An interferometric study of transient natural convection in a partially open enclosure with different positions of a cylindrical obstacle

Steady-state natural convection in open enclosures has been widely studied; however, transient natural convection and influence of obstacle position in such configurations remain insufficiently explored, particularly through interferometric study. The present study addresses this gap by performing real-time transient experiments using Mach-Zehnder interferometry in a partially open square enclosure containing an adiabatic cylindrical obstacle and a heat source at bottom wall. The enclosure has a partial opening occupying 50% of the left vertical wall height. The effects of obstacle position and Rayleigh number 2.35×107≤Ra≤1.34×108 on transient and steady natural convection behavior are systematically investigated. Experimental temperature fields obtained from interferograms are compared with numerical predictions using a 2D laminar model in ANSYS Fluent. The results show that thermal plume development intensifies with time and exhibits faster, more irregular evolution at higher Rayleigh numbers. Heat transfer is strongly influenced by obstacle position, with maximum and minimum average Nusselt numbers observed when the obstacle is located at the bottom and left positions, respectively. A steady-state enhancement of up to 16% in average Nusselt number is achieved by relocating the obstacle from the left to the bottom position. Obstacle placement significantly affects flow structure, maximum cavity temperature, and exit velocity at the opening.