Supersonic Flow Structure in the Entrance Part of a Mixing Chamber of 2D Model Ejector

The paper deals with experimental and numerical results of investigation into supersonic and transonic flow past a two-dimensional model ejector. Results of optical measurements show a flow structure and flow parameter development in the entrance part of the mixing chamber of the ejector. Numerical results are obtained by means of both the straight solution of shock waves in supersonic flow field using classical relations of parameters of shock waves and the Fluent 6 program. Results of numerical solutions are compared with experimental pictures of flow fields. Flow structure development in the mixing chamber is analysed in detail.     

Experimental and Numerical Analysis on the Internal Flow of Supersonic Ejector Under Different Working Modes

Supersonic ejectors involve very complex phenomena such as interaction between supersonic and subsonic flows, shock trains, instabilities, which strongly influences the performance of supersonic ejector. In this study, the static pressure distribution along the ejector wall and Mach number distribution along the axis are used to investigate the internal flow field of supersonic ejector. Results indicate that when the back pressure is much less than the critical back pressure, there are two series of shock trains, and the change of the back pressure will not affect the flow field before the effective area section, so the entrainment ratio would remain constant. The second shock train moves further upstream and is combined with the first shock train to form a single shock train as the back pressure rises. When the back pressure is greater than the critical back pressure, the position of the shock train, the static pressure at its upstream and the entrainment ratio, will be affected. The “effective area section” in the mixing tube is obtained. The effective area section position moves downstream with the increase of the primary flow pressure, while it moves upstream with the increase of the secondary flow pressure. The entrainment ratio shows inversely proportional relationship with the effective section position. Besides, the first shock train length increases with the increase of primary flow pressure or secondary flow pressure. The critical back pressure represents direct proportional relationship to the first shock train length.     

Numerical analysis of Chevron nozzle effects on performance of the supersonic ejector-diffuser system

The supersonic nozzle is the most important device of an ejector-diffuser system.The best operation condition and optimal structure of supersonic nozzle are hardly known due to the complicated turbulent mixing,compressibility effects and even flow unsteadiness which are generated around the nozzle extent.In the present study,the primary stream nozzle was redesigned using convergent nozzle to activate the shear actions between the primary and secondary streams,by means of longitudinal vortices generated between the Chevron lobes.Exactly same geometrical model of ejector-diffuser system 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 supersonic flows and shock waves inside the ejector.It is observed that the flow structure and shock system were changed and primary numerical analysis results show that the Chevron nozzle achieve a positive effect on the supersonic ejector-diffuser system performance.The ejector with Chevron nozzle can entrain more secondary stream with less primary stream mass flow rate.     

Experimental investigation on starting process of supersonic single-stage air ejector

This paper deals with experimental study of flow field of starting process in two-dimensional, single-stage supersonic ejector on different air total pressure. Schlieren pictures of flow field were taken, static pressure distribu-tions on side wall were measured. The obtained results show that, on critical pressure, the starting main shock waves in ejector oscillated back and forth between the second throat and the middle section of the mixing chamber, it causes the pressure in the second half of the mixing chamber acutely fluctuated .When the working pressure of the active flow is higher than the critical starting pressure, ejector starts normally and the inner flow-field of the mixing chamber keeps stable and the shock waves in the second throat have a certain degree of oscillation . After ejector starts, the operating pressure of the active flow may be lower than the starting pressure .     

Computational Analysis of a Variable Ejector Flow

The present study addresses a variable ejector which can improve the ejector efficiency and control the re-circulation ratio under a fixed operating pressure ratio. The variable ejector is a facility to obtain specific recirculation ratio under a given operating pressure ratio by varying the ejector throat area ratio. The numerical simulations are carried out to provide an understanding of the flow characteristics inside the variable ejector. The sonic and supersonic nozzles are adopted as primary driving nozzles in the ejector system, and a movable cone cylinder, inserted into a conventional ejector-diffuser system, is used to change the ejector throat area ratio. The numerical simulations are based on a fully implicit finite volume scheme of the compressible, Reynolds-Averaged Navier-Stokes equations. The results show that the variable ejector can control the recirculation ratio at a fixed operating pressure ratio.     

Navier—Stokes Computations of the Supersonic Ejector—Diffuser System with a Second Throat

The supersonic ejector-diffuser system with a second throat was simulated using CFD.An explicit finite volume scheme was applied to solve two-dimensional Navier-Stokes equations with standard κ-εturbulence model.The vacuum performance of the supersonic ejector-diffuser system was investigated by changing the ejector throat area ration and the operating pressure ratio.Two convergent-divergent nozzles with design Mach number of 2.11 and 3.41 were selected to give the supersonic operation of the ejector-diffuser system.The presence of a second throat strongly affected the shock wave structure inside the mixing tube as well as the spreading of the under-expanded jet discharging from the primary nozzle.There were optimum values of the operating pressure ratio and ejector throat area ratio for the vacuum performance of the system to maximize.     

Structural optimization and experimental investigation of supersonic ejectors for boosting low pressure natural gas

The supersonic ejector was introduced into boosting the production of low pressure natural gas wells. The energy of high pressure gas wells, which was usually wasted through choke valves, was used as its power supply to boost the low gas production. The operating performance of natural gas ejectors was determined not only by the operating parameters but also by the structural parameters. This study focused on the structural optimization and operating performance of natural gas ejectors. The optimal structural parameters were obtained by numerical simulation when the maximum pressure ratio was obtained, and the numerical results were validated by experimental investigation. The numerical results showed that the optimal diameter ratio of mixing tube to primary nozzle throat was 1.6, the optimal length to diameter ratio of mixing tube was 4.0 and the optimal inclination angle of mixing chamber was 28°. The entrainment ratios and pressure ratios from the numerical simulation agreed well with the field experimental data, with the maximum value of pressure ratio up to 60%. The operating performance of the supersonic ejector was also investigated by the field experiment, and the results showed that the induced gas flowrate and entrainment ratio showed nonlinear characteristics with peak values when the motive pressure ranged from 8 MPa to 13 MPa. These experimental results have proved the optimized structural parameters of the supersonic ejector. The investigation will help to the further application in boosting natural gas production of supersonic ejector.     

Navier-Stokes Computstions of the Supersonic Ejector Diffuser System with a Second Throat

INTRODUCTIONUnloosetheconvenhonalfluidmachineryinwhichusuallyhavesomerotatingormovingparts,theejectorisadevicewhichemploysahigh-velocityprimalmotivefluidtoentrainandaccelerateasecondalsuctionfluidwhichmovesslower.Theresulhngkinehcenergyofthefutureissubsequentlyusedforself-compressiontOahigherPressure,thusPerformingthefunchonofacompressor.TheejectorsystemhaslongbeenappliedtOjetpumps,vacuumPumps,high-altitUdesimulators,V/STOLs,etc['-'l;becauseofthemajoradvantagesofitsstrUcturalsimplicit…     

Application of profiled ejector in chemical lasers

Recently, the use of profiled ejectors based on constant rate of momentum change [I.W. Eames, Applied Thermal Engineering 22 (2002) 121] along the mixing chamber has been proposed for enhancing the recovery ratio across an ejector stage by minimizing shock losses for application in ejector based refrigeration system. Such ejectors can achieve pressure recovery ratio in excess of 150, thus making the system a compact one. Chemical lasers in general and chemical oxygen-iodine laser (COIL) in particular fall in the high power lasers category and find numerous applications in defense and industry. However, these lasers have not been exploited fully because these require pressure recovery systems for their operation and as such the practical systems are extremely voluminous and bulky. The profiled ejectors find direct applications in these lasers and thus can make the system extremely compact. The conventional supersonic COIL systems operate at a typical stagnation pressure of nearly 20 torr and a cavity static pressure of approximately 3 torr, which are amongst the lowest in the class of chemical lasers. Thus, a low-pressure operation of the laser system demands a high capacity vacuum system. Alternatively, efficient ejector based pressure recovery system has been utilized for achieving direct atmospheric exhaust of the lasing medium. However, a minimum of two-stage conventional supersonic ejectors need to be employed for the operation of the laser system. Multiple stages of the ejector are essential on account of the stagnation pressure loss occurring across a normal shock at the exit of the mixing chamber in each ejector stage. The present study presents a general treatment on the design of a profiled ejector for the case of dissimilar motive and suction fluids that are typical of these lasers. Also, determinations for the increase in recovery ratio for various conditions of entrainment ratio over the conventional ejectors have also been presented. Finally, a computational study using McCormack’s method for Euler system of equations has been carried out to numerically validate the analytical studies for a peripheral air ejector system suitable for a 500 W class COIL employing a flow rate of 3 gm/s with an entrainment ratio of 0.025. It has been concluded that a single-stage profiled ejector is sufficient to achieve atmospheric pressure recovery even in the low-pressure systems.     

Hysteretic Phenomenon of Shock Wave in a Supersonic Nozzle

In recent years, hysteretic phenomena in fluid flow systems drew attention for their great variety of industrial and engineering applications. When the high-pressure gas is exhausted to atmosphere from the nozzle exit, the expanded supersonic jet with the Mach disk is formed at a specific condition. In two-dimensional expanded supersonic jet, the hysteresis phenomenon for the reflection type of shock wave is occurred under the quasi-steady flow and the transitional pressure ratio between the regular reflection and Mach reflection is affected by this phe- nomenon. However, so far, there are very few researches for the hysteretic phenomenon of shock wave in a supersonic internal flow and the phenomenon has not been investigated satisfactorily. The present study was concemed with the experimental and numerical investigations of hysteretic phenomena of shock wave in a supersonic nozzle, and discussed the relationship between hysteresis phenomenon and rate of the change of pressure ratio with time.     

Effects of cavity-induced mixing enhancement under oblique shock wave interference: Numerical study

In this research, the effects of oblique shock on the mixing characteristics in a supersonic combustor equipped with a cavity is numerically investigated. To reveal the flow structure of the supersonic flow field under oblique shock wave interference, three-dimensional steady RANS equations and SST k-ω turbulence model are adopted. The current work focuses on comparing the interaction effects between oblique shock wave and bow shock wave, which are formed by fuel jet on fuel mixing under different conditions. The numerical analysis demonstrates that an optimal angle exists for the mixing efficiency of the ramp. The optimal angle diminishes as the jet-to-crossflow pressure ratio increases. The oblique shock wave in a certain range is conducive to enhance the penetration depth of ethylene. The smaller angle of the ramp does not cause large stagnation pressure losses.     

Numerical Investigation of Two-Phase Flow in Natural Gas Ejector

Increasing production and recovery from the mature oil and gas fields often requires a boosting system when the gas pressure is lower than that demanded by the transportation or process system. The supersonic ejector, considered to be a cost-effective way to boost the production of a low-pressure gas well, was introduced into the industrial field. However, the exploitation of natural gas often accompanies with water. The computational fluid dynamics (CFD) technique was employed to investigate the two-phase effect (water droplets) on the performance of natural gas ejector for the motive pressure ranging from 11.0 MPa to 13.0 MPa, induced pressure from 3.0 MPa to 5.0 MPa, and backpressure from 5.1 MPa to 5.6 MPa, while the injected water flow rate was less than 0.03 kg s^?1. The numerical results show that the entrainment ratio of the two-phase operation was higher than that of the single-phase operation with the variation of backpressure. Meanwhile, the entrainment ratio increased with the increase of injected water flow rate into the primary flow. When the water was injected into the secondary flow, the entrainment ratio decreased as the injected water flow rate increased, but the critical backpressure remained unchanged.     

Numerical Simulation of the Supersonic Flows in the Second Throat Ejector —Diffuser Systems

INTRODUCTIONThe ejector system is a device which employs ahigh-velocity primary motive fluid to enirain and accelerate a slower moving secondary fluid. The resulting kinetic energy of the mixture is subsequently usedfor self-compression to a higher pressure, thus performing the function of a compressor. The ejectorsystem has lOng been applied to jet pumps, vacuumpumps, high-altitude simulators, V/STOLs, etc[lrv4],because of the major advantages of its structural simplicity and reliabili…     

The effect of secondary flows on the starting pressure for a second-throat supersonic ejector

The effect of the secondary flow on the starting pressure of a second-throat supersonic ejector has been investigated by adapting the height of the secondary flow inlet. The obtained results show that an optimum value of the secondary inlet height exists, and the starting pressure of the ejector becomes a minimum at that condition. Based on the results of the pressure measurements, a qualitative analysis has been made to clarify the flow behavior and the physical meaning of the performance diagram. It appears that the choking phenomenon of the secondary flow plays an important role in the starting process of the ejector. When the secondary inlet height is relatively small, the choked secondary flow and the supersonic primary flow could be employed to protect the static pressure in the suction chamber from being disturbed by the back pressure effect at a certain primary stagnation pressure, which is lower than the starting pressure for the case of the zero-secondary flow. However, as the secondary inlet height increases and exceeds a critical value, the static pressure in the suction chamber rapidly increases, and the starting pressure of the ejector increases accordingly.     

二维流动模型的喷射器性能分析研究

采用二维轴对称流动模型，计算分析了吸入通道内回流现象、喷射器“恒能力”现象与静压力在轴线上分布情况之间的关系；探讨了工作压力对喷射器性能的影响。结果表明：持续降低出口压力会在混合室内形成激波，喷射因数保持不变；工作压力过高会在混合室内产生壅塞，反而降低喷射因数；吸入压力过低会在喷射器吸入通道内产生回流现象，影响喷射式制冷系统运行的安全性。     

An improvement on the efficiency of a single rotor transonic compressor by reducing the shock wave strength on the blade suction surfaces

It is well known that increasing the rotational velocity is an effective way to increase the total pressure ratio. With increasing flow velocity especially under the condition of transonic flow in the supersonic region, where exist strong shock waves, the shock wave loss becomes main and important. Simultaneously, there occurs boundary layer separation due to the shock wave / boundary layer interaction. In the present paper the transonic compressor blades were studied and analyzed to find a proper and simple way to reduce the shock wave loss by optimizing the suction surface configuration or controlling the gradient of isentropic Mach number on the suction surface. A Navier-Stokes solver combined with a modified design algorithm was developed and used. The NASA single rotor for transonic flow compressor was served as a numerical example to show the effectiveness of this method. Two cases for both original and modified rotors were analyzed and compared.     

Shock wave in supersonic moist air jet for a low pressure ratio

In the present study,a computational fluid dynamics work was performed to investigate the occurrence of the shock wave by condensation in supersonic moist air jet.The unsteady,compressible axisymmetric Navier-Stokes equation is solved by TVD(Total Variation Diminishing) scheme in this study.The numerical simulations have been performed for low pressure ratio and various humidities.The results show the occurrence of the shock wave in supersonic moist air jet for a low pressure ratio when Mach disk does not occur,depending on humidity of the air.     

A novel thermally driven rotor-vane/pressure-exchange ejector refrigeration system with environmental benefits and energy efficiency

The latest results of an ongoing coordinated experimental and computational program on the design and performance of a novel supersonic rotor-vane/pressure-exchange ejector for thermally driven ejector refrigeration systems are presented. For the supersonic rotor-vane/pressure-exchange ejector, careful management of the entropy rise through the oblique shocks and boundary layers is required for obtaining an advance in ejector performance. Since the invention of this new ejector is quite recent, understanding its aerodynamics, with the consequent optimization of performance, is in the formative stage. This paper shows how the supersonic aerodynamics is managed to provide the desirable flow induction characteristics through computational study and, in parallel, experimental results including flow visualization showing actual behavior with different-shaped rotor vanes. The importance of the existence of the tail part with a long expansion ramp, the sharp leading edge such as knife-edge, the proper height of leading edges, for the overall shape of rotor vane, were observed. Also the larger spin-angle rotor vane produces better flow induction and mixing between primary flow and secondary flow.     

超音速分离管中水蒸气凝结相变的数值研究

基于超音速分离管中混合气体流动属于伴随凝结相变的可压缩、跨音速的特点,建立了考虑传质效应与非平衡凝结过程的数学模型,并采用数值方法对伴随水蒸气凝结的超音速分离管中的流动进行分析研究。以空气、水蒸气及液态水为流动介质,采用两相流动中的VOF模型结合凝结相变模型以及组分传输模型,研究不同进出口参数及不同水蒸气含量对凝结流场的影响。研究结果表明,所建立的分离管内部非平衡凝结相变模型可以较好的再现超音速流中的凝结成核及液滴生长过程;数值计算结果表明,入口压力、温度及水蒸气含量对分离管内流动凝结过程有直接且重要的影响。因此在进行超音速分离管设计时,考虑温度压力参数的同时,考虑水蒸气含量对分离管性能的影响也是非常重要的。     

蒸汽喷射器流动参数与性能的数值分析

通过二维流动数值计算，分析了以水蒸气为工质的喷射器内工作流体压力、引射流体压力及出口压力对喷射系数的影响；探讨了各工作参数变化对喷射系数产生影响的原因，以及激波产生的条件、激波的位置、强度，产生引射流体雍塞的条件等。结果表明：喷射器存在临界的出口压力pd，当喷射器出口压力大于pd时，喷射器的喷射系数随出口压力升高而降低；当喷射器出口压力小于pd时，喷射器的喷射系数将保持不变。在计算模拟的制冷工况范围内，工作流体压力升高，引起喷射系数降低，pd升高；而引射流体压力升高时，喷射系数与pd都升高。