TRANSITIONAL FLOW MODELLING OF A HYBRID LAMINAR FLOW CONTROL AND VARIABLE CAMBER TRANSONIC TRANSPORT AIRCRAFT WING

This paper presents computational fluid dynamics (CFD) results of the transitional flow field around a transonic transport aircraft wing. The framework for the analyses is formed by the german LuFo VI-1 project CATeW (Coupled Aerodynamic Technologies for Aircraft Wings), where benefits of the technology coupling between a hybrid laminar flow control (HLFC) system and a variable camber (VC) wing on aerodynamic drag is assessed. The computational fluid dynamics framework for the modelling of both technologies is presented in the paper, followed by CFD results considering a variation in both suction strength and deflection angle of an Adaptive Dropped Hinge Flap (ADHF), the latter integrating the VC capability to the aircraft wing. Transition prediction is performed following two strategies; on the one hand, the γ -Re_θ +CF turbulence model is applied, predicting an overall drag reduction with suitable suction and deflection angle settings reflecting the downstream shift of the transition location with increasing suction strength. On the other hand, linear stability theory with a two-N-factor integration strategy for transition prediction is applied. This allows for a quantitative assessment of targeted synergy effects between the coupled HLFC and VC application, namely suppression of Tollmien-Schlichting instabilities through a favorable adaptation of the wing's surface pressure distribution downstream of the HLFC suction panel. A reduction in N-factors is reflected for adapted deflection angles of the ADHF, indicating the synergy potential of the presented HLFC-VC coupling. As a last step, predicted transition location of both methods are compared, showing accordance in predicting transition in direct vicinity of the wing's leading edge for large sections of the wing's span for the no suction case. Generally, the transition location of the two-N-factor method lies upstream with respect to the location of the γ - Re_θ +CF model. Differences arise in the outboard section of the wing's suction side, where the two-N-factor method predicts a change in transition mechanism to critical amplification of Tollmien-Schlichting waves for the chosen critical N-factors.