Mach-6 Receptivity Measurements of Laser-Generated Perturbations on a Flared Cone.

摘要

A better understanding of receptivity can contribute to the development of an amplitude-based method of transition prediction. This type of prediction model would incorporate more physics than the widely-used semi-empirical methods. The experimental study of receptivity requires a characterization of the external disturbances and a study of their effect on the boundary-layer instabilities. Characterization measurements for a laser-generated perturbation were made in two different wind tunnels. These measurements were made with hot-wire probes optical techniques, and pressure transducer probes. Existing methods all have limitations so better measurements will require the development of new instrumentation. Nevertheless, the freestream laser-generated perturbation has been shown to be about 8 mm in diameter at a freestream static density of about 0.040 kg/cu m. The amplitude of the perturbation is large, with a pitot pressure deficit at the center of the perturbation of about 65%. This amplitude may be too large for the study of linear growth. The laser-generated perturbation was then placed in the freestream of the Boeing/AFOSR Mach-6 Quiet Tunnel (BAM6QT) upstream of a model. It was aligned to the centerline of a flared cone at zero angle of attack. The interaction of this laser-generated perturbation with the flared cone was measured with surface-mounted fast pressure transducers. A wave packet was generated by the perturbation and grew to nonlinear amplitudes along the length of the cone. Initial amplitudes of this wave packet were estimated to be very small compared to the freestream disturbance amplitude. A marked difference was seen when different radii nosetips were used. On the flared cone with a blunt 1-mm nosetip, the generated wave packet only appeared near the aft end of the cone. On the flared cone with a nearly sharp nosetip, the generated wave packet appeared at all sensor locations.