# Pressure problems with inlet variable velocity

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 June 10, 2015, 20:20 Pressure problems with inlet variable velocity #1 New Member   Diego Jaimes Join Date: Feb 2015 Posts: 8 Rep Power: 10 Hi everyone, I'm modeling a laminar flow of water through a tube in axisymmetric way with 5°. From a fully developed flow on t=0[s] and I'm decreasing the main inlet velocity every timestep with a constant aceleration but in the first timestep when the inlet velocity is decreasing I got a pressure drop of total pressure that results false. First I ran one steady state to get my fully developed flow with: Inlet: Velocity profile (Poiseuille Flow) Wall: no slip. smooth outlet: Total pressure After that I got my initial conditions solution. I tried to run a transient with the steady state as t=0[s] with: Inlet: Velocity profile - V wall: no slip. smooth outlet: Total pressure (the same of the steady state) with V as a variable V=aceleration(constant)*t As I have a simulation of incompressible flow, I should have no pressure drop in my tube, as I have on my first steady state, but I get a false pressure drop proportional to my aceleration. I also ran another steady state of my final time step expected, with: Inlet: Velocity profile - V V=a*tf= final velocity Wall: no slip. smooth outlet: Total pressure and I have a good result with no pressure drop. I want to obtain the same result with my transient but unfortunately I can't. If someone knows why I have this problem, how to fix it or what am I doing wrong, please let me know. Thanks for your help!

 August 31, 2016, 12:33 cfd fluent Heat Transfer #2 New Member   Ibrahim Join Date: Aug 2016 Posts: 1 Rep Power: 0 Hi All, I have been started to use Ansys fluent to simulation thermal resistance, overall heat transfer coefficient, and heat loss through cylinder with insulation material of tow layers. Any one has been worked on it pleas help me. Slam

September 1, 2016, 03:31
#3
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Jiri
Join Date: Mar 2014
Posts: 200
Rep Power: 12
Quote:
 Originally Posted by jaimesdiegop As I have a simulation of incompressible flow, I should have no pressure drop in my tube
1) Incompressible does not mean there are no losses, even if you have free slip on walls, you still have losses in the liquid.

2) Try setting static pressure outlet instead of total pressure.

3) How many iterations per time step do you have?

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