Design study of Coanda devices for transonic circulation control

Abstract

Circulation control via blowing over Coanda surfaces at transonic freestream Mach numbers is investigated using numerical simulations. The performance and sensitivity of several circulation control devices applied to a supercritical aerofoil are assessed. Different Coanda devices were studied to assess the effect of Coanda radius-to-slot height ratio, nozzle shape and Coanda surfaces with a step. The range of operating conditions for which a supersonic Coanda jet remained attached at transonic freestream conditions were extended by increasing the radius of curvature at the slot exit for Coanda devices with a converging nozzle. Additional improvements were found by reducing the strength of shock boundary-layer interactions on the Coanda surface by expanding the jet flow using a converging-diverging nozzle and also by introducing a step between the Coanda surface and the nozzle exit. The performance when using a converging-diverging nozzle can be matched using a simple stepped Coanda device. It is shown that circulation control has the potential to match the performance of traditional control surfaces during regimes of attached flow at transonic speeds, up to an equivalent aileron deflection angle of 10°. In addition, lift augmentation ratios ΔCl/Cμof over 100 were achieved.

Mixing enhancement of a compressible jet over a convex wall

“…Gregory-Smith & Senior (1994) and Carpenter & Green (1997) achieved the same effect as Cornelius & Lucius (2012) by setting a step between the nozzle exit and the Coanda surface. Forster & Steijl (2017) further verified the effectiveness of these methods in the supersonic Coanda jet under transonic free streams. Bevilaqua & Lee (1980) reported a characteristics design method that skews the velocity and pressure profile along the jet exit, resulting in a favourable velocity and pressure gradient at the Coanda surface to promote the jet attachment.…”

Airfoil gust load alleviation by circulation control

“…Keller et al [23] conducted a number of experiments to test the effectiveness of CC for lift augmentation or reduction under steady conditions. Numerical work has been done to validate the numerical methods for the simulation of CC by Min et al [24] and Forster et al [25]. The results show that RANS with k-ω SST turbulence model is able to capture the changes of pressure distributions on the airfoil caused by CC.…”

“…The results show that RANS with k-ω SST turbulence model is able to capture the changes of pressure distributions on the airfoil caused by CC. The design and optimization of Coanda surface and the effectiveness of CC as means of maneuverability control of fixed and rotary-wing aircraft have also been studied numerically by Forster et al [25] and Cook et al [26].…”