scholarly journals SCARLET-1.0: SpheriCal Approximation for viRtuaL aggrEgaTes

2021 ◽  
Vol 14 (7) ◽  
pp. 4379-4400
Author(s):  
Eduardo Rossi ◽  
Costanza Bonadonna
Keyword(s):  
Turbulent Flows ◽  
Volcanic Ash ◽  
Spherical Approximation ◽  
Current Standard ◽  
Stl File ◽  
The Core ◽  
Final Porosity ◽  
Matlab Package ◽  
Centers Of Mass ◽  
Ash Aggregates

Abstract. Aggregation of particles occurs in a large variety of settings and is therefore the focus of many disciplines, e.g., Earth and environmental sciences, astronomy, meteorology, pharmacy, and the food industry. In particular, in volcanology, ash aggregation deeply influences the sedimentation of volcanic particles in the atmosphere during and after a volcanic eruption, affecting the accuracy of model predictions and the evaluation of hazard and risk assessments. It is thus very important to provide an exhaustive description of the outcome of an aggregation process, starting from its basic geometrical features such as the position in space of its components and the overall porosity of the final object. Here we present SCARLET-1.0, a MATLAB package specifically created to provide a 3D virtual reconstruction for volcanic ash aggregates generated in central collision processes. In centrally oriented collisions, aggregates build up their own structure around the first particle (the core), acting as a seed. This is appropriate for aggregates generated in turbulent flows in which particles show different degrees of coupling with respect to the turbulent eddies. SCARLET-1.0 belongs to the class of sphere-composite algorithms, a family of algorithms that approximate 3D complex shapes in terms of a set of sphere-composite nonoverlapping spheres. The conversion of a 3D surface to its equivalent sphere-composite structure then allows for an analytical detection of the intersections between different objects that aggregate together. Thus, provided a list of colliding sizes and shapes, SCARLET-1.0 places each element in the vector around the core, minimizing the distances between their centers of mass. The user can play with different parameters that control the minimization process. Among them the most important ones are the cone of investigation (Ω), the number of rays per cone (Nr), and the number of orientations of the object (No). All the 3D shapes are described using the Standard Triangulation Language (STL) format, which is the current standard for 3D printing. This is one of the key features of SCARLET-1.0, which results in an unlimited range of applications of the package. The main outcome of the code is the virtual representation of the object, its size, porosity, density, and the associated STL file. In addition, the object can be potentially 3D printed. As an example, SCARLET-1.0 has been applied here to the investigation of ellipsoid–ellipsoid collisions and to a more specific analysis of volcanic ash aggregation. In the first application we show that the final porosity of two colliding ellipsoids is less than 20 % if flatness and elongation are greater than or equal to 0.5. Higher values of porosities (up to 40 %–50 %) can instead be found for ellipsoids with needle-like or extremely flat shapes. In the second application, we reconstruct the evolution in time of the porosity of two different aggregates characterized by different inner structures. We find that aggregates whose population of particles is characterized by a narrow distribution of sizes tend to rapidly reach a plateau in the porosity. In addition, to reproduce the observed densities, almost no compaction is necessary in SCARLET-1.0, which is a result that suggests how ash aggregates are not well described in terms of the maximum packing condition.

scholarly journals SCARLET-1.0: SpheriCal Approximation for viRtuaL aggrEgaTes

2020 ◽  
Author(s):  
Eduardo Rossi ◽  
Costanza Bonadonna
Keyword(s):  
Spherical Approximation ◽  
Full Description ◽  
Stl File ◽  
The Core ◽  
Specific Analysis ◽  
Final Porosity ◽  
3D Printed ◽  
Matlab Package ◽  
Centers Of Mass ◽  
Basic Features

Abstract. Aggregation of particles occurs in a large variety of settings, and, therefore, it is the focus of many disciplines, e.g. Earth and environmental sciences, astronomy, meteorology, pharmacy, food industry. It is thus very important to provide a full description of the outcome of an aggregation process, starting from its basic features such as the position in space of its components and the overall porosity of the final object. We present SCARLET-1.0, a Matlab package specifically created to provide a 3D virtual reconstruction of aggregates in central oriented collisions that can be later 3D printed. With aggregates in central oriented collisions we refer to aggregates that build up their own structure around the first particle (the core) acting as a seed. SCARLET-1.0 belongs to the class of sphere-composite algorithms, a family of algorithms that approximate 3D complex shapes in terms of not-overlapping spheres. The conversion of a 3D surface in its equivalent spherical approximation allows an analytical computation of their intersections. Thus, provided a vector of sizes and shapes, SCARLET-1.0 places each element in the vector around the core minimizing the distances between their centers of mass. The user can play with three main parameters that are in charge of controlling the minimization process, namely the solid angle of the cone of investigation (Ω), the number of rays per cone (Nr), and the number of orientations of the object (No). All the 3D shapes are described using the STL format, the nowadays standard for 3D printing. This is one of the key features of SCARLET-1.0, which results in an unlimited range of application of the package. The main outcome of the code is the virtual representation of the object, its size, porosity, density and the associated STL file. As an example, here SCARLET-1.0 has been applied to the investigation of ellipsoid-ellipsoid collisions and to a more specific analysis of volcanic ash aggregation. In the first application we show that the final porosity of two colliding ellipsoids is less than 20 % if flatness and elongation are greater than or equal to 0.5. Higher values of porosities (up to 40–50 %) can be, instead, found for ellipsoids with needle-like or extremely flat shapes. In the second application, we reconstruct the evolution in time of the porosity of two different aggregates characterized by different inner structures. We find that aggregates whose population of particles is characterized by a narrow distribution of sizes tend to rapidly reach a plateau in the porosity. In addition, to reproduce the observed densities, almost no minimization is necessary in SCARLET-1.0; a result that suggests how these objects are quite far from the maximum packing condition often investigated in literature.

scholarly journals Simulation of Volcanic Ash Ingestion Into a Large Aero Engine: Particle–Fan Interactions

2018 ◽  
Vol 141 (1) ◽  
Author(s):  
Andreas Vogel ◽  
Adam J. Durant ◽  
Massimo Cassiani ◽  
Rory J. Clarkson ◽  
Michal Slaby ◽  
...  
Keyword(s):  
Particle Size ◽  
Stream Flow ◽  
Mass Concentration ◽  
Volcanic Ash ◽  
Particle Mass ◽  
Core Flow ◽  
Turbine Engine ◽  
The Core ◽  
Core Section ◽  
Particle Mass Concentration

Volcanic ash (VA) clouds in flight corridors present a significant threat to aircraft operations as VA particles can cause damage to gas turbine engine components that lead to a reduction of engine performance and compromise flight safety. In the last decade, research has mainly focused on processes such as erosion of compressor blades and static components caused by impinging ash particles as well as clogging and/or corrosion effects of soft or molten ash particles on hot section turbine airfoils and components. However, there is a lack of information on how the fan separates ingested VA particles from the core stream flow into the bypass flow and therefore influences the mass concentration inside the engine core section, which is most vulnerable and critical for safety. In this numerical simulation study, we investigated the VA particle–fan interactions and resulting reductions in particle mass concentrations entering the engine core section as a function of particle size, fan rotation rate, and for two different flight altitudes. For this, we used a high-bypass gas-turbine engine design, with representative intake, fan, spinner, and splitter geometries for numerical computational fluid dynamics (CFD) simulations including a Lagrangian particle-tracking algorithm. Our results reveal that particle–fan interactions redirect particles from the core stream flow into the bypass stream tube, which leads to a significant particle mass concentration reduction inside the engine core section. The results also show that the particle–fan interactions increase with increasing fan rotation rates and VA particle size. Depending on ingested VA size distributions, the particle mass inside the engine core flow can be up to 30% reduced compared to the incoming particle mass flow. The presented results enable future calculations of effective core flow exposure or dosages based on simulated or observed atmospheric VA particle size distribution, which is required to quantify engine failure mechanisms after exposure to VA. As an example, we applied our methodology to a recent aircraft encounter during the Mt. Kelud 2014 eruption. Based on ambient VA concentrations simulated with an atmospheric particle dispersion model (FLEXPART), we calculated the effective particle mass concentration inside the core stream flow along the actual flight track and compared it with the whole engine exposure.

scholarly journals Turbulent Flows Inside Pipes Equipped With Novel Perforated V-Shaped Rectangular Winglet Turbulators: Numerical Simulations

2020 ◽  
Vol 142 (11) ◽  
Author(s):  
M. Erfanian Nakhchi ◽  
M. T. Rahmati
Keyword(s):  
Turbulent Flows ◽  
Cfd Simulation ◽  
Vortex Generators ◽  
Fluid Mixing ◽  
Turbulent Model ◽  
Recirculating Flow ◽  
The Core ◽  
Turbulent Characteristics ◽  
Efficiency Parameter ◽  
Computational Fluid Dynamics Cfd

Abstract In this study, computational simulations have been performed to investigate the turbulent characteristics and energy consumption through heat exchanger tubes equipped by new perforated V-shaped rectangular winglet (PVRW) turbulators. The effects of the holes intensity on the velocity and temperature contours are additionally investigated. The Reynolds number, hole diameter ratio, and the number of holes selected are in the range of 5000 ≤ Re ≤ 18,000, 0 ≤ DR ≤ 0.40, and 0 ≤ N ≤ 14, respectively. Renormalization group (RNG) k–ε turbulent model which is a finite volume solver is utilized for the computational fluid dynamics (CFD) simulation. It was noticed that the proposed perforated turbulators could considerably intensify the thermal performance compared to typical VRW inserts. It is found that the recirculating flow generated by the PVRW augments the fluid mixing and transfers the heat from the pipe walls to the core of the tube. The simulations illustrate that the amount of heat transfer enhances 25.2% reducing the DR from 0.4 to 0.13 at Re = 18,000 and N = 14. Also, using PVRW turbulators with N = 7 and DR = 0.26 augments the average Nusselt number around 354.3% compared to the circular pipe without inserts. The highest thermal efficiency parameter of η = 2.25 could be obtained at Re = 5000 for the heat exchangers fitted by vortex generators with N = 14 and DR = 0.26.

Experimental and Numerical Mixing Studies Inside a Reactor Pressure Vessel

2003 ◽  
Author(s):  
T. Ho¨hne ◽  
S. Kliem ◽  
H.-M. Prasser ◽  
U. Rohde
Keyword(s):  
Turbulent Flows ◽  
High Performance ◽  
Transient Flow ◽  
Wire Mesh ◽  
Test Facility ◽  
Mixing Processes ◽  
Pressurized Water ◽  
Flow Measurements ◽  
The Core ◽  
Start Up

The work was aimed at the experimental investigation and numerical simulation of coolant mixing in the downcomer and the lower plenum of pressurized water reactors (PWR). For the investigation of the relevant mixing phenomena, the Rossendorf test facility ROCOM has been designed. ROCOM is a 1:5 scaled Plexiglas model of a German PWR allowing conductivity measurements by wire mesh sensors and velocity measurements by LDA technique. The CFD calculations were carried out with the CFD-code CFX-4. For the design of the facility, calculations were performed to analyze the scaling of the model. It was found, that the scaling of 1:5 to the prototype meets both: physical and economical demands. Flow measurements and the corresponding CFD calculations in the ROCOM downcomer under steady state conditions showed a Re number independency at nominal flow rates. The flow field is dominated by recirculation areas below the inlet nozzles. Transient flow measurements with high performance LDA-technique showed in agreement with CFX-4 results, that in the case of the start up of a pump after a laminar stage large vortices dominate the flow. In the case of stationary mixing, the maximum value of the averaged mixing scalar at the core inlet was found in the sector below the inlet nozzle, where the tracer was injected. At the start-up case of one pump due to a strong impulse driven flow at the inlet nozzle the horizontal part of the flow dominates in the downcomer. The injection is distributed into two main jets, the maximum of the tracer concentration at the core inlet appears at the opposite part of the loop where the tracer was injected. For turbulent flows the CFD-Code CFX-4 was validated and can be used in reactor safety analysis. Due to the good agreement between measured results and the corresponding CFD-calculation efficient modules for the coupling of thermal hydraulic computer codes with three-dimensional neutron-kinetic models using the results of this work can be developed. A better description of the mixing processes inside the RPV is the basis of a more realistic safety assessment.

scholarly journals Triggered formation and collapse of molecular cloud cores

2006 ◽  
Vol 2 (S237) ◽  
pp. 251-257
Author(s):  
Anthony P. Whitworth
Keyword(s):  
Mass Spectrum ◽  
Star Formation ◽  
Turbulent Flows ◽  
Molecular Cloud ◽  
External Pressure ◽  
Minimum Mass ◽  
Core Formation ◽  
Core Mass ◽  
The Core ◽  
Cloud Cores

AbstractFirst I discuss the dynamics of core formation in two scenarios relevant to triggered star formation, namely the fragmentation of shock-compressed layers created by colliding turbulent flows and the fragmentation of shells swept up by expanding nebulae. Second I discuss the influence of thermodynamics on the core mass spectrum, on determining which cores are ‘pre-stellar’ (i.e. destined to spawn stars) and on the minimum mass for a pre-stellar core. Third, I discuss the properties of pre-existing cores whose collapse has been triggered by an increase in external pressure, and compare the results with observations of collapsing pre-stellar cores and evaporating gaseous globules (EGGs).

scholarly journals Diversity of soluble salt concentrations on volcanic ash aggregates from a variety of eruption types and deposits

2019 ◽  
Vol 81 (7) ◽  
Author(s):  
Mathieu Colombier ◽  
Sebastian B. Mueller ◽  
Ulrich Kueppers ◽  
Bettina Scheu ◽  
Pierre Delmelle ◽  
...  
Keyword(s):  
Volcanic Ash ◽  
Soluble Salt ◽  
Ash Aggregates

scholarly journals Motion of the Core, and Its Influence on the Earth's Axis

1972 ◽  
Vol 48 ◽  
pp. 185-188
Author(s):  
Jose Mateo
Keyword(s):  
Gravitational Force ◽  
Slow Motion ◽  
The Core ◽  
Artificial Earth Satellites ◽  
The Earth ◽  
Accurate Knowledge ◽  
Secular Variations ◽  
Artificial Earth ◽  
Rotation Of The Earth ◽  
Centers Of Mass

After the advent of artificial Earth satellites, an accurate knowledge of the harmonic coefficients of the Earth's potential has enabled us to determine the size and shape of the Earth with extraordinary accuracy.The gravitational force between the core and the rest of the Earth, which makes both centers of mass tend to coincide, is so enormous that there is a strong possibility of a very slow motion of the core forcing its way into the mantle. It includes secular variations in both latitude and the time of rotation of the Earth.

Interaction of a vortex ring with a single bubble: bubble and vorticity dynamics

2015 ◽  
Vol 773 ◽  
pp. 460-497 ◽  
Author(s):  
Narsing K. Jha ◽  
R. N. Govardhan
Keyword(s):  
Vortex Ring ◽  
Turbulent Flows ◽  
Vortex Core ◽  
Bubble Diameter ◽  
Single Bubble ◽  
Base Case ◽  
Single Vortex ◽  
The Core ◽  
Vorticity Dynamics ◽  
Convection Speed

The interaction of a single bubble with a single vortex ring in water has been studied experimentally. Measurements of both the bubble dynamics and vorticity dynamics have been done to help understand the two-way coupled problem. The circulation strength of the vortex ring (${\it\Gamma}$) has been systematically varied, while keeping the bubble diameter ($D_{b}$) constant, with the bubble volume to vortex core volume ratio ($V_{R}$) also kept fixed at about 0.1. The other important parameter in the problem is a Weber number based on the vortex ring strength $(\mathit{We}=0.87{\it\rho}({\it\Gamma}/2{\rm\pi}a)^{2}/({\it\sigma}/D_{b});a=\text{vortex core radius},{\it\sigma}=\text{surface tension})$, which is varied over a large range, $\mathit{We}=3{-}406$. The interaction between the bubble and ring for each of the $\mathit{We}$ cases broadly falls into four stages. Stage I is before capture of the bubble by the ring where the bubble is drawn into the low-pressure vortex core, while in stage II the bubble is stretched in the azimuthal direction within the ring and gradually broken up into a number of smaller bubbles. Following this, in stage III the bubble break-up is complete and the resulting smaller bubbles slowly move around the core, and finally in stage IV the bubbles escape. Apart from the effect of the ring on the bubble, the bubble is also shown to significantly affect the vortex ring, especially at low $\mathit{We}$ ($\mathit{We}\sim 3$). In these low-$\mathit{We}$ cases, the convection speed drops significantly compared to the base case without a bubble, while the core appears to fragment with a resultant large decrease in enstrophy by about 50 %. In the higher-$\mathit{We}$ cases ($\mathit{We}>100$), there are some differences in convection speed and enstrophy, but the effects are relatively small. The most dramatic effects of the bubble on the ring are found for thicker core rings at low $\mathit{We}$ ($\mathit{We}\sim 3$) with the vortex ring almost stopping after interacting with the bubble, and the core fragmenting into two parts. The present idealized experiments exhibit many phenomena also seen in bubbly turbulent flows such as reduction in enstrophy, suppression of structures, enhancement of energy at small scales and reduction in energy at large scales. These similarities suggest that results from the present experiments can be helpful in better understanding interactions of bubbles with eddies in turbulent flows.

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