Design and Control of Crossflow Instability Field

In order to find out the transition mechanism of crossflow dominant boundary layers in detail, experimental model which is composed of yawed flat plate with displacement upper body, is designed and full transition process from onset of transition to fully turbulent state is generated in the flat plate boundary layer Systematic measurement is conducted on this crossflow instability field using hot wire velocimetry with accurate traversing mechanism and effective flow visualizations. Results show that such a complicated flow condition, where several different disturbances are appearing and interacting, is occurring in the transition region. Such flow condition is quite similar to that of swept wing boundary layer flow. In the transition region, stationary crossflow vortices, crossflow instability unsteady mode, high frequency secondary instability mode are also measured. Schematic sketch of the obtained flow field where these instabilities are most amplified is drown. Directions and phase velocities of obtained disturbances are also measured, and indicated in one figure together with twisted boundary profiles. Secondary instability is successfully visualized by smoke visualization technique, and physical structure of the secondary instability is compared with the results of hot wire measurement. Good agreement is obtained especially for the travel direction of the secondary instability, discussions are also made concerning obtained interesting results.

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