A global approach to turbomachinery flow control: Loss reduction using endwall suction and midspan vortex generator jet blowing

A flow control scheme using endwall suction and vortex generator jet (VGJ) blowing was employed in an effort to reduce the turbine passage losses associated with the endwall flow field and midspan separation. Unsteady midspan control at low Re had a significant impact on the wake area-average total pressure losses, decreasing the losses by 54%. Initially, the focus of the endwall control was the horseshoe vortex system. The addition of leading edge endwall suction resulted in an area-average total pressure loss reduction of 57%. The minimal additional gains achieved with leading edge endwall suction showed that the horseshoe vortex was a secondary contributor to endwall loss production (primary contributor-passage vortex).;A similar flow control strategy was then employed with an emphasis on passage vortex (PV) control. During the design, a theoretical model was used that effectively predicted the trajectory of the passage vortex. The model required inviscid results obtained from two-dimensional CFD. It 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 on the endwall below the passage vortex trajectory. The redirection approach attempted to alter the trajectory of the PV by removing boundary layer fluid through judiciously placed suction holes. Suction hole positions were chosen using a potential flow model that emphasized the alignment of the endwall flow field with inviscid streamlines. Model results were validated using flow visualization and particle image velocimetry (PIV) in a linear turbine cascade comprised of the highly-loaded L1A blade profile.;Detailed wake total pressure losses were measured while matching the suction and VGJ massflow rates, for the removal and redirection approaches at ReCx=25000 and blowing ratio, B, of 2. When compared with the no control results, the addition of steady VGJs and endwall suction reduced the wake losses by 69% (removal approach) and 68% (redirection approach). The majority of the total pressure loss reduction resulted from the steady spanwise VGJs, while the suction schemes provided modest additional reductions (<2%). At ReCx=50000, the endwall control effectiveness was assessed for a range of suction rates without midspan VGJs. Area-average total pressure loss reductions of up to 28% were measured in the wake at ReCx=50000, B=0, with applied endwall suction employed using the removal scheme (compared to no suction at ReCx=50000). At which point, the total pressure loss core was almost completely eliminated. Two-dimensional PIV showed that the endwall suction changed the location of the PV eliminating its influence on the suction surface of the turbine blade. More significantly, suction with the removal approach removed the corner vortex (CV) increasing the available span by more than 10%. The redirection approach was less effective at higher suction rates due to the continual presence of the CV.;A system analysis was also performed that compared the power needed to operate the flow control system (combined suction and VGJs) to the power gained by the system. The power gains were assessed by comparing the change in lift and wake total pressure losses (available work of the fluid) with and without flow control. The resultant power ratio showed that only 23% of the total power gained was needed to operate the flow control system for an L1A rotor at ReCx=50000, B=2.