Approach for Aerodynamic Gust Load Alleviation by Means of Spanwise-Segmented Flaps

Abstract

Active gust load alleviation techniques exhibit a high potential in significantly reducing the transient gust loads on aircraft. In this work the aerodynamic potential of trailing-edge flaps and leading-edge flaps is numerically studied with the purpose to significantly reduce the structural gust loads. The utilized spanwise-segmented flaps represent slight modifications of existing devices for high-lift and maneuvering. The investigations based on unsteady Reynolds-averaged Navier–Stokes computations are conducted by employing a generic wing–fuselage aircraft configuration at transonic flow conditions. Idealized discrete “[Formula: see text]”-type vertical gusts that are relevant for the certification process are used as representative atmospheric disturbances. The focus of this paper is to introduce a practicable prediction method for required trailing- and leading-edge flap deflections for a significant mitigation of gust-induced wing loads. The three-dimensional flap deflections are determined by parametric two-dimensional simulations at representative wing sections. Different extensions of the estimation approach are investigated to assess the influence of the wing planform, the finite wing span, the aerodynamic phase lags, and the flap scheduling. It is shown that the trailing- and leading-edge flaps are promising in terms of alleviation of gust-induced wing bending and wing torsional moments, respectively. However, at high leading-edge flap deflections that are necessary for a full compensation of the wing torsional moment large-scale flow separation is identified. The introduced gust load alleviation approach indicates a good transferability between two-dimensional airfoil and three-dimensional wing aerodynamics for unsteady flap deflections.

An Aeroelastic Flight Dynamics Model for Gust Load Alleviation of Energy-Efficient Passenger Airplanes

“…The lack of an effect at higher speeds can be justified by two important aspects. Firstly, in [15,21,22], the lift coefficients at the considered design point are higher than those of the present aircraft's design point, such that there is overall less margin to stall. Secondly, these studies all considered fixed, rigid structures, whereas the aircraft model shown here is flexible and free to move in the vertical plane.…”

“…Figure 12 instead examines the effect of the stall model on loads for the MTOW mass case of the 2.5 g aircraft. It is shown in [15,21,22] that stall may have an important effect on the peak gust loads by reducing the peak aerodynamic loads. Indeed, Fig.…”

“…Aerodynamics models range from Modified Strip Theory (MST) [13] to potential theory models such as the Doublet Lattice Method (DLM) and the Unsteady Vortex Lattice Method (UVLM) to Computational Fluid Dynamics (CFD) methods [4,14]. CFD models, such as the Unsteady Reynolds-Averaged Navier-Stokes (URANS) simulation models [15] are only used at selected operating points due to the very high computational cost. MST is implemented in both CA 2 LM and UM/NAST and used in other publications [16][17][18].…”

“…In addition to the low computational cost, MST has the advantage over DLM and UVLM that dynamic stall [19,20] can be considered. CFD studies of gust interactions of rigid and unaccelerated aircraft have shown that dynamic stall may have a significant effect on loads [15,21,22]. However, it is questionable whether a similar quality as with DLM and UVLM can be achieved with MST for the spanwise lift distribution.…”