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January 16, 2013, 21:58 
JST Artificial Dissipation

#1 
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Join Date: May 2012
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Hi,
I was looking through the JST artificial dissipation code implemented in the function CCentJST_Flow::SetResidual() in numerics_convective.cpp. I have not been able to find references for some of the scaling factors used in the JST artificial dissipation code. Can you explain the meaning of "StretchingFactor", "sc2" and "sc4"? Alternatively, can you point out the paper that this is from? Do they have something to do with the aspect ratio of the elements? Code:
Local_Lambda_i = (fabs(ProjVelocity_i)+SoundSpeed_i*Area); Local_Lambda_j = (fabs(ProjVelocity_j)+SoundSpeed_j*Area); MeanLambda = 0.5*(Local_Lambda_i+Local_Lambda_j); Phi_i = pow(Lambda_i/(4.0*MeanLambda+EPS), Param_p); Phi_j = pow(Lambda_j/(4.0*MeanLambda+EPS), Param_p); StretchingFactor = 4.0*Phi_i*Phi_j/(Phi_i+Phi_j+EPS); sc2 = 3.0*(double(Neighbor_i)+double(Neighbor_j))/(double(Neighbor_i)*double(Neighbor_j)); sc4 = sc2*sc2/4.0; Epsilon_2 = Param_Kappa_2*0.5*(Sensor_i+Sensor_j)*sc2; Epsilon_4 = max(0.0, Param_Kappa_4Epsilon_2)*sc4; /* Compute viscous part of the residual */ for (iVar = 0; iVar < nVar; iVar++) val_resvisc[iVar] = (Epsilon_2*Diff_U[iVar]  Epsilon_4*Diff_Lapl[iVar])*StretchingFactor*MeanLambda; Code:
Epsilon_2 = Param_Kappa_2*max(Sensor_i, Sensor_j); Thanks, KW 

January 17, 2013, 04:29 

#2 
Super Moderator

I would also like to know more about this scheme.
This may be a basic question since I am not very familiar with JST scheme. The JST scheme in SU2 also has first order dissipation, e.g., the config files have Code:
% 1st, 2nd and 4th order artificial dissipation coefficients AD_COEFF_FLOW= ( 0.15, 0.5, 0.02 )
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January 18, 2013, 22:32 

#3  
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Francisco Palacios
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Cheers, Francisco 

January 18, 2013, 22:44 

#4  
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Francisco Palacios
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January 20, 2016, 00:20 

#5 
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Kan
Join Date: Feb 2014
Location: Australia
Posts: 51
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Hi,
I am also curious with the following code: /* Computes differences btw. Laplacians and conservative variables, with a correction for the enthalpy */ Diff_U[nVar1] = Density_i*Enthalpy_iDensity_j*Enthalpy_j; I guess this is used for the artificial diffusion term of energy conservation equation, but why do you change from total energy to enthalpy? Thank you, Kan 

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artificial dissipation, jst 
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