Coandă effect

Abstract: The present study describes the fundamentals of droop nose design for improving the aerodynamics of airfoils with active high-lift using an internally blown Coanda-type flap. The main objectives are to increase the stall angle of attack and reduce the power required by the high-lift system. A two-dimensional sensitivity analysis explores the effects of varying airfoil camber and thickness in the first 20% of the chord. The resulting droop nose configuration improves the maximum lift coefficient by about 20% and increases the stall angle of attack by around 10–15 deg. A target lift coefficient of about 4.7 is reached with 28% less jet momentum coefficient, compared to the clean nose. As the modified leading-edge geometry presents different stall mechanisms, the aerodynamic response to variations of jet momentum is also different. In particular, for a jet momentum coefficient above 0.035, the stall angle of attack increases with jet momentum, in contrast with the behavior observed with the clean nose.

Abstract: The purpose of this research is to investigate the operation condition of fluidic thrust vector using injection of the control flow tangential to the main jet direction; co-flow injection. The physical model of concern includes a chamber and a supersonic nozzle for supersonic main jet injection, and two chambers with slots for control flow injection. Steadystate numerical and experimental studies were conducted to investigate operating parameters; detailed flow structures, jet deflection angles, and shock effects were observed near the nozzle exit. An unsteady numerical calculation was conducted to analyze the dynamic characteristics of fluidic control of jet vectoring up- and downward from the nozzle axis, so that the response time of jet deflection to control flow injection and the pressure dispersion on the nozzle wall were investigated. Internal nozzle performance was predicted for total pressure range of the jet from 300 kPa to 1000 kPa to the control flow pressure from 120 to 200 kPa. To take into account the important features of high-speed flows, including shock-boundary layer interactions, a low Reynolds number k-e turbulence model with compressible-dissipation and pressure-dilatation effects was applied.

Abstract: A static investigation was conducted in the static test facility of the Langley 16-Foot Transonic Tunnel of two thrust-vectoring concepts which utilize fluidic mechanisms for deflecting the jet of a two-dimensional convergent-divergent nozzle. One concept involved using the Coanda effect to turn a sheet of injected secondary air along a curved sidewall flap and, through entrainment, draw the primary jet in the same direction to produce yaw thrust vectoring. The other concept involved deflecting the primary jet to produce pitch thrust vectoring by injecting secondary air through a transverse slot in the divergent flap, creating an oblique shock in the divergent channel. Utilizing the Coanda effect to produce yaw thrust vectoring was largely unsuccessful. Small vector angles were produced at low primary nozzle pressure ratios, probably because the momentum of the primary jet was low. Significant pitch thrust vector angles were produced by injecting secondary flow through a slot in the divergent flap. Thrust vector angle decreased with increasing nozzle pressure ratio but moderate levels were maintained at the highest nozzle pressure ratio tested. Thrust performance generally increased at low nozzle pressure ratios and decreased near the design pressure ratio with the addition of secondary flow.