Background oriented schlieren technique with fast Fourier demodulation for measuring large density-gradient fields of fluids

Shimazaki, Takaaki; Ichihara, Sayaka; Tagawa, Yoshiyuki

doi:10.1016/j.expthermflusci.2022.110598

Cited by 20 publications

(17 citation statements)

References 36 publications

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“…The experimental methods follow those of [26] and [58]. The camera, target, and background are placed on the same line, as shown in Fig.…”

Section: Methodsmentioning

confidence: 99%

“…In this subsection, we describe the procedure for analyzing the BOS. Fast checkerboard demodulation (FCD) ( [57,58]) is applied to the two background images taken in the experiment (Figs. 6(a) and 6(b)) to obtain the x-direction displacement vector field of the shock wave, as shown in Fig.…”

Section: Pressure Calculation Methodsmentioning

confidence: 99%

“…The camera takes the background image with and without the measurement target. The apparent local displacement vector (u, v) on the image is obtained from the two images using an image analysis technique such as digital image correlation (DIC)[52,53], optical flow[54,55], or fast checkerboard demodulation (FCD)[56,57,58]. An (x, y, z) coordinate system is adopted, with the background image in the xy plane and the camera's line of sight in the z direction (Fig.2).…”

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confidence: 99%

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Background-oriented Schlieren technique with vector tomography for measurement of axisymmetric pressure fields of laser-induced underwater shock waves

Ichihara¹,

Shimazaki²,

Tagawa³

2022

Preprint

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This study aims to overcome the problems that existing background-oriented schlieren (BOS) techniques based on computed tomography (CT-BOS) face when measuring pressure fields of laser-induced underwater shock waves. To do this, it proposes a novel BOS technique based on vector tomography (VT-BOS) of an axisymmetric target. The remarkable feature of the proposed technique is the reconstruction of an axisymmetric vector field with nonzero divergence, such as the field of a laser-induced underwater shock wave. This approach is based on an approximate relation between the projection of the axisymmetric vector field and the reconstructed vector field. For comparison, the pressure fields of underwater shock waves are measured with VT-BOS, CT-BOS, and a needle hydrophone. It is found that VT-BOS is significantly better than CT-BOS in terms of better convergence, less dependence on the spatial resolution of the acquired images, and lower computational cost. The proposed technique can be applied not only to fluid dynamical fields, but also to other axisymmetric targets in other areas, such as electromagnetics and thermodynamics.

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“…The experimental methods follow those of [26] and [58]. The camera, target, and background are placed on the same line, as shown in Fig.…”

Section: Methodsmentioning

confidence: 99%

Section: Pressure Calculation Methodsmentioning

confidence: 99%

mentioning

confidence: 99%

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Background-oriented Schlieren technique with vector tomography for measurement of axisymmetric pressure fields of laser-induced underwater shock waves

Ichihara¹,

Shimazaki²,

Tagawa³

2022

Preprint

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“…∂v/∂y ∆y should be smaller than a certain threshold δv th . By comparing BOS and hydrophone measurements [8,9], we estimate that δv th ≤ 0.4. Therefore, to increase displacement field gradients (larger pressures), a smaller spatial resolution, such as ∆y ∼ δv th / ∂v/∂y is required.…”

Section: Bos Analysismentioning

confidence: 99%

Contactless pressure measurement of an underwater shock wave in a microtube using a high-resolution background-oriented schlieren technique

Yamamoto¹,

Shimazaki²,

Franco-Gomez³

et al. 2022

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A high-resolution background-oriented schlieren (BOS) technique, which utilizes a highresolution camera and a microdot background pattern, is proposed and used to measure the pressure field of an underwater shock wave in a microtube. The propagation of the shock wave subsequently reaches a concave water-air interface set in the microtube resulting in the ejection of a focused microjet. This high spatial-resolution BOS technique can measure the pressure field of a shock front with a width as narrow as the order of only 10 1 µm with a peak pressure as large as almost 3 MPa, which is significantly narrower and larger, respectively, than a previous study [1]. This significant breakthrough has enabled the simultaneous measurement of the pressure impulse of the shock front and the velocity of the microjet tip. As a result, we have experimentally observed the linear relation between the velocity of the microjet tip and the pressure impulse of the shock front for the cases without secondary cavitation in the liquid bulk. Such relation was theorectically/numerically predicted by Peters [2]. This study demonstrated the capability of the proposed high-resolution BOS technique as a microscale contactless pressure measurement tool for underwater shock waves and potentially other micro-and nanofluids.

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“…Considering the potential of the BOS technique, throughout the years, this optical method has been used for studies within different applications, including the analysis of the shock wave propagation from explosions [40], underwater shock waves [41,42], heat transfer processes [43][44][45], air leakage [46], and flame-induced flow [47,48], among others [49][50][51][52][53][54]. Recently, the BOS measurement technique began to be used for density field quantification of the DBD flow induced by plasma actuators.…”

Section: Introductionmentioning

confidence: 99%

Development of a Background-Oriented Schlieren (BOS) System for Thermal Characterization of Flow Induced by Plasma Actuators

et al. 2023

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Cold climate regions have great potential for wind power generation. The available wind energy in these regions is about 10% higher than in other regions due to higher wind speeds and increased air density. However, these regions usually have favorable icing conditions that lead to ice accumulation on the wind turbine blades, which in turn increases the weight of the blades and disrupts local airflow, resulting in a reduction in wind turbine performance. Considering this problem, plasma actuators have been proposed as devices for simultaneous flow control and deicing. These devices transfer momentum to the local airflow, improving the aerodynamic performances of the turbine blades while producing significant thermal effects that can be used to prevent ice formation. Considering the potential application of plasma actuators for simultaneous flow control and deicing, it is very important to investigate the thermal effects induced by these devices. However, due to the significant electromagnetic interference generated by the operation of these devices, there is a lack of experimental techniques that can be used to analyze them. In the current work, a background-oriented Schlieren system was developed and is presented as a new experimental technique for the thermal characterization of the plasma-induced flow. For the first time, the induced flow temperatures are characterized for plasma actuators with different dielectric materials and different dielectric thicknesses. The results demonstrate that, due to the plasma discharge, the temperature of the plasma-induced flow increases with the increase of the applied voltage and may achieve temperatures five times higher than the room temperature, which proves the potential of plasma actuators for deicing applications. The results are presented and discussed with respect to the potential application of plasma actuators for simultaneous flow control and deicing of wind turbine blades.

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Background oriented schlieren technique with fast Fourier demodulation for measuring large density-gradient fields of fluids

Cited by 20 publications

References 36 publications

Background-oriented Schlieren technique with vector tomography for measurement of axisymmetric pressure fields of laser-induced underwater shock waves

Background-oriented Schlieren technique with vector tomography for measurement of axisymmetric pressure fields of laser-induced underwater shock waves

Contactless pressure measurement of an underwater shock wave in a microtube using a high-resolution background-oriented schlieren technique

Development of a Background-Oriented Schlieren (BOS) System for Thermal Characterization of Flow Induced by Plasma Actuators

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