Flow past a 3D roughness element for a swept wing model
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DOI: 10.1134/S0869864320030014
Flow past a 3D roughness element for a swept wing model * V.S. Kaprilevskaya, A.M. Pavlenko, V.V. Kozlov, and A.V. Kryukov Khristianovich Institute of Theoretical and Applied Mechanics SB RAS, Novosibirsk, Russia E-mail: [email protected] (Received December 19, 2019, revised February 7, 2020; accepted for publication February 10, 2020) The paper presents results of experimental study for a flow on the windward side of a swept wing with disturbance generators installed on the surface. These generators are 3D roughness elements with the height comparable to the boundary layer thickness. The method of liquid crystal thermography was used for studying the impact of roughness elements with different heights on the boundary layer. There exists a zone of maximal susceptibility of the flow to the disturbance generated past the roughness element on the wing surface. Keywords: swept wing, longitudinal structures, crossflow instability, laminar-turbulent transition, local roughness element, liquid crystal thermography.
Introduction Intensive development of unmanned aerial vehicles (UAV) brings competition for characteristics of flight vehicles for performing different missions. The vehicle autonomy and low effective area of signal scattering for achieving low radar detection are the priority goals in engineering. The swept wing concept fits those criteria. In the tendency of improving the UAV parameters, the idea of reducing the drag force through flow laminarization above the airfoils looks as an attractive idea. The low Reynolds numbers (as compared to the manned flight vehicles) of the flow is in favor of this concept. Meanwhile, the swept geometry of wing benefits the flight stability. This allows shifting downstream the point of aerodynamic forces application. The flow past this kind of wing produces a 3D structure in the boundary layer (similar to the skewed wing), and this induces numerous new mechanisms of boundary layer instability: instability at the spreading line of the wing (negative gradients), Tollmien–Schlichting instability in the positive pressure gradient zone, Görtler instability for the case of convex areas of a wing. For some of those instabilities, a wise choice of wing profile can suppress the instability. However, the crossflow instability is related directly to the swept geometry and it presents a major interest for study. *
The reported study was funded by Russian Foundation for Basic Research, project number 19-31-90018.
V.S. Kaprilevskaya, A.M. Pavlenko, V.V. Kozlov, and A.V. Kryukov, 2020
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V.S. Kaprilevskaya, A.M. Pavlenko, V.V. Kozlov, and A.V. Kryukov
The results of studies revealed that crossflow instability behaves differently depending on the main stream turbulence [1]. At low main stream turbulence (lower than 0.1 %), the laminarturbulent transition occurs from the development of steady disturbances induced by the surface roughness. While the turbulence degree becomes higher, the travelling disturbances of the crossflow (induced by i
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