Analysis and reduction of spurious displacements in high-framing-rate background-oriented Schlieren

Xiong, Yaxuan; Weilenmann, Markus; Noiray, Nicolas

doi:10.1007/s00348-020-2879-y

Cited by 8 publications

(13 citation statements)

References 29 publications

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“…Spatially non-uniform spurious displacements (SDs) can be clearly identified in regions far away from the jet. Similar observations and discussions on the possible origins of the SDs were also proposed by the same group (Xiong et al 2020). A heuristic approach was adopted here to remove the SDs via reconstructing a nonuniform field of SDs based on their distributions in regions away from the helium jet.…”

Section: Helium Jet Experimentssupporting

confidence: 55%

“…(2) can be simplified by assuming a constant n∕ y over the thickness W of the Schlieren object thus, Combining Eqs. (1) and (3) and considering the equivalent equations in x-direction, an equation set can be obtained, which is usually solved in the form of a Poisson equation (1 with proper boundary conditions (Xiong et al 2020). For axisymmetric flows, n∕ y is not constant along z in Eq.…”

Section: Principle Of Bosmentioning

confidence: 99%

“…By applying proper boundary conditions, ̄ can be calculated. More details to solve this Poisson equation in BOS measurements can be found in the literature, e.g., (Xiong et al 2020). The inversion of ̄ can be achieved, for example, by inverse Abel transform as shown in Eq.…”

Section: Axisymmetric Bosmentioning

confidence: 99%

“…In practice, noises are always appearing in the BOS measurement from multiple sources (Xiong et al 2020), thus it is critical to consider the impact from the noises when…”

Section: Direct Vs Indirect Approachmentioning

confidence: 99%

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Towards robust BOS measurements for axisymmetric flows

2020

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Accurately reconstructing a radial refractive index (n) field is challenging in axisymmetric background oriented Schlieren (BOS) measurement. In this study, we systematically investigated several widely adopted inversion algorithms in BOS applications. To quantitatively assess the performance of each algorithm, a synthetic experiment mimicking a helium jet discharged into ambient air was established to provide the reference. Relying on the necessity to solve a Poisson equation for a lineof-sight projected variable, tested algorithms were categorized into two groups: direct and indirect. In the direct approach, the algorithm is applied directly to the light deflection angle () to reconstruct the radial field, defined as = (n − n 0)∕n 0 where n 0 is the reference refractive index. In the indirect group, the Poisson equation is solved first. Then, an inversion algorithm is subsequently applied to the projected to obtain in the radial plane. The two approaches were compared with the synthetic experiment both using the adaptive Fourier-Hankel methods (AFH). The comparison showed that at the cost of introducing the additional step of solving the Poisson equation, the indirect approach performed more accurately when noises were present in the measurements. To identify the proper inversion algorithm suitable for the indirect approach, we further compared four types of algorithms in the synthetic experiments including AFH, onion peeling (OP), three-point Abel (TPA), and filtered back projection tomography (FBPT). The results showed that TPA had the best performance in terms of the reconstruction accuracy with noisy data. Finally, experiments on axisymmetric helium jets were conducted to confirm the effectiveness of the proposed TPA algorithm in the indirect approach.

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Section: Helium Jet Experimentssupporting

confidence: 55%

Section: Principle Of Bosmentioning

confidence: 99%

Section: Axisymmetric Bosmentioning

confidence: 99%

“…In practice, noises are always appearing in the BOS measurement from multiple sources (Xiong et al 2020), thus it is critical to consider the impact from the noises when…”

Section: Direct Vs Indirect Approachmentioning

confidence: 99%

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Towards robust BOS measurements for axisymmetric flows

2020

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“…The components δ fsd and δ ssd are spurious displacements that are fast and slow with respect to the acquisition time of a high-speed imaging recording (in the present case, 0.4 s for 5000 frames recorded at 12.5 kHz). In our experimental set-up, the origin of δ ssd is attributed to the heating of the camera sensor between the acquisition of I r (x) and I(x, t), while δ fsd results from the vibrations induced by the camera fan (Xiong et al 2020). In (2.2), δ path is the displacement induced by temperature fluctuations along the optical path, which have here been reduced by thermally protecting this optical path.…”

Section: Experimental Set-up and Data Processing Methodsmentioning

confidence: 96%