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International Symposium on Heat Transfer in Turbomachinery
August, 24-28, 1992 , Marathon, Greece

DOI: 10.1615/ICHMT.1994.IntSympHetatTransTurb


ISBN Print: 1-56700-016-9

ISBN Print: 978-1-56700-016-0

Turbine Airfoil Heat Transfer under Simulated Wake Conditions

pages 423-436
DOI: 10.1615/ICHMT.1994.IntSympHetatTransTurb.290
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ABSTRAKT

Augmentation of heat transfer along the surface of a gas turbine blade under the influence of periodically variing inflow conditions is a well-known problem in design and operation of turbomachines. Wakes shed by upstream blade rows are the main reason for the unsteady nature of the flow inside a rotating machine and the complex interaction of the unsteady phenomena with the boundary layer along the airfoil can cause a significant increase in the heat load.
To establish a comprehensive experimental database that includes the effects of different cascade inlet Reynolds numbers, free-stream turbulence levels, wake passing frequencies and wake inclination angles, an extensive study was initiated. Flow and the heat transfer measurements have been carried out in the ITS Cascade Test Facility with a wake generator using rotating bars placed upstream of the cascade to simulate the correct wake-passing process. Numerous tests have been carried out to determine the time mean heat transfer coefficients along a convectively cooled turbine airfoil under a variety of initial conditions. The investigated range of Reynolds and Strouhal numbers, respectively, is typical for a turbomachine environment.
The result indicate that the temporary increase of the turbulence level is the dominating reason for the augmentation in heat transfer especially on the suction side. The impact of the wakes on transitional areas induces a forced transition that generates an intermittent behaviour of the boundary layer. Depending on the Strouhal number the resulting mean heat transfer level on the blade is found to be between the steady laminar and turbulent values. The influence of wakes on heat transfer in accelerated laminar boundary layers like the stagnation region and the pressure side is based on a different physical phenomenon. Following the experimental results two models axe presented that are able to predict the wake effect on heat transfer in the above mentioned areas.

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