Detached Eddy Simulation and PIV validation of the flow in a compact return diffuser

The internal flow fields in a compact return diffuser have been investigated both numerically and experimentally under multi-conditions. Three-dimensional unsteady simulations are solved on high-quality structured grids with the Detached Eddy Simulation (DES) model by using the Computational Fluid Dynamics (CFD) code ANSYSFluent. Furthermore, a special Particle Image Velocimetry (PIV) test rig is designed, and the two-dimensional PIV measurements are successfully conducted in the diffuser midplane to capture the complex flow and to validate the CFD results. The analysis of the obtained results has been focused on the flow structure in diffuser, especially under part-load conditions. In addition, the comparison between CFD and PIV results has also been carried out. The vortex and recirculation flow patterns in diffuser are captured and analyzed accordingly. Strong flow separation and back flow appeared at the part-load flow rates. Under the design and over-load conditions, the flow fields in diffuser are uniform and an accepted agreement is presented between CFD and PIV results.