Formulation and demonstrations of three-dimensional background-oriented schlieren using a mirror for near-wall density measurements

Akamine, Masahito; Teramoto, Shinji; Okamoto, Koji

doi:10.1007/s00348-023-03672-1

Cited by 3 publications

References 59 publications

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Background-oriented Schlieren tomography using gated recurrent unit

Bo,

Cai,

Song

et al. 2023

Opt. Express

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Current Background-oriented schlieren tomography (BOST) methods rely primarily on iterative algorithms for reconstruction. Before reconstruction, a weight projection matrix was generated by performing 3D ray tracing using the projection relationship between the cameras, depending on the camera calibration parameters and large weight projection matrix which introduce artifacts and greatly reduce computational efficiency in the reconstruction. Considering that CT reconstruction uses spatial projection sequences from multiple directions, this study draws inspiration from the Recurrent Neural network(RNN) and utilizes spatial correlation between adjacent projection data to propose a background-oriented schlieren reconstruction method based on a gated recurrent unit (GRU) neural network. First, the model architecture is designed and implemented. Subsequently, numerical simulations were conducted using a methane combustion model to evaluate the proposed method, which achieved an average mean relative error (MRE) of 0.23%. Finally, reconstruction experiments were performed on the actual flow-field data above a candle flame, with a reprojection correlation coefficient of 89% and an average reconstruction time of only 1.04 s per frame. The results demonstrate that the proposed method outperforms traditional iterative reconstruction methods in terms of reconstruction speed and accuracy. This provides a feasible solution for the real-time reconstruction of three-dimensional instantaneous flow fields.

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Background-oriented Schlieren tomography using gated recurrent unit

Bo,

Cai,

Song

et al. 2023

Opt. Express

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Microphones and Three-dimensional Background-Oriented Schlieren Measurements of an Ideally Expanded Supersonic Jet

Akamine,

Teramoto,

Okamoto

2024

AIAA SCITECH 2024 Forum

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Formulation and demonstrations of three-dimensional background-oriented schlieren using a mirror for near-wall density measurements, TrackAER: real-time event-based quantitative flow visualization

Okamoto,

Akamine,

Rösgen

et al. 2023

Preprint

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Formulation and demonstrations of three-dimensional background-oriented schlieren using a mirror for near-wall density measurements Three-dimensional background-oriented schlieren (3D-BOS) is an effective method for reconstructing 3D density fields from optically measured data, but it has limitations in measuring near-wall regions, where most of the light paths are blocked. This paper proposes a new extension, 3D-BOS using Mirror, which uses a wall as a mirror to provide sufficient light paths. In this paper, first, the conventional formulations are modified for the proposed method to handle the mirror reflections of the light paths. Subsequently, the proposed method is validated using artificially generated model data of an ideal axisymmetric distribution. The proposed method can reconstruct the distribution as accurately as the conventional method for all the number of cameras examined. Finally, the proposed method is experimentally demonstrated using a candle plume. The proposed method can capture cylindrical low-density regions near the wall surface. TrackAER: real-time event-based quantitative flow visualization We present a novel event-based quantitative flow visualization system, TrackAER, capable of continuously reconstructing, rendering and recording particle tracks in large test volumes without limitations on the measurement duration. Multiple event-based cameras are synchronized and calibrated to produce independent and asynchronous, yet temporally co-registered data streams of flow tracer positions. Subsequently, these data streams are merged into time-resolved three-dimensional particle tracks using photogrammetric techniques. Due to the operating principle of event cameras, the flow scenery is reduced to moving objects only, which effectively compresses the data stream at the camera source. In combination with an efficient data processing pipeline, the measurement system operates in real-time, reconstructing and rendering the investigated flow field without noticeable time lag. The data processing approach follows a “per-event” paradigm and enables the immediate observation and analysis of both, transient and long duration flow features. Specific issues resulting from event-based, frame-free processing are discussed as well as the advantages and limitations of event cameras. Exemplary results are provided to demonstrate the utility of the TrackAER system where Lagrangian particle track information is displayed in a virtual scene together with extracted quantitative information such as local flow velocities.

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Formulation and demonstrations of three-dimensional background-oriented schlieren using a mirror for near-wall density measurements

Cited by 3 publications

References 59 publications

Background-oriented Schlieren tomography using gated recurrent unit

Background-oriented Schlieren tomography using gated recurrent unit

Microphones and Three-dimensional Background-Oriented Schlieren Measurements of an Ideally Expanded Supersonic Jet

Formulation and demonstrations of three-dimensional background-oriented schlieren using a mirror for near-wall density measurements, TrackAER: real-time event-based quantitative flow visualization

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