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Research Papers: Forced Convection

On the Physics of Heat Transfer and Aerodynamic Behavior of Separated Flow Along a Highly Loaded Low Pressure Turbine Blade Under Periodic Unsteady Wake Flow and Varying of Turbulence Intensity

[+] Author and Article Information
M. T. Schobeiri, B. Öztürk

The Turbomachinery Performance and Flow Research Laboratory (TPFL), Texas A&M University, College Station, TX 77843

M. Kegalj

Fachgebiet Turbomaschinen und Fluidantriebstechnik, TU-Darmstadt, D-64287 Darmstadt, Germany

D. Bensing

 University Bochum, D-44780 Bochum, Germany

The entire data are available for CFD simulation; please contact the principal author.

Strictly speaking, there is no laminar flow within a turbine component. Comprehensive hot-wire measurements by many researchers have repeatedly shown that there are always random fluctuations associated with the velocity distribution. In turbine flow environment, the term “nonturbulent” may suitably replace the term “laminar.”

J. Heat Transfer 130(5), 051703 (Apr 10, 2008) (20 pages) doi:10.1115/1.2885156 History: Received October 13, 2006; Revised May 31, 2007; Published April 10, 2008

This paper attempts to provide a detailed insight into the heat transfer and aerodynamic behavior of a separation zone that is generated as a result of boundary layer development along the suction surface of a highly loaded low pressure turbine blade. This paper experimentally investigates the individual and combined effects of periodic unsteady wake flows and freestream turbulence intensity (Tu) on heat transfer and aerodynamic behavior of the separation zone. Heat transfer experiments were carried out at Reynolds numbers of 110,000, 150,000, and 250,000 based on the suction surface length and the cascade exit velocity. Aerodynamic experiments were performed at Re=110,000. For the above Re numbers, the experimental matrix includes Tu’s of 1.9%, 3.0%, 8.0%, and 13.0% and three different unsteady wake frequencies with the steady inlet flow as the reference configuration. Detailed heat transfer and boundary layer measurements are performed with particular attention paid to the heat transfer and aerodynamic behavior of the separation zone at different Tu’s at steady and periodic unsteady flow conditions. The objectives of the research are (a) to quantify the effect of Tu on the aerothermal behavior of the separation bubble at steady inlet flow conditions, (b) to investigate the combined effects of Tu and the unsteady wake flow on the aerothermal behavior of the separation bubble, and (c) to provide a complete set of heat transfer and aerodynamic data for numerical simulation that incorporates Navier–Stokes and energy equations. The experimental investigations were performed in a large-scale, subsonic, unsteady turbine cascade research facility at the Turbomachinery Performance and Flow Research Laboratory of Texas A&M University.

Copyright © 2008 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Turbine cascade research facility with the components and the adjustable test section

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Figure 2

Wake Generator (left), velocity distributions generated with three different reduced frequencies Ω=0 (steady), 1.59, and 3.18. Location of the data measured: 30mm upstream of the leading edge

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Figure 3

Turbine cascade research facility with three-axis traversing system

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Figure 4

(a) PSD as a function of frequency for three different grids described in Table 1. The results from (a) are used to generate the turbulence length scales as a function of turbulence intensity (b).

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Figure 5

Static pressure distribution in the blade midsection at Re=110,000, Tu=1.9, and reduced frequencies Ω=0,1.59,3.18 (no rod, 160mm, 80mm spacing), SS=separation start, SE=separation end

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Figure 6

Heat transfer blade with liquid crystal sheet, top detailed drawing, and bottom instrumented blade

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Figure 7

Distribution of time-averaged velocity (a) and turbulence fluctuation rms (b) along the suction surface for steady case Ω=0(SR=∞) and unsteady cases Ω=1.59(SR=160mm) and Ω=3.18(SR=80mm) at Re=110,000 and freestream turbulence intensity of 1.9% (without grid)

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Figure 8

Distribution of time-averaged velocity (a) and turbulence fluctuation rms (b) along the suction surface for steady case Ω=0(SR=∞) and unsteady cases Ω=1.59(SR=160mm) and Ω=3.18(SR=80mm) at Re=110,000 and Tu=3% with Grid TG1

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Figure 9

Distribution of time-averaged velocity (a) and turbulence fluctuation rms (b) along the suction surface for steady case Ω=0(SR=∞) and unsteady cases Ω=1.59(SR=160mm) and Ω=3.18(SR=80mm) at Re=110,000 and Tu=8% with Grid TG2

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Figure 10

Distribution of time-averaged velocity (a) and turbulence fluctuation rms (b) along the suction surface for steady case Ω=0(SR=∞) and unsteady cases Ω=1.59(SR=160mm) and Ω=3.18(SR=80mm) at Re=110,000 and Tu=13% with Grid TG3

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Figure 11

Ensemble-averaged velocity contours along the suction surface for different s∕s0 with time t∕τ as parameter for Ω=1.59(SR=160mm) at Re=110,000 and freestream turbulence of 1.9% (without grid). White area identifies the SB location and size.

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Figure 12

Ensemble-averaged velocity contours along the suction surface for different s∕s0 with time t∕τ as parameter for Ω=1.59(SR=160mm) at Re=110,000 and Tu=8% (with grid)

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Figure 13

Ensemble-averaged velocity contours along the suction surface for different s∕s0 with time t∕τ as parameter for Ω=3.18(SR=80mm) at Re=110,000 and freestream turbulence of 1.9% (without grid)

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Figure 14

Ensemble-averaged velocity contours along the suction surface for different s∕s0 with time t∕τ as parameter for Ω=3.18(SR=80mm) at Re=110,000 and freestream turbulence of 8.0% (with Grid TG2)

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Figure 15

((a)–(d)) Time dependent ensemble-averaged velocities and fluctuations for Re=110,000 at a constant location s∕s0=0.65mm inside the bubble for different inlet turbulence intensities ranging from 1.9% to 13%

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Figure 16

Composite picture of interaction between pressure gradient, velocity, turbulence fluctuation, and heat transfer

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Figure 17

Effect of Reynolds number on heat transfer coefficient, (a) Tu=1.9%, (b) Tu=13.0% for steady inlet flow condition

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Figure 18

Effect of Reynolds number on heat transfer coefficient, (a) Tu=1.9%, (b) Tu=3.0%, (c) Tu=8%, and (d) Tu=13% for unsteady inlet flow condition with Ω=Ω=1.59(SR=160mm)

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Figure 19

Effect of Reynolds number on heat transfer coefficient, (a) Tu=1.9%, (b) Tu=3.0%, (c) Tu=8%, and (d) Tu=13% for unsteady inlet flow condition with Ω=3.18(SR=80.0mm)

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Figure 20

Effect of unsteady wake frequency on heat transfer coefficient, (a) Tu=1.9%, (b) Tu=3.0%, (c) Tu=8%, and (d) Tu=13% for unsteady inlet flow condition with Ω=0.0, 1.59, and 3.18 that correspond to SR=∞, 160mm, and 80mm for Re=110,000

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