This paper numerically investigates laminar mixed convection flow through an octagonal cavity
enclosure where four cases with different positions and directions of its lid-driven were simulated.
The lid-driven moves in horizontal rightward and leftward on its upper wall in the first and second
cases while it moves vertical upward and downward on its right side wall in the others cases. The
numerical study was carried out by solving the governing equations (continuity, momentum and
energy), and applying the tri-diagonal matrix algorithm (TDMA) method via ANSYS 11.0
program. Four of the eight external walls of the octagonal cavity enclosure are insulation walls and
the other four walls were classified into two hot and two cold walls. The mixed convection flow
and heat transfer characteristics through isotherms, streamlines and the average Nusselt number
were considered based on different Richardson numbers (Ri = 0.01, 1, and 10). The results
demonstrated that heat transfer mechanism, the flow pattern and formation of vortices are
significantly dependent on values of the Richardson number. Within the enclosure, the lid-driven
movements showed an improvement in the heat transfer rate where the direction of the sliding wall
considerably affected the flow and temperature distributions for all values of the Richardson
number. The Nusselt number of the lid-driven increased from 50 with the upward motion to 55 (10
% increase rate) with the downward motion counterpart, and increased from 12 to 17 (40 %
increase rate) with the rightward and the leftward motions, respectively.