# Perturbation to a Steady State Solution, how to?

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 February 16, 2015, 05:56 Perturbation to a Steady State Solution, how to? #1 New Member   Ashwin N Join Date: Feb 2015 Posts: 1 Rep Power: 0 Hey all! So I am modelling a simple Laminar 2D Pipe flow in Fluent, (which I am new to btw). So, once I solve for the transient case for a certain timesteps and I get more or less a steady state solution, I want to introduce a pressure perturbation at the inlet and wanna gauge the response of the fluid. How can I go about doing this in Fluent? Kindly suggest a simple method for this. Regards.

 October 17, 2017, 06:46 introducing a perturbation #2 New Member   Rohit Join Date: Jul 2016 Posts: 9 Rep Power: 8 Hello, If you want to introduce a perturbation by changing the boundary condition, I would suggest you use a UDF. The following is a code which you can save as a .c file and compile in FLUENT /* the following UDF imposes a value of pressure p0 at the required boundary before time t1. Once t1 is crossed the this a perturbation is introduced in the form of an increased pressure, p1, at the boundary. This is done using an if-else condition */ #include "udf.h" DEFINE_PROFILE(unsteady_pressure, thread, position) { face_t f; real t = CURRENT_TIME; real t1 = 0.1; /*The time after which you want to add the perturbation*/ real p0 = 200; /*This is the initial pressure you impose at the boundary*/ real p1 = 210; /*This the perturbed value of pressure*/ begin_f_loop(f, thread) { if(t

 October 17, 2017, 06:47 #3 New Member   Rohit Join Date: Jul 2016 Posts: 9 Rep Power: 8 you may search online how to add a UDF to FLUENT

 Tags oscillations, perturbation, response