Thermal Behavior and Flow Characteristics inside a Square Cavity with Variable Horizontal Obstacles

Khan, Suvechchha; Rahaman, Md. Mahafujur; Bhowmick, Sidhartha; Saha, Suvash C

doi:10.22059/jcamech.2026.423526.1969

Thermal Behavior and Flow Characteristics inside a Square Cavity with Variable Horizontal Obstacles

Document Type : Research Paper

Authors

Suvechchha Khan ¹

Md. Mahafujur Rahaman ¹ ^{, 2}

Sidhartha Bhowmick ¹

Suvash C Saha ³

¹ Department of Mathematics, Jagannath University, Dhaka 1100, Bangladesh

² Department of Computer Science and Engineering, Z. H. Sikder University of Science and Technology, Shariatpur 8024, Bangladesh

³ School of Electrical, Mechanical and Biomedical Engineering, University of Technology Sydney, Ultimo, North South Wales, 2007, Australia

10.22059/jcamech.2026.423526.1969

Abstract

This study presents a comprehensive numerical investigation of unsteady natural convection, heat transfer, and entropy generation in a water-filled square cavity containing a centrally positioned horizontal adiabatic obstacle. The problem is relevant to buoyancy-driven transport in enclosed thermal environments, where internal obstructions can modify flow organization, thermal stratification, irreversibility, and overall energy performance. The enclosure is heated uniformly from the bottom, cooled from the top, and insulated along the vertical sidewalls. Two obstacle lengths, corresponding to 25% and 50% of the cavity width, are examined to clarify how internal blockage affects convective transport, flow stability, transition behaviour, and thermodynamic efficiency. The governing equations are solved using the finite volume method for water with a fixed Prandtl number 7.0, over a Rayleigh number range of 10^2≤Ra≤10^6. The flow and thermal responses are analysed using streamlines, isotherms, temperature time series, phase-space trajectories, power spectra, the largest Lyapunov exponent, entropy generation, Bejan number, and the ecological coefficient of thermal performance. The results show that obstacle size has a strong influence on both flow stability and thermal performance. At high Rayleigh numbers, the influence of the 25% obstacle becomes relatively weak, producing only about 1.5% reduction in heat transfer compared with the unobstructed cavity, whereas the 50% obstacle causes a more substantial reduction of approximately 9.5%. The cavity with the 50% obstacle generates slightly higher entropy than the 25% obstacle case at the largest Rayleigh number. For all cases, the average Bejan number remains greater than 0.50, indicating that heat-transfer irreversibility is the dominant source of total entropy generation. The 25% obstacle case achieves the highest ecological coefficient of thermal performance, with a maximum value of 0.1103, compared with 0.0968 for the 50% obstacle and 0.1023 for the unobstructed cavity. These findings demonstrate that a moderate internal obstacle can provide a favourable balance between heat-transfer enhancement and entropy generation, leading to improved thermodynamic performance in buoyancy-driven enclosed flows.

Keywords

Natural convection

Unsteady flow

Effect of obstacle

Entropy generation

Heat transfer

Subjects

Numerical Methods & CFD

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