Experimental Study of the Roughness Effects on the Zero Frequency Instability

Wind tunnel experiments were conducted to evaluate surface pressure distribution over a semi span swept wing with a sweep angle of 33 degrees. The wing section has a laminar flow airfoil similar to that of NACA 6-series ones. The tests were conducted at speeds ranging from 50 to 70m/s with and without surface roughness. Surface static pressure was measured on the wing upper surface at three different chordwise rows located at the inboard station, middle station, and outboard station. The differences between pressure distributions on the three sections of the wing were studied and the experimental results showed that roughness elements except at the inboard station do not influence the pressure distribution significantly. On the other hand, spectral analysis of the pressure-time signals acquired from the pressure orifices over the wing uppersurface showed that roughness had significantly affected the zero frequency amplitude. In this study, the zero frequency amplitude and its variations with roughness elements was investigated, since it played an important role over the swept wings flow field. The zero frequency distribution at three different chordwise rows was obtained with and without the surface roughness. Spectral analysis results showed that 3-D roughness elements amplified zero frequency amplitude over the swept wing.

کلیدواژه ها:

Swept wing ، Roughness effects ، Spectral analysis ، Zero frequency instability