Development of a flush ultrasonic probe for the measurement of the velocity and the angle of attack of an aircraft.

In this work, a flush ultrasonic probe has been developed for the measurement of the velocity and the angle of attack (AOA) of an aircraft. The probe is made of one emitting transducer located at the center of a rotating stage and several receiving transducers located downstream, all transducers radiating in a normal direction perpendicular to the airflow. The determination of speed and AOA are deduced from the time of flight measurement of an ultrasonic wave between the emitter and the receivers propagating in the boundary layer. Particular attention was paid to the instrumentation as well as to the signal processing to enhance the ultrasound transmission and reception and to increase the signal-to-noise ratio. Results are reported for airflow velocities up to 127 m/s (460 km/h) both as a function of the emitter-receiver distance and as a function of the wind incidence angle. These experimental results are compared to simulations that estimate the time of flight between a source and a receiver. It is shown that ultrasonic waves propagate in the boundary layer and that the simulation code can predict the time of flight as a function of the distance and the angle.