Characterisation of boundary layer transition over a low Reynolds number rotor

Abstract

An experimental investigation on the flow topology over a rotor operating atlow Reynolds numbers is presented. The feasibility of laminar to turbulenttransition experiments over small rotors is demonstrated. Phase-locked infraredthermography coupled with simultaneous force and torque measurements wereused to study a three bladed rotor with a NACA0012 aerofoil section set at auniform angle of incidence of 10◦. Boundary layer transition was forced usingtwo-dimensional (2D) and three-dimensional (3D) roughness elements, placedat approximately 5% and 28% of the rotor blades chord. In the 3D roughnessconfigurations once the critical roughness Reynolds was attained the streaksdownstream developed into fully turbulent wedges. For the current rotor con-figuration, it was found that the state of the boundary layer can significantlyaffect its performance, with the non-optimal forcing of laminar to turbulenttransition generally resulting in a loss of performance when compared to thesmooth reference rotor case.Keywords:Infrared Thermography; Boundary layer transition; Low Reynoldsnumber; rotor