# need help for simulation of axial fan

 User Name Remember Me Password
 Register Blogs Members List Search Today's Posts Mark Forums Read

 LinkBack Thread Tools Display Modes
 August 20, 2010, 06:31 need help for simulation of axial fan #1 Member   Rahul Vaibhav Join Date: Nov 2009 Location: India Posts: 33 Rep Power: 10 Hi i am confuse what should be the inlet and outlet boudary condition for axial fan.the atmospheric air is axially going in the fan. and the inlet and outlet velocity can be determined by rotation of rotor... i could not predict the boundary condition for such problem. please help me in that!!!!

 August 20, 2010, 14:02 boundary conditions #2 Member   Join Date: Aug 2010 Posts: 31 Rep Power: 9 It really depends on the purpose of the simulation. If you want to determine the characteristic curve for instance, you would want to set the inlet static pressure to a known upstream condition, or ambient pressure at infinity, and vary the outlet static back- pressure. Alternatively, if your fan is required to deliver a certain amount of mass flow then you should set this as boundary condition. My best advice is to check some tutorials. There is one for axial fans.

 August 23, 2010, 06:58 #3 New Member   Join Date: Aug 2009 Location: Switzerland Posts: 11 Rep Power: 10 In similar cases I used massflow boundary condition at the inlet and static pressure at the outlet. I got stable simulations with these boundary conditions. but as "Turbomachinery" said before, it depends on what exactly you want to know. For example, if you know the velocity profile from another simulation or from experiments, you can set this as inlet-bc.

 August 30, 2010, 04:14 #4 Member   Rahul Vaibhav Join Date: Nov 2009 Location: India Posts: 33 Rep Power: 10 ok let us assume..I am designing a completely new fan and i have unavailability of experiment results. In this case i am doing study of a fan which is open to atmosphere. i am assuming the outlet and inlet both are open to atmosphere , so i have taken the static pressure zero as outlet boundary condition, because the fan inlet is also open to atmosphere i am taking total pressure = 0 in fan inlet bc. i want to to know the mass flow rate given by the fan on a given rmp.. but i am not getting appropriate results please let me know if i am making some mistake.

 August 30, 2010, 04:41 #5 New Member   Join Date: Aug 2009 Location: Switzerland Posts: 11 Rep Power: 10 Are you sure that the boundary condition is set far enough from the fan? because directly before the fan, pressure is lower, after the fan higher than atmosphere. Otherwise you wouldn't have a pressure difference over the fan, and that's nonsense. you should also consider, that the fan is usually a part of a whole machine, with inlet casing etc. usually the pressure and velocity profiles in front of the fan are not uniform over the 360°. this might have a strong impact on efficiency!

 August 30, 2010, 05:57 #6 Member   Rahul Vaibhav Join Date: Nov 2009 Location: India Posts: 33 Rep Power: 10 indeed i refer the boundary condition given in a thread for similar situation http://www.cfd-online.com/Forums/flu...onditions.html by Razvan. Actually i don't want to give mass flow rate boundary condition because it is a forced boundary condition.i was expecting to do simulation for 0 static pressure at outlet.

 August 30, 2010, 07:04 #7 New Member   Join Date: Aug 2009 Location: Switzerland Posts: 11 Rep Power: 10 I completely agree with what Razvan says. But as he says, you need to model some space before and after the fan: "let's say we have an axial fan in a tube, and both ends of this tube are directly connected to the atmosphere." If you put you atmospheric pressure condition directly in front and after the fan, it can't work, as the fan can't produce a pressure gradient. That's why I asked you "Are you sure that the boundary condition is set far enough from the fan?"

 August 30, 2010, 07:52 #8 Member   Rahul Vaibhav Join Date: Nov 2009 Location: India Posts: 33 Rep Power: 10 i agree with you that i should perform the same simulation in a tube and i will be going to perform simulation in a tube as Razvan and you suggest. i'll discuss the results tomorrow, but here i am not just talking about the pressure only.. i am applying static pressure and total pressure boudnary condition, which are quite logical bc for such case. Last edited by rahulv; August 30, 2010 at 23:02.

 August 30, 2010, 23:30 #9 Member   Rahul Vaibhav Join Date: Nov 2009 Location: India Posts: 33 Rep Power: 10 I didn't even work out this way

 August 31, 2010, 04:33 #10 New Member   Join Date: Aug 2009 Location: Switzerland Posts: 11 Rep Power: 10 hmmm, I guess I can't help you Did the simulation run and the results were strange, or didn't it run at all?

 August 31, 2010, 06:32 #11 Member   Rahul Vaibhav Join Date: Nov 2009 Location: India Posts: 33 Rep Power: 10 simulation runs but the results are not appropriate... when i look the result details i found that there is no effect of blade rotation in the domain. i have performed some test to simulation of simple problems with rotating solid part , but even in tests i couldnt see the effect of rotating part on fluid motion.may be i am doing some mistake for appling rotating boundary condition.

 August 31, 2010, 06:36 #12 New Member   Join Date: Aug 2009 Location: Switzerland Posts: 11 Rep Power: 10 If you like, you can send me the *.out-file, so I can check the boundary conditions. (baraka.so(at)hotmail.com)

 September 1, 2010, 07:19 #13 Member   Rahul Vaibhav Join Date: Nov 2009 Location: India Posts: 33 Rep Power: 10 i got the solution... with the same boundary condition. i kept the blade stationary and i rototate the fluid over the blate at given rpm.

 September 3, 2010, 05:24 #14 Senior Member   Saima Join Date: Apr 2009 Location: Canada Posts: 185 Rep Power: 9 Rahul, i am doing the 2D rotor blade and having problem in solution. I made my mesh in ICE CFD like a cascade vertical (inlet and outlet). Then i try to solve in CFX. CFX converted this 2D into 3D. I have calculated my boundary condition through velocity triangles. I know experimental data but with blade rotatng point of view. Now, i solved it in CFX but i have not found option for moving mesh. (As i cant take rotating option because it is not complete blade just a section of blade) Could u pls let me know how did u setup and wat are your boundary conditions plus your software? Last edited by Saima; September 3, 2010 at 06:22.

 September 3, 2010, 06:54 #15 Member   Rahul Vaibhav Join Date: Nov 2009 Location: India Posts: 33 Rep Power: 10 hi saima i have performed 3d simulation of a mixed flow impeller in cfx.. I think there is no need of rotating mesh in ur problem.. you can perform the simulation with section of blade only. you keep the blades stationary and give rotation to the fluid . this way cfx will just add a tengential velocity component at the each fluid control volume. "just imagine you are sitting on the blade. For you blade is stationary and the whole world is revolving around you." in my case i want to know the mass flow rate on a given rmp and at zero static pressure.. so i gave outlet bc = static pressure =0 inlet bc = total pressure = 0 or you can contact me on rah00002004[at]gmail.com

 August 2, 2014, 08:57 Finding fan curve #16 Member   hashim chaudhry Join Date: Jun 2014 Location: turkey Posts: 46 Rep Power: 5 Hi I am quite new to CFD i am trying to find out the fan curve. My fan diameter is 71mm and what did uptill now I made inlet duct 15 times of fan dia with pressure inlet (0.0 Pa), outlet duct 30 times of fan dia with pressure outlet (0.0 Pa) and I am giving fixed rpm to the rotating region in between. I am measuring pressure in inlet and outlet duct at a position 10 times of fan dia. but Still I didnt find the relevant pressure difference across the fan and also the solution is not converges. If i want to give the value of dynamic pressure at the inlet then how can i calculate this value as i know the flowrate. I would be very grateful if you people help me out

 August 4, 2014, 11:23 #17 Senior Member   Edmund Singer P.E. Join Date: Aug 2010 Location: Minneapolis, MN Posts: 512 Rep Power: 14 Start your own new thread and quit multiposting. Glenn answered you in the other post. If you have further questions please update with regards to what you learned in facts and how it applies to what you are doing.

December 21, 2015, 13:12
#18
New Member

---
Join Date: Dec 2012
Location: Turkey
Posts: 8
Rep Power: 6
Quote:
 Originally Posted by rahulv hi saima i have performed 3d simulation of a mixed flow impeller in cfx.. I think there is no need of rotating mesh in ur problem.. you can perform the simulation with section of blade only. you keep the blades stationary and give rotation to the fluid . this way cfx will just add a tengential velocity component at the each fluid control volume. "just imagine you are sitting on the blade. For you blade is stationary and the whole world is revolving around you." in my case i want to know the mass flow rate on a given rmp and at zero static pressure.. so i gave outlet bc = static pressure =0 inlet bc = total pressure = 0 or you can contact me on rah00002004[at]gmail.com
For the next steps , i mean in the performance curve like 100 Pa , 200 Pa ie. what is the boundary conditions for Pressure İnlet - Pressure Outlet solutions ?

 Tags rotating machines

 Thread Tools Display Modes Linear Mode

 Posting Rules You may not post new threads You may not post replies You may not post attachments You may not edit your posts BB code is On Smilies are On [IMG] code is On HTML code is OffTrackbacks are On Pingbacks are On Refbacks are On Forum Rules

 Similar Threads Thread Thread Starter Forum Replies Last Post VIPUL FLUENT 0 October 24, 2008 02:01 Russ FLUENT 8 July 7, 2006 13:59 J FLUENT 0 April 18, 2006 02:25 Vishu FLUENT 4 January 13, 2004 18:52 Chien-Chi Chao Siemens 1 February 1, 2001 23:13

All times are GMT -4. The time now is 18:16.

 Contact Us - CFD Online - Privacy Statement - Top