# UDF at pressure inlet[pleas help me!!]

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 February 2, 2011, 12:55 UDF at pressure inlet[pleas help me!!] #1 New Member   denny lee Join Date: Feb 2011 Posts: 7 Rep Power: 7 Hello All, I would like to increase pressure and temperature at pressure inlet boundary. As like this, 1~1000 iteration : pressure - 101325 pa, temperature - 250K 1001~2000 iteration : pressure - 101325* 2 , temperature - 500K How do i do complete my goal? I could compile and hook, but it is all!! I try to code UDF to find a solution by myself. but it does not work!!

 February 2, 2011, 22:09 #2 Senior Member   Real Name :) Join Date: Jan 2010 Location: United States Posts: 193 Rep Power: 8 Kokoory, A few things: 1) Are you really trying to change boundary conditions on a per-iteration basis? Is this a steady state or a transient problem? If you're actually trying to do a steady state simulation and you want to change inlet conditions after a specified number of iterations, don't. Simply put your boundary conditions to what you want them to be at t=infinity and let the simulation solve. 2) If you're trying to solve a transient case, and by iterations you mean "time steps" or "simulation time, in seconds" have a look at this Time dependent flows in Fluent with UDFs 3) Finally, more of a numerics issue...The changes you're imposing are fairly dramatic over what, presumably, will be a short period of time. This often causes convergence difficulties, and rightfully so -- the physics you're trying to impose are almost non-physical. In one timestep (very short) the pressure and temperature across an entire face double. Typically, one would impose a slightly more gentle ramp than a step change, and take fractional timesteps in the "in between" part to allow the solver to get to a more stable answer. I hope this helps! ComputerGuy

 February 3, 2011, 09:40 #3 New Member   denny lee Join Date: Feb 2011 Posts: 7 Rep Power: 7 Thanks, ComputerGuy. I refer your opinion for the model. So, I use the below code for pressure and temperature. Code: ```#include "udf.h" DEFINE_PROFILE(temperature_magnitude, t, i) { real temperature_mag; real current_time; face_t f; current_time = CURRENT_TIME; temperature_mag=300+220*current_time; begin_f_loop(f,t) { F_PROFILE(f,t,i) = temperature_mag; } end_f_loop(f,t) }``` Code: ```#include "udf.h" DEFINE_PROFILE(pressure_magnitude, t, i) { real pressure_mag; real the_current_time; face_t f; the_current_time = CURRENT_TIME; pressure_mag=101325*the_current_time; begin_f_loop(f,t) { F_PROFILE(f,t,i) = pressure_mag; } end_f_loop(f,t) }``` after that, I interpreted_ and compiled and hooked to pressure_inlet B.C. For pressure code, I hook to Gauge total pressure and for temperaturee code, to temperature. Next, I set the time step size = 0.001 and number of time steps = 10000 and Max iterations per step = 1. Because I would like to increase the pressure at 1013250 and the temperature at 2500K after all calculating. Is it OK what I thought to be?

 Tags inlet, pressure, temperature profile, udf

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