Some recent effort showed that usage of Krueger flaps helps to maintain laminar flow in cruise flight. Such flaps are positioned higher relative to the chord to shield the leading edge from the insect contamination during take-off. The flap passes several through critical intermediate position during the deployment to its design position. The purpose of this paper is to analyse the aerodynamics.
To better understand such flow phenomena, the combined approach of computational fluid dynamics and experimental methods were used. Flow simulation was performed with in-house finite volume Navier–Stokes solver in fully turbulent unsteady RANS regime. The experimental data were obtained by means of force and pressure measurements and some areas of the flow field were examined with 2 C particle image velocimetry.
The airfoil with flap in critical position has a very limited maximum lift coefficient. The maximum achievable lift coefficient during the deployment is significantly affected by the vertical position of the trailing edge of the flap. The most unfavourable position during the deployment is not the flap perpendicular to the chord, but the flap inclined closer to it is the retracted position.
The flap movement was not simulated either in the simulation or in the experiment. Only intermediate static positions were examined.
A better understanding of aerodynamic phenomena connected with the deployment of a Krueger flap can contribute to the simpler and lighter of kinematics and also to decrease time-to-market.
Limited experimental and computational results of Krueger flap in critical positions during the deployment are published in the literature.
The authors gratefully acknowledge the financial support of the Grant Agency of the Czech Republic, project No. 17-01088S and Project UHURA: Unsteady High-Lift Aerodynamics – Unsteady RANS Validation, Grant agreement ID: 769088 from EU H2020 programme.
Kulhánek, R., Pátek, Z., Vrchota, P., Procházka, P. and Uruba, V. (2020), "Experimental and CFD study of slotted Krueger flaps aerodynamics in critical locations", International Journal of Numerical Methods for Heat & Fluid Flow, Vol. ahead-of-print No. ahead-of-print. https://doi.org/10.1108/HFF-09-2019-0687Download as .RIS
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