Problem comparing CFD results with experiment.

Sogolpb89 · April 14, 2015, 00:34

I am using STARCCM+ to simulate tubes with internally helical grooved (the ratio of tube length to pitch size is over 100 )with Re ranged between (4000-10000). Fluid model is solved with K-epsilon turbulent model in steady state. The mesh independence study have been done and the wall y+ is around 1. I calculated the Nu and F value for different Re which there are huge errors between experimental and CFD values especially in large Re. Since the groove is too small and generate swirl, I am thinking the realizable K-Epsilon two layer model ( I used all y+ wall treatment) cannot capture swirl effect inside the tube. Do you have any suggestion?

TimCFD · April 18, 2015, 07:55

First of all, you have to be absolutely sure that you are comparing apples with apples and not something else. The Nu number can be automatically calculated in STAR-CCM+ (be careful with the inputs). You are comparing the experimental and numerical results at the same location? The boundary conditions are correct?

I think a two equation turbulence model is not suitable for such an application. Give it a try with V2F or an eliptic blending version of the k-epsilon.

Sogolpb89 · April 18, 2015, 13:59

Thanks Tim,
I tried to be as accurate as possible to match the boundary condition of simulation to study. Also, I am using the exact formula of the study to calculate Nu and friction factor. In Tubes with groove that has a larger pitch sizes, the results is acceptable but for smaller pitch the results is far off from the study. Again thanks, I 'll try with these two version to see if it is going to change.

April 14, 2015, 00:34	Problem comparing CFD results with experiment.	#1
Sogolpb89 New Member Sogol Join Date: Apr 2015 Posts: 2 Rep Power: 0	I am using STARCCM+ to simulate tubes with internally helical grooved (the ratio of tube length to pitch size is over 100 )with Re ranged between (4000-10000). Fluid model is solved with K-epsilon turbulent model in steady state. The mesh independence study have been done and the wall y+ is around 1. I calculated the Nu and F value for different Re which there are huge errors between experimental and CFD values especially in large Re. Since the groove is too small and generate swirl, I am thinking the realizable K-Epsilon two layer model ( I used all y+ wall treatment) cannot capture swirl effect inside the tube. Do you have any suggestion? Last edited by Sogolpb89; April 14, 2015 at 21:48.

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
CFD Online Celebrates 20 Years Online	jola	Site News & Announcements	22	January 31, 2015 01:30
CFD vs Experimetal Results for Aerofoil	owhelan	Main CFD Forum	3	March 25, 2010 11:54
CFD vs Experimetal Results for Aerofoil	owhelan	FLUENT	0	March 25, 2010 08:03
Impact of Humidity on CFD Results	Jerry	Main CFD Forum	2	January 26, 2004 15:39
CFD - Trends and Perspectives	Jonas Larsson	Main CFD Forum	16	August 7, 1998 17:27

April 18, 2015, 07:55		#2
TimCFD New Member Tim Meier Join Date: Mar 2015 Posts: 16 Rep Power: 11	First of all, you have to be absolutely sure that you are comparing apples with apples and not something else. The Nu number can be automatically calculated in STAR-CCM+ (be careful with the inputs). You are comparing the experimental and numerical results at the same location? The boundary conditions are correct? I think a two equation turbulence model is not suitable for such an application. Give it a try with V2F or an eliptic blending version of the k-epsilon.

April 18, 2015, 13:59		#3
Sogolpb89 New Member Sogol Join Date: Apr 2015 Posts: 2 Rep Power: 0	Thanks Tim, I tried to be as accurate as possible to match the boundary condition of simulation to study. Also, I am using the exact formula of the study to calculate Nu and friction factor. In Tubes with groove that has a larger pitch sizes, the results is acceptable but for smaller pitch the results is far off from the study. Again thanks, I 'll try with these two version to see if it is going to change.