Vertical Tail Buffet Research Articles

Prediction of Vertical Tail Buffet Using CFD/CSD Coupling Method

The vertical tail buffet induced by the vortex breakdown flow is numerically investigated. The unsteady flow is calculated by solving the RANS equations. The structural dynamic equations are decoupled in the modal coordinates. The radial basis functions (RBFs) are employed to generate the deformation mesh. The buffet response of the flexible tail is predicted by coupling the three sets of equations. The results show that the presence of asymmetry flow on the inner and outer surface of the tail forced the structural deflection offsetting the outboard. The frequency of the 2nd bending mode of the tail structure meets the peak frequency of the pressure fluctuation upon the tail surface, and the resonance phenomenon was observed. Therefore, the 2nd bending responses govern the flow field surrounding the vertical tail. Finally, the displacement of the vertical tail is small, while the acceleration with a large quantitation forces the vertical tail undergoing severe addition inertial loads.

Investigation of vertical tail buffeting alleviation controlled by nanosecond plasma actuators

An experimental study was conducted with the aim of alleviating the vertical tail buffeting of a 55° delta wing using pulsed nanosecond dielectric barrier discharge plasma actuators. The flow physics in the event of wing stall, flow reattachment, vortex breakdown, shear layer under plasma actuation were obtained and analyzed, and results indicate that plasma actuation promotes flow attachment and manipulates the shear layer. The acceleration results indicate that the structural response of the vertical tail increases with an increasing angle of attack, and the first bending mode response increases most significantly at the post-stall angle. Manipulation of flow field by plasma actuation produces a considerable reduction in buffeting response and mainly controls the first bending mode. The characteristics of velocity fluctuations show two important factors affecting buffeting: the redistribution of loads and the spectrum change of fluctuations, both of which are related to the movement of the impingement point of the shear layer onto the vertical tail controlled by plasma actuation. Theoretical analysis indicates that the impingement point moving downward in the vertical direction of the vertical tail under plasma actuation is the main reason for reduction of the first bending mode response.

Experimental and computational investigation of novel vertical tail buffet suppression method for high sweep delta wing

Our research aim is to investigate the buffet alleviation effect of static or vibrating bulges attached on the forebody surface of the model. Experiments and numerical simulations on a model consisting of a sharp-edged, 70°-leading edge sweep delta wing and twin swept back vertical tails were conducted. Models with different bulges were tested and computed at 10 and 20 m/s of free stream velocity at angles of attack ranging from 20°-50°. Dynamic strain gauge and multichannel data acquisition and analysis system were employed for the measurement of unsteady root strain on the vertical tails. Experimental and computational results show that both static and vibrating bulges behave effectively as a novel tool to alleviate tail buffet, and the alleviation effect depends largely on the vibrating frequency. Besides, one-sided bulge can only alleviate the buffeting response for the tail of the same side, and it has no obvious alleviation effect for the opposite tail. Results of the spectral analysis reveal that there are generally three peaks of spectral density for aircrafts of this configuration, and bulges used in this paper could alleviate tail buffeting, but the total lift and drag of the whole model show no obvious deviation compared to the base model and the dominant frequency of the vibration of the tails has not shifted.

An embedded boundary framework for compressible turbulent flow and fluid–structure computations on structured and unstructured grids

SUMMARYThe finite volume method with exact two‐phase Riemann problems (FIVER) is a two‐faceted computational method for compressible multi‐material (fluid–fluid, fluid–structure, and multi‐fluid–structure) problems characterized by large density jumps, and/or highly nonlinear structural motions and deformations. For compressible multi‐phase flow problems, FIVER is a Godunov‐type discretization scheme characterized by the construction and solution at the material interfaces of local, exact, two‐phase Riemann problems. For compressible fluid–structure interaction (FSI) problems, it is an embedded boundary method for computational fluid dynamics (CFD) capable of handling large structural deformations and topological changes. Originally developed for inviscid multi‐material computations on nonbody‐fitted structured and unstructured grids, FIVER is extended in this paper to laminar and turbulent viscous flow and FSI problems. To this effect, it is equipped with carefully designed extrapolation schemes for populating the ghost fluid values needed for the construction, in the vicinity of the fluid–structure interface, of second‐order spatial approximations of the viscous fluxes and source terms associated with Reynolds averaged Navier–Stokes (RANS)‐based turbulence models and large eddy simulation (LES). Two support algorithms, which pertain to the application of any embedded boundary method for CFD to the robust, accurate, and fast solution of FSI problems, are also presented in this paper. The first one focuses on the fast computation of the time‐dependent distance to the wall because it is required by many RANS‐based turbulence models. The second algorithm addresses the robust and accurate computation of the flow‐induced forces and moments on embedded discrete surfaces, and their finite element representations when these surfaces are flexible. Equipped with these two auxiliary algorithms, the extension of FIVER to viscous flow and FSI problems is first verified with the LES of a turbulent flow past an immobile prolate spheroid, and the computation of a series of unsteady laminar flows past two counter‐rotating cylinders. Then, its potential for the solution of complex, turbulent, and flexible FSI problems is also demonstrated with the simulation, using the Spalart–Allmaras turbulence model, of the vertical tail buffeting of an F/A‐18 aircraft configuration and the comparison of the obtained numerical results with flight test data. Copyright © 2014 John Wiley & Sons, Ltd.

Buffeting numerical simulation coupled with aerodynamics and structure based on MDDES

Unsteady effect of seriously separated flow is the main factor of modern aircraft buffeting. So accurate simulation of this complex flow becomes the basis associated with the research of aircraft buffeting. This paper constructs an unsteady numerical simulation method for separation flow based on modified delayed detached eddy simulation (MDDES) method by considering both modern computer resources and the credibility of simulating separation flow. The proposed method is also verified through the simulation of the separated flow by a typical fighter at high angle of attack. And then a robust and efficient technology for deforming mesh is established using radial basis function (RBF) and infinite interpolation method. Moreover, the platform for numerical simulation of buffeting is set up in combination with the structural dynamics equations in the modal space, by which the research of vertical tail buffeting caused by edge vortex is carried out on a fighter at large angle of attack. Through spectrum analysis of time-domain response of pressure pulsation on the location of vortex rupture, the results show that the pulsation frequency of vortex structure with different scales covers the inherent modal frequency of vertical tail structure. Compared to the Reynolds-averaged Navier-Stokes equations, the MDDES method can distinguish the more detailed and higher frequency small-scale vortex structure. Unlike flutter, displacement acceleration response of each mode in buffeting is dominated by its own mode. There exists strong coupling between the first bending mode and first torsion mode, and it leads to acceleration and large inertia impact of structure, which is the main factor causing structural fatigue. In sum, the obtained results verify the validity of the numerical means and the corresponding methods in the paper.

Active Control of Vertical Tail Buffeting by Piezoelectric Actuators

A simplified method for analyzing and designing a vertical tail buffeting alleviation system is developed. The vertical tail model in this study is equipped with surface-bonded piezoelectric actuators to suppress the buffeting responses induced by aerodynamic forces. The structural dynamics of the vertical tail and the electrodynamics of piezoelectric actuators are modeled using a finite element method and realized by commercial software packages ANSYS®. Afterward, the finite element model for both the host structure and the piezoelectric patches are imported into MATLAB®, in which the dynamic equations of the system in modal coordinates are obtained through modal truncation. The motion-induced aerodynamic forces are computed by using the doublet-lattice method. The buffet input excitations are simulated by the proper orthogonal decomposition-based method. The suboptimal controller is designed to compute suitable control voltages needed to drive piezoelectric actuators. Finally, the effectiveness of the piezoelectric actuators in reducing vibratory responses due to buffet loads on the vertical tail is investigated numerically. The results demonstrate that the proposed method is feasible and effective.

Experimental and Computational Studies of Twin-Vertical-Tail Buffet

Characteristics and mechanism of twin-vertical-tail buffet response on airplane configuration with wing root leading edge extension (LEX) were studied by both experiment and computation. Low-speed wind tunnel experiments were carried out to measure the root bending moment and tip acceleration of vertical tail. Vortical flow patterns were visualized via laser light sheet technique. Three-dimensional computation was performed to solve the unsteady Euler equations on rigid model. The results indicate that (1) bursting of vortices emanating from LEX is the main source of twin-vertical-tail buffet; (2) the Euler equations is able to predict the general characteristics of vertical-tail buffet response reasonably.

Low Speed Wind Tunnel Buffet Testing on the F/A-22

Buffet results from the F/A-22 V-9 model test conducted in the Lockheed Martin Aeronautics Marietta Low Speed Wind Tunnel (LSWT) between 515-02 and 5-18-02 are presented. The purpose of the test was to determine the effect on stability and control parameters of CFD derived potential aerodynamic solutions for attenuating vertical tail buffet. Instrumentation was added to permit assessment of the effects of these potential configurations on buffet loads. The data from the test show buffet attenuation benefit from several of the configurations tested, with two fence configurations showing significant reductions in the buffet response up to approximately 32 degrees angle-of attack. CFD analysis predicted significant effects of Mach number, engine inlet mass flow, and scaling on buffet onset. Therefore, any consideration of incorporating such configurations as determined by wind tunnel test should be verified by model testing with these effects present and by full-scale evaluation. Significant buffet attenuation is also shown with side weapons bay doors open. (Note: The configuration showing most promise for buffet attenuation resulted in a loss in lateral stability at 32 degrees)

Active Control of a hybrid actuation system for aircraft vertical fin buffet load alleviation

AbstractTwin-tail fighter aircraft may experience intense buffet loads when flying at high angles of attack. One such aircraft is the F/A-18 where the broadband buffet loads primarily excite the first bending and torsional modes of the vertical fin, resulting in significant vibration and dynamic stresses on the vertical tail structure. This buffet phenomenon reduces the fatigue life of the aircraft structure while decreasing mission availability.An international technical co-operation program was initiated to develop a novel hybrid actuation system to actively alleviate the buffet response of a full-scale F/A-18 vertical fin. A hydraulic rudder actuator was used to control the bending mode of the vertical fin using rudder inertia forces. Multiple macro fiber composite actuators were distributed optimally to provide maximum induced strain control authority for the torsional mode. In order to develop an effective control law, a system identification approach was conducted to obtain a state-space model of the vertical fin using open-loop test data. An LQG control law was selected to minimise the dynamic response of the vertical fin at critical locations. The effectiveness of the control law was verified through extensive simulation prior to closed-loop experiments. The LQG control law demonstrated high robustness in all excitation load conditions; both bending and torsional vibration modes of the vertical tail were suppressed effectively and simultaneously. The dynamic stress and acceleration response at critical locations were also reduced significantly. A closed-loop experiment was conducted on a full-scale F/A-18 empennage using the IFOSTP test rig, and the experimental results verified the effectiveness of the control law development methodology used for the full-scale hybrid buffet load system for the F/A-18 aircraft. In addition, the ground vibration test demonstrated that the hybrid actuation system is a feasible solution to alleviate the vertical tail buffet loads in high performance fighter aircraft.

Active smart material control system for buffet alleviation

Vertical tail buffeting is a serious multidisciplinary problem that limits the performance and maneuverability of twin-tail fighter aircraft. The buffet problem occurs at high angles of attack when the vortical flow breaks down ahead of the vertical tails resulting in unsteady and unbalanced loads on the tails leading to their premature fatigue failure. An active smart material control system, using distributed piezoelectric (PZT) actuators, is developed for buffet alleviation and is presented. The surfaces of the vertical tail are equipped with PZT actuators to control the buffet responses in the first bending and torsion modes. The electrodynamics of the PZT actuators are modeled using a finite-element model. A single-input/single-output controller is designed to drive the active PZT actuators. High-fidelity analysis modules for the fluid dynamics, structural dynamics, electrodynamics of the PZT actuators, control law, fluid–structure interfacing, and grid motion are integrated into a multidisciplinary computing environment that controls the temporal synchronization of the analysis modules. The results of this study indicate that the actively controlled PZT actuators are an effective tool for buffet alleviation over wide range of angels of attack. Peak values of power spectral density of tail-tip acceleration are reduced by as much as 22% in the first bending mode and by as much as 82% in the first torsion mode. The root mean square values of tail-tip acceleration are reduced by as much as 12%.

Alleviation of Vertical Tail Buffeting of F/A-18 Aircraft

A high-fidelity multidisciplinary computational investigation for the prediction of buffet characteristics and buffet alleviation of the vertical tail of full F/A-18 aircraft is conducted and presented. Alleviation of the vertical tail buffeting is achieved using streamwise wing fences. The problem is solved using four sets of high-fidelity analysis modules. The Reynolds-averaged full Navier‐Stokes equations are solved for the aerodynamic flowfield. The structural dynamic responses of the vertical tail are computed using direct finite element analysis. The fluid‐ structure interfacing is modeled using conservative and consistent interfacing module. A transfinite interpolation algorithm is used to deform the computational grid dynamically to accommodate the deformed shape of the vertical tail. The investigation is conducted over a wide range of high angles of attack at a Mach number of 0.243 and a Reynolds number of 11 × × 106. The LEX fences shift the onset of maximum buffet condition to higher angles of attack. The LEX fences also reduce the root-mean-square values of differential pressure and root bending moment. At 30-deg angle of attack, the acceleration power of the vertical tail tip is reduced by up to 38% at first bending mode and by up to 24% at first torsion mode. However, the effectiveness of the LEX fences for buffet alleviation is reduced for very high angles of attack.

Characteristics of F/A-18 vertical tail buffeting

A time-accurate computational analysis of vertical tail buffeting of full F/A-18 aircraft is conducted at typical flight conditions to identify the buffet characteristics of fighter aircraft. The F/A-18 aircraft is pitched at wide range of high angles of attack at Mach number of 0.243 and Reynolds number of 11 millions. Strong coupling between the fluid and structure is considered in this investigation. Strong coupling occurs when the inertial effect of the motion of the vertical tail is fed back into the flow field. The aerodynamic flow field around the F/A-18 aircraft is computed using the Reynolds-averaged full Navier–Stokes equations. The dynamical structural response of the vertical tail is predicted using direct finite-element analysis. The interface between the fluid and structure is applied using conservative and consistent interfacing methodology. The motion of the computational grid due to the deflection of the vertical tail is computed using transfinite interpolation module. The investigation revealed that the vertical tail is subject to bending and torsional responses, mainly in the first modes of vibrations. The buffet loads increase significantly as the onset of vortex breakdown moves upstream of the vertical tails. The inboard surface of the vertical tail has more significant contribution in the buffet excitation than the outboard surface. In addition, the pressure on the outboard surface of the vertical tail is less sensitive to the angle of attack than the pressure on the inboard surface. The buffet excitation peaks shift to lower frequency as the angle of attack increases. The computational results are compared, and they are in close agreement, with several flight and experimental data.

Structural dynamics-CFD interaction for computation of vertical tail buffet

AbstractThe multidisciplinary problem of tail buffeting is solved using three sets of equations. The first set is the unsteady, compressible, full Navier-Stokes equations which are used for obtaining the flowfield vector and the aerodynamic loads. The second set is the coupled aeroelastic equations which are used for obtaining the bending and torsional deflections of the tail. The third set is the grid-displacement equations which are used for updating the grid coordinates due to the tail deflections. For the computational applications, a sharp-edged delta wing of aspect ratio one and a rectangular vertical tail of aspect ratio one placed in the plane of geometric symmetry behind the wing are considered. The configuration is pitched at a critical angle of attack (α = 38°) which produces asymmetric, vortex-breakdown flow from the delta wing primary vortices. The results show the effects of coupled and uncoupled bending-torsional responses and the effects of Reynolds number.

Reduction of vertical tail buffet response using active control

The active vertical tail (AVT) successfully reduced the buffet response of structures by utilizing piezoelectric actuators, strain gauge sensors, and simple control techniques. The AVT is a 5%-scale aeroelastically tailored structure that exhibits vibration response similar to a full-scale aircraft structure, and was designed such that it's piezoelectric actuators could provide control authority in the first two bending modes. The AVT was wind-tunnel tested on a generic twin-tailed double-delta fighter model at angles of attack and dynamic pressures representative of actual aircraft flight envelopes. At high angles of attack, the model's leading-edge vortices impinge upon the AVT. Simple control algorithms were used with piezoelectric actuators and collocated strain gauge sensors to either minimize the acceleration at the AVT's tip or the strain at the root of the tail. Control gains were verified to be a nonlinear function of angle of attack, dynamic pressure, and location of the actuator/sensor pair. Spectral analysis showed that the peak response of the controlled AVT was up to 65% lower than the uncontrolled response. This represents approximately an order of magnitude improvement in the fatigue life of a similar aircraft structure. The rms response below 200 Hz was reduced by over 20%.