 ## Fluids

• veera
Subscriber
hi gd evening to all   i want to know the one simple answer for my question . actually in fluent , how Reynolds number calculated , how its setup initially , suppose i want to give that Reynolds number data means where i have to give
• Rob
Ansys Employee

If you mean the Cell Reynolds Number, it's defined in the Field Function Definitions in the Fluent User's Guide.

• veera
Subscriber

Field Function Definitions in the Fluent User's Guide - where i can see in ansys fluent?

• Rob
Ansys Employee

It's in the Help manual, click on Help and navigate to the Fluent User's Guide.

• Keyur Kanade
Ansys Employee

you can access help with following.

• Keyur Kanade
Ansys Employee

and also, you dont give input as reynolds no. you give input as say velocity. you can calculate velocity depending on your reynolds no. and then use it as input.

• veera
Subscriber

actually in Reynolds number formula , characteristics length is there, how we can give that in ansys fluent ?, yah off course i know the density,viscosity ( it was taking from material parameters what we are giving in the ansys fluent material setup ), and velocity, off course we are giving in inlet parameters , i have doubt on characteristics length only , actually where it will take ?

• Rob
Ansys Employee

You want to plot Reynolds Number in Fluent rather than Cell Reynolds Number (part of the post processing data set)?

• veera
Subscriber

no , i am just asking ..how its calculating Reynolds number itself(cell reynolds number ) re= rho v l / mu...from above formula , that l hoe its estimated itself

• DrAmine
Ansys Employee
Cell Reynolds number does rely on characteristic length scale of the cell. The definition of that scale is documented in the User's Guide.
• veera
Subscriber

sir actually still,l i did not get confident on this topics , actually my problem , they gave mach number is 0.8 , and Reynolds number is 7 million

so i can give mach number by in far filed conditions or in velocity i can give , but the thing is .. how i can give the Reynolds number of flow condition in ansys fluent setup...otherwise it would take from by giving velocity itself?

• Rob
Ansys Employee

You don't. Reynolds Number is a non-dimensional quantity that is a function of velocity, density, viscosity & length (of some sort), you set the speed (Mach Number for far field), material properties (plus operating conditions & upstream T & P) take care of the density & viscosity.

• veera
Subscriber

actually in Reynolds number formula , characteristics length is there, how we can give that in ansys fluent ?, yah off course i know the density,viscosity ( it was taking from material parameters what we are giving in the ansys fluent material setup ), and velocity, off course we are giving in inlet parameters , i have doubt on characteristics length only , actually where it will take ?

hmm i know that ...but i need to know about the characteristics length?

and for example , for same mach number or velocity , for different Reynolds number , like that flow parameters .. how we can give?

• Rob
Ansys Employee

If we have the same velocity, pressure & material on an inlet with identical geometry how can we get a different Re?

• veera
Subscriber

by viscosity wright

OK what about that characteristics length ...

• Rob
Ansys Employee

What about it? The length is whatever you decide (or literature recommends) to use. As we're modelling (usually) full scale I don't actually need Re: I need the speed/altitude/pressure/material properties to create the model.

• ps457
Subscriber

You want to plot Reynolds Number in Fluent rather than Cell Reynolds Number (part of the post processing data set)?

-- Yes, What if I would like to plot Re? [Actually I would like to plot Dean number. But I guess, I can plot dean if I find how to plot Re.]  Thank you very much. 