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Handbook of Turbomachinery Second Edition Revised - Ventech!

Handbook of Turbomachinery Second Edition Revised - Ventech!

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Figure 30 Application <strong>of</strong> PSP for film effectiveness mapping.<br />

located around the camera, provided the light source for each <strong>of</strong> the camera<br />

positions. The images <strong>of</strong> luminescence intensity distribution from the nozzle<br />

surfaces, recorded by the CCD camera, are originally gray scaled. A data<br />

reduction program compared the recorded intensity values with the<br />

calibration data to obtain surface pressure and film effectiveness distributions.<br />

For the PSP film-cooling test, four images are required: a dark image<br />

(light <strong>of</strong>f, wind <strong>of</strong>f); a reference image (wind <strong>of</strong>f, light on); an air injection<br />

image (wind on, light on, hot air injection); and a nitrogen injection image<br />

(wind on, light on, hot nitrogen injection). Hot refers to the temperature <strong>of</strong><br />

the main stream, about 170 8F (77 8C) and cold means the reference<br />

temperature, controlled at 70 8F (21 8C). The air injection image contains<br />

information <strong>of</strong> surface static pressure only, while the nitrogen injection<br />

image contains both the surface static pressure and the oxygen concentration<br />

information. The PSP is also sensitive to the surface temperature.<br />

Therefore, the nozzles are allowed to stabilize at the free-stream<br />

temperature. By obtaining ratios <strong>of</strong> intensities <strong>of</strong> the described four images,<br />

the oxygen concentration on the airfoil surface downstream from the<br />

injection can be separated from the pressure distribution. Adjusted images<br />

provide the whole picture <strong>of</strong> the airfoil surface viewed with detailed<br />

qualitative and quantitative data <strong>of</strong> local cooling effectiveness.<br />

Indirect Turbulence Measurement<br />

The most difficult requirement in a turbine heat-transfer experiment is to<br />

reproduce the character <strong>of</strong> the actual engine free-stream turbulence. The<br />

Copyright © 2003 Marcel Dekker, Inc.

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