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Experimental estimation of the applicability of the ray approximation in the scattering of ultrasonic pulses in a turbulent airflow

DOI 10.18127/j20700970-201804-02

Keywords:

I.Yu. Bychkova - Post-graduate Student, Department of Automation and Management in Technical Systems, Chuvash State University (Cheboksary)
E-mail: biy.quint@gmail.com
L.A. Slavutsky - Dr.Sc. (Phys.-Math.), Professor, Department of Automation and Management in Technical Systems, Chuvash State University (Cheboksary)
E-mail: las_co@mail.ru


The results of laboratory experimental measurements of ultrasound scattering in a convective airflow over the heated surface and in a turbulent flow of the fan are presented. Digital phase modulation and correlation processing of signals are used to estimate a small relative delay of ultrasonic pulses that arrive at the receiver along different propagation paths. Ray approximation was used to simulate the trajectory and propagation time of signals in an inhomogeneous medium. It is shown that an estimate of the relative delay of signals propagating along different trajectories for multipath pulsed measurements makes it possible to estimate the limits of applicability of the ray approximation and obtain additional information on the stratification of an inhomogeneous medium. The results of the experimental measurements show that for turbulent gas flows the possibilities of describing the propagation of ultrasound based on the refraction of the rays are limited. Significant fluctuations of the ultrasonic signal’s intensity do not allow, apparently, to use in the modelling the one-time scattering approximation and the method of smooth perturbations. In this case, the large scattering angles on turbulent fluctuations obtained in the fan flow limit the possibility of using other asymptotic methods of diffraction theory, such as the parabolic equation method (small-angle approximation).

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