Session: 04-34 Combustion Experiments III

Paper Number: 153702

Assessment of Reconstruction Error for Laser Absorption Tomography Using Large Eddy Simulation Data 

Laser absorption tomography (LAT) has previously been used and validated to produce tomographic data of flow-field properties such as temperature and species concentrations. Typically, this has been achieved on exhaust systems and simplified lab-scale flames. A project is ongoing to develop such a system for use with a reacting flow facility at Loughborough University that gives a confined, highly turbulent flame, typical of that found in gas turbine (GT) combustion systems, at elevated temperature and pressure using liquid fuels. The application of LAT techniques on this rig will give insight into the more complex flames found in GT systems, increasing understanding of conditions inside the process which may lead to higher emission production.

In LAT, absorbance measurements in the form of integrated line-of-sight measurements, are extracted and converted to a 2D pixel-wised image using an algorithm such as Tikhonov regularisation. This paper attempts to quantify the error and uncertainty in the reconstruction stage by using Computational Fluid Dynamics (CFD) data as a ‘synthetic experiment’ from which line integrated absorbances can be extracted at multiple positions and times in the simulation. Because the reconstruction is a best guess to an ill-posed problem, an inherent degree of error exists from this stage, which this paper attempts to assess in this more complex flow field where the length scales are likely to be different to previous applications.

The original cross-sectional planes from the LES simulation are compared with the reconstructed images to assess the error caused by the reconstruction. Methods of comparison include analysis of probability density functions (PDF) on the full plane or sectionally. Of particular interest is to identify the size and location of major features identified by the absorbance, which will be related to the temperature and species concentrations. The results are used to understand the uncertainty caused by the reconstruction methods and the effect of choices proposed for the experimental set-up and reconstruction, such as the resolution of the reconstructed image. The paper demonstrates the benefit of using CFD to aid design of new experimental facilities.

Presenting Author: Esther Neat Loughborough University

Presenting Author Biography: Esther Neat graduated from Loughborough University in 2022 with a MEng in Aeronautical Engineering and is now completing a PhD at the National Centre for Combustion and Aerothermal Technology. Her research focuses on computational prediction of emissions from aircraft combustion systems and works closely with the ESPRC funded LITECS project (Laser Imaging of Turbine Engine Combustion Species).

Authors:

Esther Neat Loughborough University
Abhishek Upadhay University of Edinburgh
Maxwell A Williams Loughborough University
Jon F Carrotte Loughborough University
Michael Lengden University of Strathclyde
Chang Liu University of Edinburgh
Andrew Garmory Loughborough University