PIV measurements in a two-pass 90-deg ribbed-wall parallelogram channel

A parallelogram channel has drawn very little or no attention in the open literature although it appears as a crosssectional configuration of some gas turbine rotor blades. Particle Image velocimetry is presented of local flow structure in a two-pass 90-deg ribbed-wall parallelogram channel with a 180-deg sharp turn. The channel has a cross-sectional equal length, 45.5 mm, of adjacent sides and two pairs of opposite angles are 45-deg and 135-deg. The rib height to channel height ratio is 0.1. All the measurements were performed at a fixed Reynolds number, characterized by channel hydraulic diameter of 32.17 mm and cross-sectional bulk mean velocity, of 10000 and a null rotating number. Results are discussed in terms of the distributions of streamwise and secondary-flow mean velocity vector, turbulent intensity, Reynolds stress, and turbulent kinetic energy of the cooling air. It is found that the flow is not periodically fully developed in pitchwise direction through the inline 90-deg ribbed straight inlet and outlet leg. Pitchwise variation of reattachment length is revealed and comparison with reported values in square channels is made. Whether the 180-deg sharp turn induced separation bubble exists in the ribbed parallelogram channel is also documented. Moreover, the measured secondary flow results inside the turn are successively used to explain previous heat transfer trends.