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A laminar wing test case for the flutter behavior in transonic flow with free boundary layer transition is presented. The DLR-AE-L1 airfoil and wing are designed to serve as an aeroelastic testbed to develop a better understanding for the effect of boundary layer transition on flutter stability. Coupled CFD-CSM simulations are used to determine the flutter onset in a transitional and a fully turbulent flow. It is found that flutter occurs at lower stagnation pressures for the transitional flow, which is in accordance with earlier research on laminar airfoils.

An investigation has been made into the nonlinear aeroelastic behavior of an airfoil system with free-play nonlinear stiffness in transonic flow. Computational Fluid Dynamics (CFD) and Reduced Order Model (ROM) based on Euler and Navier-Stokes equations are implemented to calculate unsteady aerodynamic forces. Results show that the nonlinear aeroelastic system experiences various bifurcations with increasing Mach number. Regular subcritical bifurcations are observed in low Mach number region. Subsequently, complex Limit Cycle Oscillations (LCOs) and even non-periodic motions appear at specific airspeed regions. When the Mach number is increased above the freeze Mach number, regular subcritical bifurcations occur again. Comparisons with inviscid solutions are used to identify and elaborate the effect of viscosity with the help of aeroelastic analysis techniques, including root locus, Single Degree of Freedom (SDOF) flutter and aerodynamic influence coefficient (AIC). For low Mach numbers in the transonic regime, the viscosity has little effect on the linear flutter characteristic because of limited influence on AIC, but a remarkable impact on the nonlinear dynamic behavior due to the sensitivity of the nonlinear structure. As the Mach number increases, the viscosity becomes significantly important due to the existence of shock-boundary layer interaction. It affects the unstable mechanism of linear flutter, impacts the aerodynamic center and hence the snap-through phenomenon, influences the AIC and consequently the nonlinear aeroelastic response. When the Mach number is increased further, the shock wave dominates the air flow and the viscosity is of minor importance.

The aeroelastic behavior of wing models is nonlinear particularly in the transonic Speed range. The interaction between aerodynamic and structural forces can lead to the occurrence of Limit-Cycle Oscillations (LCOs). If in addition the wing model is flexible and backward swept, the kinematic coupling between bending and torsion makes the Situation even more complex. In the research project ‘‘Aerostabil’’ such a wing was investigated, which was equipped with pressure transducers in three sections and accelerometers. The experiments were performed in the adaptive test section of the transonic wind tunnel TWG in Göttingen. Already Dietz et al. (2003) have reported about experimental details and preliminary results. Based on these data Bendiksen (2008) studied numerically LCO-flutter behavior using a very similar, theoretical model (G-wing) and Stickan et al. (2014) used the original data as a LCO flutter test case. The influence of flexibility on the steady aerodynamics of the wing was described in Schewe & Mai (2018). In this paper now the flutter experiments with the same flexible model were analyzed systematically in the transonic range 0.84

MHI activities on aeroelasticity and the associated fields are presented. MHI has conducted many types of aeroelastic analysis throughout the development of aircraft in the past decades. The transonic dip phenomenon is one of the most important items in the aeroelasticity field and cannot be analyzed by the linear aerodynamics tools commonly used in the aircraft design. The recent progress in the time-marching method that calculates the flow field around the airfoil in the time domain enables solving the transonic dip by the analysis. In this paper, two analysis examples using USTF3 developed at NAL are presented that studied the transonic flutter properties of the high-aspect-ratio transport wing and SST wing, both of which were done in the design phase at MHI., 資料番号: AA0047427014, レポート番号: JAXA-SP-03-002

This paper presents YSX transonic flutter study and Arrow wing flutter study as NATAS (transonic flutter Analysis code made in NAL) numerical simulation example. The objective of YSX transonic flutter study is to investigate flutter characteristics on WRI (Wing Root Insert) structure. The objective of Arrow wing flutter study is to investigate that reduction of Wash-Out tendency can improve Arrow wing flutter characteristics. In analytical results, reduction of Wash-Out tendency is effective method to improve Arrow wing flutter characteristics., 資料番号: AA0047427015, レポート番号: JAXA-SP-03-002

Aerodynamic simulations were performed in order to compute the unsteady load response of the NLR7301 airfoil for heave and pitch oscillations in the transonic range. The data were used to determine the aeroelastic flutter boundary of a rectangular two degree of freedom wing. On the one hand the DLR TAU code was used to solve the Reynolds averaged Navier-Stokes (RANS) equations applying the Spalart-Allmaras and κ-ω turbulence models. On the other hand computations were made with the DLR TDLM code, which solves the time linearised transonic small disturbance (TSD) equation. The settings were chosen according to experiments by Dietz et al. [1] in the Transonic Wind Tunnel Gottingen (TWG). The comparison between the computed and the experimental results showed that the simulation codes are capable of computing reliable results. Characteristic transonic aeroelastic phenomena were found. The appropriate modeling of viscous effects in transonic flow came out to be an indispensable condition.

This paper presents flutter and forced oscillation experiments in a transonic wind tunnel. For an aeroelastic supercritical 2-D airfoil configuration we studied typical transonic phenomena in as pure a form as possible. Various manifestations of small-amplitude limit cycle oscillations were observed for different flow conditions as well as coexisting limit cycles. We demonstrated how very small control forces were sufficient to excite or suppress flutter oscillations. Limit cycle oscillations occurred under free and forced turbulent boundary layer transition in a perforated wall test-section. Flutter calculations based on experimental aerodynamic forces yield stability limits which show good agreement with directly measured experimental flutter values. The results indicate that flow separation at the trailing edge, and the interactions between the shock and the marginal region of separated flow beneath it, may be responsible for limiting the amplitude of the observed limit cycle oscillations.