Unsteady flow characteristics in the double-tongue volute of an open-type pump based on modal decomposition

The open-type pump represents a key technological innovation for achieving pipeline-free cleaning systems, however, the complexity of its internal flow dynamics remains incompletely elucidated. To reveal the unsteady flow characteristics within the double-tongue volute of an open-type pump, proper orthogonal decomposition (POD), dynamic mode decomposition (DMD), and POD-based DMD methods were employed to analyze the evolution of vortex structures and pressure pulsations. The results reveal complex vortex structures featuring multiple frequency couplings within the double-tongue volute. All three model decomposition methods can effectively identify the spatiotemporal evolution characteristics of vortex structures. The dominant energy distribution is characterized by large-scale, alternating quasi-ordered structures at the volute inlet, associated with the blade-passing frequency. Under design condition, vortex shedding occurs at a frequency of 1.5 times the shaft rotational frequency. Under off-design conditions, a significant energy concentration is observed near the tongue, indicating that the energy loss in this region has a great impact on pump efficiency. In contrast, higher-order harmonic frequencies correspond to smaller-scale, alternating quasi-ordered structures that contribute to energy dissipation. The reconstructed flow fields based on the first 20 modes yield root mean square errors of 0.24% (POD), 0.37% (DMD), and 0.28% (POD-based DMD), demonstrating the feasibility of these methods for constructing surrogate models of the flow field and realizing optimization in the open-type pump.