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Comparison Of Continuous And Truncated Ribs On Internal Blade Tip Cooling

In English

Författare

Summary, in English

In the present work, an experimental study related to turbulent flow inside the bend part of a U-duct geometry was performed concerning pressure drop and heat transfer. Such duct geometries can be found inside gas turbine blades, where the cooling air extracts heat from hot internal walls while it is flowing inside the cooling passage. Both friction factors and convective heat transfer coefficients were established inside the bend part of the U-duct for two different rib cases, namely continuous and truncated ribs with varying Reynolds number from 8,000 to 20,000. For the continuous rib case, the length of the ribs was equal to the height of the duct while in the truncated rib case two different rib lengths, i.e., 46 mm and 40 mm, respectively, were considered. The rib height-to-hydraulic diameter ratio, e/Dh, was 0.1 and the pitch ratio was 10. The test rig has been built in such a way that various experimental setups can be handled as the outer wall of the bend (turn) part of the U-duct can easily be removed and the ribs can be changed. Both the U-duct and the ribs were made from acrylic material to allow optical access for measuring the surface temperature by using a high-resolution measurement technique based on the narrow band thermochromic liquid crystals (TLC R35C5W) and a CCD camera placed facing the bend (turn) part of the U-duct. The calibration of the TLC is based on the hue-based color decomposition system using an in-house designed calibration box. The ribs were placed transversely to the direction of the main flow at the outer wall of the bend (turn) part where the wall was heated by an electrical heater. The pressure drop was almost identical for the continuous and truncated rib cases, while the heat transfer coefficient is 10 % higher for the continuous rib case at Re=20000. The uncertainties in the evaluated properties were 3% and 6% for the Nusselt number and friction factor, respectively.

Avdelning/ar

Publiceringsår

2012

Språk

Svenska

Publikation/Tidskrift/Serie

[Host publication title missing]

Dokumenttyp

Konferensbidrag

Förlag

American Society Of Mechanical Engineers (ASME)

Ämne

  • Energy Engineering

Conference name

ASME Turbo Expo 2012

Conference date

2011-06-11

Conference place

Copenhagen, Denmark

Status

Published

ISBN/ISSN/Övrigt

  • GT2012-68028