The Experts below are selected from a list of 294 Experts worldwide ranked by ideXlab platform
Ke Tang - One of the best experts on this subject based on the ideXlab platform.
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performance comparison of Jet Pumps with round and sharp edge of small opening in oscillatory flow
Applied Thermal Engineering, 2018Co-Authors: Ye Feng, Ke Tang, Kaihao Zhang, Rui YangAbstract:Abstract Owing to the capability to induce a time-averaged pressure drop in oscillatory flow, a Jet pump has been used to suppress the Gedeon streaming in a looped thermoacoustic engine. The suppression capacity originates from the asymmetric pressure drop through the Jet pump, and could be enhanced by rounding the edge of the Jet pump in traditional view. This paper systematically probes the rounding effect on a Jet pump and compares the performance of Jet Pumps with round and with sharp edge on small opening. The performance dependences on the taper angle and the cross-sectional area ratios, including the big-to-small opening area ratio of the Jet pump and the small opening-to-pipe cross sectional area ratio, are analyzed and compared for the two types of Jet pump. The results reveal a reversed and higher time-averaged pressure drop in the shape edge Jet pump in contrast to that in the rounded Jet pump. However, the round edge of the small opening can improve working efficiency of a Jet pump.
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effect of taper angle on the performance of Jet Pumps for a loop structured thermoacoustic engine
Journal of the Acoustical Society of America, 2017Co-Authors: Ye Feng, Ke TangAbstract:Gedeon streaming, which circulates throughout the loop configuration with a time-averaged manner in the oscillating flow, can considerably deteriorate the efficiency of traveling-wave thermoacoustic engine. A Jet pump is characterized by a tapered channel with different opening areas, which can produce a time-averaged pressure drop to suppress Gedeon streaming. Three Jet Pumps with different taper angles, i.e., 5°, 9°, 15°, are studied. Following Iguchi's hypothesis, the turbulent oscillating flow can be considered as a steady flow. The flow structures though the Jet Pumps are numerically simulated. Meanwhile, an experimental apparatus has been built to measure the performance of Jet pump operating in the turbulent oscillating flow. The results show that the simulation is in a good agreement with the experiment data for the Jet Pumps with small taper angles. For the Jet pump with 15° taper angle, the simulation results match well with the experiment data when the velocity at small opening of Jet pump is h...
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performance comparison of Jet Pumps with rectangular and circular tapered channels for a loop structured traveling wave thermoacoustic engine
Applied Energy, 2015Co-Authors: Ke Tang, Ye Feng, Mingchun LiAbstract:Gedeon streaming can considerably deteriorate the thermal efficiency of a traveling-wave thermoacoustic engine employing a loop configuration. Introducing a Jet pump into the loop configuration is one of the effective ways to suppress Gedeon streaming. This paper focuses on the performance comparison between the Jet Pumps with rectangular and circular tapered channels, by numerically simulating and analyzing the time-averaged pressure drop induced by the Jet Pumps. Three parameters, i.e., the coefficient of time-averaged resistance, the coefficient of overall resistance, and the coefficient of effectiveness, are proposed to evaluate the performance of a Jet pump. The emphasis is put on the effects of cross-sectional shape, thickness-to-diameter ratio, and rounding radius of the tapered channels. In absence of rounding the edge of the tapered channel, the Jet pump with a rectangular tapered channel is more efficient to produce the time-averaged pressure drop at a large thickness-to-diameter ratio, while the Jet pump with a circular tapered channel is more efficient at a small thickness-to-diameter ratio. However, it should be noted that the directions of the induced time-averaged pressure drops in these two cases are opposite. Rounding the edge of the small opening of the tapered channel can effectively improve Jet pump’s performance. Upon rounding, the Jet pump with a circular tapered channel can produce a higher time-averaged pressure drop and work more efficiently than the one with a rectangular tapered channel.
Joris P. Oosterhuis - One of the best experts on this subject based on the ideXlab platform.
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Flow Separation and Turbulence in Jet Pumps for Thermoacoustic Applications
Flow Turbulence and Combustion, 2017Co-Authors: Joris P. Oosterhuis, Simon Bühler, Douglas Wilcox, Antonie Alex Verbeek, Theo H. Van Der MeerAbstract:The effect of flow separation and turbulence on the performance of a Jet pump in oscillatory flows is investigated. A Jet pump is a static device whose shape induces asymmetric hydrodynamic end effects when placed in an oscillatory flow. This will result in a time-averaged pressure drop which can be used to suppress acoustic streaming in closed-loop thermoacoustic devices. An experimental setup is used to measure the time-averaged pressure drop as well as the acoustic power dissipation across two different Jet pump geometries in a pure oscillatory flow. The results are compared against published numerical results where flow separation was found to have a negative effect on the Jet pump performance in a laminar flow. Using hot-wire anemometry the onset of flow separation is determined experimentally and the applicability of a critical Reynolds number for oscillatory pipe flows is confirmed for Jet pump applications. It is found that turbulence can lead to a reduction of flow separation and hence, to an improvement in Jet pump performance compared to laminar oscillatory flows.
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on the performance and flow characteristics of Jet Pumps with multiple orifices
Journal of the Acoustical Society of America, 2016Co-Authors: Joris P. Oosterhuis, Simon Bühler, Michael Andreas Gerardus Timmer, T H Van Der Meer, Douglas WilcoxAbstract:The design of compact thermoacoustic devices requires compact Jet pump geometries, which can be realized by employing Jet Pumps with multiple orifices. The oscillatory flow through the orifice(s) of a Jet pump generates asymmetric hydrodynamic end effects, which result in a time-averaged pressure drop that can counteract Gedeon streaming in traveling wave thermoacoustic devices. In this study, the performance of Jet Pumps having 1–16 orifices is characterized experimentally in terms of the time-averaged pressure drop and acoustic power dissipation. Upon increasing the number of orifices, a significant decay in the Jet pump performance is observed. Further analysis shows a relation between this performance decay and the diameter of the individual holes. Possible causes of this phenomenon are discussed. Flow visualization is used to study the differences in vortex ring interaction from adjacent Jet pump orifices. The mutual orifice spacing is varied and the corresponding Jet pump performance is measured. The orifice spacing is shown to have less effect on the Jet pump performance compared to increasing the number of orifices
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oscillatory flows in Jet Pumps towards design guidelines for thermoacoustic applications
2016Co-Authors: Joris P. OosterhuisAbstract:Thermoacoustic engines are an interesting alternative to conventional heat engines (such as Stirling engines) due to the absence of moving parts in the hot region and the small temperature difference required to operate. These engines can provide a durable solution in, for example, waste heat recovery applications. Using a traveling wave based configuration, consisting of a toroidal geometry, thermal-to-acoustic efficiencies of up to 30% have been obtained. However, the traveling wave configuration has a major disadvantage: due to the closed looped geometry a time-averaged mass flow, known as "Gedeon streaming", can occur. This type of acoustic streaming can lead to a drastic reduction in efficiency or even prevent the engine from running. Therefore, control of Gedeon streaming is essential in the development of traveling wave thermoacoustic engines. A solution to avoid Gedeon streaming is the application of a Jet pump, which is a component with one or more tapered holes. The oscillatory flow through such an asymmetric geometry results in a time-averaged pressure drop across the Jet pump. By balancing this time-averaged pressure drop with the pressure drop that exists across the regenerator of the thermoacoustic device, Gedeon streaming can be suppressed. In this thesis, the oscillatory flow in Jet Pumps is analyzed. The relation between oscillatory flow features and the performance of Jet Pumps is investigated. Based on this, Jet pump design guidelines have been formulated for laminar oscillatory flows. Flow separation is identified as a main source of performance loss in Jet Pumps and can be avoided by introducing a smooth transition to the tapered inner surface. Compact Jet pump designs can be realized by using multiple smaller tapered holes, but this is accompanied by a slight reduction in performance due to the smaller diameter of the individual holes. Identifying and understanding the flow phenomena in Jet Pumps is shown to be the key to more reliable design calculations for Jet Pumps in thermoacoustic applications.
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characterization and reduction of flow separation in Jet Pumps for laminar oscillatory flows
Journal of the Acoustical Society of America, 2016Co-Authors: Michael Andreas Gerardus Timmer, Joris P. Oosterhuis, Simon Bühler, Douglas Wilcox, T H Van Der MeerAbstract:A computational fluid dynamics model is used to predict the oscillatory flow through tapered cylindrical tube sections (Jet Pumps). The asymmetric shape of Jet Pumps results in a time-averaged pressure drop that can be used to suppress Gedeon streaming in closed-loop thermoacoustic devices. However, previous work has shown that flow separation in the diverging flow direction counteracts the time-averaged pressure drop. In this work, the characteristics of flow separation in Jet Pumps are identified and coupled with the observed Jet pump performance. Furthermore, it is shown that the onset of flow separation can be shifted to larger displacement amplitudes by designs that have a smoother transition between the small opening and the tapered surface of the Jet pump. These design alterations also reduce the duration of separated flow, resulting in more effective and robust Jet Pumps. To make the proposed Jet pump designs more compact without reducing their performance, the minimum big opening radius that can be implemented before the local minor losses have an influence on the Jet pump performance is investigated. To validate the numerical results, they are compared with experimental results for one of the proposed Jet pump designs.
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reducing flow seperation in Jet Pumps
3rd International Workshop on Thermoacoustics 2015, 2015Co-Authors: Michael Andreas Gerardus Timmer, Joris P. Oosterhuis, Simon Bühler, Douglas Wilcox, T H Van Der MeerAbstract:Introduction Jet Pumps are static components that can be used in closed-loop, traveling wave thermoacoustic devices to suppress a time-averaged mass flux (Gedeon streaming) that can exist [2]. The minimization of convective heat transport caused by this mass flux is of vital importance due to the detrimental effect it has on the device’s efficiency. Jet Pumps have an asymmetric shape, resulting in asymmetric minor losses. This causes a time-averaged pressure drop that suppresses Gedeon streaming when the minor losses are tuned correctly [1]. Current Jet pump designs are mainly based on a quasi-steady approximation using minor loss coefficients [1]. A recent numerical study on conventional Jet pump designs has shown that the quasi-steady approximation is only accurate in a small range of operating conditions [4]. It is shown that, above certain wave amplitudes, flow separation occurs during the half-cycle where the bulk flow is moving in the diverging direction of the Jet pump. The flow separation originates from the small Jet pump opening as a result of the local adverse pressure gradient. Due to the flow separation the asymmetry in minor losses diminishes, resulting in a severe downgrade of the Jet pump performance compared with the quasi-steady approximation. The current work will investigate the flow separation behavior by varying the geometry of the Jet pump. The goal is to minimize the flow separation and shift it to higher wave amplitudes, therewith increasing the effectiveness and robustness of Jet Pumps.
Ye Feng - One of the best experts on this subject based on the ideXlab platform.
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performance comparison of Jet Pumps with round and sharp edge of small opening in oscillatory flow
Applied Thermal Engineering, 2018Co-Authors: Ye Feng, Ke Tang, Kaihao Zhang, Rui YangAbstract:Abstract Owing to the capability to induce a time-averaged pressure drop in oscillatory flow, a Jet pump has been used to suppress the Gedeon streaming in a looped thermoacoustic engine. The suppression capacity originates from the asymmetric pressure drop through the Jet pump, and could be enhanced by rounding the edge of the Jet pump in traditional view. This paper systematically probes the rounding effect on a Jet pump and compares the performance of Jet Pumps with round and with sharp edge on small opening. The performance dependences on the taper angle and the cross-sectional area ratios, including the big-to-small opening area ratio of the Jet pump and the small opening-to-pipe cross sectional area ratio, are analyzed and compared for the two types of Jet pump. The results reveal a reversed and higher time-averaged pressure drop in the shape edge Jet pump in contrast to that in the rounded Jet pump. However, the round edge of the small opening can improve working efficiency of a Jet pump.
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effect of taper angle on the performance of Jet Pumps for a loop structured thermoacoustic engine
Journal of the Acoustical Society of America, 2017Co-Authors: Ye Feng, Ke TangAbstract:Gedeon streaming, which circulates throughout the loop configuration with a time-averaged manner in the oscillating flow, can considerably deteriorate the efficiency of traveling-wave thermoacoustic engine. A Jet pump is characterized by a tapered channel with different opening areas, which can produce a time-averaged pressure drop to suppress Gedeon streaming. Three Jet Pumps with different taper angles, i.e., 5°, 9°, 15°, are studied. Following Iguchi's hypothesis, the turbulent oscillating flow can be considered as a steady flow. The flow structures though the Jet Pumps are numerically simulated. Meanwhile, an experimental apparatus has been built to measure the performance of Jet pump operating in the turbulent oscillating flow. The results show that the simulation is in a good agreement with the experiment data for the Jet Pumps with small taper angles. For the Jet pump with 15° taper angle, the simulation results match well with the experiment data when the velocity at small opening of Jet pump is h...
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performance comparison of Jet Pumps with rectangular and circular tapered channels for a loop structured traveling wave thermoacoustic engine
Applied Energy, 2015Co-Authors: Ke Tang, Ye Feng, Mingchun LiAbstract:Gedeon streaming can considerably deteriorate the thermal efficiency of a traveling-wave thermoacoustic engine employing a loop configuration. Introducing a Jet pump into the loop configuration is one of the effective ways to suppress Gedeon streaming. This paper focuses on the performance comparison between the Jet Pumps with rectangular and circular tapered channels, by numerically simulating and analyzing the time-averaged pressure drop induced by the Jet Pumps. Three parameters, i.e., the coefficient of time-averaged resistance, the coefficient of overall resistance, and the coefficient of effectiveness, are proposed to evaluate the performance of a Jet pump. The emphasis is put on the effects of cross-sectional shape, thickness-to-diameter ratio, and rounding radius of the tapered channels. In absence of rounding the edge of the tapered channel, the Jet pump with a rectangular tapered channel is more efficient to produce the time-averaged pressure drop at a large thickness-to-diameter ratio, while the Jet pump with a circular tapered channel is more efficient at a small thickness-to-diameter ratio. However, it should be noted that the directions of the induced time-averaged pressure drops in these two cases are opposite. Rounding the edge of the small opening of the tapered channel can effectively improve Jet pump’s performance. Upon rounding, the Jet pump with a circular tapered channel can produce a higher time-averaged pressure drop and work more efficiently than the one with a rectangular tapered channel.
S A Sherif - One of the best experts on this subject based on the ideXlab platform.
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analysis of two phase supersonic flow in Jet Pumps
ASME 2005 Fluids Engineering Division Summer Meeting, 2005Co-Authors: S M Kandil, W E Lear, S A SherifAbstract:A Jet pump may be constructed from a pair of concentric tubes in which the center tube is shaped as a converging-diverging nozzle. Primary fluid is allowed to accelerate through the nozzle, thus creating a low-pressure region at the nozzle exit. Secondary fluid flowing in the peripheral region is drawn into the low-pressure region and is thus accelerated. In this study, the Jet pump is employed as part of a space thermal-management system based on a cycle known as the Solar Integrated Thermal Management and Power (SITMAP). The latter is a combined vapor compression cycle and a Rankine cycle with the compression device being a Jet pump instead of the regular compressor. The Jet pump has several advantages for space applications as it involves no moving parts, a feature that results in decreasing the weight and vibration level while increasing the system reliability. The working fluid is cryogenic nitrogen, which is readily present onboard the spacecraft. This study presents a detailed component analysis of the Jet pump allowing for two-phase supersonic flow. The model also accounts for Fabri choking either at the inlet or at an aerodynamic throat in the mixing chamber. The model also accounts for flow choking at the exit of the mixing chamber. The different choking situations limit the ability of the Jet pump to entrain more secondary flow once the flow is choked at any location. In this study the various choking regimes will be identified and the entrainment ratios corresponding to the different choking scenarios will be calculated.Copyright © 2005 by ASME
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design considerations of Jet Pumps with supersonic two phase flow and shocks for refrigeration and thermal management applications
International Journal of Energy Research, 2000Co-Authors: W E Lear, S A Sherif, J SteadhamAbstract:This paper describes results of a design-oriented model for two-phase Jet Pumps and ejectors for refrigeration and thermal management aerospace and terrestrial applications. The primary motivation for the work is the development of a reliable but simple design methodology that captures the important flow physics while being sufficiently fast in order to reduce the design cycle time. This work is particularly relevant to the flow boiling test facility under development at the NASA Marshall Space Flight Center as it allows rapid design optimization of the Jet pump as well as the integrated system. The results presented in the paper show optimal geometric area ratio as well as system state point information as a function of the inlet states and entrainment ratio. Qualitative agreement with single-phase ejector performance is predicted, lending additional confidence in the results. Copyright © 2000 John Wiley & Sons, Ltd.
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Effect of Fabri choking on the performance of two-phase Jet Pumps
Collection of Technical Papers. 35th Intersociety Energy Conversion Engineering Conference and Exhibit (IECEC) (Cat. No.00CH37022), 2000Co-Authors: W E Lear, S A Sherif, G.m. ParkerAbstract:This paper explores two-phase flow through a supersonic Jet pump with a constant-area mixing chamber. This work is a continuation of previous work which considered supersonic, two-phase flow through a Jet pump with a constant-pressure mixing chamber. Also considered is the possibility of a phenomenon known as Fabri choking, in which the secondary fluid reaches sonic velocity in the mixing chamber, before mixing with the primary fluid.
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analysis and modeling of a two phase Jet pump of a thermal management system for aerospace applications
International Journal of Mechanical Sciences, 2000Co-Authors: S A Sherif, W E Lear, J Steadham, P Hunt, Jon HolladayAbstract:Jet Pumps are devices capable of pumping fluids to a higher pressure by inducing the motion of a secondary fluid employing a high-speed primary fluid. The main components of a Jet pump are a primary nozzle, secondary fluid injectors, a mixing chamber, a throat, and a diffuser. The work described in this paper models the flow of a two-phase primary fluid inducing a secondary liquid (saturated or subcooled) injected into the Jet pump mixing chamber. The model is capable of accounting for phase transformations due to compression, expansion, and mixing. The model is also capable of incorporating the effects of the temperature and pressure dependency in the analysis. The approach adopted utilizes an isentropic constant-pressure mixing in the mixing chamber and at times employs iterative techniques to determine the flow conditions in the different parts of the Jet pump.
Xinping Long - One of the best experts on this subject based on the ideXlab platform.
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experimental investigation of cavity length pulsation characteristics of Jet Pumps during limited operation stage
Energy, 2018Co-Authors: Jiong Wang, Bin Ji, Shuangjie Xu, Huaiyu Cheng, Junqiang Zhang, Xinping LongAbstract:Abstract Experiments were conducted to investigate the cavity length pulsation characteristics in Jet Pumps with different area ratios during limited operation stage. Images of various cavitating flows were captured and analyzed to study the cavity length pulsation characteristics by high speed camera technology. It was found that the development tendency of time-averaged cavity length can be divided into two sections with different pulsation intensity by throat length. Further analysis indicated that the time-averaged cavity length is a function of area ratio and outlet pressure ratio independent of the inlet pressure. And the time-averaged cavity length decreases slowly and then faster with the increase of comprehensive parameters. Meanwhile, the cavity length pulsation can be decomposed into low frequency component and high frequency component. The pulsation intensity of low frequency component is relatively high during unstable limited operation stage, while it is at a low level during stable limited operation stage. Besides, smaller area ratio and inlet pressure result in larger pulsation intensity of low frequency component during unstable limited operation stage. The experimental points of high frequency component pulsation intensity collapsed around a V-shaped curve and it reached the minimum value when time-averaged cavity length is approximate to the throat length.
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numerical investigation of turbulent flow coherent structures in annular Jet Pumps using the les method
Science China-technological Sciences, 2018Co-Authors: Maosen Xu, Xuelong Yang, Xinping Long, Bin JiAbstract:Annular Jet Pumps that are used in hydraulic machinery have a very simple structure but very complex internal flow fields. Large eddy simulations were used to study the coherent structures in the turbulent flows in annular Jet Pumps with various area ratios, m. The distribution, movement and evolution of the coherent structure in the annular Jet Pumps are described based on vorticity, pressure and Q criteria. All the criteria demonstrate that the vortexes are mainly distributed in the recirculation region and in the mixing and the boundary layers, which have large velocity gradients. The various characteristics of the coherent structures are shown by the different criteria with the vorticity criterion describing the distribution, movement and evolution of the vortexes, the pressure criterion describing the movement and the Q criterion describing the vortex movement and evolution. The vorticity variation in the spanwise direction is larger than the variation in the streamwise direction; however, the streamwise vortex is the main mechanism driving the entrainment of the secondary flow and the mixing. The annular Jet pump with m=3.33 had a higher vortex shedding frequency (about 1000 Hz) than that with m=1.72 (313–417 Hz). The azimuthal instability is the main reason for the generation of the streamwise vortex from the spanwise vortex. The vortex structures in the recirculation region are very strong, but small and disordered with no periodic vortex rings.
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implementation of design of experiment for structural optimization of annular Jet Pumps
Journal of Mechanical Science and Technology, 2016Co-Authors: Zhihuai Xiao, Qinlong Zeng, Longzhou Xiao, Xinping LongAbstract:The DOE (Design of experiments) method together with CFD (Computational fluid dynamics) was applied to optimize structural combination of the Annular Jet Pumps (AJPs). An AJP with an area ratio of 1.75 was selected as the simulation prototype and the numerical results were validated by experiments. According to the DOE method, four impact factors were selected for simulation. The results showed that two-factor’s reciprocal action is more applicable than that of single factor on the AJP’s performance, especially the two groups, α*l t and l t*β, respectively. The structure of AJPs with different area ratios ranging from 1.5 to 40 were optimized by the DOE method. The corresponding optimum structural parameters and performance curves were plotted to acquire the performance envelope lines, the efficiency envelope line and the peak efficiency lines, which are useful for AJP’s structure design and obtaining its operation condition.
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cavitating flow in annular Jet Pumps
International Journal of Multiphase Flow, 2015Co-Authors: Longzhou Xiao, Xinping LongAbstract:Abstract Based on the experimental and numerical methods, the pump performance and inner flow details of annular Jet Pumps under three area ratios (cross sectional area ratio of throat and nozzle) were studied in the present paper. The cavity clouds forming at the shearing layer, recirculation center and throat inlet were captured via high speed video. The realizable k – e turbulence model combined with mixture cavitation model was well validated by experimental results on the pump performance (pressure ratio and pump efficiency) and the static wall pressure distribution. When the annular Jet pump works under the critical working condition, the pressure ratio and the pump efficiency experience a sudden drop. Simultaneously, the flow rate ratio and cavitation number keep constant regardless of the decreasing outlet pressure, since the main flow is filled with cavity clouds. Moreover, the inception and development of cavity cloud induced at the throat inlet were particularly studied in this paper. The cavitation in the throat experiences three stages (incipient, stable and unstable stage) before extending into the diffuser, in which the unstable stage signals the approaching of the critical working condition. The cavity cloud there fluctuates slowly and faintly, while it may suddenly expand over the whole throat and vanish immediately. When the cavity cloud extends into the diffuser with the closure place x / D t D t is the diameter of throat length), there is a low frequency cavity cloud surge. However, the surge disappears as the cavity cloud increases to the intermediate part of the diffuser. Additionally, based on imaging analysis method, the frequency characteristic of the cavity shedding in the diffuser was also studied. The shedding of cavity cloud in the diffuser experiences multiple periodicities when L cav = 3.25 D t (cavity length in diffuser), while there are two fundamental frequencies (58 Hz and 6 Hz) for L cav = 1.1 D t with the higher one corresponding to the shedding frequency. In the case of L cav = 3.25 D t , the detached cavity cloud in the diffuser is pushed downstream only by the re-entrant Jet. However, the main flow plays an important role on accelerating the detached part downstream in the case of L cav = 1.1 D t .
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numerical investigation on the impact of the converging angle of the suction chamber on annular Jet Pumps
IOP Conference Series: Materials Science and Engineering, 2013Co-Authors: Longzhou Xiao, Xinping Long, Weifeng Wu, Yong KangAbstract:The internal flow of an annular Jet pump is an annular wall Jet developed in a limited space, which is affected by its structure, shape, area ratio and flow rate ratio. In this paper, numerical simulation of an annular Jet pump with area ratio A=1.75 was conducted based on realizable k-e turbulence model. And the impact of the converging angle of the suction chamber to the pump performance and the expansion of annular Jet is investigated. According to the simulated results, the following conclusion is obtained. With the converging angle of the suction chamber (α) being 20°, the pump performance turns out to be the best. And with the increasing α, the maximal axial velocity and the squeezing effect to the annular Jet are larger, while the mixing level of the two flows drops. In addition, the half-width of the annular Jet, in the suction chamber, is proportional to tan(α/2) which is the tangent of the half angle of the suction chamber.