Steps for analysis of a flow

rskrishna87 · January 26, 2011, 10:55

Hi guys,

I am very new to CFX modeling so hello fellos.

And right now i am using ANSYS Workbench 13.0 to model a gas flow of a impingement plate with neumann boundary conditions and varying the design

I have a gas flow that is running through an impingement jet(from top to bottom) with a diameter of 0.0006(set as one of the design parameter) and a length of 0.00425(from top to bottom) with a static pressure of 1.95kPa and Static Temperature of 450°C at the top(colder side) and 1250°C at the bottom surface(hotter side).
I have the results of simulations for different design variations(like platedepth,inlet,outlet diameter)
So can anyone suggest me few steps that are generally done in a flow process analysis?

Thanks a lot in advance

Krishna

ghorrocks · January 26, 2011, 19:29

Do the CFX tutorials, they are a good start. Have a look at the tutorials on the CFX-Community website as well. Do a literature search for similar applications to get a feel for how other people have done this sort of model.

rskrishna87 · January 27, 2011, 04:46

I am using a shear stress transport model...so for solving the problem theoretically what kind of equations do i have to solve??

ghorrocks · January 27, 2011, 17:20

What do you mean"theoretically"?

rskrishna87 · January 28, 2011, 06:20

The thing is i have all the post process results...including heat flux and heat transfer coefficient and Reynolds number and the give ngeometrical and fluid parameters...Can you tell me theoretically how to predict the Cooling efficiency

ghorrocks · January 28, 2011, 06:32

You have the parameters from your simulation so you can work out the cooling performance from that. Or are you asking what is the expected cooling efficiency? In that case go to any heat transfer textbook and they should cover heat transfer from impinging jets.

rskrishna87 · January 28, 2011, 07:35

yup thanks man...experimentally i can figure out the cooling efficiency ...But theoretically i need to know the expected cooling efficiency..Can you please tell me which text book is good for that.

Thanks,

Krishna

ghorrocks · January 28, 2011, 08:03

I go back to my original question - what do you mean by "theoretically"? I do not know of any theory which will tell me this, only empirical models and simulation results.

rskrishna87 · January 28, 2011, 10:14

Ok i am really sorry....can u please tell me how to experimentally determine the Cooling efficiency of a SST model with Thermal energy conditions as i said above using the post processing simulation results of CFX?...the last time i typed the message i have typed it by mistake..sry

ghorrocks · January 28, 2011, 16:19

Nothing to be sorry about, it just seems you don't know what some of the terms you are using mean and imply. Here's some definitions:

Simulation = a numerical model of a physical process
Numerical Model = an approx answer to an analytical mathematical model of a physical process
Experiment = Measurements of a physical process
Empirical Model = A curve fit onto experimental results, with no reference to the underlying theory of the process.
Theoretical model = A mathematical model which describes the underlying physical process

In complex flows like impinging jets you usually only get empirical models and simulation results. Both are only approximations.

So is your question - Are you trying to measure the modelled heat transfer from a impinging jet simulation?

rskrishna87 · January 29, 2011, 11:50

hi,

yes exactly...so let mw know how to do this please...thaks

ghorrocks · January 30, 2011, 05:35

OK, now that I know what you are asking I can answer you

Easy: areaInt(Wall Heat Flux)@Surface should do it. Either put this CEL expression on a monitor point or in the CFD-Post function calculator for post-processing.

rskrishna87 · January 31, 2011, 05:13

Thanks you man,

It was bugging me since a week.Now I will try it tomorrow.Since i am outside today and do not have access to work.

And one more thing is this gives me the heat flux at any point right. And mine is a thermal energy transfer SST model. So is there anything like Is entropic efficiency or anything that i can find??

ghorrocks · January 31, 2011, 07:21

Quote:

this gives me the heat flux at any point right.

No. Read the documentation - the function I gave integrates the Wall Heat Flux over the wall boundary called "Surface 1".

Define a CEL expression for the entropic efficiency, that's all you need do.

rskrishna87 · February 1, 2011, 09:23

does anyone know the expresion for the entropic efficiency in CFD Post?

rskrishna87 · February 1, 2011, 12:08

I have one more question...Mine is a heat exhanger.. with impinging jets...So does anyone know hwo do you calculate the cooling efficiency using mass flow, Specific heat,Temperature ,pressure ??

January 26, 2011, 10:55	Steps for analysis of a flow	#1
rskrishna87 Member Join Date: Jan 2011 Posts: 37 Rep Power: 15	Hi guys, I am very new to CFX modeling so hello fellos. And right now i am using ANSYS Workbench 13.0 to model a gas flow of a impingement plate with neumann boundary conditions and varying the design I have a gas flow that is running through an impingement jet(from top to bottom) with a diameter of 0.0006(set as one of the design parameter) and a length of 0.00425(from top to bottom) with a static pressure of 1.95kPa and Static Temperature of 450°C at the top(colder side) and 1250°C at the bottom surface(hotter side). I have the results of simulations for different design variations(like platedepth,inlet,outlet diameter) So can anyone suggest me few steps that are generally done in a flow process analysis? Thanks a lot in advance Krishna

January 27, 2011, 04:46	Shear stress transport model	#3
rskrishna87 Member Join Date: Jan 2011 Posts: 37 Rep Power: 15	I am using a shear stress transport model...so for solving the problem theoretically what kind of equations do i have to solve??

January 28, 2011, 06:20	theoretically how to predict the Cooling efficiency??	#5
rskrishna87 Member Join Date: Jan 2011 Posts: 37 Rep Power: 15	The thing is i have all the post process results...including heat flux and heat transfer coefficient and Reynolds number and the give ngeometrical and fluid parameters...Can you tell me theoretically how to predict the Cooling efficiency

February 1, 2011, 09:23	entropic efficiency?	#15
rskrishna87 Member Join Date: Jan 2011 Posts: 37 Rep Power: 15	does anyone know the expresion for the entropic efficiency in CFD Post?

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January 26, 2011, 19:29		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,870 Rep Power: 144	Do the CFX tutorials, they are a good start. Have a look at the tutorials on the CFX-Community website as well. Do a literature search for similar applications to get a feel for how other people have done this sort of model.

January 27, 2011, 17:20		#4
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,870 Rep Power: 144	What do you mean"theoretically"?

January 28, 2011, 06:32		#6
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,870 Rep Power: 144	You have the parameters from your simulation so you can work out the cooling performance from that. Or are you asking what is the expected cooling efficiency? In that case go to any heat transfer textbook and they should cover heat transfer from impinging jets.

January 28, 2011, 07:35		#7
rskrishna87 Member Join Date: Jan 2011 Posts: 37 Rep Power: 15	yup thanks man...experimentally i can figure out the cooling efficiency ...But theoretically i need to know the expected cooling efficiency..Can you please tell me which text book is good for that. Thanks, Krishna

January 28, 2011, 08:03		#8
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,870 Rep Power: 144	I go back to my original question - what do you mean by "theoretically"? I do not know of any theory which will tell me this, only empirical models and simulation results.

January 28, 2011, 10:14		#9
rskrishna87 Member Join Date: Jan 2011 Posts: 37 Rep Power: 15	Ok i am really sorry....can u please tell me how to experimentally determine the Cooling efficiency of a SST model with Thermal energy conditions as i said above using the post processing simulation results of CFX?...the last time i typed the message i have typed it by mistake..sry

January 28, 2011, 16:19		#10
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,870 Rep Power: 144	Nothing to be sorry about, it just seems you don't know what some of the terms you are using mean and imply. Here's some definitions: Simulation = a numerical model of a physical process Numerical Model = an approx answer to an analytical mathematical model of a physical process Experiment = Measurements of a physical process Empirical Model = A curve fit onto experimental results, with no reference to the underlying theory of the process. Theoretical model = A mathematical model which describes the underlying physical process In complex flows like impinging jets you usually only get empirical models and simulation results. Both are only approximations. So is your question - Are you trying to measure the modelled heat transfer from a impinging jet simulation?

January 29, 2011, 11:50		#11
rskrishna87 Member Join Date: Jan 2011 Posts: 37 Rep Power: 15	hi, yes exactly...so let mw know how to do this please...thaks

January 30, 2011, 05:35		#12
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,870 Rep Power: 144	OK, now that I know what you are asking I can answer you Easy: areaInt(Wall Heat Flux)@Surface should do it. Either put this CEL expression on a monitor point or in the CFD-Post function calculator for post-processing.

January 31, 2011, 05:13		#13
rskrishna87 Member Join Date: Jan 2011 Posts: 37 Rep Power: 15	Thanks you man, It was bugging me since a week.Now I will try it tomorrow.Since i am outside today and do not have access to work. And one more thing is this gives me the heat flux at any point right. And mine is a thermal energy transfer SST model. So is there anything like Is entropic efficiency or anything that i can find??

February 1, 2011, 12:08		#16
rskrishna87 Member Join Date: Jan 2011 Posts: 37 Rep Power: 15	I have one more question...Mine is a heat exhanger.. with impinging jets...So does anyone know hwo do you calculate the cooling efficiency using mass flow, Specific heat,Temperature ,pressure ??