Reference values in Sutherland's law at an altitude

Adithya_11 · August 31, 2021, 18:47

Hello

I am using the Sutherland's law to compute my viscosity. This is for an aircraft flying at an altitude. Hence, the free-stream flow properties such as density, temperature, and viscosity are different from sea level.

The reference T0 and mu0 in the Sutherland's law dialog box need not be changed correct? Those references are for curve fitting for the law.

Then, where do I input these quantities? I basically need these for computing my Reynolds number and also for non-dimensionalizing the forces.

The 'Reference values' tab in Fluent does not use any of the input variables for the computations. Hence, if I change the values there, it will not affect my simulation of an aircraft flying at an altitude?

LuckyTran · September 1, 2021, 11:23

The reference values pane in Fluent is for calculating non-dimensional things. Those values you can change to anything and not affect the simulation results for primitive variables. These you can leave alone.

The reference temperature and reference viscosity in Sutherland's law go into the material properties. The reference temperature and viscosity may or may not need to be changed. It just depends on how accurate you want to be. Sutherland's law takes into account viscosity changes with temperature, but not pressure. But not that many people take pressure changes into account.

If you were trying to be super duper accurate you would curve fit the viscosity at the new altitude and come up new coefficients for Sutherland's law and put those into the material properties dialog box.

August 31, 2021, 18:47	Reference values in Sutherland's law at an altitude	#1
Adithya_11 Member Adithya Join Date: May 2021 Posts: 73 Rep Power: 5	Hello I am using the Sutherland's law to compute my viscosity. This is for an aircraft flying at an altitude. Hence, the free-stream flow properties such as density, temperature, and viscosity are different from sea level. The reference T0 and mu0 in the Sutherland's law dialog box need not be changed correct? Those references are for curve fitting for the law. Then, where do I input these quantities? I basically need these for computing my Reynolds number and also for non-dimensionalizing the forces. The 'Reference values' tab in Fluent does not use any of the input variables for the computations. Hence, if I change the values there, it will not affect my simulation of an aircraft flying at an altitude?

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
[OpenFOAM.org] Compile OpenFOAM with OpenMPI+FCA v4.0.2	guilleTessi	OpenFOAM Installation	6	October 18, 2019 14:13
Domain Reference Pressure and mass flow inlet boundary	AdidaKK	CFX	75	August 20, 2018 05:37
OpenFOAM 1.6-ext git installation on Ubuntu 11.10 x64	Attesz	OpenFOAM Installation	45	January 13, 2012 12:38
Constant velocity of the material	Sas	CFX	15	July 13, 2010 08:56
G95 + CGNS	Bruno	Main CFD Forum	1	January 30, 2007 00:34

September 1, 2021, 11:23		#2
LuckyTran Senior Member Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,682 Rep Power: 66	The reference values pane in Fluent is for calculating non-dimensional things. Those values you can change to anything and not affect the simulation results for primitive variables. These you can leave alone. The reference temperature and reference viscosity in Sutherland's law go into the material properties. The reference temperature and viscosity may or may not need to be changed. It just depends on how accurate you want to be. Sutherland's law takes into account viscosity changes with temperature, but not pressure. But not that many people take pressure changes into account. If you were trying to be super duper accurate you would curve fit the viscosity at the new altitude and come up new coefficients for Sutherland's law and put those into the material properties dialog box.