scholarly journals A continuum model for flow induced by metachronal coordination between beating cilia

2011 ◽  
Vol 684 ◽  
pp. 137-162 ◽  
Author(s):  
Jeanette Hussong ◽  
Wim-Paul Breugem ◽  
Jerry Westerweel
Keyword(s):  
Continuum Model ◽  
Fluid Transport ◽  
Numerical Study ◽  
Plane Channel ◽  
Spatial Variations ◽  
Design Tool ◽  
Correct Prediction ◽  
Parameter Study ◽  
Efficient Design ◽  
Metachronal Wave

AbstractIn this numerical study we investigate the flow induced by metachronal coordination between beating cilia arranged in a densely packed layer by means of a continuum model. The continuum approach allows us to treat the problem as two-dimensional as well as stationary, in a reference frame moving with the speed of the metachronal wave. The model is used as a computationally efficient design tool to investigate cilia-induced transport of a Newtonian fluid in a plane channel. Contrary to prior continuum models, the present approach accounts for spatial variations in the porosity along the metachronal wave and thus ensures conservation of mass within the cilia layer. Using porous-media theory the governing volume-averaged Navier–Stokes (VANS) equations are derived and closure formulations are given explicitly for the model. This makes it possible to investigate cilia-induced flow with a continuum model in both the viscous regime and the inertial regime. The results show that metachronal coordination can act as a transport mechanism in both regimes. Porosity variations appear to be the key mechanism for correct prediction of the fluid transport in the viscous flow regime. The reason is that spatial variations in the porosity break the symmetry of the drag distribution along the metachronal wave. A new insight that has been gained is that the fluid transport reverses, thus switches from plectic to antiplectic metachronism, for the same cilia beat cycle when the wavespeed is increased such that inertial effects occur. Based on a parameter study, the net transport in the channel is described by a power-law relation of the amplitude, length and speed of the metachronal wave. It is found that the wavelength has the strongest effect on the viscosity-dominated fluid transport.

scholarly journals Mixing and transport by ciliary carpets: a numerical study

2014 ◽  
Vol 743 ◽  
pp. 124-140 ◽  
Author(s):  
Yang Ding ◽  
Janna C. Nawroth ◽  
Margaret J. McFall-Ngai ◽  
Eva Kanso
Keyword(s):  
Fluid Transport ◽  
Numerical Study ◽  
Mixing Time ◽  
Three Dimensional ◽  
Chemical Diffusion ◽  
Metachronal Wave ◽  
Mixing Rates ◽  
Infinite Array ◽  
Transport Region ◽  
Transport And Mixing

AbstractWe use a three-dimensional computational model to study the fluid transport and mixing due to the beating of an infinite array of cilia. In accord with recent experiments, we observe two distinct regions: a fluid transport region above the cilia and a fluid mixing region below the cilia tip. The metachronal wave due to phase differences between neighbouring cilia is known to enhance the fluid transport above the ciliary tip. In this work, we show that the metachronal wave also enhances the mixing rates in the sub-ciliary region, often simultaneously with the flow rate enhancement. Our results suggest that this simultaneous enhancement in transport and mixing is due to an enhancement in shear flow. As the flow above the cilia increases, the shear rate in the fluid increases and this shear enhances stretching, which is an essential ingredient for mixing. Estimates of the mixing time scale indicate that, compared to diffusion, the mixing due to the cilia beat may be significant and sometimes dominates chemical diffusion.

scholarly journals A Parameter Study of Localization

1996 ◽  
Vol 3 (1) ◽  
pp. 1-10 ◽  
Author(s):  
Sandor Stephen Mester ◽  
Haym Benaroya
Keyword(s):  
Periodic Structures ◽  
Numerical Study ◽  
Vibration Characteristics ◽  
Periodic Pattern ◽  
Parameter Study ◽  
Structural Damping ◽  
One Dimensional

Extensive work has been done on the vibration characteristics of perfectly periodic structures. Disorder in the periodic pattern has been found to lead to localization in one-dimensional periodic structures. It is important to understand localization because it causes energy to be concentrated near the disorder and may cause an overestimation of structural damping. A numerical study is conducted to obtain a better understanding of localization. It is found that any mode, even the first, can localize due to the presence of small imperfections.

Numerical Study on the Performance of a Tube With Inserted Porous Media of Various Thermal Conductivities

2016 ◽  
Author(s):  
Tariq Amin Khan ◽  
Wei Li
Keyword(s):  
Thermal Conductivity ◽  
Porous Medium ◽  
Porous Media ◽  
Velocity Profile ◽  
Fluid Transport ◽  
Energy Transport ◽  
Numerical Study ◽  
Darcy Number ◽  
Local Thermal Equilibrium ◽  
Working Fluid

Numerical study is performed on the effect of thermal conductivity of porous media (k) on the Nusselt number (Nu) and performance evaluation criteria (PEC) of a tube. Two-dimensional axisymmetric forced laminar and fully developed flow is assumed. Porous medium partially inserted in the core of a tube is investigated under varied Darcy number (Da), i.e., 10−6 ≤ Da ≤ 10−2. The range of Re number used is 100 to 2000 and the conductivity of porous medium is 1.4 to 202.4 W/(m.K) with air as the working fluid. The momentum equations are used to describe the fluid flow in the clear region. The Darcy-Forchheimer-Brinkman model is adopted for the fluid transport in the porous region. The mathematical model for energy transport is based on the one equation model which assumes a local thermal equilibrium between the fluid and the solid phases. Results are different from the conventional thoughts that porous media of higher thermal conductivity can enhance the performance (PEC) of a tube. Due to partial porous media insertion, the upstream parabolic velocity profile is destroyed and the flow is redistributed to create a new fully develop velocity profile downstream. The length of this flow redistribution to a new developed laminar flow depends on the Da number and the hydrodynamic developing length increases with increasing Da number. Moreover, the temperature profile is also readjusted within the tube. The Nu and PEC numbers have a nonlinear trend with varying k. At very low Da number and at a lower k, the Nu number decreases with increasing Re number while at higher k, the Nu number first increases to reach its peak value and then decreases. At higher Re number, the results are independent of k. However, at a higher Da number, the Nu and PEC numbers significantly increases at low Re number while slightly increases at higher Re number. Hence, the change in Nu and PEC numbers neither increases monotonically with k, nor with Re number. Investigation of PEC number shows that at very low Da number (Da = 10−6), inserting porous media of a low k is effective at low Re number (Re ≤ 500) while at high Re number, using porous material is not effective for the overall performance of a tube. However, at a relatively higher Da number (Da = 10−2), high k can be effective at higher Re number. Moreover, it is found that the results are not very sensitive to the inertia term at lower Da number.

scholarly journals Numerical Study of Flow Characteristics Around Confined Cylinder using OpenFOAM

2018 ◽  
Vol 7 (4.35) ◽  
pp. 617
Author(s):  
P. Mathupriya ◽  
L. Chan ◽  
H. Hasini ◽  
A. Ooi
Keyword(s):  
Reynolds Number ◽  
Vortex Shedding ◽  
Numerical Study ◽  
Vortex Formation ◽  
Plane Channel ◽  
Flow Characteristics ◽  
Strong Interactions ◽  
Two Dimensional ◽  
Computational Fluid Dynamics Cfd ◽  
Shedding Frequency

The numerical study of the flow over a two-dimensional cylinder which is symmetrically confined in a plane channel is presented to study the characteristics of vortex shedding. The numerical model has been established using direct numerical simulation (DNS) based on the open source computational fluid dynamics (CFD) code named OpenFOAM. In the present study, the flow fields have been computed at blockage ratio, β of 0.5 and at Reynolds number, Re of 200 and 300. Two-dimensional simulations investigated on the effects of Reynolds number based on the vortex formation and shedding frequency. It was observed that the presence of two distinct shedding frequencies appear at higher Reynolds number due to the confinement effects where there is strong interactions between boundary layer, shear layer and the wake of the cylinder. The range of simulations conducted here has shown to produce results consistent with that available in the open literature. Therefore, OpenFOAM is found to be able to accurately capture the complex physics of the flow.

Investigation of ammonia and hydrogen as CO2-free fuels for heavy duty engines using a high pressure dual fuel combustion process

2020 ◽  
pp. 146808742096787
Author(s):  
Stephanie Frankl ◽  
Stephan Gleis ◽  
Stephan Karmann ◽  
Maximilian Prager ◽  
Georg Wachtmeister
Keyword(s):  
High Pressure ◽  
High Pressures ◽  
Numerical Study ◽  
Combustion Process ◽  
Combustion Efficiency ◽  
Dual Fuel ◽  
Parameter Study ◽  
Fuel Injector ◽  
Cfd Model ◽  
Pilot Fuel

This work is a numerical study of the use of ammonia and hydrogen in a high-pressure-dual-fuel (HPDF) combustion. The main fuels (hydrogen and ammonia) are direct injected and ignited by a small amount of direct injected pilot fuel. The fuels are injected using a dual fuel injector from Woodward L’Orange, which can induce two fuels independently at high pressures up to 1800 bar for the pilot fuel and maximum 500 bar for the main. The numerical CFD-model gets validated for of hydrogen-HPDF with experimental data. Due to safety issues at the test rig it was not possible to use ammonia in the experiments, so it is modelled using the numerical model. It is assumed that the CFD-model also gives qualitative correct results for the use of ammonia as main fuel, so a parameter study of ammonia-HPDF is made. The results for the hydrogen-HPDF show, that hydrogen can be used in the engine without any further modifications. The combustion is very stable, and the hydrogen ignites almost immediately when it enters the combustion chamber. The results of the ammonia combustion indicate, that the HPDF combustion mode can handle ammonia effectively. It seems beneficial to inject the ammonia at higher pressures than hydrogen. Also pre-heating the ammonia can increase the combustion efficiency.

Numerical and Experimental Study of the Evaporation and Solid Layer Formation of a Bi-Component Droplet Under Various Drying Conditions

2014 ◽  
Author(s):  
Holger Grosshans ◽  
Matthias Griesing ◽  
Srikanth R. Gopireddy ◽  
Werner Pauer ◽  
Hans-Ulrich Moritz ◽  
...  
Keyword(s):  
Droplet Size ◽  
Mass Fraction ◽  
Numerical Study ◽  
Droplet Evaporation ◽  
Droplet Surface ◽  
Parameter Study ◽  
Layer Formation ◽  
Gas Temperature ◽  
Solid Layer ◽  
Initial Droplet

This paper presents a combined experimental and numerical study of the evaporation and solid layer formation of a single bi-component mannitol-water droplet in air. For spherically symmetric droplets, the problem is described mathematically by the unsteady, one-dimensional conservation equations of mass and energy. The effect of the formation of a solid layer at the droplet surface on the droplet evaporation and thermal diffusion rate is included in the present approach. The simulations are validated by comparison with experiments using acoustically levitated droplets. The study includes initial droplet diameters varying from 350 to 450 μm, gas temperatures ranging from 80 to 120 °C, and the initial mannitol mass fraction inside the droplet varies from 0.05 to 0.15. The numerical results are analyzed to identify the occurrence of solid layer formation, and the temporal evolutions of both the droplet size and mass are presented. A parameter study of the initial gas temperature, the initial droplet size, and the initial mannitol mass fraction inside the droplet on droplet evaporation and solid layer formation is presented. The present model accurately captures the initial stages of droplet drying under all conditions investigated.

scholarly journals Initial User Experience With an Artificial Intelligence Program for the Preliminary Design of Centrifugal Compressors

1987 ◽  
Author(s):  
Carol J. Russo ◽  
Dennis J. Nicklaus ◽  
Siu S. Tong
Keyword(s):  
Artificial Intelligence ◽  
Design Tool ◽  
Parameter Study ◽  
Balance Performance ◽  
New Approach ◽  
Trade Offs ◽  
Component Design ◽  
Small Set ◽  
Development Risks ◽  
Artificial Intelligence Program

A new approach is evaluated for the design of turbomachinery components using existing analysis codes coupled to a generic Artificial Intelligence (AI) software framework called ENGINEOUS. This AI framework uses intelligent search techniques with a small set of basic component design rules to iterate to an optimized solution and to quantify parameter trade-offs. Initial experience with ENGINEOUS indicates that it is a powerful design tool which quickly identifies non-obvious solutions balanced for conflicting multiple goals in a small number of iterations which vary linearly with the number of variables. The solution path and driving logic are easily visible to the designer and a parameter study option can rapidly quantify potential design trade-offs which together allow a critique of the selected design to balance performance against development risks. Because this AI design approach fosters intelligent interface with the designer and is generic, the potential application areas and productivity benefits appear enormous.

Mixing Field Analysis of a Gas Turbine Burner

2002 ◽  
Author(s):  
Peter Flohr ◽  
Patrick Schmitt ◽  
Christian Oliver Paschereit
Keyword(s):  
Gas Turbine ◽  
Recirculation Zone ◽  
Numerical Study ◽  
Turbulence Models ◽  
Design Tool ◽  
Field Analysis ◽  
Mixing Process ◽  
Fuel Injector ◽  
Air Mixing ◽  
Gas Turbine Burner

An analytical and numerical study has been carried out with the view on the understanding of the physical mechanisms of the mixing process in a gas turbine burner. To this end, three methods at various levels of approximation have been used: At the simplest level an analytical model of the burner flow and the mixing process has been developed. It is demonstrated how this approach can be used to understand basic issues of the fuel-air mixing and how it can be applied as a design tool which guides the optimisation of a fuel injector device. At an intermediate level of approximation, steady-state CFD simulations, based on the k–ε- and RSM-turbulence models are used to describe the mixing process. All steady simulations fail to either predict the recirculation zone or the turbulence level correctly, and can therefore not be expected to capture the mixing correctly. At the most involved level of modelling time-accurate CFD based on unsteady RSM and LES-turbulence models are performed. The simulations show good agreement with experiments (and in the case of LES excellent agreement) for both, velocity and turbulence fields. Mixing predictions close to the fuel injectors suffer from a simplification used in the numerical setup, but the mixing field is predicted very well towards the exit of the burner. The contribution of the asymmetric coherent flow structure (which is associated with the internal recirculation zone) to the mixing process is quantified through a triple decomposition technique.

An efficient design tool for transmission line on SIMOX substrates

2002 ◽  
Author(s):  
J.P. Raskin ◽  
I. Huynen ◽  
R. Gillon ◽  
D. Vanhoenacker ◽  
J.P. Colinge
Keyword(s):  
Transmission Line ◽  
Design Tool ◽  
Efficient Design

EFFECTS OF OPERATING CONDITIONS ON THE DEPOSITION OF GaAs IN A VERTICAL CVD REACTOR

2008 ◽  
Vol 15 (01n02) ◽  
pp. 111-116 ◽  
Author(s):  
JAE-SANG BAEK ◽  
JIN-HYO BOO ◽  
YOUN-JEA KIM
Keyword(s):  
Fluid Transport ◽  
Numerical Study ◽  
Three Dimensional ◽  
Chemical Vapor ◽  
Rotation Velocity ◽  
Operating Conditions ◽  
Deposition Condition ◽  
Three Dimensional Model ◽  
Trimethyl Gallium ◽  
Vertical Cvd Reactor

A numerical study is needed to gain insight into the growth mechanism and improve the reactor design or optimize the deposition condition in chemical vapor deposition (CVD). In this study, we have performed a numerical analysis of the deposition of gallium arsenide ( GaAs ) from trimethyl gallium (TMG) and arsine in a vertical CVD reactor. The effects of operating parameters, such as the rotation velocity of susceptor, inlet velocity, and inlet TMG fraction, are investigated and presented. The three-dimensional model which is used in this investigation includes complete coupling between the thermal-fluid transport and species transport with chemical reaction.

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