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CMU value for k-epsilon model

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Old   July 20, 2017, 11:28
Default CMU value for k-epsilon model
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Vedamt Chittlangia
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Hello,

I want to define C_\mu as a local variable in FLUENT for low-Reynolds Number k-epsilon model. I am using Abe-Kondoh-Nagano model. To proceed further with full implementation I am testing only two values. I am able to get the exact results from my UDF from C_\mu = 0.09. But when I change the value of C_\mu to 0.05 in the UDF then these results don't match to results that are obtained by changing C_\mu = 0.05 from the GUI panel.
Can anyone please help me resolve this issue? I am attaching my UDF below.

Code:
#include "udf.h"
#include "mem.h"
#include "math.h"

#define C_MU 0.05
#define SIG_K 1.4
#define SIG_D 1.4

/* user defined Turbulent viscosity */
DEFINE_TURBULENT_VISCOSITY(turb_vis,c,t)
{ 
	real c_k, c_d, ReT, ReD, muT, fmu;
	c_k = C_K(c,t);
	c_d = C_D(c,t);
	/*flooring the values */	
	if (c_k < 1.e-10)
		c_k = 1.e-10;
	if (c_d < 1.e-10)
		c_d = 1.e-10;
	
	ReT = C_R(c,t)*SQR(c_k)/(C_MU_L(c,t)*c_d);
	ReD = C_WALL_DIST(c,t)*pow(C_MU_L(c,t)*c_d/C_R(c,t),0.25)*C_R(c,t)/C_MU_L(c,t);
	
	fmu = SQR( 1. - exp( -ReD/14.0 )) * ( 1. + 5.0*exp( -SQR(ReT/200.0 ))/(pow(ReT,0.75)) );	/* damping function */
	muT = C_R(c,t)*C_MU*fmu*SQR(c_k)/c_d;	
	if (muT > 1.e5)
		muT = 1.e5;		
	return muT;
}   


DEFINE_PRANDTL_K(tke_PR,c,t)
{
	return SIG_K;
}


DEFINE_PRANDTL_D(tdr_PR,c,t)
{
	return SIG_D;
}

/* AKN turbulence model: viscosity function */
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Old   July 21, 2017, 17:50
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Lucky Tran
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Is this maybe a wall function or wall modelling problem? The Cmu in the GUI panel I think only affects the Cmu for the transport equation but not the near wall stuff.
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Old   July 21, 2017, 18:09
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Vedamt Chittlangia
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Quote:
Originally Posted by LuckyTran View Post
Is this maybe a wall function or wall modelling problem? The Cmu in the GUI panel I think only affects the Cmu for the transport equation but not the near wall stuff.
I am using low-Reynolds model by Abe-Kondoh-Nagano. There are no wall functions for this model.
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Old   December 26, 2020, 12:15
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Ashhar
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I want to change the C2_Epsilon Model constant of low Reynolds number Abe-Kondoh-Nagano model to a function using UDF functions in Fluent. I am relatively new to udf funcitons. Can anyone guide me how to change a constant model constant to a function in ANSYS Fluent.
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