Computational evaluation of geometric effects on aerodynamic performance of circulation control airfoils

The geometric effects of Coanda trailing edges on the aerodynamic performance of an airfoil are numerically evaluated for a range of different freestream Mach numbers and momentum coefficients. A Circulation control (CC) airfoil with a circular trailing edge (ACTE) proves to have better control effectiveness at low subsonic freestream speeds (Mach = 0.1). A CC airfoil having an elliptic trailing edge (AETE) outperforms the ACTE at high subsonic flow conditions. The occurrence of C μ-stall for the AETE is greatly postponed, and meanwhile the maximum net lift coefficient increment achieved for the AETE (Δ C L = 0.51) is slightly higher than that of the ACTE (Δ C L = 0.50) at Mach 0.6. Compared to the ACTE, the AETE is found to have better control consistency at different operating velocities and better control stability when the Coanda jet is supersonic. Through careful consideration of the aerodynamic performance and the control effects, the most appropriate axial ratio for an AETE ellipse is within the interval from 1.5 to 2. Finally, the flow field instability phenomenon and the jet detachment induced by the supersonic Coanda jet are investigated. A self-sustained shock-wave instability phenomenon without jet detachment is first observed in this paper.

Improving Aerodynamic Performance of a Highly Loaded Compressor Based on Coanda Jet Flap

A novel blowing flow control technique, called Coanda jet flap, to improve the performance of the highly loaded axial compressor is numerically and experimentally investigated in this study. A theoretical model is initially built to guide the preliminary design of the jet velocity. The design and effectiveness of the Coanda jet flap are then studied for two different blade designs: a highly-loaded double-arc blade cascade and a highly-loaded axial compressor stator. The optimal aerodynamic shape of the Coanda jet flap is achieved based on the genetic algorithm in conjunction with the artificial neural networks. A comparison of the flow details between the optimization result and the prototype is then conducted to understand the flow mechanisms responsible for the performance enhancement. The numerical and experimental results show that the Coanda jet effectively improves the aerodynamic performance of the highly loaded cascade. The total pressure loss is reduced by a maximum of 22.4% when the normalized mass flow rate of Coanda jet is equal to 1%. Meanwhile, the static pressure rise coefficient is increased by up to 14% with a 1.5% jet mass flow rate. The cantilevered stator vanes with Coanda jet flap is well-designed and embedded in a 1.5-stage highly loaded axial compressor stage. The numerical data shows that the total number of stator blades can be successfully reduced by 35% with the uncompromised overall performance when the Coanda jet flap is applied.

Design study of Coanda devices for transonic circulation control

ABSTRACTCirculation 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.

Numerical simulation of circulation control turbine cascade with Coanda jet and counter-flow blowing at high Mach numbers

ABSTRACTThe performance of a circulation-control inlet guide vane that makes use of the Coanda effect was studied numerically in a high Mach number turbine cascade. The effect of different shapes (elliptic and circular) of the Coanda surface at the blade trailing edge was investigated by implementing both a Coanda jet and a counter-flow blowing. Under high subsonic flow conditions, with a total blowing ratio of 3% of the mainstream, the circulation control cascade can reach the same performance as the reference stator with a 13.5% reduction in the axial chord length, with minimal increase of the energy loss coefficient. The Coanda surfaces with small curvature are more efficient in entraining the mainstream flow, and they achieve better aerodynamic performance. The wall attachment of the Coanda jet is improved by employing counter-flow blowing, resulting in a slight increase of both the exit flow angle and the expansion ratio. Under supersonic flow conditions at the cascade exit, it is more difficult for the circulation control cascade to reach the appropriate flow turning due to a premature shock wave, which is absent in the original cascade until the very end of the suction surface.

First principle analysis of Coandă Micro Air Vehicle aerodynamic forces for preliminary sizing

Purpose The purpose of this paper is to reformulate the governing equations incorporating major variables and parameters for the design a Micro Air Vehicle (MAV), to meet the desired mission and design requirements. Design/methodology/approach Mathematical models for various spherical and cylindrical Coandă MAV configurations were rederived from first principles, and the performance measures were defined. To verify the theoretical prediction to a certain extent, a computational fluid dynamic (CFD) simulation for a Coandă MAV generic models was performed. Findings The major variables and parameters of Coandă MAV have been formulated into practical guidelines, which relate the lift (or thrust) produced for certain input variables, particularly the Coandă MAV jet momentum coefficient. The influences of the geometrical parameters are elaborated. Research limitations/implications The present analysis on Coandă jet-configured MAV is focused on the lift generation due to the Coandă jet effect through a meticulous analysis. The effects of viscosity, the Coandă jet thickness, the radius of curvature of the surface and the stability of Coandă jet are not considered and will be the subject of the following work. Practical implications The results obtained can be used for sizing in the preliminary design of Coandă MAVs. Originality/value Physical and mathematical models were developed which can describe the physical phenomena of the flow field near the Coandă MAV surfaces influenced by Coandă jet sheets and for obtaining a relationship between relevant variables and parameters to the lift of practical interest.

Application of Coandă Jet for Generating Lift of Micro Air Vehicles - Preliminary Design Considerations

Coandă effect, which has been widely utilized in many engineering applications for circulation control, is here reviewed for the design of Coandă Micro-Air-Vehicles (MAVs). Based on the review, a basic spherical configuration is analyzed to obtain the relationship between relevant parameters to the lift that can be produced based on fundamental principles. The results can be used for preliminary design purposes and are discussed in view of existing literature.