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The effects of gas models on the predicted performance and flow of a centrifugal refrigeration compressor stage

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Science China(Technological Sciences) 2008年第8期51卷 1160-1168页

作者： wang zhiheng XI Guang School of Energy and Power Engineering Xi’an Jiaotong UniversityXi’an 710049China

In this paper three perfect gas models with constant specific heat or with variable specific heat and one real gas model based on the gas property tables are respec- tively considered to implement into the three-dimensional CFD (computational fluid dynamics) analysis of a centrifugal refrigeration compressor stage. The results show that the gas models applied to the CFD code have significant influences on the performance of stage and the flow structures in the stage. Although the ther- modynamics operating condition of evolving fluid in the centrifugal refrigeration compressor has a significant deviation from the perfect gas, the perfect gas model with the modified value of gas constant and the variable specific heat offers a good prediction of stage performance. To predict some basic fluid flow parameters and flow structure accurately, the real gas effects should be considered and the rea- sonably accurate thermodynamic properties based on the analytical gas equation of state or numerical interpolation of gas tables should be applied to the CFD code.

关键词： gas model numerical analysis centrifugal refrigeration compressor

Aerodynamic effects of impeller-diffuser axial misalignment in low-flow-coefficient centrifugal compressor

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Science China(Technological Sciences) 2015年第1期58卷 29-36页

作者： wang zhiheng XI Guang LIU QingFang School of Energy and Power Engineering Xi'an Jiaotong University School of Mathmatics and Statistics Xi'an Jiaotong University

A numerical investigation on the aerodynamic effects of impeller-diffuser axial misalignment in the low-flow-coefficient centrifugal compressor is conducted through three-dimensional CFD *** results show that the flow,especially near the diffuser inlet,is influenced by the axial misalignment *** the impeller offsets to one side,the pressure at diffuser inlet close to this side will descend,and the vortex in the cavity on the other side will partially enter the diffuser and then result in the back *** performances of the stage and its components also change with the impeller-diffuser axial *** exists an optimum offset making the efficiency maximum at a given operating ***,the effect of impeller-diffuser axial misalignment on the axial thrust is *** axial thrust is nearly increased linearly with the increase of axial *** aerodynamic effects of impeller-diffuser axial misalignment in the low-flow-coefficient centrifugal compressor behaves more remarkably at the large flow *** alleviate the aerodynamic effects of impeller-diffuser misalignment,a rounding in the meridional plane at the diffuser inlet can be applied.

关键词： misalignment compressor low flow coefficient impeller

Unsteady flow structures in the tip region for a centrifugal compressor impeller before rotating stall

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Science China(Technological Sciences) 2017年第6期60卷 924-934页

作者： ZHAO HuiJing wang zhiheng XI Guang School of Energy and Power Engineering Xi 'an Jiaotong University Xi'an 710049 China

To get an insight into the occurrence and the mechanism of flow unsteadiness in the tip region of centrifugal compressor impellers, the flow in Krain’s impeller is investigated by using both steady and unsteady RANS solver techniques. It is found that the flow unsteadiness on the pressure side is much stronger than that on the suction side. The periodical frequency of the unsteady flow is around half of the blade passing frequency. The originating mechanism of the flow unsteadiness is illustrated with the time-dependent tip leakage flow and blade loading at the tip region. Due to the blockage caused by the joint effects of broken-downed tip leakage vortex, separated fluids and tip leakage flow at downstream, a low pressure region is formed on the pressure side, consequently the blade loadings is altered. In turn, the changed blade loadings will alter the intensity of tip leakage flow. Such alternative behavior finally results in the periodic process. By comparing the calculated flow field in the cases of single-passage and four-passage models, it is confirmed that the investigated flow unsteadiness is confined in each single passage, as no phase differences are found in the model of four passages. This is different from the situation in axial compressor when the rotating instability is encountered. The flow unsteadiness only occurs at the working conditions with small mass flow rates, and the oscillation intensity will be enhanced with the decrease of mass flow rate. When the mass flow rate is too small, the flow unsteadiness in a single passage may trigger rotating stall, as the disturbance propagates in the circumferential direction.

关键词： centrifugal compressor impeller flow unsteadiness tip leakage flow blade loading

Multi-domain physics-informed neural network for solving heat conduction and conjugate natural convection with discontinuity of temperature gradient on interface

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Science China(Technological Sciences) 2022年第10期65卷 2442-2461页

作者： wang TongSheng wang zhiheng HUANG Zhu XI Guang School of Energy and Power Engineering Xi’an Jiaotong UniversityXi’an 710049China

Deep learning has been increasingly recognized as a promising tool in solving kinds of physical problems beyond powerful approximations. A multi-domain physics-informed neural network(mPINN) is proposed to solve the non-uniform heat conduction and conjugate natural convection with the discontinuity of temperature gradient on the interface. Local radial basis function method(LRBF) is applied to compute the case without the analytical solution and is regarded as the benchmark *** physical domain matches a private neural network and all neural networks are connected by the shared information of temperature and heat flux on the interface. Joint training and separate training are utilized to minimize the loss function, which usually consists of the residual of boundary conditions, interface conditions and governing equations. Joint training minimizes the sum of all losses from neural networks with one shared optimizer, while separate training owns its private optimizer. Local adaptive activation function(LAAF) is used to accelerate the convergence and acquire a lower loss value when compared with its fixed counterpart. The numerical experiments on three types of residual points, uniform, Gauss-Lobatto and random, are conducted and it can be concluded that the uniform residual points can obtain the most accurate solution than the random and Gauss-Lobatto. Joint training is more accurate than the separate training when the number of residual points is relatively small,while the separate training performs better than the joint training for the large number of residual points. Numerous test cases on multi-domain heat transfer and fluid flow show the accuracy of the proposed m PINN. Local and global heat transfer rates show good agreements with the results from LRBF. Excepting the forward problems, the thermal conductivity ratio, the constant source and the characteristic parameters of natural convection are accurately learned from sparsely distributed data points.

关键词： multi-domain physics-informed neural network heat conduction conjugate natural convection interface condition

Real-time object segmentation based on convolutional neural network with saliency optimization for picking

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Journal of Systems Engineering and Electronics 2018年第6期29卷 1300-1307页

作者： CHEN Jinbo wang zhiheng LI Hengyu School of Mechatronic Engineering and Automation Shanghai University

This paper concerns the problem of object segmentation in real-time for picking system. A region proposal method inspired by human glance based on the convolutional neural network is proposed to select promising regions, allowing more processing is reserved only for these regions. The speed of object segmentation is significantly improved by the region proposal *** the combination of the region proposal method based on the convolutional neural network and superpixel method, the category and location information can be used to segment objects and image redundancy is significantly reduced. The processing time is reduced considerably by this to achieve the real time. Experiments show that the proposed method can segment the interested target object in real time on an ordinary laptop.

关键词： convolutional neural network object detection object segmentation superpixel saliency optimization

Investigation of the spike-stall warning method using the blade passing signal

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Science China(Technological Sciences) 2018年第6期61卷 830-842页

作者： ZHAO JiaYi XI Guang wang zhiheng ZHAO Yang School of Energy and Power Engineering Xi＇an Jiaotong University Xi ＇an 710049 China

The vaned-diffuser usually brings compressor instability problems under the small flow rate, for instance the spike-type rotating stall phenomenon which restricts the operation range and may cause the trouble of blade fatigue. Since it is difficult to mathematically predict the spike-type stall for its randomness, finding out a practical method to warning this stall precursor appears to be meaningful. The paper explains the relationship between the spike-type precursor and the blade passing irregularity coefficient to analyze whether this coefficient is appropriate for the spike-stall warning inside a centrifugal compressor with the vaned-diffuser. The advanced wireless measurements were conducted on a 1.5 stages test centrifugal compressor to capture the unsteady behavior progressing from the design to stall inception within the region between the impeller trailing edge(TE) and diffuser leading edge(LE). The circumferential distribution of the blade passing irregularity has been quantitatively *** steep increase of the blade passing irregularity at some "special locations", which is responsible for the onset of the spiketype precursor, is highlighted. Also, to further understand the spike precursor inside the diffuser passage corresponding to the circumferential "special location" with maximum irregularity, the high-response transient measurement within this passage is presented. With the help of full-annulus computational fluid dynamics(CFD) simulation and the mathematical model, it is proved that the blade passing irregularity precisely reflects the flow characteristics during the spike precursor, which presents the guidance for this stall warning method.

关键词： centrifugal compressor transient measurement stall warning blade passing irregularity coefficient

Experimental investigation of transient characteristics of mild surge and diffuser rotating stall in a centrifugal compressor with vaned diffuser

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Science China(Technological Sciences) 2020年第7期63卷 1212-1223页

作者： ZHAO Yang XI Guang ZOU HanSen SUN Ya Wei wang zhiheng National Engineering Research Centre of Fluid Machinery&Compressors Xi’an Jiaotong UniversityXi'an 710049China

The centrifugal compressor is widely used for gas compression in various industrial fields such as aero-engine, gas turbine and turbocharger. However, the stable operating range is usually restricted by the occurrence of flow instability such as stall and surge. The paper experimentally examines the developing process of surge and stall occurring in a centrifugal compressor to advance the understanding on flow mechanism of flow instability. It is found that three types of pressure fluctuation can be observed at low flowrate region. At the critical point, the local stall firstly occurs in some specific diffuser passages and the enlarged local diffuser stall eventually induces the mild surge of compression system indicated by the sinusoidal pressure fluctuation. At lower mass flow rate, the diffuser stall cell begins to circumferentially propagate along the impeller rotating direction at 11% of rotor speed with the existence of mild surge. In comparative analysis of IGV pre-swirl angle on the occurrence of mild surge, the mild surge still occurs at the operating condition when the slope of the characteristic map of test stage is still obviously negative, in which the compression system is supposed to be stable in previous study. And a new suggested criterion for the prediction of mild surge is demonstrated that the occurrence of mild surge depends on the destabilization effect of downstream components about diffuser and volute. Combined with the experimental data, the streamwise distribution characteristic of diffuser stall can be used to develop the simplified model of lumped parameters for the analysis on the generation mechanism of the diffuser rotating stall. The quantitative investigation on the relation between the pressure-rise characteristic of subcomponents and the occurrence of mild surge and diffuser rotating stall not only advances the prediction of stability limit but also lays the theoretic foundation for controlling these unsteady behaviors to improve t

关键词： centrifugal compressor mild surge diffuser rotating stall transient measurement

Review of smart robots for fruit and vegetable picking in agriculture

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International Journal of Agricultural and Biological Engineering 2022年第1期15卷 33-54页

作者： zhiheng wang Yi Xun Yingkuan wang Qinghua Yang Key Laboratory of Special Purpose Equipment and Advanced Processing Technology Ministry of Education&Zhejiang ProvinceCollege of Mechanical EngineeringZhejiang University of TechnologyHangzhou 310023China Academy of Agricultural Planning and Engineering Ministry of Agriculture and Rural AffairsBeijing 100125China Chinese Society of Agricultural Engineering Beijing 100125China

The fruit and vegetable picking has posed a great challenge on the production and markets during the harvest *** picking cannot fully meet the rapid requirements of each market,mainly due to the high labor-intensive and time-consuming tasks,even the aging and shortage of agricultural labor force in recent ***,smart robotics can be an efficient solution to increase the planting areas for the markets in combination with changes in cultivation,preservation,and processing ***,some improvements still need to be performed on these picking *** document the progress in and current status of this field,this study performed a bibliometric *** analysis evaluated the current performance characteristics of various fruit and vegetable picking robots for better prospects in the *** perspectives were proposed covering the robotic arms,end effectors,vision systems,picking environments,and picking performance for the large-scale mechanized production of fruits and vegetables in modern *** current problems of fruit and vegetable picking robots were ***,the outlook of the fruit and vegetable picking robots prospected from four aspects:structured environment for fruit planting,the algorithm of recognition and positioning,picking efficiency,and cost-saving picking *** study comprehensively assesses the current research status,thus helping researchers steer their projects or locate potential collaborators.

关键词： picking robot agricultural robot robot precision agriculture harvest computer vision

Regional differences in the timing of recent air warming during the past four decades in China

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Chinese Science Bulletin 2010年第19期55卷 1968-1973页

作者： wang ShaoPeng wang zhiheng PIAO ShiLong FANG JingYun Department of Ecology College of Urban and Environmental Sciences and Climate Change Research Center Peking University Beijing 100871 China School of Mathematical Sciences Peking University Beijing 100871 China

Global surface temperature has dramatically increased in the past *** is critical to evaluate such a change using appropriate *** previous studies for assessment of the change usually used overall trends of temperature series(*** of simple linear regression of temperature versus year based on a least-square analysis) for entire study *** trends,however,differ among different periods,*** are often breakpoints in the temperature ***,the overall linear trend of a temperature series may conceal some of the temporal characteristics of the temperature *** precisely characterize the temporal and spatial patterns of air temperature change in China,we analyze the annual mean temperature series between the year of 1961?2004 for 536 meteorological stations across China,using piecewise linear regression *** found remarkable breakpoints in the annual mean temperature during the study period across the *** annual mean temperature started to increase in 1984 at a rate of 0.058°C/a at the country *** year when warming started appeared to be gradually later from the north to the south:temperature increased since the 1970s in the north(north of 40°N),and did not rise until the 1980s in most areas of the south(south of 40°N),with warming starting in 1983 in the Tibetan *** trends in annual mean temperatures showed a large spatial heterogeneity across China:a relatively small rising with a rate of 0.025-0.05°C/a in the Sichuan Basin,Central China and South China;the greatest increase in some parts of northwest China(***) with up to a rate of 0.1°C/a;and rising at a rate of >0.05°C/a for most regions of the *** feedbacks of cold waves and snow may be responsible for such regional differences in the timing and rates of warming in China.

关键词：中国西北区域差异气候变暖时间空气年平均气温温度趋势最小二乘分析