Motion of Descending Solid Particles and Local Flow Around the Particles in Downward Turbulent Water Duct Flow (Keynote)

2011 ◽  
Author(s):  
Yoshimichi Hagiwara ◽  
Hideto Fujii ◽  
Katsutoshi Sakurai ◽  
Takashi Kuroda ◽  
Atsuhide Kitagawa
Keyword(s):  
Reynolds Number ◽  
Time Scale ◽  
High Speed ◽  
Fluid Velocity ◽  
Stokes Number ◽  
Solid Particles ◽  
Duct Flow ◽  
Local Flow ◽  
Particle Reynolds Number ◽  
Turbulent Water

The Stokes number, the ratio of the particle time scale to flow time scale, is a promising quantity for estimating changes in statistics of turbulence due to particles. First, we explored the Stokes numbers in some recent studies. Secondly, we discussed the results of our direct numerical simulation for turbulent flow with a high-density particle in a vertical duct. In the discussion, we defined the particle Reynolds number from the mean fluid velocity in the near-particle region at any time. We evaluated a new local Stokes number for the particle. It is found that the Stokes number is effective for the prediction of the distance between the particle center and one wall. Finally, we carried out experiments for turbulent water flow with aluminum balls of 1 mm in diameter in a vertical channel. The motions of aluminum balls and tracer particles in the flow were captured with a high-speed video camera. We found that the experimental results for the time changes in the wall-normal distance of the ball and the particle Reynolds number for the ball are similar to the predicted results.

scholarly journals Experimental study of inertial particles clustering and settling in homogeneous turbulence

2019 ◽  
Vol 864 ◽  
pp. 925-970 ◽  
Author(s):  
Alec J. Petersen ◽  
Lucia Baker ◽  
Filippo Coletti
Keyword(s):  
Reynolds Number ◽  
Fluid Velocity ◽  
Stokes Number ◽  
Terminal Velocity ◽  
Solid Particles ◽  
Homogeneous Turbulence ◽  
Small Scale ◽  
Inertial Particles ◽  
Mean Flow ◽  
Integral Scale

We study experimentally the spatial distribution, settling and interaction of sub-Kolmogorov inertial particles with homogeneous turbulence. Utilizing a zero-mean-flow air turbulence chamber, we drop size-selected solid particles and study their dynamics with particle imaging and tracking velocimetry at multiple resolutions. The carrier flow is simultaneously measured by particle image velocimetry of suspended tracers, allowing the characterization of the interplay between both the dispersed and continuous phases. The turbulence Reynolds number based on the Taylor microscale ranges from $Re_{\unicode[STIX]{x1D706}}\approx 200{-}500$, while the particle Stokes number based on the Kolmogorov scale varies between $St_{\unicode[STIX]{x1D702}}=O(1)$ and $O(10)$. Clustering is confirmed to be most intense for $St_{\unicode[STIX]{x1D702}}\approx 1$, but it extends over larger scales for heavier particles. Individual clusters form a hierarchy of self-similar, fractal-like objects, preferentially aligned with gravity and with sizes that can reach the integral scale of the turbulence. Remarkably, the settling velocity of $St_{\unicode[STIX]{x1D702}}\approx 1$ particles can be several times larger than the still-air terminal velocity, and the clusters can fall even faster. This is caused by downward fluid fluctuations preferentially sweeping the particles, and we propose that this mechanism is influenced by both large and small scales of the turbulence. The particle–fluid slip velocities show large variance, and both the instantaneous particle Reynolds number and drag coefficient can greatly differ from their nominal values. Finally, for sufficient loadings, the particles generally augment the small-scale fluid velocity fluctuations, which however may account for a limited fraction of the turbulent kinetic energy.

scholarly journals Numerical investigation on the solid particle erosion in elbow with water–hydrate–solid flow

2019 ◽  
Vol 103 (1) ◽  
pp. 003685041989724 ◽  
Author(s):  
Liang Zhang ◽  
JiaWei Zhou ◽  
Bo Zhang ◽  
Wei Gong
Keyword(s):  
Reynolds Number ◽  
Flow Velocity ◽  
Erosion Rate ◽  
Particle Diameter ◽  
Stokes Number ◽  
Solid Particles ◽  
Curvature Radius ◽  
Premature Failure ◽  
Solid Flow ◽  
Erosion Zone

Erosion in pipeline caused by solid particles, which may lead to premature failure of the pipe system, is regarded as one of the most important concerns in the field of oil and gas. Therefore, the Euler–Lagrange, erosion model, and discrete phase model are applied for the purpose of simulating the erosion of water–hydrate–solid flow in submarine hydrate transportation pipeline. In this article, the flow and erosion characteristics are well verified on the basis of experiments. Moreover, analysis is conducted to have a good understanding of the effects of hydrate volume, mean curvature radius/pipe diameter ( R/ D) rate, flow velocity, and particle diameter on elbow erosion. It is finally obtained that the hydrate volume directly affects the Reynolds number through viscosity and the trend of the Reynolds number is consistent with the trend of erosion rate. Taking into account different R/ D rates, the same Stokes number reflects different dynamic transforms of the maximum erosion zone. However, the outmost wall (zone D) will be the final erosion zone when the value of the Stokes number increases to a certain degree. In addition, the erosion rate increases sharply along with the increase of flow velocity and particle diameter. The effect of flow velocity on the erosion zone can be ignored in comparison with the particle diameter. Moreover, it is observed that flow velocity is deemed as the most sensitive factor on erosion rate among these factors employed in the orthogonal experiment.

High-Speed Shadowgraphy Measurements of an Erosive Particle-Laden Jet Under High-Pressure Compressor Conditions

2017 ◽  
Author(s):  
M. Hufnagel ◽  
C. Koch ◽  
S. Staudacher ◽  
C. Werner-Spatz
Keyword(s):  
Dimensional Analysis ◽  
Particle Velocity ◽  
High Speed ◽  
Fluid Velocity ◽  
Measurement Techniques ◽  
Real Life ◽  
Negative Influence ◽  
Solid Particles ◽  
Flat Plates ◽  
Aerodynamic Properties

Erosive damage done to jet engine compressor blading by solid particles has a negative influence on the compressor aerodynamic properties and hence decreases performance. The erosive change of shape has been investigated in a multitude of experiments ranging from eroding flat plates to eroding full engines. The basic challenge to transfer the results from very simple tests to real life erosion remains. Up to date measurement techniques today allow closing this gap. The necessary experimental and analytical steps are shown. The erosion resistance of Ti-6Al-4V at realistic flow conditions with fluid velocities ranging from 200 to 400 m/s is used. The erodent used was quartz sand with a size distribution corresponding to standardized Arizona Test Dust A3 (1 to 120 μm). Flat plates out of Ti-6Al-4V were eroded at different impingement angles. The particle velocities and sizes were investigated using a high speed laser shadowgraphy technique. A dimensional analysis was carried out to obtain nondimensional parameters suitable for describing erosion. Different averaging methods of the particle velocity were examined in order to identify a representative particle velocity. Compared to the fluid velocity and the mean particle velocity, the energy averaged particle velocity is found to be the best representation of the erosiveness of a particle stream. The correlations derived from the dimensional analysis are capable of precisely predicting erosion rates for different rig operating points. The results can be applied to the methodology published in [1].

scholarly journals Particle–wall collisions in a viscous fluid

2001 ◽  
Vol 433 ◽  
pp. 329-346 ◽  
Author(s):  
G. G. JOSEPH ◽  
R. ZENIT ◽  
M. L. HUNT ◽  
A. M. ROSENWINKEL
Keyword(s):  
Reynolds Number ◽  
Viscous Fluid ◽  
High Speed ◽  
Particle Density ◽  
Particle Surface ◽  
Density Ratio ◽  
Experimental Studies ◽  
Stokes Number ◽  
Coefficient Of Restitution ◽  
The Impact

This paper presents experimental measurements of the approach and rebound of a particle colliding with a wall in a viscous fluid. The particle's trajectory was controlled by setting the initial inclination angle of a pendulum immersed in a fluid. The resulting collisions were monitored using a high-speed video camera. The diameters of the particles ranged from 3 to 12 mm, and the ratio of the particle density to fluid density varied from 1.2 to 7.8. The experiments were performed using a thick glass or Lucite wall with different mixtures of glycerol and water. With these parameters, the Reynolds number defined using the velocity just prior to impact ranged from 10 to approximately 3000. A coefficient of restitution was defined from the ratio of the velocity just prior to and after impact.The experiments clearly demonstrate that the rebound velocity depends on the impact Stokes number (defined from the Reynolds number and the density ratio) and weakly on the elastic properties of the material. Below a Stokes number of approximately 10, no rebound of the particle occurred. For impact Stokes number above 500 the coefficient of restitution appears to asymptote to the values for dry collisions. The coefficients of restitution were also compared with previous experimental studies. In addition, the approach of the particle to the wall indicated that the particle slowed prior to impacting the surface. The distance at which the particle's trajectory varied due to the presence of the wall was dependent on the impact Stokes number. The particle surface roughness was found to affect the repeatability of some measurements, especially for low impact velocities.

scholarly journals Study of the Reynolds Number Effect on the Process of Instability Transition Into the Turbulent Stage

2014 ◽  
Vol 136 (9) ◽  
Author(s):  
N. V. Nevmerzhitskiy ◽  
E. A. Sotskov ◽  
E. D. Sen'kovskiy ◽  
O. L. Krivonos ◽  
A. A. Polovnikov ◽  
...  
Keyword(s):  
Reynolds Number ◽  
Turbulent Mixing ◽  
High Speed ◽  
Reynolds Numbers ◽  
Short Wave ◽  
Solid Particles ◽  
Reynolds Number Effect ◽  
Long Wave ◽  
Compressed Gas ◽  
Perturbation Growth

The results of the experimental study of the Reynolds number effect on the process of the Rayleigh–Taylor (R-T) instability transition into the turbulent stage are presented. The experimental liquid layer was accelerated by compressed gas. Solid particles were scattered on the layer free surface to specify the initial perturbations in some experiments. The process was recorded with the use of a high-speed motion picture camera. The following results were obtained in experiments: (1) Long-wave perturbation is developed at the interface at the Reynolds numbers Re < 104. If such perturbation growth is limited by a hard wall, the jet directed in gas is developed. If there is no such limitation, this perturbation is resolved into the short-wave ones with time, and their growth results in gas-liquid mixing. (2) Short-wave perturbations specified at the interface significantly reduce the Reynolds number Re for instability to pass into the turbulent mixing stage.

scholarly journals The slip velocity of nearly neutrally buoyant tracers for large-scale PIV

2021 ◽  
Vol 62 (9) ◽  
Author(s):  
David Engler Faleiros ◽  
Marthijn Tuinstra ◽  
Andrea Sciacchitano ◽  
Fulvio Scarano
Keyword(s):  
Reynolds Number ◽  
Numerical Simulations ◽  
Slip Velocity ◽  
Large Scale ◽  
Empirical Relation ◽  
Density Ratio ◽  
Local Flow ◽  
Soap Bubbles ◽  
Particle Reynolds Number ◽  
Neutrally Buoyant

AbstractThe behaviour of nearly neutrally buoyant tracers is studied by means of experiments with helium-filled soap bubbles and numerical simulations. The current models used for estimating the slip velocity of heavy micro particles and neutrally buoyant particles are reviewed and extended to include the effect of unsteady forces and particle Reynolds number. The particle motion is analysed via numerical simulations of a rectilinear oscillatory flow and in the flow around an airfoil within a particle flow parameter space that is typical of large-scale PIV experiments. An empirical relation is obtained that estimates the particle slip velocity, depending on the particle-to-fluid density ratio, the particle Reynolds number and frequency of the local flow fluctuations. The model developed is applied to assess the slip velocity of helium-filled soap bubbles in a large-scale experiment conducted at the German–Dutch wind (DNW) tunnels in the flow around an airfoil, with chord Reynolds numbers up to three millions. Furthermore, a procedure is proposed that can be used to retrieve the bubbles mean density and dispersion from measurements of mean velocity and fluctuations, respectively. Graphic abstract

On the Average Settling Rate of Heavy Particles in Decaying Homogeneous Isotropic Turbulence

1998 ◽  
Vol 14 (3) ◽  
pp. 111-118
Author(s):  
C. Y. Yang ◽  
U. Lei
Keyword(s):  
Time Scale ◽  
Isotropic Turbulence ◽  
Stokes Equations ◽  
Fluid Velocity ◽  
Solid Particles ◽  
Settling Rate ◽  
Stationary Turbulence ◽  
Turbulence Decay ◽  
Decaying Turbulence ◽  
Inertia Response

ABSTRACTThe average settling rate of spherical solid particles, 〈vs〉, under a body force field is studied numerically in decaying homogeneous isotropic turbulent flows generated by the direct numerical simulation of the continuity and Navier-Stokes equations. The increase of the average settling rate, 〈Δvs〉, is maximized when Tp/Tk ≈ 1 and vd/u′ ≈ 0.5, and is of order 0.lu′, which is qualitatively similar to that in stationary turbulence. Here 〈Δvs〉 = 〈vs〉 − vd, Tp is the particle's relaxation time, Tk is the Kolmogorov time scale, vd is the settling rate of particles in still fluid, and u′ is the root mean square of the fluid velocity fluctuation. However, the magnitude of the maximum value of 〈Δvs〉 in decaying turbulence is substantially greater (about 40%) than that in the corresponding stationary turbulence due to the inertia response of particles to turbulence decay. Although 〈Δvs〉/u′ does not reach a stationary state as the flow is evolving, it is a slowly time varying function for the parameters of interest as Tp (≈ Tk when 〈Δvs〉 is maximized) is in general of one order less than the time scale of turbulence decay.

High-Speed Shadowgraphy Measurements of an Erosive Particle-Laden Jet Under High-Pressure Compressor Conditions

2017 ◽  
Vol 140 (1) ◽  
Author(s):  
Max Hufnagel ◽  
Christian Werner-Spatz ◽  
Christian Koch ◽  
Stephan Staudacher
Keyword(s):  
High Pressure ◽  
Dimensional Analysis ◽  
Particle Velocity ◽  
High Speed ◽  
Fluid Velocity ◽  
Measurement Techniques ◽  
Real Life ◽  
Solid Particles ◽  
Flat Plates ◽  
Erosive Change

Erosive damage done to jet engine compressor blading by solid particles has a negative influence on the compressor aerodynamic properties and hence decreases performance. The erosive change of shape has been investigated in a multitude of experiments ranging from eroding flat plates to eroding full engines. The basic challenge to transfer the results from very simple tests to real life erosion remains. Up to date measurement techniques today allow closing this gap. The necessary experimental and analytical steps are shown. The erosion resistance of Ti–6Al–4V at realistic flow conditions with fluid velocities ranging from 200 to 400 m/s is used. The erodent used was quartz sand with a size distribution corresponding to standardized Arizona Test Dust A3 (1–120 μm). Flat plates out of Ti–6Al–4V were eroded at different impingement angles. The particle velocities and sizes were investigated using a high-speed laser shadowgraphy technique. A dimensional analysis was carried out to obtain nondimensional parameters suitable for describing erosion. Different averaging methods of the particle velocity were examined in order to identify a representative particle velocity. Compared to the fluid velocity and the mean particle velocity, the energy averaged particle velocity is found to be the best representation of the erosiveness of a particle stream. The correlations derived from the dimensional analysis are capable of precisely predicting erosion rates for different rig operating points (OPs). The results can be applied to the methodology published by Schrade et al. (2015, “Experimental and Numerical Investigation of Erosive Change of Shape for High-Pressure Compressors,” ASME Paper No. GT2015-42061).

Pressure and Temperature Effects on Particle Deposition in an Impinging Flow

2017 ◽  
Author(s):  
Ryan K. Lundgreen
Keyword(s):  
Reynolds Number ◽  
Particle Deposition ◽  
Stokes Equations ◽  
Focal Point ◽  
Three Dimensional ◽  
Stokes Number ◽  
Particle Impact ◽  
Internal Cooling ◽  
Particle Reynolds Number ◽  
Impinging Flow

Particle deposition is a significant problem in gas turbine engines. Internal cooling passages are of particular interest because deposition build up is observed at far lower temperatures than it is for external flows. Computational fluid dynamics were employed to investigate how changes in the particle Reynolds number affected deposition in an impinging flow. Three-dimensional, steady Reynolds-Averaged Navier-Stokes equations were solved for a single impinging jet that had a jet to wall spacing of H/D = 2. Pressure ratios of 1.015 and 1.03 were considered at three different discharge pressures, 0.1, 1 , and 3 MPa. Three different flow temperatures were also considered, 300, 700, and 1000 K. Five different particle diameters ranging from 0.5 – 10 μm were tracked in each solution. The aerodynamic lensing focal point of the particle tracks, particle impact velocities, particle impact angles, and particle impact locations were all characterized well by the effective Stokes number. The effective Stokes number adjusts the Stokes number by the non-Stokes drag correction factor, which is a function of the particle Reynolds number.

scholarly journals The discrete Green's function paradigm for two-way coupled Euler–Lagrange simulation

2021 ◽  
Vol 931 ◽  
Author(s):  
J.A.K. Horwitz ◽  
G. Iaccarino ◽  
J.K. Eaton ◽  
A. Mani
Keyword(s):  
Reynolds Number ◽  
Green’S Function ◽  
Green's Function ◽  
Stokes Equations ◽  
Fluid Velocity ◽  
Reynolds Numbers ◽  
Function Approach ◽  
Particle Reynolds Number ◽  
Discrete Green’S Function ◽  
Particle Laden Flows

We outline a methodology for the simulation of two-way coupled particle-laden flows. The drag force that couples fluid and particle momentum depends on the undisturbed fluid velocity at the particle location, and this latter quantity requires modelling. We demonstrate that the undisturbed fluid velocity, in the low particle Reynolds number limit, can be related exactly to the discrete Green's function of the discrete Stokes equations. In addition to hydrodynamics, the method can be extended to other physics present in particle-laden flows such as heat transfer and electromagnetism. The discrete Green's functions for the Navier–Stokes equations are obtained at low particle Reynolds number in a two-plane channel geometry. We perform verification at different Reynolds numbers for a particle settling under gravity parallel to a plane wall, for different wall-normal separations. Compared with other point-particle schemes, the Stokesian discrete Green's function approach is the most robust at low particle Reynolds number, accurate at all wall-normal separations. To account for degradation in accuracy away from the wall at finite Reynolds number, we extend the present methodology to an Oseen-like discrete Green's function. The extended discrete Green's function method is found to be accurate within $6\,\%$ at all wall-normal separations for particle Reynolds numbers up to 24. The discrete Green's function approach is well suited to dilute systems with significant mass loading and this is highlighted by comparison against other Euler–Lagrange as well as particle-resolved simulations of gas–solid turbulent channel flow. Strong particle–turbulence coupling is observed in the form of turbulence modification and turbophoresis suppression, and these observations are placed in context of the different methods.

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