Numerical Study of the Lift Enhancement Mechanism of Circulation Control in Transonic Flow

The lift of an aircraft can be effectively enhanced by circulation control (CC) technology at subsonic speeds, but the efficiency at transonic speeds is greatly decreased. The underlying mechanism of this phenomenon is not fully understood. In this study, Reynolds averaged Navier—Stokes simulation with k−ω shear stress transport model was utilized to investigate the mechanism of lift enhancement by CC in transonic flow. For validation, the numerical CC results were compared with the NASA experimental data obtained for transonic CC airfoil. Thereafter, the RAE2822 airfoil was modified with a Coanda surface. The lift enhancement effects of CC via steady blowing with different momentum coefficients were tested at Ma=0.3 and 0.8 at α=3∘, and various fluid mechanics phenomena were investigated. The results indicate that the flow structure of the CC jet is insensitive to the incoming flow conditions because of the similarity to the local static pressure field around the trailing edge of the airfoil. Owing to the appearance of shockwaves on the airfoil surface in the transonic regime, the performance of the CC jet is restricted to the trailing edge of the airfoil. Transonic CC achieved a slight improvement in aerodynamic performance owing to a favorable shift in the shockwave pattern and accelerated flow in the separation region on the airfoil surfaces. Revealing the mechanism of lift enhancement of CC in the transonic regime can facilitate the rational design of new fluidic actuators with high activity and expand the potential applications of CC technology.

Experimental Investigation of Lift Enhancement and Drag Reduction of Discrete Co-Flow Jet Rotor Airfoil

Rotor airfoil design involves multi-point and multi-objective complex constraints. How to significantly improve the maximum lift coefficient and lift-to-drag ratio of rotor airfoil is a fundamental problem, which should be solved urgently in the development of high-performance helicopter rotor blades. To address this, discrete co-flow jet (DCFJ) technology is one methods with the most potential that can be harnessed to improve the performance of the rotor airfoil. In this study, wind tunnel experiments are conducted to study the effect of DCFJ technology on lift enhancement and drag reduction of OA312 airfoil. Furthermore, the performance improvement effects of the open co-flow jet (CFJ) and DCFJ technologies are studied. In addition, the influence of fundamental parameters, such as the obstruction factor and relative unit length, are analyzed. Results demonstrate that DCFJ technology is better than CFJ technology on the performance enhancement of the OA312 airfoil. Moreover, the DCFJ rotor airfoil can significantly reduce the drag coefficient and increase the maximum lift coefficient and the stall angle of attack. The maximum lift coefficient can be increased by nearly 67.3%, and the stall angle of attack can be delayed by about 12°. The DCFJ rotor airfoil can achieve the optimal performance when the obstruction factor is 1/2 and the relative unit length is 0.025.

Drag Reduction Using Biomimetic Sharkskin Denticles

This paper explores the use of sharkskin in improving the aerodynamic performance of aerofoils. A biomimetic analysis of the sharkskin denticles was conducted and the denticles were incorporated on the surface of a 2-Dimensional (2D) NACA0012 aerofoil. The aerodynamic performance including the drag reduction rate, lift enhancement rate, and Lift to Drag (L/D) enhancement rate for sharkskin denticles were calculated at different locations along the chord line of the aerofoil and at different Angles of Attack (AOAs) through Computational Fluid Dynamics (CFD). Two different denticle orientations were tested. Conditional results indicate that the denticle reduces drag by 4.3% and attains an L/D enhancement ratio of 3.6%.