Aerodynamic Performance Improvement of a Highly Loaded Compressor Airfoil with Coanda Jet Flap

Coanda jet flap is an effective flow control technique, which offers pressurized high streamwise velocity to eliminate the boundary layer flow separation and increase the aerodynamic loading of compressor blades. Traditionally, there is only single-jet flap on the blade suction side. A novel Coanda double-jet flap configuration combining the front-jet slot near the blade leading edge and the rear-jet slot near the blade trailing edge is proposed and investigated in this paper. The reference highly loaded compressor profile is the Zierke & Deutsch double-circular-arc airfoil with the diffusion factor of 0.66. Firstly, three types of Coanda jet flap configurations including front-jet, rear-jet and the novel double-jet flaps are designed based on the 2D flow fields in the highly loaded compressor blade passage. The Back Propagation Neural Network (BPNN) combined with the genetic algorithm (GA) is adopted to obtain the optimal geometry for each type of Coanda jet flap configuration. Numerical simulations are then performed to understand the effects of the three optimal Coanda jet flaps on the compressor airfoil performance. Results indicate all the three types of Coanda jet flaps effectively improve the aerodynamic performance of the highly loaded airfoil, and the Coanda double-jet flap behaves best in controlling the boundary layer flow separation. At the inlet flow condition with incidence angle of 5°, the total pressure loss coefficient is reduced by 52.5% and the static pressure rise coefficient is increased by 25.7% with Coanda double-jet flap when the normalized jet mass flow ratio of the front jet and the rear jet is equal to 1.5% and 0.5%, respectively. The impacts of geometric parameters and jet mass flow ratios on the airfoil aerodynamic performance are further analyzed. It is observed that the geometric design parameters of Coanda double-jet flap determine airfoil thickness and jet slot position, which plays the key role in supressing flow separation on the airfoil suction side. Furthermore, there exists an optimal combination of front-jet and rear-jet mass flow ratios to achieve the minimum flow loss at each incidence angle of incoming flow. These results indicate that Coanda double-jet flap combining the adjust of jet mass flow rate varying with the incidence angle of incoming flow would be a promising adaptive flow control technique.