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Thake, Michael PatrickInvestigation of a Laminar Airfoil with Flow Control and the Effect of Reynolds Number
Master of Science, The Ohio State University, 2011, Aero/Astro Engineering
Wind tunnel tests are performed on a NACA 643-618 airfoil at Reynolds numbers of 6.4x104, 1.8x105, 1.0x106, and 4.0x106 in order study several aspects of a laminar airfoil. Studies of flow control, separation bubbles and the effect of Reynolds number are the major topics of this effort. The tools used for investigation are surface pressure measurements, wake surveys, particle image velocimetry, hot-film anemometry, surface-oil flow visualization, and infrared imaging in order to view the problem from many angles. Preliminary testing at a Reynolds number of 64,000 determined that four distinct flow regimes exist with respect to angle of attack: weak laminar separation, moderate laminar separation, laminar separation bubble, and strong leading edge laminar separation. A portion of the study investigates the cause of such dynamic flow physics. Attempts are then made to employ flow control to induce or imitate the laminar separation bubble. By creating the laminar separation bubbles, significant lift increase and drag reduction are realized over a broader range of angles of attack. Normal blowing, suction, and zigzag tape are used, which are all well-characterized devices and have the potential to enhance lift and reduce drag. Lift is increased significantly and separation is delayed in three of the four regions as a result of control, where the region of no change is when the laminar separation bubble is already in effect. It is observed that the optimal flow control device changes between regimes because different flow physics are required to induce a change. Studies of Reynolds number scaling found that the lift increased and drag decreased as Reynolds number increased. It is important to note that the laminar separation bubble becomes naturally effective at most angles of attack by a Reynolds number of 180,000. Therefore, the value of flow control diminishes except in regions where strong leading edge separation is the limiting element of the airfoil. This research suggests that the laminar airfoil can be controlled in an energy efficient manner such that high performance is gained across all flight regimes with straightforward actuation.

Committee:

Jeffrey Bons, PhD (Advisor); James Gregory, PhD (Committee Member)

Subjects:

Aerospace Engineering; Engineering

Keywords:

laminar airfoil; aerodynamics; flow control; Reynolds number; separation