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July 9, 2011, 05:22 
Displaying Acceleration Parameter

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July 10, 2011, 06:42 

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Glenn Horrocks
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What do all the variables represent?


July 10, 2011, 09:16 

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July 10, 2011, 19:00 

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Glenn Horrocks
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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 

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Glenn Horrocks
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I see. But still, isn't the dUinf/ds term zero, so it always evaluates to zero?


July 18, 2011, 06:09 

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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 

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Glenn Horrocks
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What boundary layer streamwise velocity? How far out from the wall?


July 28, 2011, 06:16 

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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 

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Glenn Horrocks
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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. 

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