11:00
Shocks
Chair: Luca Benassi
11:00
30 mins
|
Exploring the Effect of Different Shock Impingement Angles on Aeroelastic Response for a Thin Panel
Luisa Piccolo Serafim, Earl Dowell
Abstract: In this study, a novel dynamically linearized Euler time-domain approach is used to compute the generalized aerodynamic force from a CFD simulation. The aerodynamic forcing term is implemented in a theoretical/computational nonlinear aeroelastic model to assess the dynamic response of a flexible clamped-clamped panel considering the pressure profile due to different shock wedge angles. One benefit of this approach is the possibility to perform the same analysis to solve the Navier-Stokes Equation via RANS simulation and consider the viscous boundary layer effect for near transonic regimes. Different shock wedge configurations will be explored in this study in the CFD/ROM simulation and the aeroelastic solution using an inviscid solver. These results will also be compared with the same structural configuration considering a modified Piston Theory model, exploring the limitations and opportunities of this simpler and faster solution.
|
11:30
30 mins
|
Transonic shock oscillations in an oscillating finite span wing
Magan Singh, Kartik Venkatraman
Abstract: Transonic buffet, or shock oscillations, over stationary wing sections and finite span wings, is well investigated for more than two decades. There is a reasonable understanding of the mechanisms that cause shock buffet. The present work is concerned with the nature of shock oscillations in an oscillating finite span wing. Raveh (2008), besides introducing the term ‘buffet’, showed that in a transonic flow over an airfoil pitching about a mean angle of attack, the large shock oscillations interact nonlinearly with the flow-field generated due to pitching. At small amplitudes of pitching, the lift coefficient frequency response shows two distinct frequencies---the buffet frequency and the pitching frequency. However, at higher amplitudes of oscillation, the participation of the buffet frequency decreases, till at a particular amplitude of pitching, the buffet frequency vanishes, and the frequency response is entirely dominated by the pitching frequency. This is known as frequency lock-in. The amplitude at which lock-in occurs depends on the ratio of the buffet frequency and airfoil pitching frequency. In this paper, the nature of shock oscillations over the Benchmark Supercritical Wing (BSCW)--- a finite span wing with an aspect ratio 2 and a supercritical wing section---pitching about an axis, is studied at a Mach number of 0.8, Reynolds number of 4 x 106, and an angle of attack of 5o. This test case is the validation case for the 3rd Aeroelasticity Prediction Workshop (AePW-3) High Angle Working Group (Chwalowski, et al., 2024). The buffet characteristics of this test case are interesting in that there is no dominant buffet frequency. A broad band of frequencies are present in the low frequency region, and multiple peaks at higher frequencies. Therefore, the focus of the study is to investigate the influence of wing oscillations on buffet, and the frequency response of the flow field. URANS simulations with a variant of Spalart-Allmaras turbulence closure model, known as the Edwards-Chandra modification, is used for the analysis. Time domain and frequency domain results are presented at different amplitudes of oscillation of the pitching wing. The wing pitching frequency is set at 10 Hz.
References
1. Raveh, D.E. 2008. A Numerical Study of an Oscillating Airfoil in Transonic Flows With Large Shock Wave Oscillations. AIAA 2008-1756. https://doi.org/10.2514/6.2008-1756.
2. Chwalowski, P., McHugh, G. R., Massey, S. J., Poplingher, L., Raveh, D. E., Jirasek, A., Singh, M., Venkatraman, K., . . . Slotnick, J. (2024). Shock-buffet prediction report in support of the high angle working group at the third aeroelastic prediction workshop. In AIAA Dynamics Specialist Meeting-Aeroelastic Prediction Workshop Summary Results, AIAA SciTech Forum, January 8-12, 2024; Orlando, Florida, USA.
|
12:00
30 mins
|
Experimental investigation of shock control bumbs on the transonic dip of the OAT15A airfoil
Anna Altkuckatz, Marc Braune, Johannes Dillinger, Martin Müller, Thomas Büte, Charlotte Hanke, Holger Ernst, Heiko Böhlken, Patrick Hartl, Thomas Schmidt, Holger Mai
Abstract: The investigation of devices such as Shock Control Bumps (SCBs) to influence aeroelastic stability at transonic flow velocities is becoming an increasingly important focus of aeroelastic research. For instance, Geoghegan, Giannelis, and Vio [1] conducted numerical studies to examine the effects of Shock Control Bumps on Transonic Shock Oscillation Control for non-moving airfoils. Additionally, Nitzsche et al. [2] explored the influence of various bump configurations on the transonic flutter and buffeting behavior of a classical two-degree-of-freedom aeroelastic system using geometric parametrization.
For the experimental quantification of the aeroelastic effects of SBCs in the transonic flow regime, a dedicated wind tunnel flutter test was conducted in the Transonic Wind Tunnel Göttingen (TWG). An OAT15A airfoil profile, with a one-meter wingspan and a chord of 0.3 m was installed in the flutter test rig of the DLR-Institute of Aeroelasticity to provide free motion in heave and pitch. The aeroelastic behavior was investigated for Mach numbers from 0.5 to 0.83 and total pressures from 30 up to 100 kPa.
The first experiment as part of a larger measurement campaign served to test the feasibility and measure the transonic dip of the "clean profile" and three different bump configurations. The bumps, located at 50% of the chord, varied in height while the length remained constant.
Initial results show a partly complete elimination of the transonic dip and a considerable shift of the flutter velocity towards higher Mach numbers. Furthermore, there is a change in the flutter behavior. An influence of the SCBs on the occurring flutter cases is indicated. A change occurs from heave-dominated flutter with rapidly growing amplitudes to pitch-dominated limit cycle oscillations (LCOs).
In a second wind tunnel test, a detailed resolution of the three-dimensional pressure distribution will be achieved through the use of unsteady pressure-sensitive paint (iPSP). This will provide a precise assessment of the unsteady aerodynamics, including the underlying shock dynamics.
The following paper will describe in more detail the experimental test setups and the aerodynamic and aeroelastic effects observed during the wind tunnel tests on the OAT15A airfoil. The relationships between the aerodynamic influence of the SCBs on the one hand and the resulting effects with respect to the aeroelastic behavior on the other hand will be discussed.
|
|