Pressure Sensitive Paint Measurements On A Rotor Disk Surface At High Speeds

Measurement of the static-pressure distribution over the surface of a rotor disk was attempted using pressure sensitive paint (PSP). A uniform stress, high speed rotor disk, fitted with a shock generator, was built, installed and operated at speeds in excess of 20,000 RPM by a Hamilton Standard turbine driven fuel pump. A once per revolution trigger signal was converted to a transistor to transistor logic (TTL) format and used to gate an intensified charged coupled device (CCD) video camera. Multiple low intensity level camera exposures were integrated and captured to produce a single usable image. Ten captured images were averaged to increase the image's signal to noise ratio and the result was used to produce an image ratio with respect to a static reference condition. Finally, a pseudo coloring process was used to develop a color image that related intensities to both temperature and pressure distributions in accordance with the Stern-Volmer relation. Paint stripping and temperature dependence prevented the measurement of pressure at transonic speeds. The test bed facility and acquisition techniques developed here could now be used to overcome those limitations.

In the development of a surface pressure measurement system for transonic compressor rotors, it has been shown that Pressure Sensitive Paint (PSP) is also temperature dependent. In the present study, the sensitivities to pressure and temperature were examined experimentally using an electronically- gated, intensified Charged- Coupled-Device (CCD) video camera, frame-grabber software and an eight-inch diameter calibration chamber. Using a signal generator, in a procedure that matched the requirements of the rotor application, multiple low-intensity-level camera exposures were integrated and captured to produce a single usable image. Ten captured images were averaged to increase the image's signal-to-noise ratio and the result was used to produce an image ratio with respect to a static (ambient pressure/temperature) reference condition. Calibration tests of constant temperature/variable pressure and constant pressure/variable temperature were completed. The results were then compared with data obtained using the same paint and an automated, single- exposure calibration procedure at NASA Ames Research Center. It was shown that the calibration data could be used to derive the static pressure field produced over a high-speed test rotor using PSP and the same image-capture system used in the calibration. In preparation for a bench test of the procedure, a uniform- stress, high-speed test rotor disk, fitted with a shock generator was driven at speeds in excess of 30,000 RPM. Recommendations are made toward the goal of obtaining quantitative pressure measurements on transonic compressor rotors.

Pressure-sensitive paint measurement on a transonic compressor rotor required the prior development of phase-locked cumulative imaging using a disk- rotor driven by a high-speed Hamilton-Standard turbine as a developmental test- bed. The turbine was installed in a protective housing in the Gas Dynamics Laboratory and connected to an 8000 cu ft, 300 psi air supply. An hydraulic pump provided bearing lubrication. A once per revolution trigger signal was produced from a light-emitting diode and PIN photodiode pair. The imaging system consisted of an intensified CCD video camera externally triggered by the 1/rev signal via a waveform shaping circuit designed for the present application. Images were captured at camera gate speeds calculated to eliminate pixel blur and image integration times were varied to optimize image intensity and spatial resolution. Structural and modal analyses of the disk-rotor were conducted and a simplified numerical model of the flow was computed. Ratioed, colored images were produced for wheel speeds to 20,000 RPM. The effect of the radially varying stagnation temperature was evident, underscoring the importance of quantifying and accounting for the PSP temperature sensitivity so that quantitative pressure data may be obtained. Recommendations for a follow-on program are reported.

Non-destructive evaluation (NDE) methods have dominated most of the fields of applied research and technology over the last twenty years. These techniques provide information on the functional efficiency of materials and structures without causing any structural impact on the structure itself. Their use enables the monitoring of the structural inte

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