Vortex break-down during the impact of a starting subsonic compressible gas jet on a multi-plume spray

The final publication is available at Springer via https://dx.doi.org/10.1007/s12650-016-0345-yThe impact process and the consequent two-phase interaction for a compressible subsonic starting gas jet colliding on a multi-plume spray are investigated using large eddy simulation with Eulerian/Lagrangian multiphase approach, and the λ 2 criterion is used to visualize the temporal and spatial evolution of the vortical structures in the gas field. It is shown that before the impact a leading tip vortex ring is followed by smaller vortex rings in the quasi-steady region of the starting jet while the vortical structures inside the spray plumes known as spray-induced air jets are formed. After the impact the leading tip vortex ring and the following rings as well as spray-induced air jet vortices start to deform and eventually break down into smaller elongated vortex filaments. Unlike the injection of multi-plume sprays into the core of a steady cross flow gas jet, spray droplets are dispersed in a larger volume in all directions when impacted by the starting gas jet, beneficial for two-phase mixing enhancement. A pair of vortex rings is also observed merging into a new ring before reaching the impact zone.Graphical abstract Open image in new windowNatural Sciences and Engineering Research Council of Canada ["Discovery Grant"

Experimental investigation of liquid fragmentation in hypersonic cross flow

This thesis presents an experimental investigation carried out to study penetration and fragmentation of liquid injected into Mach 6 hypersonic cross flow. Flow topology, shock and vortex systems, fragmentation and atomization mechanisms are investigated using high-speed photography, Schlieren photography, flow visualization and Phase Doppler Interferometry techniques. All experiments are conducted at the H-3 Mach 6 wind tunnel facility of the von Karman Institute. Water is used for all tests. Freestream conditions of air flow are kept constant. The variation of the injector geometry and the effect of momentum flux ratio are studied throughout the experimental campaign. Droplet size measurements are analyzed and treated to characterize the atomization process of the liquid jet. The Sauter Mean Diameter and the standard deviation of the droplet size distribution are calculated and presented as a function of location and momentum flux ratio. The obtained Sauter Mean Diameter distribution is compared with the theory available in the literature for lower cross flow speed cases. The whipping phenomenon observed for the low momentum flux ratio liquid injections is explained by frequency maps, which allow one to see the flow domains with similar frequency content. This analysis proposes that the penetration of liquid jet determines the shape of the bow shock, which determines the location and angle of the separation shock. The separation shock is observed to penetrate into liquid phase, playing an important role in fragmentation of liquid, thus changing the penetration height and the shape of the bow shock. A continuous interaction between the liquid penetration, bow shock, separation shock and liquid fragmentation is believed to be the mechanism responsible of the whipping phenomenon. The fragmentation of liquid exposed to Mach 6 air flow is also investigated. Experiments are conducted using water-filled balloons mounted on sharp and blunt leading edge supports. The water-filled balloons are exposed to Mach 6 air flow and high speed camera measurements are taken during the bursting of the balloon, to study the fragmentation of water. Shock patterns and flow topology are visualized by Schlieren photography

Multiphase modelling of the characteristics of close coupled gas atomization

Not withstanding the high demand of metal powder for automotive and High Tech applications, there are still many unclear aspects of the production process. Only recentlyhas supercomputer performance made possible numerical investigation of such phenomena. This thesis focuses on the modelling aspects of primary and secondary atomization. Initially two-dimensional analysis is carried out to investigate the influence of flow parameters (reservoir pressure and gas temperature principally) and nozzle geometry on final powder yielding. Among the different types, close coupled atomizers have the best performance in terms of cost and narrow size distribution. An isentropic contoured nozzle is introduced to minimize the gas flow losses through shock cells: the results demonstrate that it outperformed the standard converging-diverging slit nozzle. Furthermore the utilization of hot gas gave a promising outcome: the powder size distribution is narrowed and the gas consumption reduced. In the second part of the thesis, the interaction of liquid metal and high speed gas near the feeding tube exit was studied. Both axisymmetric andnon-axisymmetric geometries were simulated using a 3D approach. The filming mechanism was detected only for very small metal flow rates (typically obtained in laboratory scale atomizers). When the melt flow increased, the liquid core overtook the adverse gas flow and entered in the high speed wake directly: in this case the disruption isdriven by sinusoidal surface waves. The process is characterized by fluctuating values of liquid volumes entering the domain that are monitored only as a time average rate: it is far from industrial robustness and capability concept. The non-axisymmetric geometry promoted the splitting of the initial stream into four cores, smaller in diameter and easier to atomize. Finally a new atomization design based on the lesson learned from previous cases simulation is presented

Far Field Deposition Of Scoured Regolith Resulting From Lunar Landings

As a lunar lander approaches a dusty surface, the plume from the descent engine impinges on the ground, entraining loose regolith into a high velocity dust spray. Without the inhibition of a background atmosphere, the entrained regolith can travel many kilometers from the landing site. In this work, we simulate the flow field from the throat of the descent engine nozzle to where the dust grains impact the surface many kilometers away. The near field is either continuum or marginally rarefied and is simulated via a loosely coupled hybrid DSMC - Navier Stokes (DPLR) solver. Regions of two-phase and polydisperse granular flows are solved via DSMC. The far field deposition is obtained by using a staged calculation, where the first stages are in the near field where the flow is quasi-steady and the outer stages are unsteady. A realistic landing trajectory is approximated by a set of discrete hovering altitudes which range from 20m to 3m. The dust and gas motions are fully coupled using an interaction model that conserves mass, momentum, and energy statistically and inelastic collisions between dust particles are also accounted for. Simulations of a 4 engine configuration are also examined, and the erosion rates as well as near field particle fluxes are discussed.Astronom

NASA Propulsion Engineering Research Center, Volume 2

This is the second volume in the 1994 annual report for the NASA Propulsion Engineering Research Center's Sixth Annual Symposium. This conference covered: (1) Combustors and Nozzles; (2) Turbomachinery Aero- and Hydro-dynamics; (3) On-board Propulsion systems; (4) Advanced Propulsion Applications; (5) Vaporization and Combustion; (6) Heat Transfer and Fluid Mechanics; and (7) Atomization and Sprays

Multiphase modelling of the characteristics of close coupled gas atomization

Not withstanding the high demand of metal powder for automotive and High Tech applications, there are still many unclear aspects of the production process. Only recentlyhas supercomputer performance made possible numerical investigation of such phenomena. This thesis focuses on the modelling aspects of primary and secondary atomization. Initially two-dimensional analysis is carried out to investigate the influence of flow parameters (reservoir pressure and gas temperature principally) and nozzle geometry on final powder yielding. Among the different types, close coupled atomizers have the best performance in terms of cost and narrow size distribution. An isentropic contoured nozzle is introduced to minimize the gas flow losses through shock cells: the results demonstrate that it outperformed the standard converging-diverging slit nozzle. Furthermore the utilization of hot gas gave a promising outcome: the powder size distribution is narrowed and the gas consumption reduced. In the second part of the thesis, the interaction of liquid metal and high speed gas near the feeding tube exit was studied. Both axisymmetric andnon-axisymmetric geometries were simulated using a 3D approach. The filming mechanism was detected only for very small metal flow rates (typically obtained in laboratory scale atomizers). When the melt flow increased, the liquid core overtook the adverse gas flow and entered in the high speed wake directly: in this case the disruption isdriven by sinusoidal surface waves. The process is characterized by fluctuating values of liquid volumes entering the domain that are monitored only as a time average rate: it is far from industrial robustness and capability concept. The non-axisymmetric geometry promoted the splitting of the initial stream into four cores, smaller in diameter and easier to atomize. Finally a new atomization design based on the lesson learned from previous cases simulation is presented.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Institute for Computational Mechanics in Propulsion (ICOMP)

The Institute for Computational Mechanics in Propulsion (ICOMP) is a combined activity of Case Western Reserve University, Ohio Aerospace Institute (OAI) and NASA Lewis. The purpose of ICOMP is to develop techniques to improve problem solving capabilities in all aspects of computational mechanics related to propulsion. The activities at ICOMP during 1991 are described

Advances in Modeling of Fluid Dynamics

This book contains twelve chapters detailing significant advances and applications in fluid dynamics modeling with focus on biomedical, bioengineering, chemical, civil and environmental engineering, aeronautics, astronautics, and automotive. We hope this book can be a useful resource to scientists and engineers who are interested in fundamentals and applications of fluid dynamics

Aeronautical engineering: A continuing bibliography with indexes (supplement 319)

This report lists 349 reports, articles and other documents recently announced in the NASA STI Database. The coverage includes documents on the engineering and theoretical aspects of design, construction, evaluation, testing, operation, and performance of aircraft (including aircraft engines) and associated components, equipment, and systems. It also includes research and development in aerodynamics, aeronautics, and ground support equipment for aeronautical vehicles