indicating that this is a better boundary condition to enhance perforated tailboard designs for compressible model flows.