Learning Forum

[MTayyab]

Hello, I wanted to know how to display overall Reynolds number in CFD Fluent.

[DrAmine]

Use the information printed in the outfile. You will then get the value of Reynolds number printed which i NEVER rely on.n

[MTayyab]

is there any reliable way to get the reynolds number?nmaybe in the cfd post by creating an expression?.

[MTayyab]

i also checked the .out file the value of reynolds number is the same as printed on screen by the solver ..........n

[Karthik Remella]

Hi,nI'm trying to understand your end goal with the estimation of the Re. Could you please help me understand this?nThanks.nKarthikn

[DrAmine]

You calculate your Reynolds Number based on our Inlet Velocity and Inlet characteristic Length (Hydraulic Diameter). The Device Reynolds Number can be done similarly: choosing an adequate characteristic length and velocity.In my comment I was trying to explain that CFX does rely on the below information for Viscosity, Lengths and Velocity to get the Reynolds Number. That Number is not always what you want to know.nn

[subhamdas]

For your kind information, CFX doesn't know the length scale of your problem so it calculates it based on the Global Length which is computed as the cubic root of the Volume of the computational domain.nnIf you wish to calculate the Reynolds Number, you need to compute the area average of the desired quantities(density, velocity, dynamic viscosity), and the Length scale should be your estimated value(length/dia/spacing/ and so on).n

[MTayyab]

can you please help me out and explain a bit how i can change the length scale to get the real value?nand if i can find these values in cfd post by creating an expression can you please tell me the expression to calculate these values?nthanks!nn

[subhamdas]

you cannot change the length scale specified by CFX. What you can do is write an expression in CFD Post to compute the Reynolds Number based on the Area Weighted values of the parameters(density, velocity, dynamic viscosity).nRe=(rho*v*L)/ mu, nIn the above equation, L is the length scale that has to be determined by you according to your problemn