A Novel Ultrasonic Method for Locating the Boundary Layer Transition Region on a Hypersonic Vehicle

摘要

Knowledge of where air flowing across a body transitions from laminar flow to turbulent flow can provide numerous benefits to air vehicle design, thermal protection system design, and air vehicle in-flight control. We propose a novel measurement system that leverages the hypersonic body-surface heating profile to locate the boundary layer transition region. Ultrasonic sensing as the measurement strategy to detect localized changes in aeroshell temperature is suggested. For a localization system using ultrasonic transducers, the sensors would be located on the inside surface of the aeroshell away from the harsh external conditions. Consequently, the phenomenon that is being measured is not disturbed and the sensor is not exposed to deleterious environments. We hypothesize that incorporating state estimation to locate the transition region will require fewer sensors than otherwise possible. The proposed method involves a forward conduction solution and an inverse procedure based on the extended Kalman filter. Development of the proposed measurement method based on ultrasound and the extended Kalman filter is accomplished using simple, controlled experiments involving concentrated high heat flux sources on a large flat metal plate. In this work, the proposed heating source localization method is detailed, results are presented from forward conduction solution development and flat plate experimentation with a high heat flux point source, and extended Kalman filter convergence behavior is compared for heating source locations inside and outside a four-element ultrasonic transducer sensor array. The inverse procedure is able to converge to the correct heating source location if the heating source is located inside the sensor array but is unable to converge to the correct location if the heating source is located outside of the array. A key finding is the need to design a sensor array with numerous propagation paths and with paths near the heating source location.