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1.
Stereoscopic particle image velocimetry measurements of the flow around a Rushton turbine 总被引:1,自引:0,他引:1
The principles of stereoscopic particle image velocimetry (PIV), including distortion compensation, were applied to the turbulent
flow in a vessel stirred by a Rushton turbine. An angular offset configuration was used and tilt-axis lens mounts were incorporated
in order to satisfy the Scheimpflug condition, significantly reducing the ordinarily large depth of field requirements of
such configurations. A distortion compensation procedure, or in situ calibration, was utilized in place of the ray tracing,
or mechanical registration, used in previous studies. The calibration procedure was validated using two tests, one a rigid
translation of a speckle target, the other the viscous flow between two concentric cylinders. The results of the tests suggest
the success with which the distortion compensation procedure may be applied to real fluid flows. Phase-locked instantaneous
data were ensemble averaged and interpolated in order to obtain mean 3-D velocity fields on a cylindrical shell enclosing
the turbine blade. From these fields, the tip vortex pairs and the radial jet documented in previous studies of mixer flows
were easily identified.
Received: 5 February 1999/Accepted: 1 December 1999 相似文献
2.
A two-color digital particle image velocimetry and accelerometry (DPIV and DPIA) measurement technique is described that records the velocity and acceleration fields of both the solid and liquid phases simultaneously. Measurements were taken at turbulent conditions of a vertical pipe flow using glass spheres as the solid phase and fluorescent particles to indicate fluid phase motion. Nd-YAG pulse lasers acted as illumination sources and images were recorded by two monochrome CCD cameras. The two-color aspect of the technique was realized by placing optical filters in front of the cameras to discriminate between the phases. Cross-correlations and auto-correlations were applied to determine velocity and acceleration fields of the two phases. Results showing some of the capabilities of the technique as applied to a two-phase pipe flow experiment are provided. For the condition studied, it was found that there was turbulence suppression due to the solid phase and that the statistics associated with the acceleration probability distribution were different for the solid and fluid phases. 相似文献
3.
Stereoscopic particle image velocimetry measurements of the flow around a surface-mounted block 总被引:3,自引:0,他引:3
The advantages of 3D measurement techniques and the accuracy of the backward projection algorithm are discussed. The 3D calibration reconstruction used is based on an analytical relation between real and image co-ordinates. The accuracy of the stereoscopic particle image velocimetry (PIV) system is assessed by taking measurements of the flow in angular displacement configuration with prisms. A comparison is made with 2D PIV measurements and the accuracy of this stereo PIV algorithm is evaluated. By using this 3D measurement technique, the topology and the main 3D features of the flow around a surface-mounted block are investigated. 相似文献
4.
Daniel Freudenhammer Elias Baum Brian Peterson Benjamin Böhm Bernd Jung Sven Grundmann 《Experiments in fluids》2014,55(5):1-18
Magnetic resonance velocimetry (MRV) measurements are performed in a 1:1 scale model of a single-cylinder optical engine to investigate the volumetric flow within the intake and cylinder geometry during flow induction. The model is a steady flow water analogue of the optical IC-engine with a fixed valve lift of $9.21$ mm to simulate the induction flow at crank-angle $270^{\circ }$ bTDC. This setup resembles a steady flow engine test bench configuration. MRV measurements are validated with phase-averaged particle image velocimetry (PIV) measurements performed within the symmetry plane of the optical engine. Differences in experimental operating parameters between MRV and PIV measurements are well addressed. Comparison of MRV and PIV measurements is demonstrated using normalized mean velocity component profiles and showed excellent agreement in the upper portion of the cylinder chamber (i.e., $y \ge -20$ mm). MRV measurements are further used to analyze the ensemble average volumetric flow within the 3D engine domain. Measurements are used to describe the 3D overflow and underflow behavior as the annular flow enters the cylinder chamber. Flow features such as the annular jet-like flows extending into the cylinder, their influence on large-scale in-cylinder flow motion, as well as flow recirculation zones are identified in 3D space. Inlet flow velocities are analyzed around the entire valve curtain perimeter to quantify percent mass flow rate entering the cylinder. Recirculation zones associated with the underflow are shown to reduce local mass flow rates up to 50 %. Recirculation zones are further analyzed in 3D space within the intake manifold and cylinder chamber. It is suggested that such recirculation zones can have large implications on cylinder charge filling and variations of the in-cylinder flow pattern. MRV is revealed to be an important diagnostic tool used to understand the volumetric induction flow within engine geometries and is potentially suited to evaluate flow changes due to intake geometry modifications. 相似文献
5.
N. Angarita-Jaimes E. McGhee M. Chennaoui H. I. Campbell S. Zhang C. E. Towers A. H. Greenaway D. P. Towers 《Experiments in fluids》2006,41(6):881-891
We present the application of wavefront sensing to particle image velocimetry for three-component (3C), three-dimensional (3D) flow measurement from a single view. The technique is based upon measuring the wavefront scattered by a tracer particle and from that wavefront the 3D tracer location can be determined. Hence, from a temporally resolved sequence of 3D particle locations the velocity vector field is obtained. Two approaches to capture the data required to measure the wavefronts are described: multi-planar imaging using a distorted diffraction grating and an anamorphic technique. Both techniques are optically efficient, robust and compatible with coherent and incoherent scattering from flow tracers. The depth (range) resolution and repeatability have been quantified experimentally using a single mode fiber source representing a tracer particle. The anamorphic approach is shown to have the greatest measurement range and hence was selected for the first proof of principle experiments using this technique for 3D particle imaging velocimetry (PIV) on a sparsely seeded gas phase flow. 相似文献
6.
Particle image velocimetry (PIV) measurements were carried out on a backward-facing step flow at a Reynolds number of Reh=UXh/9=4,660 (based on step height and freestream velocity). In-plane velocity, out-of-plane vorticity, Reynolds stress and turbulent kinetic energy production measurements in the x-y and x-z planes of the flow are presented. Proper orthogonal decomposition was performed on both the fluctuating velocity and vorticity fields of the x-y plane PIV data using the method of snapshots. Low-order representations of the instantaneous velocity fields were reconstructed using the velocity modes. These reconstructions provided insight into the contribution that the various length scales make to the spatial distribution of mean and turbulent flow quantities such as Reynolds stress and turbulent kinetic energy production. Large scales are found to contribute to the Reynolds stresses and turbulent kinetic energy production downstream of reattachment, while small scales contribute to the intense Reynolds stresses in the vicinity of reattachment. 相似文献
7.
This paper presents laser measurements of particle velocities in a horizontal turbulent two-phase pipe flow. A phase Doppler particle analyzer, (PDPA), was used to obtain particle size, velocity, and rms values of velocity fluctuations. The particulate phase consisted of glass spheres 50 m in diameter with the volume fraction of the suspension in the range
p=10-4 to
p=10-3. The results show that the turbulence increases with particle loading.List of symbols
a
particle diameter
-
C
va
velocity diameter cross-correlation
-
d
pipe diameter
-
Fr
2
Froude number
-
g
gravitational constant
- p(a)
Probability density of the particle diameter
- Re
pipe Reynolds number based on the friction velocity
-
T
characteristic time scale of the energy containing eddies
-
T
L
integral scale of the turbulence sampled along the particle path
-
u, U, u
characteristic fluid velocities: fluctuating, mean and friction
-
v
characteristic velocity of the paricle fluctuations
- f
expected value of any random variable f
- f¦g
expected value of f given a value of the random variable g
-
p
particle volume fraction
-
p
particle response time
-
absolute fluid viscosity
-
v
kinematic fluid viscosity
-
p, f
densities, particle and fluid
-
a
2
particle diameter variance
-
va
2
velocity variance due to the particle diameter variance
-
vT
2
total particle velocity variance
-
vt
2
particle velocity variance due to the response to the turbulent field 相似文献
8.
Previous work has shown that the k
2 term in the effective cooling velocity equation for inclined hot-wires can become negative under certain probe configurations and wire length-to-diameter ratios. It was hypothesised that this was due to a downwash component of velocity along the wire when prong interference effects were expected to be minimal. Direct measurements of the flow around a typical hot-wire probe using digital particle image velocimetry have shown that this downwash velocity component does exist, leading to negative values of k
2 as calculated from the angle of deviation from the free stream.List of symbols
d
diameter of hot-wire mm
-
k
factor in equation for effective dimensionless velocity for inclined hot-wire
-
l
length of hot-wire mm
-
Q
effective velocity mm/s
-
U
free stream velocity mm/s
-
angle between free stream and degrees wire normal
-
angle through which flow is degrees deflected at working section of wire 相似文献
9.
The turbulent flow field around a circular cylinder 总被引:5,自引:0,他引:5
B. Dargahi 《Experiments in fluids》1989,8(1-2):1-12
The flow field around a circular cylinder mounted vertically on a flat bottom has been investigated experimentally. This type
of flow occurs in several technical applications, e.g. local scouring around bridge piers. Hydrogen bubble flow visualization
was carried out for Reynolds numbers ranging from 6,600 to 65,000. The main flow characteristic upstream of the cylinder is
a system of horse-shoe vortices which are shed quasi-periodically. The number of vortices depends on Reynolds number. The
vortex system was found to be independent of the vortices that are shed in the wake of the cylinder. The topology of the separated
flow contains several separation and attachment lines which are Reynolds number dependent. In the wake region different flow
patterns exist for each constant Reynolds number. 相似文献
10.
Dennis Kröninger Karsten Köhler Thomas Kurz Werner Lauterborn 《Experiments in fluids》2010,48(3):395-408
The velocity field in the vicinity of a laser-generated cavitation bubble in water is investigated by means of particle tracking
velocimetry (PTV). Two situations are explored: a bubble collapsing spherically and a bubble collapsing aspherically near
a rigid wall. In the first case, the accuracy of the PTV method is assessed by comparing the experimental data with the flow
field around the bubble as obtained from numerical simulations of the radial bubble dynamics. The numerical results are matched
to the experimental radius–time curve extracted from high-speed photographs by tuning the model parameters. Trajectories of
tracer particles are calculated and used to model the experimental process of the PTV measurement. For the second case of
a bubble collapsing near a rigid wall, both the bubble shape and the velocity distribution in the fluid around the bubble
are measured for different standoff parameters γ at several instants in time. The results for γ > 1 are compared with the
corresponding results of a boundary-integral simulation. For both cases, good agreement between simulation and experiment
is found. 相似文献
11.
12.
Particle image velocimetry is used to investigate the interaction between an incident shock wave and a turbulent boundary
layer at Mach 2.1. A particle response assessment establishes the fidelity of the tracer particles. The undisturbed boundary
layer is characterized in detail. The mean velocity field of the interaction shows the incident and reflected shock wave pattern,
as well as the boundary layer distortion. Significant reversed flow is measured instantaneously, although, on average no reversed
flow is observed. The interaction instantaneously exhibits a multi-layered structure, namely, a high-velocity outer region
and a low-velocity inner region. Flow turbulence shows the highest intensity in the region beneath the impingement of the
incident shock wave. The turbulent fluctuations are found to be highly anisotropic, with the streamwise component dominating.
A distinct streamwise-oriented region of relatively large kinematic Reynolds shear stress magnitude appears within the lower
half of the redeveloping boundary layer. Boundary layer recovery towards initial equilibrium conditions appears to be a gradual
process. 相似文献
13.
The accuracy of tomographic particle image velocimetry for measurements of a turbulent boundary layer 总被引:1,自引:0,他引:1
Callum Atkinson Sebastien Coudert Jean-Marc Foucaut Michel Stanislas Julio Soria 《Experiments in fluids》2011,50(4):1031-1056
To investigate the accuracy of tomographic particle image velocimetry (Tomo-PIV) for turbulent boundary layer measurements,
a series of synthetic image-based simulations and practical experiments are performed on a high Reynolds number turbulent
boundary layer at Reθ = 7,800. Two different approaches to Tomo-PIV are examined using a full-volume slab measurement and a thin-volume “fat” light
sheet approach. Tomographic reconstruction is performed using both the standard MART technique and the more efficient MLOS-SMART
approach, showing a 10-time increase in processing speed. Random and bias errors are quantified under the influence of the
near-wall velocity gradient, reconstruction method, ghost particles, seeding density and volume thickness, using synthetic
images. Experimental Tomo-PIV results are compared with hot-wire measurements and errors are examined in terms of the measured
mean and fluctuating profiles, probability density functions of the fluctuations, distributions of fluctuating divergence
through the volume and velocity power spectra. Velocity gradients have a large effect on errors near the wall and also increase
the errors associated with ghost particles, which convect at mean velocities through the volume thickness. Tomo-PIV provides
accurate experimental measurements at low wave numbers; however, reconstruction introduces high noise levels that reduces
the effective spatial resolution. A thinner volume is shown to provide a higher measurement accuracy at the expense of the
measurement domain, albeit still at a lower effective spatial resolution than planar and Stereo-PIV. 相似文献
14.
Mark F. Reeder Jim W. Crafton Jordi Estevadeordal Joseph DeLapp Charles McNiel Don Peltier Tina Reynolds 《Experiments in fluids》2010,48(5):889-900
Flow visualization, particle image velocimetry (PIV), and laser Doppler velocimetry (LDV) are among the most useful tools
available for experimental aerodynamics studies. Implementation of these techniques, however, requires that seed material
be introduced into the flow. The undesirable qualities of the seeding material often prevent the use of flow visualization
and velocimetry techniques in many test environments. This is particularly true for large-scale, closed-circuit tunnels where
facility operators must weigh the risks of facility contamination, sensor damage, and safety concerns that might result from
the introduction of seed particles. Identification of a practical clean seeding material that minimizes or eliminates these
concerns would enable flow visualization and velocimetry techniques to be deployed in these facilities. Here, we demonstrate
two seeding systems that have the potential to provide such a solution. The first system is a new concept which uses liquid
carbon dioxide that can be made to form discrete particles as it expands from a high-pressure tank. PIV measurements are demonstrated
in several flows, including supersonic and subsonic tunnels, using these residue-free seed particles. The second system utilizes
a combination of steam and liquid nitrogen to produce an aerosol or fog that serves as flow seeding. Water- or steam-based
seeding has been previously demonstrated for flow visualization in subsonic tunnels; here however, we utilize this seed material
for PIV and LDV measurements as well as for flow visualization in a large supersonic tunnel. 相似文献
15.
Particle image velocimetry (PIV) was used to measure mean flow and turbulence characteristics in the separated flow behind a rearward facing step. The confidence limits characterising estimates of mean velocity and turbulence intensity obtained by PIV are discussed. The relevance of background turbulence levels and sample size in determining these limits is considered. 相似文献
16.
Laser-induced fluorescent dye visualization and image correlation velocimetry were employed to delineate near-wall turbulent
structures in a pipe flow. The sweeping and ejection events near the wall and the downstream evolution of a large-scale eddy
structure rotating in a counter-clockwise direction were clearly reflected in the instantaneous fluctuating velocity fields.
This eddy structure was found to form mostly in the logarithmic region and to dominate the flow structures there, while the
ejection and sweeping events in the log layer were greatly influenced by the existence of the large-scale eddy structure.
Received: 29 January 2001 / Accepted: 22 October 2001 相似文献
17.
We compare two methods of calibrating the yaw response of hot-wire probes: (i) the assumption that an effective angle, independent
of the flow speed, can be deduced; (ii) the more general approach of determining the yaw response at a number of different
speeds. The first, simpler, approach is shown to give surprisingly reasonable results for the usual turbulence statistics,
even in high turbulence intensity flows. Some differences in the distribution of the inclination of the instantaneous velocity
vector are observed. There is no advantage in using thek
2 factor to allow for longitudinal cooling. 相似文献
18.
M. Nowak 《Experiments in fluids》2002,33(2):249-255
A turbulent boundary layer of a water flow is investigated by means of pulsed ultrasound Doppler velocimetry. The advantage of this method is the acquisition of complete velocity profiles along the sound propagation line within very short time intervals. The shear stress velocity, used for normalizing the velocity profiles, was determined by fitting the profiles to the universal profiles in a turbulent boundary layer obtained from Prandtl's mixing length theory. A coordinate transformation in the near-wall region is proposed to allocate the velocity data to "true" wall distances. From the experimental values of the wall shear stress velocity, the friction factors for a turbulent pipe flow are calculated and compared to the Blasius law. The overall error in measurement was estimated to NJ.4%. 相似文献
19.
Particle Image Velocimetry (PIV) is now a well established experimental technique to measure two components of the velocity in a planar region of a flow
field. This paper shows how its proven capabilities can be further extended by using holographic recording to register the
particle displacements. Among other unique characteristics, holography enables the acquisition of multiple images on a single
plate, and the recording of three dimensional images. These features are used to circumvent some of the limitations of conventional
PIV. Some of these possibilities are demonstrated in this study by applying the technique to a high Reynolds number swirling
flow using a lens-less off-axis orthogonal recording geometry.
Received: 25 February 1998/ Accepted: 2 September 1998 相似文献
20.
Jessica A. Palmer Ricardo Mejia-Alvarez James L. Best Kenneth T. Christensen 《Experiments in fluids》2012,52(3):809-829
Barchan dunes are crescentic planform-shaped dunes that are present in many natural environments, and may occur either in
isolation or in groups. This study uses high-resolution particle-image velocimetry (PIV) experiments using fixed-bed models
to examine the effects of barchan dune interaction upon the flow field structure. The barchan dune models were created from
an idealized contour map, the shape and dimensions of which were based upon previous empirical studies of dune morphology.
The experimental setup comprised two, co-axially aligned, barchan dune models that were spaced at different distances apart.
In this paper, two volumetric ratios (V
r, upstream dune: downstream dune) of 1.0 and 0.175 were examined. Models were placed in a boundary-layer wind tunnel and flow
quantification was achieved via PIV measurements of the mean and turbulent flow field in the streamwise–wall-normal plane,
along the centerline of the barchan(s), at an average flow Reynolds number of 59,000. The presence of an upstream barchan
dune induces a “sheltering effect” on the flow. Flow on the stoss side of the downstream dune is controlled by the developing
internal boundary layer from the upstream dune, as well as by the turbulent flow structures shed from the free shear layer
of the upstream dune leeside. At both volumetric ratios, enhanced turbulence is present over the downstream barchan dune leeside,
which is proposed to be caused by the interaction of shear layers from the upstream and downstream dunes. Both the size and
magnitude of the shear layer formed in the leeside of the upstream dune control this interaction, together with the proximity
of this shear layer to the stoss side of the downstream dune. Proper orthogonal decomposition (POD) analysis shows that the
distribution of turbulent kinetic energy is shifted to higher modes (i.e., smaller spatial scales) over interacting barchan
dunes, which also reflects the role of the leeside free shear layer in dominating the flow field by generation, or redistribution,
of TKE to smaller scales. 相似文献