Boundary Layer Transition Visualization of a Helicopter Blade in Forward Flight Using Thermography

Abstract

The boundary layer transition detection technique by thermography has been extended to a wind tunnel model simulating helicopter forward flight conditions. The helicopter blade is a generic NASA RC series airfoil 66.75 in (1.7 m) span with a 5.45 in (13.8 cm) chord as a part of a three-blade system. Testing was done at the NASA Langley 14- x 22-foot Subsonic Wind Tunnel. The image de-rotation method was employed to improve signal-to-noise and for high-frequency image acquisition to enable the use of the Differential Infrared Thermography (DIT) technique. This method allows the visualization of changes in the transition front due to varying instantaneous in-flow conditions of the blade throughout the rotor disk. This paper describes the complex imaging installation, offers sample data processed with several techniques and discusses the relevance to CFD validation.