Supersonic Ejector Research Articles

이차목을 갖는 환형 분사 초음속 이젝터 이론 해석

이차목을 갖는 환형 분사 초음속 이젝터 이론 해석

Transonic instability in entrance part of mixing chamber of high-speed ejector

The paper deals with experimental and numerical study of flow structure in two-dimensional model of supersonic ejector. Schlieren pictures of flow structure were taken, static pressure distributions on side wall were measured and Fluent software to calculate the flow structure in supersonic ejector was used. For certain region of back pressure ratio pb/p02 and stagnation pressure ratio of both streams p01/p02 the terminal shock wave is close to the trailing edge of the primary flow nozzle and a transonic instability occurs. The instability causes the movement of position of boundary layer separation, the structure of shock waves changes and all flow structure oscillates. The movie of these regimes during schlieren experiments was taken and relevant numerical modelling was performed.

Numerical assessment of ejector operation for refrigeration applications based on CFD

This paper represents numerical results of a supersonic ejector for refrigeration applications. The working fluid used for this study is R142b for which some 1-D simulation data is available in the literature for comparison purposes. One of the interesting features is that the current model is based on the NIST-REFPROP database for refrigerants properties calculations. To the authors’ knowledge, it is the first paper dealing with local CFD modeling that takes into account shock–boundary layer interactions in a real refrigerant. The numerical results obtained, contribute to understanding the local structure of the flow and demonstrate the crucial role of the secondary nozzle for the mixing rate performance. In addition, these results point out to the need for an extensive validation of the turbulence model, especially in the modeling of the off-design mode.

이차목을 갖는 초음속 이젝터 작동압력에 대한 연구

이차목을 갖는 초음속 이젝터 작동압력에 대한 연구

가변형 음속/초음속 이젝터 시스템에 관한 실험적 연구

A new method to improve the efficiency of a hydrogen fuel cell system was introduced by using variable sonic/supersonic ejectors. To obtain the variable area ratio of the nozzle throat to ejector throat which controls the mass flow rate of the suction flow, the ejectors used a movable cylinder inserted into a conventional ejector-diffuser system. Experiments were carried out to understand the flow characteristics inside the variable ejector system. The secondary mass flow rates of subsonic and supersonic ejectors were examined by varying the operating pressure ratio and area ratio. The results showed that the variable sonic/supersonic ejectors could control the recirculation ratio by changing the throat area ratio, and also showed that the recirculation ratio increased for the variable sonic ejector and decreased for the variable supersonic ejector, as the throat area ratio increases.

GAS EJECTOR AS A PRESSURE STABILIZER AT THE INLET TO COMPRESSOR POWER INSTALLATION

Optimum supersonic gas ejector design procedure for application as pressure stabilizer at the inlet to compressor power installation is developed.

화학레이저 구동용 이젝터 시스템 개발 (III) - 고출력 화학레이저용 실물 크기의 이젝터 시스템 개발 및 성능 검증 -

From the geometric parameter study, an optimal ejector design procedure of pressure recovery system for chemical lasers was acquired. For given primary flow reservoir conditions, an up-scaled ejector was designed and manufactured. In the performance test, secondary mass flow rate of 100g/s air was entrained satisfying the design secondary pressure, 40~50torr. Performance validation of a supersonic ejector system along with an investigation of effects of supersonic diffuser ws conducted. Placement of the diffuser at the secondary inlet further reduced diffuser upstream pressure to 7torr. Lastly, the duplicate of apparatus (air 500g/s secondary mass flow rate each) was built and connected in parallel to assess proportionality behavior on a system to handle larger mass flow rate. Test and comparison of the parallel unit demonstrated the secondary mass flow rate was proportional to the number of individual units that were brought together maintaining the lasing pressure.

화학레이저 구동용 이젝터 시스템 개발 (II) - 이차목 형태의 환형 초음속 이젝터 최적 설계 -

Determination of geometric design parameters of a second~throat type annual supersonic ejector is described Tested geometric parameters were primary nozzle area ratio, cross-sectional area of second-throat, L/D ratio of second-throat and primary flow Injection angle Varying these four geometric parameters, we build a test matrix made of 81 test conditions, and experimental apparatus was fabricated to accommodate them For each test condition, the stagnation pressure of primary flow and the static pressure of the secondary flow were measured simultaneously along with their transition to steady operation and finally to unstarting condition Comparing the performance curve of every case focused on starting pressure, the unstarting pressure and the minimum secondary pressure, we could derive correlations that the parameters have on the performance of the ejector and presented the optimal design method of the ejector Additional experiments were carried out to find effects of temperature and mass flow rate of the secondary flow.

Numerical and experimental investigations on supersonic ejectors

Supersonic ejectors are widely used in a range of applications such as aerospace, propulsion and refrigeration. The primary interest of this study is to set up a reliable hydrodynamics model of a supersonic ejector, which may be extended to refrigeration applications. The first part of this work evaluated the performance of six well-known turbulence models for the study of supersonic ejectors. The validation concentrated on the shock location, shock strength and the average pressure recovery prediction. Axial pressure measurements with a capillary probe performed previously [Int. J. Turbo Jet Engines 19 (2002) 71; Conference Proc., 10th Int. Symp. Flow Visuzlization, Kyoto, Japan, 2002], were compared with numerical simulations while laser tomography pictures were used to evaluate the non-mixing length. The capillary probe has been included in the numerical model and the non-mixing length has been numerically evaluated by including an additional transport equation for a passive scalar, which acted as an ideal colorant in the flow. At this point, the results show that the k–omega–sst model agrees best with experiments. In the second part, the tested model was used to reproduce the different operation modes of a supersonic ejector, ranging from on-design point to off-design. In this respect, CFD turned out to be an efficient diagnosis tool of ejector analysis (mixing, flow separation), for design, and performance optimization (optimum entrainment and recompression ratios).

Visualization of secondary flow choking phenomena in a supersonic air ejector

The present study deals with the visualization of the air flow inside a supersonic ejector. Our attention is more precisely focused on the choked flow phenomenon which occurs along the mixing chamber of the secondary nozzle and which can be visualized by CFD. Laser tomography visualizations are used to validate the CFD model. The evolution of flow configuration in the ejector with the primary stagnation pressure is examined both in the case of zero secondary flow and in the case of free entrainment of induced air.

The effect of operating conditions on the performance of a supersonic ejector for refrigeration

A previously developed one-dimensional model, based on a forward marching solution technique of the conservation equations has been used to study ejector operation and performance in a large range of refrigeration working conditions. Several important features of ejector operation characteristics were simulated. Global parameter values, their local distributions along the ejector including the temperature, the pressure and the Mach number were calculated for design and off design conditions. Operation parameters such as the entrainment ratio ω, compression ratios P exit/ P ev, P g/ P exit and the geometric ratio ( D/ D c) 2 were found to significantly affect performance. The impact of the generator, the evaporator, the condenser and related thermodynamic parameters, which have been assessed in this study, are summarized as: Fluid mixing conditions dictated by the fluid type, the mixing chamber geometry, the inlet and outlet constraints, may lead to off design operation with related stability and performance deterioration Internal superheat generation, due to inefficient mixing and normal shock waves is very important in off design operation Some degree of inlet superheat (around 5 °C) is necessary to prevent internal condensation but excess superheat is detrimental to the condenser efficiency at exit Generator pressure conditions and the evaporator temperature significantly affect ejector performance.

Boundary-Layer Separation in a Turn-Around Duct

to approach a constant value for high values of M1e and that L P extends over 6‐15 times the diameter of flow passages for upstream Mach numbers larger than 2. Conclusions This Note deals with the study of the shock train structure that appears in the constant-area duct of a supersonic ejector. A CFD model of the airflow inside the ejector has been developed to predict the pressure recovery by pseudoshock. The computational results obtained in the case of the zero-secondary flow configuration of the ejector are in fairly good agreement with experiments. The computational model has demonstrated its capability in accurately capturing the shocks that are formed in the secondary nozzle of the ejector and allows the prediction of the length necessary to fully achieve the pressure recovery. Furthermore, we intend to extend this computational work to more complex flow configurations in ejectors (entrainment of induced flow, choking of the secondary nozzle).

An experimental study of supersonic dual coaxial free jet

A supersonic dual coaxial jet has been employed popularly for various industrial purposes, such as gasdynamic laser, supersonic ejector, noise control and enhancement of mixing. Detailed characteristics of supersonic dual coaxial jets issuing from an inner supersonic nozzle and outer sonic nozzles with various ejection angles are experimentally investigated. Three important parameters, such as pressure ratios of the inner and outer nozzles, and outer nozzle ejection angle, are chosen for a better understanding of jet structures in the present study. The results obtained from the present experimental study show that the Mach disk diameter becomes smaller, and the Mach disk moves toward the nozzle exit, and the length of the first shock cell decreases with the pressure ratio of the outer nozzle. It was also found that the highly underexpanded outer jet produces a new oblique shock wave, which makes jet structure much more complicated. On the other hand the outer jet ejection angle affects the structure of the inner jet structure less than the pressure ratio of the outer nozzle, relatively.

화학레이저 구동용 이젝터 시스템 개발 (I) - 화학레이저 구동용 초음속 이젝터 설계 변수 연구 -

It is essential to operate chemical lasers with supersonic ejector system as the laser output power goes up. In this research, ejector design parameter study was carried out for optimal ejector design through understanding the ejector characteristics and design requirements for chemical lasers operating. Designed ejector was 3D annular type with 2^nd_throat geometry and pressurized air was used for primary flow. Ejector design was carried out with two steps, quasi-ID gas dynamics was used for first design and commercial code was used to verify the first design. In this study, to get the effect of ejector geometry on its performance, three cases of primary nozzle area ratio and 2^nd_throat cross sectional area and two cases of 2^nd-throat L/D ratio experiments were carried out. Primary and secondary pressures were measured to get the mass flow rate ratio, minimum secondary pressure, ejector starting pressure and un starting pressure at every case. In the result, better performance than design level was shown and optimal ejector design method for chemical lasers was obtained.

음속/초음속 이젝터 유동에 관한 실험적 연구

An experimental investigation of the sonic and supersonic air ejector systems has been conducted to develop design and prediction programs for practical ejector system. Five different primary nozzles have been employed to operate the ejector systems in the ranges of low and moderate operating pressure ratios. The ejector operating pressure ratio for the secondary chamber pressure to be minimized has a strong influence of the ejector throat ratio. The pressure inside the ejector diffuser is not dependent on the primary nozzle configurations employed but only a function of the ejector operating pressure ratio. Experimental results show that a supersonic ejector system is more desirable for obtaining high vacuum pressure of the secondary chamber than a sonic ejector system.

Computations of the Supersonic Ejector Flows with the Second Throat

Pumping action in ejector systems is generally achieved through the mixing of a high-velocity and high-energy stream with a lower-velocity and lower-energy stream within a duct. The design and performance evaluation of the ejector systems has developed as a combination of scale-model experiments, empiricism and theoretical analyses applicable only to very simplified configurations, because of the generic complexity of the flow phenomena. In order to predict the detailed performance characteristics of such systems, the flow phenomena throughout the operating regimes of the ejector system should be fully understood. This paper presents the computational results for the two-dimensional supersonic ejector system with a second throat. The numerical simulations are based on a fully implicit finite volume scheme of the compressible Reynolds-averaged Navier-Stokes equation in a domain that extends from the stagnation chamber to the diffuser exit. For a wide range of the operating pressure ratio the flow field inside the ejector system is investigated in detail. The results show that the supersonic ejector systems have an optimal throat area for the operating pressure ratio to be minimized.

Analysis of partially mixed supersonic ejector

This article presents an analytical model of a supersonic/subsonic, constant-area ejector whose exit flow is not uniformly mixed. The primary and secondary streams, separated by the dividing streamline, are treated as quasi-one-dim ensional. The shear stress on the dividing streamline, the resulting heat transfer, and the wall stresses are applied artificially on the streams. Axisymmetric and two-dimensional configurations are considered. The model predicts that the axisymmetric ejector provides better thrust augmentation than the two-dimensional one, the latter suffering from higher skin-friction losses. Thrust increases with ejector length, but at a diminishing rate. For all configurations, thrust augmentation decreases with flight Mach number and becomes zero at a flight Mach number of about 0.7. Increasing the primary-to-secondary area ratio has a minimal effect on thrust. The results compare favorably with available experimental data on pressure distributions and mass-flow ratios. Nomenclature A = cross-sectional area a = speed of sound b = ejector radius (A/5) or half-height (two dimensional) cp = specific heat at constant pressure H = total enthalpy h = static enthalpy / = length scale, Eq. (11) M - Mach number Mc = cpnvective Mach number m = mass flux p = pressure q = heat transfer R = gas constant r = velocity ratio, U^/U^ $ = entropy flux 5- = entropy T = temperature U = velocity x = streamwise coordinate y = transverse coordinate y = specific-heat ratio A£7 = tfcol - t/oc* 6W = shear-layer vorticity thickness 77 = density ratio, IJL = viscosity p = density T = shear stress

Discrete tones generated by a supersonic jet ejector

Results of an experimental investigation are presented that describe the characteristics of discrete sound generated by a constant area ejector that uses an underexpanded rectangular jet as the primary flow. The variation of screech tones, which are commonly observed in the spectrum of free shock-containing jets with stagnation pressure and area ratio, show a staging behavior due to the presence of the ejector duct. Such a behavior is explained with the use of a feedback loop. In addition to screech tones, a different type of resonant oscillation within the duct is identified. These consist of acoustic resonances whose frequencies and mode shapes are related to the unsteady flow in the duct and the size of the duct. Two dominant symmetric (varicose) and antisymmetric (flapping) modes of the primary jet determine the nature of the ejector tones that are observed in the spectrum. Using a phase-locked schlieren system, different longitudinal and transverse duct modes are photographed.

Thrust characteristics of a supersonic mixer ejector

This article describes recent findings relative to the thrust performance of supersonic mixer ejectors. Mixer ejectors are a candidate means to mix out the high-velocity engine exhaust on the High Speed Civil Transport (HSCT) aircraft, thereby reducing jet noise at takeoff and landing. In the present work, data and analyses are presented that demonstrate that mixer ejectors can provide rapid mixing of a supersonic jet for acoustic benefits, all while increasing aircraft system static thrust. Jet engine thrust data is presented that demonstrates that a properly designed choked mixer nozzle has essentially no thrust loss when compared to conventional axisymmetric nozzles and mixer ejector thrust gains are invariant over a range of pressure ratios that choke the lobed nozzle. Model data of higher pressure-ratio mixer ejectors (i.e., consistent with HSCT applications) are analyzed to provide relevant thrust parameters. Comparisons are made with a conventional slot-nozzle ejector. A principal finding of this study is that the mixer ejector thrust performance is particularly sensitive to secondary inlet flowfield conditions and geometry. With proper inlet geometries, mixer ejector thrust performance was found to substantially exceed that of the slot-nozzle ejector.

Les paramètres géométriques optima d'un éjecto-compresseur frigorifique

The performances of supersonic R11 ejectors have been experimentally studied over a large range of mixing chamber to nozzle throat area ratio φ. For a given compression ratio r, in the plane giving the mass ratio U as a function of the motoring ratio ξ, it has been shown that an envelope of the maxima of the curves at constant φ, occurs corresponding to the ξ optφ values. Furthermore, there exists on this envelope an optimal value for φ for which the corresponding ξ optAB gives the absolute maximum of U: i.e. the cooling efficiency ϵ f,max. These results permit optimal design of the system when the temperatures of the sources are known.