LES Analysis of Gas Flow and Mixing Process in an Unsteady Jet

2007 ◽  
Author(s):  
Chihiro Kondo ◽  
Hiroshi Kawanabe ◽  
Hidemasa Kosaka ◽  
Masahiro Shioji
Keyword(s):  
Turbulent Mixing ◽  
Gas Flow ◽  
Air Entrainment ◽  
Mixing Process ◽  
Ambient Fluid ◽  
Turbulent Eddy ◽  
Large Eddy ◽  
Unsteady Jets ◽  
The Difference ◽  
Unsteady Jet

The flow and mixing process of unsteady jets are fundamentally analyzed by large eddy simulations. The effects of nozzle velocity and turbulence intensity on the turbulent eddy structure and mixing process between the nozzle fluid and ambient fluid were investigated. The results show that a toroidal-shaped vortex, which emerges around the jet tip, primarily accelerates the entraining flow. Furthermore, the difference of jet density affects the shape of toroidal vortex formed near jet tip and the air entrainment. Jet with lower density is less entrained and suppresses turbulent mixing.

scholarly journals Evaluation of a Humidified Nasal High-Flow Oxygen System, Using Oxygraphy, Capnography and Measurement of Upper Airway Pressures

2011 ◽  
Vol 39 (6) ◽  
pp. 1103-1110 ◽  
Author(s):  
J. E. Ritchie ◽  
A. B. Williams ◽  
C. Gerard ◽  
H. Hockey
Keyword(s):  
Healthy Volunteers ◽  
Airway Pressure ◽  
Gas Flow ◽  
Air Entrainment ◽  
High Flow ◽  
Positive Pressure ◽  
Mean Airway Pressure ◽  
Flow Rates ◽  
Oxygen Fraction ◽  
Airway Pressures

In this study, we evaluated the performance of a humidified nasal high-flow system (Optiflow™, Fisher and Paykel Healthcare) by measuring delivered FiO2 and airway pressures. Oxygraphy, capnography and measurement of airway pressures were performed through a hypopharyngeal catheter in healthy volunteers receiving Optiflow™ humidified nasal high flow therapy at rest and with exercise. The study was conducted in a non-clinical experimental setting. Ten healthy volunteers completed the study after giving informed written consent. Participants received a delivered oxygen fraction of 0.60 with gas flow rates of 10, 20, 30, 40 and 50 l/minute in random order. FiO2, FEO2, FECO2 and airway pressures were measured. Calculation of FiO2 from FEO2 and FECO2 was later performed. Calculated FiO2 approached 0.60 as gas flow rates increased above 30 l/minute during nose breathing at rest. High peak inspiratory flow rates with exercise were associated with increased air entrainment. Hypopharyngeal pressure increased with increasing delivered gas flow rate. At 50 l/minute the system delivered a mean airway pressure of up to 7.1 cmH2O. We believe that the high gas flow rates delivered by this system enable an accurate inspired oxygen fraction to be delivered. The positive mean airway pressure created by the high flow increases the efficacy of this system and may serve as a bridge to formal positive pressure systems.

Large Eddy Simulation of the fuel transport and mixing process in a scramjet combustor with rearwall-expansion cavity

2016 ◽  
Vol 126 ◽  
pp. 375-381 ◽  
Author(s):  
Zun Cai ◽  
Xiao Liu ◽  
Cheng Gong ◽  
Mingbo Sun ◽  
Zhenguo Wang ◽  
...  
Keyword(s):  
Large Eddy Simulation ◽  
Mixing Process ◽  
Eddy Simulation ◽  
Scramjet Combustor ◽  
Large Eddy ◽  
Transport And Mixing

Mixing Enhancement of Two Gases in a Microchannel Using DSMC

2013 ◽  
Vol 307 ◽  
pp. 166-169 ◽  
Author(s):  
Masoud Darbandi ◽  
Elyas Lakzian
Keyword(s):  
Gas Flow ◽  
Flow Analysis ◽  
Direct Simulation Monte Carlo ◽  
Equilibrium Composition ◽  
Mass Composition ◽  
Mixing Enhancement ◽  
Mixing Process ◽  
Result Section ◽  
Flow Through ◽  
Simulation Monte Carlo

Microgas flow analysis may not be performed accurately using the classical CFD methods because of encountering high Knudsen number regimes. Alternatively, the gas flow through micro-geometries can be investigated reliably using the direct simulation Monte Carlo (DSMC) method. Our concern in this paper is to use DSMC to study the mixing of two gases in a microchannel. The mixing process is assumed to be complete when the mass composition of each species deviates by no more than ±1% from its equilibrium composition. To enhance the mixing process, we focus on the effects of inlet-outlet pressure difference and the pressure ratios of the incoming CO and N2 streams on the mixing enhancement. The outcome of this study is suitably discussed in the result section.

LESbrary: A library of large eddy simulation data for the calibration and uncertainty quantification of ocean surface boundary layer turbulence parameterizations

2021 ◽  
Author(s):  
Gregory Wagner ◽  
Andre Souza ◽  
Adeline Hillier ◽  
Ali Ramadhan ◽  
Raffaele Ferrari
Keyword(s):  
Boundary Layer ◽  
Turbulent Mixing ◽  
Large Scale ◽  
Ocean Surface ◽  
Limited Area ◽  
Surface Boundary ◽  
Model Errors ◽  
Surface Boundary Layer ◽  
Large Eddy ◽  
Free Parameters

<p>Parameterizations of turbulent mixing in the ocean surface boundary layer (OSBL) are key Earth System Model (ESM) components that modulate the communication of heat and carbon between the atmosphere and ocean interior. OSBL turbulence parameterizations are formulated in terms of unknown free parameters estimated from observational or synthetic data. In this work we describe the development and use of a synthetic dataset called the “LESbrary” generated by a large number of idealized, high-fidelity, limited-area large eddy simulations (LES) of OSBL turbulent mixing. We describe how the LESbrary design leverages a detailed understanding of OSBL conditions derived from observations and large scale models to span the range of realistically diverse physical scenarios. The result is a diverse library of well-characterized “synthetic observations” that can be readily assimilated for the calibration of realistic OSBL parameterizations in isolation from other ESM model components. We apply LESbrary data to calibrate free parameters, develop prior estimates of parameter uncertainty, and evaluate model errors in two OSBL parameterizations for use in predictive ESMs.</p>

scholarly journals Inhomogeneous Mixing in Lagrangian Cloud Models: Effects on the Production of Precipitation Embryos

2018 ◽  
Vol 76 (1) ◽  
pp. 113-133 ◽  
Author(s):  
Fabian Hoffmann ◽  
Takanobu Yamaguchi ◽  
Graham Feingold
Keyword(s):  
Turbulent Mixing ◽  
Cloud Model ◽  
Small Scale ◽  
New Approach ◽  
Air Masses ◽  
Lagrangian Particles ◽  
Cloud Models ◽  
Large Eddy ◽  
Salutary Effect ◽  
Linear Eddy Model

Abstract Although small-scale turbulent mixing at cloud edge has substantial effects on the microphysics of clouds, most models do not represent these processes explicitly, or parameterize them rather crudely. This study presents a first use of the linear eddy model (LEM) to represent unresolved turbulent mixing at the subgrid scale (SGS) of large-eddy simulations (LESs) with a coupled Lagrangian cloud model (LCM). The method utilizes Lagrangian particles to provide the trajectory of air masses within LES grid boxes, while the LEM is used to redistribute these air masses among the Lagrangian particles based on the local features of turbulence, allowing for the appropriate representation of inhomogeneous to homogeneous SGS mixing. The new approach has the salutary effect of mitigating spurious supersaturations. At low turbulence intensities, as found in the early stages of an idealized bubble cloud simulation, cloud-edge SGS mixing tends to be inhomogeneous and the new approach is shown to be essential for the production of raindrop embryos. At higher turbulence intensities, as found in a field of shallow cumulus, SGS mixing tends to be more homogeneous and the new approach does not significantly alter the results, indicating that a grid spacing of 20 m may be sufficient to resolve all relevant scales of inhomogeneous mixing. In both cases, droplet in-cloud residence times are important for the production of precipitation embryos in the absence of small-scale inhomogeneous mixing, either naturally due to strong turbulence or artificially as a result of coarse resolution or by not using the LEM as an SGS model.

scholarly journals Implicit large eddy simulation of shock-driven material mixing

2013 ◽  
Vol 371 (2003) ◽  
pp. 20120217 ◽  
Author(s):  
F. F. Grinstein ◽  
A. A. Gowardhan ◽  
J. R. Ristorcelli
Keyword(s):  
Large Eddy Simulation ◽  
Turbulent Mixing ◽  
Initial Conditions ◽  
Spatial Scales ◽  
Late Time ◽  
Eddy Simulation ◽  
Geometrical Complexity ◽  
Planar Shock ◽  
Large Eddy ◽  
Implicit Large Eddy Simulation

Under-resolved computer simulations are typically unavoidable in practical turbulent flow applications exhibiting extreme geometrical complexity and a broad range of length and time scales. An important unsettled issue is whether filtered-out and subgrid spatial scales can significantly alter the evolution of resolved larger scales of motion and practical flow integral measures. Predictability issues in implicit large eddy simulation of under-resolved mixing of material scalars driven by under-resolved velocity fields and initial conditions are discussed in the context of shock-driven turbulent mixing. The particular focus is on effects of resolved spectral content and interfacial morphology of initial conditions on transitional and late-time turbulent mixing in the fundamental planar shock-tube configuration.

Sign in / Sign up

Export Citation Format

Share Document