Download or read book Numerical Simulation of the Internal Two Phase Flow Within an Aerated Liquid Injector and Its Injection Into the Corresponding High speed Crossflows written by and published by . This book was released on 2004 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The current study investigates the flow structures within an aerated-liquid (barbotage) injector, which is designed to facilitate the rapid breakup of a hydrocarbon fuel jet prior to its entering a scramjet combustor, and the spray structures in the corresponding crossflow. Simulations of the transient, three-dimensional, two-phase flow within the "out-in" injector operating at different gas-to-liquid (GLR) mass ratios and in the corresponding crossflow domain have been performed, and the results compared with experimental pressure measurements of the injector and shadowgraph images of the crossflow. The numerical method solves a "mixture" model of two-phase flow using a preconditioning strategy. High-order spatial accuracy and good interface-capturing properties are facilitated by the use of shock-capturing schemes combined with second order TVD methods. Also, an immersed boundary method is used to investigate the probe effects, and a droplet transport model is used in the crossflow simulations to get more details about effect of droplet size. The injector simulation results highlight the effects of mesh refinement and turbulence model on the predicted solutions. The pressure drop across the injector is predicted reasonably well by the computational methodology, and the trend of increasing injector pressure with increasing GLR is captured properly. Predictions of the absolute pressure level within the injector show some discrepancies in comparison with experimental data but agree well with theoretical estimates. The results of the injector simulations with plenum included are consistent with the results of the discharge tube cases. If the centerline pressure is close to the experimental data, the gas mass flow rate at outlet will approach a value below the experimental data. If the gas mass flow rate at outlet approaches the experimental data, then the centerline pressure will be higher than the experimental data, but agrees well with theoretical analyses. The intr.

Download or read book Numerical Simulation of the Internal Two Phase Flow Within an Aerated Liquid Injector and Its Injection Into the Corresopnding High speed Crossflows written by and published by . This book was released on 2002 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Aerated-liquid atomization, which is produced by the introduction of gas directly into a liquid flow immediately upstream of the injector exit orifice to generate a two-phase flow, has been shown to produce well-atomized sprays in a quiescent environment with only a small amount of aerating gas at relatively low injection pressures. A time-derivative preconditioning method using the Low-Diffusion Flux-Splitting Scheme (LDFSS) has been extended to a 'mixture' model of two-phase flow and applied to simulate the structure of internal two-phase flow for aerated-liquid injectors, with each phase governed by its own equation of state. The Continuum Surface Force (CSF) model of Brackbill, et al. is adapted to model compressible fluid flow influenced by interfacial surface tension. A sub-iterative time integration method based on a planar Gauss-Seidel partitioning of the system matrix is used with implicit source terms as a means of solving the three-dimensional, time-dependent form of the governing equations. The calculations are parallelized using domain-decomposition and Message-Passing Interface (MPI) methods, and are optimized for operation on the 720 processor IBM SP-2 at the North Carolina Supercomputing Center (NCSC). Simulation results for 2-D aerated-liquid injector flowfields at gas-to-liquid (GLR) mass ratios of 0.08% and 2.45% are discussed. In accord with experimental visualization data, the results for GLR = 0.08% indicate a combination of slugging and core-annular two-phase flow in the injector. Results at GLR = 2.45% indicate that a core-annular flow mode dominates, again in agreement with experimental results. The effects of the choice of reference velocity and the level of surface tension on the injector flowfield solutions are also examined.

Download or read book A Numerical Simulation of Internal Two phase Flow for Aerated liquid Injectors written by Ming Tian and published by . This book was released on 2002 with total page 84 pages. Available in PDF, EPUB and Kindle. Book excerpt: Keywords: two-phase flow, aerated-liquid injector, CFD.

Download or read book Numerical Simulation of Transient Two phase Flow Within Aerated Liquid Injectors written by M. Tian and published by . This book was released on 2003 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Modeling of the Internal Two Phase Flow in a Gas Centered Swirl Coaxial Fuel Injector written by and published by . This book was released on 2009 with total page 14 pages. Available in PDF, EPUB and Kindle. Book excerpt: Predicting the liquid film dynamics inside the injector cup of gas-centered swirl coaxial fuel injectors requires a general two-phase approach that is appropriate for all liquid volume fractions, high Weber number, and complex geometries. The rapid exchange of momentum at the highly convoluted interface requires tight numerical coupling between the gas and liquid phases. An Eulerian two-phase model is implemented to represent the liquid and gas interactions in the injector as well as the atomization processes at the rough interface. The model, originally proposed by Vallet et al, assumes that in the limit of infinite Reynolds and Weber number, features of the atomization process acting at large length scales are separable from small scale mechanisms. A transport equation for the liquid volume fraction represents the dispersion of the liquid into the gas via a traditional turbulent diffusion hypothesis. A model for the growth of mean interfacial surface area is then used to characterize the growth of instability at the interface, allowing a characterization of Sauter mean diameter. The model shows promise as a computationally inexpensive tool for characterizing spray quality in regions where optical experimental data are difficult to obtain and two-phase direct numerical simulation methods are too demanding.

Download or read book High Speed Flow Simulation in Fuel Injector Nozzles written by Sukanta Rakshit and published by . This book was released on 2012 with total page 94 pages. Available in PDF, EPUB and Kindle. Book excerpt: Atomization of fuel is essential in controlling combustion inside a direct injection engine. Controlling combustion helps in reducing emissions and boosting efficiency. Cavitation is one of the factors that significantly affect the nature of spray in a combustion chamber. Typical fuel injector nozzles are small and operate at a very high pressure, which limit the study of internal nozzle behavior. The time and length scales further limit the experimental study of a fuel injector nozzle. Simulating cavitation in a fuel injector will help in understanding the phenomenon and will assist in further development. The construction of any simulation of cavitating injector nozzles begins with the fundamental assumptions of which phenomena will be included and which will be neglected. To date, there has been no consensus about whether it is acceptable to assume that small, high-speed cavitating nozzles are in thermal or inertial equilibrium. This diversity of opinions leads to a variety of modeling approaches. If one assumes that the nozzle is in thermal equilibrium, then there is presumably no significant delay in bubble growth or collapse due to heat transfer. Heat transfer is infinitely fast and inertial effects limit phase change. The assumption of inertial equilibrium means that the two phases have negligible slip velocity. Alternatively, on the sub-grid scale level, one may also consider the possibility of small bubbles whose size responds to changes in pressure. Schmidt et al. developed a two dimensional transient homogeneous equilibrium model which was intended for simulating a small, high speed nozzle flows. The HEM uses the assumption of thermal equilibrium to simulate cavitation. It assumes the two-phase flow inside a nozzle in homogeneous mixture of vapor and liquid. This work presents the simulation of high-speed nozzle, using the HEM for cavitation, in a multidimensional and parallel framework. The model is extended to simulate the non-linear effects of the pure phase in the flow and the numerical approach is modified to achieve stable result in multidimensional framework. Two-dimensional validations have been presented with simulation of a venturi nozzle, a sharp nozzle and a throttle from Winklhofer et al. Three-dimensional validations have been presented with simulation of 'spray A' and 'spray H' injectors from the Engine Combustion Network. The simulated results show that equilibrium assumptions are sufficient to predict the mass flow rate and cavitation incidence in small, high-speed nozzle flows.

Download or read book Experimental and Computational Study on Liquid Atomization by Slinger Injector written by Carmen Sescu and published by . This book was released on 2011 with total page 219 pages. Available in PDF, EPUB and Kindle. Book excerpt: In this research work the flow characteristics of a type of rotary atomizer, referred to as slinger injector, were experimentally and numerically investigated at relatively low rotational speeds. Although slinger injectors provide a good level of atomization at high rotational speeds where they are intended to operate (30,000 rpm or higher), a critical aspect in small gas turbines is related to the start-up phase, which typically takes place at speeds around 10,000 rpm. The quality of atomization is very important, especially at these low speeds where smaller mean fuel droplet diameters are desirable. The current work focused on the study of atomization provided by slinger injectors at rotational speed related pertinent to the start-up phase (up to 15,000 rpm). An optical measurement system was implemented to investigate the liquid atomization provided by the slinger injector. The qualitative behavior of fuel emerging from the slinger was evaluated to determine whether a satisfactory atomization was provided within a distance compatible with the size of a small gas turbine engine combustion chamber. The size of the droplets was measured using the Global Sizing Velocimetry (GSV) system. Visualization of the primary liquid breakup process, determination of breakup lengths, and measurement of droplet size were performed by varying rotational speed, liquid flow rate, injector hole shape, size and orientation, and number of holes. Photographs of the liquid breakup, various mean and representative diameters, droplet size histograms and cumulative volume distribution are presented. The findings of this thesis show that droplet size decrease with an increase in rotational speed, as expected. Moreover, hole diameter, hole shape and flow rates affect the slinger atomization. For a given flow rate and a given rotational speed, the experimental data show that the droplet sizes decrease by increasing the hole diameter. The droplets increase in size when the flow rates is increased for a given hole size. The atomization was found to be characteristically different for a slit compared to a circular hole injector. However, the orientation of the emerging jet relative to the axis of rotation insignificantly influenced the slinger atomization for the cases studied. A correlation equation was obtained for a slinger with circular hole, estimating the Sauter mean diameter as a function of the rotational speed of the slinger, the hole diameter, the liquid flow rate and the liquid properties. Two-dimensional and three-dimensional numerical simulations of the internal flow and the external near-field flow for a slinger atomizer were conducted. The simulations were carried out using the commercial Computational Fluid Dynamics code FLUENT, wherein the Volume of Fluid model was used to track the interface between the two phases. A User Defined Function was developed to take into account the centrifugal and Coriolis forces needed for FLUENT computations. The numerical simulations focused on the study of formation of the liquid film along the channel injector wall, and on the upstream characteristics of the liquid jet near the exit of the atomizer. The numerical simulations were in qualitative agreement with the experiment, showing that an annular jet exiting from the channel collapses and the liquid breaks up into droplets a short distance from the exist. The results show that the Volume of Fluid model is appropriate for developing simulation models of the working of a slinger atomizer.

Download or read book Numerical Simulation of Aerated Liquid Injection written by Brett Joseph Bornhoft and published by . This book was released on 2016 with total page 82 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book LES of Atomization and Cavitation for Fuel Injectors written by Aqeel Ahmed and published by . This book was released on 2019 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: This thesis presents Large Eddy Simulation (LES) of fuel injection, atomization and cavitation inside the fuel injector for applications related to internal combustion engines. For atomization modeling, Eulerian Lagrangian Spray Atomization (ELSA) model is used. The model solves for volume fraction of liquid fuel as well as liquid-gas interface surface density to describe the complete atomization process. In this thesis, flow inside the injector is also considered for subsequent study of atomization. The study presents the application of ELSA model to a typical diesel injector, both in the context of RANS and LES. The model is validated with the help of experimental data available from Engine Combustion Network (ECN). The ELSA model which is normally designed for diffused (unresolved) interfaces, where the exact location of the liquid-gas interface is not considered, is extended to work with Volume of Fluid (VOF) type formulation of two phase flow, where interface is explicitly resolved. The coupling is achieved with the help of Interface Resolution Quality (IRQ) criteria, that takes into account both the interface curvature and modeled amount of interface surface. ELSA model is developed first considering both phases as incompressible, the extension to compressible phase is also briefly studied in this thesis, resulting in compressible ELSA formulation that takes into account varying density in each phase. In collaboration with Imperial College London, the Probability Density Function (PDF) formulation with Stochastic Fields is also explored to study atomization. In modern fuel injection systems, quite oftenthe local pressure inside the injector falls below the vapor saturation pressure of the fuel, resulting in cavitation. Cavitation effects the external flow and spray formulation. Thus, a procedure is required to study the phase change as well as jet formulation using a single and consistent numerical setup. A method is developed in this thesis that couples the phase change inside the injector to the external jet atomization. This is achieved using the volume of fluid formulation where the interface is considered between liquid and gas; gas consists of both the vapor and non condensible ambient air.

Download or read book A Numerical Simulation Model for Transient Two phase Flow Inapipeline written by Myles Wilson Scoggins and published by . This book was released on 1977 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Numerical Simulation of Cantilevered Ramp Injector Flow Fields for Hypervelocity Fuel air Mixing Enhancement written by Jurgen Schumacher and published by . This book was released on 2000 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Increasing demand for affordable access to space and high speed terrestrial transport has spawned research interest into various air-breathing hypersonic propulsion systems. Propulsion concepts such as the supersonic combustion ramjet (scramjet) and the shock-induced combustion ramjet (shcramjet) utilize oxygen freely available in the atmosphere and thereby substantially reduce the weight penalty of on-board oxidizer tankage used in rocket based systems. Of key importance to the ultimate success of an air-breathing concept is the ability to efficiently mix the fuel with atmospheric air. In the case of a hypersonic air-breather the challenge is accentuated due to the requirement of supersonic combustion. Flow velocities through the combustor on the order of thousands of meters per second provide the fuel and air with only a brief time to adequately combine. Contemporary mixing augmentation methods to address this issue have focused on fuel injection devices which promote axial vortices to enhance the mixing process. Much research effort has been expended on investigation of ramp injectors for this purpose. The present study introduces a new ramp injector design, based on the conventional ramp injector, dubbed the cantilevered ramp injector. A two-pronged numerical approach was employed to investigate the mixing performance and characteristics of the cantilevered injector consisting of, (1) comparison with conventional designs and (2) a parametric study of various cantilevered injector geometries. A laminar, three-dimensional, multispecies flowsolver was developed in generalized coordinates to solve the Navier-Stokes equations for the flow fields of injected H2 into high-enthalpy air. The scheme consists of an upwind TVD scheme for discretization of the convective fluxes coupled with a semi-implicit LU-SGS scheme for temporal discretization. Through analysis of the numerical solutions, it has been shown that the cantilevered ramp injector is a viable fuel injection system facilitating enhanced mixing of fuel and air. Comparison with conventional designs have revealed a competitive and, in most cases, superior design in the context of mixing performance. A strong counter-rotating vortex pair generated under the cantilevered injector was shown to be the distinguishing characteristic of this design and largely accounted for improved mixing performance. Results also elucidated the importance of a coupled design approach between the fuel injector and propulsive duct to optimize mixing performance.

Download or read book Numerical Investigation of the Influence of the Injector Geometry on Flashing Behavior written by Lionel [Verfasser] Gury and published by . This book was released on 2015 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: So-called Green Propellants for in-space propulsion gained attention during the last years and are a growing field of research due to the anticipation of the ban of traditional toxic liquid monopropellants. Liquid propellants based on highly energetic inorganic salt Ammonium Dinitramide (ADN) were identified as a possible alternative. Prior to the design of new families of thrusters using new propellants, knowledge has to be gained the injection of propellants under near vacuum conditions involves intense phase change which can be problematic in the case of the injection of a dissolved salt. Injection tests were carried out at DLR Lampoldshausen. Eight different geometries were tested with water and saline solution in order to identify the parameters driving the spray behavior.The aim of this study is to simulate with the help of computational fluid dynamics software, the flow behavior in the injector, and particularly the interphase mass transfer. Secondly, parameters influencing the shattering of the spray and the internal flow behavior are identified.The simulations were carried out for four different injectors with different geometries and under different temperatures. The phase change in the injectors was modeled from the Rayleigh-Plesset equation for bubble growth and a test case was validated against experimental results. The results of the simulations indicated that the pressure drop in the injector reached the saturation pressure under certain conditions, which led to cavitation and subsequently to the choking of the injector. Qualitative comparison with experimental data showed that the shattering of the spray in a two phase effluent was coincident with the cavitation in the injector nozzle. It was also established that not only the pressure loss, but also the mechanism of pressure loss in the injector had an important influence on the spray behavior.*****So-called Green Propellants for in-space propulsion gained attention during the last years and are a growing field of research due to the anticipation of the ban of traditional toxic liquid monopropellants. Liquid propellants based on highly energetic inorganic salt Ammonium Dinitramide (ADN) were identified as a possible alternative. Prior to the design of new families of thrusters using new propellants, knowledge has to be gained the injection of propellants under near vacuum conditions involves intense phase change which can be problematic in the case of the injection of a dissolved salt. Injection tests were carried out at DLR Lampoldshausen. Eight different geometries were tested with water and saline solution in order to identify the parameters driving the spray behavior.The aim of this study is to simulate with the help of computational fluid dynamics software, the flow behavior in the injector, and particularly the interphase mass transfer. Secondly, parameters influencing the shattering of the spray and the internal flow behavior are identified.The simulations were carried out for four different injectors with different geometries and under different temperatures. The phase change in the injectors was modeled from the Rayleigh-Plesset equation for bubble growth and a test case was validated against experimental results. The results of the simulations indicated that the pressure drop in the injector reached the saturation pressure under certain conditions, which led to cavitation and subsequently to the choking of the injector. Qualitative comparison with experimental data showed that the shattering of the spray in a two phase effluent was coincident with the cavitation in the injector nozzle. It was also established that not only the pressure loss, but also the mechanism of pressure loss in the injector had an important influence on the spray behavior.

Download or read book Understanding the Breakdown of Classic Two phase Theory and Spray Atomization at Engine relevant Conditions written by and published by . This book was released on 2016 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: We present a generalized framework for multi-component liquid injections to understand and predict the breakdown of classic two-phase theory and spray atomization at engine-relevant conditions. The analysis focuses on the thermodynamic structure and the immiscibility state of representative gas-liquid interfaces. The most modern form of Helmholtz energy mixture state equation is utilized which exhibits a unique and physically-consistent behavior over the entire two-phase regime of fluid densities. It is combined with generalized models for non-linear Gradient Theory and for liquid injections to quantify multi-component two-phase interface structures in global thermal equilibrium. Then, the Helmholtz free energy is minimized which determines the interfacial species distribution as a consequence. This minimal free energy state is demonstrated to validate the underlying assumptions of classic two-phase theory and spray atomization. However, under certain engine-relevant conditions for which corroborating experimental data is presented, this requirement for interfacial thermal equilibrium becomes unsustainable. A rigorously derived probability density function quantifies the ability of the interface to develop internal spatial temperature gradients in the presence of significant temperature differences between injected liquid and ambient gas. Then, the interface can no longer be viewed as an isolated system at minimal free energy. Instead, the interfacial dynamics become intimately connected to those of the separated homogeneous phases. Hence, the interface transitions toward a state in local equilibrium whereupon it becomes a dense-fluid mixing layer. A new conceptual view of a transitional liquid injection process emerges from a transition time scale analysis. Close to the nozzle exit, the two-phase interface still remains largely intact and more classic two-phase processes prevail as a consequence. Further downstream, however, the transition to dense- fluid mixing generally occurs before the liquid length is reached. The significance of the presented modeling expressions is established by a direct comparison to a reduced model, which utilizes widely-applied approximations but fundamentally fails to capture the physical complexity discussed in this paper.

Download or read book Structures of Integral Flow and the Corresponding Spray for Aerated liquid Injectors written by K.-C. Lin and published by . This book was released on 2001 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Numerical Simulation of Diesel Injector Internal Flow Field written by and published by . This book was released on 2015 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book A Numerical Simulation of Injection of Droplets in a Compressible Flow written by E. Daniel and published by . This book was released on 1992 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Fluid Mechanics Internal Flow written by Engineering Sciences Data Unit and published by . This book was released on 1964 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: