11:00   Gust 2 Chair: Wolf Krüger 11:00 30 mins Gust Encounter of a Supersonic Fighter Aircraft using CFD Methods Arne Voß Abstract: The gust encounter of a supersonic fighter aircraft is investigated with the CFD code SU2 and the aerodynamic panel methods VLM and ZONA51. The interaction of the elastic aircraft, the flight controller and the gust is captured in a closed-loop time domain simulation. The comparisons show a moderate agreement between aerodynamic panel methods and CFD in terms of section loads, which has multiple reasons: first, the two aerodynamic methods yield different pitching moment characteristics, which have an influence on the flight mechanical reaction of the aircraft and the reaction of the flight controller. Second, due to the increase of the effective angle of attack during the gust encounter, vortices develop, which are not present in the horizontal level flight condition. Because of the large suction peaks due to the vortices, the surface pressure distribution changes significantly, an effect that is missed completely by the aerodynamic panel methods. The section loads predicted by the CFD based approach are higher, which eventually influences the structural sizing of the aircraft. Also, there is a significant structural dynamic reaction, which shows that for fighter aircraft, a transient gust analysis including structural elasticity is essential for the aircraft design. The comparisons show a moderate agreement between aerodynamic panel methods and CFD, which has multiple reasons: first, the two aerodynamic methods yield different longitudinal characteristics, which have an influence on the flight mechanical reaction of the aircraft and the reaction of the flight controller. Second, due to the increase of the effective angle of attack during the gust encounter, vortices develop, which were not present in the horizontal level flight condition. Because of the large suction peaks due to the vortices, the topology of the surface pressure distribution changes significantly as shown in Figure 1 - an effect that is missed completely by the aerodynamic panel methods. The section loads are higher using CFD, which possibly influences the structural sizing of the aircraft. Also, there is a significant structural dynamic reaction, which shows that for fighter aircraft, a transient gust analysis including structural elasticity is necessary. The final version of this paper will present the underlying aeroelastic models, extended by a longitudinal flight controller. The findings described above will be substantiated by inspecting the flight mechanical reaction of the aircraft and the differences due to the non-linearities in the CFD aerodynamic. The section loads are be quantified in terms of bending and torsional moments and at the wing root. Large parts of the results have been prepared already, so that the author is confident to finish the final paper in time. 11:30 30 mins Flutter and Gust Response of a Wing with Aerodynamic Gaps Dale Pitt Abstract: The proposed paper presents recent research on the effects of spanwise and chordwise aerodynamic gaps incorporated in a simple swept wing. The wing flutter and gust response is systematically investigated for a series of aerodynamic gaps This paper will present the results of a systematic approach to modeling aerodynamic gaps in both the spanwise and chordwise directions of a simple swept wing. Forty different chordwise aerodynamic gaps and forty different spanwise gaps were examined. A process was employed that utilized ZAERO to zero the box pressures that simulate the aerodynamic gap. This process involved a MATLAB script to zero the pressures of the wing boxes that were in turn inputted to ZAERO for flutter and gust analysis. The simulated aerodynamic gaps allowed the author to perform the eighty different analyses without physically modifying the aerodynamic geometry. 12:00 30 mins A numerical study of transonic buffet onset sensitivity to gust excitation Nicholas Giannelis Abstract: While significant recent research efforts in transonic buffet have been dedicated to understanding the nature of the aeroelastic response of wing sections experiencing autonomous shock oscillations, a limited understanding of the sensitivity of this phenomenon to gust fields exists. Tartinville et al. [1] have considered the effect of discrete gust excitation on the transonic flow of a rigid OAT15A profile computationally, finding a correlation between shock displacement and gust length. Giannelis et al. [2] found that discrete gust perturbations have the potential to incite shock buffet for an aeroelastic profile at pre-buffet conditions. Similarly, Gao et al. [3] showed the potential for a reduction in shock buffet onset incidence when moving from a rigid to aeroelastic system. The goal of this present work is to systematically study the sensitivity of shock buffet onset to gust excitation for a two degree-of-freedom aeroelastic system, with both rigid and elastic computations are validated against available experimental data. This study will employ unsteady Reynolds-Averaged Navier-Stokes (URANS) simulations using the commercial finite volume code ANSYS Fluent to represent the transonic flow unsteadiness of the OAT15A profile. These rigid buffet computations have been extensively validated in prior work by the authors [4]. For the aeroelastic computations, two-degree-of-freedom coupled pitch-heave dynamics are incorporated via Fluent’s 6-DoF Rigid Body Solver. The gust excitation is modelled through a source term in the y-momentum equations, in a manner similar to Golubev et. al. [5], and excellent agreement in the dynamic response is found with the experiments of Huvelin et al. [6]. The final manuscript will offer a parametric study on the sensitivity of the dynamic response of the system to various gust loads. The paper will map the sensitivity of buffet onset and the dynamic response to gust excitation. From the pre-buffet validation condition, sinusoidal, stochastic and discrete gust perturbations will be implemented (of varying intensities, lengths and frequency content). For a single case of each type of gust, the freestream conditions (angle of attack) and structural composition (mass and damping ratios) of the system will also be varied. Combining these results, this study will obtain a comprehensive understanding of the sensitivity of this complex system to its constituent parameters.

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