Effects of riblet surfaces on boundary-layer-induced surface pressure fluctuations and surface vibration

Kurzfassung

Riblet surfaces are an effective means for drag reduction. The skin friction can be reduced by up to 10% with a dimensionless rib spacing in a range of about 14- 18, applying the viscous length scale as normalization length. Apart from the drag reduction, the effect of riblet surfaces on surface pressure fluctuations and surface vibration might be of interest, especially for aircraft cabin noise. Experiments were performed at a plate configuration in the Acoustic Wind-Tunnel Braunschweig (AWB). Two riblet foils (102 μm and 150 μm rib spacing) and one foil without ribs but comparable mass were tested. The dimensionless rib spacing in the test is between 5 and 20.9. The results show no noticeable effect on the surface pressure fluctuations in the measurable frequency range (ca. 200 Hz-10 kHz) compared to the case without foils. However, riblet foils cause a vibration reduction of 1–2 dB compared to the foil without ribs. The greater stiffness of the riblet foils in the ribs direction might explain this behavior.