
[Sponsors] 
October 8, 2012, 04:39 
CFD Analysis of Airfoil at Mach = 0.0

#1 
Senior Member
Ali
Join Date: Jan 2012
Location: Pakistan
Posts: 130
Rep Power: 8 
Hi folks
I want to perform a 2D airfoil CFD analysis at Reynolds number of 9.0M and Mach number 0.0. Is this possible?
__________________
Best Regards Ali 

October 8, 2012, 04:47 

#2 
Senior Member
Philipp
Join Date: Jun 2011
Location: Germany
Posts: 1,296
Rep Power: 19 
No.
Check your numbers, there must be a typo. Mach number = 0.0 means your velocity is zero. 

October 8, 2012, 07:46 

#3 
Senior Member
Stuart Buckingham
Join Date: May 2010
Location: United Kingdom
Posts: 267
Rep Power: 17 
Technically yes, as the Mach number is just a function of the compressibility of the fluid. If you have not turned the energy equation on, the physics modelled disregard any compressibility effects, and therefore Ma = 0. Effectively, the bulk modulus and ratio of specific heats go to infinity; but your velocity can still be nonzero.
You can set your Re by changing the fluid viscosity, scaling the model (to achieve a specific L) or modifying the velocity. Assuming Ma = 0 for low Ma numbers (~<0.3) is common and generally accepted within the industry. Hope this helps, Stu
__________________
http://bc247.wordpress.com 

October 8, 2012, 07:57 

#4 
Senior Member
Philipp
Join Date: Jun 2011
Location: Germany
Posts: 1,296
Rep Power: 19 
Ok, thats true. If you have M = v/a with a = infinity. But if you artificially remove the speed of sound from your equations, it does not seem appropriate to me to use the phrasing "Mach number" at all. Maybe this is the common practice .


October 8, 2012, 08:07 

#5 
Senior Member
Stuart Buckingham
Join Date: May 2010
Location: United Kingdom
Posts: 267
Rep Power: 17 
Rodriguez,
You're right, I think it is quite illogical to think of modelling a flow with Ma = 0.0; but I bet if Ali had said "incompressible flow", you would have no problem realising what he meant. Ma = 0.0 is just a bad (or at least, unnatural) way of saying flow is incompressible! Stu
__________________
http://bc247.wordpress.com 

October 8, 2012, 08:11 

#6 
Senior Member
Philipp
Join Date: Jun 2011
Location: Germany
Posts: 1,296
Rep Power: 19 
Absolutely! I'm no "airodynamics"guy, so thanks for the free lecture


October 8, 2012, 10:19 

#7 
Super Moderator

What if, you put the very very very large enclosure (order of 500 as compared to body characteristic length) and specify the same static and total pressure (101325 pa to be specific)?
In fact we did this for the Fan simulation, by specifying this condition so that we can truly model the engine and atmosphere. Although the flow in the vicinity of fan was not with Mach = 0.0. Therefore it is just a technique to model the flow with real boundary conditions. What you guys think about this? 

October 10, 2012, 22:49 

#8  
Senior Member
Ali
Join Date: Jan 2012
Location: Pakistan
Posts: 130
Rep Power: 8 
Quote:
Flow is incompressible (M < 0.3), So what will be the velocity then for M=0.0.
__________________
Best Regards Ali 

October 11, 2012, 05:40 

#9 
Senior Member
Philipp
Join Date: Jun 2011
Location: Germany
Posts: 1,296
Rep Power: 19 

Thread Tools  
Display Modes  


Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
Help could anyone post a simple cylinder mesh  guilherme  OpenFOAM Native Meshers: blockMesh  32  March 25, 2016 08:45 
Urgent Naca4415  ck3  FLUENT  3  June 9, 2012 08:36 
problem in running icoFoam  Alucard  OpenFOAM  2  March 17, 2012 10:01 
FDM vs FVM vs FEM in CFD analysis  ck5285  FLOW3D  1  September 1, 2009 10:51 
correction of KIVA Itape  hama  Main CFD Forum  0  May 2, 2006 03:41 