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 th is paper, a numerical simulation is performed to make clear the deflec tion characteristics of the incident measuring rays passing through th e thermal boundary layer developing along an isothermally heated plate . Then the additional fringe order shift and fringe position displacem ent due to light deflection in holographic interferometry are calculat ed, and compensation for the deflection measurement uncertainty is mad e by analyzing the fringes of real holographic interferograms. The val idity of this compensation is confirmed by experimentation on the comb ined free and forced convection flow fields in the thermal entrance re gion of a horizontal rectangular duct with a constant wall temperature . As a result, this compensation method is found to be useful in impro ving the measurement accuracy.