Volumetric imaging of flame refractive index, density, and temperature using background-oriented Schlieren tomography
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lumetric imaging of flame refractive index, density, and temperature using background-oriented Schlieren tomography LIU HeCong, HUANG JianQing, LI Lei & CAI WeiWei
*
School of Mechanical Engineering, Shanghai Jiao Tong University, Shanghai 200240, China Received April 5, 2020; accepted June 1, 2020; published online August 26, 2020
Volumetric imaging represents one of the major development trends of flow diagnostics due to both the advancement in hardware and the requirement for more information to further understand complicated turbulent and/or reactive flows. Backgroundoriented Schlieren tomography (BOST) has become increasingly popular due to its experimental simplicity. It has been demonstrated to be capable of simultaneously recovering the distributions of refractive index, density, and temperature of flows. However, its capability in thermometry has only been demonstrated under the axisymmetric assumption, which greatly limits its applicability. In this work, we dedicated to developing a cost-effective BOST system for the simultaneous retrieval of refractive index, density, and temperature distributions for the asymmetric flame. A few representative tomographic inversion algorithms were assessed as well. Both numerical and experimental demonstrations were conducted and the results show that our implemented BOST can successfully reconstruct the three-dimensional temperature distribution with a satisfactory accuracy. Schlieren, tomography, combustion diagnostics, temperature Citation:
Liu H C, Huang J Q, Li L, et al. Volumetric imaging of flame refractive index, density, and temperature using background-oriented Schlieren tomography. Sci China Tech Sci, 2020, 63, https://doi.org/10.1007/s11431-020-1663-5
1 Introduction Optical imaging methods have been prevalent for decades due to their non-intrusiveness, versatility in measuring a variety of physical quantities, and capability in resolving the non-uniformities within the flames [1–3]. Laser sheet methods have been widely adopted for spatially-resolved flow diagnostics for the past decades. However, for practical applications, the flames are usually turbulent and feature salient three-dimensional (3D) characteristics which can only be fully resolved with 3D imaging methods [4], which have attracted surged research efforts recently [5,6]. Typically, 3D flame imaging can be realized via the scanning laser sheet [7], light field imaging [8,9], and volumetric tomography (VT) [10,11], respectively. For the first strategy, the flame is scanned layer by layer in a time series, which *Corresponding author (email: [email protected])
compromises the spatial continuity between neighbor slices. Strictly speaking, the resulting 3D rendering can neither capture transient nor phase-averaged properties of the turbulent flames. Light field imaging is the second means for volumetric imaging, which only employs a single camera equipped with a micro-lens array and can record and distinguish spatial information from different perspectives, based on which the 3D field can be r
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