Study on the Ejector-Diffuser System Driven by a Chevron Nozzle

Fanshi Kong,Heuy Dong Kim,Yingzi Jin 대한기계학회 2012 대한기계학회 춘추학술대회 Vol.2012 No.11

Supersonic ejector-diffuser system makes use of high pressure primary stream to propel the secondary stream through pure shear action for the purposes of transport or compression of fluid. The optimization of the ejector-diffuser system and its optimal operation condition are hardly known due to the complicated turbulent mixing, compressibility effects and even flow unsteadiness which are generated inside the ejector-diffuser system. In the present study, a Chevron nozzle was applied to activate the shear actions between the primary and secondary streams, by means of longitudinal vortices generated from the Chevron. Exactly same geometrical model was created to validate the results of experimental data. The operation characteristics of the ejector system were compared between Chevron nozzle and conventional convergent nozzle for the primary stream. A CFD method has been applied to simulate the ejector-diffuser flow field of the supersonic flows and shock waves. The ejector-diffuser system performance is discussed in terms of the entrainment ratio, ejector efficiency, pressure recovery as well as total pressure loss.

Study on the Transient Flows in a Rocket Nozzle

Fanshi Kong,Deng Ruoyu,Heuy Dong Kim 한국추진공학회 2013 한국추진공학회 학술대회논문집 Vol.2013 No.12

Typical rocket nozzle flows are often subject to shock-boundary layer interaction during the engine start or shut-down process. The resulting interaction flows appear as two different salient patterns, free shock separation (FSS) and restricted shock separation (RSS), both of which significantly affect the engine thrust performance. In the present study, FSS and RSS structures in a thrust-optimized rocket nozzle were studied using CFD methods. The Reynolds-Averaged Navier?Stokes equations were numerically solved using a fully implicit finite volume scheme based on a two-dimensional axisymmetric geometry. Reynolds stress turbulence model was used to best predict unsteady flow behaviors. The present numerical results were compared with the experimental Schlieren photographs. The unsteady side-load generated by shock-boundary layer interaction during shut-down operations is investigated in detail. The maximum nozzle wall pressure is found during the oscillatory transition from FSS to RSS. Based on the present simulated results, several control strategies to alleviate the undesirable side forces are suggested in terms of step, cavity, blowing and bleeding.

An Investigation of the Performance of a Two-Stage Ejector-Diffuser System

Fanshi Kong,Heuy-Dong Kim(김희동) 한국추진공학회 2014 한국추진공학회 학술대회논문집 Vol.2014 No.12

In the present study, the flow phenomena inside single-stage and two-stage ejector-diffuser systems have been critically predicted by means of the numerical approach using Reynolds averaged Navier-theoretical results were validated with existing experimental data. Detailed explanation and comparison has been given to detect the performance of two-stage ejector and single-stage ejector. Essential benefit coefficients obtained in the present study were specified in terms of entrainment ratio, mass flow flux ratio and the coefficient of power (COPR). Primary results of the two-stage ejector-diffuser system showed favorable capacity of collecting the extra momentum and increasing the entrainment effects of the system.

Computational Study of Supersonic Chevron Ejector Flows

Fanshi Kong,Heuy Dong Kim,Yingzi Jin 한국추진공학회 2012 한국추진공학회 학술대회논문집 Vol.2012 No.11

Generally speaking, the flow field in the ejector-diffuser system is very difficult to be predicted due to the complicated turbulent mixing, compressibility effects and even flow unsteadiness. Many works have been done in the past years to achieve a higher efficiency and improve the performance of the ejector system, but not yet satisfactory, compared with that of other fluid machinery. Considering the complexity and difficulty on the researching, how to enhance the performance of ejector-diffuser system effectively became a significant task. In the present study, the supersonic nozzle was redesigned using Chevrons installed at the inlet of the secondary stream of the ejector-diffuser system for the purpose of the performance improvement. A CFD method based on Fluent has been applied to simulate the supersonic flows and shock waves inside the ejector. Primary numerical analysis results show that the Chevrons get a positive effect on the ejector flows. The comparison of ejector performance with and without the Chevron was obtained and optimal number of mixing guide vane is discussed to increase the performance. The ejector-diffuser system performance is discussed in terms of the entrainment ratio, pressure recovery as well as total pressure loss.

Compound Choking Phenomenon inside a Supersonic Ejector-Diffuser System

Fanshi Kong,Heuy Dong Kim 한국추진공학회 2015 한국추진공학회 학술대회논문집 Vol.2015 No.11

Major characteristics of the choking phenomenon inside a supersonic nozzle of the ejector-diffuser system has been well known due to the existence of only one primary stream. However, the choking phenomenon inside the mixing chamber, as known as the compound choking, is hardly specified by the conventional nozzle flow physics. That is because two streams are mixed inside the mixing chamber, where the individual streams are subject to different inlet pressures and Mach numbers. In the present study, a one-dimensional theory based upon compound choking flow relationships is presented for analyzing the behavior of two streams flowing through the ejector-diffuser system. This phenomenon is also verified by a two-dimensional CFD simulation using a fully implicit finite volume scheme based on Reynolds averaged Navier–Stokes equations coupled with a standard k-ω turbulence model. Present results show that the compound-compressible flow is found to be choked at the ejector throat, although the individual stream Mach numbers there are not equal to one.

A Numerical Study on the Performance of a Two-Stage Ejector-Diffuser System

Fanshi Kong,Heuy Dong Kim 한국마린엔지니어링학회 2015 한국마린엔지니어링학회지 Vol.39 No.5

Study of the Supersonic Ejector-Diffuser System with a Mixing Guide Vane

Fanshi Kong,Yingzi Jin,Heuydong Kim(김희동) 한국추진공학회 2013 한국추진공학회지 Vol.17 No.1

Study of the Supersonic Ejector-Diffuser System with a Mixing Guide Vane at the Inlet of Secondary Stream

Fanshi Kong,Vincent Lijo,Heuy Dong Kim,Yingzi Jin 한국추진공학회 2011 한국추진공학회 학술대회논문집 Vol.2011 No.11

Ejector-diffuser system has long been used in many diverse fields of engineering applications and it has advantages over other fluid machinery, because of no moving parts and structural simplicity. This system makes use of high-pressure primary stream to entrain the low-pressure secondary stream through pure shear actions between two streams. In general, the flow field in the ejector-diffuser system is highly complicated due to turbulent mixing, compressibility effects and sometimes flow unsteadiness. A fatal drawback of the ejector system is in its low efficiency. Many works have been done to improve the performance of the ejector system, but not yet satisfactory, compared with that of other fluid machinery. In the present study, a mixing guide vane was installed at the inlet of the secondary stream for the purpose of the performance improvement of the ejector system. A CFD method has been applied to simulate the supersonic flows inside the ejectordiffuser system. The present results obtained were validated with existing experimental data. The mixing guide vane effects are discussed in terms of the entrainment ratio, total pressure loss as well as pressure recovery.

Computational Study of Supersonic Chevron Ejector Flows

Fanshi Kong,Heuy Dong Kim(김희동),Yingzi Jin 한국추진공학회 2013 한국추진공학회지 Vol.17 No.6

Starting transient flows in a chevron ejector-diffuser system

Fanshi Kong,김희동,Toshiaki Setoguchi,김정수 대한기계학회 2015 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.29 No.3

The vacuum ejector-diffuser system has been widely used in many applications such as refrigeration systems, high altitude test facilitiesand fluid transportation devices. We simulated the starting transient flows of a supersonic vacuum ejector-diffuser system and itsperformance characteristics and analyzed by the numerical methods. Newly designed chevron lobes were installed at the inlet of the primarystream of the vacuum ejector-diffuser system for the purpose of its performance improvement. A CFD method based on transientscheme was applied to simulate the equilibrium flow behavior inside the secondary chamber. Primary numerical analysis results showthat the performance of the vacuum ejector-diffuser system is considerably improved under chevron effects. Compared to the conventionalejector-diffuser system with a convergent nozzle, the updated system with a chevron nozzle leads to a lower equilibrium pressureinside the secondary chamber with less starting time. The flow characteristics obtained from the numerical results highlight the importanceof the vortex generation effects of the chevron nozzle. The generation process of the longitudinal vortexes and its effects on theejector-diffuser performance has been discussed in detail.