Application of ultrasound for the estimation of flight velocity direction on an aircraft fuselage

A flush mounted ultrasound device is potentially of interest for the non-intrusive measurement of the velocity field around a moving body.Ultrasound sending and receiving transducers might combine in one technique that could determine certain parameters of flow direction as, for example, around the fuselage of an aircraft in flight.The study reported here focused on the measurement and the prediction of times of flight in the configuration of a flat wall surrounded by a turbulent boundary layer. The presence of sheared flow and a turbulent boundary layer affects the propagation of acoustic waves.Time of flight was first estimated by a simplified model involving the convection effect and ignoring the shear layer.A numerical model based on the ray theory was also developed to take into account the propagation effect of the boundary layer. Indeed, the approximation of geometric acoustics was valid for high frequencies.In the first part, a comparison is presented to show that both approaches demonstrated similar trends at low Mach numbers. However, experiments conducted in a wind tunnel up to Mach 0.15 showed that the measurements were in better agreement with the estimates provided by ray theory.