Unsteady Wake Measurements of Airfoil

An experimental investigation was carried out to study the unsteady wake behind a sinusoidally pitching airfoil. Streamwise mean velocity in the wake was measured by hot-wire anemometry at 3 downstream distances from trailing edge of 0.25 chord, 0.5 chord and 0.8 chord. To assess the effect of mean incidence and reduced frequency, data were taken at mean incidence angles of 0 and 2.5 degrees, and reduced frequencies of 0.091, 0.182 and 0.273. The oscillation amplitudes were 8 and 10 degrees. The corresponding Reynolds number, based on the chord length, was 50000. The momentum deficit coefficients were obtained, too, as an extension to the studying. It was found that the mean incidence angle and reduced frequency have important influence on the velocity profiles. The results show that with increasing mean incidence, the velocity defect and momentum deficit increase. But, increasing reduced frequency decreases the momentum deficit and wake thickness. Furthermore, effect of downstream distances from trailing edge on wake is discussed.

Keywords:

Unsteady wake , reduced frequency , mean incidence angle , EPPLER 361 airfoil