# UDF source term

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 April 20, 2006, 06:03 UDF source term #1 Rajani Kanth.B Guest   Posts: n/a Hi I am new to UDF in CFD.Iam doing two way coupling(turbulence modulationarticles effecting turbulence) problem in a vertical pipe In writing the code for source term for k equation I am struggling to define ds[eqn] my source term for k equation is 1-(t*/(t*+t_p)) where 1/t*=[1/(0.135(k/e))]+[urel/(0.22k^1.5/e)(turbulent time scale) t_p=rho_p*d_p^2/18*mu (particle response time or particle time constant) rho_p density of the particle d_p diameter of the particle mu viscosity of the fluid urel relative velocity whcich is equal to t_p*g I am trying in this way. #include "udf.h" #define alpha 1 #define dp 0.003 #define rhop 1020 #define u_rel 1 DEFINE_SOURCE(k_source,c,t,dS,eqn) { /* real x[ND_ND]; */ real source; t_p=((dp*dp)*rhop)/(18*C_MU_L(c,t)); /* particle time constant */ 1/t_t=(1/(0.135*(C_K(c,t)/C_D(c,t))))+(u_rel*C_D(c,t)/(0.22*C_K(c,t)^1.5));/* effective turbulent time scale */ source=(2*C_K(c,t)*alpha/t_p)(1-(t_t/(t_t+t_p)); /* dS[eqn]= */ return source; } could you please figure out my problem in writing the proper source code

 April 20, 2006, 11:16 Re: UDF source term #2 Kasper Skriver Guest   Posts: n/a I THINK that you have two options: 1) setting dS = 0 or 2) setting dS = d(Source-term)/d(k), where k is the variable that you are solving for. I think k is then you turbulent energy. Kasper/Denmark

 April 21, 2006, 05:05 Re: UDF source term #3 Rajani Kanth.B Guest   Posts: n/a Thank you Kasper.U gave me little idea to work.I think I have to do some more changes to the code to run. If it has to derive the Source term with k do I need to assume all the remaining as constants?Please Let me know

 January 11, 2013, 04:08 Temperature-dependent heat source #4 Senior Member   Join Date: Nov 2009 Posts: 125 Rep Power: 7 Dear all, i want to apply a heat source that is temperature-dependent. It is a copper winding of an electrical machine, and the resistance of the winding increases with temperature, and consequently the heat loss increases with it. i've look at the following: 1) starting with understanding how DEFINE_PROFILE works for a wall heat generation. 2) looked into a simple code example for DEFINE_SOURCE in ansys help. But, am i right to take the following approach? 1) use DEFINE_SOURCE 2) use C_T to feedback temperature into the temperature-dependent equation to calculate the 'new' heat source value Any comments is greatly appreciated. Thanks! __________________ Thank you for your kind attention. Kind regards, mactech001 Currently using: ANSYS v13

 May 1, 2013, 09:31 #5 Member   Sheng Join Date: Jun 2011 Posts: 58 Rep Power: 6 It looks you missed a multiply sign in the source term: source=(2*C_K(c,t)*alpha/t_p)(1-(t_t/(t_t+t_p)); source=(2*C_K(c,t)*alpha/t_p)*(1-(t_t/(t_t+t_p)); Define ds[eqn] is simple for this case. Just find the partial derivative to C_K(c,t) of the source term. An undergraduate level math knowledge can get it.

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