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Numerical Simulation on the Effect of Tip Clearance Size on unsteadiness in Tip Clearance Flow

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Journal of Thermal Science 2008年第4期17卷 337-342页

作者： Juan Du Feng Lin Hongwu Zhang Jingyi Chen Institute of Engineering Thermophysics Chinese Academy of Sciences Beijing 100190 China Key Laboratory of Advanced Energy and Power Chinese Academy of Sciences （Institute of Engineering Thermophysics） Beijing 100190 China Graduate School of Chinese Academy of Sciences Beijing 100190 China

unsteadiness of tip clearance flow with three different tip clearance sizes is numerically investigated in this paper. NASA Rotor 67 is chosen as the computational model. It is found that among all the simulated cases, the un- steadiness exists when the size of the tip clearance is equal to or larger than design tip clearance size. The relative total pressure coefficient contours indicate that region of influence by tip leakage flow augments with the increase of tip clearance size at a fixed mass flow rate. Root Mean Square contours of static pressure distribution in the rotor tip region are provided to illustrate that for design tip clearance （1.1% tip chord） the strongest fluctuating region is located on pressure side of blade near leading edge, while for the larger tip clearance （2.2% tip chord）, it is in the region of the interaction between the shock wave and the tip leakage flow.

关键词： tip clearance flow tip leakage flow unsteadiness transonic rotor

The Self-induced unsteadiness of Tip Leakage Flow in an Axial Low-Speed Compressor with Single Circumferential Casing Groove

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Journal of Thermal Science 2013年第6期22卷 565-572页

作者： DU Juan LI Jichao WANG Kai LIN Feng NIE Chaoqun Institute of Engineering Thermophysics Chinese Academy of Sciences Key Laboratory of Advanced Energy and Power Chinese Academy of Sciences

Numerical investigation on the self-induced unsteadiness of tip leakage flow(TLF) for an axial low-speed compressor with smooth wall and six single grooved casings are presented. A ten-passage numerical scheme is used to solve the unsteady Reynolds averaged Navier-Stokes(URANS) equations. It is found that the single grooves at various axial locations could have a large impact on the self-induced unsteadiness and the stall margin improvement(SMI) of compressor. The trend of SMI with groove center location demonstrates that the groove located near the mid of blade tip chord generates the best SMI. The worst groove is located about 20% Cax after the blade leading edge. The root-mean-squre of static pressure(RMSP) contours at 99.5% span and fast Fourier transform for the static pressure traces recorded in the tip clearance region for each casing are analyzed. The results demonstrate that the single groove location not only affects the oscillating strength but also the frequency of the unsteady tip leakage flow. At the near-stall point of smooth casing, the self-induced unsteadiness of TLF is enhanced most by the best grooved casing for SMI. While, the self-induced unsteadiness disappears when the worst groove for SMI is added. The characteristic frequency of TLF is about 0.55 blade passing frequency(BPF) with smooth casing. The frequency components become complicated as the single groove moves from the leading edge to the trailing edge of the blade.

关键词： Tip leakage flow unsteadiness circumferential groove stall margin improvement

unsteadiness in non-transferred dc arc plasma generators

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Theoretical & Applied Mechanics Letters 2011年第2期1卷 1-7页

作者： Chengkang Wu~(a) and Wenxia Pan Institute of Mechanics,Chinese Academy of Sciences,Beijing 100190,China Institute of Mechanics Chinese Academy of Sciences Beijing 100190 China

Non-transferred dc arc plasma generators are widely used in materials *** are generally considered steadily-operating ***,unsteady phenomena do exist in them, and may cause non-ideal effects in processes which require high controllability and reproducibility. These unsteady phenomena can cause parameter fluctuations in the arc and the plasma jet,some of which have been studied in recent *** types and mechanisms of these phenomena have been *** paper reviews the research progress in this specific area,hoping to present a more complete picture of this subject.

关键词： unsteadiness fluctuation arc plasma jet plasma generator

The diagnosis of central vestibular disorders based on the complementary examination of the vestibulospinal reflex

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Journal of Otology 2022年第1期17卷 1-4页

作者： Stefani Maihoub Andras Molnar Laszl Tamas Agnes Szirmai Department of Otorhinolaryngology and Head and Neck Surgery Faculty of MedicineSemmelweis UniversityBudapestHungary

Objectives:Stance and gait unsteadiness along with vertigo contribute to a central vestibular *** objective analysis ultrasound-computer-craniocorpography(US-COMP-CCG)can be *** of the study was to characterize the unsteadiness in central vestibular disorders and discuss the possible diagnostic usage of *** and results:Hundred-and-ninety patients(70 male and 120 female,mean age±SD,58.94±15.27)suffering from central vestibular disorder and 230 healthy control patients(78 male and 152 female,mean age±SD,50.94±15.27)were *** and gait analysis was according to vestibulospinal tests of *** SPSS V24 software was used for statistical ***-Whitney U test and Chi-square test were used,along with sensitivity and specificity *** significance level was p<*** to schematic and statistical analysis instability and postural sway were increased in the vertigo population and statistically significant difference was *** categorical analysis significant correlation was detected[standing test:longitudinal sway(p<0.00001),lateral sway(p<0.00001),forehead covering area parameters(p=0.0001);stepping test:longitudinal deviation(p=0.05),lateral sway(p=0.011)parameters].Conclusions:Clinicians should consider that postural instability is prominently present in this population and might be of a diagnostic importance.

关键词： unsteadiness Central vestibular disorder Vestibulospinal reflex Ultrasound-computer-craniocorpography

Numerical Investigation of the Unsteady Tip Leakage Flow and Rotating Stall Inception in a Transonic Compressor

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Journal of Thermal Science 2010年第4期19卷 310-317页

作者： Yanfeng Zhang Xingen Lu Wuli Chu Junqiang Zhu School of Power and Energy Northwestern Polytechnical University Xi'an Shaanxi 710072 China Institute of Engineering Thermophysics Chinese Academy of Sciences Beijing 100190 China

It is well known that tip leakage flow has a strong effect on the compressor performance and stability. This paper reports on a numerical investigation of detailed flow structures in an isolated transonic compressor rotor-NASA Rotor 37 at near stall and stalled conditions aimed at improving understanding of changes in 3D tip leakage flow structures with rotating stall *** and unsteady 3D Navier-Stokes analyses were conducted to investigate flow structures in the same *** steady analysis,the predicted results agree well with the experimental data for the estimation of compressor rotor global *** unsteady flow analysis, the unsteady flow nature caused by the breakdown of the tip leakage vortex in blade tip region in the transonic compressor rotor at near stall condition has been captured with a single blade *** the other hand, the time-accurate unsteady computations of multi-blade passage at near stall condition indicate that the unsteady breakdown of the tip leakage vortex triggered the short length-scale-spike type rotating stall inception at blade tip *** was the forward spillage of the tip leakage flow at blade leading edge resulting in the spike stall inception. As the mass flow ratio is decreased,the rotating stall cell was further developed in the blade passage.

关键词： transonic axial-flow compressor tip clearance flow stall inception unsteadiness

Start-up Characteristics of Linear Compressors in a Refrigeration System

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Journal of Thermal Science 2021年第2期30卷 598-609页

作者： ZOU Huiming LI Xuan TANG Mingsheng TIAN Changqing Key Laboratory of Cryogenics Technical Institute of Physics and ChemistryChinese Academy of SciencesBeijing 100190China University of Chinese Academy of Sciences Beijing 100049China

This work investigates the start-up characteristics of linear compressors in a refrigeration system through experiment and *** are carried out by a refrigeration test system with a linear compressor controlled by a LabVIEW platform.A simulation model that considers the nonlinear process of gas force is set up on the basis of Runge-Kutta method for linear *** with the experimental results,the simulation errors are within 15%,including the unstable *** influences of ambient temperature and power frequency on linear compressors are studied through *** phenomena exist at 25℃ ambient temperature compared with the designed ambient temperature of 35℃.The unsteadiness mechanism is analyzed by *** analysis indicated that two sensitive stages of linear compressors,namely,starting to pump and touching top dead center,are ***,properly increasing equivalent mass (approximately 3%) or spring stiffness doring the design stage can be a practical method to improve the stability of linear compressors.

关键词： linear compressor start-up dynamic characteristics unsteadiness

Investigation on reversible pump turbine flow structures and associated pressure field characteristics under different guide vane openings

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Science China(Technological Sciences) 2019年第11期62卷 2052-2074页

作者： BINAMA Maxime SU WenTao CAI WeiHua LI FengChen WEI XianZhu MUHIRWA Alex GONG RuZhi WEKESA David W School of Energy Science and Engineering Harbin Institute of TechnologyHarbin 150001China School of Energy and Power Shenyang Institute of Engineering Shenyang 110136China School of Energy and Power Engineering Northeast Electric Power UniversityJilin 132012China Sino-French Institute of Nuclear Engineering and Technology Sun Yat-Sen UniversityZhuhai 519082China State Key Laboratory of Hydropower Equipment Harbin Institute of Large Electric MachineryHarbin 150040China

The use of reversible pump turbines(RPT) within pumped storage power plants goes with prolonged periods of off-design operating conditions, which leads to the onset of operating mode-dependent instabilities. In order to decrease the gravity of RPT flow instabilities and associated damages or even completely eliminate them, a deep understanding of its onset and development mechanism is needed. In line with this, the present study seeks to numerically investigate the onset and development mechanism of RPT unsteady flow structures as well as the evolutional characteristics of associated pressure pulsations throughout the RPT complete flow passage, under off-design conditions for three GVOs namely 17, 21, and 25 mm. The study results showed that low torque operating conditions and associated vaneless space back flow structures were the trigger of flow unsteadiness onset within the RPT vaneless space, the instabilities which grew to cause the S-shape characteristics appearance. Moreover, the runner flow unsteadiness was found to decrease with the GVO increase. On the other hand, the GVO increase worsened the pressure pulsation levels within RPT flow zones, where pressure pulsations within the vaneless space and flow zones in its vicinities were found to be the most sensitive to GVO changes.

关键词： reversible pump-turbine flow unsteadiness pressure pulsation guide vane opening numerical simulation

The assessment of time dependent flow of Williamson fluid with radiative blood flow against a wedge

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Propulsion and Power Research 2020年第1期9卷 87-99页

作者： K.Subbarayudu S.Suneetha P.Bala Anki Reddy Department of Applied Mathematics Yogi Vemana UniversityKadapa516005India Department of Mathematics S.A.S.Vellore Institute of TechnologyVellore632014India

The present pagination reports both Brownian diffusion and thermophoresis aspects subject to magneto hydrodynamic Williamson fluid *** the flow is unsteady and blood is treated as Williamson fluid over a wedge with *** governing equations are transformed into ordinary differential equations by using similarity *** analytical solutions of the transformed governing equations are obtained by using the RK 4th order method along with shooting technique *** effects of various physical parameters such as Hartmann number,local Weissenberg number,radiation parameter,unsteadiness parameter,Prandtl number,Lewis number,Brownian diffusion,thermophoresis,wedge angle parameter,moving wedge parameter,on velocity,temperature,concentration,skin friction,heat transfer rate and mass transfer rate have been discussed in *** velocity and temperature profile deprives for larger We and an opposite trend is observed for *** radiation parameter is propositional to temperature and a counter behaviour is observed for Pr.

关键词： The present pagination reports both Brownian diffusion and thermophoresis aspects subject to magneto hydrodynamic Williamson fluid model. Assuming the flow is unsteady and blood is treated as Williamson fluid over a wedge with radiation. The governing equations are transformed into ordinary differential equations by using similarity variables. The analytical solutions of the transformed governing equations are obtained by using the RK 4th order method along with shooting technique solver. The effects of various physical parameters such as Hartmann number local Weissenberg number radiation parameter unsteadiness parameter Prandtl number Lewis number Brownian diffusion thermophoresis wedge angle parameter moving wedge parameter on velocity temperature concentration skin friction heat transfer rate and mass transfer rate have been discussed in detail. The velocity and temperature profile deprives for larger We and an opposite trend is observed for concentration. The radiation parameter is propositional to temperature and a counter behaviour is observed for Pr.

A modified predictive model for estimating gas flow rate in horizontal drain hole

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Petroleum 2019年第1期5卷 35-41页

作者： Fadairo Adesina Oladepo Adebowale Adeyemi Gbadegesin Petroleum Engineering Department Covenant UniversityOtaNigeria

Accurate prediction of the flow rate of horizontal gas well is necessary for economic feasibility,planning and development of gas *** of the early models assumed that the production from the horizontal well is infinitely conductive except few recent *** recent models reported in the literature for estimating flow rate in horizontal well where the pressure losses due to friction along horizontal drain hole was *** improved model that checks the impact of all possible well bore pressure losses on gas production rate of horizontal well is *** neglected impact of well bore pressure losses due to fluid accumulation and kinetic energy in the past models is thought to be a conceivable reason for the inconsistency between computed rates from the models and rates got from production *** new model was validated using the same field contextual investigation utilized by Guo et *** outcome got from the new model yields more satisfactory results.A more realistic results that evident all flow phenomena in gas well include the initial unsteady,pseudo-steady and steady state flow condition hence flow rate at any given production time has been established for flow of gas along horizontal *** outcomes of the study demonstrate that the percentage deviation of the new model at steady state flow condition is less than 5.0%compared with 11.05%acquired from Guo et *** following by 259.7%from Furui's model,and 1118.2%got from Joshi's *** work gives field operators a precise and helpful device for prediction and assessment of production in a gas horizontal well.

关键词： Flow rate Horizontal well unsteadiness Steadiness Well bore pressure losses