Investigation of the Flow behind the Roughness Element on the UAV Surface at a Favorable Pressure Gradient

In a wind tunnel of low subsonic speeds, an experimental study was conducted of the windward flow of a trapezoidal model of a flying wing (UAV) with a locally installed perturbation generator in the region of maximum susceptibility on its surface. The generator was a three-dimensional roughness element whose height was comparable to the thickness of the boundary layer. The uniqueness of the work was that the experiments were carried out in a wind tunnel at real flight Reynolds numbers on a UAV model at a scale of 1:1. The results of visualization of the flow near a smooth surface and behind roughness were obtained using the method of liquid crystal thermography. The internal structure and processes of development of the longitudinal perturbation behind the roughness downstream were studied in detail using the thermoanemometry method.

1. Bippes H. Basic experiments on transition in three-dimensional boundary layers dominated by crossflow instability. Progress in Aerospace Sci., 1999, vol. 35, no. 4, p. 363–412.

2. Kozlov V. V., Grek G. R., Litvinenko Yu. A., Tolkachev S. N., Chernoray V. G. Experimental Studies of the Localized Disturbances and their Secondary High-Frequency Instability in the Flat Plate, Unswept and Swept Wing Boundary Layer (Review). Vestnik NSU. Series: Physics, 2014, vol. 9, no. 4, p. 39–64. (in Russ.)

3. Chernoray V. G., Kozlov V. V., Löfdahl L., Chun H. H. Visualization of sinusoidal and varicose instabilities of streaks in a boundary layer. J. Visualization, 2006, vol. 9, no. 4, p. 437– 444.

4. Carpenter A. L., Saric W. S., Reed H. L. Roughness receptivity in swept-wing boundary layers – experiments. Intern. J. Engng. Systems Modelling and Simulation, 2010, vol. 2, no. 1/2, p. 123–128.

5. Boiko A. V., Kozlov V. V., Syzrantsev V. V., Shcherbakov V. A. Experimental Study of the Transition to Turbulence at a Single Stationary Disturbance in the Boundary Layer of an Oblique Airfoil. Journal of Applied Mechanics and Technical Physics, 1995, vol. 36, no. 1, p. 67–77. DOI 10.1007/BF02369675"10.1007/BF02369675

6. Boiko A. V., Kozlov V. V., Syzrantsev V. V., Shcherbakov V. A. Experimental Investigation of High-Frequency Secondary Disturbances in a Swept-Wing Boundary Layer. Journal of Applied Mechanics and Technical Physics, 1995, vol. 36, no. 3, p. 385–393. DOI 10.1007/BF02369776

7. Boiko A. V., Grek G. R., Dovgal A. V., Kozlov V. V. The Emergence of Turbulence in Wall Flows. Novosibirsk, Nauka, 1999. 328 p. (in Russ.)

8. Tolkachev S. N., Kaprilevskaya V. S., Kozlov V. V. The Role of Two-Dimensional Roughness Element in the Laminar-Turbulent Process in the Favourable Pressure Gradient of the Swept Wing. Vestnik NSU. Series: Physics, 2014, vol. 9, no. 4, p. 65–73. (in Russ.)

9. Tolkachev S. N., Gorev V. N., Kozlov V. V. Study of Longitudinal Vortices behind Roughness and their Secondary Instability at the Oblique Wing Leading Edge. Doklady Physics, 2014, vol. 59, no. 11, p. 524–527. DOI 10.1134/S1028335814090110

10. Kaprilevskaya V. S., Tolkachev S. N., Kozlov V. V. Influence of Two-Dimensional Roughness on the Swept Wing Boundary Layer Structure in the Favourable Pressure Gradient Region. Siberian Journal of Physics, 2017, vol. 12, no. 3, p. 24–34. (in Russ.)

11. Pavlenko A. M., Zanin B. Yu., Katasonov M. M. Flow around a small-sized UAV model in a turbulent trace. In: XIX Intern. Conference on the Methods of Aerophysical Research (ICMAR 2018) (Novosibirsk, Russia, 13–19 Aug., 2018): AIP Conference Proceedings. S. l, 2018, vol. 2027, no. 1, p. 040004-1–040004-7.

12. Kaprilevskaya V. S., Pavlenko A. M., Kozlov V. V., Kryukov A. V. Flow past a 3D roughness element for a swept wing model. Thermophysics and Aeromechanics, 2020, vol. 27, no. 3, p. 321–330.

13. Zharkova G. M., Kovrizhina V. N., Khachaturyan V. M. Experimental Study of Subsonic Flows by Liquid-Crystal Thermography. Journal of Applied Mechanics and Technical Physics, 2002, vol. 43, no. 2, p. 274–279.

14. Zharkova G. M., Zanin B. Yu., Kovrizhina V. N., Brylyakov A. P. Free stream turbulence effect on the flow structure over the finite span straight wing. J. Vizualization (The Vizualization Soc. of Japan), 2002, vol. 5, no. 2, p. 169–176.

15. Kawamura T., Hiwada M., Hibino T., Mabuchi I., Kumada M. Flow around a finite circular cylinder on a flat plate. Bulletin of JSME, 1984, vol. 27, no. 232, p. 2142–2151.

16. Pattenden R. J., Turnok S. R., Zhang X. Measurements of the flow over a low aspect ratio cylinder mounted on a ground plane. Experiments in Fluids, 2005, vol. 39, no. 1, p. 10–21.