Numerical investigation of particle trapping in various groove configurations in straight and bent flow channels

SIMULATION ◽  
2020 ◽  
Vol 96 (8) ◽  
pp. 679-699
Author(s):  
LA Florio
Keyword(s):  
High Speed ◽  
Particle Interaction ◽  
Flow Path ◽  
Particle Flow ◽  
Computational Technique ◽  
Straight Channel ◽  
Particle Trapping ◽  
Flow Interactions ◽  
Groove Configurations ◽  
Channel Configuration

A novel computational technique is applied to investigate particle trapping in straight and bent channel flow paths with various groove configurations in high-speed compressible, particle laden flow. The technique is valid for particle sizes of the same order of magnitude as the groove dimensions and where the particle–flow path, particle–particle, and particle–flow interactions play significant roles in determining the particle motion. The sacrificial grooves within the flow path can remove particles from the flow to reduce particle impact-induced wear. The feasibility of the trapping grooves and the conditions for which they are most beneficial can be gleaned from analysis of the model results. Three groove configurations are studied: a straight groove, a flared groove, and a 45 degree angle groove, for the same groove entrance size, groove depth, and spacing in a straight channel and a channel with a 90 degree bend. A transient maximum of 22% of the particles were trapped for the flared groove for the bent channel and a transient maximum of 15% of the particles for the straight channel configuration. The second groove of the bent channel produces the greatest single groove particle holding of 8.25% of all of the particles for the flared grove configuration. The contributions of the groove positioning, groove shape, gas flow, and particle interaction conditions to the trapping characteristics can be readily obtained from examination of the model results since the modeling technique includes detailed treatment of particle–flow path and flow interactions, allowing for the study of the mechanisms acting to trap the particles within the grooves.

scholarly journals Optical-Trapping Laser Techniques for Characterizing Airborne Aerosol Particles and Its Application in Chemical Aerosol Study

Micromachines ◽  
2021 ◽  
Vol 12 (4) ◽  
pp. 466
Author(s):  
Aimable Kalume ◽  
Chuji Wang ◽  
Yongle Pan
Keyword(s):  
Light Scattering ◽  
High Speed ◽  
Optical Trapping ◽  
Aerosol Particles ◽  
Particle Interaction ◽  
Raman Laser ◽  
General Description ◽  
Sample Collection ◽  
Laser Technologies ◽  
Laser Induced Breakdown

We present a broad assessment on the studies of optically-trapped single airborne aerosol particles, particularly chemical aerosol particles, using laser technologies. To date, extensive works have been conducted on ensembles of aerosols as well as on their analogous bulk samples, and a decent general description of airborne particles has been drawn and accepted. However, substantial discrepancies between observed and expected aerosols behavior have been reported. To fill this gap, single-particle investigation has proved to be a unique intersection leading to a clear representation of microproperties and size-dependent comportment affecting the overall aerosol behavior, under various environmental conditions. In order to achieve this objective, optical-trapping technologies allow holding and manipulating a single aerosol particle, while offering significant advantages such as contactless handling, free from sample collection and preparation, prevention of contamination, versatility to any type of aerosol, and flexibility to accommodation of various analytical systems. We review spectroscopic methods that are based on the light-particle interaction, including elastic light scattering, light absorption (cavity ring-down and photoacoustic spectroscopies), inelastic light scattering and emission (Raman, laser-induced breakdown, and laser-induced fluorescence spectroscopies), and digital holography. Laser technologies offer several benefits such as high speed, high selectivity, high accuracy, and the ability to perform in real-time, in situ. This review, in particular, discusses each method, highlights the advantages and limitations, early breakthroughs, and recent progresses that have contributed to a better understanding of single particles and particle ensembles in general.

scholarly journals In situ damage assessment using synchrotron X-rays in materials loaded by a Hopkinson bar

2014 ◽  
Vol 372 (2015) ◽  
pp. 20130191 ◽  
Author(s):  
Weinong W. Chen ◽  
Matthew C. Hudspeth ◽  
Ben Claus ◽  
Niranjan D. Parab ◽  
John T. Black ◽  
...  
Keyword(s):  
High Speed ◽  
Particle Interaction ◽  
Tensile Failure ◽  
High Rate ◽  
X Rays ◽  
Contrast Imaging ◽  
X Ray ◽  
Damage Initiation ◽  
Dynamic Experiments

Split Hopkinson or Kolsky bars are common high-rate characterization tools for dynamic mechanical behaviour of materials. Stress–strain responses averaged over specimen volume are obtained as a function of strain rate. Specimen deformation histories can be monitored by high-speed imaging on the surface. It has not been possible to track the damage initiation and evolution during the dynamic deformation inside specimens except for a few transparent materials. In this study, we integrated Hopkinson compression/tension bars with high-speed X-ray imaging capabilities. The damage history in a dynamically deforming specimen was monitored in situ using synchrotron radiation via X-ray phase contrast imaging. The effectiveness of the novel union between these two powerful techniques, which opens a new angle for data acquisition in dynamic experiments, is demonstrated by a series of dynamic experiments on a variety of material systems, including particle interaction in granular materials, glass impact cracking, single crystal silicon tensile failure and ligament–bone junction damage.

CFD Investigation of the Flow of Trailing Edge Cooling Slots

2018 ◽  
Author(s):  
Y. Jiang ◽  
N. Gurram ◽  
E. Romero ◽  
P. T. Ireland ◽  
L. di Mare
Keyword(s):  
Mach Number ◽  
Kinetic Energy ◽  
Flow Separation ◽  
Film Cooling ◽  
High Speed ◽  
Turbine Blades ◽  
Cross Flow ◽  
Turbulent Energy ◽  
Trailing Edge ◽  
Flow Interactions

Slot film cooling is a popular choice for trailing edge cooling in high pressure (HP) turbine blades because it can provide more uniform film coverage compared to discrete film cooling holes. The slot geometry consists of a cut back in the blade pressure side connected through rectangular openings to the internal coolant feed passage. The numerical simulation of this kind of film cooling flows is challenging due to the presence of flow interactions like step flow separation, coolant-mainstream mixing and heat transfer. The geometry under consideration is a cutback surface at the trailing edge of a constant cross-section aerofoil. The cutback surface is divided into three sections separated by narrow lands. The experiments are conducted in a high speed cascade in Oxford Osney Thermo-Fluids Laboratory at Reynolds and Mach number distributions representative of engine conditions. The capability of CFD methods to capture these flow phenomena is investigated in this paper. The isentropic Mach number and film effectiveness are compared between CFD and pressure sensitive paint (PSP) data. Compared to steady k–ω SST method, Scale Adaptive Simulation (SAS) can agree better with the measurement. Furthermore, the profiles of kinetic energy, production and shear stress obtained by the steady and SAS methods are compared to identify the main source of inaccuracy in RANS simulations. The SAS method is better to capture the unsteady coolant-hot gas mixing and vortex shedding at the slot lip. The cross flow is found to affect the film significantly as it triggers flow separation near the lands and reduces the effectiveness. The film is non-symmetric with respect to the half-span plane and different flow features are present in each slot. The effect of mass flow ratio (MFR) on flow pattern and coolant distribution is also studied. The profiles of velocity, kinetic energy and production of turbulent energy are compared among the slots in detail. The MFR not only affects the magnitude but also changes the sign of production.

Cooling Injection Effect on a Transonic Squealer Tip—Part II: Analysis of Aerothermal Interaction Physics

2017 ◽  
Vol 139 (5) ◽  
Author(s):  
H. Ma ◽  
Q. Zhang ◽  
L. He ◽  
Z. Wang ◽  
L. Wang
Keyword(s):  
Heat Transfer ◽  
Transonic Flow ◽  
High Speed ◽  
Base Flow ◽  
Vortical Flow ◽  
Flow Interactions ◽  
Blade Tip ◽  
Local Base ◽  
Subsonic Region ◽  
Cavity Floor

A basic attribute for turbine blade film cooling is that coolant injected should be largely passively convected by the local base flow. However, the effective working of the conventional wisdom may be compromised when the cooling injection strongly interacts with the base flow. Rotor blade tip of a transonic high-pressure (HP) turbine is one of such challenging regions for which basic understanding of the relevant aerothermal behavior as a basis for effective heat transfer/cooling design is lacking. The need to increase our understanding and predictability for high-speed transonic blade tip has been underlined by some recent findings that tip heat transfer characteristics in a transonic flow are qualitatively different from those at a low speed. Although there have been extensive studies previously on squealer blade tip cooling, there have been no published experimental studies under a transonic flow condition. The present study investigates the effect of cooling injection on a transonic squealer tip through a closely combined experimental and computational fluid dynamics (CFD) effort. The experimental and computational results as presented in Part I have consistently revealed some distinctive aerothermal signatures of the strong coolant-base flow interactions. In this paper, as Part II, detailed analyses using the validated CFD solutions are conducted to identify, analyze, and understand the causal links between the aerothermal signatures and the driving flow structures and physical mechanisms. It is shown that the interactions between the coolant injection and the base over-tip leakage (OTL) flow in the squealer tip region are much stronger in the frontal subsonic region than the rear transonic region. The dominant vortical flow structure is a counter-rotating vortex pair (CRVP) associated with each discrete cooling injection. High HTC stripes on the cavity floor are directly linked to the impingement heat transfer augmentation associated with one leg of the CRVP, which is considerably enhanced by the near-floor fluid movement driven by the overall pressure gradient along the camber line (CAM). The strength of the coolant-base flow interaction as signified by the augmented values of the HTC stripes is seen to correlate to the interplay and balance between the OTL flow and the CRVP structure. As such, for the frontal subsonic part of the cavity, there is a prevailing spanwise inward flow initiated by the CRVP, which has profoundly changed the local base flow, leading to high HTC stripes on the cavity floor. On the other hand, for the rear high speed part, the high inertia of the OTL flow dominates; thus, the vortical flow disturbances associated with the CRVP are largely passively convected, leaving clear signatures on the top surface of the suction surface rim. A further interesting side effect of the strong interaction in the frontal subsonic region is that there is considerable net heat flux reduction (NHFR) in an area seemingly unreachable by the injected coolant. The present results have confirmed that this is due to the large reduction in the local HTC as a consequence of the upstream propagated impact of the strong coolant-base flow interactions.

Geometrical Effects of Channel Configuration on the Performance of Membraneless Fuel Cells

2017 ◽  
Author(s):  
Hector Gomez ◽  
Usama Tohid ◽  
Arturo Pacheco-Vega
Keyword(s):  
Mathematical Model ◽  
Fuel Cell ◽  
Stokes Equations ◽  
Single Channel ◽  
Numerical Data ◽  
Operating Conditions ◽  
Straight Channel ◽  
Wavy Channel ◽  
Channel Configuration ◽  
The Impact

In this study, numerical simulations were performed to find the current-voltage distribution for a laminar flow-based membraneless fuel cell (LFFC). The system uses formic acid and oxygen as the fuel and oxidant, respectively, and has a Y-shaped geometry with two separate inlets that merge into a single channel. The main objective of this work is to analyze the impact of geometry and operating conditions on the performance of these devices. This is done by proposing a novel wavy-channel-based geometry for the side walls, along with planar top and bottom walls, and comparing the behavior of the corresponding system to that of LFFCs based on straight-channel walls. Special attention is placed on the effect of both the amplitude of the sinusoid and its wavelength on the performance of the device. The effect of flow rates — in the range of [200, 350] μL/min — is also studied. The mathematical model is formulated by considering the Navier-Stokes equations along with Butler-Volmer and Fick’s law. For each fuel-cell configuration, the governing equations are discretized and solved using finite elements, and the solutions given in terms of the polarization curves. The model was first verified using published numerical data for a straight-channel-based LFFC. The simulations show that the performance achieved by the device, based on the proposed wavy channel geometry, is slightly better than that of the LFFC with straight channel walls. On the other hand, higher flowrates significantly improve the power density of the device. Although the current mathematical model may be useful in a variety of applications, improvements on it are currently underway to account for the effects of potential distributions on ions within the flow channel, and results from it will be reported in the future.

Capsule chemistry technology for high-speed clinical chemistry analyses.

1985 ◽  
Vol 31 (9) ◽  
pp. 1453-1456 ◽  
Author(s):  
M Cassaday ◽  
H Diebler ◽  
R Herron ◽  
M Pelavin ◽  
D Svenjak ◽  
...  
Keyword(s):  
High Speed ◽  
Analytical Approach ◽  
Clinical Chemistry ◽  
Flow Path ◽  
Physical Interaction ◽  
Carrier Materials ◽  
Line Detector ◽  
Selective Analysis

Abstract We describe a new analytical approach--"capsule chemistry"--for high-speed, selective analysis of a wide variety of analytes. Sequential micro-aliquots of sample and reagents are encapsulated within an inert fluorocarbon liquid. The resulting "test capsule" is introduced into a single analytical flow path, composed of a solid fluorocarbon, Teflon, where the sample is incubated, mixed, reacted, and measured as a moving series of individual tests. These randomly selective assays are processed at a rate of 720 per hour. The unique physical interaction between the liquid and solid fluorocarbon carrier materials effectively prevents detectable "carryover" of aqueous constituents between the successive test capsules. Reactions are monitored through the walls of the Teflon analytical channel at nine in-line detector stations for colorimetric and nephelometric measurements.

Full-scale CFD investigation of gas-particle flow, interactions and combustion in tangentially fired pulverized coal furnace

Energy ◽  
2019 ◽  
Vol 179 ◽  
pp. 1036-1053 ◽  
Author(s):  
Srdjan Belošević ◽  
Ivan Tomanović ◽  
Nenad Crnomarković ◽  
Aleksandar Milićević
Keyword(s):  
Full Scale ◽  
Pulverized Coal ◽  
Particle Flow ◽  
Flow Interactions

scholarly journals Enhancement of particle trapping in the wave-particle interaction

2008 ◽  
Vol 13 (3) ◽  
pp. 660-665 ◽  
Author(s):  
R. Bachelard ◽  
A. Antoniazzi ◽  
C. Chandre ◽  
D. Fanelli ◽  
M. Vittot
Keyword(s):  
Particle Interaction ◽  
Particle Trapping ◽  
Wave Particle Interaction

Effect of a Flexible Wall on a Reattaching Turbulent Shear Layer

2010 ◽  
Vol 132 (4) ◽  
Author(s):  
Alexey Velikorodny ◽  
Graham Duck ◽  
Peter Oshkai
Keyword(s):  
High Speed ◽  
Turbulent Shear ◽  
Bottom Surface ◽  
High Speed Photography ◽  
Rigid Surface ◽  
Turbulence Statistics ◽  
Inflow Condition ◽  
Diverging Channel ◽  
Flexible Wall ◽  
Channel Configuration

Digital particle image velocimetry was applied to investigate turbulent flow of air between a flexible wall and a rigid surface containing a backward-facing step (BFS). The inflow condition corresponded to a Coanda jet issuing from a nozzle that was located upstream of the BFS. The flexible wall was represented by a sheet of paper under tension that was positioned above the BFS. Two additional configurations, which involved the BFS without the flexible wall and the BFS in proximity to an inclined rigid upper wall, were considered in this study. In all three cases, the flow fields were characterized in terms of patterns of time-averaged velocity, out-of-plane vorticity, streamline topology, and turbulence statistics. High-speed photography and unsteady pressure measurements were employed to characterize the flow-induced deformation of the flexible wall and the flow oscillations. The profile of the paper sheet could be approximated by linear segments, which, in conjunction with the rigid surface that contained the BFS, formed a diverging channel configuration. Confinement of the incoming flow by the flexible wall delayed flow reattachment to the rigid bottom surface downstream of the BFS. Patterns of turbulence statistics in the presence of the flexible wall shared qualitative similarity with the corresponding parameters of diverging channel flows as well as classical Couette–Poiseuille flows.

Numerical Modeling of Fragmentation Characteristics of Explosive Fragmentation Munitions

2002 ◽  
Author(s):  
Vladimir M. Gold
Keyword(s):  
High Speed ◽  
Average Length ◽  
Three Dimensional ◽  
Fragmentation Model ◽  
Computational Technique ◽  
Entire Body ◽  
Detonation Products ◽  
Explosive Fragmentation ◽  
Break Up ◽  
The Moment

Numerical simulations of explosive fragmentation munitions presented in this work integrate three-dimensional axisymmetric hydrocode analyses with analytical fragmentation modeling. The developed analytical fragmentation model is based on the Mott’s theory of break-up of cylindrical “ring-bombs” (Mott, 1947), in which the average length of fragments is a function of the radius and velocity of the ring at the moment of break-up, and the mechanical properties of the metal. The fundamental assumption of the model is that the fragmentation occurs instantly throughout the entire body of the shell. Adopting Mott’s critical fracture strain concept (Mott, 1947), the moment of the shell break-up is identified in terms of the high explosive detonation products volume expansions, V/V0. The assumed fragmentation time determined from the high-speed photographic data of Pearson (1990) had been approximately three volume expansions, the fragmentation being defined as the instant at which the detonation products first appear as they emanate from the fractures in the shell. The newly developed computational technique is applied to both the natural and preformed explosive fragmentation munitions problems. Considering relative simplicity of the model, the accuracy of the prediction of fragment spray experimental data is rather remarkable.

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