Requirements and Limitations of Controlling Turbine Tip Shroud Cavity Flow Mixing With Bladelets on Rotating Shroud

A potential means of significantly reducing the cavity exit mixing loss, a dominant primary loss mechanism in turbine tip shroud cavity flow, is assessed. The operational constraints on the turbine stage dictate that losses may only be mitigated through configuration changes within the cavity. A configuration, known herein as the Hybrid Blade, features a shrouded main blade with a row of high aspect ratio bladelets affixed to the rotating shroud is formulated and shown to nearly eliminate the cavity exit mixing loss. However the Hybrid Blade configuration incurs a penalty associated with bladelet low Reynolds number effects, cavity inlet flow asymmetry introduced by the scalloped shroud, and a resulting mismatch with the upstream vane as well as downstream diffuser. This penalty offsets the efficiency gain from mitigating cavity exit mixing loss. For the Hybrid Blade system, it can thus be inferred that the turbine stage and the diffuser need to be reconfigured to accommodate the modified tip shroud, and the bladelets redesigned for low Reynolds number operation and cavity inlet flow asymmetry to achieve an overall benefit.

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Effects of Shroud Asymmetry on the Turbine Tip Shroud Cavity Flow Field

Volume 2A: Turbomachinery ◽

10.1115/gt2015-43721 ◽

2015 ◽

Cited By ~ 1

Author(s):

Timothy R. Palmer ◽

Choon S. Tan ◽

Matthew Montgomery ◽

Anthony Malandra ◽

David Little ◽

...

Keyword(s):

Flow Field ◽

Cavity Flow ◽

Main Flow ◽

Toroidal Vortex ◽

Turbine Stage ◽

Numerical Computations ◽

Velocity Difference ◽

Inlet Flow ◽

Toroidal Vortices ◽

Tip Shroud

The effects of shroud asymmetry (known as a scalloped shroud) on loss generation and stage performance are assessed by numerical computations, steady as well as unsteady, in a turbine stage with tip shroud cavity. Introducing shroud asymmetry leads to cavity mixing at higher flow velocities with larger velocity difference, hence higher loss relative to a baseline axisymmetric shroud. Shroud asymmetry alters the system of toroidal vortices which characterizes tip shroud cavity flow. Specifically, the asymmetry downstream of the tip seal prevents the formation of two large, continuous toroidal vortex cores. Instead, several small, discrete cores are formed immediately downstream of the tip seal due to the onset of mixing with the main flow. Unsteady vane-rotor-shroud interaction results in a redistribution of vorticity in the cavity inlet. Compatibility requirement between main flow and cavity flow provides quantitative limits on the existence of the cavity inlet vortex as well as explains why the cavity inlet flow field looks the way it does and not otherwise.

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A multipole direct and indirect BEM for 2D cavity flow at low Reynolds number

Engineering Analysis with Boundary Elements ◽

10.1016/s0955-7997(97)00021-0 ◽

1997 ◽

Vol 19 (1) ◽

pp. 17-31 ◽

Cited By ~ 56

Author(s):

J.E. Gómez ◽

H. Powert

Keyword(s):

Reynolds Number ◽

Low Reynolds Number ◽

Cavity Flow ◽

Low Reynolds

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Aerodynamic and Heat Flux Measurements in a Single-Stage Fully Cooled Turbine—Part I: Experimental Approach

Journal of Turbomachinery ◽

10.1115/1.2750676 ◽

2008 ◽

Vol 130 (2) ◽

Cited By ~ 22

Author(s):

C. W. Haldeman ◽

R. M. Mathison ◽

M. G. Dunn ◽

S. A. Southworth ◽

J. W. Harral ◽

...

Keyword(s):

Heat Flux ◽

Reynolds Number ◽

Experimental Approach ◽

Low Reynolds Number ◽

Surface Heat ◽

Pressure Data ◽

Turbine Stage ◽

Wide Range ◽

Temperature And Pressure ◽

Low Reynolds

This paper describes the experimental approach utilized to perform experiments using a fully cooled rotating turbine stage to obtain film effectiveness measurements. Significant changes to the previous experimental apparatus were implemented to meet the experimental objectives. The modifications include the development of a synchronized blowdown facility to provide cooling gas to the turbine stage, installation of a heat exchanger capable of generating a uniform or patterned inlet temperature profile, novel utilization of temperature and pressure instrumentation, and development of robust double-sided heat flux gauges. With these modifications, time-averaged and time-accurate measurements of temperature, pressure, surface heat flux, and film effectiveness can be made over a wide range of operational parameters, duplicating the nondimensional parameters necessary to simulate engine conditions. Data from low Reynolds number experiments are presented to demonstrate that all appropriate scaling parameters can be satisfied and that the new components have operated correctly. Along with airfoil surface heat transfer and pressure data, temperature and pressure data from inside the coolant plenums of the vane and rotating blade airfoils are presented. Pressure measurements obtained inside the vane and blade plenum chambers illustrate passing of the wakes and shocks as a result of vane/blade interaction. Part II of this paper (Haldeman, C. W., Mathison, R. M., Dunn, M. G., Southworth, S. A., Harral, J. W., and Heltland, G., 2008, ASME J. Turbomach., 130(2), p. 021016) presents data from the low Reynolds number cooling experiments and compares these measurements to CFD predictions generated using the Numeca FINE/Turbo package at multiple spans on the vanes and blades.

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Aerodynamic and Heat Flux Measurements in a Single Stage Fully Cooled Turbine: Part I — Experimental Approach

Volume 3: Heat Transfer, Parts A and B ◽

10.1115/gt2006-90966 ◽

2006 ◽

Cited By ~ 4

Author(s):

C. W. Haldeman ◽

R. M. Mathison ◽

M. G. Dunn ◽

S. Southworth ◽

J. W. Harral ◽

...

Keyword(s):

Heat Flux ◽

Reynolds Number ◽

Experimental Approach ◽

Low Reynolds Number ◽

Surface Heat ◽

Pressure Data ◽

Turbine Stage ◽

Wide Range ◽

Temperature And Pressure ◽

Low Reynolds

This paper describes the experimental approach utilized to perform experiments using a fully cooled rotating turbine stage to obtain film effectiveness measurements. Significant changes to the previous experimental apparatus were implemented to meet the experimental objectives. The modifications include the development of a synchronized blowdown facility to provide cooling gas to the turbine stage, installation of a heat exchanger capable of generating a uniform or patterned inlet temperature profile, novel utilization of temperature and pressure instrumentation, and development of robust double-sided heat flux gauges. With these modifications, time-averaged and time-accurate measurements of temperature, pressure, surface heat flux, and film effectiveness can be made over a wide range of operational parameters duplicating the non-dimensional parameters necessary to simulate engine conditions. Data from low Reynolds number experiments are presented to demonstrate that all appropriate scaling parameters can be satisfied and that the new components have operated correctly. Along with airfoil surface heat transfer and pressure data, temperature and pressure data from inside the coolant plenums of the vane and rotating blade airfoils are presented. Pressure measurements obtained inside the vane and blade plenum chambers illustrate passing of the wakes and shocks as a result of vane/blade interaction. Part II of this paper presents data from the low Reynolds number cooling experiments and compares these measurements to CFD predictions generated using the Numeca FINE/Turbo package at multiple spans on the vanes and blades.

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