Kozlov V.V.   Katasonov M.   Pavlenko A.M.  

Experimental investigation of localized dis-turbances in the straight wing boundary lay-er, generated by finite surface vibrations

Reporter: Kozlov V.V.

Downstream development of artificial disturbances were investigated experimentally using hot-wire constant temperature anemometry. Investigations were carried out in the subsonic low-turbulent wind tunnels T-324 of ITAM SB RAS. The free stream turbulence level was 0.04%U at U=7.5 m/s. The model was an airfoil with a 476 mm chord and 1000 mm span. The airfoil was mounted vertically in the test section of the wind tunnel at positive angle of attack 10. The flexible membrane with dimension of 14x14 mm was placed at 44 mm from model noise at the favorable pressure gradient region. Membrane was driven by 200 ms pulse, which repeat every 500 ms. Amplitude of membrane deflection was 0.35 mm. The longitudinal component of velocity fluctuations u and the mean velocity U were measured along the wing chord. It is shown that high
-amplitude vibrations of a three-dimensional surface lead to formation of two types of perturbations in the boundary layer: quasi-stationary streamwise structures and wave packets accompanying them. The streamwise structures developed in the flow give birth to unstable regions at the fore and aft fronts, where an intense growth of Tollmien
-Shlichting wave packets occurs in the case of an adverse pressure gradient. Further downstream, the amplitude of streamwise structures decay, but the amplitude of T-S wave packets, in contrast, start rapidly grow, and wave packets finally transforms to the turbulent spot. The stall of flow is exponentially intensify of the wave packet amplitude.
This work was supported by the project of the President of the Russian Federation for Leading Scientific Schools (NSH- НШ-8788.2016.1) and Russian Science Foundation 16-19-10330.

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