Airfoil Performance Sensitivity to Laminar Separation Bubble Characteristics

The current study examines the effect of laminar separation bubble characteristics on airfoil performance coefficients. To achieve this, wind tunnel experiments were conducted to investigate the laminar separation bubble formed over an airfoil geometry. Surface pressure distributions, integral force coefficients, infrared thermography, and particle image velocimetry data were collected during these experiments. The results showed significant agreement with viscous-inviscid airfoil analysis software when tested under similar freestream turbulence intensity. The study found that changes in transitional flow features across the airfoil surface caused substantial variation in drag characteristics and lift-curve linearity. The greatest decrease in lift-curve linearity and increase in drag occurred when laminar boundary-layer separation was observed without reattachment. Subsequently, a laminar separation bubble formed at the airfoil leading edge resulting in rapid recovery to lift linearity and parabolic drag behaviors. The study also found that as Reynolds number increased, there was less variation in the aerodynamic performance of the airfoil due to the decreased prevalence of laminar separation without turbulent reattachment. Furthermore, the separation point of the laminar separation bubble remained relatively constant with changing Reynolds number, while the reattachment point moved upstream.