Design of a swept wing wind tunnel model for study of cross-flow instability

The need to investigate the cross-ow instability resides on the fact that this is the main cause of laminar to turbulent transition for swept wing ows in free ight. In this paper the procedure to design a wind tunnel model for cross-ow instability investigation is illustrated. The steps that are presented involve the airfoil and the wall liners design and the estimation of the boundary layer growing on the model for the experiment con- ditions. Furthermore linear stability theory is applied to numerically computed boundary layer profiles in order to evaluate the ow stability to standing cross-ow waves of several wavelengths and for two different angles of attack. A preliminary evaluation of the wave- length of the most amplified cross-ow standing mode and its angle with respect to the free stream direction are presented. Wind tunnel tests encompassing oil ow visualization, surface pressure and boundary layer hot-wire measurements were performed validating the design procedure. The effectiveness of the wall liners to constrain the ow to a spanwise invariant arrangement is showed to be limited for the presented case. The results of linear stability theory are compared to the experimental observations showing good agreement for both the estimated wavelengths and wave angles. The validity of oil ow visualization for qualitative investigation of cross-ow instability is confirmed by hot-wire measurements. Natural occurring transition and forced cross-ow instability ows are investigated giving results in good agreement with published literature.