0
Research Papers

Flow Physics and Profiling of Recessed Blade Tips: Impact on Performance and Heat Load

[+] Author and Article Information
Bob Mischo

Turbomachinery Laboratory, Swiss Federal Institute of Technology, CH-8092 Zürich, Switzerlandbob.mischo@lsm.iet.mavt.ethz.ch

Thomas Behr, Reza S. Abhari

Turbomachinery Laboratory, Swiss Federal Institute of Technology, CH-8092 Zürich, Switzerland

J. Turbomach 130(2), 021008 (Feb 29, 2008) (8 pages) doi:10.1115/1.2775485 History: Received June 27, 2006; Revised August 18, 2006; Published February 29, 2008

In axial turbine, the tip clearance flow occurring in rotor blade rows is responsible for about one-third of the aerodynamic losses in the blade row and in many cases is the limiting factor for the blade lifetime. The tip leakage vortex forms when the leaking fluid crosses the gap between the rotor blade tip and the casing from pressure to suction side and rolls up into a vortex on the blade suction side. The flow through the tip gap is both of high velocity and of high temperature, with the heat transfer to the blade from the hot fluid being very high in the blade tip area. In order to avoid blade tip burnout and a failure of the machine, blade tip cooling is commonly used. This paper presents the physical study and an improved design of a recessed blade tip for a highly loaded axial turbine rotor blade with application in high pressure axial turbines in aero engine or power generation. With use of three-dimensional computational fluid dynamics (CFD), the flow field near the tip of the blade for different shapes of the recess cavities is investigated. Through better understanding and control of cavity vortical structures, an improved design is presented and its differences from the generic flat tip blade are highlighted. It is observed that by an appropriate profiling of the recess shape, the total tip heat transfer Nusselt number was significantly reduced, being 15% lower than the flat tip and 7% lower than the base line recess shape. Experimental results also showed an overall improvement of 0.2% in the one-and-a-half-stage turbine total efficiency with the improved recess design compared to the flat tip case. The CFD analysis conducted on single rotor row configurations predicted a 0.38% total efficiency increase for the rotor equipped with the new recess design compared to the flat tip rotor.

Copyright © 2008 by American Society of Mechanical Engineers
Your Session has timed out. Please sign back in to continue.

References

Figures

Grahic Jump Location
Figure 1

Three-dimensional computational grid turbine rotor blade with standard recess cavity

Grahic Jump Location
Figure 2

Geometrical parameters studied for improved recess cavity design

Grahic Jump Location
Figure 3

Three-dimensional CFD predicted flow over flat tip blade

Grahic Jump Location
Figure 4

Three-dimensional CFD predicted flow through nominal recess cavity

Grahic Jump Location
Figure 5

Two-dimensional CFD predicted flow through nominal recess cavity

Grahic Jump Location
Figure 6

Three-dimensional CFD predicted flow through new recess cavity

Grahic Jump Location
Figure 7

Two-dimensional CFD predicted flow through new recess cavity

Grahic Jump Location
Figure 8

Pressure side CFD predicted normalized tip mass flow

Grahic Jump Location
Figure 9

CFD predicted tip rim static pressure

Grahic Jump Location
Figure 10

Suction side CFD predicted normalized tip mass flow

Grahic Jump Location
Figure 11

CFD predicted blade tip nusselt number distribution

Grahic Jump Location
Figure 12

CFD predicted normalized heat load for flat tip, nominal recess, and new recess

Grahic Jump Location
Figure 13

Experimental relative total pressure coefficient distribution at 14% axial chord downstream rotor blade trailing edge for flat tip blade

Grahic Jump Location
Figure 14

CFD predicted relative total pressure coefficient distribution at 14% axial chord downstream rotor blade trailing edge, flat tip blade

Grahic Jump Location
Figure 15

Steady CFD prediction versus pitch averaged experimental relative yaw angle at 14% axial chord downstream rotor blade trailing edge, flat tip blade

Grahic Jump Location
Figure 16

Experimental relative total pressure coefficient distribution at 14% axial chord downstream rotor blade trailing edge, new recess tip blade

Grahic Jump Location
Figure 17

CFD predicted relative total pressure coefficient distribution at 14% downstream rotor blade trailing edge for new recess tip blade

Grahic Jump Location
Figure 18

CFD predicted versus experimental pitch averaged relative yaw angle at 14% axial chord downstream rotor blade trailing edge for new recess tip blade

Grahic Jump Location
Figure 19

Experimental pitch averaged relative yaw angle at 14% axial chord downstream rotor blade trailing edge for new recess tip blade

Tables

Errata

Discussions

Some tools below are only available to our subscribers or users with an online account.

Related Content

Customize your page view by dragging and repositioning the boxes below.

Related Journal Articles
Related eBook Content
Topic Collections

Sorry! You do not have access to this content. For assistance or to subscribe, please contact us:

  • TELEPHONE: 1-800-843-2763 (Toll-free in the USA)
  • EMAIL: asmedigitalcollection@asme.org
Sign In