A Multi-Point Heterodyne Interferometer for Hypersonic Boundary Layer Transition Measurements

The high cost of development testing and pressure to reduce program timescales in the development of aircraft structures has led to increased use of advanced instrumentation. Of growing interest has been the integration of sensors into airfoil components, both to look outward at the behavior of the flow, and to look inward at the temperature and strain in the component itself. Surface-mounted sensors may allow measurement of the growth, spatial distribution and frequency content of instability waves in hypersonic boundary layers. Such measuremenmts are required in the short term to aid in airfoil design and testing, and in the long term as part of active control surface instrumentation. Fiber and Sensor Technologies (F&S) proposes to investigate the feasibility of novel types of surface-mounted optical fiber sensors for the measurement of hypersonic boundary layer instability modes. Such sensors, based in part on fiber strain gage concepts commercialized by F&S, have been demonstrated by F&S and their subcontractor, the Fiber & Electro-Optics Research Center at Virginia Tech, for detection of stress wave displacement fields on and in metals, ceramics and composites. This related prior work has been performed for numerous government laboratories, airframe manufacturers and engine manufacturers.