Effect of acoustic perturbations on flow structure in boundary layer with unfavorable pressure gradient
Abstract
An experimental study was made concerning the effect of an acoustic field on the flow in a laminar boundary layer with an unfavorable pressure gradient. A boundary layer with a longitudinal pressure gradient was realized on a foil facing the air stream at a zero angle of attack along the channel axis. A dynamic loud-speaker in the diffuser emitted sound waves in the upstream direction, thus exciting acoustic velocity and pressure perturbations. The frequency of sound was varied over the 30-250 Hz range in 4 Hz bands and the sound pressure within the test zone was maintained within 90-105 dB or 20-30 dB above the integral-spectral ambient noise pressure, at a stream velocity V infinity = 5.7 m/s. Both average and fluctuation velocity profiles were measured with a constant-temperature hot-wire anemometer. The results reveal accordingly that two-dimensional eddy fluctuations, occurring at the acoustic frequency, become appreciable farther downstream where the pressure gradient becomes unfavorable and acoustic perturbations transform into Tollmin-Schlichting waves within the instability frequency range.
- Publication:
-
USSR Rept Eng Equipment JPRS UEQ
- Pub Date:
- April 1984
- Bibcode:
- 1984RpEE........36D
- Keywords:
-
- Laminar Boundary Layer;
- Perturbation;
- Pressure Gradients;
- Velocity Distribution;
- Hot-Wire Anemometers;
- Sound Pressure;
- Tollmien-Schlichting Waves;
- Fluid Mechanics and Heat Transfer