Line-of-sight gas radiation effects on near-infrared two-color ratio pyrometry measurements during plasma wind tunnel experiments

TL;DR

This study models how plasma gas radiation affects near-infrared two-color pyrometry measurements in plasma wind tunnel tests, revealing potential biases and proposing correction methods to improve temperature accuracy.

Contribution

The paper introduces a comprehensive model combining CFD and radiation simulations to quantify and correct gas radiation effects on pyrometry measurements during plasma experiments.

Findings

Gas radiation causes significant measurement bias during heating.

The model accurately predicts measurement errors observed in experiments.

Proposed correction improves temperature measurement accuracy.

Abstract

Two-color ratio pyrometry is commonly used to measure the surface temperature of aerospace materials during plasma wind tunnel experiments. However, the effect of the plasma radiation on the measurement accuracy is often neglected. In this paper we formulate a model of the instrument response to analyze the systematic error induced by the gas radiation along the optical path. CFD simulations of the plasma flow field, together with a radiation code, allow to compute the gas spectral radiance within the instrument wavelength range. The measurement error is numerically assessed as a function of the true object temperature and emittance value. Our simulations explain the typical behavior observed in experiments, showing that a significant bias can affect the measured temperature during the material heating phase. For an actual experiment on a ceramic-matrix composite, a correction to the measured data is proposed, while comparative measurements with a spectrometer corroborate the results.