Flow distortion in a circular-to-rectangular transition duct

Experiments were made for three circular-to-rectangular transition ducts with different transition lengths at Reynolds numbers which ranged from 4 × 10 3 to 2 × 10 4 . The Reynolds number is based on the inlet boundary-layer thickness and a reference freestream velocity measured upstream of the transition duct. The secondary flow pattern developed at the exit cross-sectional plane was mapped out in detail by a three-dimensional velocity measurement technique