CFD Review  
Serving the CFD Community with News, Articles, and Discussion
 
CFD Review

User Preferences
Site Sponsorship
Headline Feeds
Mobile Edition
Privacy Policy
Terms of Service
twitter

Submit a CFD Story

Site Sponsors
Siemens PLM Software
Pointwise: Reliable CFD meshing
Software Cradle

Tell a Friend
Help this site to grow by sending a friend an invitation to visit this site.

CFD News by Email
Did you know that you can get today's CFD Review headlines mailed to your inbox? Just log in and select Email Headlines Each Night on your User Preferences page.

 
Improving Understanding of Turbine Shroud Losses
Posted Tue June 04, 2002 @02:26PM
Print version Email story Tweet story
Application by Paul Roach, ALSTOM Power UK Ltd.

A world-leading supplier to the energy market, ALSTOM offers its customers a comprehensive range of power generation solutions from turnkey power plants to gas-, steam- and hydro-turbines, generators and boilers. Gas turbine design and manufacture has been undertaken at Alstom's Lincoln site since the late 1940ís, with engine ratings up to the 13MW Cyclone introduced in 1997.

To help maximize powerplant efficiency, the Company uses state-of-the-art CFD methods to design compressor and turbine blading. In addition to in-house software, ALSTOM has also been making use of CFX-TASCflow in the last few years. To date, its main use in the Turbine Department has been to examine secondary and parasitic gas flows, such as can occur in blade cooling passages.


Sponsor CFD Review

In a recent study, we have used CFX-TASCflow to examine leakage flows in shrouded turbine blade passages. We have modeled the gas flow through the complete stage, including the shroud, disc cavities and associated leakage gaps. The operating conditions for the modeled stage were a stagnation pressure ratio of 4.0, with exit Mach numbers from both blade rows of about 1.1. Using CFX-TASCflow, we could appreciate the full impact of the shroud leakages, and understand how their domination of the main flow features immediately downstream of the stage means that they cannot be neglected. Flow patterns through the shroud itself were also complex and highly three-dimensional. Again CFX-TASCflow revealed significant effects, with the small tangential gaps running the full length of the shroud potentially causing very strong temperature gradients in the shroud metal.

Comparison of the results with available experimental data for the performance characteristics showed that the inclusion of shroud and other leakages is essential for accurate prediction of the flow field. CFX-TASCflow is helping us to understand these complex shroud cavity flows, and improve future turbine designs.

flow pathlines

flow pathlines
Highly three-dimensional and complex flow distribution through the axial gaps upstream and downstream of the shroud, with a gap running the full length of the shroud. Surface contours are of static temperature, the yellow streaklines originate in the inlet plane of the upstream axial gap, the blue streaklines in the tangential gap.

flow pathlines

flow pathlines
3-D views of the mainstream flows, without shroud leakage. These show contours of entropy on the blade surfaces and in the wakes, with streaklines introduced at the stator/rotor interface very near the hub wall. Clearly visible are the locations of the strong shock waves on the suction surfaces, and the rotor wakes downstream. Secondary flows are evidenced by the larger "blobs" of entropy in the wakes, also highlighted by the streaklines. This shows that the shroud leakage clearly dominates the flow features immediately downstream of the stage.

Variation of Mach number
Numerical and experimental radial variation of Mach number showing the importance of leakage flows.

Predicted isentropic efficiency
When all of the shroud leakages are included, predicted stage isentropic efficiencies are in close agreement with experiments.

The author gratefully acknowledges the financial support from the EU Framework 5 Programme (ENK5-CT2000-00065).

[ Post Comment ]

SCRYU/Tetra for Windows, Version 4 | CGNS Version 2.1 Released  >

 

 
CFD Review Login
User name:

Password:

Create an Account

Related Links
  • ALSTOM
  • CFX
  • CFX-TASCflow
  • More on Application
  • Also by nwyman
  • This discussion has been archived. No new comments can be posted.

    Lay on, MacDuff, and curs'd be him who first cries, "Hold, enough!". -- Shakespeare All content except comments
    ©2017, Viable Computing.

    [ home | submit story | search | polls | faq | preferences | privacy | terms of service | rss  ]