Numerical investigation of flow mechanisms of tandem impeller inside a centrifugal compressor

This study numerically investigated a single stage centrifugal compressor ‘‘Radiver’’ with a wedge diffuser and several tandem-designed impellers to explore the flow phenomena within the tandem impeller and the potential to enhance compressor performance. The results demonstrate that tandem design and clocking fraction (λ_s) significantly affects the compressor performance. The compressor stage with tandem impellers of Series A of boundary layer growth interruption alone are observed to have a widely operating range but efficiency and total pressure ratio penalty compared with that of conventional impeller. The tandem impeller with at least the same impeller efficiency as the conventional design is considered as a critical design criteria so that further modification process based on the flow characteristic of tandem impeller is necessary. In order to restrain the inducer wake and exducer shock losses, parameters modification of blade angle and thickness distributions are necessary and the modified tandem impeller of Series B is obtained. The modified tandem impeller with 25% clocking arrangement shows an 8.45% stall margin increase and maintains the total pressure ratio and efficiency as the conventional design, which proves the potential of tandem impeller to improve compressor stage performance. It is noteworthy that the tandem impellers of Radiver have not shown obviously balanced exit flow field and the fundamental mechanism of stall margin extending of tandem impeller lies on the improved impeller/diffuser matching performance resulting from the incidence angle variation at diffuser inlet.     

离心压气机内不同非定常源影响实验研究

使用热线风速仪对扩压器内的非定常流场进行了测量,采用锁相采样—集平均技术对热膜测量的瞬时信号进行了处理,对离心压气机内扩压器势反冲效应和叶轮尾流的非定常影响进行了分离,采用＂逆频谱分析＂方法求解了不确定性非定常性,研究了离心压气机内不同非定常源的影响。结果表明,扩压器的势反冲效应同叶轮叶片的非定常影响处于同一数量级,扩压器的势反冲效应略小一些。扩压器的势反冲效应同叶轮叶片的非定常影响均是沿流向不断减小,且二者之间的差距沿流向也不断减小。叶轮叶片的非定常影响对扩压器叶片的位置较为敏感,靠近扩压器凸面侧的测点受叶轮叶片的非定常影响较大。径向间隙内不确定非定常度受扩压器叶片的反冲影响较大。     

凸肩叶片接触状态的非线性动力学研究

针对航空发动机凸肩叶片系统的运动特点 ,将其简化为单自由度系统进行了分析 ,推导出该系统的李雅谱诺夫指数的计算公式。虽然接触面上的正压力作谐波变化 ,系统的李雅谱诺夫指数均不大于零 ,其稳态响应只有周期或拟周期运动 ,不会出现混沌。同时数值计算也表明 ,系统的稳态响应是周期或拟周期运动 ,而且出现 (v-1 )的次谐波成分 ,由此看出对凸肩接触状态进行非线性动力学分析是必要的     

点阵压气机叶轮轻量化设计及力学性能分析

以压气机叶轮为研究对象,轻量化设计为研究目标,设计了一种适合旋转周期对称结构应用的点阵填充点阵胞元.其目的是在保证满足设计要求的前提下,使叶轮刚度和强度具有可调性的同时降低叶轮质量.对转速为8×104r/min极限工况下的无填充轮、实心轮和不同点阵梁直径点阵填充轮进行了分析对比.结果表明,单个胞元梁直径为0.2mm,0...     

离心式叶轮内部湍流及出口“射流尾迹”结构的成因分析

使用压力修正算法及kε湍流模式求解Reynolds时均的NS方程,数值分析了离心式压气机叶轮内部湍流流动及叶轮出口“射流尾迹”结构的形成过程,计算与实验结果的比较表明,二次流对低能流体的输运是形成射流尾迹结构的主要原因。     

低压离心叶轮小流量失速特性的实验观察

在一离心压缩系统喘振实验台上,对小流量工况下沿叶轮出口圆周的压力波动进行了动态测量。实验观测到离心叶轮在小流量工况下存在一种低于转速频率的、且非旋转类型的失速自激振荡,观察到这种波动在局部及个别瞬间是不稳定的,沿叶轮圆周波动强度的分布也不均衡     

三元整体叶轮的几何造型与数控加工刀具路径规划

采用三次B样条曲线对叶轮中性面上盖盘和轴盘的两组数据点进行插值，得到盖盘曲线和轴盘曲线，进而得到直纹面形式的叶轮中性面；按照叶片的厚度做盖盘曲线和轴盘曲线的变距偏置曲线，得到叶片曲面的直纹化表达式；在此基础上，讨论了三元叶轮加工的刀具路径规划方法，给出了确定球头刀刀心位置和计算残留误差的两种迭代算法，最后给出了加工实例。     

Multi-parameter optimization of machining impeller surface based on the on-machine measuring technique

Selecting the optimal machining parameters for impeller surface is a challenging task in the automatic manufacturing industry, due to its free-form surface and deep-crooked flow channel. Existing experimental methods require lots of machining experiments and off-line tests, which may lead to high machining cost and low efficiency. This paper proposes a novel method of machining parameters optimization for an impeller based on the on-machine measuring technique. The absolute average error and standard deviation of the measured points are used to define the grey relational grade for reconstructing the objective function, and the complex problem of multi-objective optimization is simplified into a problem of single-objective optimization. Then, by comparing the values of the defined grey relational grade in a designed orthogonal experiment, the optimal combination of the machining parameters is obtained. The experiment-solving process of the objective function corresponds to the minimization of the used errors, which is advantageous to reducing the machining error. The proposed method is efficient and low-cost, since it does not require re-clamping the workpiece for off-line tests. Its effectiveness is verified by an on-machine inspection experiment of the impeller blade.     

应用于燃气轮机余热回收系统的超临界CO2径流式透平性能探究

为研究应用于燃气轮机余热回收系统的超临界CO₂（SCO₂）径流式透平整机性能,基于RANS（雷诺时均）模型,对透平整机系统内部流场进行数值模拟,获得了SCO₂径流式透平整机在起动、升速、自持及额定工况下的运行情况,并针对出口压力变化分析了透平非设计工况下的性能。模拟结果表明：透平起动工况下会发生运行失稳,产生“倒吸”现象且通道内出现大面积的低速区域,但随转速增加流动趋于稳定;叶顶间隙的泄漏流会对透平的性能产生不利影响,额定工况下0.5 mm的间隙使透平减少近47 kW的功率输出,等熵效率降低6%左右;轮背密封可以起到良好密封作用,密封引入气还提高了透平整机的功率和效率;在偏离设计点工况运行时,透平可以有效应对出口压力的变化;通过对比简化通道和全周通道的仿真数据,透平轴功率和等熵效率的误差均在0.5%以内,可知应用简化通道模型仿真能够保证计算精度。因此,在SCO₂径流式透平的仿真与应用过程中,研究人员要注重透平低速起动工况下的运行,以及叶顶间隙对这种小尺寸高转速透平机性能的影响。     

整体叶轮侧铣数控加工刀位轨迹生成新方法

为提高整体叶轮的加工质量和效率,提出了分段侧铣的方法,在每一段曲面上,基于斜等距曲面的原理,推导出叶片分段侧铣加工时刀位轨迹的生成和计算;并用计算仿真和刀心轨迹图对刀位进行了验证。结果表明,采用分段侧铣的方法,生成的刀位轨迹刀轴矢量变化均匀,刀轴未发生干涉,且加工效率和加工质量明显得到提高。