CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > General Forums > Main CFD Forum

First CFD Analysis - Results Question

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

Like Tree1Likes
  • 1 Post By FMDenaro

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   May 19, 2019, 10:51
Default First CFD Analysis - Results Question
  #1
Member
 
Join Date: May 2019
Posts: 30
Rep Power: 3
FCKW36 is on a distinguished road
Hello,

I did my first CFD Analysis with Ansys CFX and it worked pretty well. I have different shaped Bodys (different simulations) and I want to compare how they affect the flow (Mach 0,3 - Mach 0,7) behind the body. I want to find out, which one has the at least bad effect on a rotor, which will be placed 200 mm behind the body. (the rotor is not part of the CFD analysis) What would be a good approach to analyze the results I've got from the CFD Analysis?

I hope you can help me, I'm not experienced (still studying) and if you need some information which I forgot, please ask me.

Best Regards
FCKW36 is offline   Reply With Quote

Old   May 23, 2019, 11:55
Default
  #2
Senior Member
 
Matt
Join Date: Aug 2014
Posts: 847
Rep Power: 14
fluid23 is on a distinguished road
Look at the total pressure deficit and uniformity in the wake. Loss of total pressure can be correlated back to drag. It is a direct indication of the loss of energy of the flow. The more energy that is lost, the harder the rotor will have to work to accomplish the same task. The uniformity will give you some idea as to the flow conditions the rotor would see. Assuming this is an axial (rather than centrifugal) rotor, they generally prefer nice uniform flow fields... or are at least designed under the assumption of one.
fluid23 is offline   Reply With Quote

Old   May 29, 2019, 09:53
Default
  #3
Member
 
Join Date: May 2019
Posts: 30
Rep Power: 3
FCKW36 is on a distinguished road
Hi,

thank you very much for your answer. So I plot the total pressure with a contour like on the picture below (total pressure) and then I compare it between the different shapes? Would maybe calculating the drag coefficient with CFX be another good approach?



I have a question regarding my Mesh. Today I checked Y+ on the body, the used turbulence model is k-Epsilon. The Normal Speed on the Inlet is Mach 0,3 in one simulation and Mach 0,7 in the other one. Outlet Option for Mass and Momentum is an average static pressure with a relative pressure of 100000 Pa. I have 5 prism layers, first layer has a thickness of 0.1 mm. I have 5 layers with a grow rate of 1.2. I read that a y+ beyond 100 should be fine with this turbulence model.Does the Y+-Plot looks okay? (check the picture y+ plot)

Thank you for your help.

Attached Images
File Type: jpg total pressure.JPG (57.6 KB, 21 views)
File Type: jpg y+ plot.JPG (56.3 KB, 21 views)
FCKW36 is offline   Reply With Quote

Old   June 14, 2019, 13:27
Default
  #4
Member
 
Join Date: May 2019
Posts: 30
Rep Power: 3
FCKW36 is on a distinguished road
So, I'm now at the point, where i want to compare the different profile shapes and it's effect on a rotor which would be downstream the profile. As fluid23 said, I want to check the total pressure loss and uniformity in the wake at Mach 0.7.

I have 3 different Profile shapes, which you can see on the Picture Profile shapes. (please ignore the blue Points on the leading edges of the profiles)

I ploted the total pressure contour for all 3 shapes with a direct flow and for an angle at 20, as you can see at the two other Pictures.

My questions:

It seems like there is no difference for the 3 Profile shapes if the flow comes directly with no angle Variation. Does this seem legit?

Why is the total pressure loss for both rounded profiles weaker for the case where the flow comes with an angle of 20? This doesn't make any sense to me. What could be an explanation?

Thank you guys very much.
Attached Images
File Type: jpg profile shapes.JPG (128.2 KB, 9 views)
File Type: jpg Total pressure1.jpg (71.1 KB, 15 views)
File Type: jpg total pressure 2.jpg (65.4 KB, 12 views)
FCKW36 is offline   Reply With Quote

Old   June 14, 2019, 13:40
Default
  #5
Senior Member
 
Filippo Maria Denaro
Join Date: Jul 2010
Posts: 5,620
Rep Power: 60
FMDenaro has a spectacular aura aboutFMDenaro has a spectacular aura aboutFMDenaro has a spectacular aura about
Quote:
Originally Posted by FCKW36 View Post
So, I'm now at the point, where i want to compare the different profile shapes and it's effect on a rotor which would be downstream the profile. As fluid23 said, I want to check the total pressure loss and uniformity in the wake at Mach 0.7.

I have 3 different Profile shapes, which you can see on the Picture Profile shapes. (please ignore the blue Points on the leading edges of the profiles)

I ploted the total pressure contour for all 3 shapes with a direct flow and for an angle at 20, as you can see at the two other Pictures.

My questions:

It seems like there is no difference for the 3 Profile shapes if the flow comes directly with no angle Variation. Does this seem legit?

Why is the total pressure loss for both rounded profiles weaker for the case where the flow comes with an angle of 20? This doesn't make any sense to me. What could be an explanation?

Thank you guys very much.



Actually, I see differences at zero AOA ...the lengt of penetration of the recirculation zone appear different (see the yellow/orange region).
I suggest to do a 1D cut at several locations behind the body and superimpose the 3 pressure plot in the same figure for each station
FCKW36 likes this.
FMDenaro is offline   Reply With Quote

Old   June 14, 2019, 13:58
Default
  #6
Member
 
Join Date: May 2019
Posts: 30
Rep Power: 3
FCKW36 is on a distinguished road
Okay, thank you very much. Than I think it would be a good idea to measure the total pressure on various points on different horizontal lines behind th Body and plot it into a diagram.

Is the total pressure loss a good indicator to find out how the flow downstream the body is affected? As i said in my case there will be an axial rotor in a at the Moment not known distance behind the body. Or would compare the velocity would be better?

How can it be explained, that the total pressure loss for the rounded bodys seems to be smaller at an angle of 20?
FCKW36 is offline   Reply With Quote

Old   June 14, 2019, 14:02
Default
  #7
Senior Member
 
Filippo Maria Denaro
Join Date: Jul 2010
Posts: 5,620
Rep Power: 60
FMDenaro has a spectacular aura aboutFMDenaro has a spectacular aura aboutFMDenaro has a spectacular aura about
Quote:
Originally Posted by FCKW36 View Post
Okay, thank you very much. Than I think it would be a good idea to measure the total pressure on various points on different horizontal lines behind th Body and plot it into a diagram.

Is the total pressure loss a good indicator to find out how the flow downstream the body is affected? As i said in my case there will be an axial rotor in a at the Moment not known distance behind the body. Or would compare the velocity would be better?

How can it be explained, that the total pressure loss for the rounded bodys seems to be smaller at an angle of 20?

Smaller than the case of the same body at zero AOA? After you get the 1D plot you can quantify the difference in a better way
FMDenaro is offline   Reply With Quote

Old   June 14, 2019, 14:37
Default
  #8
Member
 
Join Date: May 2019
Posts: 30
Rep Power: 3
FCKW36 is on a distinguished road
Quote:
Originally Posted by FMDenaro View Post
Smaller than the case of the same body at zero AOA? After you get the 1D plot you can quantify the difference in a better way
Yes, as you can see in the picture. On one picture you can see the total pressure plot at 0 AOA for all 3 profile shapes and on the other pictures you can see the total pressure plot for the same shapes at an angle of 20. The chosen range for the total pressure and the number of contours is the same for every plot.
FCKW36 is offline   Reply With Quote

Old   June 14, 2019, 14:40
Default
  #9
Senior Member
 
Filippo Maria Denaro
Join Date: Jul 2010
Posts: 5,620
Rep Power: 60
FMDenaro has a spectacular aura aboutFMDenaro has a spectacular aura aboutFMDenaro has a spectacular aura about
Quote:
Originally Posted by FCKW36 View Post
Yes, as you can see in the picture. On one picture you can see the total pressure plot at 0 AOA for all 3 profile shapes and on the other pictures you can see the total pressure plot for the same shapes at an angle of 20. The chosen range for the total pressure and the number of contours is the same for every plot.



I see a different setting of the max value ....
FMDenaro is offline   Reply With Quote

Old   June 14, 2019, 14:48
Default
  #10
Member
 
Join Date: May 2019
Posts: 30
Rep Power: 3
FCKW36 is on a distinguished road
Quote:
Originally Posted by FMDenaro View Post
I see a different setting of the max value ....
Yes you are right, but it's only a small difference and for ne NACA-shaped leading edge profile it's the same value. Could this be explained or does it have to be wrong? I will check it in 1D tomorrow.
FCKW36 is offline   Reply With Quote

Old   June 15, 2019, 16:19
Default
  #11
Member
 
Join Date: May 2019
Posts: 30
Rep Power: 3
FCKW36 is on a distinguished road
I made 2D Plots today and measured the specific total pressure values for the different shapes at different distances to the body at horizontal lines (through the wakes).

I got the results as you guys can see in the plots I posted yesterday. The total pressure loss for the U- and "NACA"-Profile is much more lower for an flow angle of 20 than for the flow with an AOA of 0. How is this possible? Is there any explanation?
FCKW36 is offline   Reply With Quote

Old   June 16, 2019, 13:59
Default
  #12
Member
 
Join Date: May 2019
Posts: 30
Rep Power: 3
FCKW36 is on a distinguished road
The volicity on one side of the u-shaped profile goes up to 500 m/s. Could this be a problem?
FCKW36 is offline   Reply With Quote

Old   June 16, 2019, 14:40
Default
  #13
Senior Member
 
Filippo Maria Denaro
Join Date: Jul 2010
Posts: 5,620
Rep Power: 60
FMDenaro has a spectacular aura aboutFMDenaro has a spectacular aura aboutFMDenaro has a spectacular aura about
Quote:
Originally Posted by FCKW36 View Post
The volicity on one side of the u-shaped profile goes up to 500 m/s. Could this be a problem?



Mach about 1.8? No, that's wrong
FMDenaro is offline   Reply With Quote

Old   June 16, 2019, 16:32
Default
  #14
Member
 
Join Date: May 2019
Posts: 30
Rep Power: 3
FCKW36 is on a distinguished road
I set the Inlet speed to Mach 0.7.

You can find the plot of the streamlines below.

What could be the mistake?
Attached Images
File Type: jpg Bild1.jpg (199.8 KB, 14 views)
FCKW36 is offline   Reply With Quote

Old   June 16, 2019, 16:50
Default
  #15
Senior Member
 
Filippo Maria Denaro
Join Date: Jul 2010
Posts: 5,620
Rep Power: 60
FMDenaro has a spectacular aura aboutFMDenaro has a spectacular aura aboutFMDenaro has a spectacular aura about
The acceleration in that region is right but such a high value of the averaged velocity seems excessive. Try to refine the mesh and check also the density field
FMDenaro is offline   Reply With Quote

Old   June 17, 2019, 10:03
Default
  #16
Member
 
Join Date: May 2019
Posts: 30
Rep Power: 3
FCKW36 is on a distinguished road
Okay, thank you for your answer.

My Default Domain Turbulence model is k-Epsilon.
I have a question regarding the Inlet Boundary conditions. For Turbulance I Chose "Medium Intensity 5%". Is this a mistake? I can also chose k and Epsilon there, but than I have to define values for "Turb. Kinetic Energy" and "Turb. Eddy Dissipation". Is this what I should use or is "Medium Intensity 5%" good enough? If not, what should I chose for values for "Turb. Kinetic Energy" and "Turb. Eddy Dissipation"? THank you very much in advance.

Best Regards
FCKW36 is offline   Reply With Quote

Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

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 Off
Trackbacks are Off
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
General question about CFD applied to moving parts Voxel Main CFD Forum 0 May 11, 2019 13:35
CFD Analysis Over Three Dimensional CD Nozzle vickyroczzz Main CFD Forum 0 March 25, 2018 03:19
Validating CFD results with Experimental results for Indoor climate Mikki FLUENT 0 January 4, 2016 17:34
Is it usual in CFD community to guarantee the results? oj.bulmer Main CFD Forum 8 November 12, 2014 08:05
Is it usual in CFD community to guarantee the results? oj.bulmer CFX 0 November 5, 2014 06:31


All times are GMT -4. The time now is 21:09.