IMPROVEMENT OF THE VARIABLE N-FACTOR METHOD FOR PREDICTING THE LAMINAR-TURBULENT TRANSITION LOCATION IN THE BOUNDARY LAYER ON A SWEPT WING
A. V. Boyko, V. I. Borodulin, A. V. Ivanov, S. V. Kirilovsky, D. A. Mishchenko, T. V. Poplavskaya, A. D. Cherepanov
Khristianovich Institute of Theoretical and Applied Mechanics, Siberian Branch of the Russian Academy of Sciences, Novosibirsk, Russia
Keywords: swept wing, boundary layer, laminar-turbulent transition, cross-flow instability, receptivity, surface roughness
Abstract
The variable N-factor method, which is one of the most effective modern approaches for predicting the laminar-turbulent transition location in boundary layers, is improved. The determination of the threshold N-factor for swept wings is refined by taking into account the range of transverse roughness scales on the wing leading edge that are dangerous from the standpoint of cross-flow instability and boundary-layer receptivity. The proposed modification does not require additional numerical analysis, as it is based on standard linear stability theory calculations and empirical data on the efficiency of boundary-layer receptivity to roughness in the generation of cross-flow instability vortices. The resulting dependences of the critical N-factor on the dimensionless leading-edge roughness are presented and calibrated against our own experimental data.
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