Instantaneous velocity field measurements in unsteady gas flow by speckle velocimetry
TL;DR: An application of speckle photography techniques to unsteady gas flow measurements is presented and it is shown that 2-D velocity fields can be measured even when the flow is not perfectly 2D.
Abstract: An application of speckle photography techniques to unsteady gas flow measurements is presented. The instrumentation developed for the analysis of double-exposure photographs by digital signal processing is described. It is shown that 2-D velocity fields can be measured even when the flow is not perfectly 2-D. Accuracy and limitations of these techniques are discussed.
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TL;DR: The development of the method of particle image velocimetry (PIV) is traced by describing some of the milestones that have enabled new and/or better measurements to be made.
Abstract: The development of the method of particle image velocimetry (PIV) is traced by describing some of the milestones that have enabled new and/or better measurements to be made. The current status of PIV is summarized, and some goals for future advances are addressed.
1,284 citations
TL;DR: In this paper, a set of six non-dimensional parameters that are the most significant in optimizing particle image velocimeter performance are identified, which are the data validation criterion, the particle image density, the relative in-plane image displacement, a velocity gradient parameter, and the ratio of the mean image diameter to the interrogation spot diameter.
Abstract: The spatial resolution, detection rate, accuracy and reliability of a particle image velocimeter (PIV) depend critically upon the careful selection of a number of parameters of the PIV system and the fluid motion. An analytical model and a Monte Carlo computer simulation have been developed to analyse the effects of experimental parameters and to optimize the system parameters. A set of six nondimensional parameters that are the most significant in optimizing PIV performance are identified. They are the data validation criterion, the particle image density, the relative in-plane image displacement, the relative out-of-plane displacement, a velocity gradient parameter, and the ratio of the mean image diameter to the interrogation spot diameter. These parameters are studied for the case of interrogation by autocorrelation analysis. By a single transformation, these results can be applied to interrogation by two-dimensional Fourier transform analysis of the Young's fringes.
762 citations
TL;DR: Using twisted light, Lavery et al. detected rotation with an analogous angular Doppler shift, which may be useful for remote sensing and observational astronomy, and the multiplicative enhancement of the frequency shift may have applications for the remote detection of rotating bodies in both terrestrial and astronomical settings.
Abstract: The linear Doppler shift is widely used to infer the velocity of approaching objects, but this shift does not detect rotation. By analyzing the orbital angular momentum of the light scattered from a spinning object, we observed a frequency shift proportional to product of the rotation frequency of the object and the orbital angular momentum of the light. This rotational frequency shift was still present when the angular momentum vector was parallel to the observation direction. The multiplicative enhancement of the frequency shift may have applications for the remote detection of rotating bodies in both terrestrial and astronomical settings.
740 citations
01 Jan 1989
TL;DR: In this paper, a set of six non-dimensional parameters which are most significant in optimizing the PIV autocorrelation algorithm are derived, which are the data validation criterion, the particle image density, the relative in-plane image displacement, relative out-of-plane displacement, a velocity gradient parameter and the ratio of the mean image diameter to the interrogation spot diameter.
Abstract: The spatial resolution, detection rate, accuracy and reliability of a particle image velocimeter depend critically upon careful selection of a number of parameters of the PIV system and the fluid. An analytical model has been developed to analyze the effects of variation of experimental parameters which optimize the system. A set of six nondimensional parameters which are most significant in optimizing the PIV autocorrelation algorithm are derived. They are the data validation criterion, the particle image density, the relative in-plane image displacement, the relative out-of-plane displacement, a velocity gradient parameter and the ratio of the mean image diameter to the interrogation spot diameter. A comparison is made with the method of analysis by Young’s fringes to show this set of parameters is most significant there and the analysis is valid for both methods of PIV system interrogation.A study of a range of specific velocity fields has been undertaken to determine the influence of these parameters in each case and recommendations are made for interrogation of these velocity fields. The presence of velocity gradients in the velocity field has been examined for the cases of pure shear and solid body rotation. Corrections for the statistical bias are developed, with recommendations for minimizing bias effects and loss of signal strength.The spatial resolution, detection rate, accuracy and reliability of a particle image velocimeter depend critically upon careful selection of a number of parameters of the PIV system and the fluid. An analytical model has been developed to analyze the effects of variation of experimental parameters which optimize the system. A set of six nondimensional parameters which are most significant in optimizing the PIV autocorrelation algorithm are derived. They are the data validation criterion, the particle image density, the relative in-plane image displacement, the relative out-of-plane displacement, a velocity gradient parameter and the ratio of the mean image diameter to the interrogation spot diameter. A comparison is made with the method of analysis by Young’s fringes to show this set of parameters is most significant there and the analysis is valid for both methods of PIV system interrogation.A study of a range of specific velocity fields has been undertaken to determine the influence of these parameters ...
400 citations
TL;DR: Optical techniques for measuring large numbers of simultaneous velocity vectors in two-and three-dimensional regions of fluid flows are reviewed in this article, which provides spatial information of the type that is available from flow visualization with accuracy approaching that of single-point methods such as laser Doppler velocimetry and hot wire.
268 citations
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TL;DR: In this paper, the streamwise and perpendicular components of the velocity field were investigated, in the mid-span plane of a two-dimensional mixing layer, with a 6:1 velocity ratio.
Abstract: Using digital image processing of particle streak photography, the streamwise and perpendicular components of the velocity field were investigated, in the mid‐span plane of a two‐dimensional mixing layer, with a 6:1 velocity ratio. The Reynolds number of the flow, based on the local vorticity thickness and the velocity difference across the layer, ranged from 1360 to 2520, in the plane of observation. The significant result of this experiment was that the region of vorticity bearing fluid is confined to a small fraction of the flow. A second finding, consistent with the small regions of concentrated vorticity, was the observation of instantaneous streamwise velocity reversal, in the laboratory frame, in small regions of the flow.
94 citations
TL;DR: In this paper, the authors used laser speckle photography adapted for the study of fluid dynamics to obtain two-dimensional full-field velocity information from a selected plane within the volume of moving liquid at any given instant in time.
Abstract: Quantitative velocity measurements of unsteady convection in a Benard cell suddenly cooled from above to a supercritical Rayleigh number are reported. The results are obtained by a novel application of laser speckle photography adapted for the study of fluid dynamics. This technique allows two-dimensional full-field velocity information to be obtained solely from a selected plane within the volume of moving liquid at any given instant in time. The convective rolls are found to be regular and oriented parallel to the short side of the cell. The number of rolls within the cell is approximately twice as great as the number reported for steady conditions. The maximum vertical velocity distribution is observed to be a sinusoidal function of the horizontal distance with a detectable third-harmonic component.
85 citations
01 Jan 1978
TL;DR: A Young's fringe processor for speckle photographs is described and automatically measures fringe separation and orientation with an accuracy of 1% and 1 degrees, respectively.
69 citations
TL;DR: An electro-optical read-out system for measuring displacement and strain fields from a double exposure speckle photograph is described in this article, where the optical system uses a cylindrical element to project the 1-D Fourier transform, with minimal distortion of the spacing of the fringe pattern.
Abstract: An electro-optical read-out system for measuring displacement and strain fields from a double exposure speckle photograph is described. The optical system uses a cylindrical element to project the 1-D Fourier transform cylindrical element to project the 1-D Fourier transform from a point on the photograph on to a self-scanning linear photodiode array, with minimal distortion of the spacing of the fringe pattern. The output from the array is processed electronically and fed to a computer which calculates displacements and strains. Experimental results obtained with a partially automated system show the accuracy and reliability achieved.
67 citations
66 citations