Net Heat Flux Reduction and Overall Effectiveness for a Turbine Blade Leading Edge

2005 ◽  
Author(s):  
Brian D. Mouzon ◽  
Elon J. Terrell ◽  
Jason E. Albert ◽  
David G. Bogard
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Turbine Blade ◽  
Film Cooling ◽  
Leading Edge ◽  
Cooling Performance ◽  
Net Heat Flux ◽  
Laboratory Models ◽  
Overall Effectiveness ◽  
Blade Leading Edge

The external cooling performance of a film cooled turbine airfoil can be quantified as a net reduction in heat transfer relative to the turbine airfoil without film cooling. This quantification is generally accomplished by using measurements of the adiabatic effectiveness and the change in heat transfer coefficients (hf/h0) for the film cooled surface to determine the net heat flux reduction (Δqr). Although measurement of Δqr for laboratory models give an indication of the ultimate film cooling performance, this does not show how much the surface temperature of the airfoil is reduced by film cooling. Measurement of scaled surface temperatures can be accomplished by using laboratory models constructed so that the Biot number is matched with that of the actual airfoil. These measurements provide a scaled temperature distribution on the airfoil that is referred to as the overall effectiveness, φ. For the current study, measurements of Δqr and φ have been made for a simulated turbine blade leading edge. The simulated leading edge incorporated shaped coolant holes, and had three rows of coolant holes. Improvements due to the shaped holes were determined by comparisons with previously measured round hole configurations. Spatially distributed hf/h0 show increases of 5% to 15% for M = 1.0 and 10% to 30% for M = 2.0. Results show that local variation in Δqr much greater than variation in φ, but laterally averaged Δqr distributions are reasonable predictors of the laterally averaged φ distributions.

Experimental Study of the Effects of an Oscillating Approach Flow on Overall Cooling Performance of a Simulated Turbine Blade Leading Edge

2009 ◽  
Author(s):  
Ross Johnson ◽  
Jonathan Maikell ◽  
David Bogard ◽  
Justin Piggush ◽  
Atul Kohli ◽  
...  
Keyword(s):  
Turbine Blade ◽  
Film Cooling ◽  
Density Ratio ◽  
Leading Edge ◽  
Stagnation Line ◽  
Cooling Performance ◽  
Blowing Ratio ◽  
Oscillation Frequencies ◽  
Overall Effectiveness ◽  
Blade Leading Edge

When a turbine blade passes through wakes from upstream vanes it is subjected to an oscillation of the direction of the approach flow resulting in the oscillation of the position of the stagnation line on the leading edge of the blade. In this study an experimental facility was developed that induced a similar oscillation of the stagnation line position on a simulated turbine blade leading edge. The overall effectiveness was evaluated at various blowing ratios and stagnation line oscillation frequencies. The location of the stagnation line on the leading edge was oscillated to simulate a change in angle of attack between α = ± 5° at a range of frequencies from 2 to 20 Hz. These frequencies were chosen based on matching a range of Strouhal numbers typically seen in an engine due to oscillations caused by passing wakes. The blowing ratio was varied between M = 1, M = 2, and M = 3. These experiments were carried out at a density ratio of DR = 1.5 and mainstream turbulence levels of Tu ≈ 6%. The leading edge model was made of high conductivity epoxy in order to match the Biot number of an actual engine airfoil. Results of these tests showed that the film cooling performance with an oscillating stagnation line was degraded by as much as 25% compared to the performance of a steady flow with the stagnation line aligned with the row of holes at the leading edge.

CFD Predictions of Pulsed Film Cooling Heat Flux on a Turbine Blade Leading Edge

2008 ◽  
Author(s):  
James L. Rutledge ◽  
Paul I. King ◽  
Richard Rivir
Keyword(s):  
Heat Flux ◽  
Turbine Blade ◽  
Film Cooling ◽  
Computational Study ◽  
Leading Edge ◽  
Time Resolved ◽  
Average Mass ◽  
Blowing Ratio ◽  
Net Heat Flux ◽  
Blade Leading Edge

Unsteadiness in film cooling jets may arise due to inherent unsteadiness of the blade-vane interaction or may be induced as a means of flow control. A computational study was conducted to determine how leading edge film cooling performance is affected by pulsing the coolant flow. A cylindrical leading edge with a flat afterbody is used to simulate the turbine blade leading edge region. A single coolant hole was located 21.5° from the leading edge, angled 20° to the surface and 90° from the streamwise direction. The leading edge diameter to hole diameter ratio is D/d = 18.7. Time resolved adiabatic effectiveness and heat transfer coefficient are used to calculate the temporally averaged, spatially resolved net heat flux reduction for several pulsing scenarios. The net heat flux reduction with pulsed film cooling is compared to the steady jet with matched average mass flow rate. Steady blowing ratios of M = 0.25 and 0.50 are each compared with two pulsed jet cases with matching averaging blowing ratio, M, at a nondimensional frequency, F = 0.151 and duty cycle, DC = 50%. Simulations were performed at ReD = 60000. Net heat flux is generally increased by pulsing the film coolant, with greater degradation for higher pulsation amplitudes relative to the average blowing ratio.

Numerical Study on Influencing Factors of Film Cooling on Turbine Blade Leading Edge Under Rotating State

2018 ◽  
Author(s):  
Yiwen Ma ◽  
Haiwang Li ◽  
Meisong Yang ◽  
Min Wu ◽  
Huimin Zhou
Keyword(s):  
Heat Transfer ◽  
High Temperature ◽  
Turbine Blade ◽  
Rotation Number ◽  
Film Cooling ◽  
Leading Edge ◽  
Heat Transfer Characteristics ◽  
Transfer Characteristics ◽  
Flow And Heat Transfer ◽  
Blade Leading Edge

Engine turbine blades operate at a high speed of rotation and are subjected to high temperature and pressure prevailing gas from the combustion chamber, making the working condition very harsh. In particular, the leading edge of the blade, which is directly subjected to high-temperature gas impacts, is the hottest part of the turbine. Therefore, it is of great importance to improve the protection of the blade leading edge and enhance the understanding of this part of the flow field and temperature field. This paper will focus on the phenomenon of wake deflection and study the film cooling characteristics of the turbine blade under rotating condition. The characteristics of pressure surface and suction surface of the blade are verified by numerical simulation. The contents cover the influence of the film hole diameter, pitch, blowing ratio, rotation number and the development process, the film cooling efficiency on the outflow of coolant film. The result shows that Coriolis force, centrifugal force and secondary flow induced by rotation will change the mainstream flow along the blade, which will lead to changes of pattern concerning the development of the film on the blade surface. In the process of wake development, deflection occurs in different directions at different positions, and the greater the rotation number is, the more obvious the degree of deflection will be. Studying the model with film holes on the leading edge of the blade, these phenomena can be observed along the downstream on the pressure and suction surfaces. Also, models with film holes independently set on the pressure and suction surfaces can be used as proof of these features. At the same time, this paper studies the flow and heat transfer characteristics of the leading-edge gas film under rotating condition and focuses on the influence of rotation on the outflow and the development processes of the wake. The gas film cooling models in rotating state of different film hole diameters and film hole radial spacing will also be compared to further understand the flow and heat transfer characteristics of film cooling on the leading edge of the blade.

Film Cooling Parameter Waveforms on a Turbine Blade Leading Edge Model With Oscillating Stagnation Line

2016 ◽  
Vol 138 (7) ◽  
Author(s):  
James L. Rutledge ◽  
Tylor C. Rathsack ◽  
Matthew T. Van Voorhis ◽  
Marc D. Polanka
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Turbine Blade ◽  
Film Cooling ◽  
Leading Edge ◽  
Stagnation Line ◽  
Inverse Heat Transfer ◽  
Adiabatic Effectiveness ◽  
Blade Leading Edge

It is necessary to understand how film cooling influences the external convective boundary condition involving both the adiabatic wall temperature and the heat transfer coefficient in order to predict the thermal durability of a gas turbine hot gas path component. Most studies in the past have considered only steady flow, but studies of the unsteadiness naturally present in turbine flow have become more prevalent. One source of unsteadiness is wake passage from upstream components which can cause fluctuations in the stagnation location on turbine airfoils. This in turn causes unsteadiness in the behavior of the leading edge coolant jets and thus fluctuations in both the adiabatic effectiveness and heat transfer coefficient. The dynamics of h and η are now quantifiable with modern inverse heat transfer methods and nonintrusive infrared thermography. The present study involved the application of a novel inverse heat transfer methodology to determine time-resolved adiabatic effectiveness and heat transfer coefficient waveforms on a simulated turbine blade leading edge with an oscillating stagnation position. The leading edge geometry was simulated with a circular cylinder with a coolant hole located 21.5 deg downstream from the leading edge stagnation line, angled 20 deg to the surface and 90 deg to the streamwise direction. The coolant plume is shown to shift in response to the stagnation line movement. These oscillations thus influence the film cooling coverage, and the time-averaged benefit of film cooling is influenced by the oscillation.

Convective Heat Transfer Through Film Cooling Holes of a Gas Turbine Blade Leading Edge

2005 ◽  
Author(s):  
Elon J. Terrell ◽  
Brian D. Mouzon ◽  
David G. Bogard
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Gas Turbine ◽  
Turbine Blade ◽  
Convective Heat ◽  
Film Cooling ◽  
Leading Edge ◽  
Gas Turbine Blade ◽  
Film Cooling Holes ◽  
Blade Leading Edge

Studies of film cooling performance for a turbine airfoil predominately focus on the reduction of heat transfer to the external surface of the airfoil. However, convective cooling of the airfoil due to coolant flow through the film cooling holes is potentially a major contributor to the overall cooling of the airfoil. This study used experimental and computational methods to examine the convective heat transfer to the coolant as it traveled through the film cooling holes of a gas turbine blade leading edge. Experimental measurements were conducted on a model gas turbine blade leading edge composed of alumina ceramic which approximately matched the Biot number of an engine airfoil leading edge. The temperature rise in the coolant from the entrance to the exit of the film cooling holes was measured using a series of internal thermocouples and an external traversing thermocouple probe. A CFD simulation of the model of the leading edge was also done in order to facilitate the processing of the experimental data and provide a comparison for the experimental coolant hole heat transfer. Without impingement cooling, the coolant hole heat transfer was found to account for 50 to 80 percent of the airfoil internal cooling, i.e. the dominating cooling mechanism.

Experimental Simulation of a Film Cooled Turbine Blade Leading Edge Including Thermal Barrier Coating Effects

2010 ◽  
Vol 133 (1) ◽  
Author(s):  
Jonathan Maikell ◽  
David Bogard ◽  
Justin Piggush ◽  
Atul Kohli
Keyword(s):  
Thermal Barrier Coating ◽  
Turbine Blade ◽  
Film Cooling ◽  
Leading Edge ◽  
Experimental Simulation ◽  
Thermal Barrier ◽  
Stagnation Line ◽  
Barrier Coating ◽  
Overall Effectiveness ◽  
Blade Leading Edge

For this study, a simulated film cooled turbine blade leading edge, constructed of a special high conductivity material, was used to determine the normalized “metal temperature” representative of actual engine conditions. The Biot number for the model was matched to that for operational engine conditions, ensuring that the normalized wall temperature, i.e., the overall effectiveness, was matched to that for the engine. Measurements of overall effectiveness were made for models with and without thermal barrier coating (TBC) at various operating conditions. This was the first study to experimentally simulate TBC and the effects on overall effectiveness. Two models were used: one with a single row of holes along the stagnation line, and the second with three rows of holes straddling the stagnation line. Film cooling was operated using a density ratio of 1.5 and for range of blowing ratios from M=0.5 to M=3.0. Both models were tested using a range of angles of attack from 0.0 deg to ±5.0 deg. As expected, the TBC coated models had significantly higher external surface temperatures, but lower metal temperatures. These experimental results provide a unique database for evaluating numerical simulations of the effects of TBC on leading edge film cooling performance.

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