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October 15, 2014, 07:22 |
UDF for pressure outlet (resistance)
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#1 |
Senior Member
Join Date: Feb 2011
Posts: 140
Rep Power: 15 |
Dear all, I try to write a UDF to set the pressure at the outlets of my geometry according to the equation p=R*Q (p: pressure, R: resistance and Q: volume flow rate) for a fixed value of “R” at each outlet which corresponds to the resistance of the downstream vessels. Therefore, I have to use/readout the outflow at each outlet to calculate the pressure. My first guess of the UDF was: #include "udf.h" #include "math.h" #define Density 1050. #define R1 3.590987710898600e+10 real QMout1; real Qout1; real Pout1; DEFINE_PROFILE(outlet1_pressure,thread,nv) { face_t f; QMout1=0.0; //initial value begin_f_loop(f,thread) { QMout1+=F_FLUX(f,thread); //sum of mass flow rate of all faces of the outlet at the same time step } end_f_loop(f,thread) Qout1=QMout1/Density; //calculate volume flow rate Pout1=R1*Qout1; //calculate pressure begin_f_loop(f,thread) { F_PROFILE(f,thread,nv)=Pout1; } end_f_loop(f,thread) } I checked the results (static pressure and volume flow rate) for several time steps at several outlets and found the equation was satisfied. However, I am not sure, if this makes sense, since I thought I must e.g. use the volume flow rate of the previous time step and solve the equation iteratively. But I am a bit confused how to integrate this at the UDF!? And what about the first time step? I certainly need to make a proper initial guess, don’t I? Does anybody have an idea how to fix this UDF? I am thankful for any help and idea! Lilly |
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