Significance of Vocal Tract Geometrical Variations and Loudness on Airflow and Droplet Dispersion in a Two-Dimensional Representation of [F]

2021 ◽  
Author(s):  
Amir A. Mofakham ◽  
Brian T. Helenbrook ◽  
Tanvir Ahmed ◽  
Byron D. Erath ◽  
Andrea R. Ferro ◽  
...  
Keyword(s):  
Vocal Tract ◽  
Two Dimensional ◽  
Discrete Phase Model ◽  
Ansys Fluent ◽  
Lower Lip ◽  
Large Size ◽  
Discrete Phase ◽  
Respiratory Droplets ◽  
Droplet Transmission ◽  
Shed Light

Abstract The significance of respiratory droplet transmission in spreading respiratory diseases such as COVID-19 has been identified by researchers. Although one cough or sneeze generates a large number of respiratory droplets, they are usually infrequent. In comparison, speaking and singing generate fewer droplets, but occur much more often, highlighting their potential as a vector for airborne transmission. However, the flow dynamics of speech and the transmission of speech droplets have not been fully investigated. To shed light on this topic, two-dimensional geometries of a vocal tract for a labiodental fricative [f] were generated based on real-time MRI of a subject during pronouncing [f]. In these models, two different curvatures were considered for the tip tongue shape and the lower lip to highlight the effects of the articulator geometries on transmission dynamics. The commercial ANSYS-Fluent CFD software was used to solve the complex expiratory speech airflow trajectories. Simultaneously, the discrete phase model of the software was used to track submicron and large size respiratory droplets exhaled during [f] utterance. The simulations were performed for high, normal, and low lung pressures to explore the influence of loud, normal, and soft utterances, respectively, on the airflow dynamics. The presented results demonstrate the variability of the airflow and droplet propagation as a function of the vocal tract geometrical characteristics and loudness.

Enhancing Turbine Deposition Prediction Capability With Conjugate Mesh Morphing

2021 ◽  
Author(s):  
Christopher P. Bowen ◽  
Jeffrey P. Bons
Keyword(s):  
Effective Conductivity ◽  
Road Dust ◽  
Discrete Phase Model ◽  
Ansys Fluent ◽  
Mesh Morphing ◽  
Average Flow Velocity ◽  
Impingement Jet ◽  
Discrete Phase ◽  
The Ohio State University ◽  
Original Metal

Abstract A framework for performing mesh morphing in a conjugate simulation in the commercial Computational Fluid Dynamics (CFD) software ANSYS Fluent is presented and validated. A procedure for morphing both the fluid and solid domains to simulate the protrusion of deposit into the fluid while concurrently altering and adding to the solid regions is detailed. The ability to delineate between the original metal sections of the solid and the morphed regions which represent deposit characteristics is demonstrated. The validity and predictive capability of the process is tested through simulation of a canonical impingement jet. A single over-sized impingement jet (6.35 mm) at 894 K and an average flow velocity of 56.5 m/s is used to heat a nickel-alloy target plate. One gram of 0-5 μm Arizona Road Dust (ARD) is delivered to the target and a Particle Shadow Velocimetry (PSV) technique is used to capture the transient growth of the deposit structure on the target. Thermal infrared images are taken on the backside of the target and synchronized with the PSV images. The experiment is modeled computationally using the Fluent Discrete Phase Model (DPM) and the Ohio State University (OSU) Deposition Model for sticking prediction. The target is morphed according to the particulate volume prediction. The deposit regions are assigned an effective conductivity (keff) representative of porous deposit, and the fluid and thermal computations are reconverged. 10 mesh morphing iterations are performed accounting for the first half of the experiment. The morphed deposit volume and height are compared to the experiment and show reasonable agreement. The backside target temperatures are also compared, and the simulations show the ability to predict the reduction in temperature that occurs as the growing deposit insulates the metal surface. It is demonstrated that the assignment of unique thermal conductivities to the deposit and metal cells within the solid is critical. With a more robust and accurate implementation of the deposit keff, this conjugate mesh morphing framework shows potential as a tool for predicting the thermal impact of deposition.

Assessment of an Eulerian multi-fluid VOF model for simulation of multiphase flow in an industrial Ruhrstahl–Heraeus degasser

2019 ◽  
Vol 116 (6) ◽  
pp. 617
Author(s):  
Gujun Chen ◽  
Qiangqiang Wang ◽  
Shengping He
Keyword(s):  
Multiphase Flow ◽  
Molten Steel ◽  
Mixing Time ◽  
Interface Tracking ◽  
Discrete Phase Model ◽  
Eulerian Model ◽  
Ansys Fluent ◽  
Vof Model ◽  
Discrete Phase ◽  
Sharp Interfaces

An Eulerian multi-fluid VOF model, the coupling of the Eulerian model and the “VOF” interface tracking method, offered by ANSYS Fluent has been first applied to investigate the complex multiphase flow in an industrial Ruhrstahl–Heraeus (RH) degasser. The idea of this study is to use the Eulerian model in the regions of the domain where the argon bubbles are dispersed in molten steel; in the regions of the domain where the sharp interfaces between the steel and slag or argon are of interest, the “VOF” method is adopted. The calculated flow characteristic, mixing time and circulation flow rate of molten steel in the RH degasser agree well with the observations reported in literature. Compared with the widely accepted Eulerian method and the discrete phase model–volume of fluid (DPM–VOF) coupled method, the Eulerian multi-fluid VOF model demonstrates the suitability for modeling the multiphase flow in the RH degasser where both dispersed and sharp interfaces are present.

On Scouring Efficiency of Flush Waves in Sewers: A Numerical and Experimental Study

2019 ◽  
Author(s):  
Maryam Alihosseini ◽  
Paul Uwe Thamsen
Keyword(s):  
Sediment Transport ◽  
Multiphase Model ◽  
Discrete Phase Model ◽  
Sluice Gate ◽  
Ansys Fluent ◽  
Sediment Bed ◽  
Complex Process ◽  
Discrete Phase ◽  
Sand And Gravel ◽  
The Waves

Abstract In sewer sediment management, the removal of depositions using hydraulic flushing gates has recently gotten great attention. Despite numerous investigations, the complex process of sediment transport under flushing waves is not yet well understood. The present work aims to calibrate and validate a coupled computational fluid dynamics and discrete element method (CFD-DEM) to study the fluid-sediment interaction in sewers. The CFD part of the simulation was carried out in the software Ansys Fluent which is two-way coupled to the DEM software EDEM. The multiphase model volume of fluid (VOF) was used to simulate the flushing wave, while the sediments were handled as DEM particles using the discrete phase model (DPM). To validate the 3D model, experimental work has been performed in a circular laboratory pipe with sand and gravel of different size distributions. A construction of a sluice gate was installed to realize the flushing event, which is similar to a dam-break wave. The evolution of the sediment bed and the scouring efficiency of the waves were examined under different flushing conditions. The results showed that the CFD-DEM method could be used to investigate the performance of flushing devices and various features of sediment transport which are not easy to obtain in the laboratory or field.

scholarly journals Experimental validation of CFD simulations of bioaerosol movement in a mechanically ventilated airspace

2019 ◽  
pp. 5.01-5.14
Author(s):  
Amy La ◽  
Qiang Zhang
Keyword(s):  
Steady State ◽  
Mesh Size ◽  
Respiratory Syndrome Virus ◽  
Discrete Phase Model ◽  
Cfd Simulations ◽  
Ansys Fluent ◽  
Mechanically Ventilated ◽  
Discrete Phase ◽  
Optimal Mesh ◽  
Ventilation Rates

A CFD (computational fluid dynamics) model was developed to simulate the movement of bioaerosols in mechanically-ventilated chambers and the results were validated with experiments. Liquid aerosols containing Porcine Reproductive and Respiratory Syndrome Virus (PRRSV) were artificially generated in the chambers. Bioaerosol concentration was monitored with an optical particle counter until steady-state conditions were achieved (aerosols containing viruses are referred to as bioaerosols in this paper). Four treatments with two ventilation rates and two bioaerosol generation rates were tested. The standard k-ɛ turbulence model and a discrete phase model with unsteady tracking was used in an ANSYS Fluent CFD model to simulate the airflow and bioaerosol movement until steady-state was reached. A mesh refinement test was performed to select an optimal mesh size for simulations. The CFD simulations showed good agreement with the measured bioaerosol concentrations at steady-state with differences of 2% to 8%, normalized mean square error of 0.01 to 0.19, and fractional bias of 0.02 to 0.08. Simulations and validation during the transient phase could not be verified because of limited measurement locations.

scholarly journals The Operation of a Three-Bladed Horizontal Axis Wind Turbine under Hailstorm Conditions—A Computational Study Focused on Aerodynamic Performance

Inventions ◽  
2021 ◽  
Vol 7 (1) ◽  
pp. 2
Author(s):  
Dimitra Douvi ◽  
Eleni Douvi ◽  
Dionissios P. Margaris
Keyword(s):  
Wind Turbine ◽  
Cross Sections ◽  
Computational Study ◽  
Three Dimensional ◽  
Aerodynamic Performance ◽  
Horizontal Axis ◽  
Discrete Phase Model ◽  
Horizontal Axis Wind Turbine ◽  
Ansys Fluent ◽  
Discrete Phase

The aim of this study is the aerodynamic degradation of a three-bladed Horizontal Axis Wind Turbine (HAWT) under the influence of a hailstorm. The importance and originality of this study are that it explores the aerodynamic performance of an optimum wind turbine blade during a hailstorm, when hailstones and raindrops are present. The commercial Computational Fluid Dynamics (CFD) code ANSYS Fluent 16.0 was utilized for the simulation. The first step was the calculation of the optimum blade geometry characteristics for a three-bladed rotor, i.e., twist and chord length along the blade, by a user-friendly application. Afterwards, the three-dimensional blade and the flow field domain were designed and meshed appropriately. The rotary motion of the blades was accomplished by the application of the Moving Reference Frame Model and the simulation of hailstorm conditions by the Discrete Phase Model. The SST k–ω turbulence model was also added. The produced power of the wind turbine, operating in various environmental conditions, was estimated and discussed. Contours of pressure, hailstone and raindrop concentration and erosion rate, on both sides of the blade, are presented. Moreover, contours of velocity at various cross sections parallel to the rotor are demonstrated, to understand the effect of hailstorms on the wake behavior. The results suggest that the aerodynamic performance of a HAWT degrades due to impact and breakup of the particles on the blade.

scholarly journals Numerical simulation of liquid fuel prechamber ignition

2021 ◽  
Author(s):  
Levon Larson
Keyword(s):  
Turbulence Modeling ◽  
Spray Angle ◽  
Navier Stokes ◽  
Discrete Phase Model ◽  
Lean Burn ◽  
Penetration Length ◽  
Ansys Fluent ◽  
Eddy Simulation ◽  
Discrete Phase ◽  
Rans Models

A Computational Fluid Dynamics (CFD) model was built that simulates the transient, compressible, reacting, multi-phase environment that exists within a reciprocating engine's combustion chamber(s). ANSYS Fluent v13.0 was used with the Euler-Lagrangian Discrete Phase Model (DPM), the Shell autoignition model, and the Large Eddy Simulation (LES) method of turbulence modeling. Validation of the spray dynamics was performed by comparing simulation results with experiments of liquid and vapour penetration length of an n-Heptane spray experiment done by Sandia National Laboratories. It was found that LES produced more accurate results than several Reynolds Averaged Navier-Stokes (RANS) models. The Shell autoignition model was coded to function with C10.17H19.91 and compared with experimental ignition results in a Rapid Compression Machine (RCM) environment. All of the above models were then combined to simulate a directly-fueled lean-burn combustion prechamber configuration wherein the effects of spray angle, timing, and duration were studied.

scholarly journals Two-Dimensional Analysis Of Flow Field And Associated Scour Parameters At Downstream Of Weir With And Without Sloping Apron

2019 ◽  
Vol 8 (6) ◽  
pp. 1027-1036
Keyword(s):  
Flow Structure ◽  
Particle Tracking ◽  
Control Structure ◽  
Model Simulation ◽  
Maximum Velocity ◽  
Discrete Phase Model ◽  
Eulerian Model ◽  
Ansys Fluent ◽  
Flow Features ◽  
Discrete Phase

The downstream scour of the control structure is a more common and very complex issue in river engineering. Flow structure in the vicinity of the control structure is entirely different from other parts of the river. Ansys Fluent Multiphase Eulerian model combined with hybrid Dense Discrete Phase Model (DDPM) provides much accurate and precise view of flow structure. This model provides a better understanding of flow structure, and it is associated scour development at upstream and downstream. Model simulation is performed on the trapezoidal weir and trapezoidal weir with sloping apron platforms to compare the flow structure, and it is associated scour. The erosion is computed by Mc Laury erosion model, and particle tracking is done using DDPM through a Lagrangian approach stimulate the movement of particles within the flow domain, velocity and other properties. This research focused on delivering much better anticipation about all flow features and sediment particle tracking captured in a closer manner. In this analysis with the trapezoidal weir, the velocity reached around 0.835 ms -1. However, as in the case of trapezoidal weir with sloping apron, the maximum velocity goes approximately 0.505 ms-1 which are nearly equal to inlet velocity. From the analysis, the sloping apron proves to be significant in protecting the downstream side of the control structure

scholarly journals High Concentration Fine Particle Separation Performance in Hydrocyclones

Minerals ◽  
2021 ◽  
Vol 11 (3) ◽  
pp. 307
Author(s):  
Yuekan Zhang ◽  
Meng Yang ◽  
Lanyue Jiang ◽  
Hui Wang ◽  
Jinguang Xu ◽  
...  
Keyword(s):  
Particle Size ◽  
Fine Particle ◽  
Fine Particles ◽  
Volume Fraction ◽  
Separation Performance ◽  
Centrifugal Separation ◽  
Discrete Phase Model ◽  
High Concentration ◽  
Ansys Fluent ◽  
Discrete Phase

The vast majority of current research on hydrocyclone field centrifugal separation focuses on low concentration fluids having volume fraction less than 3%. For high-concentration fluids having volume fractions greater than 10%, which are often encountered in engineering, the law governing particle motion and the classification mechanism are still unclear. In order to gain insights into the interaction between fine particles in the high concentration hydrocyclone field and to improve the hydrocyclone separation performance of these particles, a Dense Discrete Phase Model (DDPM) of the Euler-Eulerian method under the Ansys Fluent 14.5 software was employed. Numerical simulations were carried out to study the characteristics of the hydrocyclone field of dense particles and the influence of parameters, such as the diameter of the overflow outlet, diameter of the underflow outlet, and material concentration, on separation performance. The trajectories and separation efficiencies of two kinds of fine particles with different densities and six different particle sizes at high concentration were obtained. The results show that for the hydrocyclone classification of high-concentration fine particles, particles with large density and small particle size are more likely to enter the internal cyclone and discharge from the overflow. Particles with small density and large particle size are more likely to enter the external cyclone and discharge from the underflow. The research results of this topic could provide a feasible reference and theoretical basis for the centrifugal separation of high-concentration fine particle fluid.

scholarly journals Numerical Analysis of RTD Curves and Inclusions Removal in a Multi-Strand Asymmetric Tundish with Different Configuration of Impact Pad

Metals ◽  
2020 ◽  
Vol 10 (7) ◽  
pp. 849
Author(s):  
Markéta Tkadlečková ◽  
Josef Walek ◽  
Karel Michalek ◽  
Tomáš Huczala
Keyword(s):  
Dead Volume ◽  
Discrete Phase Model ◽  
Inclusion Removal ◽  
Ansys Fluent ◽  
Assembly Method ◽  
Cut Cell ◽  
Computational Mesh ◽  
Discrete Phase ◽  
Steel Flow ◽  
The Impact

To effectively remove non-metallic inclusions from the steel during the flowing in a five-strand asymmetric tundish, the novel configuration of the impact pad was developed. For analysis, complex numerical modelling in the programme ANSYS Fluent was used. The Lagrangian Discrete Phase Model of inclusion tracking was applied. The distribution of inclusions, with sizes ranging from 2 µm to 100 µm and density from 2500 to 3500 kg·m−3, was considered only through the shroud tube. The residence time distribution (RTD) curves and inclusion removal efficiency were used for evaluation of steady state steel flow character depending on internal configuration of a tundish with an impact pad in two design modifications (Modification 1—M1, Modification 2—M2). The preliminary results showed that in the case of asymmetric geometry plays a role the computational mesh independency. The assembly method with cut cell approach was satisfactory even when the tundish geometry was changed. The RTD curves with an M1 showed a huge dead volume in the tundish. In the case with an M2, the RTD curves are more or less uniform for all casting strands, and the removal of inclusions to slag increased from about 55% up to 70% in comparison with M1.

scholarly journals Numerical simulation of liquid fuel prechamber ignition

2021 ◽  
Author(s):  
Levon Larson
Keyword(s):  
Turbulence Modeling ◽  
Spray Angle ◽  
Navier Stokes ◽  
Discrete Phase Model ◽  
Lean Burn ◽  
Penetration Length ◽  
Ansys Fluent ◽  
Eddy Simulation ◽  
Discrete Phase ◽  
Rans Models

A Computational Fluid Dynamics (CFD) model was built that simulates the transient, compressible, reacting, multi-phase environment that exists within a reciprocating engine's combustion chamber(s). ANSYS Fluent v13.0 was used with the Euler-Lagrangian Discrete Phase Model (DPM), the Shell autoignition model, and the Large Eddy Simulation (LES) method of turbulence modeling. Validation of the spray dynamics was performed by comparing simulation results with experiments of liquid and vapour penetration length of an n-Heptane spray experiment done by Sandia National Laboratories. It was found that LES produced more accurate results than several Reynolds Averaged Navier-Stokes (RANS) models. The Shell autoignition model was coded to function with C10.17H19.91 and compared with experimental ignition results in a Rapid Compression Machine (RCM) environment. All of the above models were then combined to simulate a directly-fueled lean-burn combustion prechamber configuration wherein the effects of spray angle, timing, and duration were studied.

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