Study on Busemann Biplane Airfoil in Low-Speed Smoke Wind Tunnel

Abstract

The Busemann biplane airfoil is considered one of the candidates for reducing sonic boom. In aircraft designs utilizing the biplane concept, high-lift devices must be used for takeoff and landing in low-speed conditions. In this work, flow visualizations were performed around a Busemann biplane airfoil equipped with leading and trailing edge flaps in a smoke wind tunnel. The lift coefficient of the biplane airfoil was estimated by utilizing a method based on measurements of smoke line patterns. The aspect ratio of the baseline Busemann biplane model was 0.75, the thickness ratio of the single element was 5%, and the wave cancellation condition was designed for Mach number 1.7. The length of each of the flap chords was 30% of the baseline. The Reynolds number, which is based on the chord length of the airfoil, is about 2.8×105. The results of the study are summarized as follows. For the baseline Busemann airfoil without flaps, the lift coefficient increases linearly as the angle of attack increases. The slope of the lift coefficient cl is 0.062 (1/deg.), which is in good agreement with reference data. This indicates that measuring smoke line patterns is a valid method for estimating the lift coefficient of biplane airfoils. Based on the visualization of the flow around the biplane model equipped with deflected leading and trailing edge flaps, confirmed that the separation bubble is smaller than in the baseline model due to the effective increase in camber. When the deflection angle of the trailing edge flap is increased, the lift coefficient also increases. The trend of the increasing cl is similar to that of conventional monoplane airfoil models with trailing edge flaps. Therefore, such flaps can be considered effective high-lift devices for Busemann biplane airfoils.