[Kim yongchul]

Dear all,
I would like to validate NACA0012 with experimental result which is available in NASA site. The input mentioned in NASA website is M=0.15 and Re=6 million. I can give M=0.15 in terms of velocity at inlet in FLUENT, but my doubt is "HOW CAN I GIVE RE=6 MILLION IN FLUENT". Thanks for understanding my silly question and please give me the solution.

Thank you so much

[ghost82]

Hi,
you cannot input directly the Reynolds number in fluent.
As you know Re number is defined as:
Re=rho*v*d/mu

Re=Reynolds number
rho=fluid density
v=fluid velocity
d=characteristic length
mu=dynamic viscosity

All in SI units

d in your case, since you have external flow, can be the chord length.

So you can calculate the velocity by fixing your Re number and other physical properties of the fluid and set a velocity input boundary condition in fluent.

Daniele

[Kim yongchul]

Hi Daniele,

Thank you so much for your reply!!
But, i have still some doubt..
As you said, i can fix my "Re" and i can calculate "Velocity". But my objective is inlet Mach number should be 0.15, my Re should be 6 million for validation.
When i calculate Velocity based on my required "Re", the velocity may be different from my Velocity calculated from my required Mach number.

So, how can i my purpose will serve?
Mr.Daniele, i am sorry for struggling you with my silly questions!

Thanks
kim.

Originally Posted by ghost82

Hi,
you cannot input directly the Reynolds number in fluent.
As you know Re number is defined as:
Re=rho*v*d/mu
Re=Reynolds number
rho=fluid density
v=fluid velocity
d=characteristic length
mu=dynamic viscosity

All in SI units

d in your case, since you have external flow, can be the chord length.

So you can calculate the velocity by fixing your Re number and other physical properties of the fluid and set a velocity input boundary condition in fluent.

Daniele

[ghost82]

Hi,
you can calculate velocity based on Reynolds number or Mach number.
If you want to fix Mach number simply calculate velocity as v=(Mach number)*(sound velocity).

Daniele

[Kim yongchul]

Dear Daniele,

Yes you said is right, we can calculate velocity based on Mach number also. Experimental data (for M=0.15 and Re=6 million) for NACA0012 airfoil is available in NASA website. I need to do simulation on naca0012 in FLUENT and validate with the above mentioned experimental data. So, i have to use M=0.15 and Re=6 million to validate my fluent results with experimental data. So, i can calculate velocity using M=0.15 and i give this velocity at inlet in fluent. But if we calculate the "Re" using my velocity (M=0.15), i will get different "Re" other than Re=6million. So, i cannot validate with experimental data. So, how can i validate now? That is why i asked how can i give Re=6million in fluent as input.
Please let me clarify my doubt in this regard.
Thank you Daniele.

Originally Posted by ghost82

Hi,
you can calculate velocity based on Reynolds number or Mach number.
If you want to fix Mach number simply calculate velocity as v=(Mach number)*(sound velocity).

Daniele

[LiteCFD]

Originally Posted by Kim yongchul

Dear Daniele,

But if we calculate the "Re" using my velocity (M=0.15), i will get different "Re" other than Re=6million. So, i cannot validate with experimental data.

You can try to vary other parameters which are included to Re=rho*v*d/mu
Calculate velocity from M and then decrease/increase mu, for example.
Note that other dimensionless parameters from your equations should be changed correspondingly.

[ghost82]

LiteCFD is right; make a pseudo fluid with custom density and/or viscosity to have reynolds=6 million.
Can you share the article you are trying to validate?

[Kim yongchul]

Hi Danieli,

Please look into the link below

http://turbmodels.larc.nasa.gov/naca0012_val.html

I would like to validate in the above link (naca0012 airfoil)

Thank you

Originally Posted by ghost82

LiteCFD is right; make a pseudo fluid with custom density and/or viscosity to have reynolds=6 million.
Can you share the article you are trying to validate?

[Kim yongchul]

LiteCFD, thank you very much for your clarification!!

Originally Posted by LiteCFD

You can try to vary other parameters which are included to Re=rho*v*d/mu
Calculate velocity from M and then decrease/increase mu, for example.
Note that other dimensionless parameters from your equations should be changed correspondingly.

[Farshid021]

hello everyone
I have simple question
how can I change Reynolds number in fluent

[ghost82]

There are various definitions of Reynolds number, depending on your application.
For flow in pipe you have the Reynods (Re) definition:

Re=rho*v*d/mu

rho: fluid density
v: fluid velocity
d: pipe diameter
mu: fluid viscosity

So, accordingly, to change Re you need to change one or more of the above parameters.

[Farshid021]

hello all dear
I have a simple question
how can I change rey number in fluent
for example, I want to insert my rey number 33000

[ghost82]

Originally Posted by Farshid021

hello all dear
I have a simple question
how can I change rey number in fluent
for example, I want to insert my rey number 33000

Message #11

[Farshid021]

my dear friend, I want to simulate passing flow from the plate by fluent but the problem is I don't know which items depends on rey number

[Thusitha]

Originally Posted by Farshid021

my dear friend, I want to simulate passing flow from the plate by fluent but the problem is I don't know which items depends on rey number

I presume when you say "which items depend" means the quantities that describe the Reynolds number. As far as I remember, its the plate length, flow density, flow velocity, and flow viscosity.

[derdiyzoe94]

hey,i have one question. I do project aerodynamic analysis on car, the problem is I couldn't tell, whether fluent use which type of characteristic length(length or width of my car) to calculate Reynolds number to compute the coefficient of drag .Anyone knows?Thanks in advance.

[Jennifer Von]

I think Cd is related to your flow projected area A=width*height. in 2D flow around cylinders , A=width*1=diameter of cylinder *1

[Omar Faruk]

Can I fixed Re=1*10^6 where velocity is 10m/s and the fluid is air??? if yes then how i can do this?

[Msvsraj]

how can we give reynolds number for flow over airfoil

[Hitesh12]

Originally Posted by ghost82

Hi,
you cannot input directly the Reynolds number in fluent.
As you know Re number is defined as:
Re=rho*v*d/mu

Re=Reynolds number
rho=fluid density
v=fluid velocity
d=characteristic length
mu=dynamic viscosity

All in SI units

d in your case, since you have external flow, can be the chord length.

So you can calculate the velocity by fixing your Re number and other physical properties of the fluid and set a velocity input boundary condition in fluent.

Daniele

Seems easy when the geometry is simple but what happens when it is not? I have a complex geometry with varying diameter and varying cross-sectional area even for the same dia (because of obstruction in the flow).


What can be done in such a case? What I'm thinking is that we'll have to break down the geometry in different parts and have to calculate Reynold's number for each. Is that the right approach?