- The overarching objective of this research project was to gain improved basic understanding of the fluid mechanisms governing the development of secondary flow structures in complex, three-dimensional inlet ducts. To accomplish this objective, particle image velocimetry measurements were employed to document the mean and turbulent flow properties within the complex flow regions. Complimentary, surface oil flow visualizations and static pressures were obtained to aid in the interpretation of the PIV data. Using these diagnostic techniques, the formation of a pair of counter-rotating vortices was revealed. Two-dimensional PIV measurements were conducted along 20 planes near the two bends of the duct model. All data was collected with an incoming freestream of 40 m/s. Over 2000 image pairs were collected for each measurement location, which were then processed and averaged to generate mean velocity, variance intensity, and velocity gradient statistics. The data was analyzed and it was determined that the experimental PIV data corresponded well with the qualitative flow visualization. This research will contribute to the particle image velocimetry database and subsequent analyses, which will provide additional insight into the flow structure and provide a new database for numerical model validation.