Investigation on the unstable flow characteristics of stator-rotor clearance flow of full tubular pump operating under stall condition

Influenced by the hydrodynamic pressure difference, stator-rotor clearance flow (SRCF) inevitably exists during the operation of full tubular pump (FTP), disturbing the internal flow field and generating additional energy loss. Based on numerical simulation and experiment, this paper investigated the unstable flow characteristics of SRCF under stall conditions. By conducting boundary vorticity flux (BVF) diagnosis, the temporal and spatial distribution of the fluid force in rotor was analyzed and the variation law of the intensity, occurrence domain and entropy generation of the vortex region derived from the intersection of SRCF, and the flowing separative vortex (SPV) were deduced, revealing the formation mechanism of the special “saddle zone” of FTP. The results showed that the trajectory of SRCF in stator-rotor clearance (SRC) was spiral reflux, and normally, SRCF was entrapped by the mainstream of high momentum, merging into the impeller chamber after flowing out of SRC. While under stall condition, SRCF instead gradually moved toward the fore guide vane after intersecting with SPV, then merging into the mainstream in the form of spiral vortex with its axial direction toward the hub, leading to a special “saddle zone” with 0.06Qd preposition compared with that of semi-tubular pump (STP). The region with high entropy production rate in rotor basically overlapped with that of the unsteady SRCF occurred in, where the turbulence dissipation of impeller was 527.7 W/K, accounting for the most. This paper revealed the unstable flow characteristics of FTP-SRCF, which is of great significance for improving the internal flow stability and hydraulic performance of FTP.