Date of Graduation
Statler College of Engineering and Mineral Resources
Mechanical and Aerospace Engineering
James E Smith
Circulation control is a high-lift methodology that can be used on the wing of an aircraft. This technology has been in the research and development phase for over sixty years primarily for fixed wing aircraft when the early models were referred to as "blown flaps." Circulation control works by increasing the near surface velocity of the airflow over the leading edge and/or trailing edge of a specially designed aircraft wing using a series of blowing slots that eject high velocity jets of air. The wing has a rounded trailing edge, and ejects the air tangentially, through these slots inducing the Coandaˇ effect. This phenomenon keeps the boundary layer jet attached to the wing surface longer than a conventional wing and thus increases the lift generated on the wing surface due to the relaxation of the Kutta condition for the rounded trailing edge. The circulation control airflow adds energy to the lift force through conventional airfoil lift production and by altering the circulation of stream lines around the airfoil.;The main purpose of circulation control for fixed wing aircraft is to increase the lifting force when large lifting forces and/or slow speeds are required, such as at take-off and landing. Wing flaps and slats are currently used during landing on almost all fixed wing aircraft and on take-off by larger jets. While flaps and slats are effective in increasing lift, they do so with a penalty of increased drag. The benefit of the circulation control wing is that no extra drag is created from the movement of conventional surfaces into the airflow around the wing and the lift coefficient is greatly increased. However, with the use of circulation control to increase the lift coefficient, there is the inherent increase in the induced drag over the airfoil.;For circulation control to be feasible for use on rotary aircraft (helicopters in particular), the effective angles of attack have to be studied. Because propellers on rotorcraft see wide ranges of angles of attack caused by the inflow of air through the rotor plane, it is necessary to study the effect that circulation control has on the stall angles of the rotor blade. Stall occurs when a sudden reduction in lift occurs over a lifting surface caused by a flow separation between the incoming air flow and the wing body. The angle at which this happens is commonly called the critical angle of attack, and is typically between eight and twenty degrees depending on the wing profile, aspect ratio, camber, and planform area.;For this study, a 10:1 aspect ratio elliptical airfoil with a chord length of 11.8 inches and a span of 31.5 inches was inserted into the West Virginia University Closed Loop Wind Tunnel and was tested at varying wind speeds (80, 100, and 120 feet per second), angle of attack (zero to sixteen degrees), and blowing coefficients, ranging from 0.0006 to 0.0127 depending on plenum pressure. By comparing the non-circulation controlled wing with the active circulation control data, a trend was found as to the influence of circulation control on the stall characteristics of the wing for both leading and trailing edge active control. For this specific case, when the circulation control is in use on the 10:1 elliptical airfoil, the stall angle decreased, from eight degrees to six degrees, while providing a 70% increase in lift coefficient.
Kweder, Jonathan, "Effect of Circulation Control Blowing Slots on Stall Angles of a 10:1 Elliptical Airfoil" (2008). Graduate Theses, Dissertations, and Problem Reports. 4394.