Ultrasound Technique for Prediction of Statistical Characteristics of Grid-Generated Turbulence

Abstract

Ultrasonic measurement techniques can be used to determine some characteristics of turbulent flows. In this work measurements of the difference in propagation times of ultrasonic waves along two paths are combined with the Kolmogorov (j)-power law to study characteristics of grid-generated turbulence. The paper focuses on ultrasonic measurements of turbulent flow using the travel-time technique. The present research is of interest from two points of view. First, it demonstrates an ultrasonic method of investigation of turbulence, and second, it furthers understanding of the effect of turbulence on sound propagation.T

Experimental investigation of the travel-time variance of an acoustic wave propagating through the grid-generated turbulence

“…A detailed descrip tion of the experimental apparatus can be found in [15,22]. The experiment falls into two parts.…”

“…provided by the DAQs, allowed determination of the travel time t very precisely. A more detailed descrip tion of the experimental particulars may be found in [15]. O.OOE+OO I.00E-04 2.00E-04 3.00E-04 4.00E-04 5.00E-04 1 (s) Figure 2.…”

“…The level of amplitude fluctuations is expressed through the wave amplitude a X = In(AI Ao) and, consequently, the variance of the log amplitude variations is a~ = {(X -(X»2). In figure 7 experimental data for the standard deviation of log amplitude variations versus actual travel distance are plotted for undisturbed medium JO mIs, 15 mIs, 20 m/s. Experimental data were collected for both, small and large grids to examine the influence of the outer scale.…”

“…The techniques employed have been used in previous work by the current authors [15]. wherein a locally isotropic velocity field WaS considered, which was realized by introducing a grid in a uniform flow [16].…”

Experimental investigation of grid-generated turbulence using ultrasonic travel-time technique

“…The probability of the appearance of the caustics in a random field was explored theoretically [8], [9], [11] and numerically. [4], [5], [10] The fact that an acoustic wave carries some structure information of the turbulent medium after interacting with a medium makes it possible to use some statistical characteristics of the acoustic wave as a diagnostic tool to obtain some statistical information about the medium [6], [5], [12], [13], [14]. The modern theory of sound propagation in a moving random medium has been developing intensively since mid-1980s and is systematically described in Ostashev [15].…”