3-DIMENSIONAL TEMPERATURE-MEASUREMENT BY LASER-HOLOGRAPHIC INTERFEROMETRY - (NUMERICAL-SIMULATION OF LIGHT DEFLECTION AND ITS QUANTITATIVE COMPENSATION FOR MEASUREMENT ERROR)

The measuring beam rays of real-time holographic interferometry curve due to light deflection in the temperature field of interest, and this results in a significant error in the temperature measurements. In this paper, a numerical simulation is performed to make clear the deflection characteristics of the incident measuring rays passing through the thermal boundary layer developing along an isothermally heated plate. Then the additional fringe order shift and fringe position displacement due to light deflection in holographic interferometry are calculated, and compensation for the deflection measurement uncertainty is made by analyzing the fringes of real holographic interferograms. The validity of this compensation is confirmed by experimentation on the combined free and forced convection flow fields in the thermal entrance region of a horizontal rectangular duct with a constant wall temperature. As a result, this compensation method is found to be useful in improving the measurement accuracy.