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Research Papers

A Novel Transient Technique to Determine Recovery Temperature, Heat Transfer Coefficient, and Film Cooling Effectiveness Simultaneously in a Transonic Turbine Cascade

[+] Author and Article Information
Song Xue, Arnab Roy, Wing F. Ng, Srinath V. Ekkad

Mechanical Engineering Department,
Virginia Polytechnic Institute and State University,
Blacksburg, VA 24061

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF THERMAL SCIENCE AND ENGINEERING APPLICATIONS. Manuscript received May 2, 2014; final manuscript received November 4, 2014; published online December 17, 2014. Assoc. Editor: Samuel Sami.

J. Thermal Sci. Eng. Appl 7(1), 011016 (Mar 01, 2015) (10 pages) Paper No: TSEA-14-1112; doi: 10.1115/1.4029098 History: Received May 02, 2014; Revised November 04, 2014; Online December 17, 2014

The study presented in this article provides detailed description about a newly developed experimental technique to determine three key convective heat transfer parameters simultaneously in hot gas path of a modern high pressure turbine–recovery temperature (Tr), heat transfer coefficient (HTC), and adiabatic film cooling effectiveness (Eta). The proposed technique, dual linear regression technique (DLRT), has been developed based on the 1D semi-infinite transient conduction theory, is applicable toward film cooled heat transfer experiments especially under realistic engine environment conditions (high Reynolds number along with high Mach numbers). It addresses the fundamental three temperature problem by a two-test strategy. The current popular technique, curve fitting method (CFM) (Ekkad and Han, 2000, “A Transient Liquid Crystal Thermography Technique for Turbine Heat Transfer Measurements,” Meas. Sci. Technol., 11(7), pp. 957–968), which is widely used in the low speed wind tunnel experiments, is not competent in the transonic transient wind tunnel. The CFM (including schemes for both film cooled and nonfilm cooled experiments) does not provide recovery temperature on the film cooled surface. Instead, it assumes the recovery temperature equal to the mainstream total temperature. Its basic physics model simplifies the initial unsteady flow development within the data reduction period by assuming a step jump in mainstream pressure and temperature, which results in significant under prediction of HTC due to the gradual ramping of the flow Mach/Reynolds number and varying temperature in a transient, cascade wind tunnel facility. The proposed technique is advantageous due to the elimination of these added assumptions and including the effects of compressible flow physics at high speed flow. The detailed discussion on theory and development of the DLRT is followed by validation with analytical calculation and comparisons with the traditional technique by reducing the same set of experimental data. Results indicate that the proposed technique stands out with a higher accuracy and reliability.

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References

Figures

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Fig. 1

Virginia Tech Transonic Wind Tunnel facility: (a) over view of the wind tunnel and (b) close-up view of the test section

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Fig. 2

Tunnel response of free stream temperature and Mach number

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Fig. 3

Linear regression of surface temperature and heat flux data

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Fig. 4

LRM including the ramping duration data

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Fig. 5

Data processing time window

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Fig. 6

Linear regression of two data sets calculated with tentative guessed Tr value

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Fig. 7

Typical relationship between R-square and normalized recovery temperature

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Fig. 8

DLRT plot when searching converged in singular region

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Fig. 9

Different steps of the searching process for DLRT

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Fig. 10

Technique validation with Nusselt number comparison

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Fig. 11

Comparison of Nusselt number distribution using (a) LRM, (b) CFM, and (c) CFM using reduced color scale

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Fig. 12

Endwall Nusselt number distribution with 1.0% MFR film cooling (a) CFM, (b) DLRT, and (c) CFM using reduced color scale

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Fig. 13

Endwall adiabatic effectiveness distribution for 1.0% MFR film cooling (a) CFM and (b) DLRT

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Fig. 14

Endwall normalized recovery temperature distribution (a) nonfilm cooled endwall and (b) film cooled endwall (1.0% MFR)

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