No abstract

Recent circulation control testing at West Virginia University, in a closed loop wind tunnel, has been conducted on models where the trailing edge radius was selected to be smaller than that used in literature, such as Loth and Boasson [1], 1.5 inches and Englar [2], 0.4375 inches. The reduced size was chosen in an attempt to minimize the drag experienced during periods of non-activation of the circulation control, and the smaller size was more compatible to the wind tunnel test section size. However, while the drag is lessened by a smaller trailing edge, the performance of circulation control also appears to be dependent upon a multitude of variables including, but not limited to, the trailing edge radius and jet velocity. Through a modeled experiment, the two attributes that influence the circulation control performance were concurrently manipulated by varying the radius of curvature and the velocity of the blown jet. The combination of these characteristics were experimentally explored to determine the location where the jet leaves the surface of the cylinder, also known as the separation point. The optimum separation point is defined as the farthest angular displacement from the plane of the blown jet exit slot, which corresponds to the greatest increase in the circulation around the cylinder, representing the trailing edge of a circulation control airfoil. From the known radius and jet velocity, an expression that relates the separation point and the mass flow rate velocity quantity are compared. Understanding the blowing coefficient and its impact on the separation point, results in a predictive relationship between these two attributes of circulation control. The results of this two-dimensional cylinder study found that an increase in trailing edge radius decreased the location of the separation point. In addition, an increase in the jet velocity resulted in an increase in the separation point location. The combination of these two quantities produced a relationship similar to each individually, illustrated by the mass flow rate velocity value, which is the blowing coefficient excluding free stream conditions, versus the angle of separation. Data is therein compared to the theory by Newman [3], which predicts a maximum separation point location at 245 degrees beyond the jet exit plane and an increase in the separation point as the radius of curvature increases. The results of this study found a separation point maximized at 231 degrees, and, contrary to Newman [3], a decrease in the separation point was found as the radius of the cylinders increased.

No abstract

No abstract

Circulation control and a lifting surface influenced by ground effect have both individually proven to augment the generation of lift. Recent research at West Virginia University has explored the feasibility of amalgamating the two phenomena, in an attempt to enhance each other. This effort experimentally explores the impact that operation in close proximity to the ground has on a NACA 0018 circulation control modified model in West Virginia University's Closed Loop Wind Tunnel. To simulate the ground, a plane of symmetry methodology was employed by including a second NACA 0018 circulation control modified model as a mirror image to the instrumented model. Since the models have identical geometries, along with the same blowing coefficients, the vertical velocities generated by the two models interact at the center and nullify each other, creating the symmetry plane. While there are many variables that influence the two phenomena separately, this effort only considers the impact the ground and the blowing coefficient has on the aerodynamic quantities. To create this effect, one of the models remains fixed while the other model varies at three designated distances, corresponding to an h/c value of 0.258, 0.646, and 0.984. This research effort demonstrates that with the constraints of zero angle of attack and low blowing coefficients, the combinataion of circulation control and ground effect detract from one another, in terms of L/D, however more research is necessary to explore the aforementioned constraints. Nomenclature A jet= area of the jet T plenum = temperature of the plenum b = wing span u(x) = horizontal velocity contributionlift coefficient out of ground effect γ = specific heat ratio of air C p = coefficient of pressure ΔP = local pressure differential C μ = blowing coefficient ρ j = density of the jet c = chord length ρ ∞ = free stream density H = height at the lowest point of the wing from the ground h/c = height from ground to chord length ratio h(x) = height of the lower surface of the airfoil h te = height of the trailing edge = mass flow rate P plenum = pressure of the plenum P ∞ = free stream pressure P = pressure at location x q,q ∞ = dynamic pressure R = universal gas constant T = thrust of the jet 1 Undergraduate Researcher, Mechanical and Aerospace Engineering, P.O. Box 6070, Student Member 2 Post-Doctoral Fellow, Mechanical and Aerospace Engineering,