Measuring temperature distribution on the sample surface while testing in thermal wind tunnel

Optical and optical-electronic devices and complexes


Аuthors

Kazakov V. A.1*, Senyuev I. V.2**

1. National Research University "MPEI", 14, Krasnokazarmennaya, Moscow, 111250, Russia
2. Central Aerohydrodynamic Institute named after N.E. Zhukovsky, TsAGI, 1, Zhukovsky str., Zhukovsky, Moscow Region, 140180, Russia

*e-mail: kazakov44@rambler.ru
**e-mail: senyuev@gmail.com

Abstract

While conducting experiments in the thermal wind tunnel it is necessary to measure the temperature distribution on the sample surface within the range up to 3000°C. This task is solved with pyrometry, allowing temperature measuring by equilibrium radiation’s registration of the studied object in visible or near infrared spectral range.

The complexity of the optical temperature measurement is caused by the absence of precise information on the tested model’s materials emissivity. Very often, these materials are novel, and information on their optical properties is inaccessible. Furthermore, the chemical composition of the sample surface may alter during the experiment and, in some cases, the surface destruction may occur. All these processes can change surface emissivity significantly. It should be noted, that emissivity change over the surface could appear rather non-uniform. Thus, it is necessary to use temperature-measuring methods, which do not require information on the tested object emissivity. As a rule, the tested objects are axisymmetric or flat bodies, and, therefore, the information on a temperature distribution along one line on the sample surface is sufficient.

The multi-channel spectrometer based on digital CCD camera was developed. It ensures a momentary acquisition of emission spectra along a certain line. The spectrometer consists of two lenses, slit diaphragm, diffraction grating and CCD camera with a lens. The radiation of the heated object is passing through two lenses and falls on diffraction grating. Lenses are combined to form the Kepler telescope scheme, producing the parallel beam. The third lens is used to form the spectral image of the slit on CCD array.

The developed multi-channel spectrometer was tested in TsAGI together with NRU MPEI. Tests proved the performance of the spectrometer and the ability to measure temperature distribution in the absence of emissivity value of the sample material.

Keywords:

thermal aerodynamic installations, induction heating, plasma, noncontact temperature measurement, brightness pyrometry, spectral pyrometry, emissivity coefficient, temperature field

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