ISO-Gradient Lines in a Differentially Heated Cylindrical Fluid Layer Using Coherent Gradient Sensing Interferometer

Non-invasive flow visualization and measurement of temperature fields in convective fluid systems continues to be a challenging problem for researchers. Radiation based measurements such as laser interferometry are one of the few available tool for this purpose. Laser interferometry allows for an accurate and convenient full field visualization and measurement of fluid properties. In the present study a single-beam Coherent Gradient Sensing (CGS) interferometer is used to obtain line-of-sight projections of a three-dimensional temperature field in a convective fluid medium. Due to its inherent insensitivity to vibrations, simple and cost effective optical layout and, most importantly, the absence of a separate reference beam, this interferometer is an ideal choice for measurements in convective fluids. In the present study, line-of-sight interferometric projections of a differentially heated water medium in a cylindrical cavity are presented. The cavity employed has an aspect ratio (diameter/height) of 3.9. The interferograms represent contours of gradient in the temperature field. Each of the interferograms is evaluated to obtain the two-dimensional projection of the temperature field. The temperature field obtained shows the absence of a radial-symmetric pattern at a Rayleigh number of 1.6×10⁵.