scholarly journals Turbulence attenuation in particle-laden flow in smooth and rough channels

2015 ◽  
Vol 773 ◽  
pp. 103-136 ◽  
Author(s):  
A. W. Vreman
Keyword(s):  
Gas Flow ◽  
Point Particle ◽  
Solid Particles ◽  
Spherical Particles ◽  
Wall Roughness ◽  
Particle Collisions ◽  
Wall Unit ◽  
Rough Walls ◽  
The Mean ◽  
Particle Laden Flow

Results of point-particle direct numerical simulations of downward gas–solid flow in smooth and rough vertical channels are presented. Two-way coupling and inter-particle collisions are included. The rough walls are shaped as fixed layers of tiny spherical particles with diameter much smaller than the viscous wall unit. The turbulence attenuation induced by the free solid particles in the gas flow is shown to be enhanced with increasing wall roughness. The so-called feedback force, the force exerted by the free particles on the gas, is decomposed into three contributions: the domain average of the mean feedback force, the non-uniform part of the mean feedback force and the fluctuating part of the feedback force. Since the non-uniformity of the mean feedback force increases with wall roughness, the effect of the non-uniform part of the mean feedback force is investigated in detail. For both smooth and rough walls, the non-uniform part of the mean feedback force is shown to contribute significantly to the particle-induced turbulence attenuation.

LES of Particle-Laden Flow With Inter-Particle Collisions

2003 ◽  
Author(s):  
Mikhael Gorokhovski ◽  
Anna Chtab
Keyword(s):  
Gas Flow ◽  
Particle Interaction ◽  
Solid Particles ◽  
Particle Interactions ◽  
Particle Collisions ◽  
Cpu Time ◽  
Eddy Simulation ◽  
Preferential Concentration ◽  
Large Eddy ◽  
Particle Laden Flow

By analogy with kinetic approach, the gas-solid turbulent flow was considered as an ensemble of interacting both stochastic liquid and solid particles. In this way, the motion equation for the solid particle along a smoothed trajectory has been derived. To close this equation, the statistical temperature of particles has been introduced and expressed by statistical properties of turbulence. The smoothed particles dynamics was then computed along with large-eddy simulation (LES) of turbulent channel gas flow with “two-way” coupling of momentum. The calculated results are compared with the experiment of Kulick et. al. (1994) and with computation of Yamomoto et. al. (2001), where the inter-particle interaction has been simulated by hard-sphere collisions with prescribed efficiency. It has been shown that our computation with smoothed motion of particle is relatively in agreement with experiment and computations of Yamomoto et. al. (2001). At the same time, the model presented in the paper has a following advantage: it, practically, does not require an additional CPU time to account for inter-particle interactions. The turbulence attenuation by particles and the preferential concentration of particles in the low-turbulence region have been shown.

Structure and Pressure Drop in Particle-Laden Gas Flow Through a Pipe Bend: A Numerical Analysis by the Euler/Lagrange Approach

2009 ◽  
Author(s):  
S. Lai´n ◽  
M. Sommerfeld
Keyword(s):  
Pressure Drop ◽  
Gas Flow ◽  
Gas Flows ◽  
Wall Roughness ◽  
Mass Loading ◽  
Particle Collisions ◽  
Pipe Bend ◽  
Flow Through ◽  
Fully Coupled ◽  
Lagrange Approach

The structure of particle-laden gas flows in a horizontal-to-vertical elbow is investigated numerically for analysing the required modelling depth. The numerical computations are performed with the fully coupled Euler-Lagrange approach considering all the relevant forces: drag, gravity-buoyancy and lift forces (slip-shear and slip-rotational). Moreover, interparticle and particle-rough wall collisions are taken into account by means of stochastic approaches. The effect of the different mechanisms, i.e. wall roughness, inter-particle collisions and mass loading, on the flow structure in the bend and the resulting pressure drop are investigated.

Particle Dispersion Simulation in Turbulent Flow Due to Particle-Particle and Particle-Wall Collisions

2015 ◽  
Vol 32 (2) ◽  
pp. 237-244 ◽  
Author(s):  
J.-H. Lin ◽  
K.-C. Chang
Keyword(s):  
Cost Effective ◽  
Small Mass ◽  
Particle Dispersion ◽  
Hard Sphere Model ◽  
Wall Roughness ◽  
Mass Loading ◽  
Particle Collisions ◽  
Carrier Fluid ◽  
Turbulent Channel Flows ◽  
The Mean

AbstractSimulation of the 3-D, fully developed turbulent channel flows laden with various mass loading ratios of particles is made using an Eulerian-Lagrangian approach in which the carrier-fluid flow field is solved with a low-Reynolds-number k-ε turbulence model while the deterministic Lagrangian method together with binary-collision hard-sphere model is applied for the solution of particle motion. Effects of inter-particle collisions and particle-wall collisions under different extents of wall roughness on particle dispersion are addressed in the study. A cost-effective searching algorithm of collision pair among particles is developed. It is found that the effects of inter-particle collisions on particle dispersion cannot be negligible when the ratio of the mean free time of particle to the mean particle relaxation time of particle is less or equal to O(10). In addition, the wall roughness extent plays an important role in the simulation of particle-wall collisions particularly for cases with small mass loading ratios.

Particulate Flow Solutions Through Centrifugal Impeller With Two Splitters

1986 ◽  
Author(s):  
Salah Elfeki ◽  
Widen Tabakoff
Keyword(s):  
Equations Of Motion ◽  
Computer Code ◽  
Solid Particles ◽  
Centrifugal Impeller ◽  
Meridional Plane ◽  
Particle Collisions ◽  
Performance Deterioration ◽  
The Mean ◽  
And Performance ◽  
Small Engines

Centrifugal impeller with splitters is one of the design techniques used in small engines. Many such engines are operating in different environmental conditions. One of which is where the atmosphere is polluted by small solid particles. Engines operating in such particulate environment are exposed to erosion and performance deterioration. In this paper the flow field through an impeller with two different size splitters is presented. The mean streamline pattern in the meridional plane was estimated by the computer code ‘MERDIL’, and an improved panel method was used to calculate the blade-to-blade flow solution. In addition, the particle trajectories were calculated by direct integration of the particle equations of motion. Particle collisions with the blade, hub and casing surfaces were determined. The data obtained from this analysis can be applied for calculating the erosion and performance deterioration in turbomachinery with such impellers.

A numerical study of the sedimentation of fibre suspensions

1998 ◽  
Vol 376 ◽  
pp. 149-182 ◽  
Author(s):  
MICHAEL B. MACKAPLOW ◽  
ERIC S. G. SHAQFEH
Keyword(s):  
Monte Carlo ◽  
Steady State ◽  
Monte Carlo Simulations ◽  
Numerical Study ◽  
Point Particle ◽  
Hydrodynamic Interactions ◽  
Dynamic Simulations ◽  
Slender Body Theory ◽  
Fibre Suspensions ◽  
The Mean

The sedimentation of fibre suspensions at low Reynolds number is studied using two different, but complementary, numerical simulation methods: (1) Monte Carlo simulations, which consider interparticle hydrodynamic interactions at all orders within the slender-body theory approximation (Mackaplow & Shaqfeh 1996), and (ii) dynamic simulations, which consider point–particle interactions and are accurate for suspension concentrations of nl3=1, where n and l are the number density and characteristic half-length of the fibres, respectively. For homogeneous, isotropic suspensions, the Monte Carlo simulations show that the hindrance of the mean sedimentation speed is linear in particle concentration up to at least nl3=7. The speed is well predicted by a new dilute theory that includes the effect of two-body interactions. Our dynamic simulations of dilute suspensions, however, show that interfibre hydrodynamic interactions cause the spatial and orientational distributions to become inhomogeneous and anisotropic. Most of the fibres migrate into narrow streamers aligned in the direction of gravity. This drives a downward convective flow within the streamers which serves to increase the mean fibre sedimentation speed. A steady-state orientation distribution develops which strongly favours fibre alignment with gravity. Although the distribution reaches a steady state, individual fibres continue to rotate in a manner that can be qualitatively described as a flipping between the two orientations aligned with gravity. The simulation results are in good agreement with published experimental data.

scholarly journals A Prospective Study of Single Breath Vital Capacity Inhalation Induction with High Concentration of Sevoflurane (Sbvc-Hc) for LMA Insertion in Adults for Short Surgical Cases

2020 ◽  
Vol 5 (1) ◽  
pp. 30-33
Author(s):  
Kailash Prabhudev ◽  
Naveen Kumar K
Keyword(s):  
Prospective Study ◽  
Short Duration ◽  
Gas Flow ◽  
Vital Capacity ◽  
Randomized Study ◽  
High Concentration ◽  
Inhalation Induction ◽  
Inhalation Anesthesia ◽  
Volatile Anesthetic Agent ◽  
The Mean

Background: Sevoflurane is a new volatile anesthetic agent with rapid induction and recovery. A randomized study was carried to access conditions for LMA insertion using Sevoflurane in 25 ASA I & II patients undergoing short duration surgeries.Subjects and Methods:This prospective study was conducted at Department of Anesthesiology and Critical Care, SVS Medical College and Hospital, Mahabubnagar, Telangana, India. After obtaining the institutional ethics committee and written informed consent from the patients, 25 subjects of either sex were included in this study. Age of the subjects was 18 to 60 years. Patients received injection Fentanyl 1 – 2mcg/kg prior to induction. All patients were pre-oxygenated for 3 min with 100% oxygen using a fresh gas flow of 81/min. All patients received inhalational induction with 8% Sevoflurane and O2 flow at 8 L/min with single vital capacity breathe technique. Loss of verbal contact was considered as the desired endpoint for induction, which was assessed by the response to calling out the patient’s name. Then the time of loss of eyelash reflex and jaw relaxation was assessed by anesthesiologist. After adequate jaw relaxation, LMA insertion was attempted.Results:The mean loss of verbal contact was 65.40±9.67second, while the mean for time for loss of eyelash reflex and jaw relaxation were found to be 81.20±9.39 seconds and 103.20 ±12.07 seconds respectively. The mean time for LMA insertion was 122.00±15.61 and the mean attempts for successful LMA insertion was 1.12±0.33. LMA insertion was easy in 23 cases as against difficult in 2 cases. In 2 cases transient cough and biting were recorded. LMA insertion was excellent and satisfactory in 88.0 and 12 percent. However, the mean heart rate at 5 minute after induction showed a significant fall at 5 minutes after induction. The mean values of SBP, DBP and MAP did not differ significantly at pre and induction. However, a significant decrease in SBP was noticed at 1, 2 and at 5 minutes.Conclusion:Sevoflurane is an smooth inhalation anesthesia with rapid onset with adequate jaw relaxation for insertion of LMA in Adults for short duration surgeries. Sevoflurane has got good hemodynamic profile with lesser complications owing to choice of inhalation agent for insertion of LMA.

scholarly journals HYDRODYNAMIC FEATURES OF SUSPENSIONS AND EMULSIONS FLOWS.

2021 ◽  
Vol 2 (446) ◽  
pp. 99-104
Author(s):  
S.R. Rasulov ◽  
G.R. Mustafayeva
Keyword(s):  
Gas Flow ◽  
Fine Particles ◽  
Mutual Influence ◽  
Transport Coefficients ◽  
Spherical Particles ◽  
Scientific Article ◽  
Two Phase ◽  
Real Picture ◽  
Turbulent Gas Flow ◽  
Gas Pulsations

This scientific article is devoted to the problems associated with the flow of suspensions and emulsions and some simplifications of the real picture of the flow of a polydisperse medium are made. It is also stipulated that differential equations characterizing the motion of suspensions and emulsions should take into account the fundamental discontinuity of the medium and the physicochemical processes of heat and mass transfer occurring in it. Taking into account all these factors, a general equation for multiphase systems is proposed with certain simplifications that do not change. The behavior of particles in two-phase systems, their concentration, collision and coagulation are considered. As a result, it was concluded that there is a multifactorial interaction and mutual influence of both phases in a dispersed flow. A differential equation of motion of a single i-th spherical particle in suspension was proposed, and an equation describing the drag force of a solid spherical particles. Equations of conservation of mass and momentum are presented for one-dimensional laminar motion of two incompressible phases in a gravity field with the same pressure in the phases. Having studied the parameters of the flow of fine particles in a turbulent gas flow, some assumptions were made. It was found that the pulsating motion of particles, performed by them during one period of gas pulsations, can be represented as a change in the pulsating gas velocity in time. The parameter of entrainment of particles by a pulsating medium is an important characteristic in determining the transport coefficients in a turbulent flow. It is concluded that the presence of various kinds of particles in the liquid complicates the problem of solving hydromechanical problems in turbulent and laminar flow, and the assumptions given in the work facilitate the study of this problem.

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