Automatic control of laminar boundary-layer transition

Interest has recently been renewed in the use of distributed suction for the production of laminar flow over substantial areas of the surface of aircraft wings and engine nacelles. Suction may be most efficiently applied by using a number of independently controllable panels through which fluid is withdrawn. The need to determine the distribution of suction flow rates that results in a given streamwise location of boundary-layer transition with minimum power consumed in providing suction gives rise to a nonlinearly constrained optimization problem. A gradient descent algorithm is shown to be successful in both experimental and numerical studies in determining the optimal suction distribution. We present results of experiments performed on a flat plate in a wind tunnel with two suction panels and an optional pressure gradient. We show that the system successfully maintains the laminar-turbulent transition at a given point and minimizes the amount of suction power required to do so.