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Abstract
Nonintrusive measurements are highly desirable in the study of modern thermal-fluid systems. One of the key bottlenecks of studying such systems stems from the experimental difficulty of resolving the governing processes with the necessary temporal and spatial resolution. The research and development of modern power and energy systems (e.g., aero-propulsion engine) require understanding such processes under extreme conditions, such as sub-millisecond time resolution, sub-millimeter spatial resolution, high temperature and pressure, and multiphase flows. Traditional experimental techniques are no longer capable of meeting all these requirements. Therefore, this paper discusses nonintrusive laser diagnostics and their prospective of meeting these challenges. Using laser beams as probes and being nonintrusive, laser diagnostics can be applied to any harsh environments, at least theoretically. This paper specifically focuses on the recent work from the author's group to apply tomographic laser techniques to obtain multidimensional measurements in thermal-fluid systems. Examples include two-dimensional imaging of temperature fields at 50 kHz, and three-dimensional measurements of combustion parameters using emission spectroscopy at multi-kilohertz. Lastly, as an example, this paper discusses our ongoing efforts of applying advanced laser diagnostics for the study of thermal management of batteries in a hybrid vehicle.
NOMENCLATURE
| a and b | = | integration limits determined by the line of sight and measurement domain |
| eT | = | overall temperature reconstruction error |
| ET | = | emission tomography |
| F(x,y,z) | = | 3D distribution of the emission to be measured |
| HT | = | hyperspectral tomography |
| ix, iy, iz | = | indices of the voxel centered at (xi, yi, zi) |
| l | = | line of sight |
| P | = | pressure |
| p(Lj, λi) | = | projection at location Lj and wavelength λi |
| P(r, θ, ϕ) | = | 2D projection array measured at r, θ, ϕ |
| PIV | = | particle image velocimetry |
| PSF | = | point spread function |
| r | = | distance |
| S | = | absorption line strength |
| T | = | temperature |
| T(l) | = | distribution of temperature along the line of sight l |
| Trecm, n | = | reconstructed temperature field |
| Tm, n | = | true temperature field |
| U | = | velocity |
| X (l) | = | distribution of mole fraction along the line of sight l |
Greek Symbols
| λi | = | wavelength of the ith absorption line |
| θ | = | azimuth angle |
| ϕ | = | inclination angle |
| Φ | = | Voigt lineshape function |
Additional information
Notes on contributors
Lin Ma
Lin Ma is an associate professor of aerospace and ocean engineering at Virginia Tech, Blacksburg, VA. He received his B.S. in thermal engineering from Tsinghua University (Beijing, China) in 2000, and his M.S. and Ph.D. in mechanical engineering from Stanford University (Stanford, CA) in 2001 and 2006, respectively. His research interests lie in the area of thermal-fluid sciences, with an emphasis on the study of combustion systems using nonintrusive optical diagnostics.