Impact of an Upstream Film-Cooling Row on Mitigation of Secondary Combustion in a Fuel Rich Environment

2013 ◽  
Vol 136 (3) ◽  
Author(s):  
Brian T. Bohan ◽  
David L. Blunck ◽  
Marc D. Polanka ◽  
Stanislav Kostka ◽  
Naibo Jiang ◽  
...  
Keyword(s):  
Heat Flux ◽  
Film Cooling ◽  
Turbine Engines ◽  
Experimental Film ◽  
Double Row ◽  
Secondary Combustion ◽  
Significant Damage ◽  
Planar Laser ◽  
Secondary Reactions ◽  
Reactive Gases

In advanced gas turbine engines that feature very short combustor sections, an issue of fuel-rich gases interacting with the downstream turbine components can exist. Specifically, in combustors with high fuel-to-air ratios, there are regions downstream of the primary combustion section that will require the use of film-cooling in the presence of incompletely reacted exhaust. Additional combustion reactions resulting from the combination of unburnt fuel and oxygen-rich cooling films can cause significant damage to the turbine. Research has been accomplished to understand this secondary reaction process. This experimental film-cooling study expands the previous investigations by attempting to reduce or mitigate the increase in heat flux that results from secondary combustion in the coolant film. Two different upstream cooling schemes were used to attempt to protect a downstream fan-shaped cooling row. The heat flux downstream was measured and compared between ejection with air compared to nitrogen in the form of a heat flux augmentation. Planar Laser Induced Fluorescence (PLIF) was used to measure relative OH concentration in the combustion zones to understand where the reactions occurred. A double row of staggered normal holes was unsuccessful at reducing the downstream heat load. The coolant separated from the surface generating a high mixing regime and allowed the hot unreacted gases to penetrate underneath the jets. Conversely, an upstream slot row was able to generate a spanwise film of coolant that buffered the reactive gases off the surface. Essentially no secondary reactions were observed aft of the shaped coolant hole ejection with the protective slot upstream. A slight increase in heat transfer was attributed to the elevated freestream temperature resulting from reactions above the slot coolant. Creating this full sheet of coolant will be a key toward future designs attempting to control secondary reactions in the turbine.

Impact of an Upstream Film-Cooling Row on Mitigation of Secondary Combustion in a High Fuel-Air Environment

2012 ◽  
Author(s):  
Brian T. Bohan ◽  
David L. Blunck ◽  
Marc D. Polanka ◽  
Stanislav Kostka ◽  
Naibo Jiang ◽  
...  
Keyword(s):  
Heat Flux ◽  
Film Cooling ◽  
Laser Induced Fluorescence ◽  
Turbine Engines ◽  
Experimental Film ◽  
Gas Turbine Engines ◽  
Negative Effects ◽  
Secondary Combustion ◽  
Planar Laser ◽  
Negative Impacts

In advanced gas turbine engines that feature very short combustor sections, an issue of fuel-rich gases interacting with downstream components exists. In all of these engines there are regions downstream of the primary combustion section that will require the use of film-cooling in the presence of incompletely reacted exhaust. This will lead to the possibility of additional combustion reactions resulting from the combination of unburnt fuel and oxygen-rich cooling films. Research has been accomplished to understand this secondary reaction process. This experimental film-cooling study expands the previous investigations by attempting to reduce or remove the negative effects that result from secondary combustion in the coolant film. An upstream row of holes was added to a row of previously tested shaped coolant holes to understand if the reactions could be mitigated at the downstream locations. Several combinations of cooling schemes were investigated and the heat flux downstream was measured. Planar Laser Induced Fluorescence (PLIF) was used to measure OH concentration in the combustion zones to understand where the reactions occurred. It was discovered that creating a full sheet of air upstream could effectively protect the downstream row from the negative impacts of the fuel-rich crossflow.

Minimization of Heat Load Due to Secondary Reactions in Fuel Rich Environments

2015 ◽  
Vol 137 (12) ◽  
Author(s):  
Andrew T. Shewhart ◽  
Marc D. Polanka ◽  
Jacob J. Robertson ◽  
Nathan J. Greiner ◽  
James L. Rutledge
Keyword(s):  
Heat Flux ◽  
Film Cooling ◽  
Turbine Blades ◽  
Local Heat ◽  
Turbine Engines ◽  
Inlet Temperature ◽  
Gas Turbine Engines ◽  
Engine Efficiency ◽  
Secondary Reactions ◽  
Local Heat Flux

The demand for increased thrust, higher engine efficiency, and reduced fuel consumption has increased the turbine inlet temperature and pressure in modern gas turbine engines. The outcome of these higher temperatures and pressures is the potential for unconsumed radical species to enter the turbine. Because modern cooling schemes for turbine blades involve injecting cool, oxygen-rich air adjacent to the surface, the potential for reaction with radicals in the mainstream flow, and augmented heat transfer to the blade arises. This result is contrary to the purpose of film cooling. In this environment, there is a competing desire to consume any free radicals prior to the flow entering the rotor stage while still maintaining surface temperatures below the metal melting temperature. This study evaluated various configurations of multiple cylindrical rows of cooling holes in terms of both heat release and effective downstream cooling. Results were evaluated based on net heat flux reduction (NHFR) and a new wall absorption (WA) parameter which combined the additional heat available from these secondary reactions with the length of the resulting flame to determine which schemes protected the wall more efficiently. Two particular schemes showed promise. The two row upstream configuration reduced the overall augmentation of heat by creating a short, concentrated reaction area. Conversely, the roll forward configuration minimized the local heat flux enhancement by spreading the reaction area over the surface being cooled.

Minimization of Heat Load due to Secondary Reactions in Fuel Rich Environments

2014 ◽  
Author(s):  
Andrew T. Shewhart ◽  
Marc D. Polanka ◽  
Jacob J. Robertson ◽  
Nathan J. Greiner ◽  
James L. Rutledge
Keyword(s):  
Film Cooling ◽  
Turbine Blades ◽  
Local Heat ◽  
Turbine Engines ◽  
Inlet Temperature ◽  
Gas Turbine Engines ◽  
Engine Efficiency ◽  
Secondary Reactions ◽  
Local Heat Flux ◽  
Metal Melting

The demand for increased thrust, higher engine efficiency, and reduced fuel consumption has increased the turbine inlet temperature and pressure in modern gas turbine engines. The outcome of these higher temperatures and pressures is the potential for unconsumed radical species to enter the turbine. Because modern cooling schemes for turbine blades involve injecting cool, oxygen rich air adjacent to the surface, the potential for reaction with radicals in the mainstream flow and augmented heat transfer to the blade arises. This result is contrary to the purpose of film cooling. In this environment there is a competing desire to consume any free radicals prior to the flow entering the rotor stage while still maintaining surface temperatures below the metal melting temperature. This study evaluated various configurations of multiple cylindrical rows of cooling holes in terms of both heat release and effective downstream cooling. Results were evaluated based on a new Wall Absorption parameter which combined the additional heat available from these secondary reactions with the length of the resulting flame to determine which schemes protected the wall more efficiently. Two particular schemes showed promise. The two row upstream configuration reduced the overall augmentation of heat by creating a short, concentrated reaction area. Conversely, the roll forward configuration minimized the local heat flux enhancement by spreading the reaction area over the surface being cooled.

Gas Turbine Engine Durability Impacts of High Fuel-Air Ratio Combustors—Part II: Near-Wall Reaction Effects on Film-Cooled Heat Transfer

2003 ◽  
Vol 125 (3) ◽  
pp. 751-759 ◽  
Author(s):  
D. R. Kirk ◽  
G. R. Guenette ◽  
S. P. Lukachko ◽  
I. A. Waitz
Keyword(s):  
Heat Flux ◽  
Gas Turbine ◽  
Chemical Reactions ◽  
Film Cooling ◽  
Surface Heat Flux ◽  
Gas Turbine Engine ◽  
Surface Heat ◽  
Turbine Engine ◽  
Secondary Reactions ◽  
Near Wall

As commercial and military aircraft engines approach higher total temperatures and increasing overall fuel-to-air ratios, the potential for significant chemical reactions on a film-cooled surface is enhanced. Currently, there is little basis for understanding the effects on aero-performance and durability due to such secondary reactions. A shock tube experiment was employed to generate short duration, high temperature (1000–2800 K) and pressure (6 atm) flows over a film-cooled flat plate. The test plate contained two sets of 35 deg film cooling holes that could be supplied with different gases, one side using air and the other nitrogen. A mixture of ethylene and argon provided a fuel rich freestream that reacted with the air film resulting in near wall reactions. The relative increase in surface heat flux due to near wall reactions was investigated over a range of fuel levels, momentum blowing ratios (0.5–2.0), and Damko¨hler numbers (ratio of flow to chemical time scales) from near zero to 30. For high Damko¨hler numbers, reactions had sufficient time to occur and increased the surface heat flux by 30 percent over the inert cooling side. When these results are appropriately scaled, it is shown that in some situations of interest for gas turbine engine environments significant increases in surface heat flux can be produced due to chemical reactions in the film-cooling layer. It is also shown that the non-dimensional parameters Damko¨hler number (Da), blowing ratio (B), heat release potential (H*), and scaled heat flux Qs are the appropriate quantities to predict the augmentation in surface heat flux that arises due to secondary reactions.

Gas Turbine Engine Durability Impacts of High Fuel-Air Ratio Combustors: Part 2 — Near Wall Reaction Effects on Film-Cooled Heat Transfer

2002 ◽  
Author(s):  
Daniel R. Kirk ◽  
Gerald R. Guenette ◽  
Stephen P. Lukachko ◽  
Ian A. Waitz
Keyword(s):  
Heat Flux ◽  
Gas Turbine ◽  
Chemical Reactions ◽  
Film Cooling ◽  
Surface Heat Flux ◽  
Gas Turbine Engine ◽  
Surface Heat ◽  
Turbine Engine ◽  
Secondary Reactions ◽  
Near Wall

As commercial and military aircraft engines approach higher total temperatures and increasing overall fuel-to-air ratios, the potential for significant chemical reactions on a film-cooled surface is enhanced. Currently there is little basis for understanding the effects on aero-performance and durability due to such secondary reactions. A shock tube experiment was employed to generate short duration, high temperature (1000–2800 K) and pressure (6 atm.) flows over a film-cooled flat plate. The test plate contained two sets of 35° film cooling holes that could be supplied with different gases, one side using air and the other nitrogen. A mixture of ethylene and argon provided a fuel rich freestream that reacted with the air film resulting in near wall reactions. The relative increase in surface heat flux due to near wall reactions was investigated over a range of fuel levels, momentum blowing ratios (0.5–2.0), and Damko¨hler numbers (ratio of flow to chemical time scales) from near zero to 30. For high Damko¨hler numbers, reactions had sufficient time to occur and increased the surface heat flux by 30 percent over the inert cooling side. When these results are appropriately scaled, it is shown that in some situations of interest for gas turbine engine environments significant increases in surface heat flux can be produced due to chemical reactions in the film-cooling layer. It is also shown that the non-dimensional parameters Damko¨hler number (Da), blowing ratio (B), heat release potential (H*), and scaled heat flux (Qs) are the appropriate quantities to predict the augmentation in surface heat flux that arises due to secondary reactions.

scholarly journals A Three-Dimensional Coupled Internal/External Simulation of a Film-Cooled Turbine Vane

1999 ◽  
Author(s):  
James D. Heidmann ◽  
David L. Rigby ◽  
Ali A. Ameri
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Film Cooling ◽  
Three Dimensional ◽  
High Heat ◽  
Operating Conditions ◽  
High Heat Flux ◽  
Nasa Lewis Research ◽  
Turbine Vane ◽  
Film Cooling Holes

A three-dimensional Navier-Stokes simulation has been performed for a realistic film-cooled turbine vane using the LeRC-HT code. The simulation includes the flow regions inside the coolant plena and film cooling holes in addition to the external flow. The vane is the subject of an upcoming NASA Lewis Research Center experiment and has both circular cross-section and shaped film cooling holes. This complex geometry is modeled using a multi-block grid which accurately discretizes the actual vane geometry including shaped holes. The simulation matches operating conditions for the planned experiment and assumes periodicity in the spanwise direction on the scale of one pitch of the film cooling hole pattern. Two computations were performed for different isothermal wall temperatures, allowing independent determination of heat transfer coefficients and film effectiveness values. The results indicate separate localized regions of high heat flux in the showerhead region due to low film effectiveness and high heat transfer coefficient values, while the shaped holes provide a reduction in heat flux through both parameters. Hole exit data indicate rather simple skewed profiles for the round holes, but complex profiles for the shaped holes with mass fluxes skewed strongly toward their leading edges.

Effects of a Reacting Cross-Stream on Turbine Film Cooling

2010 ◽  
Vol 132 (5) ◽  
Author(s):  
Wesly S. Anderson ◽  
Marc D. Polanka ◽  
Joseph Zelina ◽  
Dave S. Evans ◽  
Scott D. Stouffer ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Film Cooling ◽  
Thermal Protection ◽  
Critical Role ◽  
Cylindrical Hole ◽  
Gas Temperature ◽  
Transfer Coefficients ◽  
Secondary Combustion ◽  
Cooling Hole ◽  
Reactor Operating

Film cooling plays a critical role in providing effective thermal protection to components in modern gas turbine engines. A significant effort has been undertaken over the last 40 years to improve the distribution of coolant and to ensure that the airfoil is protected by this coolant from the hot gases in the freestream. This film, under conditions with high fuel-air ratios, may actually be detrimental to the underlying metal. The presence of unburned fuel from an upstream combustor may interact with this oxygen rich film coolant jet resulting in secondary combustion. The completion of the reactions can increase the gas temperature locally resulting in higher heat transfer to the airfoil directly along the path line of the film coolant jet. This secondary combustion could damage the turbine blade, resulting in costly repair, reduction in turbine life, or even engine failure. However, knowledge of film cooling in a reactive flow is very limited. The current study explores the interaction of cooling flow from typical cooling holes with the exhaust of a fuel-rich well-stirred reactor operating at high temperatures over a flat plate. Surface temperatures, heat flux, and heat transfer coefficients are calculated for a variety of reactor fuel-to-air ratios, cooling hole geometries, and blowing ratios. Emphasis is placed on the difference between a normal cylindrical hole, an inclined cylindrical hole, and a fan-shaped cooling hole. When both air and nitrogen are injected through the cooling holes, the changes in surface temperature can be directly correlated with the presence of the reaction. Photographs of the localized burning are presented to verify the extent and locations of the reaction.

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