Velocity fidelity of flow tracer particles

Mei, Renwei

doi:10.1007/bf01893300

Cited by 228 publications

(131 citation statements)

References 49 publications

Supporting

Mentioning

127

Contrasting

Order By: Relevance

“…The density of the particles was close to that of water. Even when considering the maximum rotational frequency of the strongest tip vortex, with a typical azimuthal velocity of 7 m/s at 1 mm from the vortex center, the particles still remained high-fidelity flow tracers (Mei 1996). This corresponds to 5 × 10 3 times the gravitational acceleration, which is challenging for a PIV experiment.…”

Section: Methodsmentioning

confidence: 99%

Flow field measurement around vortex cavitation

2015

View full text Add to dashboard Cite

stage. These involve the smooth transport of vapor into the tip vortex, leading harmful implosions away from the propeller surface. The tip vortex cavity dynamics are not directly related to the propeller rotation rate. The excitation of this cavity often leads to high amplitude broadband pressure fluctuations between the fourth and seventh blade rate frequency (Wijngaarden et al. 2005).To better understand the sound production from vortex cavitation, a model for the waves on a tip vortex cavity was developed and was shown to be able to describe the interface dynamics in detail (Pennings et al. 2015). As a result, a condition could be predicted where a cavity resonance frequency could be amplified to produce high amplitude sound, as reported by Maines and Arndt (1997).The part that remains to be validated is a vortex model for the cavity size and cavity angular velocity. It has been shown that a Lamb-Oseen vortex model poorly estimates the cavity size as a function of cavitation number (Pennings et al. 2015). It is possible that overestimation of the vortex peak azimuthal velocity could have led to an overestimation of the cavity size. The main goal of the present study was to configure a simple low-order vortex model, to serve as an input into a vortex cavity wave dynamics model, to describe the tip vortex resonance frequency. It is based on the following steps.1. Model the tip vortex velocity field without cavitation (further referred to as wetted vortex) 2. Model the cavity size as a function of cavitation number based on wetted vortex properties 3. Show the difference in velocity field around a wetted and cavitating vortex 4. Obtain the cavity angular velocity value that gives the best correlation to the tip vortex cavity resonance frequency Abstract Models for the center frequency of cavitatingvortex induced pressure-fluctuations, in a flow around propellers, require knowledge of the vortex strength and vapor cavity size. For this purpose, stereoscopic particle image velocimetry (PIV) measurements were taken downstream of a fixed half-wing model. A high spatial resolution is required and was obtained via correlation averaging. This reduces the interrogation area size by a factor of 2-8, with respect to conventional PIV measurements. Vortex wandering was accounted for by selecting PIV images for a given vortex position, yielding sufficient data to obtain statistically converged and accurate results, both with and without a vapor-filled vortex core. Based on these results, the loworder Proctor model was applied to describe the tip vortex velocity outside the viscous core, and the cavity size as a function of cavitation number. The flow field around the vortex cavity shows, in comparison with a flow field without cavitation, a region of retarded flow. This layer around the cavity interface is similar to the viscous core of a vortex without cavitation.

show abstract

Section: Methodsmentioning

confidence: 99%

Flow field measurement around vortex cavitation

2015

View full text Add to dashboard Cite

show abstract

“…This is correct only for some specific conditions. For example, small particles with a density comparable to that of the fluid tend to follow the flow and can be used as tracers in flow measurements (15). Particles having a higher density than that of the carrier fluid can cross the streamlines and eventually collide with walls (16); nonetheless the particles leave the junction.…”

mentioning

confidence: 99%

Unexpected trapping of particles at a T junction

Vigolo

Radl

Stone

2014

Proc. Natl. Acad. Sci. U.S.A.

View full text Add to dashboard Cite

A common element in physiological flow networks, as well as most domestic and industrial piping systems, is a T junction that splits the flow into two nearly symmetric streams. It is reasonable to assume that any particles suspended in a fluid that enters the bifurcation will leave it with the fluid. Here we report experimental evidence and a theoretical description of a trapping mechanism for low-density particles in steady and pulsatile flows through Tshaped junctions. This mechanism induces accumulation of particles, which can form stable chains, or give rise to significant growth of bubbles due to coalescence. In particular, low-density material dispersed in the continuous phase fluid interacts with a vortical flow that develops at the T junction. As a result suspended particles can enter the vortices and, for a wide range of common flow conditions, the particles do not leave the bifurcation. Via 3D numerical simulations and a model of the two-phase flow we predict the location of particle accumulation, which is in excellent agreement with experimental data. We identify experimentally, as well as confirm by numerical simulations and a simple force balance, that there is a wide parameter space in which this phenomenon occurs. The trapping effect is expected to be important for the design of particle separation and fractionation devices, as well as used for better understanding of system failures in piping networks relevant to industry and physiology.fluid dynamics | bubble trapping | vortex breakdown | 3D simulations

show abstract

“…Developments concerning unsteady dynamic forces on a particle were reviewed by Mei (1996). Mei derived particle frequency response and energy transfer functions for solid particles and contaminated microbubbles in gas or liquid flows.…”

Section: Particle Motionmentioning

confidence: 99%

“…For a neutrally buoyant particle, (Figure 1 by Mei, 1996) indicates that the range 0.56 < < 1.62 should provide very good particle response; outside this range, interpolation formulae are given to estimate the cut-off frequency (Mei, 1996 Eqns. 24b and 25).…”

Section: Particle Motionmentioning

confidence: 99%

See 1 more Smart Citation

Estimated Uncertainties in the Idaho National Laboratory Matched-Index-of-Refraction Lower Plenum Experiment

McEligot¹,

McIlroy²,

Johnson³

2007

View full text Add to dashboard Cite

The purpose of the fluid dynamics experiments in the MIR (Matched-Index-of-Refraction) flow system at Idaho National Laboratory (INL) is to develop benchmark databases for the assessment of Computational Fluid Dynamics (CFD) solutions of the momentum equations, scalar mixing, and turbulence models for typical Very High Temperature Reactor (VHTR) plenum geometries in the limiting case of negligible buoyancy and constant fluid properties. The experiments use optical techniques, primarily particle image velocimetry (PIV) in the INL MIR flow system. The benefit of the MIR technique is that it permits optical measurements to determine flow characteristics in passages and around objects to be obtained without locating a disturbing transducer in the flow field and without distortion of the optical paths. The objective of the present report is to develop understanding of the magnitudes of experimental uncertainties in the results to be obtained in such experiments. Unheated MIR experiments are first steps when the geometry is complicated. One does not want to use a computational technique, which will not even handle constant properties properly. This report addresses the general background, requirements for benchmark databases, estimation of experimental uncertainties in mean velocities and turbulence quantities, the MIR experiment, PIV uncertainties, positioning uncertainties, and other contributing measurement uncertainties.The accuracy of the velocity field determination is ultimately limited by the ability of the scattering particles to follow the unsteady motion of the continuous phase. For the particles in the MIR VHTR experiment, the estimated cutoff frequency is about 40 kHz. The frequency of shedding from the posts in the MIR model is estimated to be of the order of 1 Hz and, therefore, the particles should follow the flow.Based on review of the literature, we estimate that the random uncertainty in measured particle displacement for our system and experiment is about 0.3 pixel for a single realization away from the walls. As an example, we estimated the uncertainties in measurements for the maximum velocity in an inlet jet flow operating at about its minimum flow rate. Consequently, this example would provide worst-case estimates in some senses. For the uncertainty in the mean velocity at this location, one could report With the current MIR model and the 3D PIV system, McIlroy and colleagues examined the effects of sample size for a typical set of measurements. Trends were generally as observed by Uzol and Camci. Preliminary conclusions were that (for this view and processing parameters) about 750 images should be collected to reduce the scatter in mean velocity statistics to between 0.4 and 10% v for velocities greater than about 2 m/s. The trends predicted by an uncertainty analysis are consistent with the observations, but, for the most part, the expected values are less than the scatter observed. Preliminary conclusions from the comparisons are that (1) more samples should be collected than predict...

show abstract

Velocity fidelity of flow tracer particles

Cited by 228 publications

References 49 publications

Flow field measurement around vortex cavitation

Flow field measurement around vortex cavitation

Unexpected trapping of particles at a T junction

Estimated Uncertainties in the Idaho National Laboratory Matched-Index-of-Refraction Lower Plenum Experiment

Contact Info

Product

Resources

About