Studies of Mixing Processes in Gases and Effects on Combustion and Stability

STUDIES OF MIXING PROCESSES IN GASES AND EFFECTS ON COMBUSTION AND STABILITY Frank P. Kozusko, Jr. Old Dominion University, 1995 Director: Dr. D. Glenn Lasseigne Three physical models of laminar m ixing of in itia lly separated gases are studied. Two models study the effects of the m ixing dynamics on the chemical reactions between the gases. The th ird model studies the structure and stab ility of a laminar m ixing layer in a binary gas. The three models are: 1. Two ideal and incompressible gases representing fuel and oxidizer are in itia lly at rest and separated across an infin ite linear interface in a two dimensional system. Combustion, expected as the gases m ix. w ill lead to a rapid rise in temperature in a localized area, i.e. ignition. The mixing of the gases is enhanced bv two counter-rotating vortices w ith centers located on the in itia l interface. The ignition process is studied by an asymptotic analysis. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Ignition times for the double vortex lay between the no vortex and the single vortex times. As the distance between the two counter-rotating vortices gets smaller, ignition times approach the no vortex case, for increasing distance the ignition times approach the single vortex case. 2. Lam inar m ixing of compressible gases representing two reduced chemical systems is studied. The gases are in itia lly separated in to two sem i-infinite planes and have different freestream flow velocities. Combustion is followed through ignition to the post-ignition steady flame. The ignition distance is an inverse logarithmic function of the in itia lly required loading of a non-fuel, non-oxidizer radical. The post-ignition flame tempera­ ture is not effected by the in itia l radical concentration. 3. Lam inar compressible non-reacting m ixing of two real gases of different free­ stream temperatures and flow velocities is studied. Realistic values of trans­ port properties are obtained from various tables or calculated from theory. The transport properties are dynamically calculated as functions of the changing temperature and gas concentrations across the m ixing layer. A steady state mixed solution is found. Items of interest are the stab ility characteristics, the profiles of temperature and gas concentrations and the variations o f the Prandtl and Lewis numbers. The Lewis number and Prandtl numbers may vary significantly through the m ixing layer. Neutral phase speeds and growth rates for spatial s tab ility are also shown to be effected by the molecular weights and physical properties. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Acknowledgment I wish to acknowledge all those who have encouraged and assisted me in this eight year quest. M y thanks to the chairman, Dr. Tweed, and m y three graduate advisors: Dr. Wohl, Dr. Dorrepaal and Dr. Swetits. Dr. Wohl firs t encouraged me to go forward w ith my dream during my in it ia l inquiries into the possibility of graduate study. Dr. Dorrepaal scheduled courses tha t could f it into my work schedule during m y parttim e studies. Dr. Swetits helped me transition from a part-tim e to fu ll-tim e student. Dr. Tweed always scheduled m y teaching assignments to best f it my course work and research schedule. A ll my professors at ODU were helpful in working around my Naval duty schedule and helping me relearn some of the fundamentals buried by a long academic hiatus. I wish to thank Drs. Hu, Grosch and Lasseigne for mentoring me in computer system techniques and flu id dynamics. M y three years of research have been conducted at the Institu te for Computer Applications in Science and Engineering (ICASE). The staff and scientists were always helpful and I learned much from them. The superior computing facilities and the p roxim ity to my house, more than doubled my output. I am thankful to Dr Hussaini, D irector o f ICASE, for his fa ith in me and for my appointed as an ICASE graduate fellow. A special acknowledgment goes to Dr. Tom Jackson. He taught the very first course in my recommenced graduate career in Fall, 1987. He later agreed to be my thesis advisor and continued to provide me constant mentorship these last three years,