
[Sponsors] 
July 9, 2011, 05:22 
Displaying Acceleration Parameter

#1 
New Member
Join Date: Apr 2011
Posts: 12
Rep Power: 7 

July 10, 2011, 06:42 

#2 
Super Moderator
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 11,965
Rep Power: 93 
What do all the variables represent?


July 10, 2011, 09:16 

#3 
New Member
Join Date: Apr 2011
Posts: 12
Rep Power: 7 

July 10, 2011, 19:00 

#4 
Super Moderator
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 11,965
Rep Power: 93 
Sounds like a strange definition of acceleration. Isn't the kinematic vis and Uinf constant? Doesn't that mean dUinf/ds = 0, so your equation is always 0?


July 17, 2011, 19:43 

#6 
Super Moderator
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 11,965
Rep Power: 93 
I see. But still, isn't the dUinf/ds term zero, so it always evaluates to zero?


July 18, 2011, 06:09 

#7 
Super Moderator

yes you are right. this definition is little bit wrong.
The actual definition is : The derivative does not contain the free stream velocity, rather it is the rate of change of boundary layer stream wise velocity at onset of transition w.r.t to the local distance (in this case it is the suction side length) and again in first term in denominator i.e the velocity is not the free stream, it is again the boundary layer streamwise velocity just at onset of transition. Hope now it is clear. Now we are looking for your help. as I was also in search that how to plot the acceleration parameter in CFX. Best Regards Far 

July 18, 2011, 07:01 

#8 
Super Moderator
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 11,965
Rep Power: 93 
What boundary layer streamwise velocity? How far out from the wall?


July 28, 2011, 06:16 

#9 
New Member
Join Date: Jul 2011
Posts: 3
Rep Power: 6 
The acceleration parameter is:
: viscosity at boundary layer edge : velocity at boundary layer edge : for 2D: arclength along the airfoil can be calculated from the surface pressure distribution by assuming constant pressure normal to the wall inside the boundary layer (boundary layer theory, ) and applying the (compressible) Bernoulli equation. can be assumed constant, I think, or can be calculated again with Bernoulli and applying isentropic relations and the Sutherland law. 

July 28, 2011, 08:21 

#10 
Super Moderator
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 11,965
Rep Power: 93 
Thanks for explaining the equation more fully. I had no idea what Far was talking about.
I cannot see how you will calculate this in CFDPost. In that case I would export the required variables and calculate it externally in excel or matlab. I assume you wish to plot this function over a foil surface? In that case export the temperature, velocity and any other field from the foil surface and do the calculation of the parameter externally. 

Thread Tools  
Display Modes  


Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
Error when input new parameter in Fluent  micro11sl  FLUENT  0  July 1, 2011 06:42 
compile errors of boundary condition "expDirectionMixed"  liying02ts  OpenFOAM Bugs  2  February 1, 2010 21:11 
MAxium residual...confusion with expert parameter  KK  CFX  3  February 8, 2008 11:47 
Expert Parameter for compressible transient  ioannis  CFX  0  November 2, 2005 20:28 
averaging parameter in Tascflow  sudar  CFX  1  January 20, 2003 12:06 