The public reporting burden for this collection of information is estimated to average 1 hour per... more The public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden, to Department of Defense, Washington Headquarters Services, Directorate for Information Operations and Reports (0704-0188), 1215 Jefferson Davis Highway, Suite 1204, Arlington, VA 22202-4302. Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to any penalty for failing to comply with a collection of information if it does not display a currently valid OMB control number. PLEASE DO NOT RETURN YOUR FORM TO THE ABOVE ADDRESS.
Scramjets are air-breathing propulsion devices and have long been recognized as suitable for hype... more Scramjets are air-breathing propulsion devices and have long been recognized as suitable for hypersonic propulsion. Because of the high speed in scramjet combustors, the flow has a very short residence time before leaving the engine, during which air and fuel must mix on a molecular level and chemical reactions have to be completed. Although some ground and flight experiments have successfully demonstrated the feasibility of supersonic combustion, experimental testing requires a large investment and presents numerous difficulties. Computational tools are thus a key element toward the development of an efficient, high-performance scramjet engine, and because mixing and heat release are at the heart of a scramjet operation, the development and use of accurate combustion models for supersonic combustion are critical. The open questions in supersonic combustion span the spectrum from scientific pursuit, e.g., shock/flame interactions, to engineering applications like prediction of unstart phenomena in scramjets. In this study, direct numerical simulations (DNS) of a compressible reacting mixing layer with finite rate chemistry are performed. The DNS databases are used to explore the physics of supersonic combustion. An efficient combustion model based on the flamelet/progress variable is then introduced. In this approach, only two or three additional scalar transport equations need to be solved, independently of the complexity of the reaction mechanism. The proposed combustion model is validated using DNS databases. Finally, the compressible flamelet/progress variable model is applied to the case of an under-expanded hydrogen jet in a supersonic cross-flow and HIFiRE scramjet. ix x
iv I hereby declare that all the information in this document has been obtained and presented in ... more iv I hereby declare that all the information in this document has been obtained and presented in accordance with academic rules and ethical conduct. I also declare that, as required by these rules and conduct, I have fully cited and referenced all material and results that are not original to this work. Name, Last Name: Ramin Rouzbar Signature: v ABSTRACT THREE DIMENSIONAL REACTING FLOW ANALYSIS OF A CAVITY-BASED SCRAMJET COMBUSTOR Rouzbar, Ramin M.S., Department of Aerospace Engineering Supervisor: Assoc. Prof. Dr. Sinan Eyi February 2016, 120 pages Scramjet engines have become one of the main interest areas of the supersonic propulsion systems. Scramjets are rather a new technology and they possess unsolved issues and problems regarding their operation, especially in the combustion process.
iv I hereby declare that all the information in this document has been obtained and presented in ... more iv I hereby declare that all the information in this document has been obtained and presented in accordance with academic rules and ethical conduct. I also declare that, as required by these rules and conduct, I have fully cited and referenced all material and results that are not original to this work. Name, Last Name: Ramin Rouzbar Signature: v ABSTRACT THREE DIMENSIONAL REACTING FLOW ANALYSIS OF A CAVITY-BASED SCRAMJET COMBUSTOR Rouzbar, Ramin M.S., Department of Aerospace Engineering Supervisor: Assoc. Prof. Dr. Sinan Eyi February 2016, 120 pages Scramjet engines have become one of the main interest areas of the supersonic propulsion systems. Scramjets are rather a new technology and they possess unsolved issues and problems regarding their operation, especially in the combustion process.
Large eddy simulations of supersonic non-reactive and reactive flows have been performed with an ... more Large eddy simulations of supersonic non-reactive and reactive flows have been performed with an immersed boundary method on two configurations. The first test-case is a non-reactive Mach 3.5 flow past a cylinder and an excellent agreement with the theory was observed. The second configuration is a supersonic hydrogen-air burner. A reduced kinetic scheme is used and chemical source terms are evaluated based on filtered quantities. Comparisons with available experimental data lead also to a good agreement for species mass fractions and temperature measurements. Impact of the burner geometry on the velocity and species field is studied with the immersed boundary method.
Large eddy simulations of a supersonic hydrogen-air burner have been performed with the SiTComB n... more Large eddy simulations of a supersonic hydrogen-air burner have been performed with the SiTComB numerical code. A reduced kinetic scheme is used and chemical source terms are evaluated based on resolved quantities. Three mesh resolutions have been considered: 2, 30 and 113 million of points (MP). With 2MP the flame is unstable and no comparison with experimental data becomes possible. However, the flame lift-off height is over predicted for the case 30MP. Refining the mesh (113MP) improves the capture of mixing and the flame lift-off height gets close to the experimental results. However this case must be be further converged to get accurate and final conclusions. Scatterplots of temperature and species mass fractions follows the trends already observed in past studies. A lookup table of auto-ignition is built for different levels of pressure and composition corresponding to the values found in the large-eddy simulation. Delays of auto-ignition are found of the order of magnitude of the time required to convect a pocket of pure fuel at a constant speed equal to the fuel inlet velocity.
Understanding the nature of premixed combustion in highly turbulent conditions and in compressibl... more Understanding the nature of premixed combustion in highly turbulent conditions and in compressible flow offers a new paradigm shift in the design of future high-pressure gas turbines and scramjets. Experimental data in these regimes provides hitherto unavailable insight and offer new ways to develop accurate and efficient computational models of turbulent premixed combustion, especially subgrid-scale (SGS) models for large-eddy simulation (LES). In these studies, comprehensive experimental efforts were performed to study turbulent premixed combustion in a configuration that deliberately avoided mean strain effects and focused solely on the interaction of a premixed flame in high Reynolds number, isotropic turbulence over a range of Mach numbers. Two experiments were developed to create this uniform premixed flow with upstream active turbulence generation in the subsonic and supersonic regimes. Turbulent statistics are reported for a variety of conditions using hotwire anemometry and PIV. Flame kernels were generated via laser plasma ignition, and their growth monitored using chemiluminescence, Schlieren, and PLIF imaging. Flame growth statistics show good agreement with classical flame bomb studies in low speeds but deviate with increasing Mach number.
The public reporting burden for this collection of information is estimated to average 1 hour per... more The public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden, to Department of Defense, Washington Headquarters Services, Directorate for Information Operations and Reports (0704-0188), 1215 Jefferson Davis Highway, Suite 1204, Arlington, VA 22202-4302. Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to any penalty for failing to comply with a collection of information if it does not display a currently valid OMB control number. PLEASE DO NOT RETURN YOUR FORM TO THE ABOVE ADDRESS.
Scramjets are air-breathing propulsion devices and have long been recognized as suitable for hype... more Scramjets are air-breathing propulsion devices and have long been recognized as suitable for hypersonic propulsion. Because of the high speed in scramjet combustors, the flow has a very short residence time before leaving the engine, during which air and fuel must mix on a molecular level and chemical reactions have to be completed. Although some ground and flight experiments have successfully demonstrated the feasibility of supersonic combustion, experimental testing requires a large investment and presents numerous difficulties. Computational tools are thus a key element toward the development of an efficient, high-performance scramjet engine, and because mixing and heat release are at the heart of a scramjet operation, the development and use of accurate combustion models for supersonic combustion are critical. The open questions in supersonic combustion span the spectrum from scientific pursuit, e.g., shock/flame interactions, to engineering applications like prediction of unstart phenomena in scramjets. In this study, direct numerical simulations (DNS) of a compressible reacting mixing layer with finite rate chemistry are performed. The DNS databases are used to explore the physics of supersonic combustion. An efficient combustion model based on the flamelet/progress variable is then introduced. In this approach, only two or three additional scalar transport equations need to be solved, independently of the complexity of the reaction mechanism. The proposed combustion model is validated using DNS databases. Finally, the compressible flamelet/progress variable model is applied to the case of an under-expanded hydrogen jet in a supersonic cross-flow and HIFiRE scramjet. ix x
iv I hereby declare that all the information in this document has been obtained and presented in ... more iv I hereby declare that all the information in this document has been obtained and presented in accordance with academic rules and ethical conduct. I also declare that, as required by these rules and conduct, I have fully cited and referenced all material and results that are not original to this work. Name, Last Name: Ramin Rouzbar Signature: v ABSTRACT THREE DIMENSIONAL REACTING FLOW ANALYSIS OF A CAVITY-BASED SCRAMJET COMBUSTOR Rouzbar, Ramin M.S., Department of Aerospace Engineering Supervisor: Assoc. Prof. Dr. Sinan Eyi February 2016, 120 pages Scramjet engines have become one of the main interest areas of the supersonic propulsion systems. Scramjets are rather a new technology and they possess unsolved issues and problems regarding their operation, especially in the combustion process.
Large eddy simulations of supersonic non-reactive and reactive flows have been performed with an ... more Large eddy simulations of supersonic non-reactive and reactive flows have been performed with an immersed boundary method on two configurations. The first test-case is a non-reactive Mach 3.5 flow past a cylinder and an excellent agreement with the theory was observed. The second configuration is a supersonic hydrogen-air burner. A reduced kinetic scheme is used and chemical source terms are evaluated based on filtered quantities. Comparisons with available experimental data lead also to a good agreement for species mass fractions and temperature measurements. Impact of the burner geometry on the velocity and species field is studied with the immersed boundary method.
Large eddy simulations of a supersonic hydrogen-air burner have been performed with the SiTComB n... more Large eddy simulations of a supersonic hydrogen-air burner have been performed with the SiTComB numerical code. A reduced kinetic scheme is used and chemical source terms are evaluated based on resolved quantities. Three mesh resolutions have been considered: 2, 30 and 113 million of points (MP). With 2MP the flame is unstable and no comparison with experimental data becomes possible. However, the flame lift-off height is over predicted for the case 30MP. Refining the mesh (113MP) improves the capture of mixing and the flame lift-off height gets close to the experimental results. However this case must be be further converged to get accurate and final conclusions. Scatterplots of temperature and species mass fractions follows the trends already observed in past studies. A lookup table of auto-ignition is built for different levels of pressure and composition corresponding to the values found in the large-eddy simulation. Delays of auto-ignition are found of the order of magnitude of the time required to convect a pocket of pure fuel at a constant speed equal to the fuel inlet velocity.
The public reporting burden for this collection of information is estimated to average 1 hour per... more The public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden, to Department of Defense, Washington Headquarters Services, Directorate for Information Operations and Reports (0704-0188), 1215 Jefferson Davis Highway, Suite 1204, Arlington, VA 22202-4302. Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to any penalty for failing to comply with a collection of information if it does not display a currently valid OMB control number. PLEASE DO NOT RETURN YOUR FORM TO THE ABOVE ADDRESS.
Scramjets are air-breathing propulsion devices and have long been recognized as suitable for hype... more Scramjets are air-breathing propulsion devices and have long been recognized as suitable for hypersonic propulsion. Because of the high speed in scramjet combustors, the flow has a very short residence time before leaving the engine, during which air and fuel must mix on a molecular level and chemical reactions have to be completed. Although some ground and flight experiments have successfully demonstrated the feasibility of supersonic combustion, experimental testing requires a large investment and presents numerous difficulties. Computational tools are thus a key element toward the development of an efficient, high-performance scramjet engine, and because mixing and heat release are at the heart of a scramjet operation, the development and use of accurate combustion models for supersonic combustion are critical. The open questions in supersonic combustion span the spectrum from scientific pursuit, e.g., shock/flame interactions, to engineering applications like prediction of unstart phenomena in scramjets. In this study, direct numerical simulations (DNS) of a compressible reacting mixing layer with finite rate chemistry are performed. The DNS databases are used to explore the physics of supersonic combustion. An efficient combustion model based on the flamelet/progress variable is then introduced. In this approach, only two or three additional scalar transport equations need to be solved, independently of the complexity of the reaction mechanism. The proposed combustion model is validated using DNS databases. Finally, the compressible flamelet/progress variable model is applied to the case of an under-expanded hydrogen jet in a supersonic cross-flow and HIFiRE scramjet. ix x
iv I hereby declare that all the information in this document has been obtained and presented in ... more iv I hereby declare that all the information in this document has been obtained and presented in accordance with academic rules and ethical conduct. I also declare that, as required by these rules and conduct, I have fully cited and referenced all material and results that are not original to this work. Name, Last Name: Ramin Rouzbar Signature: v ABSTRACT THREE DIMENSIONAL REACTING FLOW ANALYSIS OF A CAVITY-BASED SCRAMJET COMBUSTOR Rouzbar, Ramin M.S., Department of Aerospace Engineering Supervisor: Assoc. Prof. Dr. Sinan Eyi February 2016, 120 pages Scramjet engines have become one of the main interest areas of the supersonic propulsion systems. Scramjets are rather a new technology and they possess unsolved issues and problems regarding their operation, especially in the combustion process.
iv I hereby declare that all the information in this document has been obtained and presented in ... more iv I hereby declare that all the information in this document has been obtained and presented in accordance with academic rules and ethical conduct. I also declare that, as required by these rules and conduct, I have fully cited and referenced all material and results that are not original to this work. Name, Last Name: Ramin Rouzbar Signature: v ABSTRACT THREE DIMENSIONAL REACTING FLOW ANALYSIS OF A CAVITY-BASED SCRAMJET COMBUSTOR Rouzbar, Ramin M.S., Department of Aerospace Engineering Supervisor: Assoc. Prof. Dr. Sinan Eyi February 2016, 120 pages Scramjet engines have become one of the main interest areas of the supersonic propulsion systems. Scramjets are rather a new technology and they possess unsolved issues and problems regarding their operation, especially in the combustion process.
Large eddy simulations of supersonic non-reactive and reactive flows have been performed with an ... more Large eddy simulations of supersonic non-reactive and reactive flows have been performed with an immersed boundary method on two configurations. The first test-case is a non-reactive Mach 3.5 flow past a cylinder and an excellent agreement with the theory was observed. The second configuration is a supersonic hydrogen-air burner. A reduced kinetic scheme is used and chemical source terms are evaluated based on filtered quantities. Comparisons with available experimental data lead also to a good agreement for species mass fractions and temperature measurements. Impact of the burner geometry on the velocity and species field is studied with the immersed boundary method.
Large eddy simulations of a supersonic hydrogen-air burner have been performed with the SiTComB n... more Large eddy simulations of a supersonic hydrogen-air burner have been performed with the SiTComB numerical code. A reduced kinetic scheme is used and chemical source terms are evaluated based on resolved quantities. Three mesh resolutions have been considered: 2, 30 and 113 million of points (MP). With 2MP the flame is unstable and no comparison with experimental data becomes possible. However, the flame lift-off height is over predicted for the case 30MP. Refining the mesh (113MP) improves the capture of mixing and the flame lift-off height gets close to the experimental results. However this case must be be further converged to get accurate and final conclusions. Scatterplots of temperature and species mass fractions follows the trends already observed in past studies. A lookup table of auto-ignition is built for different levels of pressure and composition corresponding to the values found in the large-eddy simulation. Delays of auto-ignition are found of the order of magnitude of the time required to convect a pocket of pure fuel at a constant speed equal to the fuel inlet velocity.
Understanding the nature of premixed combustion in highly turbulent conditions and in compressibl... more Understanding the nature of premixed combustion in highly turbulent conditions and in compressible flow offers a new paradigm shift in the design of future high-pressure gas turbines and scramjets. Experimental data in these regimes provides hitherto unavailable insight and offer new ways to develop accurate and efficient computational models of turbulent premixed combustion, especially subgrid-scale (SGS) models for large-eddy simulation (LES). In these studies, comprehensive experimental efforts were performed to study turbulent premixed combustion in a configuration that deliberately avoided mean strain effects and focused solely on the interaction of a premixed flame in high Reynolds number, isotropic turbulence over a range of Mach numbers. Two experiments were developed to create this uniform premixed flow with upstream active turbulence generation in the subsonic and supersonic regimes. Turbulent statistics are reported for a variety of conditions using hotwire anemometry and PIV. Flame kernels were generated via laser plasma ignition, and their growth monitored using chemiluminescence, Schlieren, and PLIF imaging. Flame growth statistics show good agreement with classical flame bomb studies in low speeds but deviate with increasing Mach number.
The public reporting burden for this collection of information is estimated to average 1 hour per... more The public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden, to Department of Defense, Washington Headquarters Services, Directorate for Information Operations and Reports (0704-0188), 1215 Jefferson Davis Highway, Suite 1204, Arlington, VA 22202-4302. Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to any penalty for failing to comply with a collection of information if it does not display a currently valid OMB control number. PLEASE DO NOT RETURN YOUR FORM TO THE ABOVE ADDRESS.
Scramjets are air-breathing propulsion devices and have long been recognized as suitable for hype... more Scramjets are air-breathing propulsion devices and have long been recognized as suitable for hypersonic propulsion. Because of the high speed in scramjet combustors, the flow has a very short residence time before leaving the engine, during which air and fuel must mix on a molecular level and chemical reactions have to be completed. Although some ground and flight experiments have successfully demonstrated the feasibility of supersonic combustion, experimental testing requires a large investment and presents numerous difficulties. Computational tools are thus a key element toward the development of an efficient, high-performance scramjet engine, and because mixing and heat release are at the heart of a scramjet operation, the development and use of accurate combustion models for supersonic combustion are critical. The open questions in supersonic combustion span the spectrum from scientific pursuit, e.g., shock/flame interactions, to engineering applications like prediction of unstart phenomena in scramjets. In this study, direct numerical simulations (DNS) of a compressible reacting mixing layer with finite rate chemistry are performed. The DNS databases are used to explore the physics of supersonic combustion. An efficient combustion model based on the flamelet/progress variable is then introduced. In this approach, only two or three additional scalar transport equations need to be solved, independently of the complexity of the reaction mechanism. The proposed combustion model is validated using DNS databases. Finally, the compressible flamelet/progress variable model is applied to the case of an under-expanded hydrogen jet in a supersonic cross-flow and HIFiRE scramjet. ix x
iv I hereby declare that all the information in this document has been obtained and presented in ... more iv I hereby declare that all the information in this document has been obtained and presented in accordance with academic rules and ethical conduct. I also declare that, as required by these rules and conduct, I have fully cited and referenced all material and results that are not original to this work. Name, Last Name: Ramin Rouzbar Signature: v ABSTRACT THREE DIMENSIONAL REACTING FLOW ANALYSIS OF A CAVITY-BASED SCRAMJET COMBUSTOR Rouzbar, Ramin M.S., Department of Aerospace Engineering Supervisor: Assoc. Prof. Dr. Sinan Eyi February 2016, 120 pages Scramjet engines have become one of the main interest areas of the supersonic propulsion systems. Scramjets are rather a new technology and they possess unsolved issues and problems regarding their operation, especially in the combustion process.
Large eddy simulations of supersonic non-reactive and reactive flows have been performed with an ... more Large eddy simulations of supersonic non-reactive and reactive flows have been performed with an immersed boundary method on two configurations. The first test-case is a non-reactive Mach 3.5 flow past a cylinder and an excellent agreement with the theory was observed. The second configuration is a supersonic hydrogen-air burner. A reduced kinetic scheme is used and chemical source terms are evaluated based on filtered quantities. Comparisons with available experimental data lead also to a good agreement for species mass fractions and temperature measurements. Impact of the burner geometry on the velocity and species field is studied with the immersed boundary method.
Large eddy simulations of a supersonic hydrogen-air burner have been performed with the SiTComB n... more Large eddy simulations of a supersonic hydrogen-air burner have been performed with the SiTComB numerical code. A reduced kinetic scheme is used and chemical source terms are evaluated based on resolved quantities. Three mesh resolutions have been considered: 2, 30 and 113 million of points (MP). With 2MP the flame is unstable and no comparison with experimental data becomes possible. However, the flame lift-off height is over predicted for the case 30MP. Refining the mesh (113MP) improves the capture of mixing and the flame lift-off height gets close to the experimental results. However this case must be be further converged to get accurate and final conclusions. Scatterplots of temperature and species mass fractions follows the trends already observed in past studies. A lookup table of auto-ignition is built for different levels of pressure and composition corresponding to the values found in the large-eddy simulation. Delays of auto-ignition are found of the order of magnitude of the time required to convect a pocket of pure fuel at a constant speed equal to the fuel inlet velocity.
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