CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > Software User Forums > ANSYS > CFX

too high efficiency for steam turbine

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

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   October 31, 2006, 00:11
Default too high efficiency for steam turbine
  #1
Qiang
Guest
 
Posts: n/a
I performed a simulation of one stage in a steam turbine, but I got a unreasonable high total-total efficiency about 0.97(the design is 0.8),steam table I used is iapws if97.

Is there anyone know the reason?
  Reply With Quote

Old   October 31, 2006, 02:34
Default Re: too high efficiency for steam turbine
  #2
Ermanno
Guest
 
Posts: n/a
Hi,

Have you used the steam table to evaluate the efficency (but you used a different fluid model in your simulation, such as Redlich-Kwong...etc), or have you loaded the steam table as fluid model in CFX?

How have you evaluated the efficency?
  Reply With Quote

Old   October 31, 2006, 18:05
Default Re: too high efficiency for steam turbine
  #3
Qiang
Guest
 
Posts: n/a
Dear Ermanno

I used the iapws IF97 steam table in the material labrary in CFX, also for calculating efficiency, but the total-total efficiency I got is 0.95(actual enthalpy drop/isentropic enthalpy drop),the design is 0.80

How about your case? Did you get a turbine efficiency lower than 0.85 before? I have not.

  Reply With Quote

Old   November 2, 2006, 18:02
Default Re: too high efficiency for steam turbine
  #4
Ermanno
Guest
 
Posts: n/a
Hi,

My latest simulation was one HP stage of steam turbine. The efficiency I got is 0.94 about (higher than design efficiency 0.90 about). In my simualtion I have a low Mach number (0.2), therefore I can neglect differences between static and total enthalpy: have you evalueted the velocity (isentropic) correctly in your simulation?

During the use of steam table I had a problem (as I wrote few weeks ago): static pressure was higher than total pressure. Have you checked it ?

  Reply With Quote

Old   November 2, 2006, 19:04
Default Re: too high efficiency for steam turbine
  #5
Qiang
Guest
 
Posts: n/a
The key problem of me is the efficiency from CFX is too much higher than designed condition(0.95/0.8),I think that's due to fewer flow losses in the stage in simulation. I don't know why the efficiency of my simulation is so high.

Which steam table do you use? Virial or ispws if97 ?

Which version of CFX do you use? I learned it from Ansys support that version 10 had bugs on this issue(I also faced this pressure problem before),you can use CFX-5.7 or 5.7.1, that will be OK.

I'm an engineer in turbomachinery. Maybe we can have technical discussion by e-mail or MSN. my e-mail: lu.qiang@doosan.com

  Reply With Quote

Old   November 7, 2006, 22:48
Default Re: too high efficiency for steam turbine
  #6
HekLeR
Guest
 
Posts: n/a
Qiang,

If you are using IAPWS then you are using CFX 11. IAPWS was not released in versions of CFX earlier than that.

CFX 11 can automatically calculate efficiency as a global (overall) device based quantity or local field (at every node) based quantity for you based on mass average inlet entropy & enthalpy. Look in the output control -> export tab and read the doc on it as well in the basic capability modelling section.

HekLeR
  Reply With Quote

Old   November 11, 2006, 08:18
Default Re: too high efficiency for steam turbine
  #7
Qiang
Guest
 
Posts: n/a
HekLeR

Thank you very much for your kind advice, I will check it tomorrow.

Regards
  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
High torque coefficient Cm for Vertical Axis Wind Turbine (VAWT) tony00 FLUENT 11 July 23, 2018 07:13
how to set up high temperature gas turbine flow simulation? adam2008 CFX 1 July 22, 2009 19:33
Help! How to find efficiency of hydro turbine? Sanjay Jain FLUENT 0 May 9, 2008 13:09
very high thermal efficiency carno FLUENT 0 January 28, 2007 00:03
Multicomponent fluid Andrea CFX 2 October 11, 2004 06:12


All times are GMT -4. The time now is 05:51.