Hypersonic Fluid–Structure Interactions Due to Intermittent Turbulent Spots on a Slender Cone

Fluid–structure interactions due to intermittent turbulent spots were studied on a 7 deg half-angle cone in the Sandia Hypersonic Wind Tunnel at Mach 5 and 8 and in the Purdue Boeing/U.S. Air Force Office of Scientific Research Mach 6 Quiet Tunnel. A thin composite panel was integrated into the cone and the response to boundary-layer disturbances was characterized by accelerometers on the backside of the panel. Under quiet flow conditions at Mach 6, the cone boundary layer remained laminar. Artificially generated turbulent spots excited a directionally dependent panel response. When the spot generation frequency matched a structural natural frequency of the panel, resonance would occur, and responses over 200 times greater than under a laminar boundary layer were obtained. At Mach 5 and 8 under noisy flow conditions, natural transition driven by the wind-tunnel acoustic noise dominated the panel response. A single turbulent spot could not change this forced response. However, at higher spot burst rates, an elevated vibrational response was observed during transition at frequencies corresponding to the distribution of turbulent spots in the transitional flow. Once turbulent flow developed, the structural response dropped because the intermittent forcing from the spots no longer drove panel vibration.