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

Abstract

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 fluidstructure 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 × × 10 6 . 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. Nomenclature A t= reference area of vertical tail, 4.842 m 2 C P = coefficient of pressure, (P − P ∞ )/q ∞ C rbm = root bending moment coefficient, M B /q ∞ A tC C = mean aerodynamic chord of the wing, 3.5 m C P = mean pressure coefficient,dimensionless buffet pressure power spectral densitŷ F i = inviscid flux vector F v = viscous flux vector f = frequency, Hz M B = vertical tail root bending moment N = number of sample points n = nondimensional frequency, fC/U ∞ P i = pressure on inboard tail surface P o = pressure on outboard tail surfacê Q = vector of conservative variables q ∞= freestream dynamic pressure U ∞ = freestream velocity α = angle of attack P = differential pressure, P i − P o

Computational aeroelastic modelling of airframes and turbomachinery: progress and challenges

“…Comparisons of the aeroelastic computations using this method correlate well with wind tunnel and flight test r.m.s. pressures with respect to magnitudes and onset angles of attack (Sheta 2004). Further analysis using a LEX fence has shown a reduction in the r.m.s.…”

“…At low angles of attack, the buffeting is in the first torsional mode of the vertical tail. Several computational aeroelastic studies have been conducted in an attempt to increase understanding of the phenomena, such as that by Sheta (2004). That analysis used a Navier-Stokes solver for the flow field coupled with a finite element structural solver.…”

“…The computations show that the influence on the vertical tail is a reduction in r.m.s. pressures predominantly on the inboard side (Sheta 2004).…”

Comparisons of computational fluid dynamics solutions of static and manoeuvring fighter aircraft with flight test data

“…8, would be to accurately simulate the aeroelastic impact of the LEX vortices on the twin vertical tails. Previous predictions of the HARV flowfield include RANS computations with solid tails [50], DES predictions showing the impact of the breakdown region on the vertical tails [51], and fully aeroelastic tails with laminar off-body flow and flow control methods for alleviating tail buffet [52]. The current level of the simulation technology, however, has not allowed for accurate prediction of vortex breakdown and the unsteady flow downstream of breakdown at flight Reynolds numbers.…”