Abstract
Time-resolved particle image velocimetry (TR-PIV) measurements were conducted to analyze the unsteady flow field developing in a centrifugal pump. The flow structures in the impeller passage under different flow rates were investigated. The overall statistical characteristics of the flow were obtained with the study of relative phase-averaged flow field, phase-averaged turbulent kinetic energy (TKE), and the analysis of frequency. Through the study of the first few proper orthogonal decomposition (POD) modes of the flow field, the coherent flow structures under several flow rates were revealed, consequently, the flow fields were reconstructed by the POD modes. Results show that the main flow structures could be reflected by the first few modes of the flow field: when the fluid follows the blade contour well, the first few modes corresponded to the “jet-wake” structures; when the large-scale flow structures appear in the passage, the 1st and 2nd modes were associated in pairs and corresponded to the stall cells, the 3rd and 4th modes corresponded to the “jet-wake” structures, and the 5th and 6th modes corresponded to the passage vortexes or the “jet-wake” structures (for the extreme part-load conditions). The flow structures that were reflected by the first few modes change as the decrease of flow rate, especially, at the extreme part-load condition, not only the shapes of the flow structures changed, but also the flow direction is reversed. This indicates that the generation mechanism of turbulent kinetic energy in the flow passage changed at the extreme part-load conditions.
Highlights
Centrifugal pumps consume about 20% of the total generated energy in the world due to their extensive usage in petrochemical, chemical, coal, chemical, pharmaceutical, and other process fields (Arun Shankar et al, 2016; Bozorgasareh et al, 2021)
Ghorani et al (2020) studied the irreversible energy losses within the pump as turbine (PAT), and they found that the blade inlet shock, flow deviation at the blade outlet, flow separation, backflow, and vortices in flow passages were categorized as the main reasons for irreversible hydraulic losses within the PAT components
When the flow rate is 0.4 QBEP, the inlet fluid deviates from the suction surface more severely, causing the suction side of the vortex to increase in size, and a smaller vortex appears at the pressure side
Summary
Centrifugal pumps consume about 20% of the total generated energy in the world due to their extensive usage in petrochemical, chemical, coal, chemical, pharmaceutical, and other process fields (Arun Shankar et al, 2016; Bozorgasareh et al, 2021). Ghorani et al (2020) studied the irreversible energy losses within the pump as turbine (PAT), and they found that the blade inlet shock, flow deviation at the blade outlet, flow separation, backflow, and vortices in flow passages were categorized as the main reasons for irreversible hydraulic losses within the PAT components Their results indicate that the turbulent entropy generation is the dominant mechanism for hydraulic losses. In order to further enrich the theory of rotational stall, Li et al (2020a) and Li et al (2020b) explored the mechanism of internal energy loss in the mixed-flow pump under stall conditions They found that the high-value region of turbulent kinetic energy was basically corresponding to the backflow region of the impeller outlet and the separation region of the boundary layer near the suction surface, which led to a great increase of energy loss in the impeller. Understanding the dynamic and energy dissipation characteristics of the unstable flow structure in the pump would allow inventing improved design methods for delaying or suppressing the unstable flow structures
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