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  • 1
    Publication Date: 1968-11-01
    Print ISSN: 0034-6748
    Electronic ISSN: 1089-7623
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
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  • 2
    Publication Date: 2019-06-28
    Description: A series of non-reacting parametric experiments was conducted to investigate the effect of geometric and flow variations on mixing of cold jets in an axis-symmetric, heated cross flow. The confined, cylindrical geometries tested represent the quick mix region of a Rich-Burn/Quick-Mix/Lean-Burn (RQL) combustor. The experiments show that orifice geometry and jet to mainstream momentum-flux ratio significantly impact the mixing characteristic of jets in a cylindrical cross stream. A computational code was used to extrapolate the results of the non-reacting experiments to reacting conditions in order to examine the nitric oxide (NO) formation potential of the configurations examined. The results show that the rate of NO formation is highest immediately downstream of the injection plane. For a given momentum-flux ratio, the orifice geometry that mixes effectively in both the immediate vicinity of the injection plane, and in the wall regions at downstream locations, has the potential to produce the lowest NO emissions. The results suggest that further study may not necessarily lead to a universal guideline for designing a low NO mixer. Instead, an assessment of each application may be required to determine the optimum combination of momentum-flux ratio and orifice geometry to minimize NO formation. Experiments at reacting conditions are needed to verify the present results.
    Keywords: Aircraft Propulsion and Power
    Type: NASA-CR-194473 , NAS 1.26:194473 , E-8614
    Format: application/pdf
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  • 3
    Publication Date: 2019-06-28
    Description: Mixing of gaseous jets in a cross-flow has significant applications in engineering, one example of which is the dilution zone of a gas turbine combustor. Despite years of study, the design of the jet injection in combustors is largely based on practical experience. The emergence of NO(x) regulations for stationary gas turbines and the anticipation of aero-engine regulations requires an improved understanding of jet mixing as new combustor concepts are introduced. For example, the success of the staged combustor to reduce the emission of NO(x) is almost entirely dependent upon the rapid and complete dilution of the rich zone products within the mixing section. It is these mixing challenges to which the present study is directed. A series of experiments was undertaken to delineate the optimal mixer orifice geometry. A cross-flow to core-flow momentum-flux ratio of 40 and a mass flow ratio of 2.5 were selected as representative of a conventional design. An experimental test matrix was designed around three variables: the number of orifices, the orifice length-to- width ratio, and the orifice angle. A regression analysis was performed on the data to arrive at an interpolating equation that predicted the mixing performance of orifice geometry combinations within the range of the test matrix parameters. Results indicate that the best mixing orifice geometry tested involves eight orifices with a long-to-short side aspect ratio of 3.5 at a twenty-three degree inclination from the center-line of the mixing section.
    Keywords: Aircraft Propulsion and Power
    Type: NASA-CR-198482 , UCICL-ARTR-93-4 , NAS 1.26:198482 , E-10247
    Format: application/pdf
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  • 4
    Publication Date: 2019-06-28
    Description: Staged combustion, such as Rich-Burn/Quick-Mix/Lean-Burn (RQL), is a viable strategy to meet nitric oxide (NO) emission goals for both stationary and propulsion gas turbine engines. A critical element of the design is the quick mixer section where the potential for NO production is high. While numerical calculations of the quick mixer under reacting conditions have been conducted, the hostile environment and lack of appropriate diagnostics have, to date, precluded experimental probing of the reacting case. As an alternative to understanding the effect of geometry and flow variations on the production of NO in the quick mixer, the present paper presents (1) a series of non-reacting parametric studies, and (2) a computational method to extrapolate the results of the non-reacting experiments to reacting conditions. The results show that the rate of NO production is highest in the immediate vicinity of the injection plane. For a given momentum flux ratio between the jets and mainstream, the most effective mixing geometry is that which mixes effectively in both (1) the plane of injection, and (2) the wall regions downstream of the plan of injection. The tailoring of the mixing is key to minimize the NO formed. As a result, the best overall mixer with respect to the minimization of NO production may depend on the system specific characteristics of the particular application.
    Keywords: Aircraft Propulsion and Power
    Type: NASA-TM-105639 , E-6985 , NAS 1.15:105639
    Format: application/pdf
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  • 5
    Publication Date: 2019-06-28
    Description: Conventional and advanced gas turbine engines are coming under increased scrutiny regarding pollutant emissions. This, in turn, has created a need to obtain in-situ experimental data at practical conditions, as well as exhaust data, and to obtain the data in combustors that reflect modern designs. The in-situ data are needed to (1) assess the effects of design modifications on pollutant formation, and (2) develop a detailed data base on combustor performance for the development and verification of computer modeling. This paper reports on a novel high pressure, high temperature facility designed to acquire such data under controlled conditions and with access (optical and extractive) for in-situ measurements. To evaluate the utility of the facility, a model gas turbine combustor was selected which features practical hardware design, two rows of jets (primary and dilution) with four jets in each row, and advanced wall cooling techniques with laser drilled effusive holes. The dome is equipped with a flat-vaned swirler with vane angles of 60 degrees. Data are obtained at combustor pressures ranging from 2 to 10 atmospheres of pressure, levels of air preheat to 427 C, combustor reference velocities from 10.0 to 20.0 m/s, and an overall equivalence ratio of 0.3. Exit plane and in-situ measurements are presented for HC, O2, CO2, CO, and NO(x). The exit plane emissions of NO(x) correspond to levels reported from practical combustors and the in-situ data demonstrate the utility and potential for detailed flow field measurements.
    Keywords: INORGANIC AND PHYSICAL CHEMISTRY
    Type: AGARD, Fuels and Combustion Technology for Advanced Aircraft Engines; 10 p
    Format: text
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  • 6
    Publication Date: 2019-06-28
    Description: To examine the mixing characteristics of jets in an axi-symmetric can geometry, temperature measurements were obtained downstream of a row of cold jets injected into a heated cross stream. Parametric, non-reacting experiments were conducted to determine the influence of geometry and flow variations on mixing patterns in a cylindrical configuration. Results show that jet to mainstream momentum flux ratio and orifice geometry significantly impact the mixing characteristics of jets in a can geometry. For a fixed number of orifices, the coupling between momentum flux ratio and injector determines (1) the degree of jet penetration at the injection plane, and (2) the extent of circumferential mixing downstream of the injection plane. The results also show that, at a fixed momentum flux ratio, jet penetration decreases with (1) an increase in slanted slot aspect ratio, and (2) an increase in the angle of the slots with respect to the mainstream direction.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: AIAA PAPER 92-0773
    Format: text
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  • 7
    Publication Date: 2019-06-28
    Description: This paper reports on in situ and exit plane emissions measurements from a model gas turbine combustor at practical air preheat temperatures and pressures for a range of operating conditions. The model combustor chosen for the study features two rows of jets (primary and dilution) with four jets per row, and utilizes effusive air cooling holes on the liner wall. The combustor dome is equipped with a flat-vaned swirler with a vane angle of 60 deg. Data are obtained at combustor pressures ranging from 2 to 10 atmospheres, air preheat temperatures from 204 C to 427 C, and combustor reference velocities from 10.0 to 20.0 m/s. An overall equivalence ratio of 0.3 was constant for all conditions. Exit plane and in situ measurements are presented for HC, O2, CO2, CO, and NO(x). The results from exit plane NO(x) measurements illustrate that the model combustor is representative of current gas turbine combustors. The in situ data reveal effects of fuel/air and wall jet mixing on emission performance.
    Keywords: AIRCRAFT PROPULSION AND POWER
    Type: ISABE 93-7023 , In: ISABE - International Symposium on Air Breathing Engines, 11th, Tokyo, Japan, Sept. 20-24, 1993, Proceedings. Vol. 1 (A93-53976 23-07); p. 244-253.
    Format: text
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  • 8
    Publication Date: 2019-06-28
    Description: To lower NO(x) emissions from gas-turbine engines the effect of dome design and operational changes on the mixing quality in the fuel-rich region is studied. A statistical analysis is employed to establish the parametric sensitivity in this complex flow. A mixing-effectiveness index is defined and used to optimize the gas-species uniformity and the extent of reaction at the exit plane of the dome. Mixing effectiveness is tied to the fuel and air injection locations, the macroscale structure of the dome aerodynamics, and the level of turbulence. Increases in nozzle/air to fuel ratio, reference velocities, and the dome expansion angle increased the level of turbulence. The optimum configuration featured counter-swirling fuel and air streams and produced a strong torroidal recirculation zone, an effective spray angle of 45 degrees, and azimuthal velocities that decayed to zero inside of two duct diameters. The results underscore the system specific nature of mixing optimization.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: AIAA PAPER 92-3089
    Format: text
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  • 9
    Publication Date: 2019-07-13
    Description: To examine the mixing characteristics of circular jets in an axisymmetric can geometry, temperature measurements were obtained downstream of a row of cold jet injected into a heated cross stream. The objective was to obtain uniform mixing within one duct radius downstream of the leading edge of the jet orifices. An area weighted standard deviation of the mixture fraction was used to help quantify the degree of mixedness at a given plane. Non-reacting experiments were conducted to determine the influence of the number of jets on the mixedness in a cylindrical configuration. Results show that the number of orifices significantly impacts the mixing characteristics of jets injected from round hole orifices in a can geometry. Optimum mixing occurs when the mean jet trajectory aligns with the radius which divides the cross sectional area of the can into two equal parts at one mixer radius downstream of the leading edge of the orifice. The optimum number of holes at momentum-flux ratios of 25 and 52 is 10 and 15 respectively.
    Keywords: AIRCRAFT PROPULSION AND POWER
    Type: NASA-TM-105984 , AIAA Paper 93-0249 , NAS 1.15:105984 , E-7508 , Aerospace Sciences Meeting and Exhibit; Jan 11, 1993 - Jan 14, 1993; Reno, NV; United States
    Format: application/pdf
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  • 10
    Publication Date: 2019-07-13
    Description: To examine the mixing characteristics of jets in an axi-symmetric can geometry, temperature measurements were obtained downstream of a row of cold jets injected into a heated cross stream. Parametric, non-reacting experiments were conducted to determine the influence of geometry and flow variations on mixing patterns in a cylindrical configuration. Results show that jet to mainstream momentum flux ratio and orifice geometry significantly impact the mixing characteristics of jets in a can geometry. For a fixed number of orifices, the coupling between momentum flux ratio and injector determines (1) the degree of jet penetration at the injection plane, and (2) the extent of circumferential mixing downstream of the injection plane. The results also show that, at a fixed momentum flux ratio, jet penetration decreases with (1) an increase in slanted slot aspect ratio, and (2) an increase in the angle of the slots with respect to the mainstream direction.
    Keywords: AIRCRAFT PROPULSION AND POWER
    Type: NASA-TM-105390 , E-6780 , NAS 1.15:105390 , AIAA PAPER 92-0773 , Aerospace Sciences Meeting and Exhibit; Jan 06, 1992 - Jan 09, 1992; Reno, NV; United States
    Format: application/pdf
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