A numerical modelling investigation of the development of a human cough jet

2021 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Ran Bi ◽  
Shady Ali ◽  
Eric Savory ◽  
Chao Zhang
Keyword(s):  
Experimental Data ◽  
Numerical Study ◽  
Computational Cost ◽  
Numerical Results ◽  
Spatial Average ◽  
Axial Distance ◽  
Hot Wire ◽  
Content Type ◽  
Velocity Magnitude ◽  
Jet Penetration

PurposeThis study aims (1) to numerically investigate the characteristics of a human cough jet in a quiescent environment, such as the variation with time of the velocity field, streamwise jet penetration and maximum jet width. Two different turbulence modelling approaches, the unsteady Reynolds-averaged Navier–Stokes (URANS) and large eddy simulation (LES), are used for comparison purposes. (2) To validate the numerical results with the experimental data.Design/methodology/approachTwo different approaches, the URANS and LES, are used to simulate a human cough jet flow. The numerical results for the velocity magnitude contours and the spatial average of the two-dimensional velocity magnitude over the corresponding particle image velocimetry (PIV) field of view are compared with the relevant PIV measurements. Similarly, the numerical results for the streamwise velocity component at the hot-wire probe location are compared with the hot-wire anemometry (HWA) measurements. Furthermore, the numerical results for the streamwise jet penetration are compared with the data from the previous experimental work.FindingsBased on the comparison with the URANS approach and the experimental data, the LES approach can predict the temporal development of a human cough jet reasonably well. In addition, the maximum width of the cough jet is found to grow practically linearly with time in the far-field, interrupted-jet stage, while the corresponding axial distance from the mouth of the jet front increases with time in an approximately quadratic manner.Originality/valueCurrently, no numerical study of human cough flow has been conducted using the LES approach due to the following challenges: (1) the computational cost is much higher than that of the URANS approach; (2) it is difficult to specify the turbulent fluctuations at the mouth for the cough jet properly; (3) it is necessary to define the appropriate conditions for the droplets to obtain statistically valid results. Therefore, this work fills this research gap.

Modeling the sloshing problem in a rectangular tank with submerged incomplete baffles

2016 ◽  
Vol 26 (3/4) ◽  
pp. 722-744 ◽  
Author(s):  
Marcela A. Cruchaga ◽  
Carlos Ferrada ◽  
Nicolás Márquez ◽  
Sebastián Osses ◽  
Mario Storti ◽  
...  
Keyword(s):  
Experimental Data ◽  
Free Surface ◽  
Wave Height ◽  
Numerical Study ◽  
Free Surface Flows ◽  
Numerical Results ◽  
Surface Evolution ◽  
Content Type ◽  
Near Resonance ◽  
Wave Heights

Purpose – The present work is an experimental and numerical study of a sloshing problem including baffle effects. The purpose of this paper is to assess the numerical behavior of a Lagrangian technique to track free surface flows by comparison with experiments, to report experimental data for sloshing at different conditions and to evaluate the effectiveness of baffles in limiting the wave height and the wave propagation. Design/methodology/approach – Finite element simulations performed with a fixed mesh technique able to describe the free surface evolution are contrasted with experimental data. The experiments consist of an acrylic tank of rectangular section designed to attach baffles of different sizes at different distance from the bottom. The tank is filled with water and mounted on a shake table able to move under controlled horizontal motion. The free surface evolution is measured with ultrasonic sensors. The numerical results computed for different sloshing conditions are compared with the experimental data. Findings – The reported numerical results are in general in good agreement with the experiments. In particular, wave heights and frequencies response satisfactorily compared with the experimental data for the several cases analyzed during steady state forced sloshing and free sloshing. The effectiveness of the baffles increases near resonance conditions. From the set of experiments studied, the major reduction of the wave height was obtained when larger baffles were positioned closer to the water level at rest. Practical implications – Model validation: evaluation of the effectiveness of non-massive immersed baffles during sloshing. Originality/value – The value of the present work encompass the numerical and experimental study of the effect of immersed baffles during sloshing under different imposed conditions and the comparison of numerical results with the experimental data. Also, the results shown in the present work are a contribution to the understanding of the role in the analysis of the proposed problem of some specific aspects of the geometry and the imposed motion.

scholarly journals Cooling of a heating cylinder by confined impacting air jets

2016 ◽  
Vol 26 (7) ◽  
pp. 2013-2032 ◽  
Author(s):  
Nicolas Chauchat ◽  
Eric Schall ◽  
Mathieu Mory ◽  
Marta de la Llave Plata ◽  
Vincent G. Couaillier
Keyword(s):  
Experimental Data ◽  
Mechanical Energy ◽  
Electrical Power ◽  
Electrical Energy ◽  
Numerical Results ◽  
Content Type ◽  
Air Jets ◽  
Velocity Magnitude ◽  
Air Jet ◽  
Set Up

Purpose The purpose of this paper is to investigate a new cooling process of a heated cylinder with confined impacting air jet. Design/methodology/approach To do this the authors used experience-numerical and numerical-numerical comparisons. The experimental facility, designed and built at the Pau University, consists in air jets impacting around a heated circular cylinder. As the inlet velocity magnitude is low (Vin=4.37 m/s – Machin=0.0125), using a compressible solver for numerical simulations presents a number of difficulties. For this low Mach number configuration, the authors compare the performance of three different solvers in this paper. Two of them are compressible, one based on the finite volume approach and the other on a discontinuous Galerkin method, and the third one is an incompressible solver. Some of the numerical results are compared to experimental data. Findings Comparisons between the results from 3D and 2D computations support the relevance of 2D models. Some of the numerical results are compared to experimental data. Research limitations/implications The confined aspect of the set-up reduces experimental measurement to intrusive measures. It should be noted that the temperature measurement given by thermocouples is always considered as “global” or “average”. Originality/value Future aircraft technology will increasingly rely on electrical power. The substitution of mechanical energy by electrical energy will lead to an increasing amount of heat power that need be evacuated. Innovative cooling processes have to be set up according to constraints imposed by the technological design.

scholarly journals Investigation of the effects of opening size and location on punching shear resistance of flat slabs using Abaqus

2021 ◽  
Vol 15 (4) ◽  
pp. 136-147
Author(s):  
Nguyen Tuan Trung ◽  
Pham Thanh Tung
Keyword(s):  
Experimental Data ◽  
Numerical Model ◽  
Numerical Study ◽  
Shear Resistance ◽  
Design Principles ◽  
Numerical Results ◽  
Punching Shear ◽  
Shear Reinforcement ◽  
Flat Slabs ◽  
Abaqus Model

The paper presents a numerical study on the effects of opening size and location on punching shear resistance of flat slabs without drop panels and shear reinforcement using ABAQUS. The study proposes an ABAQUS model that is enable to predict the punching shear resistance of flat slabs with openings. The model is validated well with the experimental data in literature. Using the validated numerical model, the effects of opening size and location on the punching shear resistance of flat slabs are then investigated, and the numerical results are compared with those predicted by ACI 318-19 and TCVN 5574:2018. The comparison between experimental and numerical results shows that the ABAQUS model is reliable. The punching shear resistances calculated by ACI 318-19 and TCVN 5574:2018 with different opening sizes and locations are agreed well to each other, since the design principles between two codes now are similar.

Modelling Non-Uniform Bleed in Axial Compressors

2015 ◽  
Author(s):  
S. D. Grimshaw ◽  
G. Pullan ◽  
T. P. Hynes
Keyword(s):  
Experimental Data ◽  
Computational Cost ◽  
Three Dimensional ◽  
Flow Coefficient ◽  
Axial Distance ◽  
Two Dimensional ◽  
Flow Angle ◽  
Axial Compressors ◽  
Two Dimensional Flow ◽  
Satisfactory Prediction

The coupling between the bleed system and the flowfield of a downstream compressor stage is studied using two approaches. In the first, three-dimensional, full annulus, unsteady computations simulate the flow in a low speed research compressor with non-uniform bleed extraction. Comparisons with experimental data show that the flow prediction in the main annulus is accurate to within 0.005 of flow coefficient and 0.5° of flow angle. The CFD is then used to provide a description of flow within the bleed system itself. In the second approach, a two-dimensional mean radius model, similar to that adopted by Hynes and Greitzer in previous work on compressor stability, is used to simulate the response of the compressor to non-uniform bleed. This model is validated against experimental data for a single stage compressor and despite the inherent assumptions (two dimensional flow and simplified compressor response) provides a satisfactory prediction of the flow for preliminary design purposes with orders of magnitude less computational cost than full 3D CFD. The model is then used to investigate the effect of different levels of bleed non-uniformity and of varying the axial distance between the bleed and the downstream stage. Reducing bleed non-uniformity and moving the stage away from the bleed slot are predicted to reduce the circumferential non-uniformity of the flow entering the stage.

Biomass pyrolysis modeling of systems at laboratory scale with experimental validation

2018 ◽  
Vol 28 (2) ◽  
pp. 413-438 ◽  
Author(s):  
Stefano Cordiner ◽  
Alessandro Manni ◽  
Vincenzo Mulone ◽  
Vittorio Rocco
Keyword(s):  
Experimental Data ◽  
Numerical Model ◽  
Fast Pyrolysis ◽  
Experimental System ◽  
High Energy ◽  
Numerical Results ◽  
Small Scale ◽  
Content Type ◽  
Slow Pyrolysis ◽  
Bio Oil

Purpose Thermochemical conversion processes are one of the possible solutions for the flexible production of electric and thermal power from biomass. The pyrolysis degradation process presents, among the others, the interesting features of biofuels and high energy density bio-oil production potential high conversion rate. In this paper, numerical results of a slow batch and continuous fast pyrolyzers, are presented, aiming at validating both a tridimensional computational fluid dynamics-discrete element method (CFD–DEM) and a monodimensional distributed activation energy model (DAEM) represents with data collected in dedicated experiments. The purpose of this paper is then to provide reliable models for industrial scale-up and direct design purposes. Design/methodology/approach The slow pyrolysis experimental system, a batch of small-scale constant-pressure bomb for allothermic conversion processes, is presented. A DEM numerical model has been implemented by means of a modified OpenFOAM solver. The fast pyrolysis experimental system and a lab scale screw reactor designed for biomass fast pyrolysis conversion are also presented along with a 1D numerical model to represent its operation. The model which is developed for continuous stationary feeding conditions and based on a four-parallel reaction chemical framework is presented in detail. Findings The slow pyrolysis numerical results are compared with experimental data in terms of both gaseous species production and reduction of the bed height showing good predictive capabilities. Fast pyrolysis numerical results have been compared to the experimental data obtained from the fast pyrolysis process of spruce wood pellet. The comparison shows that the chemical reaction modeling based on a Gaussian DAEM is capable of giving results in very good agreement with the bio-oil yield evaluated experimentally. Originality/value As general results of the proposed activities, a mixed experimental and numerical approach has demonstrated a very good potential in developing design tools for pyrolysis development.

Numerical study of the flow field characteristics over a backward facing step using k-kl-ω turbulence model: comparison with different models

2018 ◽  
Vol 15 (1) ◽  
pp. 173-180 ◽  
Author(s):  
Yasser M. Ahmed ◽  
A.H. Elbatran
Keyword(s):  
Experimental Data ◽  
Fluid Mechanics ◽  
Turbulence Model ◽  
Flow Separation ◽  
Flow Characteristics ◽  
Turbulence Models ◽  
Numerical Results ◽  
Backward Facing Step ◽  
Content Type ◽  
Case Comparison

Purpose This paper aims to investigate numerically the turbulent flow characteristics over a backward facing step. Different turbulence models with hybrid computational grid have been used to study the detached flow structure in this case. Comparison between the numerical results and the available experiment data is carried out in the present study. The results of the different turbulence models were in a good agreement with the experimental results. The numerical results also concluded that the k-kl-ω turbulence model gave favorable results compared with the experiment. Design/methodology/approach It is very important to study the flow characteristics of detached flows. Therefore, the current study investigates numerically the flow characteristics in backward facing step by using two-, three- and seven-equation turbulence models in the finite volume code ANSYS Fluent. In addition, hybrid grid has been used to improve the capability of the unstructured mesh elements for predicting the flow separation in this case. Comparison between the different turbulence models and the available experimental data was done to find the most suitable turbulence model for simulating such cases of detached flows. Findings The present numerical simulations with the different turbulence models predicted efficiently the flow characteristics over the backward facing step. The transition k-kl-ω gave the best acceptable results compared with experimental data. This is a good concluded remark in the fields of fluid mechanics and hydrodynamics because the phenomenon of flow separation is not easy to be predicted numerically and can affect greatly on the predicted drag of moving bodies in many engineering applications. Originality/value The CFD results of using different turbulence models have been validated with the experimental work, and the results of k-kl-ω proven acceptable with flow characteristics. The results of the current study conclude that the use of k-kl-ω turbulence model will contribute towards a more efficient utilization in the fields of fluid mechanics and hydrodynamics.

Experimental and Numerical Study of the Response of an Axial Compressor to Distorted Inlet Flow

1988 ◽  
Vol 110 (4) ◽  
pp. 355-360 ◽  
Author(s):  
G. Billet ◽  
J. Huard ◽  
P. Chevalier ◽  
P. Laval
Keyword(s):  
Experimental Data ◽  
Numerical Simulation ◽  
Numerical Study ◽  
Axial Compressor ◽  
Numerical Approach ◽  
Compressor Blade ◽  
Numerical Results ◽  
Test Stand ◽  
Viscous Effects ◽  
Inlet Flow

A model representing the response of fixed or rotating axial compressor blade-rows is coupled to a 3-D numerical simulation of the flow outside the blade rows. The code can be used to study nonuniform compressible 3-D flows through turbomachines. The fluid is assumed to be inviscid in the space outside the rows, while the viscous effects are taken into account inside. Numerical results are compared with experimental data obtained on a test stand with steady distorted inflow. This comparison shows that this numerical approach is capable of predicting the response of the compressor. This work is part of a larger project aimed at predicting the response of a compressor to a nonuniform inlet flow that is periodic in time, or fully unsteady.

Experimental and Numerical Study of Cavitation in Centrifugal Pumps

2010 ◽  
Author(s):  
Erfan Niazi ◽  
M. J. Mahjoob ◽  
Ardeshir Bangian
Keyword(s):  
Experimental Data ◽  
Numerical Model ◽  
Mass Flow Rate ◽  
Computer Simulations ◽  
Mass Flow ◽  
Flow Rate ◽  
Numerical Study ◽  
Numerical Results ◽  
Centrifugal Pumps ◽  
Cavitation Threshold

Cavitation in pumps is one of the most important causes of damage to pumps impellers/inducers. A numerical model is developed here to simulate the pump hydraulics in different conditions. Experiments are also conducted to validate the computer simulations. To verify the numerical model, the h–m˙ (head versus mass flow rate) of the model is compared with the experimental data. The system is then run under cavitation state. Two methods are applied to monitor the cavitation threshold: first by using stroboscope and observing cavitation bubbles through the transparent casing of the pump and second by checking the NPSHA value for cavitation based on ISO3555. The paper then compares the experimental and numerical results to find the strengths and weaknesses of the numerical model.

Numerical Investigation Into Non-Synchronous Vibrations of Axial Flow Compressors by the Resonant Tip Clearance Flow

2009 ◽  
Author(s):  
Martin Drolet ◽  
Jean Thomassin ◽  
Huu Duc Vo ◽  
Njuki W. Mureithi
Keyword(s):  
Experimental Data ◽  
Numerical Study ◽  
Axial Flow ◽  
Numerical Results ◽  
Tip Clearance ◽  
Inlet Temperature ◽  
Compressor Blades ◽  
Turbine Engine ◽  
Tip Clearance Flow ◽  
Clearance Flow

This work investigates Non-Synchronous Vibrations (NSV) encountered in a turbine engine axial flow compressor using a Computational Fluid Dynamics (CFD) approach. It has been proposed that the resonance of the tip clearance flow in compressor blades could be the physical mechanism behind NSV. This work’s emphasis is on being able to computationally capture this resonance and predict the critical NSV speed using CFD. This would considerably reduce the costs involved in future hardware design and testing. The model uses the same compressor blade geometry on which experimental validation of the proposed NSV theory was conducted. The flow interaction with blade vibratory motion is modeled using a moving mesh capability and a SAS-SST turbulence model is used for computation. A review of the proposed theory on NSV is done. The CFD model is first verified with experimental data and then characterized to ensure that the simulations are conducted at the proper NSV conditions, in order to assess the resonance of the tip clearance flow. Evidence of this resonance behavior is presented and critical NSV speeds are identified based on numerical results for two different inlet temperature cases and are validated against experimental data. Further study of the actual flow structure associated with NSV is done. Additional remarks on the numerical results are discussed. An iterative design methodology to account for NSV is also proposed based on the current numerical study.

Sensitivity analysis of finite volume simulations of a breaking dam problem

2015 ◽  
Vol 25 (7) ◽  
pp. 1718-1745 ◽  
Author(s):  
Pablo A. Caron ◽  
Marcela A. Cruchaga ◽  
Axel E. Larreteguy
Keyword(s):  
Surface Tension ◽  
Finite Volume ◽  
Numerical Solutions ◽  
Numerical Study ◽  
Mesh Size ◽  
Numerical Results ◽  
Numerical Techniques ◽  
Interface Evolution ◽  
Interface Position ◽  
Content Type

Purpose – The present work is a numerical study of a breaking dam problem. The purpose of this paper is to assess the effect of turbulence and surface tension models in the prediction of the interface position in a long-term analysis. Additionally, dimensional effects are analyzed by carrying out both 2D and 3D simulations. Design/methodology/approach – Finite volume simulations performed with the different models are compared between them and contrasted with numerical results computed using other numerical techniques and experimental data. Findings – The reported numerical results are in general in good agreement with experimental results available in the literature. They are also consistent with numerical solutions of other authors obtained using different numerical techniques. The results show that the laminar simulations exhibit strong mesh size dependency, while the turbulence models seem to help in producing mesh-independent solutions. Surface tension modeling does not seem to play a relevant role in the interface evolution. Practical implications – Model validation. Originality/value – The value of the present work encompass the comparison of different flow conditions used to simulate a free surface problem and their validation by contrasting numerical results with experiments. Also, the results shown in the present work are a contribution to the understanding of the role of some specific aspects of the models in the simulation of the proposed problem.

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