Active and adaptive flow control of twin-tail buffet and applications

ACTIVE AND ADAPTIVE FLOW CONTROL OF TWIN-TAIL BUFFET AND APPLICATIONS Zhi Yang Old Dominion University, 2002 Director: Dr. Osama A. Kandil Modem fighter aircraft with dual vertical tails are operated at high angles of attack. The vortex generated by leading edge extension (LEX) breaks down before reaching the two vertical tails. The wake of highly unsteady, turbulent flow causes unbalanced broadband aerodynamic loading on the tails and may produce severe buffet on the tails and lead to tail fatigue failure. Flow suction along the vortex cores (FSVC) is investigated as an active control method for tail-buffet alleviation. Suction tubes have been tilted at different angles to study the control effectiveness of suction tubes orientation. Flow field response, aerodynamic loading and aeroelastic results are compared with the no-control case. These flow modifications produce lower tip bending and rotation angle deflections and accelerations. Moreover, the root bending and twisting moments are reduced in comparison with the no-control case. However, there was no shift in the frequencies at which the peaks of the power spectral density (PSD) responses occurred. The primary effect o f the FSVC methods is the amplitude reduction of the aeroelastic responses up to 30%. A parametric investigation is conducted and the best control effectiveness is obtained with the suction tubes tilted at -10°. Next, the twin-tail buffet alleviation is addressed by using adaptive flow control, and an adaptive active control method is developed. Control ports, whose locations are determined according to the locations of a range o f high-pressure difference, are placed within a small area on the tail surfaces. Flow suction and blowing are applied through these controL ports in order to equalize the pressures on the two surfaces o f the tail. Mass flow rate through each port is proportional to the pressure difference across the tail at the location of this port. Comparing the flow field and aeroelastic response with the no-control case, the normal-force and twistingReproduced with permission of the copyright owner. Further reproduction prohibited without permission. moment distributions are substantially decreased along with the damping of their amplitudes of variation. The bending-deflection and rotation-angle responses have not changed their sign. The PSD o f the root bending moment and root twisting moment have shown substantial decreases o f more than 70%. The tail tip acceleration responses have shown similar decreases too. Next, a parallel high-order compact-scheme code (PHCC) is developed to investigate flow control more accurately and more efficiently. The validation cases are presented and compared with theoretical results, experimental results and other computational results. The PHCC results show good accuracy and high efficiency. Flow computational simulations o f Jet and Vortex Actuator (JaVA) or synthetic jet have been investigated. The computational results show good agreement with the experimental data and other computational results. Simplified 2D models, which include an airfoil under the effect of JaVAs and synthetic jet actuators, are developed and investigated for control effectiveness. Simulation results show: with properly selected parameters, the oscillating amplitude of pressure difference and normal force acting on airfoil can be reduced, the peak of the normal force PSD can be reduced and the frequencies at which the peaks of the pressure difference PSD responses occurred can be shifted to higher frequency levels. Too low or too high exciting frequencies have no effect or adverse effect. Low exciting velocity may not produce enough disturbances to suppress the pressure oscillation. Reproduced with permission of the copyright owner. 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LIST OF SYMBOLS a coefficient of compact scheme a acceleration vector K covariant base vector a . speed of sound in freestream A cross section area of blowing/suction tube A Roe average matrix b coefficient o f compact scheme b wing span b(z) tail cross-section width c speed of sound, Sutherland’s constant C constant Cij coefficient of compact scheme at boundary Cp pressure coefficient Cq blowing/suction coefficient Crbm coefficient of root bending moment (M ^ / q„stc ) Crtm coefficient of root twisting moment (M RT f q_stc ) CFL Courant-Friedrichs-Lewy number e total energy per unit mass e,eigenvectors of the Jacobian matrix E modulus of elasticity El function of Q at left interface Er function of Q at right interface E inviscidflux Ev viscous flux El bending stiffness f frequency GJ torsional rigidity Hl stagnation enthalpy per unit mass at left interface Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Hit stagnation enthalpy per unit mass at right interface I, metric identities I the number of bending modes I(z) area moment of inertia I z z c m ( z ) mass moment of inertia about the center of mass axis h mass moment of inertia about the elastic axis J Jacobian of coordinate transformation k coefficient of thermal conductivity KiI terms of stiffness matrix L reference length m mass Mrb root bending moment Mrt root twisting moment M Mach number Ma Mach number M o o Mach number of freestream Mt twisting moment per unit length M the number of bending modes and torsion modes M y terms of mass matrix n non-dimensional frequency A. n unit normal vector A nb/, unit normal vector for blowing and suction N normal force per unit length N e terms of force vector P static pressure Pr Prandtl number qfc heat-flux component qt generalized coordinates for bending qr generalized coordinates for torsion Q flow vector in the Cartesian coordinates Reproduced with permission of the copyright owner. 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Ql flow variables at left interface Qr flow variables at right interface Q vector of conserved flow variables in generalized coordinates r displacement vector R residual terms Re Reynolds number Rv residual due to viscous terms S wing area Sta velocity gradient tensor t dimensional tune, thickness T temperature, period of oscillation uk filtered velocity Ur friction velocity Uco velocity of free stream V volume of the computational domain vb/s velocity vector of blowing/suction w bending deflection of the tail x x-coordinate Xj cartesian coordinates xe distance between the elastic axis and the inertial axis y~ normal distance from a solid wall in wall unit a angle of attack or dynamic pitch angle, coefficient of compact scheme oii projection of the difference in Q between the right and left interface otf free parameter P; frequencies computational coordinates p density p . density in freestream p. molecular viscosity coefficient Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Mmolecular viscosity coefficient in freestream ^kn shear stress tensor m boundary enclosing the computational domain A, bulk viscosity coefficient U eigenvalues Y constant £w i 68 error in bending and torsion ♦ free vibration modes, flow variables ¥ spatial derivative of A A2 spatial filter width T non-dimensional time Tw wall shear stress e torsion deflection angle in radians or dynamic roll angle tail-up torsion acceleration «» Kronecker delta function (0 natural frequency metrics flx,riy,riz metrics y£ z metrics Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.