Expanding the applications of holographic interferometry to the quantitative visualization of oscillatory thermofluid processes using temperature as tracer

Abstract

 In this paper we discuss a novel application of holographic interferometry in the simultaneous quantitative visualization of high-speed, oscillatory flow and temperature fields in complex flow geometries. We consider cases of (i) self-sustained oscillatory flows with main flow imposed in grooved and communicating channels as well as (ii) oscillating thermofluid processes with zero mean velocity in a thermoacoustic refrigerator model. Examples showing unsteady temperature distributions obtained by real-time holographic interferometry combined with high-speed cinematography illustrate the possibilities of the approach introduced in the paper. Our study shows that temperature distributions accurately mirror flow structures in certain types of complex, unsteady flows, thus allowing, apart from the measurement of temperature profiles and heat transfer, also the measurement of oscillatory amplitudes, frequencies, wavelengths as well as the speed of propagation of traveling waves by applying digital image processing techniques. In the grooved and communicating channels it is possible to visualize the structure of the Tollmien–Schlichting waves through isotherms by using the infinite fringe field alignment of holographic interferometry. In the thermoacoustic refrigerator model, small amplitude temperature oscillations generated by the acoustic standing wave are visualized and measured. Image processing as well as data reduction procedures used in the analysis of these flow fields are discussed in the paper. Experimental data obtained by applying the techniques introduced in the paper show good agreement with theory and results of numerical simulations. Our study suggests that using temperature as tracer offers numerous advantages in the study of certain types of complex, unsteady flows.