What is it about?
We have developed and validated a new infrared (IR) thermography data reduction technique for convective heat flux meauseremnts over a sharp cone in hypersonic flow tested in the Boeing/AFOSR Mach-6 Quiet Tunnel. Firstly, the infrared raw data are converted into temperature values by means of a radiometric calibration including the effect of the presence of the wind tunnel viewing window and the infrared directional emissivity of the model is considered. Temperature maps onto a 3D surface grid from 2D infrared images are reconstructed by means of an optical calibration taking into account lens distortions. Model oscillations, due to sting mechanism vibrations, increase the temperature noise which is reduced with a single-step Discrete Fourier Transform (DFT) approach. Convective heat flux is computed by means of an Inverse Heat Transfer Problem (IHTP). The 1D IHTP is solved and the experimental results are validated against the theoretical solution with an average relative error of 3.6% by performing runs with the cone at 0 deg angle of attack. A 2D IHTP is developed to take into account tangential conduction caused by the crossflow vortices on the cone at 6 deg angle of attack.
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Why is it important?
Our findings show that it is possible to estimate the convective heat transfer over a model in hypersonic flow with high accuracy by using infrared thermography in respect with other tecniques. Heat flux measurements in the hypersonic regime are extremely important to several science and engineering problems such as the investigation of hypersonic laminar-to-turbulent transition, which is crucial to lifting re-entry vehicles, air-breathing cruise vehicles, and high-speed missiles. In fact, boundary-layer state analysis is a key factor in the design of the thermal protection system and it deeply affects the skin friction, drag, and moments.
Perspectives
Carring out the experiments explained in this article was a great pleasure since I collaborated with an oustanding research group and worked in an high-technology facility as the Boeing/AFOSR Mach-6 Quite Tunnel is. This article will help all the researchers and engineers involved in the heat transfer evaluation for hypersonic aircraft design and it shows how accurate can be the infrared thermography applied for heat transfer evaluation in respect with other technique with an average error of about 3.6% against the theoretical heat transfer which is a primising results for future works.
Mirko Zaccara
Universita degli Studi di Napoli Federico II
Read the Original
This page is a summary of: Infrared Thermography Data Reduction Technique for Heat Transfer Measurements in the Boeing/AFOSR Mach-6 Quiet Tunnel, January 2019, American Institute of Aeronautics and Astronautics (AIAA),
DOI: 10.2514/6.2019-0894.
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