Effect of Unsteady Wake With Trailing Edge Coolant Ejection on Film Cooling Performance for a Gas Turbine Blade

The effect of unsteady wakes with trailing edge coolant ejection on surface heat transfer coefficients and film cooling effectiveness is presented for a downstream film-cooled turbine blade. The detailed heat transfer coefficient and film effectiveness distributions on the blade surface are obtained using a transient liquid crystal technique. Unsteady wakes are produced by a spoked wheel-type wake generator upstream of the five-blade linear cascade. The coolant jet ejection is simulated by ejecting coolant through holes on the hollow spokes of the wake generator. For a blade without film holes, unsteady wake increases both pressure side and suction side heat transfer levels due to early boundary layer transition. Adding trailing edge ejection to the unsteady wake further enhances the blade surface heat transfer coefficients particularly near the leading edge region. For a film-cooled blade, unsteady wake effects slightly enhance surface heat transfer coefficients but significantly reduces film effectiveness. Addition of trailing edge ejection to the unsteady wake has a small effect on surface heat transfer coefficients compared to other significant parameters such as film injection, unsteady wakes, and grid generated turbulence, in that order. Trailing edge ejection effect on film effectiveness distribution is stronger than on the heat transfer coefficients.

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Influence of Unsteady Wake on Heat Transfer Coefficient From a Gas Turbine Blade

Journal of Heat Transfer ◽

10.1115/1.2911386 ◽

1993 ◽

Vol 115 (4) ◽

pp. 904-911 ◽

Cited By ~ 38

Author(s):

J.-C. Han ◽

L. Zhang ◽

S. Ou

Keyword(s):

Heat Transfer ◽

Reynolds Number ◽

Gas Turbine ◽

Strouhal Number ◽

Turbine Blade ◽

Surface Heat ◽

Transfer Coefficients ◽

Heat Transfer Coefficients ◽

Unsteady Wake ◽

Wake Passing

The effect of unsteady wake on surface heat transfer coefficients of a gas turbine blade was experimentally determined using a spoked wheel type wake generator. The experiments were performed with a five-airfoil linear cascade in a low-speed wind tunnel facility. The cascade inlet Reynolds number based on the blade chord was varied from 1 to 3 × 105. The wake Strouhal number was varied between 0 and 1.6 by changing the rotating wake passing frequency (rod speed and rod number), rod diameter, and cascade inlet velocity. A hot-wire anemometer system was located at the cascade inlet to detect the instantaneous velocity, phase-averaged mean velocity, and turbulence intensity induced by the passing wake. A thin foil thermocouple instrumented blade was used to determine the surface heat transfer coefficients. The results show that the unsteady passing wake promotes earlier and broader boundary layer transition and causes much higher heat transfer coefficients on the suction surface, whereas the passing wake also significantly enhances heat transfer coefficients on the pressure surface. The blade heat transfer coefficients for a given Reynolds number flow increase with the wake Strouhal number by increasing the rod speed, rod number, or rod diameter. For a given wake passing frequency and rod diameter, the blade heat transfer coefficients decrease with decreasing Reynolds number, although the corresponding wake Strouhal number is increased. The results suggest that both the Reynolds and Strouhal numbers are important parameters in determining the blade heat transfer coefficients in unsteady wake flow conditions.

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Effect of Squealer Cavity Depth and Oxidation on Turbine Blade Tip Heat Transfer

Volume 3: Heat Transfer; Electric Power; Industrial and Cogeneration ◽

10.1115/2001-gt-0155 ◽

2001 ◽

Cited By ~ 22

Author(s):

Ronald S. Bunker ◽

Jeremy C. Bailey

Keyword(s):

Heat Transfer ◽

Mach Number ◽

Turbine Blade ◽

Surface Heat ◽

Transfer Coefficients ◽

Cavity Depth ◽

Surface Heat Transfer ◽

Heat Transfer Coefficients ◽

Blade Cascade ◽

Blade Tip

An experimental study has been performed to investigate the effect of squealer cavity depth on the detailed distribution of convective heat transfer coefficients of a turbine blade tip surface. This paper presents full surface information on heat transfer coefficients within a blade cascade which develops an appropriate pressure distribution about an airfoil blade tip and shroud model. A stationary blade cascade experiment has been run consisting of three airfoils, the center airfoil having a variable tip gap clearance. The airfoil models the aerodynamic tip section of a high pressure turbine blade with inlet Mach number of 0.21, exit Mach number of 0.74, pressure ratio of 1.41, Reynolds number of 2.8•106, and total turning of about 100 degrees. The cascade inlet turbulence intensity level is 9%. Tip surface heat transfer coefficient distributions are first shown for a flat, square-edge tip with a clearance gap of 2.03 mm. Heat transfer distributions are then shown for full-perimeter squealer tip cavities having the same clearance gap above the squealer rim, and clearance-to-cavity depth ratios from 0.67 to 2. Regionally averaged heat transfer coefficients are analyzed to discern a relationship between tip heat transfer and cavity depth. Further tests demonstrate the effect of partial squealer rim oxidation, or material loss, on the surface heat transfer distributions.

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Effects of Rotation on Blade Surface Heat Transfer: An Experimental Investigation

Volume 3: Heat Transfer; Electric Power; Industrial and Cogeneration ◽

10.1115/97-gt-188 ◽

1997 ◽

Cited By ~ 1

Author(s):

Roger W. Moss ◽

Roger W. Ainsworth ◽

Tom Garside

Keyword(s):

Thin Film ◽

Heat Transfer ◽

Experimental Investigation ◽

Turbine Blade ◽

Time History ◽

Surface Heat ◽

Blade Surface ◽

Surface Heat Transfer ◽

Effects Of Rotation ◽

Wake Passing

Measurements of turbine blade surface heat transfer in a transient rotor facility are compared with predictions and equivalent cascade data. The rotating measurements involved both forwards and reverse rotation (wake free) experiments. The use of thin-film gauges in the Oxford Rotor Facility provides both time-mean heat transfer levels and the unsteady time history. The time-mean level is not significantly affected by turbulence in the wake; this contrasts with the cascade response to freestream turbulence and simulated wake passing. Heat transfer predictions show the extent to which such phenomena are successfully modelled by a time-steady code. The accurate prediction of transition is seen to be crucial if useful predictions are to be obtained.

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Heat Transfer Coefficients and Film Cooling Effectiveness on the Squealer Tip of a Gas Turbine Blade

Journal of Turbomachinery ◽

10.1115/1.1622712 ◽

2003 ◽

Vol 125 (4) ◽

pp. 648-657 ◽

Cited By ~ 31

Author(s):

Jae Su Kwak ◽

Je-Chin Han

Keyword(s):

Heat Transfer ◽

Gas Turbine ◽

Turbine Blade ◽

Film Cooling ◽

Rotor Blade ◽

Transfer Coefficients ◽

Cooling Effectiveness ◽

Film Cooling Effectiveness ◽

Heat Transfer Coefficients ◽

Blowing Ratio

Experimental investigations were performed to measure the detailed heat transfer coefficients and film cooling effectiveness on the squealer tip of a gas turbine blade in a five-bladed linear cascade. The blade was a two-dimensional model of a first stage gas turbine rotor blade with a profile of the GE-E3 aircraft gas turbine engine rotor blade. The test blade had a squealer (recessed) tip with a 4.22% recess. The blade model was equipped with a single row of film cooling holes on the pressure side near the tip region and the tip surface along the camber line. Hue detection based transient liquid crystals technique was used to measure heat transfer coefficients and film cooling effectiveness. All measurements were done for the three tip gap clearances of 1.0%, 1.5%, and 2.5% of blade span at the two blowing ratios of 1.0 and 2.0. The Reynolds number based on cascade exit velocity and axial chord length was 1.1×106 and the total turning angle of the blade was 97.9 deg. The overall pressure ratio was 1.2 and the inlet and exit Mach numbers were 0.25 and 0.59, respectively. The turbulence intensity level at the cascade inlet was 9.7%. Results showed that the overall heat transfer coefficients increased with increasing tip gap clearance, but decreased with increasing blowing ratio. However, the overall film cooling effectiveness increased with increasing blowing ratio. Results also showed that the overall film cooling effectiveness increased but heat transfer coefficients decreased for the squealer tip when compared to the plane tip at the same tip gap clearance and blowing ratio conditions.

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