Dynamic stability testing in DLR Wind Tunnels using a new free oscillation device

Abstract

A new dynamic stability test device has been designed and manufactured for the wind tunnels of DLR, based on the free-oscillation measurement technique. A key feature of the device is its versatility: it can be used in different wind tunnels, covering flow regimes from subsonic to hypersonic. By exchanging the cross-springs, free oscillation tests can be performed in pitch, yaw, or roll. A series of cross-springs with different stiffness values are available, enabling tests with models of varying load and stiffness requirements. The device is suitable for both capsule-like and lifting body configurations. The first application was a dynamic pitch stability test with the ReFEx model (Reusable Flight Experiment of DLR), a lifting space vehicle. The results demonstrated dynamic stability along the designed trajectory. For this test, data were evaluated both from the cross-spring signal and from Schlieren images. Both methods showed excellent agreement, confirming the validity of the signal processing approach. A second application was a dynamic pitch stability test with an Inflatable Heat Shield model in the framework of EFESTO-2, a Horizon Europe project. Two cross-springs with different stiffness values were used, yielding test data at different reduced pulsations. Additional Reynolds number variations were performed, allowing the influence of reduced pulsation and Reynolds number on the dynamic derivatives to be assessed.