# head losses or static pressure

 Register Blogs Members List Search Today's Posts Mark Forums Read

 November 17, 2011, 09:19 head losses or static pressure #1 New Member   Juan Join Date: Dec 2010 Posts: 17 Rep Power: 6 Hi I am computing head losses i a 90º elbow. The difference height between inlet point and outlet point is 1m. When I compute it using fluent the difference between both points regarding to static pressure is close to 0,5 m. The head losses into the elbow is 0,5 or 1,5 m?. Does fluent considere the difference of height between two points in order to compute the static pressure or i should add the difference height to the static pressure obtained with fuent Thanks

 November 18, 2011, 07:19 gravity option #2 New Member   Juan Join Date: Dec 2010 Posts: 17 Rep Power: 6 If I have an elbow and I measure the static pressure in 2 points with different height. If I don´t consider gravity, the static pressure will be different?. Shoul I considered the gravity when you try to find out the head losses between 2 points with different height? What does it happen if i do not consider gravity? Thanks

 November 18, 2011, 09:37 #3 Senior Member   Andrew Join Date: Mar 2009 Location: Washington, DC Posts: 194 Rep Power: 8 static pressure and head loss are two different things..head loss is due to the velocity and losses and includes gravity..static pressure has nothing to do with the velocity. You should calculate out both and compare to your Fluent answer..it is pretty straight forward and any fluids book will show you how. good luck mohammad azizinia likes this.

 November 21, 2011, 05:55 head losses #4 New Member   Juan Join Date: Dec 2010 Posts: 17 Rep Power: 6 hi thanks i have understand you said. I try to explain what i have done I have measured difference pressure static between 2 points in the elbow with Fluent. The different static pressure obtained by using Fluent was 0,04 m. I know it is not the head losses (i should consider the differente height between both points), so after that, as I know the different height between inlet point and outlet point (0,05 m), my head losses are 0,09 m (0,05m + 0,04m)(similar to my experimental results), considering similar velocity between the 2 points. I have done it without considering gravity, is it right? if I would consider gravity, could I say that the pressure static obtained in fluent is the same as the head losses? I have made simulation using an horizontal pipe and other one with a vertical pipe. Simulating both of them i have obtained the same values for static pressure, dynamic pressure and total pressure. How is it possible?. I know the head losses should be the same but I do not understand how the static pressure are similar. How can I explain fluent if it is a vertical pipe or horizontal pipe? Using gravity maybe? Thanks Last edited by Tres; November 21, 2011 at 07:14.

 November 21, 2011, 17:02 #5 Senior Member   Andrew Join Date: Mar 2009 Location: Washington, DC Posts: 194 Rep Power: 8 it sounds like you don't have your fluent model set up correctly, and Fluent is seeing both pipes as the same. If I remember correctly, you can define which axis gravity is following, and that will tell fluent if it is vertical or horizontal.

 November 22, 2011, 04:03 #6 New Member   Juan Join Date: Dec 2010 Posts: 17 Rep Power: 6 Thanks OK, I have made a simulation in a vertical pipe including gravity for axis Y (-9.81m/s2). Now I have obtained different static pressure (higher in the point which has less height and lower in the point which has more height). After measure static pressure with fluent when I consider the different height between the 2 points I obtain the same head losses than a horizontal pipe. In spite of this, I have a question about specified operating density option. When you choose gravity you can choose a specified operating density option. In several tutorial says that you can choose 0 kg/m3 as density but I do not understand why I can not use the density of water. Ihave used velocity inlet and outflow as boundary conditions Thanks again

 November 22, 2011, 09:28 #7 Senior Member   Andrew Join Date: Mar 2009 Location: Washington, DC Posts: 194 Rep Power: 8 I believe if you defined your 'fluid' section of the model as water you don't have to apply any density definitions. You can try changing that and seeing how it affects your answer.

 November 22, 2011, 12:51 #8 New Member   Juan Join Date: Dec 2010 Posts: 17 Rep Power: 6 Thanks I try to understand my solutions. When I choose 0 kg/m3 as density I obtain a difference static pressure between 2 points which is not the same as my head losses, but when I consider the different height betweem both points the solution is right. On the other hand If I do not choose anything density the difference static pressure is the same as my head losses, but it must be wrong because the static pressure in fluent is not the same as head losses. Thanks

 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 MASOUD Fluent UDF and Scheme Programming 0 June 5, 2010 00:49 Miry CFX 0 September 16, 2007 18:14 pi CFX 3 May 26, 2004 10:35 Alfonso Ferrandez FLUENT 2 May 23, 2000 08:53 DS & HB Main CFD Forum 0 January 8, 2000 16:00

All times are GMT -4. The time now is 11:06.