Tatiana A. Andreeva

ULTRASOUND TECHNIQUE FOR PREDICTION OF STATISTICAL CHARACTERISTICS OF GRID-GENERATED TURBULENCE

Ultrasonic technique 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 (2/3)-power law to study characteristics of grid-generated turbulence. The paper focuses on ultrasonic measurements of turbulent flow using the travel-time technique. The theoretical analysis is based on the well-known Kolmogorov theory and supported by experimental data. The present research is of interest from two points of view. First, it demonstrates a non-invasive method of investigation of turbulence, and second, it furthers understanding of the effect of turbulence on sound propagation.

EXPERIMENTAL INVESTIGATION OF STATISTICAL MOMENTS OF TRAVEL TIME IN GRID-GENERATED TURBULENCE

An experimental tech nique for investigation of the behavior of acoustic wave propagation through a turbulent medium is discussed. The present study utilizes the ultrasonic travel -time technique to diagnose a grid -generated turbulence. The statistics of the travel -time variat ions of ultrasonic wave propagation along a path are used to determine some metrics of the turbulence. Experimental data obtained using ultrasonic technique confirms numerical and theoretical predictions of nonlinear increase of the first -order travel time variance with propagation distance.

Ultrasonic flowmeters in determination of correlation functions of velocity and ultrasound wave fluctuations in grid-generated turbulence.

Worcester Polytechnic Institute, Worcester, MA, 01609 The paper is devoted to the experimental investigation of the statistical characteristics of the grid-generated turbulence produced in a wind tunnel. Ultrasonic time-of-flight method using dual transducers is utilized to develop a methodology for determination of the correlation functions of turbulent velocity and sound speed fluctuations. The ultrasonic flowmeter equation is considered in the form that includes effects of turbulent velocity and sound speed fluctuations. The influence of temperature inhomogeneities on ultrasonic wave propagation is investigated using a set of experiments with a heated grid. Utilization of high-speed digital data acquisition cards and LabView software for the experiments allows collecting a significant amount of statistical data.

The effect of turbulence and acoustic waves on underwater acoustic propagation

The primary objective of this study was to develop a predictive methodology for received signal variation as a function of ocean perturbations using a ray‐based analysis of the effects of internal waves and ocean turbulence on underwater acoustic propagation. In the present formulation the eikonal equations are considered in the form of a second‐order, nonlinear ordinary differential equation with harmonic excitation due to an internal wave. The harmonic excitation is taken imperfect, i.e., with a random phase modulation due to Gaussian white noise, accounting for both chaotic and stochastic behavior. Small scale and geostrophic turbulence are represented using the potential theory two‐wave‐number model for a vortex array. The focus is to numerically study the influence of these fluid velocity and sound speed fluctuations and the role of initial ray angle on underwater acoustic propagation to provide a realistic characterization of acoustic arrivals. Predicted arrival behavior is analyzed using ray trace,...

Experimental Investigation of the Travel-time Variance of an Acoustic Wave Propagating Through The Grid-generated Turbulence

An experimental technique for the investigation of the behaviour of acoustic wave propagation through a turbulent medium is discussed. The present study utilizes the ultrasonic travel-time technique to diagnose a grid-generated turbulence. Travel-time variance is studied versus mean flow velocity, travel distance and outer turbulence scale. The effect of thermal fluctuations, which result in fluctuations of sound speed, is studied using a heated-grid experiment. Experimental data obtained using ultrasonic technique confirm numerical and theoretical predictions of nonlinear increase of the travel-time variance with propagation distance, which could be connected to the occurrence of caustics. The effect of turbulent intensity on the travel-time variance and appearance of caustics is studied. It is demonstrated experimentally that the higher turbulence intensity leads to the shorter distance, at which the first caustic occurs. The probability density for caustics appearance is analysed against the measured wave amplitude fluctuations. The analysis reveals that the region of high-amplitude fluctuations corresponds to the region where the probability of formation of random caustics differs from zero. Experimental results are in very good agreement with theoretical and numerical predictions.

Influence of internal wave fluctuations on acoustic underwater propagation

The work presents a ray acoustic based analysis of the effect of ocean internal waves and its fluctuations on acoustic wave propagation. In the present work, it is shown that consideration of only perfect internal waves simplifies the real problem, disregarding the fluctuations of internal waves. The focus of the paper is to study numerically the influence of internal wave fluctuations and the role of an initial ray angle onto underwater acoustic propagation. In the present formulation the eikonal equation is considered in the form of a second order, nonlinear ordinary differential equation with harmonic excitation due to internal wave. The harmonic excitation is taken imperfect, i.e., with a random phase modulation due to Gaussian white noise. The amplitude and wavelength of the acoustic waves are used as the principle signal characteristics in bifurcation analysis. The regions of instability are identified using the bifurcation and phase diagrams. The effect of internal waves phase modulation is demonst...

Ultrasound technique for prediction of statistical characteristics of grid-generated turbulence

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.