Laminar Separation Control for Eppler 387 Airfoil Based on Resolvent Analysis

Abstract

By actively controlling laminar separation, the aerodynamic loading can be increased. In the context of turbomachinery, an increased loading allows for more power to be extracted or for a lower part count. Active flow control can be made more effective and efficient if the actuator location and forcing frequency are chosen well. Large-eddy simulations of the flow over an E387 airfoil were carried out for a chord Reynolds number of 100,000. For an angle of attack of zero degrees, the suction-side boundary layer separates laminar to form a large separation bubble. With 1% freestream turbulence intensity, the boundary layer reattaches earlier, and the length of the separated region is in better agreement with available measurements. A resolvent analysis suggests that forcing immediately upstream of separation with an angular frequency of 50 (based on freestream velocity and chord length) provides the maximum forcing-response gain. Guided by the resolvent analysis, active flow control by wall-normal blowing and suction was then investigated in the simulation. Forcing introduces laminar, two-dimensional “rollers” that effectively suppress separation. Without freestream turbulence, transition occurs close to the trailing edge. With freestream turbulence, the flow transitions further upstream and active flow control is less effective.