Fluidic Fences for Swept Wing Flow Control
Abstract
Naval air operations impose unique design and operational constraints for aircraft that operate from carrier decks. Reducing approach (stall) speed can increase operational safety, reduce dynamic loads, decrease structural weight, and ultimately reduce life-cycle costs. High-lift is traditionally achieved through multi-element airfoils that are deployed at low speed to increase the lifting surface area and cLmax. These traditional approaches to attain high lift conflict with desires for low observability and anticipated future directions for aircraft enhancement through tailless control. An alternative to these “passive” means for achieving high lift is through the application of active flow control to augment cLmax. Active flow control has the distinct advantage that it does not involve moving wing surfaces and can be implemented “on demand” for landing, take-off, or aggressive maneuvering. Decades of research with various forms of active flow control have demonstrated the ability to augment lift, reduce drag, and mitigate stall/separation on lifting surfaces; however, the majority of this work has been conducted on 2D airfoils or straight wings with long or infinite aspect ratio (AR). By contrast, most carrier-based aircraft have short (low AR), swept wings. From the limited low AR, swept-wing flow control data in the open literature, there are significant differences between flow control effectiveness on long, straight vs. short, swept wings. In particular, the presence of spanwise flow leads to stall migration inboard from the wing tip trailing edge to the wing root leading edge. Since the introduction of swept wings, engineers have looked for ways to limit this spanwise flow to improve stall performance and pitch stability. Passive boundary layer fences have been included on numerous military and civilian aircraft with considerable success. While fences are effective at reducing the spanwise flow that contributes to wingtip stall, they also incur a drag penalty and an undesirable side force during sideslip for normal operation (when the fence is not needed). With the advent of flow control, there is the possibility that fluidic fences could be used to produce the same result as a passive boundary layer fence, with the significant benefit that they could be turned OFF when not needed. OSU recently compared passive and active (fluidic) fences on a 30° swept airfoil at Re=100k. The fluidic fence was created with a 0.4mm wide wall-normal slot jet extending over approximately the same extent as the passive fence. Global force measurements showed the slot jet to be more effective than the passive fence over much of the operating window. Off-wing and on-wing flow measurements indicated the presence of streamwise vorticity and greater flow attachment. A subsequent study corroborated the initial findings while adding additional data for multiple spanwise locations for the fluidic fence. The goal of the proposed research is to capitalize on OSU’s recent successful fluidic fence results. This will require a detailed investigation into the fluid mechanics responsible for the effectiveness of the fluidic fence, as well as tailoring the flow control for maximum efficiency. The proposed 3-year research effort will address the following questions: (1) What is the fundamental physics responsible for the effectiveness of the fluidic fence? (2) How can the fluidic fence be optimized for minimum massflow using non-steady blowing? and (3) How does the effectiveness change with Reynolds number and sweep (?)? This proposal constitutes a comprehensive study to provide the aerospace community with the relevant data necessary to meet the US Navy’s future needs for highly maneuverable aircraft (manned and unmanned).
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Mar 15, 2021
- Source ID
- N000142112108
Entities
People
- Jeffrey Bons
Organizations
- Office of Naval Research
- Ohio State University
- United States Navy