A Transient Calorimeter Technique for Determining Regional Heat Transfer Coefficients in the Three-Temperature Flowfield at a Turbine Airfoil Leading Edge

2005 ◽  
Author(s):  
Scott R. Nowlin ◽  
David R. H. Gillespie ◽  
Peter T. Ireland ◽  
Ralf Knoche ◽  
T. Robert Kingston
Keyword(s):  
Heat Transfer ◽  
Film Cooling ◽  
Internal Flow ◽  
Leading Edge ◽  
Internal Surface ◽  
Reynolds Numbers ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Novel Method ◽  
Exposed Surface Area

In this paper, the authors develop a novel method of obtaining regionally-averaged heat transfer coefficients in flowfields characterized by three temperatures using the well-known transient calorimeter technique. The technique is used to determine heat transfer in aluminum models of idealized turbine blade leading edges cooled through internal surface impingement, film cooling feed passages, and external convective film cooling. The external surface is subject to a stagnating mainstream crossflow. Importantly, the contributions to heating from the external flow and cooling from the internal flow can be separately resolved solely by heating the internal flow. Results for a basic showerhead geometry and an advanced intersecting-passage cooling configuration are presented for a range of internal and external Reynolds numbers. The intersecting-passage model shows little improvement in heat transfer coefficient over the showerhead for the flow conditions tested; however, the total cooling carried out is improved by the increase in exposed surface area. The technique’s uncertainties are fully assessed.

Experimental Evaluations of the Relative Contributions to Overall Effectiveness in Turbine Blade Leading Edge Cooling

2018 ◽  
Author(s):  
Carol E. Bryant ◽  
Connor J. Wiese ◽  
James L. Rutledge ◽  
Marc D. Polanka
Keyword(s):  
Heat Transfer ◽  
Film Cooling ◽  
Leading Edge ◽  
Internal Surface ◽  
Internal Cooling ◽  
Transfer Coefficients ◽  
Impingement Cooling ◽  
External Cooling ◽  
Turbine Component ◽  
Overall Effectiveness

Gas turbine hot gas path components are protected through a combination of internal cooling and external film cooling. The coolant typically travels through internal passageways, which may involve impingement on the internal surface of a turbine component, before being ejected as film cooling. Internal cooling effects have been studied in facilities that allow measurement of heat transfer coefficients within models of the internal cooling paths, with large heat transfer coefficients generally desirable. External film cooling is typically evaluated through measurements of the adiabatic effectiveness and its effect on the external heat transfer coefficient. Efforts aimed at improving cooling are often focused on either only the internal cooling or the film cooling; however, the common coolant flow means the internal and external cooling schemes are linked and the coolant holes themselves provide another convective path for heat transfer to the coolant. Recently, measurements of overall cooling effectiveness using matched Biot number turbine component models allow evaluation of the nondimensional wall temperature achieved for the fully cooled component. However, the relative contributions of internal cooling, external cooling, and convection within the film cooling holes is not well understood. Large scale, matched Biot number experiments, complemented by CFD simulations, were performed on a fully film cooled cylindrical leading edge model to evaluate the effects of various alterations in the cooling design on the overall effectiveness. The relative influence of film cooling and cooling within the holes was evaluated by selectively disabling individual holes and quantifying how the overall effectiveness changed. Several internal impingement cooling schemes in addition to a baseline case without impingement cooling were also tested. In general, impingement cooling is shown to have a negligible influence on the overall effectiveness in the showerhead region. This indicates that the cost and pressure drop penalties for implementing impingement cooling may not be compensated by an increase in thermal performance. Instead, the internal cooling provided by convection within the holes themselves was shown, along with external film cooling, to be a dominant contribution to the overall cooling effectiveness. Indeed, the numerous holes within the showerhead region impede the ability of internal surface cooling schemes to influence the outside surface temperature. The results of this research may allow improved focus of future efforts on the forms of cooling with the greatest potential to improve cooling performance.

Heat Transfer and Film Cooling Effectiveness in a Linear Airfoil Cascade

1997 ◽  
Vol 119 (2) ◽  
pp. 302-309 ◽  
Author(s):  
N. Abuaf ◽  
R. Bunker ◽  
C. P. Lee
Keyword(s):  
Heat Transfer ◽  
Steady State ◽  
Film Cooling ◽  
Leading Edge ◽  
Transfer Coefficients ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Linear Cascade ◽  
Heat Transfer Coefficients

A warm (315°C) wind tunnel test facility equipped with a linear cascade of film cooled vane airfoils was used in the simultaneous determination of the local gas side heat transfer coefficients and the adiabatic film cooling effectiveness. The test rig can be operated in either a steady-state or a transient mode. The steady-state operation provides adiabatic film cooling effectiveness values while the transient mode generates data for the determination of the local heat transfer coefficients from the temperature–time variations and of the film effectiveness from the steady wall temperatures within the same aerothermal environment. The linear cascade consists of five airfoils. The 14 percent cascade inlet free-stream turbulence intensity is generated by a perforated plate, positioned upstream of the airfoil leading edge. For the first transient tests, five cylinders having roughly the same blockage as the initial 20 percent axial chord of the airfoils were used. The cylinder stagnation point heat transfer coefficients compare well with values calculated from correlations. Static pressure distributions measured over an instrumented airfoil agree with inviscid predictions. Heat transfer coefficients and adiabatic film cooling effectiveness results were obtained with a smooth airfoil having three separate film injection locations, two along the suction side, and the third one covering the leading edge showerhead region. Near the film injection locations, the heat transfer coefficients increase with the blowing film. At the termination of the film cooled airfoil tests, the film holes were plugged and heat transfer tests were conducted with non-film cooled airfoils. These results agree with boundary layer code predictions.

Heat Transfer and Film Cooling Effectiveness in a Linear Airfoil Cascade

1995 ◽  
Author(s):  
N. Abuaf ◽  
R. Bunker ◽  
C. P. Lee
Keyword(s):  
Heat Transfer ◽  
Steady State ◽  
Film Cooling ◽  
Leading Edge ◽  
Transfer Coefficients ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Linear Cascade ◽  
Heat Transfer Coefficients

A warm (315 C) wind tunnel test facility equipped with a linear cascade of film cooled vane airfoils was used in the simultaneous determination of the local gas side heat transfer coefficients and the adiabatic film cooling effectiveness. The test rig can be operated in either a steady-state or a transient mode. The steady-state operation provides adiabatic film cooling effectiveness values while the transient mode generates data for the determination of the local heat transfer coefficients from the temperature-time variations and of the film effectiveness from the steady wall temperatures within the same aero-thermal environment. The linear cascade consists of five airfoils. The 14% cascade inlet free stream turbulence intensity is generated by a perforated plate, positioned upstream of the airfoil leading edge. For the first transient tests, five cylinders having roughly the same blockage as the initial 20% axial chord of the airfoils were used. The cylinder stagnation point heat transfer coefficients compare well with values calculated from correlations. Static pressure distributions measured over an instrumented airfoil agree with inviscid predictions. Heat transfer coefficients and adiabatic film cooling effectiveness results were obtained with a smooth airfoil having three separate film injection locations, two along the suction side, and the third one covering the leading edge showerhead region. Near the film injection locations, the heat transfer coefficients increase with the blowing film. At the termination of the film cooled airfoil tests, the film holes were plugged and heat transfer tests were conducted with non-film cooled airfoils. These results agree with boundary layer code predictions.

Influence of High Mainstream Turbulence on Leading Edge Heat Transfer

1991 ◽  
Vol 113 (4) ◽  
pp. 843-850 ◽  
Author(s):  
A. B. Mehendale ◽  
J. C. Han ◽  
S. Ou
Keyword(s):  
Heat Transfer ◽  
Turbulence Intensity ◽  
Leading Edge ◽  
Local Heat Transfer ◽  
Reynolds Numbers ◽  
Local Heat ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Turbulence Decay ◽  
High Turbulence

The influence of high mainstream turbulence on leading edge heat transfer was studied. High mainstream turbulence was produced by a bar grid (Tu = 3.3–5.1 percent), passive grid (Tu = 7.6–9.7 percent), and jet grid (Tu = 12.9–15.2 percent). Experiments were performed using a blunt body with a semicylinder leading edge and flat sidewalls. The mainstream Reynolds numbers based on leading edge diameter were 25,000, 40,000, and 100,000. Spanwise and streamwise distributions of local heat transfer coefficients on the leading edge and flat sidewall were obtained. The results indicate that the leading edge heat transfer increases significantly with increasing mainstream turbulence intensity, but the effect diminishes at the end of the flat sidewall because of turbulence decay. Stagnation point heat transfer results for high turbulence intensity flows agree with the Lowery and Vachon correlation, but the overall heat transfer results for the leading edge quarter-cylinder region are higher than their overall correlation for the entire circular cylinder region. High mainstream turbulence tends not to shift the location of the separation-reattachment region. The reattachment heat transfer results are about the same regardless of mainstream turbulence levels and are much higher than the turbulent flat plate correlation.

Experimental and Numerical Study of Impingement on an Airfoil Leading Edge With and Without Showerhead and Gill Film Holes

2005 ◽  
Vol 128 (2) ◽  
pp. 310-320 ◽  
Author(s):  
M. E. Taslim ◽  
A. Khanicheh
Keyword(s):  
Heat Transfer ◽  
Turbulence Modeling ◽  
Numerical Study ◽  
Leading Edge ◽  
Suction Side ◽  
Reynolds Numbers ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Numerical Predictions ◽  
Impingement Heat Transfer

This experimental investigation deals with impingement on the leading edge of an airfoil with and without showerhead film holes and its effects on heat transfer coefficients on the airfoil nose area as well as the pressure and suction side areas. a comparison between the experimental and numerical results are also made. the tests were run for a range of flow conditions pertinent to common practice and at an elevated range of jet Reynolds numbers (8000–48,000). The major conclusions of this study were: (a) The presence of showerhead film holes along the leading edge enhances the internal impingement heat transfer coefficients significantly, and (b) while the numerical predictions of impingement heat transfer coefficients for the no-showerhead case were in good agreement with the measured values, the case with showerhead flow was under-predicted by as much as 30% indicating a need for a more elaborate turbulence modeling.

Effect of Jet Pulsation and Duty Cycle on Film Cooling From a Single Jet on a Leading Edge Model

2004 ◽  
Author(s):  
Srinath V. Ekkad ◽  
Shichuan Ou ◽  
Richard B. Rivir
Keyword(s):  
Heat Transfer ◽  
Duty Cycle ◽  
Film Cooling ◽  
Leading Edge ◽  
Pulse Frequency ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Blowing Ratio ◽  
Valve Opening ◽  
Lower Heat

The effect of jet pulsation and duty cycle on film effectiveness and heat transfer was investigated on a film hole located on the circular leading edge of a blunt body. A transient infrared technique was used to measure both heat transfer coefficients and film effectiveness from a single test. Detailed Frossling number and film effectiveness distributions were obtained for all flow conditions. Jet pulsing frequencies of 5 Hz, 10 Hz, and 20 Hz have been studied. The effect of duty cycle created by the valve opening and closing times was also set at different levels of 10%, 25%, 50%, and 75% of designated 100% fully open condition for different blowing ratios from 0.25 to 2.0. The combination of pulse frequency and duty cycle was investigated for different blowing ratios on a single leading edge hole located at 22-deg from geometric leading edge. Results indicate that higher effectiveness and lower heat transfer coefficients are obtained at the reduced blowing ratios which result from reduced duty cycles. The effect of varying the pulsing frequency from 5 Hertz to 20 Hertz is not discernable beyond the level of experimental uncertainty. Effective blowing ratio due to lowering of the duty cycle at a given blowing ratio seems to plays a more important role in combination with pulsing which provides improved cooling effectiveness at lower heat transfer coefficients.

Squealer Tip Heat Transfer With Film Cooling

2010 ◽  
Author(s):  
Sumanta Acharya ◽  
Gregory Kramer ◽  
Louis Moreaux ◽  
Chiyuki Nakamata
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Film Cooling ◽  
Leading Edge ◽  
Numerical Results ◽  
Transfer Coefficients ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Heat Transfer Coefficients ◽  
Pressure Distributions

Heat transfer coefficients and film cooling effectiveness values were obtained numerically on a film cooled 2-D gas turbine blade tip model featuring a cutback squealer. In addition, pressure distributions were obtained at 50% and 98% spans. The calculations were performed for a single blade with periodic boundary conditions imposed along the two mid-passage boundaries formed by the adjacent blades. The calculations were performed with the realizable k-ε turbulence model and non-equilibrium wall function using 1.1 million elements. The numerical results are obtained for 4 blowing ratios and for Reynolds number based on axial chord and inlet velocity of 75,000. Limited experimental measurements of the blade pressure distributions and the uncooled tip heat transfer coefficients were performed for validation of the numerical results. The experiments were conducted in a six-blade low-speed wind tunnel cascade at a Reynolds number of 75,000. The heat transfer experiment involved a transient infrared thermography technique. Experimental heat transfer coefficients were extracted using a transient technique. The predicted pressure distributions agree very well with the measurements while the heat transfer coefficient predictions show qualitative agreement. From the numerical results, it can be seen that as the blowing ratio is increased, larger regions of film cooling effectiveness were seen with higher effectiveness values between the camber line and suction side. Heat transfer coefficients were largest near the leading edge for all cases.

Leading Edge Impingement With Racetrack Shaped Jets and Varying Inlet Supply Conditions

2013 ◽  
Author(s):  
C. Neil Jordan ◽  
Cassius A. Elston ◽  
Lesley M. Wright ◽  
Daniel C. Crites
Keyword(s):  
Heat Transfer ◽  
Test Section ◽  
Turbine Blades ◽  
Leading Edge ◽  
Target Surface ◽  
Reynolds Numbers ◽  
Impinging Jets ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Crossflow Velocity

Impinging jets are often employed within the leading edge of turbine blades and vanes to combat the tremendous heat loads incurred as the hot exhaust gases stagnate along the exterior of the airfoil. Relative to traditional cylindrical jets, racetrack shaped impinging jets have been shown to produce favorable cooling characteristics within the turbine airfoil. This investigation experimentally and numerically quantifies the cooling characteristics associated with a row of racetrack shaped jets impinging on a concave, cylindrical surface. Detailed Nusselt number distributions are obtained using both a transient liquid crystal technique and commercially available CFD software (Star CCM+ from CD-Adapco). Three geometrical jet inlet and exit conditions are experimentally investigated: a square edge, a partially filleted edge (r/dH,Jet = 0.25), and a fully filleted edge (r/dH,Jet = 0.667). Additionally, to investigate the effect of high crossflow velocities at the inlet of the jet, a portion of the flow supplied to the test apparatus radially bypasses the impingement section. Thus, the mass flow rate into the test section is varied to achieve the desired inlet crossflow conditions and jet Reynolds numbers. As a result, jet Reynolds numbers (ReJet) of 11500 and 23000 are investigated at supply duct Reynolds numbers (ReDuct) of 20000 and 30000. The results are compared to baseline cases where no mass bypasses the test section. Additionally, the relative jet – to – jet spacing (s/dH,Jet) is maintained at 8, the relative jet – to – target surface spacing (z/dH,Jet) is 4, the target surface curvature – to – jet hydraulic diameter (D/dH,Jet) is 5.33, and the relative thickness of the jet plate (t/dH,Jet) is 1.33. Measurements indicate that the addition of fillets at the edges of the jet orifice and the introduction of significant crossflow velocity at the inlet of the jet can significantly degrade the cooling characteristics on the leading edge of the turbine blade. The magnitude of such degradation generally increases with increasing fillet size and inlet crossflow velocity. The V2F model is adequate for predicting the flow field and target surface heat transfer in the absence of inlet crossflow; however, it is believed the turbulence within the jet is overpredicted by the CFD leading to elevated heat transfer coefficients (compared to the experimental results).

Experimental and Numerical Study of Impingement on an Airfoil Leading-Edge With and Without Showerhead and Gill Film Holes

2005 ◽  
Author(s):  
M. E. Taslim ◽  
A. Khanicheh
Keyword(s):  
Heat Transfer ◽  
Turbulence Modeling ◽  
Numerical Study ◽  
Leading Edge ◽  
Suction Side ◽  
Reynolds Numbers ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Numerical Predictions ◽  
Impingement Heat Transfer

This experimental investigation deals with impingement on the leading-edge of an airfoil with and without showerhead film holes and its effects on heat transfer coefficients on the airfoil nose area as well as the pressure and suction side areas. A comparison between the experimental and numerical results are also made. The tests were run for a range of flow conditions pertinent to common practice and at an elevated range of jet Reynolds numbers (8000–48000). The major conclusions of this study were: a) the presence of showerhead film holes along the leading edge enhances the internal impingement heat transfer coefficients significantly, and b) while the numerical predictions of impingement heat transfer coefficients for the no-showerhead case were in good agreement with the measured values, the case with showerhead flow was underpredicted by as much as 30% indicating a need for a more elaborate turbulence modeling.

Effect of Jet Pulsation and Duty Cycle on Film Cooling From a Single Jet on a Leading Edge Model

2006 ◽  
Vol 128 (3) ◽  
pp. 564-571 ◽  
Author(s):  
Srinath V. Ekkad ◽  
Shichuan Ou ◽  
Richard B. Rivir
Keyword(s):  
Heat Transfer ◽  
Duty Cycle ◽  
Film Cooling ◽  
Leading Edge ◽  
Pulse Frequency ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Blowing Ratio ◽  
Valve Opening ◽  
Lower Heat

The effect of jet pulsation and duty cycle on film effectiveness and heat transfer was investigated on a film hole located on the circular leading edge of a blunt body. A transient infrared technique was used to measure both heat transfer coefficients and film effectiveness from a single test. Detailed Frossling number and film effectiveness distributions were obtained for all flow conditions. Jet pulsing frequencies of 5 Hz, 10 Hz, and 20 Hz have been studied. The effect of duty cycle created by the valve opening and closing times was also set at different levels of 10%, 25%, 50%, and 75% of designated 100% fully open condition for different blowing ratios from 0.25 to 2.0. The combination of pulse frequency and duty cycle was investigated for different blowing ratios on a single leading edge hole located at 22 deg from geometric leading edge. Results indicate that higher effectiveness and lower heat transfer coefficients are obtained at the reduced blowing ratios, which result from reduced duty cycles. The effect of varying the pulsing frequency from 5 Hz to 20 Hz is not discernable beyond the level of experimental uncertainty. Effective blowing ratio due to lowering of the duty cycle at a given blowing ratio seems to play a more important role in combination with pulsing, which provides improved cooling effectiveness at lower heat transfer coefficients.

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