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Stereo particle image velocimetry (PIV) has been employed to study a vortex generated via tangential injection of water in a 2.25 inch (57 mm) diameter pipe for Reynolds numbers ranging from 1,118 to 63,367. Methods of decreasing pipe-induced optical distortion and the PIV calibration technique are addressed. The mean velocity field analyses have shown spatial similarity and revealed four distinct flow regions starting from the central axis of rotation to the pipe wall in the vortex flows. Turbulence statistical data and vortex core location data suggest that velocity fluctuations are due to the axis of the in-line vortex distorting in the shape of a spiral. 相似文献
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The combination of ultrasound echo images with digital particle image velocimetry (DPIV) methods has resulted in a two-dimensional, two-component velocity field measurement technique appropriate for opaque flow conditions including blood flow in clinical applications. Advanced PIV processing algorithms including an iterative scheme and window offsetting were used to increase the spatial resolution of the velocity measurement to a maximum of 1.8 mm×3.1 mm. Velocity validation tests in fully developed laminar pipe flow showed good agreement with both optical PIV measurements and the expected parabolic profile. A dynamic range of 1 to 60 cm/s has been obtained to date. 相似文献
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T. Mizukaki 《Shock Waves》2010,20(6):531-537
In this article, we attempt to validate flow visualization using the high-speed background-oriented schlieren (HiBOS) method,
which is the BOS technique combined with a high-speed video camera as the recording device in the experiment. The method has
been applied to shock-induced flow near the open end of a shock tube. Three incident shock Mach numbers were examined so that
the BOS measurements could be compared with results given in the literature of particle-image velocimetry (PIV) measurements.
Using the HiBOS technique, we were able to clearly view developing, compressible vortex rings and diffracted shock waves discharged
from the open end of the shock tube. From the BOS images, we extracted the history of the propagation velocity, the diameter
of the vortex ring, and the diameter of the vortex core, all of which agree with the corresponding PIV values reported in
the literature. 相似文献
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A generalized processing technique in digital particle image velocimetry with direct estimation of velocity gradients 总被引:1,自引:0,他引:1
S. Mayer 《Experiments in fluids》2002,33(3):443-457
A technique is proposed for the processing of digital particle image velocimetry (PIV) images, in one single step providing direct estimates of fluid velocity, out-of-plane vorticity and in-plane shear rate tensor. The method is based on a generalization of the standard PIV cross-correlation technique and substitutes the usual discrete cross-correlation of image pairs with a correlation of interpolated two-dimensional image intensity functions, being subject to affine transformations. The correlation is implemented by using collocation points, on which image intensity values are interpolated. The resulting six-dimensional correlation function is maximized using a general purpose optimization algorithm. The use of the method is demonstrated by application to different types of synthetically generated image pairs constructed with known particle displacement functions. The resulting errors are assessed and compared with those of a representative standard PIV method as well as with those of the present technique using no differential quantities in the search of the peak location. The examples demonstrate that significant improvements in accuracy can be obtained for flow fields with regions containing strong velocity gradients. 相似文献
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An extension of two color particle image velocimetry (PIV) is described where the color images are recorded onto a single
high-resolution (3060×2036 pixel) color CCD sensor. Unlike mono-color CCD sensors, this system not only eliminates the processing
time and the subsequent digitization time of film-based PIV but also resolves the directional ambiguity of the velocity vector
without using conventional image-shifting techniques. For comparing the spatial resolutions of film and CCD data, a calibration
experiment is conducted by recording the speckle pattern onto 35 mm color film and using a CCD sensor under identical conditions.
This technique has been successfully implemented for simulated turbine film-cooling flows in order to obtain a more detailed
characterization of the coolant-injection phenomenon and its interaction with freestream disturbances.
Received: 20 November 1996/Accepted: 29 January 1998 相似文献
8.
PIV error correction 总被引:15,自引:9,他引:6
D. P. Hart 《Experiments in fluids》2000,29(1):13-22
A non-post-interrogation method of reducing subpixel errors and eliminating spurious vectors from particle image velocimetry
(PIV) results is presented. Unlike methods that rely on the accuracy or similarity of neighboring vectors, errors are eliminated
before correlation information is discarded using available spatial and/or temporal data. Anomalies are removed from the data
set through direct element-by-element comparison of the correlation tables calculated from adjacent regions. The result is
a processing technique that yields a symmetric correlation profile representing the velocity at the boundary of the combined
regions. This correlation based correction (CBC) technique greatly improves subpixel accuracy, and is highly robust to out-of-boundary
particle motion, particle overlap, unmatched particle correlations, and electronic and optical imaging noise.
Received: 22 June 1999/Accepted: 21 September 1999 相似文献
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A variant of the particle image velocimetry (PIV) technique is described for measuring velocity and density simultaneously in a turbulent Rayleigh-Taylor mixing layer. The velocity field is computed by the usual PIV technique of cross-correlating two consecutive images, and deducing particle displacements from correlation peaks of intensity fields. Different concentrations of seed particles are used in the two streams of different temperature (density) fluids, and a local measure of the density is obtained by spatially averaging over an interrogation window. Good agreement is reported between the first- and second-order statistics for density obtained from this technique and from a thermocouple. Velocity-density correlations computed by cross-correlating individual time series are presented. The errors in the density measurements are quantified and analyzed, and the issue of spatial resolution is also discussed. Our purpose for this paper is to introduce the PIV-S method and validate its accuracy against corresponding thermocouple measurements. 相似文献