T O ACHIEVE revolutionary aircraft performance, advanced technologies should be pursued to drastically reduce the weight of aircraft and fuel consumption and significantly increase aircraft mission payload and maneuverability. Both the military and commercial aircraft will benefit from the same technology. Flow control is a promising technology to break through the limits of the conventional aerodynamic concepts. Recently, a novel active airfoil flow control concept with zero-net mass flux, the coflow jet (CFJ) airfoil, has been developed by Zha et al. [1–5]. The CFJ airfoil achieves three effects simultaneously in a dramatic fashion: lift augmentation, stall margin increase, and drag reduction. The energy expenditure of the CFJ airfoil is low [1], and the CFJ airfoil concept is straightforward to implement. The CFJ airfoil may create a new concept of an “engineless” airplane, which uses the CFJ to generate both lift and thrust without conventional propulsion systems of propellers or jet engines [6]. A CFJ airfoil [1–5] uses an injection slot near the leading edge (LE) and a suction slot near the trailing edge (TE) on the airfoil suction surface. Similar to tangential blowing, the LE jet is in the same direction of the main flow, but the same amount of mass flow that is injected is removed via suction near the TE, resulting in zeronet mass-flux flow control. A proposed fundamental mechanism [2] is that the severe adverse pressure gradient on the suction surface strongly augments turbulent mixing between the main flow and the jet [7]. The mixing then creates the lateral transport of energy from the jet to the main flow and enables the main flow to overcome the large adverse pressure gradient and remain attached at high angle of attack (AOA). The stall margin is hence significantly increased. At the same time, the high-momentum jet drastically increases the circulation, which significantly augments lift, reduces drag, or even generates thrust (negative drag). The objective of this paper is to demonstrate the high performance of the CFJ airfoil with the windtunnel test results.

High-Performance Airfoil Using Coflow Jet Flow Control

Three co-flow jet (CFJ) airfoils with injection slot size differed by two times consecutively are calculated by using a RANS CFD solver with 1-equation Spalart-Allmaras model. At the same angle of attack(AoA), the twice larger injection slot size airfoil passes about twice larger jet mass flow rate with the momentum coefficients also nearly doubled. The CFJ airfoil with the largest slot size has the least stall angle of attack(AoA). When the injection slot size is reduced by half, the stall AoA and the maximum lift coefficient is increased. However, when the injection slot size is further reduced by half, the stall AoA is still increased, but the maximum lift coefficient is lower due to the smaller momentum coefficient. The trend of the stall AoA and maximum lift agree with the experiment. At low AoA, both the computed lift and drag agree fairly well with the experiment. At high AoA, both the lift and drag are underpredicted. The reason may be that the RANS model can not handle the turbulence mixing well at high AoA.

Numerical investigations of injection-slot-size effect on the performance of coflow jet airfoils

The jet mixing of a co-flow jet (CFJ) airfoil is investigated to understand the mechanism of lift enhancement, drag reduction, and stall margin increase. Digital Particle Image Velocimetry, flow visualization and aerodynamic forces measurements are used to reveal the insight of the CFJ airfoil mixing process. At low AoA and low momentum coefficient, the mixing between the wall jet and mainflow is dominant with large structure coherent structures for the attached flows. When the momentum coefficient is increased, the large vortex structure disappears. At high AoA with flow separation, the CFJ creates a upstream flow strip between two counter rotating vertical shear layer, i.e., the outer shear layer and inner flow induced by CFJ. The UFS is characterized with large vortex free region. The co-flow wall jet is deflected normal to the airfoil surface characterized with a saddle point. With increased momentum coefficient of the CFJ, the saddle point moves downstream and eventually disappears when the flow is attached. Turbulence plays a key role in mixing the CFJ with mainflow to transport high kinetic energy from the jet to mainflow so that the mainflow can remain attached at high AoA to generate high lift. When the flow is separated, increased CFJ momentum coefficient also increases the turbulence intensity at jet injection mixing region.

Experimental Investigation of Jet Mixing Mechanism of Co-Flow Jet Airfoil

This paper conducts a numerical and experimental investigation of a coflow jet airfoil to quantify lift enhancement, drag reduction, and energy expenditure at a Mach number range from 0.03 to 0.4. The jet momentum coefficient is held constant at 0.08, and the angle of attack varies from 0 to 30 deg. The two-dimensional flow is simulated using a Reynolds–averaged Navier–Stokes solver with a fifth-order-weighted essentially non-oscillatory scheme for the inviscid flux and a fourth-order central differencing for the viscous terms. Turbulence is simulated with the one equation Spalart–Allmaras model. The predicted coflow jet pumping power has an excellent agreement with the experiment. At a constant Mach number, the power coefficient is decreased when the angle of attack is increased from 0 to 15 deg. When the Mach number is increased from 0.03 to 0.3, the suction effect behind the airfoil leading edge is further augmented due to the compressibility effect. This results in an increased maximum lift coefficien...

Performance and Energy Expenditure of Coflow Jet Airfoil with Variation of Mach Number

In the present work, a general subdomain boundary mapping procedure has been developed for arbitrary topology multiblock structured grids with grid points matched on subdomain boundaries. The interface of two adjacent blocks is uniquely defined according to each local mesh index system, which is specified independently.A pack/unpack procedure basedonthedefinitionoftheinterfaceisdevelopedtoexchangethedatainaone-dimensional array to minimize data communication. A secure send/receive procedure is employed to remove the possibility of blocked communication and achieve optimum parallel computationefficiency.Twoterms,“order”and“orientation”,areintroducedasthelogicsdefiningthe relationship of adjacent blocks. The procedure is applied to parallelize a three-dimensional Navier‐Stokes code, which uses an implicit time marching scheme with line Gauss‐Seidel iteration. The partitioning of the implicit matrix is done by discarding the corner matrices, which is easily implemented and is shown to have a small negative effect on the convergence rate. The message passing interface protocol is used for communicating the data. The numerical experiments presented in this paper include two- and three-dimensional flows using Reynolds averaged Navier‐Stokes equations and a detached eddy simulation with a fifth-orderweightedessentiallynon-oscillatoryscheme.Numericalexperimentsonamessage passing interface based computer cluster show that this general mapping algorithm is robust and has high parallel computing efficiency.

General Subdomain Boundary Mapping Procedure for Structured Grid Implicit CFD Parallel Computation

A control volume analysis is presented in this paper to analyze the jet effect on the coflow jet airfoil with injection and suction and on the airfoil with injection only. The formulations to calculate the duct's reactionary forces that must be included for the lift and drag calculation are given. The computational fluid dynamics solutions based on the Reynolds-averaged Navier-Stokes model are used to provide the breakdowns of lift and drag contributions from the airfoil surface force integral and jet duct's reactionary forces. The results are compared with experiment for validation. The duct reactionary forces are also validated with the result of a 3-D computational fluid dynamics calculation of the complete airfoil with jet ducts and wind tunnel walls. The study indicates that the suction occurring on the airfoil suction surface of the coflow jet airfoil is more beneficial than the suction occurring through the engine inlet such as the airfoil with injection only. For the airfoil with injection only, the drag actually acted on the aircraft, or the equivalent drag, is significantly larger than the drag measured by the wind tunnel balance due to the ram drag and captured area drag when the jet is drawn from the freestream. For a coflow jet airfoil, the drag measured by the wind tunnel balance is the actual 2-D drag that the aircraft will experience. A coflow jet airfoil does not have the ram drag and captured area drag. For a coflow jet airfoil, the suction penalty is offset by the significant circulation enhancement The coflow jet airfoil with both injection and suction yields stronger mixing, larger circulation, more filled wake, higher stall angle of attack, less drag, and lower energy expenditure.

Jet Effects on Coflow Jet Airfoil Performance

A control volume analysis is given in this paper to analyze the jet effect on co-flow jet airfoil with injection and suction and the airfoil with injection only. The ducts reaction forces formulations to be included for lift and drag calculation are given. CFD solutions based on RANS model are used to provide the breakdowns of lift and drag contributions form the airfoil surface force integral and jet ducts reaction forces. The results are compared with experiment as validation. The duct reaction forces are also validated by a 3D CFD calculation of the complete airfoil with jet ducts and wind tunnel wall. A comparative study of the jet effect on airfoil performance between the CFJ airfoil with injection and suction and the airfoil with injection only is conducted. The study indicates that the suction occurring on the airfoil suction surface such as the CFJ airfoil is more beneficial than the suction occurring through the engine inlet such as the airfoil with injection only. For the airfoil with injection only, the drag actually acted on the aircraft, the equivalent drag, could be significantly larger than the drag measured by the wind tunnel balance because of the ram and captured area drag when the jet is drawn from the freestream. For CFJ airfoil, the drag measured by the wind tunnel balance is the actual 2D drag that the aircraft will be experienced. The CFJ airfoil does not have the ram drag and captured area drag. For a CFJ airfoil, the suction penalty is offset by the significant circulation enhancement. The CFJ airfoil with both injection and suction yields stronger mixing, larger circulation, more filled wake, higher stall angle of attack, less drag, and more efficient energy expenditure. ∗ Associate Professor, AIAA Member † Graduate Student 1 44th AIAA Aerospace Sciences Meeting and Exhibit 9 12 January 2006, Reno, Nevada AIAA 2006-102 Copyright © 2006 by Ge-Cheng Zha and Wei Gao. Published by the American Institute of Aeronautics and Astronautics, Inc., with permission.

Analysis of Jet Effects on Co-Flow Jet Airfoil Performance with Integrated Propulsion System

A CFD calculation strategy is developed to simulate 2D co-flow jet airfoil. The jet ducts reaction forces are added to the surface integral of pressure and shear stress to calculate the total lift and drag. The predicted lift and drag agree well with the experiment at low angle of attack(AoA) and deviate largely at high AoA. The stall AoA of the CFJ airfoil is predicted reasonably well. Details of the flow field results and comparison between the computation and experiment are given in the paper.

Numerical simulation of co-flow jet airfoil flows

The airfoil with injection only is compared with the CFJ airfoil with both injection and suction with the similar injection momentum coefficient. The CFD simulations indicate that the suction of the CFJ airfoil significantly enhances the mixing and energy transfer between the jet and main flow, which results in higher circulation, higher lift, higher stall angle of attack, lower drag, and lower energy expenditure. The equivalent drag of the airfoil with injection only is significantly higher than the drag of the CFJ airfoil with both injection and suction. Since any airfoil with a jet injection needs to have a jet suction to satisfy the mass conservation law, this study indicates that the suction occurring on the suction surface such as the CFJ airfoil is more beneficial than drawing the jet mass flow from the aircraft engine inlet. ∗ Associate Professor † Graduate Student ‡ Graduate Student, Current address: Boeing Company, Phantom Works, Huntsville, AL § Undergraduate Student

Wei Gao

Papers

Jet Effects on Coflow Jet Airfoil Performance

Analysis of Jet Effects on Co-Flow Jet Airfoil Performance with Integrated Propulsion System

Numerical simulation of co-flow jet airfoil flows

Numerical investigations of co-flow jet airfoil with and without injection