An experimental investigation of airfoils with laminar separation bubbles and effects of distributed suction

In an effort to understand the behavior of the laminar separation bubbles on NACA 0012 and Liebeck LA2573a airfoils at different Reynolds numbers and angles of attack, the boundary layers on the solid airfoils were investigated by measuring the mean and fluctuating components of the velocity profiles over the upper surfaces of the airfoils. Surface pressure measurements were carried out to complete the mapping of the laminar separation bubble and to calculate the lift generated by the airfoils. The experiments were carried out at Reynolds numbers of 150,000 and 250,000. The locations of separation, transition and reattachment were determined as functions of angle of attack and Reynolds number for the two airfoils. The drag was estimated from wake pressure measurements based on the momentum deficit generated by the airfoil. The size and location of the laminar separation bubble on the LA2573a airfoil did not show significant changes with Reynolds number and angle of attack for values of the angle of attack between 0 and 6 degrees.;The baseline results of the size and location of the laminar separation bubble on the LA2573a airfoil were used to design a suction distribution. This suction distribution was designed based on Thwaites' criterion of separation. The effects of applying suction on the size and location of the laminar separation bubble were investigated.;The results showed that the suction distribution designed in this work was effective in controlling the size of the laminar separation bubble, maintaining an un-separated laminar boundary layer to the transition point, and controlling the location of transition. The effects of different suction rates and distributions on the drag were investigated. Drag reductions of 14-24% were achieved. A figure of merit was defined as drag reductions divided by the equivalent suction drag to assess the worthiness of utilizing suction on low Reynolds number flows. The values of the figure of merit were around 4.0 which proved that the penalty of using suction was significantly less than the gain obtained in reducing the drag.