# Inlet to Outlet Chart with Streamline Location Problem

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 June 11, 2018, 23:53 Inlet to Outlet Chart with Streamline Location Problem #1 New Member   limlibin Join Date: Jun 2018 Posts: 11 Rep Power: 7 Hi everyone, I had a problem about the Inlet to Outlet chart. My Total Pressure graph had a "jump" between the Rotor to Stator. Pressure graph plot not nice with it. Did anyone know what happen? What is the ideally graph should i had to? Thank you. pic1.png pic3.png pic2.jpg

 June 12, 2018, 01:40 #2 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,688 Rep Power: 143 You are plotting parameters across an interface. On one side of the interface the velocities are referenced to a stationary frame of reference and on the other side of the interface the velocities are referenced to a rotating frame of reference. This means that parameters which are a function of velocity (such as total pressure) will be discontinuous across the interface. If you want to see a continuous line try variables like total pressure in stationary frame. __________________ Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.

 June 12, 2018, 02:46 #3 New Member   limlibin Join Date: Jun 2018 Posts: 11 Rep Power: 7 Hi, Thanks for you reply. I had set up INLET : Total pressure 1atm and Total temperature 300K OUTLET : Static pressure 2.5atm Do I need to exchange my inlet conditions ?

 June 12, 2018, 02:59 #4 Senior Member   Gert-Jan Join Date: Oct 2012 Location: Europe Posts: 1,823 Rep Power: 27 No. It has nothing to do with the setup of your calculation. In Post you have to plot "Total Pressure in Stationary Frame". That's all.

 June 12, 2018, 08:51 #5 New Member   limlibin Join Date: Jun 2018 Posts: 11 Rep Power: 7 Sorry, I dont know what do you mean about "Total Pressure in Stationary Frame" ? Is it the frame type from CFX Setup ? I had set the frame type of rotor and stator with stationary.

 June 12, 2018, 09:16 #6 Senior Member   Gert-Jan Join Date: Oct 2012 Location: Europe Posts: 1,823 Rep Power: 27 You have a rotating domain and a stationary domain. Therefore, you have a Rotating Frame of reference and a Stationary Frame of reference. So you can plot the velocity relative to the Rotating Frame and relative to the stationary Frame. The same holds for Total Pressure. If you plot relative to stationary Frame of reference you will obtain continous graphs. Last edited by Gert-Jan; June 14, 2018 at 05:12.

 June 14, 2018, 04:49 #7 New Member   limlibin Join Date: Jun 2018 Posts: 11 Rep Power: 7 Hi, Thanks for you reply. I had another question. I had found that when total pressure in rotor is decreasing. Is it seem like abnormal? Is it about the setting or the blade problem? Thank you

 June 14, 2018, 05:13 #8 Senior Member   Gert-Jan Join Date: Oct 2012 Location: Europe Posts: 1,823 Rep Power: 27 I don't understand your question. Please rephrase..... Last edited by Gert-Jan; June 18, 2018 at 01:40.

 June 14, 2018, 06:38 #9 New Member   limlibin Join Date: Jun 2018 Posts: 11 Rep Power: 7 I am doing the centrifugal compressor. In theoretical the total pressure should be increase when the fluid flow from inlet to outlet. But I found from the graph (streamline location vs total pressure) , it had shown me the total pressure decrease. https://drive.google.com/file/d/12lZ...TAc0RNtmD/view Last edited by deii; June 14, 2018 at 08:29.

 June 14, 2018, 08:10 #10 Senior Member   M Join Date: Dec 2017 Posts: 642 Rep Power: 12 I am totally confused here. You write centrifugal compressor, but the images in your first post look very much like an axial machine? And, what kind of total pressure are you looking at? Total Pressure in Stn or Relative Frame?

 June 14, 2018, 08:28 #11 New Member   limlibin Join Date: Jun 2018 Posts: 11 Rep Power: 7 I am looking for Total Pressure in Stn. However I am not sure the graph correct or not? I had put Total Pressure in Stationary Frame. Last edited by deii; June 15, 2018 at 05:28.

 June 15, 2018, 05:14 #12 Senior Member   M Join Date: Dec 2017 Posts: 642 Rep Power: 12 Can you just attach the images directly like you did with your first post? I dont want to log into my google account from some forum links.

 June 15, 2018, 05:27 #13 New Member   limlibin Join Date: Jun 2018 Posts: 11 Rep Power: 7

 June 15, 2018, 08:39 #14 Senior Member   M Join Date: Dec 2017 Posts: 642 Rep Power: 12 Ok, obviously centrifugal compressor ... change of perspective is never a bad thing. Honestly, I don't know how the total pressure in stn frame behaves in the rotating domain of a centrifugal compressor. However, I'd recommend grabbing a piece of paper and working out velocity triangles for your geometry (look it up in a book if you don't know how to do that). Then you know how the velocity components behave at in- and outlet, and it should be easier to understand how the pressure variables behave.

July 31, 2018, 03:55
#15
New Member

limlibin
Join Date: Jun 2018
Posts: 11
Rep Power: 7
Hi,

I had changed the total pressure to stationary frame. Is it problem occurs at interface between stator to rotor?

Setting:
1) Stage (Mixing-Plane)
2) Specified Pitch Angles 360 degrees (if set with 1 degree will appear error message)
Attached Images
 1.jpg (101.1 KB, 8 views)