initial condition setting in transient from steady?

fruitkiwi · May 14, 2012, 01:04

Today come across this question,it surprise me.

I recall in fluent i once draw a pipe, which has constant velocity at the inlet as 0.1m/s, and has outlet pressure set as 0, run in steady state.

then i use it as initial condition in the transient state. which has a velocity profile start with velocity 0m/s at t=0, pressure set as 0, run in transient state.

I thought is good.But not, why i need specify the velocity 0m/s at t=0, should'nt it be replaced by the steady state solution, i should set it as 0.1m/s at t=0 to make it converge easily?

am i wrong?

fruitkiwi · May 15, 2012, 08:57

I think i do not make myself clear and there's why not reply.

My problem is to use steady solution as initial condition for a transient problem, the first time point on the velocity profile in transient must match with the velocity profile at the steady solution, so it do not create a "discontinuity" in the solver setting, to bypass the convergence issues

example: velocity is 0.01m/s in steady, then my transient velocity profile, t=0, must be 0.01m/s or can i specify it as 0?

i am struggling to find some book to prove it, is there any one agree with me?

i know it sounds silly.

May 14, 2012, 01:04	initial condition setting in transient from steady?	#1
fruitkiwi Member kiwi Join Date: Mar 2012 Location: South East Asia Posts: 58 Rep Power: 14	Today come across this question,it surprise me. I recall in fluent i once draw a pipe, which has constant velocity at the inlet as 0.1m/s, and has outlet pressure set as 0, run in steady state. then i use it as initial condition in the transient state. which has a velocity profile start with velocity 0m/s at t=0, pressure set as 0, run in transient state. I thought is good.But not, why i need specify the velocity 0m/s at t=0, should'nt it be replaced by the steady state solution, i should set it as 0.1m/s at t=0 to make it converge easily? am i wrong? Last edited by fruitkiwi; May 14, 2012 at 02:04.

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May 15, 2012, 08:57		#2
fruitkiwi Member kiwi Join Date: Mar 2012 Location: South East Asia Posts: 58 Rep Power: 14	I think i do not make myself clear and there's why not reply. My problem is to use steady solution as initial condition for a transient problem, the first time point on the velocity profile in transient must match with the velocity profile at the steady solution, so it do not create a "discontinuity" in the solver setting, to bypass the convergence issues example: velocity is 0.01m/s in steady, then my transient velocity profile, t=0, must be 0.01m/s or can i specify it as 0? i am struggling to find some book to prove it, is there any one agree with me? i know it sounds silly.