Measuring Surface Pressures on Rotor Blades Using Pressure-Sensitive Paint

This paper will present details of a pressure-sensitive paint system for measuring global surface pressures on rotor blades in simulated forward flight at the 14x22 ft subsonic tunnel at the NASA Langley Research Center. The system was designed to use a pulsed laser as an excitation source and pressure-sensitive paint data were collected using the lifetime-based approach. The higher intensity of the laser allowed pressure-sensitive paint images to be acquired using a single laser pulse, resulting in a collection of images that can be used to determine blade pressure at a specific instant in time. This is extremely important in rotorcraft applications because the blades experience dramatically different flowfields depending on their position. In addition, there can be fluctuations on the blade that vary every cycle due to factors such as lead/lag, flapping, and twisting of the blade. These effects generally preclude the use of phase averaging and thus the need for acquiring the data in a single image pair. For this test, the entire upper surface of a blade was painted and imaged. After taking into account temperature effects on the pressure-sensitive paint, the results agree both qualitatively and quantitatively with both expected results as well as with pressure transducers. Several limitations of the technique have been identified and discussion of strategies to overcome them is also presented.