Experimental and numerical study of Stairmand cyclone separators: a comparison of the results of small-scale and large-scale cyclones

2019 ◽  
Vol 55 (8) ◽  
pp. 2341-2354 ◽  
Author(s):  
Halil I. Erol ◽  
Oguz Turgut ◽  
Rahmi Unal
Keyword(s):  
Large Scale ◽  
Numerical Study ◽  
Small Scale ◽  
Comparison Of The Results

A numerical study of the transition of jet diffusion flames

1990 ◽  
Vol 431 (1882) ◽  
pp. 301-314 ◽  
Keyword(s):  
Reynolds Number ◽  
Diffusion Coefficient ◽  
Large Scale ◽  
Numerical Study ◽  
Small Scale ◽  
Surface Model ◽  
Flame Surface ◽  
Transition Mechanism ◽  
Air Stream ◽  
Scale Fluctuation

A numerical study on the transition from laminar to turbulent of two-dimensional fuel jet flames developed in a co-flowing air stream was made by adopting the flame surface model of infinite chemical reaction rate and unit Lewis number. The time dependent compressible Navier–Stokes equation was solved numerically with the equation for coupling function by using a finite difference method. The temperature-dependence of viscosity and diffusion coefficient were taken into account so as to study effects of increases of these coefficients on the transition. The numerical calculation was done for the case when methane is injected into a co-flowing air stream with variable injection Reynolds number up to 2500. When the Reynolds number was smaller than 1000 the flame, as well as the flow, remained laminar in the calculated domain. As the Reynolds number was increased above this value, a transition point appeared along the flame, downstream of which the flame and flow began to fluctuate. Two kinds of fluctuations were observed, a small scale fluctuation near the jet axis and a large scale fluctuation outside the flame surface, both of the same origin, due to the Kelvin–Helmholtz instability. The radial distributions of density and transport coefficients were found to play dominant roles in this instability, and hence in the transition mechanism. The decreased density in the flame accelerated the instability, while the increase in viscosity had a stabilizing effect. However, the most important effect was the increase in diffusion coefficient. The increase shifted the flame surface, where the large density decrease occurs, outside the shear layer of the jet and produced a thick viscous layer surrounding the jet which effectively suppressed the instability.

scholarly journals Impact Assessment of Orography on the Extreme Precipitation Event of July 2010 over Pakistan: A Numerical Study

2015 ◽  
Vol 2015 ◽  
pp. 1-20 ◽  
Author(s):  
Khan Muhammad Tahir ◽  
Yan Yin ◽  
Yong Wang ◽  
Zaheer A. Babar ◽  
Dong Yan
Keyword(s):  
Large Scale ◽  
Extreme Event ◽  
Numerical Study ◽  
Deep Convection ◽  
Temporal Distribution ◽  
Precipitation Event ◽  
Windward Side ◽  
Small Scale ◽  
Extreme Rainfall Event ◽  
Synoptic Conditions

The topography influences monsoon precipitation and gives rise to significant rainfall events in South Asia. The physical mechanism involved in such events includes mechanical uplifting, thermodynamics, small scale cloud processes, and large scale atmospheric circulations. The investigation into orographic precipitation is pursued by synoptic and model analysis. Deep convection occurs as warm moist airflow is channeling over steep mountains. WRF model coupled with Morrison double moment scheme is used to assess the relative impact of topography on extreme rainfall event of 26–30 July 2010 in Pakistan. Two sensitivity tests with full topography (CTL) and reduced topography by 50% (LOW) are carried out. Two distinct precipitation zones over Hindukush and Himalaya mountains are identified. The topographic changes significantly affect moisture divergence and spatial and temporal distribution of precipitation. A low level jet is created on windward side of big mountains, yielding enhanced moisture flux and instability. Eddy kinetic energy significantly changes with orographic height. Energy flux created further unstabilized atmosphere and deep convection, producing wide spread heavy rainfall in the area in Himalaya foothills. Under the set synoptic conditions, orographic orientation enhanced the moisture accumulation and deep convection, resulting in occurrence of this extreme event.

scholarly journals Interaction between Crustal-Scale Darcy and Hydrofracture Fluid Transport: A Numerical Study

Geofluids ◽  
2020 ◽  
Vol 2020 ◽  
pp. 1-14
Author(s):  
Tamara de Riese ◽  
Paul D. Bons ◽  
Enrique Gomez-Rivas ◽  
Till Sachau
Keyword(s):  
Fluid Flow ◽  
Numerical Model ◽  
Transport Mechanism ◽  
Large Scale ◽  
Fluid Transport ◽  
Numerical Study ◽  
Ballistic Transport ◽  
Accretionary Prism ◽  
Small Scale ◽  
Porous Flow

Crustal-scale fluid flow can be regarded as a bimodal transport mechanism. At low hydraulic head gradients, fluid flow through rock porosity is slow and can be described as diffusional. Structures such as hydraulic breccias and hydrothermal veins both form when fluid velocities and pressures are high, which can be achieved by localized fluid transport in space and time, via hydrofractures. Hydrofracture propagation and simultaneous fluid flow can be regarded as a “ballistic” transport mechanism, which is activated when transport by diffusion alone is insufficient to release the local fluid overpressure. The activation of a ballistic system locally reduces the driving force, through allowing the escape of fluid. We use a numerical model to investigate the properties of the two transport modes in general and the transition between them in particular. We developed a numerical model in order to study patterns that result from bimodal transport. When hydrofractures are activated due to low permeability relative to fluid flux, many hydrofractures form that do not extend through the whole system. These abundant hydrofractures follow a power-law size distribution. A Hurst factor of ~0.9 indicates that the system self-organizes. The abundant small-scale hydrofractures organize the formation of large-scale hydrofractures that ascend through the whole system and drain fluids in large bursts. As the relative contribution of porous flow increases, escaping fluid bursts become less frequent, but more regular in time and larger in volume. We propose that metamorphic rocks with abundant veins, such as in the Kodiak accretionary prism (Alaska) and Otago schists (New Zealand), represent regions with abundant hydrofractures near the fluid source, while hydrothermal breccias are formed by the large fluid bursts that can ascend the crust to shallower levels.

Liquid Fuel Spray Characterization for the Design of the Dual-Fuel PGT10B Combustor

2001 ◽  
Author(s):  
F. A. Tap ◽  
R. Modi ◽  
J. P. Van Buijtenen
Keyword(s):  
Liquid Film ◽  
Gas Turbine ◽  
Large Scale ◽  
Drop Size ◽  
Numerical Study ◽  
Fuel Spray ◽  
Small Scale ◽  
Dual Fuel ◽  
Test Results ◽  
Liquid Concentration

The Dry Low NOx (DLN) silo combustor of the Nuovo Pignone PGT10B gas turbine is being redesigned to meet Dual-Fuel capability. A prototype with specially designed fuel injectors, placed on airfoil-shaped elements, was tested at cold conditions (using water instead of Diesel fuel) to map the spray mass distribution at the premixer exit. The resulting profile showed high concentrations of liquid near the premixer centerline and on the premixer wall. Parallel to this test, a small-scale experimental and numerical study was made of a single atomizer of the fuel system, placed in cross flow position. This small-scale study was launched in order to gain insight in the behavior of the spray, as well as to assess the relative importance of spray modeling parameters. The PDPA experiments and 2D CFD simulations of these experiments showed fair agreement on the average drop size distribution and drop size-velocity correlation. The flow visualization also revealed liquid film formation on the surface of the airfoil, behind the injector, due to the low atomization pressure differential at cold conditions. Using this modeling experience, the spray patternation test with the prototype combustor has been modeled using an existing 3D CFD model of the premixer. The model also showed high liquid concentration on the wall, but not near the centerline. From the results of the small-scale study it is concluded that the measured high concentration near the premixer centerline is not a result of the flow field. It is assumed that in the complete assembly the liquid film from the injector vanes accumulates on the center body, resulting in a high liquid concentration downstream on the premixer centerline. Overall, the application of CFD analyses on the tests performed proved to be a very useful tool to evaluate the test results. The modeling experience identified the important factors in modeling the fuel spray in a gas turbine environment, but further evolution of computer resources is required before large-scale test results will be reproducible with CFD models.

2D and 3D Multiscale Computational Modeling of Dynamic Microorgan Devices as Drug Screening Platforms

2015 ◽  
Author(s):  
Filippos Tourlomousis ◽  
Robert C. Chang
Keyword(s):  
Large Scale ◽  
Numerical Study ◽  
Numerical Results ◽  
Scale Model ◽  
Small Scale ◽  
Optimum Process ◽  
Shear Stresses ◽  
Enzymatic Reactions ◽  
Modeling Approach

The ability to incorporate three-dimensional (3D) hepatocyte-laden hydrogel constructs using layered fabrication approaches into devices that can be perfused with drugs enables the creation of dynamic microorgan devices (DMDs) that offer an optimal analog of the in vivo liver metabolism scenario. The dynamic nature of such in vitro metabolism models demands reliable numerical tools to determine the optimum process, material, and geometric parameters for the most effective metabolic conversion of the perfused drug into the liver microenvironment. However, there is a current lack of literature that integrates computational approaches to guide the optimum design of such devices. The groundwork of the present numerical study has been laid by our previous study [1], where the authors modeled in 2D an in vitro DMD of arbitrary dimensions and identified the modeling challenges towards meaningful results. These constructs are hosted in the chamber of the microfluidic device serving as walls of the microfluidic array of channels through which a fluorescent drug substrate is perfused into the microfluidic printed channel walls at a specified volumetric flow rate assuring Stokes flow conditions (Re<<1). Due to the porous nature of the hydrogel walls, a metabolized drug product is collected at the outlet port. A rigorous FEM based modeling approach is presented for a single channel parallel model geometry (1 free flow channel with 2 porous walls), where the hydrodynamics, mass transfer and pharmacokinetics equations are solved numerically in order to yield the drug metabolite concentration profile at the DMD outlet. The fluid induces shear stresses are assessed both in 3D, with only 27 cells modeled as single compartment voids, where all of the enzymatic reactions are assumed to take place. In this way, the mechanotransduction effect that alters the hepatocyte metabolic activity is assessed for a small scale model. This approach overcomes the numerical limitations imposed by the cell density (∼1012 cells/m3) of the large scale DMD device. In addition, a compartmentalization technique is proposed in order to assess the metabolism process at the subcellular level. The numerical results are validated with experiments to reveal the robustness of the proposed modeling approach and the necessity of scaling the numerical results by preserving dynamic and biochemical similarity between the small and large scale model.

scholarly journals The Role Of Airborne Moments In The Spread Of The Coronavirus And The Course Of The Pandemic

2020 ◽  
Author(s):  
Kiran Bhaganagar ◽  
Sudheer BhimiReddy
Keyword(s):  
Large Scale ◽  
Numerical Study ◽  
Dispersion Model ◽  
Forecast Model ◽  
Initial Time ◽  
Small Scale ◽  
Turbulence Energy ◽  
Virus Concentration ◽  
Micro Particles

Abstract A numerical study using Weather Research Forecast model and Lagrangian HYSPLIT dispersion model was conducted to understand the meteorological factors influencing the transport and mixing of the blob of Corona virus-filled micro-particles (of radius 0.12mm) released into the atmosphere due to coughing, sneezing by infected patient. The study is offered as an important contribution demonstrating the role of local atmospheric dynamics in coronavirus spread during the period of March 9 – April 6, 2020 in New York City, the epicenter of the coronavirus in the USA. The results demonstrate that from the initial time of release, the virus can spread up to 30 minutes in air, covering a 200-m radius at a time, moving 1 – 2 km from the original source. Turbulence energy containing large-scale horizontal “rolls” and vertical thermal “updrafts” and “downdrafts” contribute to transport and advection processes, before small-scale turbulent eddies rapidly mix and dilute virus concentration.

scholarly journals Numerical Study of Violent Impact Flow Using a CIP-Based Model

2013 ◽  
Vol 2013 ◽  
pp. 1-12 ◽  
Author(s):  
Qiao-ling Ji ◽  
Xi-zeng Zhao ◽  
Sheng Dong
Keyword(s):  
Free Surface ◽  
Numerical Model ◽  
Large Scale ◽  
Stokes Equations ◽  
Numerical Study ◽  
Three Dimensional ◽  
Small Scale ◽  
Surface Boundary ◽  
Two Phase ◽  
Constrained Interpolation

A two-phase flow model is developed to study violent impact flow problem. The model governed by the Navier-Stokes equations with free surface boundary conditions is solved by a Constrained Interpolation Profile (CIP)-based high-order finite difference method on a fixed Cartesian grid system. The free surface is immersed in the computation domain and expressed by a one-fluid density function. An accurate Volume of Fluid (VOF)-type scheme, the Tangent of Hyperbola for Interface Capturing (THINC), is combined for the free surface treatment. Results of another two free surface capturing methods, the original VOF and CIP, are also presented for comparison. The validity and utility of the numerical model are demonstrated by applying it to two dam-break problems: a small-scale two-dimensional (2D) and three-dimensional (3D) full scale simulations and a large-scale 2D simulation. Main attention is paid to the water elevations and impact pressure, and the numerical results show relatively good agreement with available experimental measurements. It is shown that the present numerical model can give a satisfactory prediction for violent impact flow.

scholarly journals Numerical study of magnetohydrodynamic duct flow at high Reynolds and Hartmann numbers

2012 ◽  
Vol 704 ◽  
pp. 421-446 ◽  
Author(s):  
Dmitry Krasnov ◽  
Oleg Zikanov ◽  
Thomas Boeck
Keyword(s):  
Magnetic Field ◽  
Large Scale ◽  
Numerical Study ◽  
Transverse Magnetic ◽  
Field Analysis ◽  
Small Scale ◽  
Duct Flow ◽  
Mean Velocity ◽  
Magnetic Field Analysis ◽  
The Magnetic Field

AbstractHigh-resolution direct numerical simulations are conducted to analyse turbulent states of the flow of an electrically conducting fluid in a duct of square cross-section with electrically insulating walls and imposed transverse magnetic field. The Reynolds number of the flow is $1{0}^{5} $ and the Hartmann number varies from $0$ to $400$. It is found that there is a broad range of Hartmann numbers in which the flow is neither laminar nor fully turbulent, but has laminar core, Hartmann boundary layers and turbulent zones near the walls parallel to the magnetic field. Analysis of turbulent fluctuations shows that each zone consists of two layers: the boundary layer near the wall characterized by small-scale turbulence and the outer layer dominated by large-scale vortical structures strongly elongated in the direction of the magnetic field. We also find a peculiar scaling of the mean velocity, according to which the reciprocal von Kármán coefficient grows nearly linearly with the distance to the wall.

Numerical Study of Flow Control in a Diffuser by Vibration Wall and Mechanism Analysis by Establishment of a Nonlinear Simplified Model

2017 ◽  
Author(s):  
Lu Weiyu ◽  
Huang Guoping ◽  
Fu Xin ◽  
Wang Jinchun ◽  
Hong Shuli
Keyword(s):  
Flow Field ◽  
Flow Control ◽  
Large Scale ◽  
Control Method ◽  
Numerical Study ◽  
Active Flow Control ◽  
Simplified Model ◽  
Small Scale ◽  
Separation Flow ◽  
Mechanism Analysis

Vibration wall is a kind of important active flow control method, while the interaction between the vibration wall and unsteady separation flow is so complex for researchers to discover the corresponding mechanism. Current researches imply that the better controlled flow is the more ordered flow. At first, the effect of the different control parameters of vibration wall on the total pressure loss was studied by numerical simulation to reveal the control mechanism of vibration wall. Numerical results show that when the vibration frequency reaches the separation vortex frequency, with the amplitude of 0.1 characteristic length, the best flow control is resulted. Furthermore, it can be seen that, the vibration wall with effective parameters can make the large-scale vortices more dominant, while small-scales ones (or clutters) appear less in the pattern. This observation indicates that the flow field tends to be more orderly. Moreover, to further explain this ordering mechanism, a simplified model is established and analyzed, showing that valid external excitement can strengthen the dominated frequency of K-H wave which forms the large-scale separation vortices, and restrains small-scale ones. The flow field is then more orderly and less chaotic, resulting in reduction of flow loss.

Numerical study of resonant shallow flows past a lateral cavity: benchmarking the model with a new experimental data set

2020 ◽  
Author(s):  
Adrián Navas-Montilla ◽  
Sergio Martínez-Aranda ◽  
Antonio Lozano ◽  
Pilar García-Navarro
Keyword(s):  
Water Resources ◽  
Shallow Water ◽  
Large Scale ◽  
Numerical Study ◽  
Numerical Results ◽  
Small Scale ◽  
Coupling Mechanism ◽  
Data Set ◽  
Shallow Flows ◽  
Lateral Cavity

&lt;p&gt;Steady shallow flows past an open channel lateral cavity have been widely studied in the last years due to their engineering and environmental relevance, e.g. for river restoration purposes [1]. Such flows can induce the excitation of an eigenmode of a gravity standing wave inside the cavity, called seiche, which may be coupled with the shedding of vortices at the opening of the cavity. A complete understanding of such phenomenon is necessary as it may determine the mass exchange between the main channel and the cavity [2]. A numerical study of the resonant flow in a channel with a single lateral cavity is herein presented. Five different flow configurations at a fixed Froude number (Fr=0.8), measured in the laboratory [3], are used as a benchmark. Such experiments are reproduced using a high-order 2D depth-averaged URANS model based on the shallow water equations, assuming that shallow water turbulence is mainly horizontal [4]. The large-scale horizontal vortices are resolved by the model, whereas the effect of the small-scale turbulence is accounted for by means of a turbulence model. Water surface elevation and velocity measurements are used for comparison with the numerical results. A detailed comparison of the seiche amplitude distribution in the cavity-channel area is presented, showing a good agreement between the numerical results and the observations. Frequency analysis techniques are used to extract the relevant features of the flow. It is evidenced that the proposed model is able to reproduce the observed spatial distribution of oscillation nodes and anti-nodes, as well as the time-averaged flow field. The coupling mechanism between the gravity wave inside the cavity and the unstable shear layer at the opening of the cavity is also accurately captured. &lt;br&gt;&lt;br&gt;&lt;/p&gt;&lt;p&gt;[1] C. Juez, M. Thalmann, A. J. Schleiss &amp; M. J.&amp;#160; Franca, Morphological resilience to flow fluctuations of fine sediment deposits in bank lateral cavities, Advances in Water Resources,&amp;#160; 115 (2018) 44-59.&lt;/p&gt;&lt;p&gt;[2] I. Kimura &amp; T. Hosoda, Fundamental properties of flows in open channels with dead zone, Journal of Hydraulic Engineering 123 (1997) 98-107.&lt;/p&gt;&lt;p&gt;[3] S. Mart&amp;#237;nez-Aranda, J. Fern&amp;#225;ndez-Pato, D. Caviedes-Voulli&amp;#232;me, I. Garc&amp;#237;a-Palac&amp;#237;n &amp; P. Garc&amp;#237;a-Navarro, Towards transient experimental water surfaces: a new benchmark dataset for 2D shallow water solvers, Advances in water resources, 121 (2018) 130-149.&lt;/p&gt;&lt;p&gt;[4] A. Navas-Montilla, C. Juez, M.J. Franca &amp; J. Murillo, Depth-averaged unsteady RANS simulation of resonant shallow flows in lateral cavities using augmented WENO-ADER schemes, Journal of Computational Physics, 24 (2019) 203-217.&lt;/p&gt;

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