Journal of Thermal Science and Engineering Applications, Jul 26, 2021
Although awareness of the phenomenon of temperature separation in Ranque-Hilsch vortex tubes date... more Although awareness of the phenomenon of temperature separation in Ranque-Hilsch vortex tubes dates back at least nine decades, some mystery surrounding the phenomenon remains to this day. These devices split an incoming stream of fluid into two streams—one with a greater total temperature than the incoming fluid and the other with a lower total temperature. This temperature separation is accomplished with no moving parts and no external sources of energy including heat transfer to or from the device. In attempts to understand the physics of the temperature separation, previous researchers have characterized the effect through various inlet temperatures and pressures as well as various gases with different properties. Unfortunately, the findings documented in the literature are sometimes inconsistent indicating the possibility that previously uncontrolled properties and flow conditions govern temperature separation to an unappreciated degree. In the present research, two new flow characteristics are examined for their role in temperature separation—volumetric heat capacity, ρCp, and nozzle velocity. In the present experiments with air, it was found that by matching nozzle velocity and ρCp—even with disparate pressures, temperatures, Reynolds numbers, and Mach numbers—the resulting temperature separation curves are identical. This is the first known documentation of such a finding. The results suggest that nozzle velocity is fundamental to scaling the performance of a vortex tube, while the nozzle volumetric heat capacity is also relevant to its behavior.
The surface temperature of a film cooled turbine hot gas path component is typically nondimension... more The surface temperature of a film cooled turbine hot gas path component is typically nondimensionalized according to the overall effectiveness. This nondimensionalization scheme takes advantage of the fact that the surface temperature must be bounded by the coolant temperature and the freestream recovery temperature. Additional complexity arises when the surface temperature is influenced by the addition of a second coolant stream. While the surface temperature remains bounded by the cooler of the two coolant streams, the presence of the warmer stream means that the resulting overall effectiveness is now a function not only of the appropriately nondimensionalized coolant and freestream flowrates, but an additional nondimensional parameter that describes the relative difference in the two coolant temperatures. Previously, it was thought that experiments or computational fluid dynamics simulations would be required to discern this effect. In the present work, however, we introduce a linear resistive model that is based upon the exact solution to the energy equation and which accounts for the effect of any number of independent sources that influence the surface temperature. The model’s efficacy was demonstrated using experimental data acquired on conducting models in which two rows of holes ejected coolant from two independent plenums at two different temperatures.
A conjugate heat transfer analysis of the complex mechanisms of internal and external cooling of ... more A conjugate heat transfer analysis of the complex mechanisms of internal and external cooling of turbine blades can present a formidable task. Such an effort may be simplified somewhat by evaluating the normalized metal surface temperature of a turbine blade, also known as the cooling scheme’s overall effectiveness. Investigations of turbine cooling effectiveness for scenarios with multiple rows typically assume a single coolant temperature. However, scenarios may exist in which a region of interest is affected by multiple local coolant temperatures, such as when coolant is injected from different internal passages. The present work develops an appropriate reference temperature for such a situation as well as a new nondimensional parameter indicating the relative difference between coolant temperatures. The effect of this new nondimensional parameter on overall effectiveness and streamwise temperature gradients is evaluated for two double row cooling hole configurations. Each row, consisting of 7-7-7 cooling holes set in an Inconel flat plate, exhausts coolant at independently controlled temperatures; effectiveness is also evaluated at different advective capacity and momentum flux ratios. Circumstances are identified in which different coolant temperatures may present an advantage in overall cooling effectiveness and in reducing streamwise temperature gradients.
The classical method of superposition has been used for several decades to provide an estimate of... more The classical method of superposition has been used for several decades to provide an estimate of the adiabatic effectiveness for multiple sets of already well-characterized film cooling hole rows. In this way, design work is aided by classical superposition theory prior to higher fidelity experiments or simulations that would account for fluid dynamic interaction for which superposition cannot account. In the present work, we consider the additive effects of multiple rows of coolant holes, but now also with coolant issuing at different temperatures. There are a number of ways that coolant may issue from different cooling hole rows at different temperatures, one of which is simply the necessarily different internal channels through which the coolant must pass. The film cooling effectiveness is investigated for double rows of cooling holes wherein the two rows have different coolant temperatures. A double row consisting of an upstream slot and a downstream row of 7–7–7 cooling holes were first evaluated with a single coolant temperature to demonstrate that classical superposition theory applies well to the present configuration. Superposition theory is then extended to the context of multiple coolant temperatures and a new nondimensional parameter is identified, which governs cooling performance. The theory is experimentally evaluated by independently varying the coolant temperatures of the two rows. Circumstances are identified in which the second row of cooling holes may be detrimental to cooling performance.
Volume 6A: Heat Transfer — Combustors; Film Cooling
The surface temperature of a film cooled turbine hot gas path component is typically nondimension... more The surface temperature of a film cooled turbine hot gas path component is typically nondimensionalized according to the overall effectiveness. This nondimensionalization scheme takes advantage of the fact that the surface temperature must be bounded by the coolant temperature and the freestream recovery temperature. Additional complexity arises when the surface temperature is influenced by the addition of a second coolant stream. While the surface temperature remains bounded by the cooler of the two coolant streams, the presence of the warmer stream means that the resulting overall effectiveness is now a function not only of the appropriately nondimensionalized coolant and freestream flow rates, but an additional nondimensional parameter that describes the relative difference in the two coolant temperatures. Previously, it was thought that experiments or computational fluid dynamics simulations would be required to discern this effect. In the present work, however, we introduce a l...
The surface temperature of a film cooled turbine hot gas path component is typically nondimension... more The surface temperature of a film cooled turbine hot gas path component is typically nondimensionalized according to the overall effectiveness. This nondimensionalization scheme takes advantage of the fact that the surface temperature must be bounded by the coolant temperature and the freestream recovery temperature. Additional complexity arises when the surface temperature is influenced by the addition of a second coolant stream. While the surface temperature remains bounded by the cooler of the two coolant streams, the presence of the warmer stream means that the resulting overall effectiveness is now a function not only of the appropriately nondimensionalized coolant and freestream flowrates, but an additional nondimensional parameter that describes the relative difference in the two coolant temperatures. Previously, it was thought that experiments or computational fluid dynamics simulations would be required to discern this effect. In the present work, however, we introduce a li...
To improve thermal efficiency and reduce fuel consumption, gas turbine engines typically operate ... more To improve thermal efficiency and reduce fuel consumption, gas turbine engines typically operate at increasingly higher turbine inlet temperatures--well in excess of turbine blade material limits--and film cooling schemes are normally employed to reduce metal temperatures within acceptable limits and prevent structural failure. Cooling requirements vary across a blade surface, but there currently exists no means by which coolant temperatures can be locally adjusted to facilitate optimized usage across a blade. Ranque-Hilsch vortex tubes were investigated as a means of adjusting coolant temperatures solely by fluidic means, induced by the phenomenon of temperature separation. Analytical frameworks were developed to determine adiabatic and overall effectiveness in the presence of multiple coolant temperatures and validated via experiment. Through the integrated application of experimental, analytical, and computational investigations, the parameters which govern temperature separation...
Journal of Thermal Science and Engineering Applications
Although awareness of the phenomenon of temperature separation in Ranque-Hilsch vortex tubes date... more Although awareness of the phenomenon of temperature separation in Ranque-Hilsch vortex tubes dates back at least nine decades, some mystery surrounding the phenomenon remains to this day. These devices split an incoming stream of fluid into two streams—one with a greater total temperature than the incoming fluid and the other with a lower total temperature. This temperature separation is accomplished with no moving parts and no external sources of energy including heat transfer to or from the device. In attempts to understand the physics of the temperature separation, previous researchers have characterized the effect through various inlet temperatures and pressures as well as various gases with different properties. Unfortunately, the findings documented in the literature are sometimes inconsistent indicating the possibility that previously uncontrolled properties and flow conditions govern temperature separation to an unappreciated degree. In the present research, two new flow cha...
A conjugate heat transfer analysis of the complex mechanisms of internal and external cooling of ... more A conjugate heat transfer analysis of the complex mechanisms of internal and external cooling of turbine blades can present a formidable task. Such an effort may be simplified somewhat by evaluating the normalized metal surface temperature of a turbine blade, also known as the cooling scheme’s overall effectiveness. Investigations of turbine cooling effectiveness for scenarios with multiple rows typically assume a single coolant temperature. However, scenarios may exist in which a region of interest is affected by multiple local coolant temperatures, such as when coolant is injected from different internal passages. The present work develops an appropriate reference temperature for such a situation as well as a new nondimensional parameter indicating the relative difference between coolant temperatures. The effect of this new nondimensional parameter on overall effectiveness and streamwise temperature gradients is evaluated for two double row cooling hole configurations. Each row, c...
The classical method of superposition has been used for several decades to provide an estimate of... more The classical method of superposition has been used for several decades to provide an estimate of the adiabatic effectiveness for multiple sets of already well-characterized film cooling hole rows. In this way, design work is aided by classical superposition theory prior to higher fidelity experiments or simulations that would account for fluid dynamic interaction for which superposition cannot account. In the present work, we consider the additive effects of multiple rows of coolant holes, but now also with coolant issuing at different temperatures. There are a number of ways that coolant may issue from different cooling hole rows at different temperatures, one of which is simply the necessarily different internal channels through which the coolant must pass. The film cooling effectiveness is investigated for double rows of cooling holes wherein the two rows have different coolant temperatures. A double row consisting of an upstream slot and a downstream row of 7–7–7 cooling holes ...
Journal of Thermal Science and Engineering Applications, Jul 26, 2021
Although awareness of the phenomenon of temperature separation in Ranque-Hilsch vortex tubes date... more Although awareness of the phenomenon of temperature separation in Ranque-Hilsch vortex tubes dates back at least nine decades, some mystery surrounding the phenomenon remains to this day. These devices split an incoming stream of fluid into two streams—one with a greater total temperature than the incoming fluid and the other with a lower total temperature. This temperature separation is accomplished with no moving parts and no external sources of energy including heat transfer to or from the device. In attempts to understand the physics of the temperature separation, previous researchers have characterized the effect through various inlet temperatures and pressures as well as various gases with different properties. Unfortunately, the findings documented in the literature are sometimes inconsistent indicating the possibility that previously uncontrolled properties and flow conditions govern temperature separation to an unappreciated degree. In the present research, two new flow characteristics are examined for their role in temperature separation—volumetric heat capacity, ρCp, and nozzle velocity. In the present experiments with air, it was found that by matching nozzle velocity and ρCp—even with disparate pressures, temperatures, Reynolds numbers, and Mach numbers—the resulting temperature separation curves are identical. This is the first known documentation of such a finding. The results suggest that nozzle velocity is fundamental to scaling the performance of a vortex tube, while the nozzle volumetric heat capacity is also relevant to its behavior.
The surface temperature of a film cooled turbine hot gas path component is typically nondimension... more The surface temperature of a film cooled turbine hot gas path component is typically nondimensionalized according to the overall effectiveness. This nondimensionalization scheme takes advantage of the fact that the surface temperature must be bounded by the coolant temperature and the freestream recovery temperature. Additional complexity arises when the surface temperature is influenced by the addition of a second coolant stream. While the surface temperature remains bounded by the cooler of the two coolant streams, the presence of the warmer stream means that the resulting overall effectiveness is now a function not only of the appropriately nondimensionalized coolant and freestream flowrates, but an additional nondimensional parameter that describes the relative difference in the two coolant temperatures. Previously, it was thought that experiments or computational fluid dynamics simulations would be required to discern this effect. In the present work, however, we introduce a linear resistive model that is based upon the exact solution to the energy equation and which accounts for the effect of any number of independent sources that influence the surface temperature. The model’s efficacy was demonstrated using experimental data acquired on conducting models in which two rows of holes ejected coolant from two independent plenums at two different temperatures.
A conjugate heat transfer analysis of the complex mechanisms of internal and external cooling of ... more A conjugate heat transfer analysis of the complex mechanisms of internal and external cooling of turbine blades can present a formidable task. Such an effort may be simplified somewhat by evaluating the normalized metal surface temperature of a turbine blade, also known as the cooling scheme’s overall effectiveness. Investigations of turbine cooling effectiveness for scenarios with multiple rows typically assume a single coolant temperature. However, scenarios may exist in which a region of interest is affected by multiple local coolant temperatures, such as when coolant is injected from different internal passages. The present work develops an appropriate reference temperature for such a situation as well as a new nondimensional parameter indicating the relative difference between coolant temperatures. The effect of this new nondimensional parameter on overall effectiveness and streamwise temperature gradients is evaluated for two double row cooling hole configurations. Each row, consisting of 7-7-7 cooling holes set in an Inconel flat plate, exhausts coolant at independently controlled temperatures; effectiveness is also evaluated at different advective capacity and momentum flux ratios. Circumstances are identified in which different coolant temperatures may present an advantage in overall cooling effectiveness and in reducing streamwise temperature gradients.
The classical method of superposition has been used for several decades to provide an estimate of... more The classical method of superposition has been used for several decades to provide an estimate of the adiabatic effectiveness for multiple sets of already well-characterized film cooling hole rows. In this way, design work is aided by classical superposition theory prior to higher fidelity experiments or simulations that would account for fluid dynamic interaction for which superposition cannot account. In the present work, we consider the additive effects of multiple rows of coolant holes, but now also with coolant issuing at different temperatures. There are a number of ways that coolant may issue from different cooling hole rows at different temperatures, one of which is simply the necessarily different internal channels through which the coolant must pass. The film cooling effectiveness is investigated for double rows of cooling holes wherein the two rows have different coolant temperatures. A double row consisting of an upstream slot and a downstream row of 7–7–7 cooling holes were first evaluated with a single coolant temperature to demonstrate that classical superposition theory applies well to the present configuration. Superposition theory is then extended to the context of multiple coolant temperatures and a new nondimensional parameter is identified, which governs cooling performance. The theory is experimentally evaluated by independently varying the coolant temperatures of the two rows. Circumstances are identified in which the second row of cooling holes may be detrimental to cooling performance.
Volume 6A: Heat Transfer — Combustors; Film Cooling
The surface temperature of a film cooled turbine hot gas path component is typically nondimension... more The surface temperature of a film cooled turbine hot gas path component is typically nondimensionalized according to the overall effectiveness. This nondimensionalization scheme takes advantage of the fact that the surface temperature must be bounded by the coolant temperature and the freestream recovery temperature. Additional complexity arises when the surface temperature is influenced by the addition of a second coolant stream. While the surface temperature remains bounded by the cooler of the two coolant streams, the presence of the warmer stream means that the resulting overall effectiveness is now a function not only of the appropriately nondimensionalized coolant and freestream flow rates, but an additional nondimensional parameter that describes the relative difference in the two coolant temperatures. Previously, it was thought that experiments or computational fluid dynamics simulations would be required to discern this effect. In the present work, however, we introduce a l...
The surface temperature of a film cooled turbine hot gas path component is typically nondimension... more The surface temperature of a film cooled turbine hot gas path component is typically nondimensionalized according to the overall effectiveness. This nondimensionalization scheme takes advantage of the fact that the surface temperature must be bounded by the coolant temperature and the freestream recovery temperature. Additional complexity arises when the surface temperature is influenced by the addition of a second coolant stream. While the surface temperature remains bounded by the cooler of the two coolant streams, the presence of the warmer stream means that the resulting overall effectiveness is now a function not only of the appropriately nondimensionalized coolant and freestream flowrates, but an additional nondimensional parameter that describes the relative difference in the two coolant temperatures. Previously, it was thought that experiments or computational fluid dynamics simulations would be required to discern this effect. In the present work, however, we introduce a li...
To improve thermal efficiency and reduce fuel consumption, gas turbine engines typically operate ... more To improve thermal efficiency and reduce fuel consumption, gas turbine engines typically operate at increasingly higher turbine inlet temperatures--well in excess of turbine blade material limits--and film cooling schemes are normally employed to reduce metal temperatures within acceptable limits and prevent structural failure. Cooling requirements vary across a blade surface, but there currently exists no means by which coolant temperatures can be locally adjusted to facilitate optimized usage across a blade. Ranque-Hilsch vortex tubes were investigated as a means of adjusting coolant temperatures solely by fluidic means, induced by the phenomenon of temperature separation. Analytical frameworks were developed to determine adiabatic and overall effectiveness in the presence of multiple coolant temperatures and validated via experiment. Through the integrated application of experimental, analytical, and computational investigations, the parameters which govern temperature separation...
Journal of Thermal Science and Engineering Applications
Although awareness of the phenomenon of temperature separation in Ranque-Hilsch vortex tubes date... more Although awareness of the phenomenon of temperature separation in Ranque-Hilsch vortex tubes dates back at least nine decades, some mystery surrounding the phenomenon remains to this day. These devices split an incoming stream of fluid into two streams—one with a greater total temperature than the incoming fluid and the other with a lower total temperature. This temperature separation is accomplished with no moving parts and no external sources of energy including heat transfer to or from the device. In attempts to understand the physics of the temperature separation, previous researchers have characterized the effect through various inlet temperatures and pressures as well as various gases with different properties. Unfortunately, the findings documented in the literature are sometimes inconsistent indicating the possibility that previously uncontrolled properties and flow conditions govern temperature separation to an unappreciated degree. In the present research, two new flow cha...
A conjugate heat transfer analysis of the complex mechanisms of internal and external cooling of ... more A conjugate heat transfer analysis of the complex mechanisms of internal and external cooling of turbine blades can present a formidable task. Such an effort may be simplified somewhat by evaluating the normalized metal surface temperature of a turbine blade, also known as the cooling scheme’s overall effectiveness. Investigations of turbine cooling effectiveness for scenarios with multiple rows typically assume a single coolant temperature. However, scenarios may exist in which a region of interest is affected by multiple local coolant temperatures, such as when coolant is injected from different internal passages. The present work develops an appropriate reference temperature for such a situation as well as a new nondimensional parameter indicating the relative difference between coolant temperatures. The effect of this new nondimensional parameter on overall effectiveness and streamwise temperature gradients is evaluated for two double row cooling hole configurations. Each row, c...
The classical method of superposition has been used for several decades to provide an estimate of... more The classical method of superposition has been used for several decades to provide an estimate of the adiabatic effectiveness for multiple sets of already well-characterized film cooling hole rows. In this way, design work is aided by classical superposition theory prior to higher fidelity experiments or simulations that would account for fluid dynamic interaction for which superposition cannot account. In the present work, we consider the additive effects of multiple rows of coolant holes, but now also with coolant issuing at different temperatures. There are a number of ways that coolant may issue from different cooling hole rows at different temperatures, one of which is simply the necessarily different internal channels through which the coolant must pass. The film cooling effectiveness is investigated for double rows of cooling holes wherein the two rows have different coolant temperatures. A double row consisting of an upstream slot and a downstream row of 7–7–7 cooling holes ...
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