Discordance of Tracer Transport and Particulate Matter Fate in a Baffled Clarification System

2021 ◽  
Vol 143 (5) ◽  
Author(s):  
Haochen Li ◽  
S. Balachandar ◽  
John Sansalone
Keyword(s):  
Particulate Matter ◽  
Residence Time ◽  
Tracer Transport ◽  
Mean Flow ◽  
Eddy Simulation ◽  
Complex Interactions ◽  
Unit Operations ◽  
Physical Laboratory ◽  
High Turbulence ◽  
A Site

Abstract Large eddy simulation (LES) and coupled physical laboratory-scale modeling are performed to elucidate tracer transport and particulate matter (PM) fate in a baffled clarification system. Such baffled systems are common for urban water unit operations and processes. Flow hydrodynamic indices of these systems such as short-circuiting are often examined with measurement of inert tracer transport as a surrogate for chemical or PM transport and fate. Results of this study illustrate complex interactions between turbulent flow, tracer, and various PM diameters at the system scale. PM preferential accumulation and the discordance of PM transport with respect to flow hydrodynamics are observed based on the modeling results; otherwise not practical with physical model testing. Results demonstrate that baffling can promote system tracer mixing and improve volumetric utilization by extending the mean flow path through flow separation and bifurcation. The baffle tested produced high turbulence kinetic energy near the sedimentation floor and reduced PM separation (clarification) as compared to the unbaffled system used as a control. The unbaffled system in this study yields the highest PM separation, even though significant short-circuiting occurs during the residence time distribution (RTD) of the tracer. Further analysis demonstrates the mechanistic difference between the tracer transport and the finer suspended PM as compared to larger settleable and sediment PM diameters. Results illustrate that the tracer RTD, residence time (RT) and hydraulic efficiency indices are not reliable surrogates for PM or PM-bound chemical/pathogen separation. In addition, simulations suggest a site, system or condition-specific design approach given the coupled dependence on flow and design geometry.

scholarly journals A novel technique for residence time distribution (RTD) measurements in solids unit operations

2021 ◽  
Vol 32 (2) ◽  
pp. 611-618
Author(s):  
Atena Dehghani Kiadehi ◽  
Mikel Leturia ◽  
Franco Otaola ◽  
Aissa Ould-Dris ◽  
Khashayar Saleh
Keyword(s):  
Residence Time ◽  
Time Distribution ◽  
Residence Time Distribution ◽  
Novel Technique ◽  
Unit Operations

scholarly journals Large Eddy Simulation of Flow and Tracer Transport in Multichamber Ozone Contactors

2010 ◽  
Vol 136 (1) ◽  
pp. 22-31 ◽  
Author(s):  
Dongjin Kim ◽  
Doo-Il Kim ◽  
Jae-Hong Kim ◽  
Thorsten Stoesser
Keyword(s):  
Large Eddy Simulation ◽  
Tracer Transport ◽  
Eddy Simulation ◽  
Large Eddy

RANS and Large Eddy Simulation of Internal Combustion Engine Flows—A Comparative Study

2014 ◽  
Vol 136 (5) ◽  
Author(s):  
Xiaofeng Yang ◽  
Saurabh Gupta ◽  
Tang-Wei Kuo ◽  
Venkatesh Gopalakrishnan
Keyword(s):  
Large Eddy Simulation ◽  
High Speed ◽  
Combustion Engine ◽  
Flow Analysis ◽  
Partial Geometry ◽  
Computational Domain ◽  
Mean Flow ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Rans Simulations

A comparative cold flow analysis between Reynolds-averaged Navier–Stokes (RANS) and large eddy simulation (LES) cycle-averaged velocity and turbulence predictions is carried out for a single cylinder engine with a transparent combustion chamber (TCC) under motored conditions using high-speed particle image velocimetry (PIV) measurements as the reference data. Simulations are done using a commercial computationally fluid dynamics (CFD) code CONVERGE with the implementation of standard k-ε and RNG k-ε turbulent models for RANS and a one-equation eddy viscosity model for LES. The following aspects are analyzed in this study: The effects of computational domain geometry (with or without intake and exhaust plenums) on mean flow and turbulence predictions for both LES and RANS simulations. And comparison of LES versus RANS simulations in terms of their capability to predict mean flow and turbulence. Both RANS and LES full and partial geometry simulations are able to capture the overall mean flow trends qualitatively; but the intake jet structure, velocity magnitudes, turbulence magnitudes, and its distribution are more accurately predicted by LES full geometry simulations. The guideline therefore for CFD engineers is that RANS partial geometry simulations (computationally least expensive) with a RNG k-ε turbulent model and one cycle or more are good enough for capturing overall qualitative flow trends for the engineering applications. However, if one is interested in getting reasonably accurate estimates of velocity magnitudes, flow structures, turbulence magnitudes, and its distribution, they must resort to LES simulations. Furthermore, to get the most accurate turbulence distributions, one must consider running LES full geometry simulations.

Analysis of Autoignition Chemistry in Aeroderivative Premixers At Engine Conditions

2021 ◽  
Author(s):  
Sandeep Jella ◽  
Gilles Bourque ◽  
Pierre Gauthier ◽  
Philippe Versailles ◽  
Jeffrey M. Bergthorson ◽  
...  
Keyword(s):  
Residence Time ◽  
Real Life ◽  
Precursor Chemistry ◽  
Mode Analysis ◽  
Safety Factors ◽  
Eddy Simulation ◽  
Reduced Mechanism ◽  
Short Period ◽  
Large Eddy ◽  
Pure Methane

Abstract The minimization of autoignition risk is critical to premixer design. Safety factors based on ignition delays of homogeneous mixtures, are generally used to guide the choice of a residence time for a given premixer. However, autoignition chemistry at aeroderivative conditions is fast (0.5-2 milliseconds) and can be initiated within typical premixer residence times. The analysis of what takes place in this short period involves the study of low-temperature precursor chemistry. By coupling the evolution of the Chemical Explosive Modes to turbulence, it is possible to obtain a measure of spatial autoignition risk where both chemical (e.g. ignition delay) and aerodynamic (e.g. local residence time) influences are unified. In this article, we describe a method that couples Large Eddy Simulation to newly developed, reduced autoignition chemical kinetics to study autoignition precursors in an example premixer representative of real life geometric complexity. A blend of pure methane and dimethyl ether (DME), a common fuel used for experimental autoignition studies, was transported using the reduced mechanism (38 species / 238 reactions) at engine conditions at increasing levels of DME concentration until exothermic autoignition kernels were formed. The Chemical Explosive Mode analysis closely follows the large thermochemical changes in the premixer as a function of DME concentration and identifies where the premixer is sensitive and flame anchoring is likely to occur.

Loss Predictions in the High-Pressure Film-Cooled Turbine Vane of the FACTOR Project by Mean of Wall-Modeled Large Eddy Simulation

2020 ◽  
Author(s):  
Mael Harnieh ◽  
Nicolas Odier ◽  
Jérôme Dombard ◽  
Florent Duchaine ◽  
Laurent Gicquel
Keyword(s):  
Spatial Distribution ◽  
Large Eddy Simulation ◽  
Film Cooling ◽  
Total Pressure ◽  
Mean Flow ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Turbine Vane

Abstract The use of numerical simulations to design and optimize turbine vane cooling requires precise prediction of the fluid mechanics and film cooling effectiveness. This results in the need to numerically identify and assess the various origins of the losses taking place in such systems and if possible in engine representative conditions. Large-Eddy Simulation (LES) has shown recently its ability to predict turbomachinery flows in well mastered academic cases such as compressor or turbine cascades. When it comes to industrial representative configurations, the geometrical complexities, high Reynolds and Mach numbers as well as boundary condition setup lead to an important increase of CPU cost of the simulations. To evaluate the capacity of LES to predict film cooling effectiveness as well as to investigate the loss generation mechanisms in a turbine vane in engine representative conditions, a wall-modeled LES of the FACTOR film-cooled nozzle is performed. After the comparison of integrated values to validate the operating point of the vanes, the mean flow structure is investigated. In the coolant film, a strong turbulent mixing process between coolant and hot flows is observed. As a result, the spatial distribution of time-averaged vane surface temperature is highly heterogeneous. Comparisons with the experiment show that the LES prediction fairly reproduces the spatial distribution of the adiabatic film effectiveness. The loss generation in the configuration is then investigated. To do so, two methodologies, i.e, performing balance of total pressure in the vanes wakes as mainly used in the literature and Second Law Analysis (SLA) are evaluated. Balance of total pressure without the contribution of thermal effects only highlights the losses generated by the wakes and secondary flows. To overcome this limitation, SLA is adopted by investigating loss maps. Thanks to this approach, mixing losses are shown to dominate in the coolant film while aerodynamic losses dominate in the coolant pipe region.

scholarly journals Mapping landscape connectivity as a driver of species richness under tectonic and climatic forcing

2019 ◽  
Vol 7 (4) ◽  
pp. 895-910 ◽  
Author(s):  
Tristan Salles ◽  
Patrice Rey ◽  
Enrico Bertuzzo
Keyword(s):  
Species Richness ◽  
Landscape Connectivity ◽  
Tectonic Activity ◽  
Climatic Forcing ◽  
Mountainous Regions ◽  
Local Species Richness ◽  
Complex Interactions ◽  
Local Species ◽  
Elevational Range ◽  
A Site

Abstract. Species distribution and richness ultimately result from complex interactions between biological, physical, and environmental factors. It has been recently shown for a static natural landscape that the elevational connectivity, which measures the proximity of a site to others with similar habitats, is a key physical driver of local species richness. Here we examine changes in elevational connectivity during mountain building using a landscape evolution model. We find that under uniform tectonic and variable climatic forcing, connectivity peaks at mid-elevations when the landscape reaches its geomorphic steady state and that the orographic effect on geomorphic evolution tends to favour lower connectivity on leeward-facing catchments. Statistical comparisons between connectivity distribution and results from a metacommunity model confirm that to the 1st order, landscape elevation connectivity explains species richness in simulated mountainous regions. Our results also predict that low-connectivity areas which favour isolation, a driver for in situ speciation, are distributed across the entire elevational range for simulated orogenic cycles. Adjustments of catchment morphology after the cessation of tectonic activity should reduce speciation by decreasing the number of isolated regions.

scholarly journals A Design for Vortex Suppression Downstream of a Submerged Gate

Water ◽  
2020 ◽  
Vol 12 (3) ◽  
pp. 750
Author(s):  
Ender Demirel ◽  
Mustafa M. Aral
Keyword(s):  
Internal Flow ◽  
Vortex Pair ◽  
Horseshoe Vortex ◽  
Vortex Structures ◽  
Downstream Face ◽  
Mean Flow ◽  
Mean Velocity ◽  
Eddy Simulation ◽  
Drag Forces ◽  
The Stability

Interaction of recirculating and mean flow downstream of a submerged gate may form significant vortex structures, which may affect the stability of the gate. Although these flow structures that appear in submerged hydraulic jumps received considerable attention in the literature, relatively less work was devoted to the analysis and suppression of the vortex structures downstream of a submerged gate. In this work, internal flow structure and vortex dynamics around a submerged gate were investigated through laboratory tests and large-eddy simulation (LES) using computational fluid dynamics (CFD). It is shown that numerical results obtained for mean velocity field are in good agreement with the experimental measurements. A helical vortex pair connected with a horseshoe vortex system was identified within the roller region using high-resolution numerical simulations. Damping performance of different types of anti-vortex elements placed on the downstream face of the gate are evaluated based on numerical studies. It is shown that the horizontal porous baffle mounted at an elevation below the free surface reduced the vortex magnitudes in the roller region by 26.8%. With the implementation of the proposed vortex breaker, lift forces acting on the gate lip were reduced by 9.4% and drag forces acting on the downstream face of the gate were reduced by 8.6%. Finally, in this study, we assess the performance of the vortex breaker under different flow conditions.

scholarly journals Flow visualization using momentum and energy transport tubes and applications to turbulent flow in wind farms

2013 ◽  
Vol 715 ◽  
pp. 335-358 ◽  
Author(s):  
Johan Meyers ◽  
Charles Meneveau
Keyword(s):  
Turbulent Flow ◽  
Flow Visualization ◽  
Energy Transport ◽  
Three Dimensional ◽  
Wind Farms ◽  
Mean Flow ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Using Data ◽  
Large Wind

AbstractAs a generalization of the mass–flux based classical stream tube, the concept of momentum and energy transport tubes is discussed as a flow visualization tool. These transport tubes have the property that no fluxes of momentum or energy exist over their respective tube mantles. As an example application using data from large eddy simulation, such tubes are visualized for the mean-flow structure of turbulent flow in large wind farms, in fully developed wind-turbine-array boundary layers. The three-dimensional organization of energy transport tubes changes considerably when turbine spacings are varied, enabling the visualization of the path taken by the kinetic energy flux that is ultimately available at any given turbine within the array.

A Dynamic Time Filtering Technique for Hybrid RANS-LES Simulation of Non-Stationary Turbulent Flow

2019 ◽  
Author(s):  
Tausif Jamal ◽  
D. Keith Walters
Keyword(s):  
Large Eddy Simulation ◽  
Comprehensive Evaluation ◽  
Model Performance ◽  
Turbulence Models ◽  
Mean Flow ◽  
Complex Flow ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Filtering Technique ◽  
Dynamic Time

Abstract Unsteady turbulent wall bounded flows can produce complex flow physics including temporally varying mean pressure gradients, intermittent regions of high turbulence intensity, and interaction of different scales of motion. As a representative example, pulsating channel flow presents significant challenges for newly developed and existing turbulence models in computational fluid dynamics (CFD) simulations. The present study investigates the performance of the Dynamic Hybrid RANS-LES (DHRL) model with a newly proposed dynamic time filtering (DTF) technique, compared against an industry standard Reynolds-Averaged Navier-Stokes (RANS) model, Monotonically Integrated Large Eddy Simulation (MILES), and two conventional Hybrid RANS-LES (HRL) models. Model performance is evaluated based on comparison to previously documented Large Eddy Simulation (LES) results. Simulations are performed for a fully developed flow in a channel with time-periodic driving pressure gradient. Results highlight the relative merits of each model type and indicate that the use of a dynamic time filtering technique improves the accuracy of the DHRL model when compared to a static time filtering technique. A comprehensive evaluation of the results suggests that the DHRL-DTF method provides the most consistently accurate reproduction of the time-dependent mean flow characteristics for all models investigated.

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