Studies On Mixing Processes In Ejectors
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Studies On Mixing Processes In Ejectors
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Author : A. Krothpalli
language : en
Publisher:
Release Date : 1984
Studies On Mixing Processes In Ejectors written by A. Krothpalli and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 1984 with categories.
The capability of producing additional thrust along with the ability of vectoring the thrust makes the ejector an attractive device for V/STOL aircraft applications. In addition, the acoustic shielding provided by the walls of the shroud, and lowered exhaust velocities and temperatures at the ejector exit offer important advantages in the area of nozzle exhaust cooling. One of the physical processes which is known to play a large role on the performance of the total system is the mixing between the hot primary and cold secondary streams. Thus an attempt is made here to investigate the mixing process of a hot rectangular jet with an entrained cold ambient fluid in a simple form of a ejector. Primary jet heating, over the temperature range tested, has no significant effect on the velocity field within the ejector shroud. The temperature decay within the ejector shroud displayed differences in comparison with the free jet up to a location where the primary jet spreads to the mixing duct wall. Downstream of this location the centerline temperature within the ejector is higher than that of a free jet. A theoretical analysis is made to set up a determinate mathematical problem for the flow through a constant area ejector. It is shown that multiple solution (more than two) occur, and admissible ones out of these are those that fulfill the entropy condition.
Parametric Study Of A Mixer Ejector Nozzle With Mixing Enhancement Devices
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Author : National Aeronautics and Space Administration (NASA)
language : en
Publisher: Createspace Independent Publishing Platform
Release Date : 2018-06-19
Parametric Study Of A Mixer Ejector Nozzle With Mixing Enhancement Devices written by National Aeronautics and Space Administration (NASA) and has been published by Createspace Independent Publishing Platform this book supported file pdf, txt, epub, kindle and other format this book has been release on 2018-06-19 with categories.
A numerical study employing a simplified model of the High Speed Civil Transport mixer/ejector nozzle has been conducted to investigate the effect of tabs (vortex generators) on the mixing process. More complete mixing of the primary and secondary flows within the confined ejector lowers peak exit velocity resulting in reduced jet noise. Tabs were modeled as vortex pairs and inserted into the computational model. The location, size, and number of tabs were varied and its effect on the mixing process is presented here both quantitatively and qualitatively. A baseline case (no tabs) along with six other cases involving two different vortex strengths at three different orientations have been computed and analyzed. The case with the highest vorticity (six vortices representing large tabs) gives the best mixing. It is shown that the influence of the vorticity acts primarily in the forward or middle portions of the duct, significantly alters the flow structure, and promotes some mixing in the lateral direction. Unmixed pockets were found at the top and bottom of the lobe, and more clever placement of tabs improved mixing in the vertical direction. The technique of replacing tabs with vortices shows promise as an efficient tool for quickly optimizing tab placement in lobed mixers. DalBello, T. and Steffen, C. J., Jr. Glenn Research Center NASA/TM-2001-211341, E-13154, NAS 1.15:211341, ICOMP-2001-02, AIAA Paper 2001-0667
Parametric Study Of A Mixer Ejector Nozzle With Mixing Enhancement Devices
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Author :
language : en
Publisher:
Release Date : 2001
Parametric Study Of A Mixer Ejector Nozzle With Mixing Enhancement Devices written by and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2001 with categories.
Parametric Studies Of The Ejector Process Within A Turbine Based Combined Cycle Propulsion System
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Author : Nicholas J. Georgiadis
language : en
Publisher:
Release Date : 1999
Parametric Studies Of The Ejector Process Within A Turbine Based Combined Cycle Propulsion System written by Nicholas J. Georgiadis and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 1999 with categories.
Parametric Studies Of The Ejector Process Within A Turbine Based Combined Cycle Propulsion System
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Author : National Aeronautics and Space Administration (NASA)
language : en
Publisher: Createspace Independent Publishing Platform
Release Date : 2018-06-15
Parametric Studies Of The Ejector Process Within A Turbine Based Combined Cycle Propulsion System written by National Aeronautics and Space Administration (NASA) and has been published by Createspace Independent Publishing Platform this book supported file pdf, txt, epub, kindle and other format this book has been release on 2018-06-15 with categories.
Performance characteristics of the ejector process within a turbine-based combined-cycle (TBCC) propulsion system are investigated using the NPARC Navier-Stokes code. The TBCC concept integrates a turbine engine with a ramjet into a single propulsion system that may efficiently operate from takeoff to high Mach number cruise. At the operating point considered, corresponding to a flight Mach number of 2.0, an ejector serves to mix flow from the ramjet duct with flow from the turbine engine. The combined flow then passes through a diffuser where it is mixed with hydrogen fuel and burned. Three sets of fully turbulent Navier-Stokes calculations are compared with predictions from a cycle code developed specifically for the TBCC propulsion system. A baseline ejector system is investigated first. The Navier-Stokes calculations indicate that the flow leaving the ejector is not completely mixed, which may adversely affect the overall system performance. Two additional sets of calculations are presented; one set that investigated a longer ejector region (to enhance mixing) and a second set which also utilized the longer ejector but replaced the no-slip surfaces of the ejector with slip (inviscid) walls in order to resolve discrepancies with the cycle code. The three sets of Navier-Stokes calculations and the TBCC cycle code predictions are compared to determine the validity of each of the modeling approaches. Georgiadis, Nicholas J. and Walker, James F. and Trefny, Charles J. Glenn Research Center NASA/TM-1999-209172, NAS 1.15:209172, AIAA Paper 98-0936, E-11679
Thrust Augmentation Study Of High Performance Ejectors
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Author : John E. Minardi
language : en
Publisher:
Release Date : 1983
Thrust Augmentation Study Of High Performance Ejectors written by John E. Minardi and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 1983 with Aerodynamics, Supersonic categories.
A technique is developed for determining a representative value of the maximum efficiency that can be achieved with high performance ejectors when operating on the supersonic solution branch of an ejector. These efficiencies are used to calculate thrust augmentation for an ejector over a wide range of parameters including operation with a hypothetical engine. Reasonable values of thrust augmentation can be achieved at low subsonic flight mach numbers. However, at flight Mach numbers near one, little or not thrust augmentation was found. At supersonic flight Mach numbers, thrust augmentation was achieved. Basic studies indicated that the effects of temperature was opposite at subsonic and supersonic flight Mach numbers. Thrust augmentation decreased with increasing temperature at subsonic Mach number sand increased with increasing temperature at supersonic Mach numbers.
Ejectors And Mixing Of Streams
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Author : J. Seddon
language : en
Publisher:
Release Date : 1964
Ejectors And Mixing Of Streams written by J. Seddon and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 1964 with Ejector pumps categories.
Handbook Of Research On Advances And Applications In Refrigeration Systems And Technologies
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Author : Gaspar, Pedro Dinis
language : en
Publisher: IGI Global
Release Date : 2015-08-28
Handbook Of Research On Advances And Applications In Refrigeration Systems And Technologies written by Gaspar, Pedro Dinis and has been published by IGI Global this book supported file pdf, txt, epub, kindle and other format this book has been release on 2015-08-28 with Technology & Engineering categories.
In recent years, the sustainability and safety of perishable foods has become a major consumer concern, and refrigeration systems play an important role in the processing, distribution, and storage of such foods. To improve the efficiency of food preservation technologies, it is necessary to explore new technological and scientific advances both in materials and processes. The Handbook of Research on Advances and Applications in Refrigeration Systems and Technologies gathers state-of-the-art research related to thermal performance and energy-efficiency. Covering a diverse array of subjects—from the challenges of surface-area frost-formation on evaporators to the carbon footprint of refrigerant chemicals—this publication provides a broad insight into the optimization of cold-supply chains and serves as an essential reference text for undergraduate students, practicing engineers, researchers, educators, and policymakers.
Ejectors For Efficient Refrigeration
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Author : Giuseppe Grazzini
language : en
Publisher: Springer
Release Date : 2018-03-21
Ejectors For Efficient Refrigeration written by Giuseppe Grazzini and has been published by Springer this book supported file pdf, txt, epub, kindle and other format this book has been release on 2018-03-21 with Technology & Engineering categories.
Encompassing both practical applications and recent research developments, this book takes the reader from fundamental physics, through cutting-edge new designs of ejectors for refrigeration. The authors’ unique vision marries successful design, system optimization, and operation experience with insights on the application of cutting-edge Computational Fluid Dynamics (CFD) models. This robust treatment leads the way forward in developing improved ejector technologies. The book covers ejectors used for heat powered refrigeration and for expansion work recovery in compression refrigerators, with special emphasis on two-phase flows of “natural” fluids within the ejector, i.e. steam and carbon dioxide. It features worked examples, detailed research results, and analysis tools.
Development Of A Numerical Tool To Study The Mixing Phenomenon Occuring During Mode One Operation Of A Multi Mode Ejector Augmented Plused Detonation Rocket Engine
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Author : Joshua Dawson
language : en
Publisher:
Release Date : 2016
Development Of A Numerical Tool To Study The Mixing Phenomenon Occuring During Mode One Operation Of A Multi Mode Ejector Augmented Plused Detonation Rocket Engine written by Joshua Dawson and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2016 with categories.
A novel multi-mode implementation of a pulsed detonation engine, put forth by Wilson et al. [2], consists of four modes; each specifically designed to capitalize on flow features unique to the various flow regimes. This design enables the propulsion system to generate thrust through the entire flow regime. The multi-mode ejectoraugmented pulsed detonation rocket engine operates in mode one during take-o_ conditions through the acceleration to supersonic speeds. Once the mixing chamber internal flow exceeds supersonic speed, the propulsion system transitions to mode two. While operating in mode two, supersonic air is compressed in the mixing chamber by an upstream propagating detonation wave and then exhausted through the convergent-divergent nozzle. Once the velocity of the air flow within the mixing chamber exceeds the Chapman-Jouguet Mach number, the upstream propagating detonation wave no longer has sufficient energy to propagate upstream and consequently the propulsive system shifts to mode three. As a result of the inability of the detonation wave to propagate upstream, a steady oblique shock system is established just upstream of the convergent-divergent nozzle to initiate combustion. And finally, the propulsion system progresses on to mode four operation, consisting purely of a pulsed detonation rocket for high Mach number flight and use in the upper atmosphere as is needed for orbital insertion. Modes three and four appear to be a fairly significant challenge to implement, while the challenge of implementing modes one and two may prove to be a more practical goal in the near future. A vast number of potential applications exist for a propulsion system that would utilize modes one and two, namely a high Mach number hypersonic cruise vehicle. There is particular interest in the dynamics of mode one operation, which is the subject of this study. Several advantages can be obtained by use of this technology. Geometrically, the propulsion system is fairly simple and the rapid combustion process results in an engine cycle which is more efficient compared to its combined-cycle counterparts. The flow path geometry consists of an inlet system, followed just downstream by a mixing chamber where an ejector structure is placed within the flow path. Downstream of the ejector structure is a duct leading to a convergent-divergent nozzle. During mode one operation and within the ejector, products from the detonation of a stoichiometric hydrogen/air mixture are exhausted directly into the surrounding secondary air stream. Mixing then occurs between both the primary and secondary flow streams, at which point the air mass containing the high pressure, high temperature reaction products is convected downstream towards the nozzle. The engine cycle is engineered to a specific number of detonations per second, creating the pulsating characteristic of the primary flow. The pulsing nature of the primary flow serves as a momentum augmentation, enhancing the thrust and specific impulse at low speeds. Consequently, it is necessary to understand the transient mixing process between the primary and secondary flow streams occurring during mode one operation. Using OPENFOAM®, a numerical tool is developed to simulate the dynamics of the turbulent detonation process along with detailed chemistry in order to understand the physics involved with the stream interactions. The computational code has been developed within the framework of OPENFOAM®, an open-source alternative to commercial CFD software. A conservative formulation of the Farve averaged Navier-Stokes equations are used to facilitate programming and numerical stability. Time discretization is accomplished by using the Crank-Nicolson method, achieving second-order convergence in time. Species mass fraction transport equations are implemented and a Seulex ODE solver was used to resolve the system of ordinary differential equations describing the hydrogen-air reaction mechanism detailed in Appendix A. The Seulex ODE solution algorithm is an extrapolation method based on the linearly implicit Euler method with step size control. A second-order total variation diminishing method with a modified Sweby ux limiter was used for space discretization. And finally the use of operator splitting (PISO algorithm, and chemical kinetics) is essential due to the significant differences in characteristic time scales evolving simultaneously in turbulent reactive flow. Capturing the turbulent nature of the combustion process was done using the k-w-SST turbulence model, as formulated by, [1]. Mentor's formulation is well suited to resolve the boundary layer while remaining relatively insensitive to freestream conditions, blending the merits of both the k-w and k-E models. Further developement of the tool is possible, most notably with the Numerical Propulsion System Simulation application. NPSS allows the user to take advantage of a zooming functionality in which high-fidelity models of engine components can be integrated into NPSS models, allowing for a more robust propulsion system simulation. A more comprehensive understanding of the multi-mode ejector-augmented pulsed detonation rocket engine can be achieved with a systematic study of the impact pulsed flow has on thrust production. Although a significant increase in computational requirements, adding nozzle geometry to this study would illuminate any problems associated with pulsed flow through a nozzle. Additionally, a study including nozzle geometry would bring more clarity in regards to the efficiency of the propulsion design.