A Computational Study of Turbulent Airflow and Tracer Gas Diffusion in a Generic Aircraft Cabin Model

2013 ◽  
Vol 135 (11) ◽  
Author(s):  
Khosrow Ebrahimi ◽  
Zhongquan C. Zheng ◽  
Mohammad H. Hosni
Keyword(s):  
Transport Model ◽  
Computational Study ◽  
Flow Behavior ◽  
Gas Diffusion ◽  
Wall Function ◽  
Tracer Gas ◽  
Airflow Velocity ◽  
Aircraft Cabin ◽  
Cfd Models ◽  
Turbulent Airflow

In order to study the capability of computational methods in investigating the mechanisms associated with disease and contaminants transmission in aircraft cabins, the computational fluid dynamics (CFD) models are used for the simulation of turbulent airflow and tracer gas diffusion in a generic aircraft cabin mockup. The CFD models are validated through the comparisons of the CFD predictions with corresponding experimental measurements. It is found that using large eddy simulation (LES) with the Werner-Wengle wall function, one can predict unsteady airflow velocity field with relatively high accuracy. However in the middle region of the cabin mockup, where the recirculation of airflow takes place, the accuracy is not as good as that in other locations. By examining different k-ε models, the current study recommends the use of the RNG k-ε model with the nonequilibrium wall function as an Reynolds averaged Navier-Stokes model for predicting the steady-state airflow velocity. It is also found that changing the nozzle height has a significant effect on the flow behavior in the middle and upper part of the cabin, while the flow pattern in the lower part is not affected as much. Through the use of LES and species transport model in simulating tracer gas diffusion, a very good agreement between predicted and measured tracer gas concentration is achieved for some monitoring locations, but the agreement level is not uniform for all the locations. The reasons for the deviations between prediction and measurement for those locations are discussed.

Computational Study of the Effects of Particle Size, Particle Injection Configuration, and Operating Pressure Gradient on Turbulent Dispersion of Spherical Micron-Sized Particles in a Generic Mockup Aircraft Cabin

2012 ◽  
Author(s):  
Khosrow Ebrahimi ◽  
Zhongquan C. Zheng ◽  
Mohammad H. Hosni
Keyword(s):  
Particle Concentration ◽  
Particle Distribution ◽  
Computational Study ◽  
Turbulent Dispersion ◽  
Optimum Number ◽  
Airflow Velocity ◽  
Particle Injection ◽  
Aircraft Cabin ◽  
Gauge Pressure ◽  
Turbulent Airflow

Computational study of dispersion of particles is one way to evaluate the spread of contaminants and viruses amongst occupants of an enclosure, such as an aircraft cabin. In this investigation, the turbulent dispersion of particles in a ventilated generic cabin is studied. The generic cabin resembles one-half of a Boeing 767-300 aircraft cabin. In the first phase, the turbulent dispersion of particles injected through stainless steel straight vertical tube is simulated. A Lagrangian approach is used to predict the particle concentration in specified monitoring location inside the cabin. The steady RANS solutions for the airflow velocity data are used to initialize the particle-tracking calculations through the Discrete Phase Model (DPM). To calculate the effects of turbulence on the dispersion behavior of particles, a Discrete Random Walk (DRW) model is employed. The particle concentration field under steady-state, zero-gauge-pressure conditions for 3 μm and 10 μm spherical liquid particles are calculated. Through the comparisons between the measured and the calculated particle concentration data for the two examined sizes of mono-disperse particles, the effect of particle size on distribution behavior of micron-sized particles is investigated and discussed. In the second phase, in order to reduce the effect of initial injection velocity for 10 μm particles on their distribution, the straight injection tube is replaced by a cone diffuser while maintaining the upstream primary flow conditions. Using the same RANS model and under the new particle injection configuration, the characteristics of turbulent airflow in the cabin are found to be very similar to those of turbulent airflow without particle injection. A grid independency study is performed for the airflow velocity data prior to validation of the particle distribution results. The steady-state DPM simulations are performed initially for the zero-gauge-pressure condition and then the effect of pressurizing the cabin on particle distribution is investigated by increasing the gauge-pressure up to 0.025 inches of water. Through a detailed study, carried out to obtain an optimum number for the number of tries in the DRW, it is realized that the optimum number of tries is 175 for both cases of pressurized and non-pressurized cabin.

Simulation of Airflow in the Burning Cave of an Auxiliary Heating System in a Greenhouse

2018 ◽  
Vol 61 (4) ◽  
pp. 1405-1416
Author(s):  
Zhanyang Xu ◽  
Wenhe Liu ◽  
Tieliang Wang ◽  
Wei Yu ◽  
Yuqing Zhang
Keyword(s):  
Numerical Simulation ◽  
Numerical Model ◽  
Numerical Simulations ◽  
Heating System ◽  
Experimental Measurements ◽  
Wall Function ◽  
Auxiliary Heating ◽  
Airflow Velocity ◽  
Cave Entrance ◽  
Turbulent Airflow

Abstract. In this study, numerical simulations of airflow were carried out in the burning cave of an auxiliary heating system. Experimental measurements were also conducted to verify the performance of the numerical model, and turbulent airflow in the burning cave was considered. The numerical simulation in the burning cave was performed for three cases:(1) with a baffle at the bottom of the burning cave entrance, (2) without a baffle at the burning cave entrance, and (3) with a baffle at the top of the burning cave entrance. The turbulent airflow was modeled using the realizable k-e turbulence model as well as the non-equilibrium wall function. The airflow velocity was assessed in the burning cave, and some suggestions were given to improve the performance of the burning cave. The results showed that the airflow entering the burning cave differed due to different positions of the baffle. The smoldering combustion was more even and the burning rate could be controlled more easily when the baffle was placed at the top of the burning cave entrance, making the airflow enter the burning cave through the bottom of the baffle. The results also showed that the maximum airflow velocity in the burning cave increased with increased distance between the baffle and the bottom of the burning cave. Keywords: Airflow, Burning cave, Greenhouse, Simulation.

LES and RANS Simulation of Turbulent Airflow and Tracer Gas Injection in a Generic Aircraft Cabin Model

2010 ◽  
Author(s):  
Khosrow Ebrahimi ◽  
Zhongquan C. Zheng ◽  
Mohammad H. Hosni
Keyword(s):  
Gas Injection ◽  
Research Work ◽  
Measurement Data ◽  
Airflow Rate ◽  
Tracer Gas ◽  
Aircraft Cabin ◽  
Half Height ◽  
Piv Measurement ◽  
Turbulent Airflow ◽  
Full Height

This study is a continuation of a previous research in numerical simulation of a turbulent airflow in a generic aircraft cabin model. Specifically, the primary objective of this project is to use Computational Fluid Dynamics (CFD) to simulate transport of a tracer gas injected into the generic aircraft cabin. The research work reported herein is composed of three parts. First, both Large Eddy Simulation (LES) and Reynolds averaged Navier Stokes (RANS) methods are used to simulate airflow from a full-height nozzle and corresponding airflow characteristics within the mockup aircraft cabin. The computational results are validated by comparing them with Particle Image Velocity (PIV) data and published CFD predictions available in the literature. Through these comparisons, the potential for using the CFD methods to predict unsteady as well as time-averaged velocity for a generic aircraft cabin model is examined. Second, airflow characteristics are studied by reducing the inlet nozzle height to one-half of its original size but keeping the total volumetric airflow rate the same as that of the full-height nozzle. Accuracy of the LES approach in predicting airflow in the half-height nozzle is evaluated by comparing prediction results with the PIV measurement data for the mockup cabin. Third, simulation of a tracer gas injection through the injecting tube placed in different locations in the half-height nozzle cabin is investigated. In this part, carbon dioxide (CO2) is chosen as the tracer gas. The LES method is used to solve the equations of motion and the unsteady species transport equation for tracer gas concentration. The predictions are compared with the average measurement data for CO2-concentration in various locations in the cabin.

A Mass Transport Model for CVD Coating of Optical Fibers

2003 ◽  
Author(s):  
Wei Huang ◽  
Wilson K. S. Chiu
Keyword(s):  
Mass Transport ◽  
Diffusion Model ◽  
Optical Fibers ◽  
Peclet Number ◽  
Flow Reactor ◽  
Transport Model ◽  
Gas Diffusion ◽  
Transfer Model ◽  
Continuous Stirred Tank Reactor ◽  
Péclet Number

Carbon coated optical fibers are produced by the chemical vapor deposition process which includes multi-species mass transport with chemical reactions. A proper numerical model of this process will help elucidate the basic mechanisms and optimize the process to improve coating quality. A heat transfer model has been developed in our research group. We are now developing an applicable chemical kinetics model to include mass transport with gas phase and surface reactions. Several different chemical reactor models have been tried, including a continuous-stirred tank reactor (CSTR) model, a plug flow reactor (PFR) model and a multi-component diffusion model with the Maxwell-Stefan approximations. We found that in reactor conditions with well-mixed or large mass Peclet number, the CSTR and PFR models validate well with experimental results. But a multi-component gas diffusion model is needed for low mass Peclet number conditions. The model has been extended to a wider range of temperatures necessary for this optical fiber coating process.

scholarly journals Effect of Car Rear Shape on Pollution Dispersion in Near Wake Region

2015 ◽  
Vol 2015 ◽  
pp. 1-10 ◽  
Author(s):  
Xing-Jun Hu ◽  
Han-Bo Yang ◽  
Bo Yang ◽  
Xiu-Cheng Li ◽  
Yu-Long Lei
Keyword(s):  
Turbulence Model ◽  
Urban Areas ◽  
Primary Source ◽  
Gas Diffusion ◽  
Wake Flow ◽  
Vehicle Exhaust ◽  
Tracer Gas ◽  
Near Wake ◽  
Pollution Dispersion ◽  
Wake Field

Dispersion of vehicle exhaust gas is a primary source of air pollution in urban areas. Thus, it has become an important subject in the automotive field. This paper consists of two parts. First, the fastback MIRA model was selected as study object and a standardκ-εtwo-equation turbulence model was used. The simulation results were compared and analyzed with experimental data. The feasibility of the turbulence model and grid strategy was then verified, and the results were used in the next research step. Second, we used propane as tracer gas while ignoring the effect of the vehicle wake field force on this gas. The tracer gas diffusion in the wake flow field was then simulated through fastback, notchback, and square-back MIRA models. This study focuses on analyzing the characteristics of wake field diffusion effects, particularly in the near wake of a vehicle.

Evaluation of bend curvature of superheater tube using CFD analysis

2021 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Sushovan Chatterjee ◽  
Subhasish Das ◽  
Neelam Kumar Sarma
Keyword(s):  
Heat Transfer ◽  
Computational Study ◽  
Flow Behavior ◽  
Radius Of Curvature ◽  
Pass System ◽  
Maximum Heat ◽  
Curvature Ratio ◽  
Content Type ◽  
Superheater Tube ◽  
The Impact

Purpose The heat transfer within a heat exchanger is highly influenced by geometry of the components especially those with hollow structures like tubes. This paper aims to intend toward the study of efficient and optimized heat transfer in the bends of superheater tubes, with different curvature ratio at constant Reynolds Number. Design/methodology/approach The effect of changing curvature ratio on enthalpy of the fluid passing through the superheater tubes for multi-pass system has been studied with the aid of computational fluid dynamics (CFD) using ANSYS 14.0. Initially a superheater tube with two pass system has been examined with different curvature ratios of 1.425, 1.56, 1.71, 1.85 and 1.99. An industry specified curvature ratio of 1.71 with two pass is investigated, and a comparative assessment has been carried out. This is intended toward obtaining an optimized radius of curvature of the bend for enhancement of heat transfer. Findings The results obtained from software simulation revealed that the curvature ratio of 1.85 provides maximum heat transfer to the fluid flowing through the tube with two pass. This result has been found to be consistent with higher number of passes as well. The effect of secondary flow in bends of curvature has also been illustrated in the present work. Research limitations/implications The study of heat transfer in thermodynamic systems is a never-ending process and has to be continued for the upliftment of power plant performances. This study has been conducted on steady flow behavior of the fluid which may be upgraded by carrying out the same in transient mode. The impact of different curvature ratios on some important parameters such as heat transfer coefficients will certainly upgrade the value of research. Originality/value This computational study provided comprehensive information on fluid flow behavior and its effect on heat transfer in bends of curvature of superheater tubes inside the boiler. It also provides information on optimized bend of curvature for efficient heat transfer process.

Novel Sprue Designs to Reduce Casting Defects in Nickel-Aluminum Bronze: A Computational Study

2020 ◽  
Author(s):  
Philip King ◽  
Daniel Martinez ◽  
Guha P. Manogharan
Keyword(s):  
Computational Study ◽  
Flow Behavior ◽  
Original Research ◽  
Casting Defects ◽  
Aluminum Bronze ◽  
Nickel Aluminum ◽  
Determining Factors ◽  
Marine Applications ◽  
Nickel Aluminum Bronze ◽  
Casting Design

Abstract As 3D Sand-Printing technology becomes more widely available to the casting market, the search for opportunities to take advantage of its freedom of design is critical for its rapid adoption by the casting community. This original research investigates casting design principles towards defect-free alloy Nickel-Aluminum Bronze (NAB). This is an alloy of interest for marine applications due to its corrosion resistance, mechanical strength and good castability. Numerical modeling of flow within a casting is examined, and rigging redesigns are proposed to improve casting quality by controlling flow behavior. It has been demonstrated that turbulence and filling velocity are determining factors that seriously impact casting performance due to the generation of casting defects. Among these are bifilm formations, gas and sand entrapment and cold shut. This work examines the effectiveness of mathematically designed rigging components in controlling mold filling and compares the results to a conventional casting rig. Design solutions are proposed using 3DSP that can be directly applied to casting operations of Nickel-Aluminum Bronze. The results from this study demonstrate the effectiveness of mathematically designed sprues to reduce filling velocity of Nickel-Aluminum Bronze. The procedure followed here can be extended to marine casting production environments. Findings from this study can be seamlessly transferred to castings of any geometry, alloy and pouring conditions.

Study on Hydraulic Flow in Stratified Pipe Performed by Numerical Simulation

2018 ◽  
Vol 881 ◽  
pp. 3-14
Author(s):  
Ani Hairani ◽  
Djoko Legono ◽  
Adam Pamudji Rahardjo
Keyword(s):  
Reynolds Number ◽  
Flow Pattern ◽  
Flow Behavior ◽  
Area Ratio ◽  
Separation Flow ◽  
Wall Function ◽  
Road Tunnel ◽  
Three Dimensional Model ◽  
Straight Pipe ◽  
Pipe Model

An idea of introducing an underground floodway inspired by Storm-water Management and Road Tunnel (SMART) in Malaysia is considered attractive to minimize land utilization regarding to the flood problem in Jakarta. This research was aimed to know the flow behavior of this modified tunnel due to sudden transitions, pressure losses and loss coefficients using numerical modeling. The simulation was conducted in the three-dimensional model using FLUENT Software which was divided into three models, i.e., contraction, enlargement, and straight pipe model. The simulation model was followed the geometrical design of SMART which the area ratio between smaller and larger pipe, A1/A2 varied, namely 0.20, 0.50, and 0.80. Standard k-ε and equilibrium wall function were used in straight pipe model, while contraction and enlargement model used k-ε modified and non-equilibrium wall function. The effect of different Reynolds number was also studied in this research. The result of the simulation showed that hydraulic parameters and area ratio of sudden transitions pipe give significant effect towards losses along the pipe. FLUENT simulation result gave good agreement with Darcy-Weisbach formula. The results indicate that loss coefficient decreases with the increase in pipe area ratio. The increase in pressure head loss was incurred by severe separated regions in the vicinity of pipe transition which was proved by typical flow pattern. Variation of Reynolds number also showed a different area of separation flow, yet the flow pattern was somewhat similar.

Experimental Investigation of Ventilation Effectiveness in an Airliner Cabin Mockup

2016 ◽  
Author(s):  
Jignesh A. Patel ◽  
Byron W. Jones ◽  
Mohammad H. Hosni ◽  
Ali Keshavarz
Keyword(s):  
Distribution System ◽  
Ventilation Rate ◽  
Mean Value ◽  
Tracer Gas ◽  
Flight Duration ◽  
Factors Affecting ◽  
Aircraft Cabin ◽  
Local Ventilation ◽  
Effective Ventilation ◽  
Ventilation Effectiveness

Frequent air travel and long flight duration makes the study of airliner cabin environmental quality a topic of utmost importance. Ventilation effectiveness is one of the more crucial factors affecting air quality in any environment. Ventilation effectiveness, along with the overall ventilation rate, is a measure of the ability of the air distribution system to remove internally generated pollutants or contaminants from a given space. Because of the high occupant density in an aircraft cabin, local variations in ventilation are important as a passenger will occupy the same space for the duration of the flight. Poor ventilation in even a small portion of the cabin could impact multiple people for extended time periods. In this study, the local effective ventilation rates and local ventilation effectiveness in an eleven-row, full-scale, Boeing 767 cabin mockup were measured. These measurements were completed at each of the 77 seats in the mockup. Each seat was occupied by a heated mannequin. In order to simulate the thermal load inside the cabin, the mannequins were wrapped with a heating wire to generate approximately 100 W (341 BTU/hour) of heat. Carbon dioxide was used as a tracer gas for the experiments and the tracer gas decay method was employed to calculate the local effective ventilation rate and local ventilation effectiveness. The overall ventilation rate, based on total supply air flow, was approximately 27 air changes per hour. Local ventilation effectiveness ranged from 0.86 to 1.02 with a mean value of 0.94. These ventilation effectiveness values are higher than typically found in other indoor applications and are likely due to the relatively high airspeeds present in the aircraft cabin and the high degree of mixing they provide. The uniformity is also good with no areas of particularly low ventilation effectiveness being identified. No clear patterns with respect to seat location, window versus center versus aisle, were found.

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