CFD Online Logo CFD Online URL
Home > Forums > Software User Forums > ANSYS > FLUENT

Fluent vs. xFoil result for E423 airfoil: Cd is way off

Register Blogs Members List Search Today's Posts Mark Forums Read

LinkBack Thread Tools Search this Thread Display Modes
Old   November 17, 2017, 12:55
Default Fluent vs. xFoil result for E423 airfoil: Cd is way off
New Member
Join Date: Nov 2017
Posts: 1
Rep Power: 0
klu is on a distinguished road
My friends and I are currently studying the lift and drag of Eppler E423 high lift airfoil as a practice to use Fluent (we are all new to CFD). We were trying to match the Cl and Cd vs. alpha curves generated from xFoil shown in this link.

I started from the high Re cases (1M and 500K). So far, my Cl values seem to match pretty well, but my Cd values are much higher (xFoil ~ 0.01, my Fluent results are 0.03~0.07). Has anyone tried to do such comparison before? Were there some fundamental difference in the methods behind xFoil and Fluent, so the drag prediction could be so different? (If this question is too stupid, a good reading reference would be greatly appreciated.)

For my Fluent model, I used the following settings.
Transient analysis
pressure-based model
k-epsilon, realizable, standard wall treatment
SIMPLE solver
The y+ around the airfoil is above 30 (some in hundreds)
Results: Cl match pretty well, but Cd is much higher (See attached figure where blue is my Fluent results, and the light brown is xFoil.)

I also tried refining my mesh near the airfoil and used a different turbulent model.
Transient analysis
pressure-based model
k-omega, SST
PISO solver
The y+ is around 1 or slightly below 1
Results: Cl is less than what I got with k-epsilon model (not matching), Cd even higher (not matching xFoil).

If I am only interested in Cl and Cd for low Mach scenario (with various Re), what would be the more appropriate settings? Thank you for your help!
Attached Images
File Type: png Re1000k.png (95.6 KB, 24 views)
klu is offline   Reply With Quote

Old   September 22, 2023, 23:56
New Member
Francisco Herbert
Join Date: Nov 2017
Posts: 3
Rep Power: 8
Fco.Herbert is on a distinguished road
This is an old but relevant question. It deserves an answer. Long story short: your modeling in Fluent is assuming that the free-stream flow is turbulent, and XFOIL is assuming near laminar free-stream flow. For more information have a look at the following review:
Fco.Herbert is offline   Reply With Quote


drag coefficients, fluent 17.0, xfoil

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are On
Refbacks are On

Similar Threads
Thread Thread Starter Forum Replies Last Post
Question about airfoil 2D simulation using Fluent Abdelrahman Yousry FLUENT 0 November 26, 2016 07:38
Fluent export - CFD Post - Airfoil Results Wingman ANSYS 0 November 18, 2016 16:36
Trying to perform test validity of Fluent with simulation of 2D airfoil didiean FLUENT 39 December 5, 2015 13:31
Problem in using parallel process in fluent 14 Tleja FLUENT 3 September 13, 2013 10:54
problem in using parallel process in fluent 14 aydinkabir88 FLUENT 1 July 10, 2013 02:00

All times are GMT -4. The time now is 03:32.