Experimental investigation of shock control bumbs on the transonic dip of the OAT15A airfoil

ifasd2024 Tracking Number 202

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.