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<p>This study has firstly provided an instantaneous refractive index compensation on velocity measurement in a reacting field where the 3D refractive index and the velocity distribution were measured by Background-oriented Schlieren tomography (BOST) and planar particle image velocimetry (PIV). A one-to-nine endoscope system was integrated with a camera to provide nine views of a turbulent non-piloted Bunsen flame. The 3D refractive index field was reconstructed from a neural network. A low-speed PIV system was applied to capture 2D velocity distribution across the central plane simultaneously. To synchronise the BOST system with PIV, two digital delay/pulse generators were synchronised to generate two groups of signals with different frequencies for two systems with a fixed phase delay. The pixel shifting on the PIV plane was resolved by estimating the gradient of the thermal-induced refractive index between the PIV camera and the imaging plane. The magnitude of the <i>instantaneous</i> velocity error caused by the light deflection was estimated (<InlineEquation ID="IEq1"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="348_2025_4093_Article_IEq1.gif" Format="GIF" Height="16" Rendition="HTML" Resolution="72" Type="Linedraw" Width="40" /> </InlineMediaObject> <EquationSource Format="TEX">\(\pm \,2\%\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mo>±</mo> <mspace width="0.166667em" /> <mn>2</mn> <mo>%</mo> </mrow> </math></EquationSource> </InlineEquation>) for a small non-pilot flame. By inversely considering the velocity error, the error effect caused by the instantaneous refractive index displacement was firstly removed. Such a technique provides a well-defined method that can resolve the same velocity error in PIV measurement in larger flames, significantly improving the accuracy of PIV in reacting flows.</p>

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Instantaneous refractive index compensation on the velocity measurement using simultaneous PIV-BOST

  • 期刊论文

  • 发表日期：

    2025年8月12日

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  • Yutao Zheng,
  • Yuanzhe He,
  • Jingruo Chen,
  • Minshuo Li,
  • Shijie Xu,
  • Bi Wen,
  • Yingzheng Liu,
  • Weiwei Cai

摘要

This study has firstly provided an instantaneous refractive index compensation on velocity measurement in a reacting field where the 3D refractive index and the velocity distribution were measured by Background-oriented Schlieren tomography (BOST) and planar particle image velocimetry (PIV). A one-to-nine endoscope system was integrated with a camera to provide nine views of a turbulent non-piloted Bunsen flame. The 3D refractive index field was reconstructed from a neural network. A low-speed PIV system was applied to capture 2D velocity distribution across the central plane simultaneously. To synchronise the BOST system with PIV, two digital delay/pulse generators were synchronised to generate two groups of signals with different frequencies for two systems with a fixed phase delay. The pixel shifting on the PIV plane was resolved by estimating the gradient of the thermal-induced refractive index between the PIV camera and the imaging plane. The magnitude of the instantaneous velocity error caused by the light deflection was estimated ( \(\pm \,2\%\) ± 2 % ) for a small non-pilot flame. By inversely considering the velocity error, the error effect caused by the instantaneous refractive index displacement was firstly removed. Such a technique provides a well-defined method that can resolve the same velocity error in PIV measurement in larger flames, significantly improving the accuracy of PIV in reacting flows.