Flow instabilities and heat transfer in a differentially heated cavity placed at varying inclination angles: Non-intrusive measurements

Abstract

We report the non-intrusive investigation of the dependence of buoyancy-driven flow instabilities on the orientation angle of a differentially heated cavity of aspect ratio three. The cavity orientation angles considered are 60° and 30°. While moving from 60° to 30°, the cavity is inclined toward its stable configuration, wherein convection reduces. Flow instabilities have been captured through the spectral analysis of the transient history of temperature distribution recorded in a completely non-intrusive manner using a Mach–Zehnder interferometer. By virtue of the fact that in such configurations, corners of the cavity are the most active regions with regard to the interaction of buoyancy-driven fluid with the cavity walls, and the flow behavior is centrosymmetric (diagonal symmetry), the flow field in the top two corners of the cavity has been mapped. The spatio-temporally resolved interferometric measurements identified two distinct frequencies for cavity inclination angle (θ) of 60°. These two frequencies correspond to two different flow instabilities, namely, the Tollmien–Schlichting (TS) and gravity wave-induced instabilities. As the cavity is further inclined toward 30°, the instability in the boundary layer, i.e., the TS instability, ceases to exist, and only the gravity wave-induced instability is observed. The dependence of flow instabilities on cavity orientation angle is explained on the basis of interferometry-based measurements made in the form of interferograms and the corresponding whole field maps of temperature contours. The convective flow field in the differentially heated cavity has also been qualitatively captured using smoke visualization to provide direct support to interferometric measurements.