双吸泵作液力透平叶轮内非定常流动DMD分析

DMD Analysis of Unsteady Flow of Impeller in Double-suction Centrifugal Pump as Turbine

摘要:

为了精确分析双吸泵作液力透平叶轮内的非定常流动特性，采用SST k-ω湍流模型在设计工况下进行数值模拟。对一个周期的非定常速度场进行动态模态分解(DMD)，并结合Q准则，得到前4阶主要模态及其相应的时空信息。分析结果表明：DMD方法将叶轮内复杂的流场特征分解为动静干扰模态、基本模态和耗散模态。其中动静干扰模态占主导地位，频率为叶轮旋转频率，反映出叶轮内流动受静止部件干扰的流动特征，涡结构主要为点状涡和不连续的管状涡；基本模态频率为0Hz，反映出叶片流道几何特征引起的稳态流场特征，涡结构主要为连续的管状涡；3阶及4阶模态为耗散模态，反映出叶轮内流动受静止部件干扰，在叶片上产生的流动分离及不稳定涡结构脱落的特征，以片状涡和不连续的管状涡为主。在特定频率下DMD方法可以对叶轮流场结构进行分解，能够清楚地分析双吸泵作液力透平叶轮内复杂流场的非定常特性。

关键词:双吸泵作液力透平;非定常流动;动态模态分解;相干结构;Q准则

Abstract:

In order to accurately analyze the unsteady flow characteristics in the impeller of a double-suction pump as a hydraulic turbine, the SST k-ω turbulence model was used for numerical simulation under design conditions. The dynamic mode decomposition (DMD) of a periodic unsteady velocity field was carried out, and the first four main modes and their corresponding spatio-temporal information were obtained by combining the Q criterion. The analysis results showed that the DMD method decomposed the complex flow field characteristics in the impeller into dynamic and static interference modes, basic modes and dissipative modes. Among them, the dynamic and static interference modes were dominant, and the frequency was the rotation frequency of the impeller, which reflected the flow characteristics of the flow in the impeller disturbed by the static components. The vortex structure was mainly point vortex and discontinuous tubular vortex. The basic modal frequency was zero, which reflected the steady-state flow field characteristics caused by the geometric characteristics of the blade flow channel. The vortex structure was mainly continuous tubular vortex. The third-order and fourth-order modes were dissipative modes, which reflected the characteristics of flow separation and unstable vortex structure shedding on the blade caused by the interference of static components in the impeller, mainly sheet vortex and discontinuous tubular vortex. The DMD method can decompose the flow field structure of the impeller at a specific frequency, and can clearly analyze the unsteady characteristics of the complex flow field in the impeller of the double-suction pump as a hydraulic turbine.

Key words:double-suction centrifugal pump as turbine;unsteady flow;dynamic mode decomposition (DMD);coherent structure;Q criterion