Ansys Turbulent Flat Plate: reproducing results published by NASA

ghorrocks · December 6, 2015, 17:07

You are using first order turbulence numerics and upwind advection. You are never going to get very accurate results with those settings. The advection should be hydrid (with blend factor of close to 1.0) or high res. You should also consider high order turbulence numerics.

EternalSeekerX · December 6, 2015, 18:20

Quote:

Originally Posted by ghorrocks

You are using first order turbulence numerics and upwind advection. You are never going to get very accurate results with those settings. The advection should be hydrid (with blend factor of close to 1.0) or high res. You should also consider high order turbulence numerics.

Ah okay thanks I have changed advection scheme to hybrid with a blend factor of 1.0 and set the turbulence model to higher order.

Boundary conditions seem to be correct.

Here are the pictures

Front Side mesh grid mesh grid front side.jpg
Back Side mesh grid mesh grid back side.jpg
Mesh setting mesh setting.jpg
BC BC Conditions.jpg

Its running right now, even on a 8 core 16 thread with 100% utilization a run still takes 20 mins, will check back with results. Any other tips?

Thank you so far.

ghorrocks · December 6, 2015, 18:49

Here's a tip:

CFX does not run effectively on virtual cores. If you have 8 physical cores then do not run more than 8 processes.

EternalSeekerX · December 7, 2015, 00:16

Quote:

Originally Posted by ghorrocks

Here's a tip:

CFX does not run effectively on virtual cores. If you have 8 physical cores then do not run more than 8 processes.

Nice so now I am getting nice results but for some reason the reynolds number I am getting is less than what the max reynolds number is. My graph ends at 6x10e6 where I should be getting max re as 2.5x10e7.

ghorrocks · December 7, 2015, 05:22

How are you calculating Re?

EternalSeekerX · December 8, 2015, 05:07

Quote:

Originally Posted by ghorrocks

How are you calculating Re?

RE=(Density*Velocity*X)/(Dynamic Viscosity)

ghorrocks · December 8, 2015, 05:22

Yes, I already guessed that......

But what density? How did you define it? And how did you calculate it? Same for Velocity and dyn viscosity.

EternalSeekerX · December 8, 2015, 05:31

Quote:

Originally Posted by ghorrocks

Yes, I already guessed that......

But what density? How did you define it? And how did you calculate it? Same for Velocity and dyn viscosity.

I set the velocity which I calculated using the solver. The density is the density of air which I defined in cfx pre. I got dynamic viscosity from the solver.

ghorrocks · December 8, 2015, 06:15

How did you define the velocity? How did you calculate it?

Is the fluid incompressible and constant properties?

EternalSeekerX · December 8, 2015, 14:22

Quote:

Originally Posted by ghorrocks

How did you define the velocity? How did you calculate it?

Is the fluid incompressible and constant properties?

Its non compressible, constant properties, stready state

ghorrocks · December 8, 2015, 16:48

OK, so density and dyn viscosity are easy to define. Now we just need to find how you defined the velocity. You say "I set the velocity which I calculated using the solver", so which velocity? An average? Freestream? At a certain point?

EternalSeekerX · December 8, 2015, 18:22

Quote:

Originally Posted by ghorrocks

OK, so density and dyn viscosity are easy to define. Now we just need to find how you defined the velocity. You say "I set the velocity which I calculated using the solver", so which velocity? An average? Freestream? At a certain point?

I fixed it, I used the velocity at the freestream using the probe function. I am getting the correct Reynolds number at the end of the plate at x=5.09016m

December 6, 2015, 18:49		#23
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,710 Rep Power: 143	Here's a tip: CFX does not run effectively on virtual cores. If you have 8 physical cores then do not run more than 8 processes. EternalSeekerX likes this.

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Ansys SIG$ILL error	loth	ANSYS	3	December 24, 2015 05:31
2-way FSI in Ansys CFX 15	LucasGasparino	CFX	3	August 6, 2015 03:17
Flat plate and Boundary conditions	Ravenn	FLUENT	1	March 10, 2013 18:39
results for flow past flat plate normal to flow	lisa	Main CFD Forum	2	August 30, 2005 16:36
flat plate boundary layer data	Ekachai Juntasaro	Main CFD Forum	3	March 13, 2001 23:18

December 6, 2015, 17:07		#21
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,710 Rep Power: 143	You are using first order turbulence numerics and upwind advection. You are never going to get very accurate results with those settings. The advection should be hydrid (with blend factor of close to 1.0) or high res. You should also consider high order turbulence numerics.

December 7, 2015, 05:22		#25
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,710 Rep Power: 143	How are you calculating Re?

December 8, 2015, 05:22		#27
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,710 Rep Power: 143	Yes, I already guessed that...... But what density? How did you define it? And how did you calculate it? Same for Velocity and dyn viscosity.

December 8, 2015, 06:15		#29
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,710 Rep Power: 143	How did you define the velocity? How did you calculate it? Is the fluid incompressible and constant properties?

December 8, 2015, 16:48		#31
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,710 Rep Power: 143	OK, so density and dyn viscosity are easy to define. Now we just need to find how you defined the velocity. You say "I set the velocity which I calculated using the solver", so which velocity? An average? Freestream? At a certain point?