带流量调节系统的往复式压缩机连杆轴瓦润滑特性分析

往复式压缩机采用进气流量调节系统后,会导致其连杆轴瓦磨损、烧瓦故障率上升。针对这一问题,以一台2D20的压缩机为例,对流量调节状态下的往复式压缩机连杆轴瓦润滑特性进行了研究。首先,分析了压缩机活塞运动过程中传动机构的作用力,并基于压缩机热力循环过程,构建了含连杆轴瓦润滑油膜的压缩机动力学模型;然后,利用RecurDyn软件对传动机构进行了运动学和动力学仿真分析,并研究了不同流量负荷对活塞杆受力特性的影响;最后,量化分析了10%~100%流量调节负荷对于连杆轴瓦油膜润滑特性的影响。研究结果表明:相比于作用力的换向,十字头销与轴瓦水平相对位置的换向具有明显的滞后性,且在15%~40%的低流量负荷段内,十字头销和衬套组件的两侧润滑效果均有较为明显的恶化;在设备的实际运行过程中,应避免使其长期处于低调节负荷段内运行;该结果可以为设备人员进行压缩机流量优化调节提供实际的参考。

称瓶法测量压缩机流量原理

可压缩介质流量测量方法较多,但高压可压缩流体因压力高,且其气体常数是非理想气体常数,同时介质中又有可能有部分成分会液化,这给流量测量带来诸多困扰,多数常规的测量方法不适用于直接测量,而称瓶法是高压压缩机流量测量可选择的方法之一,本文介绍其原理。

柴油加氢装置中循环氢气压缩机防喘振线分析及修正

本文介绍了循环氢气压缩机的循环流程、技术参数和防喘振调节原理,分析了循环氢气压缩机运行中防喘振阀出现的问题,制定防喘振修正具体方案。通过对防喘振线实际修正,最终得到真实的防喘振线。防喘振线修正后的循环氢气压缩机的运行情况说明,该压缩机防喘振性能曲线的修正是成功的。

Research on variable block size motion estimation algorithm for airborne image

A fast motion estimation algorithm for variable block-size using the ＂line scan and block merge procedure＂ is proposed for airborne image compression modules.Full hardware implementation via FPGA is discussed in detail.The proposed pipelined architecture based on the line scan algorithm is capable of calculating the required 41 motion vectors of various size blocks supported by H.264 within a 16 × 16 block in parallel.An adaptive rate distortion cost function is used for various size block decision.The motion vectors of adjacent small blocks are merged to predict the motion vectors of larger blocks for reducing computation.Experimental results show that our proposed method has lower computational complexity than full search algorithm with slight quality decrease and little bit rate increase.Due to the high real-time processing speed it can be easily realized in hardware.

Performance analysis and improvement of a high flow coefficient centrifugal compressor

Very high flow coefficient centrifugal compressor stages are mostly performance of this type of stages is critical to the entire centrifugal applied as the first stages of multistage compressors. The compressors, but surprisingly little related information is available in the open literature. A centrifugal compressor with high inlet flow coefficient of 0.2, presenting a narrow operating range and unstable running situation even at design speed during the test, is investigated here. To reveal flow details in this centrifugal compressor, numerical simulations have been carried out and indicate that excessive impeller flow diffusion results in the poor performance of this centrifugal compressor. With the same inlet flow coefficient, six redesign cases coming from an in-house one-dimensional analysis program are proposed together with impeller trimming and equal flow area design method for corresponding vaneless diffuser. Performance comparison among these redesign centrifugal compressors is presented and the most suitable one is recommended for test in the future. In addition, three redesign cases with lower inlet flow coefficient developed by means of flow trimming are shown in the end to satisfy potential application areas. Finally, the results in this study can provide valuable reference information for multistage centrifugal compressor design.

Effect of Diffuser Vane Shape on the Performance of a Centrifugal Compressor Stage

The present paper reports the results of experimental investigations on the effect of diffuser vane shape on the performance of a centrifugal compressor stage. These studies were conducted on the chosen stage having a back- ward curved impeller of 500 turn tip diameter and 24.5 mm width and its design flow coefficient is Фd=0.0535. Three different low solidity diffuser vane shapes namely uncarnbered aerofoil, constant thickness flat plate and circular arc cambered constant thickness plate were chosen as the variants for diffuser vane shape and all the three shapes have the same thickness to chord ratio （t/c=0.1）. Flow coefficient, polytropic efficiency, total head coeffi- cient, power coefficient and static pressure recovery coefficient were chosen as the parameters for evaluating the effect of diffuser vane shape on the stage performance. The results show that there is reasonable improvement in stage efficiency and total head coefficient with the use of the chosen diffuser vane shapes as compared to conven- tional vaneless diffuser. It is also noticed that the aero foil shaped LSD has shown better performance when com- pared to flat plate and circular arc profiles. The aerofoil vane shape of the diffuser blade is seen to be tolerant over a considerable range of incidence.

Numerical and Experimental Investigation of an Axial Compressor Flow with Tandem Cascade

Basing on a prototype of DCA airfoil and axial displacement overlap of 10% chord,seven kinds of tangential displacements are taken to simulate the flow conditions in tandem cascade with numerical methods to select a better geometry with higher performance.The configuration with tangential displacement b/t=0.83 would gain better flow performance than the others.On this basis,two configurations with tangential displacement b/t=0.67 and 0.83 among several configurations are chosen to take into experimental investigations by using TR-PIV system to capture the flow velocity instantaneously.The configuration with b/t=0.83 is observed a better flow field performance than b/t=0.67.Its injection flow in the gap zone is much stronger,wake zone area of the front and rear blade is smaller and the stream flow is more improved.It shows that the flow performance in experimental investigation is quite in the same trend as the numerical results predict.

Measurement and Numerical Simulation of a Small Centrifugal Compressor Characteristics at Small or Negative Flow Rate

For centrifugal compressors used in automotive turbochargers, the extension of the surge margin is demanded because of lower engine speed. In order to estimate the surge line exactly, it is required to acquire the compressor characteristics at small or negative flow rate. In this paper, measurement and numerical simulation of the characteristics at small or negative flow rate are carried out. In the measurement, an experimental facility with a valve immediately downstream of the compressor is used to suppress the surge. In the numerical work, a new boundary condition that specifies mass flow rate at the outlet boundary is used to simulate the characteristics around the zero flow rate region. Furthermore, flow field analyses at small or negative flow rate are performed with the numerical results. The separated and re-circulated flow fields are investigated by visualization to identify the origin of losses.

Experimental and Numerical Investigation of the Unsteady Tip Leakage Flow in Axial Compressor Cascade

For convenience of both measurement and adjusting the clearance size and incidence, the current research is mainly conducted by experiments on an axial compressor linear cascade. The characteristics and the condition under which the unsteadiness of tip leakage flow would occur were investigated by dynamic measuring in different clearances, inlet velocities and incidences. From the experiment it is found that increasing tip clearance size or reducing rotor tip incidence can affect the strength of the tip clearance flow. Then the experimental results also indicate the tip leakage shows instability in certain conditions, and the frequency of unsteadiness is great influenced by inflow angle. The condition of occurrence of tip leakage flow unsteadiness is when the leakage flow is strong enough to reach the pressure side of the adjacent blade. The main cause of tip leakage flow unsteadiness is the tip blade loading.

Experimental and Numerical Investigation on Compressor Cascade Flows with Tip Clearance at a Low Reynolds Number Condition

High flow rate aeroengines typically employ axial flow compressors, where aerodynamic loss is predominantly due to secondary flow features such as tip leakage and comer vortices. In very high altitude missions, turbo- machinery operates at low density ambient atmosphere, and the recent trend toward more compact engine core inevitably leads to the reduction of blade size, which in turn increases the relative height of the blade tip clearance. Low Reynolds number fiowfield as a result of these two factors amplifies the relative importance of secondary flow effects. This paper focuses on the behavior of tip leakage flow, investigating by use of both experimental and numerical approaches. In order to understand the complex secondary flow behavior, cascade tests are usually conducted using intrusive probes to determine the loss. However relatively few experimental studies are pub- lished on tip leakage flows which take into account the interaction between a rotating blade row and its casing wall. Hence a new linear cascade facility has been designed with a moving belt casing in order to reproduce more realistic flowfield as encountered by a rotating compressor row. Numerical simulations were also performed to aid in the understanding of the complex flow features. The experimental results indicate a significant difference in the flowfield when the moving belt casing is present. The numerical simulations reveal that the leakage vortex is pulled by the shearing motion of the endwall toward the pressure side of the adjacent blade. The results highlight the importance of casing wall relative motion in analyzing leakage flow effects.

Numerical Investigation of Rotating Stall in Centrifugal Compressor with Vaned and Vaneless Diffuser

This study presents a numerical simulation of the stall and surge in a centrifugal compressor and presents a description of the stall development in two different cases.The first case is for a compressor with vaneless diffuser and the second is for a compressor with vaned diffuser of the vane island shape.The main aim of this study is to compare the flow characteristics and behavior for the two compressors near the surge operating condition and provide further understanding of the diffuser role when back flow occurs at surge.Results showed that for a location near the diffuser entrance,the amplitude of the static pressure fluctuations for the vaneless diffuser case is higher than that for the vaned diffuser case near surge condition.These pressure fluctuations in the case of the vaneless diffuser appear with a gradual decrease of the mean pressure value as a part of the surge cycle.While for the case of the vaned diffuser,the pressure drop during surge occurs faster than the case of the vaneless diffuser.Also,results indicated that during surge in the case of vaneless diffuser,there is a region with low velocity and back flow that appears as a layer connecting all impeller passages near shroud surface and this layer develops in size with time.On the other hand,for the case of vaned diffuser during surge,the low velocity regions appear in random locations in some passages and these regions expand with time towards the shroud surface.Results showed that during stall,the impeller passages are exposed to identical impact from stall cells in the case of vaneless diffuser while the stall effect varies from passage to another in the case of the vaned diffuser.

Performance of a centrifugal compressor with holed casing treatment in the large flowrate condition

As demonstrated by former work,the holed casing treatment can be used to expand the stall margin of a centrifugal compressor with unshrouded impeller.In addition,the choked margin can also be expanded as experimental results indicated.Moreover,the compressor performance,especially the efficiency,on the whole working range is improved.As shown by experiments,the stall margin and choked margin of the compressor are extended,and the maximum efficiency improvement is 14%at the large flowrate of 1.386.Numerical simulations were carried out to analyze the flow in the impeller and in the holes in the case of large flowrate.The results indicate that in large flowrate conditions,there is a low-pressure region on the throat part of the impeller passage,leading to the bypass flows appearing in the holes,which means the flow area at the inlet of the impeller is increased.The bypass flow can also contribute to the decrease of the Mach number at the throat part near the shroud end-wall which implies that the choked margin is expanded.Besides,as the bypass flow would inhibit the development of the vertexes in the tip clearance and suppress the flow recirculation in the shroud end-wall region,both the pressure ratio and efficiency of the compressor are improved,which agrees well with the experiments.

Effects of Inlet Circumferential Fluctuation on the Sweep Aerodynamic Performance of Axial Fans/Compressors

Swept blades have been widely used in the transonic fan/compressor of aircraft engines with the aids of 3D CFD simulation since the design concept of controlling the shock structure was firstly proposed and successfully tested by Dr.Wennerstrom in the 1980s.However,some disadvantage phenomenon has also been induced by excessively 3D blade geometries on the structure stress insufficiency,vibration and reliability.Much confusion in the procedure of design practice leading us to recognize a new view on the flow mechanism of sweep aerodynamical induction: the new radial equilibrium established by the influence of inlet circumferential fluctuation(CF) changes the inlet flows of blading and induces the performance modification of axial fans/compressors blade.The view is verified by simplified models through numerical simulation and circumferentially averaged analysis in the present paper.The results show that the CF source items which originate from design parameters,such as the spanwise distributions of the loading and blading geometries,contribute to the changing of averaged incidence spanwise distribution,and further more affect the performance of axial fans/compressors with swept blades.

Experimental Study on the Inlet Fogging System Using Two-Fluid Nozzles

Large-capacity compressors in industrial plants and the compressors in gas turbine engines consume a considerable amount of power. The compression work is a strong fimction of the ambient air temperature. This increase in compression work presents a significant problem to utilities, generators and power producers when electric demands are high during the hot months. In many petrochemical process industries and gas turbine engines, the in- crease in compression work curtails plant output, demanding more electric power to drive the system. One way to counter this problem is to directly cool the inlet air. Inlet fogging is a popular means of cooling the inlet air to air compressors. In the present study, experiments have been performed to investigate the suitability of two-fluid nozzle for inlet fogging. Compressed air is used as the driving working gas for two-fluid nozzle and water at am- bient conditions is dragged into the high-speed air jet, thus enabling the entrained water to be atomized in a very short distance from the exit of the two-fluid nozzle. The air supply pressure is varied between 2.0 and 5.0 bar and the water flow rate entrained is measured. The flow visualization and temperature and relative humidity measurements are carried out to specify the fogging characteristics of the two-fluid nozzle.

Effects of Suction Side Squealer Tip on the Performance of a Low-Speed Axial Compressor

This paper presents the investigation of the effects of suction side squealer tip on the performance of an axial compressor. The experiment is carded out in a single-stage large-scale low-speed compressor. The investigated tip geometries include fiat tip as the baseline and suction side squealer tip. The tip clearance of the baseline is 0.5% of the blade span. The static pressure rise characteristic curves of both the rotor and the stage are measured. The flow field at the exit of the rotor is measured by a 5-hole probe under design and off-design conditions. The static pressure on the endwall of the rotor passage is also obtained. The results show that the pressure rise characteristic curves obtained by measuring the pressure on the end wall are almost unchanged by using the suction side squealer tip. The measuring results of the 5-hole probe show the static pressure and the total pressure in tip region is slightly greater than that of the flat tip at the design condition at the exit of the rotor. It also leads to greater averaged static pressure rise and total pressure. At the near stall condition, the averaged static pressure and total pressure is lower than the baseline which is related to the redistribution of the blade load caused by the suction side squealer tip.

Non-axisymmetric Flow Characteristics in Centrifugal Compressor

The flow field distribution in centrifugal compressor is significantly affected by the non-axisymmetric geometry structure of the volute.The experimental and numerical simulation methods were adopted in this work to study the compressor flow field distribution with different flow conditions.The results show that the pressure distribution in volute is characterized by the circumferential non-uniform phenomenon and the pressure fluctuation on the high static pressure zone propagates reversely to upstream,which results in the non-axisymmetric flow inside the compressor.The non-uniform level of pressure distribution in large flow condition is higher than that in small flow condition,its effect on the upstream flow field is also stronger.Additionally,the non-uniform circumferential pressure distribution in volute brings the non-axisymmetric flow at impeller outlet.In different flow conditions,the circumferential variation of the absolute flow angle at impeller outlet is also different.Meanwhile,the non-axisymmetric flow characteristics in internal impeller can be also reflected by the distribution of the mass flow.The high static pressure region of the volute corresponds to the decrease of mass flow in upstream blade channel,while the low static pressure zone of the volute corresponds to the increase of the mass flow.In small flow condition,the mass flow difference in the blade channel is bigger than that in the large flow condition.

Homogeneous large deformation analysis of a dielectric elastomer peristaltic actuator

A series of isometric,radially expanding tubular units,made of dielectric elastomer with compliant electrodes,constitute a soft linear peristaltic pump with distributed actuation for transport of incompressible fluids.Based on the Gent strain energy model,this paper theoretically analyzes the homogeneous large deformation of the peristaltic unit.We discuss the effects of axial prestretch on the actuation of the actuator.We then predict the maximum actuation strain of this actuator which is limited by dielectric strength of the polymer.The results presented here extend the previous study based on linear elasticity,and can predict the electromechanical behaviors of the novel actuator at large deformations.