Spatial-temporal evolution of tip leakage cavitation with double-hump in a mixed flow pump with tip clearance

Tip clearance in pump induces tip leakage vortex (TLV), which interacts with the main flow and leads to instability of flow pattern and decrease in pump performance. In this work, a closed-loop experimental rig with high-speed observation for a mixed flow pump is established, and the numerical simulation on tip leakage cavitation is conducted with experimental validation. A new double-hump pattern of tip leakage cavitation is first observed in the mixed flow pump. Results show that primary tip leakage vortex cavitation develops from a linear pattern to a banded pattern and, finally, to a double-hump pattern. The spatial–temporal evolution of tip leakage cavitation with double-hump can be classified into four stages: incepting stage, growing stage, merging stage, and propagating stage. The inception of the front hump is found to correspond to the periodic evolution of the specific passage vortex-tip leakage vortex (PV-TLV) pair. Affected by the propagation of the high-pressure area at the passage outlet, the PV wanders in the downstream passage, which greatly affects the intensity of tip leakage flow. The away motion of the PV from the tip clearance brings stronger tip leakage flow and results in the intensified TLV and the lower core pressure. As a result, the front hump incepts, grows, and travels downstream. Finally, it merges with the rear hump and together propagates to the downstream passage.