分流叶片周向位置设计及其对离心叶轮内部流动的影响

利用计算流体力学软件,对某高压比、高转速、小流量离心式压气机的半开式叶轮内部三维粘性流场进行了数值模拟研究。重点分析了分流叶片周向位置对叶轮内部流动和性能的影响,提出了适合此半开式离心叶轮分流叶片周向位置的设计方案。结果表明：分流叶片不同周向位置对流场影响明显,当分流叶片偏向长叶片吸力面侧时,叶轮流道内低速区增大,流动分布不均匀。研究还发现：固定分流叶片进口而将出口位置向长叶片压力面侧偏置,可以改善叶轮内部流动情况,提高叶轮性能。     

跨音速离心压气机级间静压测量研究

为获得车用涡轮增压器离心压气机各元件进出口及周向静压分布,开展了跨音速离心压气机级间静压测试研究。研究结果表明:蜗舌结构未造成导风轮进口静压分布周向不均匀(导风轮进口周向压力波动在2.5 kPa之内);蜗舌结构导致短叶片轮缘静压分布的周向不均匀性;同一转速下,跨音速流动最高效率工况周向静压分布不均匀;叶轮跨音速时,蜗壳沿着流动方向进行减速扩压;同一转速下,扩压器静压提升变化很小(约在3 kPa之内),而叶轮静压提升变化很大(约13～50 kPa),叶轮静压提升的改变决定压比流量特性线的陡峭程度。     

来流预旋对离心压缩机级间部件性能的影响

利用CFD技术,重点研究了来流周向预旋对多级离心压缩机级间弯道与回流叶栅等静止部件内气动性能的影响.结果表明:弯道内均存在不同程度的流动分离,且分离区的大小随来流周向预旋的增强而增大;降低来流周向预旋能有效地抑制弯道内流动分离,并能使弯道出口(即回流叶栅进口)气流更趋于均匀,这有助于提高回流叶栅的气动性能;回流叶栅内的流动是非均匀、不稳定、剧烈分离的旋涡流动,沿主流方向存在着复杂的二次涡结构,这些二次流旋涡随主流经历着明显的"初生、发展、耗散、溃灭"的过程.     

预旋对迷宫密封内流动传热特性影响的研究

采用三维周期性模型对发散型光滑面迷宫密封内传热及流动特性进行了研究,得出了两种流量下有无进口预旋时密封的间隙热系数随周向马赫数的变化关系,并与实验值、经验公式、二维轴对称模型得到的结果进行了比较,结果表明:该模型能较好地模拟有进口预旋时迷宫密封内的传热特性.在相同的流量和进口预旋比条件下,间隙热系数随转速的增加而增大;在相同流量和转速下,施加进口预旋能明显降低密封内总温升、减小间隙热系数,但不会影响子午面上的速度场;在相同转速和预旋比条件下,随着流量的增大,间隙热系数减小,子午面上速度增大,但流场结构不会发生变化.     

船用燃气轮机预旋系统增压设计及仿真

为了提高船用燃气轮机进口燃气压力和温度,涡轮冷却空气应当具备更大的压力来满足叶片表面气膜冷却的需求。本文优化现有的预旋系统,通过在供气孔入口布置增压叶轮,减少气流经预旋喷嘴射入盘腔和经盘腔进入供气孔的突扩损失。运用数值计算的方法对预旋系统模型进行研究,所采用的计算模型和冷吹实验与1.0设计工况数据对比具有较好的精度。研究表明：增压预旋系统和常用预旋系统具有相似的流场结构,但预旋腔内形成的涡更小,有效抑制了气流在腔内的总压损失;在增压叶轮和结构改进的作用下,冷气相对总压提高2.90%,绝对总压提高4.59%,同时增压所产生的温升变化较小,提高了冷却空气的冷却能力。     

垂直螺旋风力叶片周围的三维流动特征分析

提出一种新型的垂直轴螺旋风力叶片,分析叶片附近的流动特征与叶轮力矩特性之间的关联.采用计算流体动力学(CFD)方法,运用Spalart-Allmaras湍流模型,对两叶片叶轮内外的三维湍流流动进行数值计算.分析设计风速下的叶轮力矩系数;在来流速度为4m/s的低风速条件下,对最大力矩系数工况和最小力矩系数工况下的流动参数分布和空间流动结构进行对比研究.研究结果表明:该叶轮的力矩特性较好;叶片两侧的压差和大尺度低压区的位置是影响该叶轮运行特性的两个重要因素;叶片附近的流动具有明显的三维空间结构.     

带进汽腔体的整圈斜置静叶的数值研究

基于某超超临界机组的汽轮机中压缸数据,对带进汽腔体的整圈斜置静叶进行了数值模拟.通过对进口流动角度的分布、不同周向位置叶片的表面压力分布、相对应的速度矢量图和压力云图以及斜置静叶下游流动参数的分析,研究了进汽腔体所带来的周向不对称性对下游叶片流动的影响,以及上游的周向不均匀性经过斜置静叶后的变化.结果表明:进汽腔周向进气的不对称性使周向进气角有偏差,导致冲角沿周向产生较大波动;气流经静叶之后,周向不均匀性会减弱.在设计第一级静叶时,应选择对来流进气角度不敏感的翼型.     

导叶预旋角对叶轮/扩压器相干的影响

在不同进口导叶预旋角度下,采用非定常的方法对进口导叶/叶轮/扩压器3部件之间非定常相干进行了数值模拟,并与实验结果作比较。研究了进口导叶预旋角度对叶轮及扩压器内部流动及非定常性的影响,同时探讨了3部件之间动静相干的机理。结果表明,计算结果同实验结果吻合很好。在同等流量下,进口导叶的尾流和大尺寸涡团的非定常作用使得叶轮和扩压器上的非定常性减小,其变化弧度仅在原来的1/4左右。进口导叶为负预旋时,由进口导叶尾流所带来的非定常影响比进口导叶正预旋角度下小的多,但叶轮尾流及扩压器的势反冲效应所引起的非定常效应却较正预旋角度下有所增大。     

离心压气机轮缘压力及间隙泄漏非轴对称现象研究

蜗壳通常被设计成螺旋状结构,其几何结构的周向不对称诱发蜗壳内部流场周向分布不均匀现象,会对压气机内部流场造成显著影响.采用试验和数值结合的方法,对两种流量工况下离心压气机内部的非轴对称流动特性进行研究.结果表明:压气机轮缘静压在周向上的分布具有与蜗壳内部相同特征的非轴对称形式;下游流场畸变在向上游逆向传播过程中对上游的影响逐渐减弱;叶轮出口轮缘周向的高压区传播至叶轮进口时,与叶轮出口高压区的周向位置存在相位差.在不同流量工况下,轮缘周向静压分布不均导致叶顶间隙泄漏流在周向的分布存在差异.在小流量工况下,泄漏流量呈现先减小后增大再减小的波动分布;在大流量工况下,泄漏流量呈现先增大后持续减小分布.     

水汽比对涡轮预旋供气系统温降影响的数值分析

为了揭示喷水冷却所引起湿空气环境对涡轮供气系统温度的影响,基于欧拉-拉格朗日多相流颗粒追踪方法,在预旋供气系统进口总压150 kPa和总温450 K条件下,开展湿空气对预旋供气系统温降的影响程度评估,分析预旋供气系统内旋转比和预旋喷嘴流量系数的变化规律,揭示预旋供气系统温降的影响规律。结果表明：在水汽比由0增加到0.3时,水汽比变化对预旋喷嘴内流动和温度变化影响显著,预旋喷嘴的气流旋转比由1.36增加到1.43,而其压比由1.523降低到1.482、流量系数由0.97降低到0.90,从而使预旋喷嘴温降由25.79 K减小到22.28 K;预旋供气系统温降由12.07 K降低到11.03 K。含湿条件会增加系统内流动阻力,限制了预旋供气系统降温能力,在涡轮叶片供气温度需求不变时,含湿条件将需要更高的供气压力。     

Unsteady internal flow conditions of mini-centrifugal pump with splitter blades

Mini centrifugal pumps having a diameter smaller than 100mm are employed in many fields. But the design method for the mini centrifugal pump is not established because the internal flow condition for these small-sized fluid machines is not clarified and conventional theory is not suitable for small-sized pumps. Therefore, mini centrifugal pumps with simple structure were investigated by this research. Splitter blades were adopted in this research to improve the performance and the internal flow condition of mini centrifugal pump which had large blade outlet angle. The original impeller without the splitter blades and the impeller with the splitter blades were prepared for experiment. The performance tests are conducted with these rotors in order to investigate the effect of the splitter blades on performance and internal flow condition of mini centrifugal pump. On the other hand, a three dimensional unsteady numerical flow analysis was conducted to investigate the change of the internal flow according to the rotor rotation. It is clarified from the experimental results that the performance of the mini centrifugal pump is improved by the splitter blades. The blade-to-blade low velocity region was suppressed in the case with the splitter blades. In addition to that, the unsteady flows near the volute casing tongue were suppressed due to the splitter blades. In the present paper, the performance of the mini centrifugal pump is shown and the unsteady flow condition is clarified with the results of the numerical flow analysis. Furthermore, the effects of the splitter blades on the performance and the unsteady internal flow condition are investigated.     

Numerical investigation of influence of the clocking effect on the unsteady pressure fluctuations and radial forces in the centrifugal pump with vaned diffuser

The relative position between the diffuser vane and the volute tongue (clocking effect) has a great effect on the performance of the single-stage centrifugal pump, which however, is often ignored by designers. In this paper, the influence of clocking effect on the unsteady pressure fluctuation in a centrifugal pump and on the radial force of impeller is investigated. The hydrodynamic performance of the centrifugal pump with vaned diffuser was experimentally measured. Numerical simulation based on the Reynolds-averaged Navier–Stokes (RANS) combined with the SST k-w turbulence model was used to obtain hydrodynamic performance of the centrifugal pump. The numerical results of the hydrodynamic performance were in agreement with the experimental data. The results show that the clocking effect has great influence on the pressure fluctuation and on the unsteady radial force imposed on the impeller. When the diffuser vane approaches the volute tongue, the pressure fluctuation intensity in volute is relatively lower. Meanwhile, relatively larger radial force on the impeller and the lower efficiency are obtained when the diffuser vane is near the volute tongue. Thus, it is suggested that the volute tongue should be located near the middle of two diffuser vanes to obtain better performance.     

Numerical simulation of flow in centrifugal pump with complex impeller

Based on the Navier-Stokes equations and the Spalart-Allmaras turbulence model, three dimensional turbulent flow fields in centrifugal pump with long-mid-short blade complex impeller are calculated and analyzed numerically. The relative velocity and pressure distributions in the flowpart are obtained. It is found that the flow in the passage of the complex impeller is unsymmetrical due to the joint action between volute and impeller. The back-flow region is at inlet of long-blade suction side, near middle part of long-blade pressure side and outlet of short-blade suction side. The flow near volute throat is affected greatly by volute. The relative velocity is large and it is easy to bring back flow at outlet of the complex impeller near volute throat. The static and total pressure rise uniformly from inlet to outlet in the impeller. At impeller outlet, the pressure periodically decreases from pressure side to suction side, and then the static pressure sharply rise near the throat. The experimental results show that the back flow in the impeller has an important influence on the performance of pump.     

Effect of Impeller Geometry and Tongue Shape on the Flow Field of Cross Flow Fans

Experiments were conducted to investigate the effect of impeller geometry and tongue shape on the flow field of cross flow fans. Three impellers (Ⅰ,Ⅱ,Ⅲ) having same outer diameter, but different radius ratio and blade angles were employed for the investigation. Each impeller was tested with two tongue shapes. Flow survey was carried out for each impeller and tongue shape at two flow coefficients, and for each flow coefficient at different circumferential positions. The flow is two-dimensional along the blade span except near the shrouds. The total pressure developed by the impellers in each case is found to be maximum at a circumferential position of around 270°. The total and static pressures at the inlet of impellers are more or less same regardless of impeller and tongue geometry, but they vary considerably at exit of the impellers. Impeller Ⅲ with tongue T2 develops higher total pressure and efficiency where as impeller Ⅱ with tongue T2 develops minimum total pressure. Higher diffusion and sma     

Numerical investigation of pressure distribution in a low specific speed centrifugal pump

To study the pressure distribution of the volute casing, front casing and back casing in a prototype centrifugal pump, the pressure experiments and numerical simulations are carried out at six working conditions in this paper. The experimental results shows that the asymmetry of static pressure distribution on volute casing and front cavity is caused by the tongue of the volute and it may result in high radial and axial resultant force which can cause vibration and noise in the centrifugal pump. With the increasing of flow rate, the asymmetry of static pressure distribution and the magnitude of static pressure values reduce. The numerical results indicate that the pressure fluctuation near the tongue is strongest and it becomes slighter at point away from the tongue. With the increasing of flow rate, the local high-pressure region in impeller passage reduces and the flow becomes smoother accordingly, whereas the fluid speed becomes much higher which may cause further flow losses. The results predicted by numerical simulation are in coincident with the experimental ones. It shows that the turbulence model for simulating the flow field in centrifugal pumps is feasible.     

射流孔分布对径流涡轮背盘冷效均匀性的改善

由于可靠性和成本限制,微型燃气轮机涡轮冷却问题尚未形成成熟的解决方案。本文提出了一种简单、高可靠性的径流涡轮背盘冲击冷却技术,并针对由于涡壳几何周向不均匀导致的涡轮背盘冷效不均匀的问题,采用射流孔周向非均匀布置措施对其进行了改善。研究结果表明,在涡舌附近加密射流孔,使其附近对应的冷效极大和极小值均明显提升,冷效均匀性最高改善17.9%。不同非均布射流孔方案对涡轮背盘平均冷效及涡轮整机膨胀比的影响可忽略,对涡轮整机的效率影响不超过0.5%。     

交错叶片式双吸泵流动特性分析

为探究交错叶片式双吸泵的内部流动特性,本文基于CFD性能预测方法,在0.19Q_0~1.54Q_0不同流量工况下对某型号交错叶片式双吸泵全流道进行了数值模拟,并研究了泵外特性变化规律,分析泵压力、流速、流线和湍动能分布情况。结果表明:交错叶片式双吸泵效率高,额定工况下效率达到86.2%,高效区范围广,在额定流量工况附近,效率保持在80%以上;泵内部流动稳定,无明显漩涡与回流;在小流量工况下,泵内部流动变得紊乱,在叶轮流道间、叶轮与压水室交界处和隔舌附近存在明显脱流与漩涡,湍动能耗散严重,导致泵效率急剧下降。通过本文研究能对这类双吸泵的高效使用提供一定指导,并为该泵的进一步优化提供一定的参考。     

Performance analysis of mini centrifugal pump with splitter blades

Design method for a mini centrifugal pump is not established because the internal flow condition for these small-sized fluid machines is not clarified and conventional theory is not suitable for small-sized pumps. Then, a semi-open impeller for the mini centrifugal pump with 55mm impeller diameter is adopted in this research to take simplicity and maintenance into consideration. Splitter blades are adopted in this research to improve the per- formance and internal flow condition of mini centrifugal pump having large blade outlet angle. The performance tests are conducted with these rotors in order to investigate the effect of the splitter blades on the performance and internal flow condition of the mini centrifugal pump. A three dimensional steady numerical flow analysis is con- ducted to analyze rotor, volute efficiency and loss caused by a vortex. It is clarified from the experimental results that the performance of the mini centrifugal pump is improved by the effect of the splitter blades. Flow condition at outlet of the rotor becomes uniform and back flow regions are suppressed in the case with the splitter blades. Further, the volute efficiency increases and the vortex loss decreases. In the present paper, the performance of the mini centrifugal pump is shown and the flow condition is clarified with the results of the experiment and the nu- merical flow analysis. Furthermore, the performance analyses of the mini centrifugal pumps with and without the splitter blades are conducted.     

Investigation on inlet recirculation characteristics of double suction centrifugal compressor with unsymmetrical inlet

The inlet recirculation characteristics of double suction centrifugal compressor with unsymmetrical inlet structures were studied in numerical method, mainly focused on three issues including the amounts and differences of the inlet recirculation in different working conditions, the circumferential non-uniform distributions of the inlet recirculation, the recirculation velocity distributions of the upstream slot of the rear impeller. The results show that there are some differences between the recirculation of the front impeller and that of the rear impeller in whole working conditions. In design speed, the recirculation flow rate of the rear impeller is larger than that of the front impeller in the large flow range, but in the small flow range, the recirculation flow rate of the rear impeller is smaller than that of the front impeller. In different working conditions, the recirculation velocity distributions of the front and rear impeller are non-uniform along the circumferential direction and their non-uniform extents are quite different. The circumferential non-uniform extent of the recirculation velocity varies with the working conditions change. The circumferential non-uniform extent of the recirculation velocity of front impeller and its distribution are determined by the static pressure distribution of the front impeller, but that of the rear impeller is decided by the coupling effects of the inlet flow distortion of the rear impeller, the circumferential unsymmetrical distribution of the upstream slot and the asymmetric structure of the volute. In the design flow and small flow conditions, the recirculation velocities at different circumferential positions of the mean line of the upstream slot cross-section of the rear impeller are quite different, and the recirculation velocities distribution forms at both sides of the mean line are different. The recirculation velocity distributions in the cross-section of the upstream slot depend on the static pressure distributions in the intake duct.