A Global Approach to Turbomachinery Flow Control: Passage Vortex Control

Abstract

A flow control scheme was implemented in a low-pressure turbine cascade that simultaneously mitigated profile and endwall losses using midspan vortex generator jets (VGJs) and endwall suction. The combined system had an approximate zero-net mass flux. During the design, a theoretical model was used that effectively predicted the trajectory of the passage vortex using inviscid results obtained from two-dimensional computational fluid dynamics (CFD). The model was used in the design of two flow control approaches: the removal and redirection approaches. The emphasis of the removal approach was the direct application of flow control along the passage vortex (PV) trajectory. The redirection approach attempted to alter the trajectory of the PV with the judicious placement of suction holes. A potential flow model was created to aid in the design of the redirection approach. The model results were validated using flow visualization and particle image velocimetry (PIV) in a linear turbine cascade. Detailed total pressure loss wake surveys were measured while matching the suction and VGJ mass flow rates for the removal and redirection approaches at ReCx = 25,000 and blowing ratio, B, of 2. When compared with the no control results, the addition of VGJs and endwall suction reduced the wake losses by 69% (removal) and 68% (redirection). The majority of the total pressure loss reduction resulted from the spanwise VGJs, while the suction schemes provided modest additional reductions (<2%). At ReCx = 50,000, the endwall control effectiveness was assessed for a range of suction rates without midspan VGJs. Area-averaged total pressure loss reductions of up to 28% were measured in the wake at ReCx = 50,000, B = 0, with applied endwall suction (compared to no suction at ReCx = 50,000), at which point the loss core of the PV was almost completely eliminated.