Time-Mean Velocity Field Measurement Using Visualized Flow Images

Okuno, Taketoshi; Nishio, S.; Kimoto, Natsuki

doi:10.1615/jflowvisimageproc.v1.i4.100

Cited by 3 publications

(3 citation statements)

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“…Note that the time interval of each visualization is 1/15 s. The magnitude and the direction of the shear stress are shown by the arrows in the figure. Each distribution shows a low shear stress in the wake region of the cylinder and a high shear stress on both sides of the cylinder, which is a wellknown behaviour of the flow around a circular cylinder and agrees qualitatively with the shear-stress measurement of the flow around a cylinder on a surface by Okuno and Nishio (1997) and Naughton and Brown (1998). These results suggest that the shear-stress distribution around the circular cylinder on the surface is reasonably evaluated by the present measurement technique.…”

Section: Measurement Of Shear-stress Distribution Around a Circular C...supporting

confidence: 85%

“…A similar full-field shearstress measurement technique was studied by Buttsworth et al (2000), but with a nematic liquid-crystal coating. On the other hand, the full-field measurement of shear-stress distribution was conducted by using an oil film visualization technique combined with the particle image velocimetry by Okuno and Nishio (1997). This technique was further extended to the shear-stress measurement over a rotating blade of a turbo-machinery by Nashimoto et al (2000).…”

Section: Introductionmentioning

confidence: 99%

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Measurement of shear-stress distribution over a surface by liquid-crystal coating

Fujisawa

Aoyama

Kosaka

2003

Meas. Sci. Technol.

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In this paper, a method for measuring the instantaneous shear-stress distribution over a solid surface in a fluid flow is studied by using a surface-flow visualization technique with a shear-sensitive liquid-crystal coating. The colour response of the liquid-crystal coating is calibrated against the various shear-stress magnitudes and directions with an experimental test section of laminar channel flow. The measurement of instantaneous shear-stress distribution is carried out using two colour CCD cameras, which are situated side by side in stereoscopic arrangement. The colour-to-shear-stress transformation is conducted by analysing the hue distribution of the visualized colour image with the calibrated relationships between the hues from the two colour CCD cameras and the shear-stress magnitude and direction. The usefulness of this technique was demonstrated by the measurement of shear-stress distribution around a circular cylinder on a surface under decelerating flow conditions.

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Section: Measurement Of Shear-stress Distribution Around a Circular C...supporting

confidence: 85%

Section: Introductionmentioning

confidence: 99%

Measurement of shear-stress distribution over a surface by liquid-crystal coating

Fujisawa

Aoyama

Kosaka

2003

Meas. Sci. Technol.

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“…However, this technique is limited to a point measurement of wall shear stresses. On the other hand, the latter technique relies on the particle image velocimetry (PIV) measurement of oilfilm displacement on the target surface (Okuno andNishio 1997, Nashimoto et al 2000). It allows for the multi-point measurements of wall shear stresses, but suffers from the influence of thick oil films on the target surface, which is apparent near the separation point of flows.…”

Section: Introductionmentioning

confidence: 99%

Measurements of wall-shear-stress distribution on an NACA0018 airfoil by liquid-crystal coating and near-wall particle image velocimetry (PIV)

Fujisawa¹,

Oguma²,

Nakano³

2009

Meas. Sci. Technol.

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Measurements of wall-shear-stress distributions along curved surfaces are carried out using non-intrusive experimental methods, such as liquid-crystal coating and near-wall particle image velocimetry (PIV). The former method relies on the color change of the liquid-crystal coating sensitive to the wall shear stress, while the latter is based on the direct evaluation of shear stresses through the near-wall PIV measurement in combination with the image deformation technique. These experimental methods are applied to the measurement of wall-shear-stress distributions of air flow at a free-stream velocity of 15 m s−1 on a flat plate and an NACA0018 airfoil. The experiments are carried out at zero angle of attack for the flat plate and at 0° and ±6° angles of attack for the airfoil, and then the variations of shear-stress distribution along these surfaces are studied. These measurements in wall shear stresses agree with each other within their experimental uncertainties, suggesting the validity of experimental methods for non-intrusive shear-stress measurements. It is found that the wall-shear-stress distribution shows a small negative value upstream of the reattachment point on the NACA0018 airfoil, which is followed by an increase in shear stresses downstream due to laminar–turbulent transition of boundary layers. Such behavior of wall-shear-stress distribution is well correlated with the mean flow and turbulence characteristics along the airfoil surfaces, which are measured by PIV.

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Statistical approach to the measurement of velocity field

Nishio

Okuno

1998

J Vis

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Present paper describes the principle and applications of a velocity measurement using statistical analysis of visualized flow images. The authors have developed a new algorithm for the measurement using the passing probability of a particle. It is known that this kind methods gives the total flow speed at each pixel unit. In this study, the method is extended by forming the governing equation using the Lagrange's differentiation. The process is similar to the so-called spatio-temporal derivative method. The extension of the equation enables to measure the velocity components with the help of the statistical technique. The idea is based on the fact that the temporal derivative of luminance function is proportional to the vector product of the flow velocity and the gradient of luminance function in space which gives the velocity component normal to the edge of particle image. This is easy to apply on the three-dimensionalflow field.

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Time-Mean Velocity Field Measurement Using Visualized Flow Images

Cited by 3 publications

References 0 publications

Measurement of shear-stress distribution over a surface by liquid-crystal coating

Measurement of shear-stress distribution over a surface by liquid-crystal coating

Measurements of wall-shear-stress distribution on an NACA0018 airfoil by liquid-crystal coating and near-wall particle image velocimetry (PIV)

Statistical approach to the measurement of velocity field

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