Physics

Reynolds number

Hele-Shaw flow

Mechanics

Laminar flow

Airfoil

Vortex

Bubble

Turbulence

Classical mechanics

Flow separation

Physics of Fluids

As typical flow characteristics in a low Reynolds number, laminar separation bubbles (LSBs) and transition to turbulence over airfoils have been extensively studied in recent years. In order to analyze their flow mechanism, numerical investigation using the finite volume method to solve the Reynolds averaged Navier-Stokes equations with a transition Shear Stress Transport (SST) four-equation transition model is performed in this work, combined with the experimental study facilitated by the oil film interferometry technique. Specifically, the transition SST four-equation transition model is solved to simulate the separation location and LSB structure at low Reynolds numbers on a Wortmann FX63-137 airfoil. Good agreement is obtained between the numerical simulation and experimental measurements regarding the separation, transition and reattachment location, aerodynamic coefficients, and overall flow structures. At higher Reynolds numbers of 200 000 and 300 000, similar bubble structures on the airfoil surface are observed, and the location of the bubble moves toward the leading edge of the airfoil by increasing the angle of attack. However, in Reynolds numbers ranging from 300 000 to 500 000, significant changes of the laminar flow separation structures emerge. The flow structure changes from the classical laminar separation bubble to the nonclassical separation flow structure that is composed of a major vortex 1(V1) and a minor vortex 2(V2). Due to the small distance between V1 and V2, it is difficult to distinguish the delicate structure of the two separation bubbles from the classical laminar separation bubble by the experimental method.

Study on flow separation and transition of the airfoil in low Reynolds number