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.

Dependence of the internal geometry for the calculation of the Helmholtz frequency in an axisymmetrical acoustic resonator.

The well-known formula of Helmholtz is well established and perfectly suited to predict the resonance frequency of cylindrical resonators when using neck length corrections. The potteries celled in the walls of medieval buildings are the object of archaeological studies where the knowledge of their volume is the starting point to deduce their origin. The frequency measurement and Helmholtz's formula is a clever way to get the volume without touching the building in situ.

Inhomogeneous diffusion process in elongated rooms: An interpretation based on the dynamics of sound particles.

Previous studies showed that the reverberant field in elongated rooms is governed by non-homogeneous diffusion. The objective of this study is to physically interpret this phenomenon by considering the dynamics of the sound particles. Starting from the original diffusion theory, a quantity that can be interpreted as a "local" mean free path has been proposed and computed from the paths of the propagating particles.

Time-domain delay-and-sum beamforming for time-reversal detection of intermittent acoustic sources in flows.

This study focuses on the identification of intermittent aeroacoustic sources in flows by using the time-domain beamforming technique. It is first shown that this technique can be seen as a time-reversal (TR) technique, working with approximate Green functions in the case of a shear flow. Some numerical experiments investigate the case of an array measurement of a generic acoustic pulse emitted in a wind-tunnel flow, with a realistic multi-arm spiral array.

Experimental localization of an acoustic sound source in a wind-tunnel flow by using a numerical time-reversal technique.

The possibility of using the time-reversal technique to localize acoustic sources in a wind-tunnel flow is investigated. While the technique is widespread, it has scarcely been used in aeroacoustics up to now. The proposed method consists of two steps: in a first experimental step, the acoustic pressure fluctuations are recorded over a linear array of microphones; in a second numerical step, the experimental data are time-reversed and used as input data for a numerical code solving the linearized Euler equations.