Vortical flow management techniques

The goal of this publication is to provide an overview of the topic of revolutionary research in aeronautics at Langley, including many examples of research efforts that offer significant potential benefits, but have not yet been applied. The discussion also includes an overview of how innovation and creativity is stimulated within the Center, and a perspective on the future of innovation. The documentation of this topic, especially the scope and experiences of the example research activities covered, is intended to provide background information for future researchers.

https://ntrs.nasa.gov/api/citations/20060005004/downloads/20060005004.pdf

Innovation in Flight: Research of the NASA Langley Research Center on Revolutionary Advanced Concepts for Aeronautics

The subject of flow control is broadly introduced in this first chapter, leaving much of the details to the subsequent chapters of the book. The ability to actively or passively manipulate a flow field to effect a desired change is of immense technological importance, and this undoubtedly accounts for the fact that the subject is more hotly pursued by scientists and engineers than any other topic in fluid mechanics. In this chapter classical tools of flow control are emphasized, leaving the more modern strategies to the following chapter. Methods of control to achieve transition delay, separation postponement, lift enhancement, drag reduction, turbulence augmentation, or noise suppression are considered. The treatment is tutorial at times, making the material accessible to the advanced graduate student in the field of fluid mechanics. Emphasis is placed on external boundary-layer flows although applicability of some of the methods reviewed for internal flows will be mentioned. An attempt is made to present a unified view of the means by which different methods of control achieve a variety of end results. Performance penalties associated with a particular method such as cost, complexity, or trade-off will be elaborated.

Introduction to Flow Control

Wind tunnel tests are carried out using a 70 · delta wing model with leading-edge vortex flaps. The structure of the leading-edge separation vortex over the leading-edge vortex flap is measured by use of a 5 holes pitot probe, surface pressure measurement technique and oil flow visualization technique. Separation vortices formed on a plain delta wing, on a vortex flap and inboard the vortex flap hinge line are clearly visualized. Results indicate that the flow around the vortex flaps is classified into several different cross flow patterns. The streamwise flap deflection angle is defined to discuss the vortex flap performance. The optimum lift to drag ratio is attained when the amount of the wing angle of attack is not far different from that of the streamwise flap deflection angle, as long as the vortex flap is deflected modestly.

Flow Field Measurements of Leading-edge Separation Vortex Formed on a Delta Wing with Vortex Flaps

Under certain conditions, wall-bounded flows separate. To improve the performance of natural or man-made flow systems, it may be beneficial to delay or advance this detachment process. The present article reviews the status and outlook of separation control for both steady and unsteady flows. Both passive and active techniques to prevent or to provoke flow detachment are considered and suggestions are made for further research.

Status and outlook of flow separation control

Exploratory wind tunnel tests are reported on a 74 deg. delta wing model. The potential of a vortex flap concept in reducing the subsonic lift dependent drag of highly swept, slender wings is examined. The suction effect of coiled vortices generated through controlled separation over leading edge flap surfaces to produce a thrust component is discussed. A series of vortex-flap configurations were investigated to explore the effect of some primary geometric variables.

/pdf/leading-edge-vortex-flap-experiments-on-a-74-deg-delta-wing-lehh8mc3hz.pdf

D. M. Rao

Papers

Leading edge vortex-flap experiments on a 74 deg delta wing