Single-shot, lifetime-based pressure-sensitive paint for rotating blades

Abstract

A single-shot, lifetime-based pressure-sensitive paint (PSP) technique is proposed as a pressure sensor for applications requiring high pressure sensitivity on a moving model such as a rotor blade. The method is based on a single pulse of high-energy excitation light and a double-frame exposure on an interline transfer charge-coupled device camera for recording luminescent lifetime. Small pressures can be measured on surfaces that are moving in an aperiodic manner (which precludes phase averaging). Measurements in environments having overall surface pressure gradients as small as 1 kPa show that the technique is capable of accurately resolving small pressure fluctuations. The pressure sensitivity to the oxygen concentration of some commonly available PSP formulations has been investigated with respect to capabilities and limitations of the paints for this single-shot lifetime application. A system with ruthenium-based pressure-sensitive paint, 532 nm wavelength laser and a CCD camera is demonstrated on a 0.126 m diameter propeller rotating at 70 Hz. Pressure data are acquired within a single pulse of excitation light energy, with no image averaging required.

Single-shot temperature- and pressure-sensitive paint measurements on an unsteady helicopter blade

“…For Ru(dpp) in PC, the lifetime is approximately 7.85 ls (Juliano et al 2011). PtTFPP in PC, with a longer lifetime of approximately 11 ls, is more than three times as sensitive as Ru(dpp) in PC, resulting in a pressure sensitivity of approximately 0.7 % per kPa at standard atmospheric conditions (Sakaue et al 2002;Gregory and Sullivan 2006;Gregory et al 2006Gregory et al , 2007.…”

“…The paint employed by Juliano et al (2011) on a hovering rotor consisted of bathophen ruthenium chloride, Ru(dpp), deposited in RTV-118 silicone doped with silica gel particles and was chosen for its high pressure sensitivity (0.81 % change in intensity per kPa). However, the RTV-118 binder has a very low rate of oxygen diffusion which directly leads to a poor frequency response on the order of a few Hz for thin paint layers and even less for thicker layers (Winslow et al 1996).…”

“…To avoid the need for phase averaging of PSP images, Kumar (2010) and Juliano et al (2011) demonstrated that acceptable signal-to-noise ratio in a single image can be achieved with a high-energy laser providing a single shot of excitation in the lifetime method. In addition to improved signal level, the high-energy, collimated excitation enables long working distances between the illumination source and the test article.…”

Deployment of a Pressure Sensitive Paint System for Measuring Global Surface Pressures on Rotorcraft Blades in Simulated Forward Flight

“…The actual acquisition of the PSP data was acquired using a double frame imaging technique in which a short exposure image was taken followed immediately by a longer exposure image, as described by Juliano et al 25 The longer exposure image was started after the interline transfer time of the pixels (200 ns) and lasted as long as it took for the first image to be read into the on-board RAM of the camera. With the arrangement, data could be acquired approximately every 400 ms, and with the current rotor speed, this corresponds to one PSP image pair acquired every 8 revolutions.…”

Pressure-Sensitive Paint Measurements on a Moving Store in the NRC 1.5 m Blowdown Wind Tunnel

“…2 Also, a simplified data processing pipeline on a model not equipped with pressure taps is proposed and demonstrated, using CFD simulations as the baseline data.…”