Turbulent Flow Development inside a Rotating Two-Pass Square Duct with Porous Blocks

This paper presents an experimental investigation of turbulent flow inside square- sectioned channels connected with a square-ended bend using particle image velocimetry (PIV). Aluminium porous foam blocks of aspect ratio of 1.5 with 0.93 porosity and pore density per cm of 2, are attached to two opposite walls of the straight section normal to the turn axis, in a staggered manner. The spacing ratio of the blocks (S=D) is 1; whereas the height ratio (h=D) is 0.6. Water is used as the working fluid at Reynolds number of 36,000. The duct is either stationary or rotates orthogonally about an axis normal to that of the turn at a rotation number of 0.32. Results show the serpentine manner of the flow in the upstream and downstream channels due to the presence of the porous blocks. While in the straight sections there is no flow separation downstream of each block, turbulence levels are raised by the blocks’ presence. Within the bend, in contrast to the case with a smooth upstream section, a single vortex dominates the flow. For the first time, the effects of orthogonal rotation are also highlighted. While rotation does not change the overall flow character, it does force more fluid through the blocks on the duct trailing (pressure) side.