Gaps in compressors are generally unfavorable because they lead to energy loss. However, gaps on diffuser blades can broaden the operation range of a compressor. To broaden the operation range of a centrifugal compressor with a tandem diffuser, gaps with different sections and widths on the diffuser blades were examined to determine their influence on the compressor performance. The results show that the compressor's surge margin increased from 33.28% to 49.2% for a 2.5% tip gap ratio, while its stability margin increased from 44% to 60.5%. However, pressure ratio and efficiency losses of 1.16% and 1.14%, respectively, were incurred. Gap widths less than 5% of the height of the diffuser blade are adequate for broadening the operation range, whereas gap ratios greater than 5% cause more energy loss without broadening the operation range further. Gaps can also reduce the Mach number in the diffuser blade channels and can be influenced by the impeller-tip gap. Moreover, diffuser gaps on the shroud side yield better performance than those on the hub side. An experiment was conducted to investigate the reliability of the calculation and conclusions in this study, and the results proved that the conclusions are valid for different types of centrifugal compressors.

离心压缩机在国民经济建设中应用广泛但消耗大量能源.在现有的多级离心式压缩机中,作者已经提出一种整体式静叶片设计方法,该叶片贯穿扩压器、弯道和回流器流道.动/静相互干涉作用对级性能影响很大,通过对比五种不同径向间距的模型进行定常分析,结果表明:当叶轮与整体式静叶片的径向间距为75mm时,模型级最大效率81.36％,压比1.473.与原模型相比,效率提高了3.08％,压比提高了1.8％.通过非定常分析方法,发现随着动叶和整体式静叶片之间距离的增加,静叶片引起压力场的变化对叶轮叶片的影响逐渐减弱,静叶片的进口和出口截面的非定常特性也减弱,即二者的相互作用减弱.同时,叶轮叶片表面静压差变化均匀,也有利于叶轮的安全运行.

The atmospheric-pressure oxygen microwave plasma is employed to enhance the methane combustion in the jet-diffusion combustor. The plasma-assisted combustion (PAC) is compared with natural combustion without plasma application in terms of the flame morphology, flame temperature, and combustion efficiency. It is found experimentally that the oxygen plasma assistance in combustion is prominent in lean oxygen condition, and the active species generated in the microwave plasma torch contribute to the combustion process more dominantly than the flame temperature change caused by heating of oxygen microwave plasma. The combustion degree of CH4 in PAC is much more enhanced in lean oxygen combustion, and the exhaust gas in combustion is effectively controlled with the use of the oxygen microwave plasma torch.

Atmospheric pressure argon plasma jet (APAPJ) is a non-equilibrium plasma producing a large number of electrons, positive ions, excited particles and active groups, which can significantly reduce the activation energy in reactions, and the dynamic effect caused by APAPJ also imposes influence on the transportation process, thereby they both play a very important role in the process of plasma-assisted combustion. In this experiment, By OES, the intermediate radicals (OH, CH and C-2) generated in the non-premixed and premixed combustions are identified. The variation of emission intensity of those radicals is measured with respect to the fuel equivalent ratio and discharge voltage, respectively. It is found that the application of the APPJ causes the overall length of flame to become short and the flame surface appears wrinkled, with the blue area of the flame root continuously enlarged, which accounts for about 1/2 of the total flame area at discharge voltage of 22 kV, indicating that the combustion becomes complete and intense. When the voltage reaches 16 kV, the spectral intensity of the free radical OH(A-X) , CH(A-X) and C-2 (d) becomes remarkable, but when the voltage is 22 kV, the spectral intensity decreases, which is because the plasma enhances the gas flow rate in the tube, causing the combustion region to move away from the nozzle so that the less intensity is collected by fiber during the spectrum acquisition process. In addition, the combustion process of premixed gas assisted by plasma jet under different fuel equivalence radio is studied. In the case of Phi = 2, it is found that the spectral intensity of OH (A - X) increases with discharge voltage, while those of CH (A - X) and C-2 (d) decline when the discharge voltage is large enough that the APPJ is merged into flame near the nozzle. It is found that APAPJ plays an importance role in CH4 combustion in open air due to the active radicals generated in APAPJ and the mixing effect caused by ion wind by APAPJ.

In this paper, the possibility of using hub gap (“ HG ”for short) to suppress gas stall and expand the range of stable working condition of compressor is verified by numerical method. The research shows that when designing flow rate, HG increases, the efficiency and pressure ratio of model level decrease. When there is a large flow, the efficiency and pressure ratio of HG model are higher than those without HG. The larger HG is, the higher the efficiency and pressure ratio is. From the analysis of the expanding stability capacity, the model-level flow margin of small HG and large HG is 5% and 15% higher than that of models without HG, and the comprehensive stall margin is 6.87% and 23.59% higher on average. When operating at unstable working conditions, the action of HG causes the airflow in the high pressure zone to flow into the gap and out of the low pressure zone, which improves the flow distribution in the blade passage and makes the flow field stable. However, when operating near the design condition, the leakage flow and its mixing with the momentum of the mainstream are the main sources of aerodynamic loss. The larger HG is, the greater the pressure loss caused by the leakage flow is. Generally speaking, HG can play the role of compressor expansion stability, but at the cost of efficiency; The bigger HG is, the stronger the role of expanding stability is and the greater the efficiency loss is.

Setting angle of the front blade row of tandem cascade diffuser was investigated experimentally to understand its influence on the performance of centrifugal compressor. Three diffusers with different setting angles were tested. The change of front blade setting angle mainly alters. The angle of attack (AOA) on the leading edge of front blades, which affects the surge point of the compressor. The throat area of the blade row is also modified, which affect the chock point of the compressor. With the increase of setting angle, performance curves of centrifugal compressor move to large flow rate side, the operation range is increased at the same time. In addition, numerical simulation was used to investigate the flow details on the passage of diffuser blades. Overall, the setting angle of front blade row has a significant influence of the performance of centrifugal compressor.

通过数值模拟将一台径向进气的离心压气机,重新设计流道改为轴向进气且增加了回流器,使之同现有的轴向进气实验台进行匹配连接,并进行实验验证.通过对比计算,表明轴向进气方案比原始的径向进气方案设计点的等熵效率降低0.27％,压比降低0.48％,喘振点基本一致,阻塞流量减小0.18％,整体特性曲线基本吻合,实验结果符合设计预期.证明了通过改变流道使径向进气压气机与轴向进气的实验台直接连接的实验方案是可靠的,为后续的实验提供参考依据.此外,还分析了两种方案结果差异的产生机理,为其他压气机设计提供参考思路.

In order to avoid collision with the end wall of the casing when the guide vane rotates around its own rotating axis in a centrifugal compressor, a circular gap will be left at the top of guide vane. Part of the gas flow through the clearance cannot be effectively regulated, and the tip clearance leakage vortex is formed, which has an impact on the mainstream and makes the compressor performance decline. In order to solve this problem, in this paper, three improved schemes of guide vane channel structure, including rectangular channel, cambered channel, and globular channel, were put forward, which can effectively improve the regulation ability of guide vane. Comparing these three improved channels with the original one, the stable operating range of the compressor was enlarged; the power consumption of the compressor was reduced and the efficiency of the compressor was improved. By comprehensive comparison, the cambered channel has better performance and is easier to process, which has potential to be widely used in practice.

The partition structure (PS) between the impeller and stationary blade of a centrifugal compressor considerably influences a compressor's performance. Based on computational fluid dynamics, this study constructed a coupling calculation model for the main flow, wheel cover, wheel disk side partition clearance, and sealing structure. Furthermore, we examined the influence that different PS shapes (i.e. circular arc, trapezoidal, and rectangular) and radial clearances (2, 4, and 6 mm) at the entrance of the cavity between the rotor and stator components have on the aerodynamic performance and loss mechanism of the centrifugal compressor using a numerical method. The influence that the PS has on the transition zone between the impeller outlet and stator inlet sections was analysed in detail. According to the results, when the PS was in a circular arc form, with a clearance of 2 mm, it achieved the highest efficiency, which increased the efficiency of the original model by 0.99% and the total pressure ratio by 1.23%. Moreover, an examination of the main flow interaction provided an enhanced insight into the microflow phenomenon in centrifugal compressors.

基于三维可压缩流体N-S方程和Spalart-Allmaras湍流模型,对多级离心压缩机中间级进行数值计算,研究了不同叶片厚度分布规律对流道式叶片性能的影响.通过分析不同模型级设计工况和变工况的特性及压力场、速度场分布,获得流道式叶片效率和损失分布的变化规律.结果 表明:0.6倍厚度(即9.00 mm)的叶片有最高的级效率82.82％和最大压比1.483,同原有叶片厚度的模型级相比较,整级效率增加1.46％.流道式叶片厚度的变化对压缩机稳定工况的范围影响不大.从近喘工况到堵塞工况,薄叶片在总体性能上优于厚叶片.在近喘工况下,旋涡区分布于叶片进口吸力面;近堵工况下,旋涡区分布于叶片压力面.

Although centrifugal compressors are widely used in construction, they consume a large amount of energy; in existing multistage centrifugal compressors, there is a serious pressure loss of ~15.13% when gas flows through the diffuser, bend, and return channel. In this study, we analyze the loss mechanisms of these stages in detail, using computational fluid dynamics. Based on this analysis, we present a new type of integrated blade, connecting the diffuser, bend, and return channels, which can eliminate the airflow stall phenomenon. Through effective control of the airflow spreading process, we minimized losses in the component, which improved its efficiency by 4.39% and increased the pressure ratio by 2.86% relative to a compressor without the newly-designed integrated blade. The concepts used in the creation of this component can provide a reference for the future design of blades for flow through parts of multistage compressors.

以某制冷用离心压缩机模型级为研究对象,利用数值模拟的方法,对其扩压器进口真实模型进行了详细分析,考察其形状对间隙泄漏量与主流道流动的影响.建立了主流道与密封腔的真实模型,分析发现密封腔的存在对流动造成了很大影响,且扩压器进口形状对内部流动有一定扰动作用.在此基础上,进行了扩压器进口的改进设计.通过分析改进前后结果发现,减小扩压器进口面积能有效减小密封腔对主流道流动的影响,提高模型级效率与压比,但同时也会造成密封泄漏量的增加.

Variable inlet guide vane (IGV) is used to control the mass flow and generate prewhirl in centrifugal compressors. The efficient operation of IGVis limited to the range of aerodynamic characteristics of their vane profiles. In order to find out the best vane profile for IGV regulation, the modern optimization method was adopted to optimize the inlet guide vane profile. The main methodology idea was to use artificial neural network for continuous fitness evaluation and use genetic algorithm for global optimization. After optimization, the regulating performance of IGV has improved significantly, the prewhirl ability has been enhanced greatly, and the pressure loss has been reduced. The mass flow and power of compressor reduced by using the optimized guide vane at large setting angles, and the efficiency increased significantly; the flow field distribution has been improved obviously, since the nonuniform distribution of flow and flow separation phenomenon greatly weakened or even completely disappeared. The achievement of this research can effectively improve the regulation ability of IGV and the performance of compressor.

为了降低叶轮安装端面变形量以及减轻叶轮质量,对快速拆装形式的叶轮轮盘结构进行多目标优化设计,使用拉丁超立方试验设计和有限元分析生成初始样本数据并构造出Kriging近似模型,运用遗传算法对近似模型进行寻优.对优化后的参数值进行工程取整并进行有限元分析得出叶轮轮盘结构设计模型,最终优化结果显示叶轮质量减小了15%,叶轮摩擦端面轴向变形量降低了29%.优化后的叶轮模型可提高拉杆螺栓连接转子结构的可靠性.

The study of Sectional multi-stage pump for a certain parameter is operated.The influence of the traditional radial guide vane (positive and anti-missile leaf) and the space guide vane on the pump performance was compared by numerical simulation,which was verified by experimental results.Based on general CFD software NUMECA,the flow field of the impeller plus the radial guide vane and the space guide vane is analyzed respectively.It is found that the space guide vane is easy to obtain good performance with the large flow area.However,the loss is bigger and it's easier to have a hump head curve under small flow condition.Thus,the radial guide vanes show better performance than the space guide vanes.

用数值模拟方法对风机的性能参数和三维流场结构变化进行分析,研究叶栅稠度对小型多翼离心风机性能的影响.数值模拟结果表明:多翼离心风机的流量、全压、全压效率都随叶栅稠度增大先增大后减小,存在最佳稠度使风机的性能最优;叶栅稠度小时,叶片的负荷大,叶轮容易产生大尺度流动分离,尤其是在径向速度较小的叶顶附近,严重时可能造成风机失速,流动损失增大,风机性能下降;叶栅稠度大时,叶片表面积大,附面层摩擦损失大,风机效率低,同时叶片数多使叶轮通流面积减小,流动阻塞,风机流量降低.

Variable inlet guide vane (VIGV) is used to control the mass flow and generate prewhirl in centrifugal compressors. Due to the tip clearance of the guide vanes and the defect of the traditional guide vane profiles, the mass flow regulation of VIGV is limited, resulting in a large waste of compressed gas. Two kinds of inlet flow channels were proposed to eliminate the influence of tip clearance. These structures were numerically investigated at different setting angles. The results show that the improved channels not only expand the range of mass flow regulation, but also reduce the power and increase the efficiency of the compressor. Ten kinds of guide vane profiles, including different thickness distribution, camber line profile, were selected to compare with the original one and with each other. In the premise of ensuring the performance of compressor, the best guide vane profile was selected. The results show that reducing the guide vane thickness, increasing the guide vane camber angle, and increasing the distance between the maximum camber position and the leading edge of guide vane can help expand the range of mass flow regulation. The achievement of this research can effectively improve the flow regulation ability of VIGV and the performance of compressor.

Impeller is the core part of a centrifugal fan. As the impeller is rotating at a very high speed, the rotor and stator part should not contact at all. The tip clearance has a great influence on the fan efficiency because of the leakage loss and the secondary flow loss. A convex structure on the impeller wheel side was proposed to reduce the strain of the impeller so as to control the impeller tip clearance more accurately. Four new structure were designed and evaluated numerically by ANSYS. The results indicate that the new structure may reduce the axial and radial displacement of the impeller effectively. The design of the convex minimize the leakage loss and secondary flow loss by optimizing the tip clearance.

In order to improve the flow regulation ability of the inlet guide vane in centrifugal compressor,a further study is made based on the previous research results of our research group.Through numerical simulation and calculation of different thickness of curved vanes and different camber position of guide vanes,flow regulation ability was compared and analyzed.The results show that although reducing the thickness of the curved vane can enlarge its flow regulation range,the flow loss can be increased,and the efficiency of the compressor can be reduced.Finally,the best vane profile was selected,which is suitable for the flow regulation of guide vanes,to reduce the waste of compressed gas.