Effect of Flexible Flaps on Lift and Drag of Laminar Profile Flow

Abstract

Experiments with elastic flaps applied on a common airfoil profile were performed to investigate positive effects on lift and drag coefficients. An NACA0020 profile was mounted on a force balance and placed in a wind tunnel. Elastic flaps were attached in rows at different positions on the upper profile surface. The Reynolds number of the flow based on the chord length of the profile is about 2 × 10 5 . The angle of attack is varied to identify the pre-and post-stall effects of the flaps. Polar diagrams are presented for different flap configurations to compare the effects of the flaps. The results showed that flaps generally increase the drag coefficient due to the additional skin friction and pressure drag. Furthermore, a significant increase of lift in the stall region was observed. The highest efficiency was obtained for the configuration with flaps at the leading and trailing edges of the profile. In this case, the critical angle was delayed and lift was increased in pre-and post-stall regions. This flap configuration was used in a gust simulation in the wind tunnel to model unsteady incoming flow at a critical angle of attack. This investigation showed that the flow separation at the critical angle was prevented. Additionally, smoke-wire experiments were performed for the stall region in order to visualize the flow around the airfoil. The averaged flow field results showed that the leading-edge flaps lean the flow more towards the airfoil surface and reduce the size of the separated region. This reduction improves the airfoil performance in the deep stall region.

Gust Modeling with State-of-the-Art Computational Fluid Dynamics (CFD) Software and Its Influence on the Aerodynamic Characteristics of an Unmanned Aerial Vehicle

“…The influence of gusts on the aerodynamic characteristics of a flying object is problematic to examine experimentally. As presented by Yitao Z. et al [14] and by Reiswich A. et al [15], it requires the installation of additional devices in a wind tunnel to change the airflow direction in proximity to the tested object. Concurrently, numerical methods, i.e., computational fluid dynamics (CFD), seem to be more convenient for the examination of transient flows, including modelling gusts.…”