离心压气机无叶扩压器旋转失速诱发的能量损失机制研究

利用ANSYS软件分别对带宽、窄无叶扩压器的离心压气机进行数值模拟,研究了在旋转失速诱发过程中离心压气机无叶扩压器的流场分布及能量损失机制。研究表明,窄无叶扩压器失速诱发时盘盖侧边界层发生局部回流并在叶高方向向内延伸,而宽无叶扩压器失速与扭曲的核心流和回流混合密切相关。随着流量的减小,扩压器内能量损失逐渐增加,旋转失速发生后,能量损失快速增加,到失速完全发展时,达到最大,且宽无叶扩压器的能量损失大于窄无叶扩压器。窄无叶扩压器失速诱发点处存在性能曲线的不连续现象,分析了宽、窄无叶扩压器旋转失速诱发过程中的能量损失机制。     

带无叶扩压器离心压气机的稳定性分析

结合实验数据,采用数值模拟方法对某带无叶扩压器离心压气机的性能与稳定性进行了详细分析,比较了设计点与近失速点下无叶扩压器内部的流动特征．结果表明：在发生喘振瞬间,扩压器进口最先出现了压力崩溃;扩压器进口流动特别是轮盖侧流动是导致压气机失稳的重要因素,对扩压器进口逆叶轮旋转方向的轮盖侧啧蒸汽能够提高扩压器的稳定性．     

叶片安装角对离心压气机扩压器气动性能及失速机理影响研究

为了研究离心压气机扩压器异常叶片对于失速现象的诱发效果，以带有叶扩压器的高速离心压气机为研究对象，通过整体或局部改变扩压器叶片安装角，开展非定常数值模拟研究并与实验结果对比验证，研究叶片安装角改变对离心压气机性能、动态特性以及失速机理的影响规律。研究表明：整体负方向旋转叶片安装角会促使扩压器更加不稳定，旋转角度从-5°到5°，最高效率点对应的质量流量逐渐增大。其中安装角偏转+5°扩压器叶片前缘靠近轮缘壁面发生流动分离，诱使无叶区间产生回流；而偏转-5°扩压器轮毂附近的流动分离主要发生在尾缘，造成扩压器叶片吸力面附近产生大范围回流。单个叶片安装角发生较大偏转(大于10°)时，扩压器比叶轮更早进入失速状态，且失速的机制可能会随着安装角偏移的增大发生改变。     

小流量下离心压气机无叶扩压器数值模拟及流动分析

无叶扩压器是离心压气机重要部件,也是涡轮增压器上应用最多的扩压器类型,详细研究其内部流场,掌握流动损失产生的机理,对于提升扩压器性能及抑制其失速的发生具有重要意义。本研究利用商用CFD软件NUMECA对离心压气机无叶扩压器进行了数值模拟,并对无叶扩压器收缩段和平行段内的流动分别进行分析,探讨了它们各自流动的特点,为进一步深入研究无叶扩压器流动,提升其性能奠定基础。     

小型离心压气机径向扩压器复杂涡系结构分析

对某小型离心压气机进行详细数值模拟,构建径向扩压器复杂涡系结构模型,重点分析设计、堵塞、失速工况下径向扩压器内部复杂涡系结构。研究表明：径向扩压器内部涡系结构主要包括前缘涡、两个通道涡（压力面侧通道涡与吸力面侧通道涡）以及喉部涡;主叶片吸力面的前缘涡是机匣侧低能流体在展向与流向压力梯度作用下形成的,喉部涡是吸力面侧通道涡沿分流叶片前缘的回流与前缘涡构成的;喉部涡在喉部的堆积是导致径向扩压器失速的原因,径向扩压器喉部的激波则是堵塞的原因;随流量的减小,前缘涡的涡核越向相邻主叶片压力面迁移。     

无叶扩压器中非定常流动的DMD模态分析

采用动力模态分解(DMD)对离心压气机无叶扩压器内的复杂流场进行分析,选取1.8kg/s设计工况和1.4kg/s非稳定工况下的非定常数值计算结果为基础数据,得到这2种工况下10%叶高平面上切向速度、径向速度的模态云图以及特征频率,评估了DMD方法分析离心压气机非定常流动特征的能力.对不同特征频率下的流场进行重构,直观深入地再现了无叶扩压器内部非定常流动的变化过程.结果表明:在小质量流量下,叶片扫描频率的影响效果虽然仍占据主导,但受到抑制;捕捉到失稳频率约为193Hz,失稳模态在扩压器内沿周向占据3个固定的位置交替波动,不稳定波动沿扩压器周向并不存在旋转.     

离心压气机预旋及扩压器调节扩稳研究

以增压器无叶扩压离心压气机为研究基础,进行了压气机预旋导叶及扩压器设计,对单预旋、固定扩压器及预旋、扩压器耦合调节等不同情况下的离心压气机特性进行了数值分析,研究了进口预旋及扩压器可调的压气机扩稳特征。结果表明:压气机进口预旋在保持压气机最高效率特性基本不变的同时可以使压气机的流量范围拓宽16.7%,叶片式扩压器则可明显提高压气机最高效率约1.7%。在无叶扩压离心压气机的基础上,采用进口预旋和叶片式扩压器耦合调节控制的方法可在拓宽压气机喘振裕度的同时可使压气机工作效率提高约1.2%。     

间隙变化对轴流压气机转子近失速工况叶顶流场的影响研究

为研究间隙变化对轴流压气机转子近失速工况下叶顶流场结构的影响,以轴流压气机转子Rotor37为研究对象,对其叶顶流场进行定常和非定常的数值模拟。计算结果表明：随着叶顶间隙的减小,压气机的总压比和等熵效率均有所提高,稳定运行范围扩大;2倍设计间隙下,叶尖泄漏涡经激波作用后发生膨胀破碎,堵塞来流通道,诱发压气机堵塞失速;0.5倍设计间隙下,吸力面流动分离加剧,发生回流,部分回流与来流在压力面前缘上游发生干涉,进口堵塞加剧,致使部分来流从前缘溢出,导致压气机叶尖失速;不同间隙下压气机失速过程的主导因素不同,大间隙下失速由叶尖泄漏涡破碎的非定常波动引起,小间隙下失速主要由流动分离引发的周期性前缘溢流所主导。     

串列叶栅扩压器弦长比对离心压气机的性能影响研究

为研究串列叶栅前后排叶片的弦长比对离心压气机性能的影响规律,采用数值模拟的方法对某离心压气机扩压器进行串列改造,并在弦长比为0.7、1.0和2.0时对离心压气机级性能进行分析。研究结果表明:串列叶栅扩压器效率优于楔形扩压器,且可以明显扩宽压气机的工作裕度;串列叶栅弦长比在一定范围内数值越大,即前排叶片越短,压气机性能越佳。在串列叶栅扩压器后排叶片前缘附近添加合适弦长的小叶片可以在不降低离心压气机效率与工作裕度的同时提高总压比,同时拓宽其最大通流能力。     

跨声速轴流压气机失速特性研究

为研究跨声速轴流压气机失速特性,采用节流阀门模型使跨声速轴流压气机Rotor35进入数值失速,得到了失速过程中的内部流场,捕捉到了失速团从产生到发展壮大的过程,发现失速起始于叶片顶部,逐渐向轴向、径向和周向发展,失速团绕着旋转轴以低于转子转速同方向旋转。通过对比不同时刻的流场特征,压气机进入失速时在转子的叶顶区域流场同时发生了"前缘溢流"和"尾缘回流"的现象。叶顶间隙泄漏流与叶片吸力面分离流形成的流道分离涡的不断发展扩大,最终使压气机完全失速。     

Numerical Simulation of Rotating Stall in a Centrifugal Compressor with Vaned Diffuser

This paper reports a numerical study on the process from normal operating conditions to rotating stall in a cen-trifugal compressor with vaned diffuser.The purpose is to better understand the flow characteristics near stallpoint under the interactions between centrifugal impeller and vaned diffuser.Numerical results show that undercertain conditions just preceding stall point the tip leakage vortex begins to fluctuate at roughly half of the bladepassing frequency.This phenomenon is similar to rotating instability in axial compressors.With the flow rate re-duced further the impeller stalls and five stall cells propagating at a frequency of 85 percent of impeller rotationspeed are found.     

离心压缩机无叶扩压器的改进新方法

研究了某高压比离心压缩机无叶扩压器的性能，提出在无叶扩压器轮盘侧加装一定高度机翼型导叶的改进方法。结果表明，这种扩压器可以改善其内部流动，提高自身的压力恢复系数和效率，从而改善离心压缩机的整级性能。     

Behavior of Vaneless Diffuser Stall in a Centrifugal Compressor

The rotating stall in a centrifugal compressor with a vaneless diffuser was investigated both experimentally and numerically with focus on the effect of the internal flow field within the impeller on the diffuser stall.Through numerical analysis,the boundary layer separation at the impeller outlet was found to play an important role in the expansion and rotation processes of the diffuser stall.In particular,the expanded boundary layer separation near the hub side at the outlet of the main blade(M.B.)suction surface passage was considered to be the main cause of the expansion and rotation processes.A longitudinal vortex existed at the throat of the M.B.passage,and the mass flow rate in the M.B.passage was significantly reduced by the blockage effect.In addition,the longitudinal vortex induced the rolling up flow near the hub side at the impeller exit.Thus,the boundary layer separation expanded.     

Unsteady behavior of leading-edge vortex and diffuser stall in a centrifugal compressor with vaned diffuser

The characteristics of a rotating stall of an impeller and diffuser and the evolution of a vortex generated at the diffuser leading-edge (i.e., the leading-edge vortex (LEV)) in a centrifugal compressor were investigated by experiments and numerical analysis. The results of the experiments revealed that both the impeller and diffuser rotating stalls occurred at 55 and 25 Hz during off-design flow operation. For both, stall cells existed only on the shroud side of the flow passages, which is very close to the source location of the LEV. According to the CFD results, the LEV is made up of multiple vortices. The LEV is a combination of a separated vortex near the leading- edge and a longitudinal vortex generated by the extended tip-leakage flow from the impeller. Therefore, the LEV is generated by the accumulation of vorticity caused by the velocity gradient of the impeller discharge flow. In partial-flow operation, the spanwise extent and the position of the LEV origin are temporarily transmuted. The LEV develops with a drop in the velocity in the diffuser passage and forms a significant blockage within the diffuser passage. Therefore, the LEV may be regarded as being one of the causes of a diffuser stall in a centrifugal compressor.     

Experimental Investigations of Micro Air Injection to Control Rotating Stall

Steady discrete micro air injection at the tip region in front of the first compressor rotor has been proved to be aneffective method to delay the inception of rotating stall in a low speed axial compressor.Considering the practicalapplication a new type of micro injector was designed and described in this paper,which was imbedded in thecasing and could be moved along the chord.In order to verify its feasibility to other cases,such as high subsonicaxial compressor or centrifugal compressor,some other cases have been studied.Experimental results of the samelow speed axial compressor showed that the new injector could possess many other advantages besides success-fully stabilizing the compressor.Experiments performed on a high subsonic axial compressor confirmed the ef-fectiveness of micro air injection when the relative velocity at the blade tip is high subsonic.Meanwhile in orderto explore its feasibility in centrifugal compressor,a similar micro injector was designed and tested on a lowspeed centrifugal compressor with vaned diffuser.The injected mass flow was a bit larger than that used in axialcompressors and the results showed micro injection could also delay the onset of rotating stall in the centrifugalcompressor.     

基于动态模式分解的离心压缩机动态流场分析

动静流道相互作用引起的非定常流动是离心式压缩机内流的主要特征,借助模态分解方法可以有效提取出该流场中相干结构,进而可以说明该动静干涉流场的主要特征。本文将动态模式分解(Dynamic Mode Decomposition,DMD)方法应用于带无叶扩压器通道的离心式压缩机流场分析中,通过对动静干涉速度场和压力场的模态提取和分析,直观揭示出动静流道中的流体运动特征。在设计流量工况下,叶轮出口叶顶间隙的流体流动和动静流道干涉效应影响了叶轮出口的速度参数和压力参数的分布。在叶轮和扩压器流道中分别出现了频率1 715和725Hz的湍流相干结构,两频率和叶轮通过频率有关。动静干涉流道中压力沿叶高方向动态规律相似,而速度场沿叶高方向波动规律存在一定的差异。该特征可以为压缩机流场测试提供参考。     

基于本征正交分解的无叶扩压器流动稳定性Galerkin降阶模型

将分析湍流拟序结构中的本征正交分解技术运用到离心压气机无叶扩压器的流动稳定性分析中,并将其与Galerkin投影法相结合建立了无叶扩压器内部流场的降阶模型。使用本征正交分解技术提取无叶扩压器在某来流入口角下非定常流场的主要流动模态,将流动控制方程通过Galerkin方法投影至由有限阶本征正交模态所组成的空间上,得到无叶扩压器流动稳定性降阶模型。计算结果表明:该模型可用于判断不同来流入口角下的扩压器流动稳定性,并将降阶模型的计算结果与流场数值模拟结果和线性稳定性预测结果进行对比,验证了此降阶方法的合理性。