Upstream Mixing Cavity Coupled with a Downstream Flameholding Cavity Behavior in Supersonic Flow (Postprint). PDF Download
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Author:
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ISBN:
Category :
Languages : en
Pages : 15
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Book Description
Experimental investigations of the flowfield associated with three upstream direct injection acoustic resonance cavities coupled with a previously designed downstream combustion cavity in a non-reacting flow are described. All of the upstream mixing cavities were acoustically open (shear layer reattachment on the downstream wall of the cavity) with the length-to-depth ratio (L/D) on the order of 1. The previously established downstream combustion cavity had an L/D of 4.7 and an aft ramp angle of 22.5 degrees. The three upstream mixing cavities were characterized in Mach 2 freestream flow with injection at three locations (upstream wall, center, downstream wall) within each cavity. Injection at the upstream wall of the cavity provided greater penetration height into the freestream as well as faster mixing with the freestream compared with injection at the center or downstream wall of the cavity. Injection at the center of the cavity resulted in the injectant diffusing laterally in the cavity before being ejected into the freestream. Injection at the downstream cavity wall displayed characteristics of both injection at the upstream wall and center of the cavity.
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 15
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Book Description
Experimental investigations of the flowfield associated with three upstream direct injection acoustic resonance cavities coupled with a previously designed downstream combustion cavity in a non-reacting flow are described. All of the upstream mixing cavities were acoustically open (shear layer reattachment on the downstream wall of the cavity) with the length-to-depth ratio (L/D) on the order of 1. The previously established downstream combustion cavity had an L/D of 4.7 and an aft ramp angle of 22.5 degrees. The three upstream mixing cavities were characterized in Mach 2 freestream flow with injection at three locations (upstream wall, center, downstream wall) within each cavity. Injection at the upstream wall of the cavity provided greater penetration height into the freestream as well as faster mixing with the freestream compared with injection at the center or downstream wall of the cavity. Injection at the center of the cavity resulted in the injectant diffusing laterally in the cavity before being ejected into the freestream. Injection at the downstream cavity wall displayed characteristics of both injection at the upstream wall and center of the cavity.
Author: Steven J. Etheridge
Publisher:
ISBN:
Category :
Languages : en
Pages : 55
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Book Description
Typical studies of scramjet combustion employ as uniform a flowpath as possible. These studies are important to isolate the effects of a given combustor configuration. However, such studies tend to ignore the effects of a shock train created by the vehicle installation and that this shock train changes over the flight envelope. Consequently, the performance of a given configuration is measured without considering the considerable effects of this shock train or how it changes with different flight conditions. This thesis includes experimental and computational studies of the effects of an incident shockwave on the flowfield, fuel distribution and combustion within a cavity flameholder with upstream fuel injection. The effect of the shockwave location (on the upstream fuel jet or over the cavity) and shock angle are controlled by adjusting a shock generator mounted in the tunnel test section. The effect of fuel injection momentum ratio is also examined. Shadowgraphy is used to characterize the flowfield while planar laser induced fluorescence of the NO and OH molecules are used to measure the fuel mixing and combustion, respectively. These experimental data are compared with CFD solutions of the Reynolds Averaged Navier-Stokes equations provided in previous CFD work. The effect of the shock on the cavity shear layer is found to control the fuel distribution within the cavity. The shock on jet impingement forces the shear layer deep within the cavity and results in higher concentrations near the cavity centerline, but low mixing uniformity. The shock on cavity case causes the shear layer to separate upstream of the cavity, mixing uniformity is enhanced by the increased breakup of the fuel plume. Combustion is stronger and more uniform in the shock on cavity case, while it is limited to the edges of the cavity with shock impingement on the jet. The greater mixing afforded in the shock on cavity case reduces the fuel concentration near the centerline and permits stronger burning in the center of the cavity. Small changes in the fuel injection momentum ratio (doubling) do not strongly affect the pattern of fuel distribution in any case. Combustion in the shock on cavity case is reduced by increasing fuel injection momentum because the fuel concentration at the centerline is too high. Small increases in the shock angle did not strongly affect the results.
Author: Sumeet Trehan
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
Design and experimental investigation of a supersonic cavity flameholder has been carried out in this study. In the first phase of the study, robust and modular design of supersonic cavity flameholder was undertaken. Experimental investigation was then carried out, focusing on planar measurements inside the cavity flameholder using optical diagnostic techniques. The cavity under consideration was an open cavity with length-to-depth ratio of 5. Scalar and velocity fields in different configurations of the cavity flameholder were investigated. While the mixing characteristics in the cavity flameholder were studied using acetone planar laser-induced fluorescence, the velocity field inside the cavity was obtained using particle image velocimetry. The fuel jet behavior was observed to be highly unsteady, and the fuel was observed to mix very efficiently in the cavity. A secondary recirculation region was observed inside the cavity, besides the main recirculation region. At Mach 5, injection of acetone-seeded air or nitrogen stream at a high pressure was observed to result in a useful signal for acetone PLIF. However, the low pressure in the cavity caused the stream to enter the cavity as an under-expanded jet. The PIV studies indicated that it was difficult to get good seeding density inside the cavity at Mach 5. The experiments conducted at Mach 2 indicated the presence of significant blockage in the test section due to mid-section mounting of the model, resulting in an inability to start the tunnel.
Author: Ghislain Jean Retaureau
Publisher:
ISBN:
Category : Combustion
Languages : en
Pages :
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Book Description
Flame-holding in a recessed cavity is investigated experimentally in a Mach 2.5 preheated cross-flow for both stable and unstable combustion, with a relatively low preheating. Self-sustained combustion is investigated for stagnation pressures and temperatures reaching 1.4 MPa and 750 K. In particular, cavity blowout is characterized with respect to cavity aspect ratio (L/D =2.84 - 3.84), injection strategy (floor - ramp), aft ramp angle (90 deg - 22.5 deg) and multi-fuel mixture (CH4-H2 or CH4-C2H4 blends). The results show that small hydrogen addition to methane leads to significant increase in flame stability, whereas ethylene addition has a more gradual effect. Since the multi-fuels used here are composed of a slow and a fast chemistry fuel, the resulting blowout region has a slow (methane dominant) and a fast (hydrogen or ethylene dominant) branch. Regardless of the fuel composition, the pressure at blowout is close to the non-reacting pressure imposed by the cross-flow, suggesting that combustion becomes potentially unsustainable in the cavity at the sub-atmospheric pressures encountered in these supersonic studies. The effect of preheating is also investigated and results show that the stability domain broadens with increasing stagnation temperature. However, smaller cavities appear less sensitive to the cross-flow preheating, and stable combustion is achieved over a smaller range of fuel flow rate, which may be the result of limited residence and mixing time. The blowout data point obtained at lower fuel flow rate fairly matches the empirical model developed by Rasmussen et al. for floor injection phi = 0.0028 Da^-.8, where phi is the equivalence ratio and Da the Damkohler number. An alternate model is proposed here that takes into account the ignition to scale the blowout data. Since the mass of air entrained into the cavity cannot be accurately estimated and the cavity temperature is only approximated from the wall temperature, the proposed scaling has some uncertainty. Nevertheless the new phi-Da scaling is shown to preserve the subtleties of the blowout trends as seen in the current experimental data.
Author: Ali Cemal Benim
Publisher: Academic Press
ISBN: 0128008261
Category : Technology & Engineering
Languages : en
Pages : 134
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Book Description
Blending fuels with hydrogen offers the potential to reduce NOx and CO2 emissions in gas turbines, but doing so introduces potential new problems such as flashback. Flashback can lead to thermal overload and destruction of hardware in the turbine engine, with potentially expensive consequences. The little research on flashback that is available is fragmented. Flashback Mechanisms in Lean Premixed Gas Turbine Combustion by Ali Cemal Benim will address not only the overall issue of the flashback phenomenon, but also the issue of fragmented and incomplete research. - Presents a coherent review of flame flashback (a classic problem in premixed combustion) and its connection with the growing trend of popularity of more-efficient hydrogen-blend fuels - Begins with a brief review of industrial gas turbine combustion technology - Covers current environmental and economic motivations for replacing natural gas with hydrogen-blend fuels
Author:
Publisher:
ISBN:
Category : Aeronautics
Languages : en
Pages : 296
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Author:
Publisher:
ISBN:
Category : Aeronautics
Languages : en
Pages : 892
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ISBN:
Category : Artificial satellites in geographical research
Languages : en
Pages : 8
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Author: National Research Council
Publisher: National Academies Press
ISBN: 0309157250
Category : Science
Languages : en
Pages : 199
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Book Description
There is a national need to educate the public about the ocean, coastal resources, atmosphere and climate. The National Oceanic and Atmospheric Administration (NOAA), the agency responsible for understanding and predicting changes in the Earth's environment and conserving and managing coastal and marine resources to meet the nation's economic, social and environmental needs, has a broad mandate to engage and coordinate education initiatives on these topics. Since its creation in 1970, the NOAA has supported a variety of education projects that cover a range of topics related to the agency's scientific and stewardship mission. NOAA uses formal and informal learning environments to enhance understanding of science, technology, engineering and mathematics (STEM) and to advance environmental education. The work of this agency overlaps and compliments the missions of other federal agencies, institutions of higher education, private and nonprofit organizations. Coordination among these agencies and organizations has been challenging. Limited education resources and the inherently global nature of NOAA's mission make strategic partnerships critical in order for the agency to accomplish its goals. Additionally, clear education goals, planning, and strategic use of resources are critical aspects for effective partnerships. NOAA's Education Program: Review and Critique provides a summary of the national education context for NOAA's role in education which is twofold: first is to advance the environmental literacy of the nation, and second is to promote a diverse workforce in ocean, coastal, Great Lakes, atmospheric and climate sciences. The book also describes the strengths and weaknesses of the education strategic plan, the education evaluation approach of the agency and strategies for improving the evaluation process.
Author: Naval Research Laboratory
Publisher: Createspace Independent Pub
ISBN: 9781479352012
Category : History
Languages : en
Pages : 146
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Book Description
The Naval Research Laboratory's mission is to conduct a broadly based multidisciplinary program of scientific research and advanced technological development directed toward maritime applications of new and improved materials, techniques, equipment, systems, and ocean, atmospheric, and space sciences and related technologies. The Naval Research Laboratory provides primary in-house research for the physical, engineering, space, and environmental sciences; broadly based applied research and advanced technology development programs in response to identified and anticipated Navy and Marine Corps needs; broad multidisciplinary support to the Naval Warfare Centers; space and space systems technology, development, and support; and assumes responsibility as the Navy's corporate laboratory. The Naval Research Laboratory is the Department of the Navy's corporate laboratory; it is under the command of the Chief of Naval Research. As the corporate laboratory of the Navy, NRL is the principal in-house component in the Office of Naval Research's (ONR) effort to meet its science and technology responsibilities. NRL has had a long and fruitful relationship with industry as a collaborator, contractor, and most recently in Cooperative Research and Development Agreements (CRADAs). NRL values this linkage and continues to develop it. NRL is an important link in the Navy Research, Development, and Acquisition (RD&A) chain. Through NRL, the Navy has direct ties with sources of fundamental ideas in industry and the academic community throughout the world and provides an effective coupling point to the R&D chain for ONR.
