[Jotomize]

Hey all,

I am trying to simulate a transient inlet pressure boundary condition that is a step function with an exponential decay using a udf codeIMG_1830.jpg. I am having trying to come up with a udf that best simulates this situation. I have attached an image to show what I am trying to say. The maximum peak pressure is 3000psi and it should settle at a pressure of around 50 psi at the end of the exponential decay. This is what I have so far:-

#include "udf.h"



DEFINE_PROFILE(unsteady_pressure,thread,position)
{

face_t f;
real ts= CURRENT_TIMESTEP;
real i;
real flow_time = RP_Get_Real("flow-time");

begin_f_loop(f, thread)
{
for(i=1;i<50;i++)
{

if (flow_time > 0 && flow_time < 0.0001)
{
F_PROFILE(f, thread, position)= 50.0;
}



else if (flow_time > 0.0001)
{
F_PROFILE(f, thread, position)=3000*exp(-flow_time);
}


else if (flow_time==0.0001)
{
F_PROFILE(f, thread, position)=3000;
}

}



end_f_loop(f, thread)

}
}

Is a for loop the best way to go about this or should I maybe use an array?
Thank you in adavnce

[pakk]

Your for loop doesn't do anything... You repeat the same code 50 times, I don't understand what you are trying to achieve with that. Why loop? Why 50 times?

It looks like you can just remove the loop...

Some remarks:
-the flowtime==0.0001 part is useless, remove it, you don't need it. If flowtime<0.0001 constant else exponential.
-your pressure profile equation for the exponential part is wrong. Should be 3000*exp(0.0001-flow_time).
-Fluent expects SI units by default. You have the right to use this silly psi unit, but be careful.