Investigation of the Formation and Further Development of Longitudinal Disturbances and Their Secondary Instability on the Flying Wing Model

Detailed investigation of two-dimensional roughness element influence on the flow behind three-dimensional roughness element was carried out. For the first time studies were conducted on the windward side of the flying wing in the range of free-stream 7,2 – 20 m/s in the favourable gradient region behind roughness elements. Secondary instability mechanisms of disturbances leading to turbulence stage were investigated. It was shown that longitudinal structure forming behind three-dimensional roughness element grows downstream and has its trajectory slightly bend. The longitudinal structure consists of two stationary disturbances different in size. This can be explained by presence of cross flow and secondary disturbances leading to the transition. On the straight wing model, influence of the distributed suction on the stationary disturbance development was investigated and quantitatively determined. It was shown that suction is able to relaminarize the flow and eliminate the separation of the boundary layer.