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Copyright of Journal of Xi'an Jiaotong University is the property of Editorial Office of Journal of Xi'an Jiaotong University and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In order to study the changes in two‐phase flow parameters after pipeline damage and the impact of gas injection on water leakage from damaged pipelines, experimental and simulation studies were conducted on the damaged pipelines. The main objective is to compare the void fraction in intact and damaged states and to investigate the factors influencing and variations in gas–liquid leakage flow rates. The results show that increasing the liquid superficial velocity can reduce the difference in void fraction distribution caused by different damage directions. The leakage flow rate is affected by the direction of damage and the superficial velocity of the respective phase. It has been discovered that gas injection in the pipeline can make it easier to find small‐area pipeline damage. The change rate of the volume void fraction shows different changes with the increase in gas proportion in different directions; the shape of the bubble has no bearing on this change. [ABSTRACT FROM AUTHOR]

Tip leakage flow affects the flow stability of high-loading compressors significantly. Therefore, a novel approach via induced shock wave near suction-side edge of blade tip was proposed to suppress the strength and influence range of leakage flow in a transonic rotor. Three new schemes with different circumferentially diverging degrees of clearance were designed to reveal the mechanism of the new approach. Through the action of the circumferentially diverging clearance (from the pressure side to the suction side over blade tip), a much more dramatic acceleration of the supersonic leakage jet flow appeared over blade tip of the new schemes. An induced shock wave was produced near the suction side edge of blade tip due to the pressure difference between the discharging leakage flow and the surrounding high-pressure mainflow in tip channel. As a result, both the mass flow rate and the outlet velocity of leakage flow were reduced significantly via the induced shock wave. Meanwhile, the suppressing effect of the new approach on the tip leakage jet flow was closely related to the strength and circumferential location of the induced shock wave. With the aids of the induced shock wave, the largest improvement of tip flow characteristics with an over 5% increase in stall margin was realized in new transonic rotor when the circumferential divergence angle equals 8°, accompanied with no more than a 0.4% decrease in isentropic efficiency. [ABSTRACT FROM AUTHOR]

Copyright of Power Generation Technology is the property of Power Generation Technology Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Power Generation Technology is the property of Power Generation Technology Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

ObjectivesThe operating state under the condition of high-pressure turbine damage will have a certain impact on the performance and vibration of the gas turbine. At present, the means to accurately assess whether the whole machine can continue to be in service was relatively lacking. Therefore, the research on the influence of the tip groove wear and block shedding of the high-pressure turbine rotor blade on the aerodynamic performance and vibration deformation had been carried out.MethodsUsing the three-dimensional numerical simulation method, based on the original tip groove structure of the blade, the influence of five different tip groove damage shapes on typical aerodynamic performance and vibration characteristics of the high pressure turbine was simulated and analyzed.ResultsThe damage of the blade tip groove on the pressure side with falling block, suction side with falling block, trailing edge with falling block, pressure side and trailing edge with falling blocks simultaneous, or pressure side, suction side and trailing edge with falling blocks simultaneous of rotor blades cause an efficiency decrease of 0.44%, 1.6%, 0.03%, 0.67%, and 3.2%, respectively. Different blade squealer tip shapes have a smaller impact on the vibration deformation of the rotor blade, while trailing edge with falling block reduces the deformation of the rotor blade.ConclusionsBased on the analysis results of comprehensive performance and vibration, rotor blades with falling blocks at pressure side, trailing edge, or both can continue to be used. However, it is not recommended to use rotor blades with falling blocks at suction side or pressure side, suction side and trailing edge.

ObjectivesIn order to obtain the refined leakage flow of brush seal and reveal its sealing mechanism, the mathematical model of the leakage flow characteristics of brush seals based on the bristle pack staggered tube bundle model was established.MethodsThe leakage flow rate and characteristics inside the bristle pack of brush seal were investigated by numerical solution of Reynolds-averaged Navier-Stokes (RANS) and shear stress transport (SST) k-ω turbulence model. The leakage and pressure distribution obtained by numerical simulation agrees well with the experimental data, which verifies the reliability of the numerical method. The leakage flow rate and characteristics inside the bristle pack of brush seal was analyzed at four kinds of pressure ratios and rotational speeds.ResultsWith the increase of pressure ratio, tiny vortex begins to appear inside the bristle pack and gradually develops. The obstruction effect on the leakage flow becomes larger, which slows down the trend of leakage increment with the pressure ratio. In addition, the pressure drop of the last row of bristle accounting for the overall pressure differential increases from 13.1% to 26.3%.ConclusionsIn the studied range of rotational speed, the influence of rotational speed on the leakage of brush seal can be ignored. When the pressure ratio is different, the difference in the radial flow strength of the leakage flow in the gap between the last row of bristle and the backing plate and the axial flow strength at the fence height will lead to the difference in the vortex system structure under the backing plate. The sealing mechanism of the brush seal was revealed using the refined leakage flow inside the bristle pack. The research results can provide reference for the leakage flow analysis of brush seal using three-dimensional staggered tube bundle model.

The hydrogen circulation pump (HCP), a device for recovering unconsumed hydrogen gas in fuel cell systems to improve efficiency, is an important equipment in fuel cell systems. Efficient calculation of the output flow rate of the HCP is crucial for accelerating the product development process, but there is a lack of an effective calculation formula for the working clearance leakage. In this paper, a series of HCP models with different working clearances are established and calculated using an overlapping grid simulation method, verifying that the traditional Roots blower leakage flow formula is feasible for HCP, although the maximum calculation error reaches 10.71%. Further study the pressure distribution law inside the HCP chamber, and revise the traditional calculation formula accordingly, so that the average calculation error of the series models is reduced from 5.75% to 3.82%, and the maximum error is also reduced to 7.73%. Compared with the prototype test data, though the flow values obtained from the two calculation formulas are slightly higher, the calculation error of the correction formula is relatively smaller. The research results indicate that the correction formula can more accurately predict the flow rate of HCP and has important application value. [ABSTRACT FROM AUTHOR]

AbstractIn this paper, the fluid-solid interaction of a jet pump of a boiling water reactor type 5 (BWR/5), with its riser subjected to a leakage flow through its slip joint, is reported. This is a fluid-elastic instability problem. A methodology is proposed for the evaluation of the velocity of the fluid at the slip joint with and without a labyrinth seal. It is calculated with computational fluid dynamics. The results show that such a seal reduces the velocity of the fluid and produces a stable and linear behavior between the inlet and the outlet fluid velocities at the slip joint. Then the first five natural frequencies of the jet pump assembly are evaluated. The range is between 24.74 Hz and 60.21 Hz. The mass of water inside and outside of such an assembly is considered. With these data and the dimensions of the slip joint, a finite element mesh is developed and the time step (∆t = 0.001 s) is determined. The fluid and structure mesh are coupled. The fluid flow through the slip joint without a labyrinth seal is evaluated with a two-way fluid-structure interaction under normal conditions of operation. Accelerations up to 8 g can be developed at the bottom of the mixer.The fluid flow is estimated during the first 0.25 s. Flow-induced vibration can be exacerbated in resonance conditions. These values are similar to those obtained in the experimental analyses reported in the open literature. One of the excitation frequencies caused by the interaction between the fluid and the structure was close to the third natural frequency of this assembly (46.99 Hz). If the integrity of the labyrinth seal is maintained, the jet pump will not present high-amplitude oscillations. Therefore, an adequate management of seal degradation is required and failures of the jet pump can be avoided. [ABSTRACT FROM AUTHOR]

Nowadays, axial fans participate in the most important areas of industry and research, including aviation, navy, wind tunnels, cooling towers, and even automobiles. Thus, more emphasis has been placed on improving their aerodynamic performances. It is important to notice that the parameters involved in designing a fan are mainly concerned with aeraulic power, torque and efficiency. This study investigates the utilization of flow control techniques to improve performances of an axial fan equipped with hollow blades, shroud, and hub. These features grant the fan crucial characteristics, namely, its lightweight and facilitate the blowing action by taking advantage on its hollow parts. The fan's performance is evaluated using a steady RANS numerical model with a k-ω SST turbulence closure, which was validated with experimental data. An active control air blowing through a slot was introduced with various positions and dimensions. The results demonstrate a significant improvement in the fan's performance, with an up to 56% increase in aeraulic power gain, accompanied by changes in the overall flow topology, noticed by closely analyzing the flow structure near the tip clearance.

Nowadays, axial fans participate in the most important areas of industry and research, including aviation, navy, wind tunnels, cooling towers, and even automobiles. Thus, more emphasis has been placed on improving their aerodynamic performances. It is important to notice that the parameters involved in designing a fan are mainly concerned with aeraulic power, torque and efficiency. This study investigates the utilization of flow control techniques to improve performances of an axial fan equipped with hollow blades, shroud, and hub. These features grant the fan crucial characteristics, namely, its lightweight and facilitate the blowing action by taking advantage on its hollow parts. The fan's performance is evaluated using a steady RANS numerical model with a k-ω SST turbulence closure, which was validated with experimental data. An active control air blowing through a slot was introduced with various positions and dimensions. The results demonstrate a significant improvement in the fan's performance, with an up to 56% increase in aeraulic power gain, accompanied by changes in the overall flow topology, noticed by closely analyzing the flow structure near the tip clearance. [ABSTRACT FROM AUTHOR]

In the present work, the Auto-Regressive Integrated Moving-Average (ARIMA) forecasting method is used to predict the remaining useful life (RUL) of an axial piston pump used in the hydraulic system applied to the sheet metal industry. The leakage volume from the piston pump is considered a significant parameter for the life prediction analysis using the ARIMA model, as the proposed model uses auto-regressive (AR) and moving-average (MA) modelling for forecasting with high prediction accuracy. The life estimation through the ARIMA model is based on the degradation method of remaining useful life prediction. The life prediction results were in an acceptable range with a forecasting root-mean-square error (RMSE) of 0.3. The investigation results concluded that out of the two forecasting models, i.e., ARIMA (1,1,2) and ARIMA (20,1,2), ARIMA (1,1,2) model has the least forecasting error and also shows better adjustment with the historical data. The RUL of the hydraulic pump considered in the present investigation is predicted to be 28 months. Additionally, the model developed can be used to determine the lifetime of the operational pump and plan its maintenance schedule for hydraulic-operated unmanned vehicles used for off-road applications like mining, agriculture, defence, etc. The proposed RUL forecasting technique can help avoid mechanical systems from uncertain breakdowns and will also play a pivotal role in maintenance. [ABSTRACT FROM AUTHOR]

On the turbocharger, two forms of intake pipe, bending and torsion, are usually used, which leads to a vortex at the inlet of the blade. It has been found that double vortices and massive vortices play a significant role in the working characteristics of the compressor. This project intends to conduct a systematic theoretical and experimental study on the effects of vortex deformation under two different working conditions of bending and torsion on the internal flow field, tip leakage flow field, and impeller load of the impeller. It has been found that the presence of a vortex near the blade entrance changes the static pressure and inflow angle near the blade entrance. The reverse transfer of vortex flow and vortex flow caused by vortex has three critical effects on the working characteristics of the compressor: 1. The change of circumferential static pressure and the pressure gradient of the flow in the impeller. 2. The location and density of the leakage flow on the top surface are significantly changed. 3. Adjust the impeller load’s change and fluctuation when it rotates.

In order to explore the influence of rectangular groove casing on the aerodynamic performance and noise of axial flow fan, the unipolar axial flow fan is taken as the research object. FLUENT is used to numerically calculate the performance of casing fan in each scheme, and Lighthill acoustic analogy is used to predict the noise. The results show that the rectangular groove casing can reduce the total pressure of the fan and improve the efficiency. The flow field in the blade tip region is more disordered, the static pressure on the blade surface is redistributed, the development of the leakage flow is slowed down, and the power capacity of the impeller is reduced. The near-field of the axial fan is dominated by discrete noise, the noise in the tip region is the largest, followed by the trailing edge region, and the noise in the leading edge region is the smallest. The rectangular groove casing has a significant effect on the noise of the fan, and a reasonable slotted structure can reduce the noise of the fan. The reliability of the numerical calculation is verified by experiments, which provides data support and experimental basis for the study of aerodynamic performance and noise of axial flow fan. [ABSTRACT FROM AUTHOR]

A mechatronic axial pump has been widely used for the energy-saving machinery in sustainable agriculture. This study aims to explore the influence of the clearance leakage on the flow field structure in the mechatronic axial pump. The RNG k-ε turbulence model was also utilized to carry out the transient numerical simulation using ANSYS CFX software. The full flow field of the pump was then obtained in the different flow conditions (1 674~2 510 m3 /h). Specifically, a systematic analysis was implemented on the pump pressure, turbulent kinetic energy, and vortex volume field distribution. Radial velocity and impeller efficiency were determined to establish the relationship between rotor friction loss and leakage with the flow rate. The leakage flow was finally clarified in the flow fields of mechatronic axial pump. The results show that the special structure of the stator-rotor clearance part was dominated in the efficiency of the whole mechatronic axial flow pump, compared with the traditional. The main reason was that the operating torque of the stator and rotor was greatly contributed to the friction loss power of the rotor and the total shaft power. 19.1% of the pump shaft power was accounted for the mechanical friction loss power on the outer wall of the rotor at rated operating point. There was the increase in the proportion with the increasing flow rate. The leakage and backflow of the clearance and the mixing effect in the main flow area of the blade were extend the low flow pattern to the main flow area of the internal flow channel of the impeller, thus reducing the operating efficiency of the pump. Therefore, the collaborative design of the motor and impeller was required for the energy saving in the mechatronic axial flow pump, in order to minimize the power lost from the rotor friction and then meet the requirements of hydraulic performance. There was the fluid flow through the motor stator-rotor clearance leakage back to the impeller inlet, the formation of jets, the localized area of high turbulent kinetic energy, strong vorticity, and high radial velocity near the edge wall of the impeller inlet. The inflow conditions were seriously disturbed to increase the hydraulic loss for the low efficiency, such as the uniform inflow at the impeller inlet and the assumption of cylinder independence. The closer to the wheel flange position was, the greater the effect was. A mutually constraining and promoting relationship was formed in the leakage and return flow velocity, as well as the pressure difference between the inlet and outlet of the return flow. Importantly, this relationship was also determined as the internal characteristics of the leakage and returns between the stator and rotor clearances of the pump. At the same time, the amount of leakage, the size and degree of influence of the leakage on the flow field structure were negatively correlated with the flow rate. The leakage flow rate of clearance was reduced to minimize the damage to the flow field at the impeller inlet. The finding can provide a strong reference to improve the performance of mechatronic axial flow pumps. [ABSTRACT FROM AUTHOR]

In order to improve the effectiveness of compressor efficiency measurement results under the influence of complex factors, several research work have been carried out, such as inverse connection of thermocouple suitable for efficiency measurement under low pressure ratio and small temperature rise conditions, torque efficiency correction considering the mechanical loss of high speed gearbox under various working conditions, and identification of the impact of seal cavity leakage flow on efficiency measurement. Compared with the conventional connection method of thermocouple, the inverse connection method of thermocouple shows obvious advantages in efficiency measurement under low pressure ratio and small temperature rise conditions. At medium and low speeds, the conventional simplified correction method will lead to the high measurement results of torque efficiency after installing the high speed gearbox. The accuracy of torque efficiency measurement can be improved by adopting the improved correction method. Increasing the oil supply pressure of the high speed gearbox or reducing the oil supply temperature will increase the mechanical loss of the high speed gearbox. The air flow in the compressor bearing seal chamber will leak into the flow passage through the labyrinth clearance, resulting in discontinuous changes of the inlet/outlet flow of compressor. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Drainage & Irrigation Machinery Engineering / Paiguan Jixie Gongcheng Xuebao is the property of Editorial Department of Drainage & Irrigation Machinery Engineering and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Lubrication Engineering (0254-0150) is the property of Editorial Office of LUBRICATION ENGINEERING and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In order to reduce leakage flow, cavity tips are often used in high-pressure turbines, at the cost of higher thermal load compared to flat tips. To better control the leakage flow and heat transfer at the blade tip, a cavity-filling geometry is proposed in this paper, and the effects of the filling area are also investigated by numerical simulation. The results indicate that the new geometries maintain the advantages of cavity tips in terms of aerodynamic performance. With the cavity filling area increasing, the heat transfer of the new geometries shows a trend of initially increasing and then decreasing. When the front 15% of the blade tip chord length is filled, the average heat transfer of this configuration is reduced by 3.7% compared to the cavity blade tip, and the high heat transfer area is reduced by 23.3%, at the cost of more intensive hot spots. As the cavity-filling area increases from 5% to 15%, the size of the vortexes at the cavity reduces, resulting in a rise in the leakage. Similar behaviors of the tip heat transfer and leakage flow were also found when the turbine pressure ratios varied from 3 to 7, with the cavity-filling geometry.

Extracorporeal centrifugal pumps are widely used in various forms of mechanical circulatory support, including extracorporeal membrane oxygenation and ventricular assist device. A durable centrifugal pump was developed by implementing a new hydrodynamic bearing design that prevents the impeller from touching to the casing wall and provides sufficient washout through the pump to prevent thrombus formation in the pump. The hydrodynamic bearings of the pump are composed of dual annular paths located on both sides of the impeller. Computational fluid dynamics analyses were performed on the flow field inside the pump to estimate the leakage flow through the gap and its impact on the pump efficiency and biocompatibility. The calculations were performed for motor speeds from 3000 to 5000 rpm and flow rates from 1.0 to 9.0 L/min. The leakage flow increased linearly with increasing pressure head of the pump, and the total leakage flow ranged from 2.0 to 27.3% of the total flow. The average wall shear stresses in the casing bottom ranged from 10.6 to 40.9 Pa. The leakage flow of the centrifugal pump with the hydrodynamically levitated impeller had a measurable impact on hydraulic energy losses while enhancing the washout flow to achieve good anti-thrombogenicity. [ABSTRACT FROM AUTHOR]

The present work reports an experimental study of the leakage flow in a low-speed fan ring. Existing 2D Particle Image Velocimetry (PIV) measurements taken in a meridional plane in front of the rotor gap have been further processed and analyzed by means of the Proper Orthogonal Decomposition (POD). Three values of the dimensionless pressure rise across the rotor have been investigated. Namely, attention has been focused on the intermediate case—the one for which a strong radial oscillation in the leakage flow has been observed: POD results have shown that, in this condition, the leakage flow exhibits periodic radial oscillations that are not correlated to the periodic blade passing. Moreover, such coherent motions have been found to promote turbulence transport at different radial positions, whereas rotor-related oscillations have a negligible effect in this sense. The present POD procedure can be generally applied to turbomachinery flows to characterize their unsteady behavior beside the classical phase-averaging methods based on rotor-related quantities. The present approach is novel for the study of leakage flow dynamics in axial fans. [ABSTRACT FROM AUTHOR]

The pressure ratio has an important influence on the performance and internal flow characteristics of the positive displacement pump. In this paper, the influence of the four pressure ratios 1.1/1.2/1.3/1.4 on the internal flow characteristics of the hydrogen circulating pump is studied, the internal relationship between the change of pressure ratio and the flow pattern in the pump are clarified, and the leakage flow pattern and its coupling mechanism in each gap are revealed. The results show that the gap leakage flow induced by pressure difference is an important reason for flow disorder in the pump, however, the generation and growth of gap leakage flow will be affected not only by the pressure difference, but also by the shear drive. The scale and influence of axial gap leakage are far greater than the other two types of gap leakage. The existence of gap leakage flow makes the rate of flow and pressure presents a large amplitude high-frequency pulsation characteristic. The research results of this paper provide a reference for the efficient and stable operation of hydrogen circulating pump in fuel cell system. [Display omitted] • The internal relationship between the pressure ratio and flow pattern is clarified. • The leakage flow pattern and its coupling mechanism in each gap are revealed. • The evolution and propagation law of leakage flow in each gap are discussed. [ABSTRACT FROM AUTHOR]

The turbine blades of aircrafts must be properly cooled to prevent engine failure. Thus, to investigate the influence of the tip structure on the film cooling effect, pressure-sensitive paint test technology was used to determine the adiabatic film cooling effectiveness in this study. The experiment was completed in a cascade comprising three straight blades. The effects of the blowing ratio, density ratio, tip clearance, and tip structure on film cooling efficiency were analyzed. The experimental results demonstrated that, as the blowing ratio increased, the film coverage area and film cooling efficiency increased under most experimental conditions. However, the film cooling efficiency was found to initially increase, and subsequently decrease, as the blowing ratio increased. The respective influences of the density ratio and tip clearance on the film cooling efficiency were found to be significant. The density ratio experiments revealed that a high-density ratio can result in better film coverage than the low-density-ratio air. The tip clearance experimental results indicated that a small tip clearance promotes an increase in film cooling efficiency; this is because the small tip clearance negatively affects the main stream leakage flow, which can reduce the film coverage area. Under the conditions of the Base case 2 configuration, a blowing ratio of 2.1, and a tip clearance of 0.6%h, the average film cooling efficiency of the blade tip was 0.22. Among the three blade tip structures applied in this study, Base case 2 demonstrated higher film cooling efficiency than the other two blade tip structures under the conditions of the same blowing ratio, tip clearance, and density ratio. [ABSTRACT FROM AUTHOR]

In order to explore the flow characteristics at tip clearance and the coupling deformation of the blade during running on the centrifugal air compressor, based on the fluid-structure coupling heat transfer theory, the hydrodynamic and structural mechanics numerical calculation models of the impeller were established. Considering centrifugal force, aerodynamic force and thermal stress, the stress and deformation distribution at the blade tip under different tip clearances were analyzed. The results show that tip clearance can generate inlet separation vortex and tip leakage flow, which together disturb the flow in the main flow zone and increase the flow loss. Under the combined action of centrifugal force, air pressure load and thermal load, the maximum deformation of the blade occurs at about 0. 3 chord length of the blade tip. The maximum deformation of the suction surface is 3. 7% larger than that of the pressure surface. With the decrease of the blade height, deformation decreases gradually. The stress value at the leading edge of blade tip is small, and the maximum stress value at the pressure surface and suction surface is not in the same axial position. With the increase of clearance value, the overall stress value at the top gradually decreases. Through the flow field and structure analysis, the optimum clearance size was determined, and the blade was optimized. The aerodynamic performance and safety of the blade were significantly improved after optimization. [ABSTRACT FROM AUTHOR]

The current study examines the impact of tooth clearance on the flow performance at the location of transition contact of the internal positive displacement trochoidal gear pump. The aim is to enhance the volumetric efficiency, which is caused by internal leakage due to tooth clearance. Two clearance models, that is, form closed and interference (forced closed) models of the pump help to elucidate the leakage phenomenon through which optimal volumetric efficiency can be achieved. Finite element investigation comprises the static structural analysis followed by 3D CFD analysis carried out for the study. The CFD model includes the contact deformations of external trochoidal gear due to the application of maximum pressure, which increases the inter-chamber leakage. Fluid velocity and pressure inside the pump have been predicated to understand the flow dynamics inside the pump. The simulation results were matched to theoretical values, and this shows a very excellent match. The volumetric efficiency of 89% with less than 1 gm/s of leakage has been achieved at a speed of 2500 rpm. Moreover, the simulation results show an increase in discharge flow with the interference model. Further, an empirical relation is established between volumetric efficiency, fluid density, and rotor speed using partial least square regression analysis. [ABSTRACT FROM AUTHOR]

Three-dimensional blading is an efficient technique in compressor aerodynamic design, and its function mechanism in the cantilevered stator needs to be addressed. This paper focuses on the sweep and dihedral in the cantilevered stator and seeks to expose their effects through detailed flow field analysis. Results show that the forward sweep could alleviate the corner flow separation by preventing the accumulation of the secondary flow toward the corner region, resulting in stronger flow separation at the blade trailing edge; in summary, forward sweep with appropriate parameters could increase static pressure rise by 14.3%. The positive dihedral will carry the endwall flow to the upper-span sections, thereby reducing blade corner separation; hence, as much as 23.5% improvement in static pressure rise could be obtained with the appropriate dihedral. Moreover, the combination of a relatively large sweep height and a moderate sweep angle with a low dihedral height and a moderate sweep angle provides optimum aerodynamic performance; the static pressure rise coefficient sees an increment of 25.5% at the near stall point. An experiment is then performed to further validate the theory, which shows a 2% improvement in efficiency of 3D blading at small mass flow rates. However, the secondary leakage should be given attention at high mass flow coefficients, while the corner separation needs further elimination at small mass flow rates. [ABSTRACT FROM AUTHOR]

Axial-flow turbomachinery is widely used in low head water transfer and electricity generation projects. As there is a gap between the impeller and casing of the tubular flow unit, the fluid will cross the gap to form tip leakage flow, which may induce intense pressure pulsation, noise and mechanical vibration, and even threaten the safe operation of the unit. In order to ensure the efficient and stable operation of hydropower units, the influence factors of tip clearance flow and its formation and development mechanism have been deeply studied in this paper. In this paper, the impact of gap width, angle of attack and inlet velocity on tip leakage flow of hydrofoil with clearance are studied by orthogonal experiment method. The results suggest that the gap width has the greatest influence on tip clearance flow, the incidence angle takes the second place, and the inlet velocity has the least effect on tip clearance flow. Then the fractal characteristics of tip leakage vortices with different gap widths are studied. The results demonstrate that the fractal dimension of tip leakage vortices in large gaps was significantly larger than that in small gaps; The fractal dimension of the leakage vortex decreases gradually along the flow direction. [ABSTRACT FROM AUTHOR]

• CFD simulations are conducted for labyrinth seals of a cryogenic liquid expander. • Flow behavior in labyrinth seals with different tooth shapes is explored. • The effect of tooth shape on the leakage is investigated. • The effect of tooth shape on the rotordynamic characteristics is studied. • A parametric study is performed for seal tooth geometric parameters. Cryogenic liquid turbine expanders have been used in many refrigeration systems to save energy, and rotor stability is a top concern in their development. The present study focuses on the influence of tooth geometrical shape on the leakage and rotordynamic characteristics of labyrinth seals in a cryogenic liquid expander, whose rotordynamic characteristics are typically special because of the thermodynamic effect of cryogenic liquid and a large pressure drop. Computational fluid dynamics (CFD) simulations are conducted in thirteen-teeth labyrinth seals with isosceles trapezoid shaped teeth and two types of right-angle trapezoid shaped teeth for a given geometric parameter through the whirling rotor method and total energy model. The flow behavior in the three labyrinth seals with different tooth geometrical shapes is explored, and their influence on the leakage and rotordynamic characteristics of the labyrinth seal is obtained. The results show that the leakage flow rate of the labyrinth seal with front right angle trapezoid shaped teeth is 1.1% and 0.6% less than that with rear right angle trapezoid shaped teeth and isosceles trapezoid shaped teeth, respectively, because of a larger divergence angle and more leakage flow involved in dissipation, while the labyrinth seal with isosceles trapezoid shaped teeth produces a larger fluid-induced tangential force opposite to the direction of whirling velocity and is more favorable for rotor stability. In addition, a parametric study is conducted to analyze the influence of clearance, tooth height, tooth thickness and inclination angle on the leakage and rotordynamic characteristics of the three labyrinth seals. [ABSTRACT FROM AUTHOR]

For the purpose of further enhancing the performance of the cascade, this study takes the high-load diffuser cascade as the research object. By simplifying the design of the cascade with leakage flow in experiments, tests and numerical simulation were conducted at design incidence angle of 0° and the minimum loss incidence angle of -4° for different leakage flow rates and leakage inflow angles. The results show that changes in leakage flow rates and inflow angles will lead to variations in the momentum thickness of the boundary layer at the leading edge of the cascade, thereby affecting the cascade performance. Increasing the leakage flow rate results in an increase in the spanwise and tangential momentum of the leakage flow, a thickening in the axial momentum thickness of the boundary layer at the cascade leading edge, a reduction in the static pressure on the endwall within the cascade passage, a decrease in the expansion capability, and a raising in losses. Increasing the leakage inflow angle results in no change in the spanwise momentum of the leakage flow, an increase in the tangential momentum, a thickening in the tangential momentum thickness of the boundary layer at the cascade leading edge, a gradual increase in the static pressure at the leading edge, but a decrease in the static pressure within the cascade passage, leading to a decrease in the expansion capability. Changes in the tangential momentum of the leakage flow mainly affect the passage vortex, the trailing shedding vortex and the concentrated shedding vortex within the cascade passage. [ABSTRACT FROM AUTHOR]

Variable-geometry turbines present significant improvements in both off-design cycle efficiency and enhanced engine responsiveness for future adaptive cycle engines. The adjustable vanes regulate the through-flow capacity by varying the installation angle and thus unavoidably require endwall clearance, resulting in profound implications for vane and downstream blade rows. Unsteady numerical simulations are carried out to investigate the vane-rotor flow interaction under the zero and partial clearance type of the adjustable vane in a 1.5-stage variable-geometry turbine. First, specific vortical structures and loss characteristics of upstream adjustable vane leakage flow at turning angles of −5°, 0°, and +5° are described. Then, the basic mechanisms of vane-rotor secondary flow interaction between acquired upstream leakage flow and downstream blade rows secondary flow is explored by the time-resolved method and quantitative detailed analysis method. The results show that adjustable vane vortex core area is the primary cause of internal loss within the vortex, and the mixing and interaction between the leakage vortex and other vortex systems contribute to secondary loss in the vane. Due to the downstream blade shear action caused by different flow velocity on the suction and pressure surfaces, the vane leakage flow fragments upon entering the R1 blade passage and develops downstream of the endwall region. Compared to the vane with zero clearance case at same turning angle, the intensity of the R1 tip leakage vortex at the design turning angle and open turning angle is reduced by 47.4 % and 23.66 % with the upstream partial clearance, respectively. The unsteady vane-rotor secondary flow interaction under different turning angles has large influence on the flow structure and loss characteristics of the downstream blade rows, and results in significant differences in the variation pattern and trend direction of the turbine performance. [Display omitted] • Vane-rotor interaction impacts endwall flow structures and turbine efficiency. • Adjustable vane leakage flow intensity varies with vane clearance and turning angles. • Partial clearance reduces downstream vortex intensity and secondary flow losses. • Vane turning angles control flow structures, potentially enhancing performance. • Unsteady effects crucial for evaluating variable-geometry turbine efficiency. [ABSTRACT FROM AUTHOR]

An intimate understanding of the temperature distribution of turbine components is required for advanced and efficient cooling systems and blade designs. Regarding the micro turbine, the stronger tip-leakage flow caused by the dimensional effect has a non-negligible impact on the flow structure in the rotor, which can modify the hot-streak migration and its influence on the turbine. In this study, a numerical simulation is performed on a 1-stage high subsonic micro axial turbine to investigate the effect of tip-clearance height on hot-streak migration. The results show that, in the micro rotor, the relative radial hot-streak migration (towards the blade tip) caused by tip leakage exists a linear relationship between this migration and the clearance height within limits. The hot-streak migration at the blade tip is influenced by the changing of leakage flow and induced vortex, which will change the temperature distribution on the blade surface and tip area. The increase of clearance height will magnify the range of the relative total temperature fluctuation at the rotor-blade surface. An increase of 4.8%h for clearance will lead to an increase of 53.3% (10.4 K from 19.5 K) for the range of the fluctuation.

In comparison to the traditional brush seal, the rotating brush seal installed on a rotating shaft eliminates the influence of friction heat effects and improves the operational stability of the rotating shaft system. Relevant investigations give sparse detailed parameters and experimental data for the rotating brush seal providing insufficient data support and prompting further investigation for the sealing characteristics of the rotating brush seal. In this article, the three-dimensional tube bundle model was regarded as the computational fluid domain of the rotating brush seal. The multi-block structured mesh was applied to discrete the computational domain. The effect of the pressure ratio and rotational speed on the leakage flow and aerodynamic characteristics of the brush seal were numerically investigated using three-dimensional Reynolds-Averaged Navier-Stokes solutions and k - ω S S T turbulence model. Similar to the traditional brush seal, the leakage flow rate of the rotating brush seal increases linearly with the pressure ratio. The effect of the pressure ratio on the flow coefficient is more significant at low pressure ratio. When the pressure ratio increases from 1.5 to 2.5, the flow coefficient increases by 44.40%. However, when the pressure ratio increases from 3.5 to 4.5, the flow coefficient just increases by 4.12%. It means that the flow coefficient shows a trend independent of the pressure ratio at higher pressure ratio. The flow coefficient obtained by computational fluid dynamics model is found to increase lightly as the rotational speed increases. The rear bristles are subjected to large axial aerodynamic force and are prone to axial deformation. The investigation provides the reference for the performance analysis and design of rotating brush seal. [ABSTRACT FROM AUTHOR]

Both the compressor performance and the 3D flows inside the stator passage are significantly impacted by the stator hub gap. The interplay between leakage flow and corner separation within a cantilevered stator of a highly loaded, low-speed axial compressor with a succession of stator hub gaps was examined numerically in this paper. Firstly, the simulated results were compared with the measured results, including the compressor characteristics, the 3D flow structures, and the flow fields at the stator outlet. The results revealed that the used CFD solver, as well as the corresponding setup, can reproduce the flow not only in terms of the trend along with the stator hub gap, but also in terms of the specific scale of the 3D flow structure. Hence, it is feasible enough to be applied in the present investigation. Secondly, the flow mechanisms of the interplay between the corner separation and the leakage flow with different stator hub gaps were analyzed. It was found that the velocity of the leakage flow is the key parameter that dominates the flow structures as well as the compressor performance. Additionally, a simple metric was proposed to be used to choose the optimum stator hub gap. By comparing our results with those from published research, this metric was proven to be feasible. Finally, it is also discussed how the stator hub gap affected the stator inlet flow and rotor performance. It is demonstrated that the stator passage flow blockage can affect the upstream flow field. As a result, the performance of the rotor tends to vary in the opposite direction to that of the stator. [ABSTRACT FROM AUTHOR]

The present work reports an experimental study of the leakage flow in a low-speed fan ring. Existing 2D Particle Image Velocimetry (PIV) measurements taken in a meridional plane in front of the rotor gap have been further processed and analyzed by means of the Proper Orthogonal Decomposition (POD). Three values of the dimensionless pressure rise across the rotor have been investigated. Namely, attention has been focused on the intermediate case—the one for which a strong radial oscillation in the leakage flow has been observed: POD results have shown that, in this condition, the leakage flow exhibits periodic radial oscillations that are not correlated to the periodic blade passing. Moreover, such coherent motions have been found to promote turbulence transport at different radial positions, whereas rotor-related oscillations have a negligible effect in this sense. The present POD procedure can be generally applied to turbomachinery flows to characterize their unsteady behavior beside the classical phase-averaging methods based on rotor-related quantities. The present approach is novel for the study of leakage flow dynamics in axial fans.

Growing performance requirements for gas turbines have led to a continuous increase in gas temperature and pressure ratios. Together with the resulting increase in cooling flows, this requires more and more minimization and control of internal gas leaks. To meet future performance goals, the application of a new seal design and an improved understanding of leakage flow characteristics are of particular importance. The air mass flow through a labyrinth seal designed for a low-pressure turbine has been determined both through analytical calculus and CFD modeling. Different radial clearances and different air temperatures have been considered. In the next stage, the results will be validated through experiments.

The squealer tip with rail crown holes (RCH) is a new tip scheme with excellent comprehensive performance in both tip cooling and leakage flow control in the turbine blade. The coolant radially impacts the leakage flow within the limited clearance space, significantly reducing the leakage flow rate (LFR). Moreover, the coolant ejected from the RCH can simultaneously cover both the rail crown surface (RCS) and cavity floor (CF), achieving efficient utilization of coolant. However, the secondary utilization of coolant within the cavity is very limited. In this study, the streamwise divider wall (SDW) is added inside the cavity to enhance the coolant reattachment on the CF, which can further improve the performance of the squealer tip. The effect of the shape and position of the SDW on the aerodynamic and cooling performance of the tip is investigated, and the evaluation indicators are LFR and film cooling efficiency (η), respectively. Numerical results prove that the SDW significantly enhances the contact effect between the coolant and cavity surface, compared with the Baseline, the average η on the CF increases by 41.76% in the camber line SDW scheme (Case 1). By altering the SDW shape, it is evident that the cavity flow can be reasonably organized by the front part of the SDW, the middle part of the SDW can scrape the pass-over coolant and limit the scraped coolant to the pressure-side cavity, and the rear part of the SDW effectively prevent the accumulation of cavity flow to ensure better coolant filling. As the SDW is shifted towards the pressure-side rail, the η on the tip surface is improved overall. In addition, the position and shape of the SDW have little effect on the total LFR, but have a significant impact on the LFR distribution. In Case 1, the leakage flow can better integrate with the mainstream in the downstream passage, which reduces the pressure gradient in the passage, and thus reduce passage loss. • A novel cooling protection scheme with rail crown holes and a streamwise divider wall is proposed. • The effect of the shape and position of the streamwise divider wall on tip performance is investigated. • The organization effect of the streamwise divider wall on the tip flow structure is summarized. [ABSTRACT FROM AUTHOR]

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The leakage of the pilot stage of the 2D valve mainly depends on the size of its initial opening. According to the Routh criterion, the pilot stage of the two-dimensional magnetically levitated servo-proportional valve (2D-MSP valve) needs to be designed to have certain positive values to increase the damping ratio to improve valve stability, which leads to the leakage flow representing a non-negligible power loss. In order to reduce leakage flow and achieve goal of energy saving, this paper presents a novel resonance stability criterion by considering nonlinear characteristics of the fluid dynamic system. First, the 2D-MSP valve is regarded as a three-way valve-controlled differential cylinder system. Based on the frequency response of the resonance state, the energy conservation method is used to solve the flow "backfilling" area, the motion equation of the cylinder piston (valve spool displacement) and the pressure waveform of the sensing chamber under different opening and pressure amplitude ratio. Then, the analytical expression of the resonance peak amplitude is obtained and the resonance stability criterion is deduced. The result is compared with the Routh stability criterion, which illustrates that the positive openings of the pilot stage can be reduced to one-third of the original value. The prototype valve is then designed and manufactured based on the resonance stability criterion. The dynamic and static characteristics under different system pressures are measured. Experimental results show that the prototype valve is an over-damped system without any overshoot, which has excellent working stability, and its static and dynamic performance can meet the demands of the industry servo-proportional control system. The research work validates the effectiveness of the proposed resonance stability criterion. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Engineering for Thermal Energy & Power / Reneng Dongli Gongcheng is the property of Journal of Engineering for Thermal Energy & Power and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The clearance gaps in twin-screw compressors are critical for their performance and reliable operation, as the leakage flows through these clearances influence the volumetric and adiabatic efficiencies. The amount of leakage flows depends on the clearance size and shape as well as various geometric and operating parameters. Usually, the isentropic nozzle equations along with appropriate flow coefficients are used for more accurate estimation of the leakage flow rates through the clearance gaps. Hence, a proper understanding of the flow coefficients and their relationship with the dimensionless parameters (such as pressure ratio, Reynolds number, and aspect ratios) is critical for an accurate prediction of the leakage flows. In the present study, considering the interlobe clearance gap in screw compressor in terms of rectangular openings, the interlobe leakage flow rates are estimated for various opening sizes and pressure conditions using isentropic nozzle equations and an iterative method. The flow coefficients are determined by comparing the experimental values obtained using a specialized test rig and the flow rates obtained from the analytical methods. The dimensionless parameters are varied to see their individual effect on the leakage mass flow rates and on the flow coefficients. The mean deviation from the experimental results when using an analytical iterative procedure (-8.5%) is substantially lower in comparison to the mean deviation (+26.8%) using the isentropic nozzle equations. The study validates that the iterative method can be preferred (for an interlobe leakage flow rate prediction) over the isentropic nozzle equation method.

Several linearly nonuniform clearances have been designed to explore a novel strategy for attenuation of leakage flow in tip region of high loading transonic rotor and the effects of axially nonuniform clearance on detailed tip flow structure and stable operating range of rotor have been discussed as well. The results showed that the tip flow characteristic of rotor is affected mainly by the combined effects of two parts of low-velocity flow, which are produced by interaction of leakage flow with passage shock and boundary layer separation near suction side, respectively. However, the stall margin of rotor and isentropic efficiency near tip region is dominated significantly by the former part, and the local changes of size and shape of tip clearance have a large influence on it. Once the strength of leakage flow decreases due to clearance size variation, the boundary layer separation near suction side of blade tip worsens gradually and increases additional aerodynamic losses in passage. Both the mass flow rate and mixing losses of the tip leakage flow can be reduced due to a smaller size of clearance existing in front part of clearance of rotor with a linearly divergent clearance shape, and the area of low-velocity region near pressure side has reduced accordingly. By contrast, a linearly convergent shape of tip clearance can increase both the area of low-velocity region and the mixing loss of leakage flow as a result of a larger size of clearance existing over the front part of blade tip of rotor. Eventually, a divergent shape of tip clearance with a reasonable minimum size near leading edge of blade tip is preferred for transonic rotor in consideration of the benefit in stall margin improvement with nearly no penalty in efficiency. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Engineering for Thermal Energy & Power / Reneng Dongli Gongcheng is the property of Journal of Engineering for Thermal Energy & Power and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The interactions of tip leakage flow with mainstream and shock wave result in larger aerodynamic losses and blockage in high loading compressors and tend to be one of the triggers for flow instability. In order to attenuate the influence of leakage flow and improve the stall margin of highly loaded compressor, the new rotors surrounded by tip winglet are investigated by a numerical method. The tip winglet is designed by extending the flat blade tip section in outer 1.5% span of rotor blade. As the angle between the leakage flow and main flow decreases due to winglet, the losses and flow blockage have been weakened near stall condition, and the stall margin of new rotor with pressure-side winglet has an increase of over 10%. The migration and accumulation of low-energy fluids near the corner of casing endwall are affected significantly by tip winglet. As a result, the pressure-side winglet causes an increase of static pressure near the casing corner of pressure surface. Although the driving pressure difference near the leading edge of blade has increased slightly in the tip region, the strength and massflow rate of leakage flow appear to be decreased. As the leakage flow weakens in the new rotor with pressure-side winglet, its interaction with mainstream and shock has been suppressed obviously, and the delay of rotating stall occurs as well. Moreover, the flowfields of the new rotor with pressure-side winglet have been simulated at 40%, 60%, and 80% design speed. It is shown that the flow blockage and losses in the tip region have also reduced near stall point, and an improvement of overall performance is present in the new rotor with pressure-side winglet. All the changes of tip flow structure caused by winglet benefit to an increase of aerodynamic performance of new rotor at full rotational speed range. [ABSTRACT FROM AUTHOR]

Flow around the Guide vanes (GV) in Francis turbine differs with the shape of hydrofoils. The difference in the pressure of fluid travelling to pressure side and suction side of GV contributes to flow behavior. This study presents the numerical technique using alternative clearance gap method to predict the flow around GV and its consequent effect on turbine performance. GV profile has a significant effect on the performance of the turbine with sediment contained fluid flow. In this paper, symmetrical NACA 0012 and cambered NACA 2412, NACA 4412 hydrofoils are studied introducing 0 mm, 2 mm, and 4 mm clearance gaps. Vortex filament can be seen when fluid leaves the clearance gap due to the leakage flow occurring through the gap. The intensity of vortex leaving clearance gap rises with an increase in the size of the clearance gap. However, in the case of asymmetrical GV profile, the velocity of fluid travelling along the vortex compared to that of symmetrical hydrofoil is lower. In case of low specific speed Francis turbines, this vortex is found to be a major reason to erode the runner surface due to high velocity of a sand particle travelling with them. With the alternative clearance gap approach, this paper compares the pressure pulsation downstream of GVs contributed by leakage flow for three NACA profiles, whose frequency is half of blade passing frequency.