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Research Papers

Influence of Channel Geometry and Flow Variables on Cyclone Cooling of Turbine Blades

[+] Author and Article Information
Martin Bruschewski

Institute of Gas Turbines
and Aerospace Propulsion,
Technische Universität Darmstadt,
Darmstadt 64287, Germany
e-mail: bruschewski@glr.tu-darmstadt.de

Christian Scherhag, Heinz-Peter Schiffer

Institute of Gas Turbines
and Aerospace Propulsion,
Technische Universität Darmstadt,
Darmstadt 64287, Germany

Sven Grundmann

Institute of Fluid Mechanics,
University of Rostock,
Rostock 18051, Germany

1Corresponding author.

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received November 16, 2015; final manuscript received December 11, 2015; published online February 9, 2016. Editor: Kenneth C. Hall.

J. Turbomach 138(6), 061005 (Feb 09, 2016) (10 pages) Paper No: TURBO-15-1261; doi: 10.1115/1.4032363 History: Received November 16, 2015; Revised December 11, 2015

A study examining the internal cooling of turbine blades by swirling flow is presented. The sensitivity of swirling flow is investigated with regard to Reynolds number, swirl intensity, and the common geometric features of blade-cooling ducts. The flow system consists of a straight and round channel that is attached to a swirl generator with tangential inlets. Different orifices and 180-deg bends are employed as channel outlets. The experiments were carried out with magnetic resonance velocimetry (MRV) for which water was used as flow medium. As the main outcome, it was found that the investigated flows are highly sensitive to the conditions at the channel outlet. However, it was also discovered that for some outlet geometries the flow field remains the same. The associated flow features a favorable topology for heat transfer; the majority of mass is transported in the annular region close to the channel walls. Together with its high robustness, it is regarded as an applicable flow type for the internal cooling of turbine blades. A large eddy simulation (LES) was conducted to analyze the heat transfer characteristic of the associated flow for S0=3 and Re=20,000. The simulation showed an averaged Nusselt number increase of factor 4.7 compared to fully developed flow. However, a pressure loss increase of factor 43 must be considered as well.

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References

Figures

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Fig. 5

Velocity field for a characteristic experiment (S0=3 and Re = 8000, the channel outlet is a fully open orifice)

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Fig. 4

Description of the investigated systems. Parts (a1) and (a2) show the swirl system that is used to simulate the effect of 180-deg bends. Part (b) is associated with all studies where the effect of orifices is investigated. In this illustration, the orifice at the channel outlet is fully open.

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Fig. 3

Tangential-type swirl generator

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Fig. 2

Simplified cooling duct. The coolant enters the duct through a swirl generator at the hub of the blade. It then leaves the duct either via an orifice at the blade tip (a) or it is redirected by a 180-deg bend (b).

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Fig. 1

Generic turbine blade with internal and external cooling

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Fig. 6

Effect of concentric orifices at the channel outlet on the axial velocity distribution (uz). Flow parameters: S0=3 and Re = 20,000.

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Fig. 7

Velocity field of the concentrated vortex (a) and the solid-body-type vortex (b). The radial velocity component is close to zero everywhere in the flow.

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Fig. 8

Effect of ring orifices at the channel outlet on the axialvelocity distribution (uz). Flow parameters: S0=3 and Re = 20,000.

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Fig. 9

Effect of 180-deg bends on the flow field before and past the bend. The tangential velocity distribution (uy) shows the rotational sense of the swirling flow. Flow parameters: S0=3 and Re = 20,000.

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Fig. 10

Axial velocity distribution (uz) for the configurations from Fig. 9. Flow parameters: S0=3 and Re = 20,000.

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Fig. 11

Effect of the swirl generator shape on the axial velocity distribution (uz). The center of the swirl is visualized by a black ribbon. Flow parameters: S0=3 and Re = 20,000.

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Fig. 12

Effect of eccentric orifices at the channel outlet on the axial velocity distribution (uz). The center of the swirl is visualized by a black ribbon. Flow parameters: S0=3 and Re = 20,000.

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Fig. 13

Swirl decay for different concentric orifices at the channel outlet but same S0 and Re

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Fig. 14

Swirl decay for different Re but same S0. The channel outlet is a concentric orifice with d1=D.

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Fig. 15

Swirl decay for different S0 but same Re. The channel outlet is a concentric orifice with d1=D.

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Fig. 16

Computational domain of the LES

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Fig. 17

Top and center graph: instant velocity components uz and uy obtained from the LES. Bottom graph: instant Courant number at vortex structures with Q=50,000 s−2.

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Fig. 18

Averaged flow field for the setup from Fig. 16. Measurement and simulation.

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Fig. 19

Evaluation of swirl decay (Eq. (1)) for MRV data and LES data. The corresponding velocity fields are shown in Fig.18.

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Fig. 20

Top graph: instant radial velocity distribution close to the channel wall (r=0.97R). Bottom graph: instant Nusselt number distribution at the channel wall.

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Fig. 21

Normalized mean Nusselt number distribution for the investigated flow including a correlation according to Hay and West [6]

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