Research Papers: Energy Conversion/Systems

Cooling of Turbine Blade Surface With Expanded Exit Holes: Computational Suction-Side Analysis

[+] Author and Article Information
Fariborz Forghan, Omid Askari, Uichiro Narusawa, Hameed Metghalchi

Department of Mechanical
and Industrial Engineering,
Northeastern University,
Boston, MA 02115

Contributed by the Advanced Energy Systems Division of ASME for publication in the JOURNAL OF ENERGY RESOURCES TECHNOLOGY. Manuscript received April 15, 2016; final manuscript received April 26, 2016; published online June 14, 2016. Assoc. Editor: Arash Dahi Taleghani.

J. Energy Resour. Technol 138(5), 051602 (Jun 14, 2016) (4 pages) Paper No: JERT-16-1173; doi: 10.1115/1.4033590 History: Received April 15, 2016; Revised April 26, 2016

Turbine blade surfaces are cooled by jet flow from expanded exit holes (EEHs) against the prevailing hot gas flow. The flow through EEH must be designed to form a film of cool air over the blade. Computational analyses are performed to examine the cooling effectiveness of flow from EEH over the suction side of a blade by solving conservation equations and the ideal gas equation of state for turbulent and compressible flow. For a sufficiently high coolant mass flow rate, the flow through EEH, which acts as a converging–diverging nozzle, is choked at the nozzle throat, resulting in a supersonic flow, a shock, and then a subsonic flow downstream. The location of the shock relative to the high-temperature gas flow determines the temperature distribution along the blade surface; which is analyzed in detail when the following conditions are varied: coolant mass flow rate, the temperature difference between gas-and coolant-flow, EEH location on the blade surface, EEH inclination angle to the blade surface, and exit-to-inlet area ratio (AR) of EEH. The film cooling effectiveness is calculated along the surface of the blade. The results show (1) increasing the coolant flow rate improves the effectiveness, (2) change in temperature difference between the mainstream and the coolant slightly affects the effectiveness, (3) inclination angle of EEH has a pronounced effect on film cooling and the corresponding effectiveness, (4) both the location of the EEH on a blade and the AR of the EEH slightly change the effectiveness.

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Fig. 1

Midplane cross section of the blade

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Fig. 2

Comparison of experimental data of Liu et al. [15] and results of this study

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Fig. 3

Mach number of coolant for different mass flow rate of coolant (a)m˙ = 0.0002 kg/s (b) m˙  = 0.0005 kg/s, (c) m˙  = 0.001 kg/s, and (d) m˙  = 0.002 kg/s

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Fig. 4

Effectiveness as a function of distance for four different flows rates of coolant of an EEH with angle of 30 deg

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Fig. 5

Effectiveness as a function of distance for three different temperature differences between mainstream and coolant static temperature

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Fig. 6

Effectiveness as a function of distance for different locations, coolant mass flow rate 0.005 kg/s, steel blade, ΔT = 1300 K, AR = 3.8 and Ø = 30 deg (negative values = upstream, positive values = downstream)

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Fig. 7

Effectiveness as a function of distance for different angle of the EEH 30 deg, −30 deg, 90 deg with respect to local tangent to the blade at location 1 (L1), ΔT = 1300 K, steel blade, and coolant mass flow rate 0.0005 kg/s (negative values = upstream, positive values = downstream)

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Fig. 8

Effectiveness as a function of distance for different EEH AR: AR = 2.72, AR = 4.38, AR = 6.88, coolant mass flow rate of 0.005 kg/s, location 1 (L1), ΔT = 1300 K, AR = 3.8 and, Ø = 30 deg (negative values = upstream, positive values = downstream)



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