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Old   June 11, 2006, 14:06
Default CFD terminologies
  #1
Logesh
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Hi,

I have following doubts about CFD terminologies

1) Going through the CFD documentents, I came across transport equation. What is that transport equation?

I know about Continuity, momentum and energy equation. Is transport equation is related to anyone of these equation?

2) What is convective acceleration? My understanding is that the acceleration due to spatial component as convective acceleration. That is u.dV/dx is convective acceleration.Other component of acceleration is due to time(dV/dt).Whether am I right? If not, pl. correct me.

3) Whether vortice, eddy, recirculation and swirl are some way similar to each other?

I came across eddy and vortice, when flow passes across circular cylinder and recirculation when flow circulates in region and doesnot progress further. I came across about swirl in combustion chambers for better mixing. It will be great, if some one can throw light on the above terminologies (Vortices,eddy, recirculation and swirl)?

Kind Regards, Logesh.E

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Old   June 13, 2006, 09:15
Default Re: CFD terminologies
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bajjal
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hi , logesh

Transport equation is a equation which describes transport phenomena it can be anything like transport of heat ,mass,fluid,momentum ,turbulent kinetic energy etc...,

the transport eq in general includes transient term ,convection term ,diffusion term ,storage term 1)transient term -for example in momentum eqution rate of change of momentum of the fluid within the control volume(cv) (ie..,change within cv w.r.t time) in continuity equation rate of change of mass within the control volume similarly for other transport equtations 2) convection term - As fluid is carried in to the cv and out due to velocity field (for example) mass can be convected in and convected out similarly due to velocity field heat can be convected in and out 3)diffusion term - see some times even if the fluid is still diffusion can occur it is transport occuring because of gradients for example due to temperature gradient heat will flow , see for example (if our transport is heat flux) . in convection we concentrate on heat but while fluid is flowing how much amount of heat it is carrying with it and taking out ,in diffusion also we concentrate on heat but heat flux occurs here due to temperature gradient based on fouriers law 4)source-any extra terms that cannot be cast into convection or diffusion is called source or sink term

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Old   June 13, 2006, 09:27
Default Re: CFD terminologies
  #3
bajjal
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to ur 2nd question yes ur right 3)yes all four u mentioned have some similarity as per me that is rotation ,the point to note is it is not rigid body rotation for example flow in a circular chamber with uniform velocity through out the section if u place a match stick and allow it to flow it doesnt bend over anywhere do to uniform velocity through out section but person outside sees it moves circulary it is rigid body rotation , where as flow in rectangular channel with velocity gradients the match stick will tilt to one side it is reffered to rotation though it moves straight it tilts . thats why if u refer vorticity equation it will be written in terms of velocity gradients
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Old   June 14, 2006, 17:33
Default Re: CFD terminologies
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logesh
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Thanks Bajjal.Explanation is simply great.

Regards, Logesh.E
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