Comparison of Rotating Stall Warning by Different Methods for Variable Speed Configurations in a Contra-Rotating Compressor

Stall in compressors can cause performance degradation and even lead to disasters.These unacceptable consequences can be avoided by timely monitoring stall inception and taking effective measures.This paper focused on the rotating stall warning in a low-speed axial contra-rotating compressor.Firstly,the stall disturbance characteristics under different speed configurations were analyzed.The results showed that as the speed ratio(RR)increased,the stall disturbance propagation speed based on the rear rotor speed gradually decreased.Subsequently,the standard deviation(SD)method,the cross-correlation(CC)method,and the discrete wavelet transform(DWT)method were employed to obtain the stall initiation moments of three different speed configurations.It was found that the SD and CC methods did not achieve significant stall warning results in all three speed configurations.Besides,the stall initiation moment obtained by the DWT method at RR=1.125 was one period after the stall had fully developed,which was unacceptable.Therefore,a stall warning method was developed in the present work based on the long short-term memory(LSTM)regression model.By applying the LSTM model,the predicted stall initiation moments of three speed configurations were at the 557th,518th,and 333rd revolution,which were44,2,and 74 revolutions ahead of stall onset moments,respectively.Furthermore,in scenarios where a minor disturbance preceded the stall,the stall warning effect of the LSTM was greatly improved in comparison with the aforementioned three methods.In contrast,when the pressure fluctuation before the stall was relatively small,the differences between the stall initiation moments predicted by these four methods were not significant.

Investigation of the Unsteady Disturbance in Tip Region of a Contra-Rotating Compressor near Stall

The present study investigated the spectrum characteristics of unsteady disturbance and the tip leakage vortex evolution during pre-stall process for a contra-rotating axial compressor(CRAC). Transient numerical simulation was carried out in a single passage of the CRAC. The original transient fluctuation and oscillation of the tip leakage vortex structure with varying flow capacity of the CRAC were revealed using circle-like pattern figure and phase-locked root mean square(PLRMS). Additionally, the tip leakage flow in terms of vortex structure evolution was visualized for the sake of revealing the flow mechanism during pre-stall process. Results show that the unsteady fluctuation first appears at φ=0.3622, and the fluctuation frequency is 2.86 BPF. Unsteady disturbance source is mainly located at the tip side of the downstream rotor leading edge. From the choking point to the near stall condition, tip leakage vortex is always found in the tip leading edge of the upstream rotor. In addition, the tip leakage vortex of upstream rotor remains in the same place over time, i.e., no fluctuation, even when the downstream rotor entered into stall state. Such a phenomenon indicates that the stall point of the contra-rotating compressor is determined by the downstream rotor. Moreover, the maximum fluctuation position is mainly concentrated on the interface between the mainstream and the tip leakage vortex of the downstream rotor. By throttling the compressor, the angle between the main leakage vortex and the circumferential direction decreases gradually. When the main leakage vortex touches and continuously impacts on the leading edge of the adjacent blade, the unsteady disturbance, which is different from that of BPF, appears firstly.

Experimental Investigation on the Development Process of Large-Scale Low-Speed Stall Disturbance in Contra-Rotating Compressor

In order to better understand the stall process of a contra-rotating compressor,the detailed characteristic and multi-channel unsteady pressure signals have been achieved by a special layout of high-frequency response pressure sensors.The array consists of thirty-one high-frequency response dynamic sensors coupled with two optical fiber sensors that were installed on the compressor casing in the direction of circumferential and chordwise of the upstream and downstream of the contra-rotating rotors.A significant hysteresis loop during the stall-recovery process of the contra-rotating compressor was captured successfully.The time series of unsteady signals when the compressor was working on the point of stall occurrence,the period of fully stall,and recovery stall were studied and discussed.Results show a large scale,and low-speed disturbance occurred abruptly at the leading-edge plane of the rear rotor and expands until it passes through both rotors.The single stall cell occupied a circumferential range of 135° and moved in the direction of the rear rotor with an 8.3%shaft speed.As the mass flow rate dropped,the stall cell speed decreases.During the stall recovery process,the rotational speed of disturbance suddenly increased from 7.5%to 18%and even increased to 47%just before the moment when flow recovered axisymmetric.Compared with the rear rotor,the front one dropped out unstable conditions earlier.

Preparation and property of seal coating for gas turbine compressor

Double-layer structure of seal coating which consisted of a Ni5Al bond coating and a Ni25 graphite top coating were prepared on steel substrate of gas turbine compressor cylinder block.Bond coating was prepared by atmospheric plasma spraying and top coating was prepared by flame spraying.The microstructure,mechanical properties and abradability of the coating were characterized by scanning elec-tron microscope(SEM),hardness tester,universal testing machine,thermal shock testing machine and abradability testing machine.The res-ults show that the overall spraying structure of the seal coating is uniform,the nickel metal phase is the skeleton supporting the entire coat-ing,and the coating is well bonded without separation.The seal coating has a bonding strength of not less than 7.7 MPa,excellent thermal stability,and thermal shock resistance cycle numbers at 500℃more than 50;the scratch length,deepest invasion depth and wear amount of the coating increase with rise of test temperature,with almost no coating adhesion,indicating that the seal coating has excellent abradability.

Numerical Study of Co-flow Jet Control on Corner Separation in Compressor Cascade

The design objectives of modern aircraft engines include high load capacity,efficiency,and stability.With increasing loads,the phenomenon of corner separation in compressors intensifies,affecting engine performance and stability.Therefore,the adoption of appropriate flow control technology holds significant academic and engineering significance.This study employs the Reynolds-averaged Navier-Stokes(RANS)method to investigate the effects and mechanisms of active/passive Co-flow Jet(CFJ)control,implemented by introducing full-height and partial height jet slots between the suction surface and end wall of a compressor cascade.The results indicate that passive CFJ control significantly reduces the impact of corner separation at small incidence,with partial-height control further enhancing the effectiveness.The introduction of active CFJ enables separation control at large incidence,improving blade performance under different operating conditions.Active control achieves this by reducing the scale of corner separation vortices,effectively reducing the size of the separation region and enhancing blade performance.

Effect of Time Step Size and Turbulence Model on the Open Water Hydrodynamic Performance Prediction of Contra-Rotating Propellers

A growing interest has been devoted to the contra-rotating propellers （CRPs） due to their high propulsive efficiency, torque balance, low fuel consumption, low cavitations, low noise performance and low hull vibration. Compared with the single-screw system, it is more difficult for the open water performance prediction because forward and aft propellers interact with each other and generate a more complicated flow field around the CRPs system. The current work focuses on the open water performance prediction of contra-rotating propellers by RANS and sliding mesh method considering the effect of computational time step size and turbulence model. The validation study has been performed on two sets of contra-rotating propellers developed by David W Taylor Naval Ship R ＆ D center. Compared with the experimental data, it shows that RANS with sliding mesh method and SST k-ω turbulence model has a good precision in the open water performance prediction of contra-rotating propellers, and small time step size can improve the level of accuracy for CRPs with the same blade number of forward and aft propellers, while a relatively large time step size is a better choice for CRPs with different blade numbers.

Experimental study on performance of contra-rotating axial flow fan

Contra-rotating axial flow fan is a kind of the vital equipment in coal mines. Their work conditions directly affect the safety of staff and production. In the paper, the performance of the contra-rotating axial flow fan is experi- mentally investigated. The study is focused on the fan performance, the shaft power and the match between the motor and fan efficiency at different blade angles. The results show that the blade angle 43°/26° has the best aerodynamic perfor- mance. The first engine has a greater impact on the fan than the second one. The blade angle with the best aerodynamic performance does not necessarily correspond to the one with the best match between the motor and fan efficiency. The blade angle 43°/24° is the best choice for the operation of the fan in the present study.

Unsteady Flow Condition between Front and Rear Rotor of Contra-Rotating Small Sized Axial Fan

Contra-rotating small-sized axial fans are used as cooling fans for electric equipment. In the case of the contra-rotating rotors, the blade row distance between front and rear rotors is a key parameter for the performance and stable operation. The wake and potential interference occur between the front and rear rotors and leakage flow from the front rotor tip influences on the flow condition of the rear rotor near the shroud when the blade row distance is small. Therefore, it is important to clarify the flow condition between front and rear rotors. The fan static pressure curves were obtained by the experimental apparatus and the numerical analysis was also conducted to investigate the internal flow between front and rear rotors. The leakage flow from the front rotor tip reaches the leading edge of the rear rotor when the blade row distance is small as L = 10 mm and the pressure fluctuations at the leading edge of the rear rotor tip becomes larger than those at other radial positions. In the present paper, the vorticity contour between front and rear rotors is shown and pressure fluctuations related to the leakage flow from the front rotor is investigated using the numerical analysis result. Then, suitable blade row distance for the contra-rotating small sized axial fan is discussed based on the internal flow condition.

Study on Contra-Rotating Small-Sized Axial Flow Hydro Turbine

It is thought that small hydropower generation is alternative energy, and the energy potential of small hydropower is large. The efficiency of small hydro turbines is lower than that of large one, and these small hydro turbine’s common problems are out of operation by foreign materials. Then, there are demands for small hydro turbines to keep high per- formance and wide flow passage. Therefore, we adopted contra-rotating rotors which can be expected to achieve high performance and low-solidity rotors with wide flow passage in order to accomplish high performance and stable opera- tion. Final goal on this study is development of an electric appliance type small hydro turbine which has high portability and makes an effective use of the unused small hydro power energy source. In the present paper, the performance and the internal flow conditions in detail of contra-rotating small-sized axial flow hydro turbine are shown as a first step of the research with the numerical flow analysis. Then, a capability adopting contra-rotating rotors to an electric appliance type small hydro turbine was discussed. Furthermore, the high performance design for it was considered by the numeri- cal analysis results.

Modeling and Numerical Simulation of Wings Effect on Turbulent Flow between two contra-rotating cylinders

Many industries in the world take part in the pollution of the environment. This pollution often comes from the reactions of combustion. To optimize these reactions and to minimize pollution, turbulence is a funda- mental tool. Several factors are at the origin of turbulence in the complex flows, among these factors, we can quote the effect of wings in the rotating flows. The interest of this work is to model and to simulate numeri- cally the effect of wings on the level of turbulence in the flow between two contra-rotating cylinders. We have fixed on these two cylinders eight wings uniformly distributed and we have varied the height of the wings to have six values from 2 mm to 20 mm by maintaining the same Reynolds number of rotation. The numerical tool is based on a statistical model in a point using the closing of the second order of the transport equations of the Reynolds stresses (Reynolds Stress Model: RSM). We have modelled wings effect on the flow by a source term added to the equation tangential speed. The results of the numerical simulation showed that all the average and fluctuating variables are affected the value of the kinetic energy of turbulence as those of Reynolds stresses increase with the height of the wings.

Modeling and Numerical Simulation of Wings Effect on Turbulent Flow between Two Contra-Rotating Discs

Turbulence is a fundamentally interesting physical phenomenon which is of fundamental interest. Indeed, it is at the origin of several industrial applications, the control of energy in these industrial applications pass by the comprehension and the modelling of turbulent flows. Several factors are at the origin of turbulence in the complex flows, among these factors, we can quote the effect of wings in the rotating flows. The interest of this work is to model and to simulate numerically the effect of wings on the level of turbulence in the flow between two contra-rotating discs. We have fixed on these two discs eight wings uniformly distributed and we have varied the height of the wings to have eleven values from 0 to 18 mm by maintaining the same Reynolds number of rotation. The numerical tool is based on a statistical model in a point using the closing of the second order of the transport equations of the Reynolds stresses （Reynolds Stress Model： RSM）. We have modelled wings effect on the flow by a source term added to the equation tangential speed. The results of the numerical simulation showed that all the average and fluctuating variables are affected the value of the kinetic energy of turbulence as those of Reynolds stresses increase with the height of the wings.

Characteristics of an Axial-flux Permanent Magnet Synchronous Machine with Contra-rotating Rotors under Unbalanced Load Condition from 3-D Finite Element Analysis

During recent years,the axial-flus PMSM with contra-rotating rotors has become a hot topic in academic research due to its high efficiency and simple structure.However,its back-EMF may be distorted under the condition of different angular positions.This paper investigates characteristics of the novel motor used for contra-propeller driving.Considering the torque ripple and current oscillation under unbalanced load condition,this paper analyzes the distorted back-EMF of the machine when its two rotors get different angular positions during rotating.The analysis results are validated by transient-magnetic 3-D FEA method,which the 3-D FEA software is used to model this motor and transient simulations are carried out to obtain its magnetic characteristic and main performances.A main focus is put on the back-EMF characteristic with different angular positions between the two rotors.Furthermore,the characteristic of torque production under unbalanced load is investigated.Finally,a prototype motor is fabricated to validate the analyses of this paper.

Internal Flow Condition between Front and Rear Rotor of Contra-Rotating Small-Sized Axial Fan at Low Flow Rate

Contra-rotating small-sized fans are used as cooling fans for electric equipment. The internal flow condition between the front and rear rotors of the contra-rotating small-sized fan is not known well especially at the low flow rate. Furthermore, the blade row distance between the front and rear rotors is an important parameter for the contra-rotating small-sized fan and its influence on the internal flow condition is not clarified at the low flow rate. Therefore, the internal flow condition of the contra-rotating small-sized fan at the low flow rate is investigated by the numerical analysis in this research. The numerical analysis results are validated by comparing the fan static pressure curves of the numerical results to the experimental results. The internal flow condition at the low flow rate is clarified using the numerical models of the different blade row distance L = 10 mm and 30 mm. In the present paper, pressure fluctuations phase locked each front and rear rotor’s rotation are shown and the influences of the wake and the potential interference are discussed by the unsteady numerical analysis results at the low flow rate.

Performance and Internal Flow of Contra-Rotating Small-Sized Cooling Fan

High pressure and large flow rate small-sized cooling fans are used for servers in data centers and there is a strong demand to increase its performance because of increase of quantity of heat from servers. Contra-rotating rotors have been adopted for some of high pressure and large flow rate cooling fans to meet the demand. The performance curve of the contra-rotating small-sized cooling fan with 40 mm square casing was investigated by an experimental apparatus and its internal flow condition was clarified by the numerical analysis. The fan static pressure of the front rotor was extremely low and it increased significantly at the rear rotor. The uniform flow was achieved at the inlet of the rear rotor because of the special shape of the casing between the front and rear rotors. On the other hand, the tip leakage flow was large enough to influence on the main flow of the test cooling fan by the design specification of high pressure with compact rotor diameter.

Hybrid URANS/LES Method of Flow Fields in Axial-flow Compressor Rotor Rotor

Accurate and efficient prediction of the aerodynamic performance and flow details of axial-flow com-pressors is of great engineering application value for the aerodynamic design and flow control of axial-flow compres-sors.In this work,a delayed detached eddy simulation method is developed and applied to numerically simulate the tur-bulent channel flow and the aerodynamic performance of NASA Rotor 35.Several acceleration techniques including parallel implementation are also used to speed up the iteration convergence.The mean velocity distribution and Reyn-olds stress distribution in the boundary layer of turbulent channel flow and the aerodynamic performance curve of NASA Rotor 35 are predicted.The good agreement between the present delayed detached eddy simulation results and the available direct numerical simulation results or experimental data confirms the effectiveness of the developed meth-od in the accurate and efficient prediction of complex flow in turbomachinery.

解决农产品配送“断链”的光伏冷链小车设计

在现有普通农用电动货运三轮车的基础上,通过增加1.3m^(3)保温车厢、600Wp太阳能电池板、4块12V100Ah蓄电池、110W直流压缩机等设备,先计算车厢从35℃降至-10℃所需要的冷量,再综合验证组件与蓄电池满足小车一天的制冷与行驶需求。通过精确的系统匹配及智能温度控制,改造成太阳能智能冷链物流小车,很好的解决了现在冷链物流配送中“最后一公里”空缺的问题,经过测试达到设计要求。本车可直接开到田间地头,有方便快捷、耐用、不付电费、造价低等优势,是现代农业物流冷链运输必不可少的中转设备,实现了农村鲜活农产品采摘−物流中心−用户的无缝对接。

多级压缩机气阀寿命评估与极限含水量预测

针对目前油田天然气回注具有介质含水多、压力高且变化范围宽等特点,多级往复式压缩机容易产生水击破坏,如何预测极限含水量以有效防止水击是亟需解决的关键问题。采用计算流体力学方法,数值模拟并分析了多级压缩机注入湿气条件下各级气阀阀片的动力学特性,得到了不同天然气含水量的气阀阀片载荷分布。进一步结合nCode计算疲劳,预测了多级压缩机气阀服役寿命与极限含水量。JGC-4型压缩机模拟计算结果表明:随着进气含水量增大,压缩机排气压力提高,气缸内不断析出水滴,致使水击产生,且对高压级影响更为显著,压缩机整机进气含水体积分数上限为0.43%。研究结果可为多级往复式压缩机的应用提供技术支撑。

涡轮压缩膨胀机的设计与性能分析

随着人们环境保护意识的加强,天然工质制冷剂重新受到研究人员的关注。空气是一种安全且对环境绝对友好的天然制冷剂,未来,压缩空气制冷循环有望成为传统蒸气压缩制冷循环的潜在替代品。压缩膨胀机作为压缩空气制冷的核心部件,其工作效率对机组性能有直接影响。为了设计出能够配合膨胀机高效工作的离心压缩机,需要对传统的设计方法进行一些修正。本文将质量、动量、能量守恒与射流尾迹区理论相结合,并将传统的离心压缩机相关参数推广到较低压力的范围中,提出了一种与现有的涡轮膨胀机相匹配的离心压缩机几何参数的设计方法。使用该方法为现有的膨胀机设计了对应的离心压缩机,并利用其他学者分析过的离心压缩机模型对该方法进行验证,利用计算流体力学方法(CFD)对压缩膨胀机变工况下的工作性能及对膨胀功的利用率进行模拟分析。按本方法设计的离心压缩机在设计工况下能够以高于92%的效率利用膨胀机的输出功。在变工况条件下能够以高于88%的效率利用膨胀机的输出功,并且在设计质量流量附近能够顺利运行。

考虑叶片造型的压气机流动稳定性模型研究进展

压气机实际稳定裕度是否达到指标直接决定了发动机是否可以投入使用.目前的压气机气动设计体系中缺乏一种高效、准确的评估失稳边界的工具,导致在设计定型后依然存在实际稳定裕度不足的风险.因此迫切需要发展快速可靠的压气机稳定性预测工具以供设计阶段使用.现代航空压气机叶片的气动设计朝着三维精细化方向发展,如何在设计阶段考虑叶片三维造型的变化对稳定性的影响愈发关键.传统的激盘/半激盘模型难以精细捕捉到三维叶片造型对流动稳定性的影响,而非定常数值模拟方法对计算资源的消耗在压气机设计阶段难以承受.为了在精细考虑叶片造型影响的同时提高计算效率,为气动设计阶段提供稳定性评估工具,本团队首先在2013年提出了叶轮机流动稳定性通用理论,通过分布式叶片力源项建模考虑复杂叶片造型的影响,通过系统特征值描述流动稳定性.继而针对不同的预测目标和应用条件,发展了3种简化模型:子午面模型、流线模型和径向展开模型.其中子午面模型能够准确刻画叶尖间隙、叶片掠和叶片加载方式等关键设计参数对流动稳定性的影响,为设计阶段提供了一种可靠的失稳边界预测工具;流线模型可以快速评估展向各条流线系统的流动稳定性,并定量地给出流动稳定性最为薄弱的区域,从而有针对性地指导叶片扩稳设计;径向展开模型可以快速地预测离心压气机的流动失稳点,定量评估离心压气机流动稳定性.以上模型可以应用于压气机气动设计体系,为设计定型的压气机提供了可靠的稳定性评估方法,为压气机气动/稳定性一体化设计提供了技术储备.

离心式压气机变工况模拟及轴向力变化机理分析

在相继增压系统切换过程中增压器轴向力的变化会严重影响其稳定性,以Garrett TBP4增压器的压气机端为研究对象,建立了压气机全流道计算域并划分多面体网格,设计7个工况,利用CFD研究了相继增压系统切换过程中的切换时间、切换转速、切换出口压力变化对压气机轴向力的影响规律,同时结合内部流场分析轴向力变化机理。结果表明:切换时间主要影响轴向力的突增时刻,切换转速幅值主要影响最终轴向力的大小,切换出口压力幅值主要影响轴向力突增与否;叶片轴向力受流场影响最大。