Backflow effects on mass flow gain factor in a centrifugal pump.

Area of Science:

• Fluid Mechanics
• Turbomachinery
• Cavitation Physics

Background:

• Inlet backflow in centrifugal pumps at low flow rates can significantly affect cavitation.
• Previous research indicates non-negligible effects on mass flow gain factor and cavitation surge.
• Understanding these effects is crucial for pump performance and stability.

Purpose of the Study:

• To analyze the influence of impeller inlet backflow on cavitating flows in centrifugal pumps.
• To compare the cavitation behaviors of two typical centrifugal pumps with different backflow characteristics.
• To investigate the relationship between backflow, cavitation, and hydraulic stability.

Main Methods:

• Computational Fluid Dynamics (CFD) simulations using a Reynolds-Averaged Naiver-Stokes (RANS) solver.
• Application of the k-ω shear stress transport turbulence model and a homogeneous multiphase model.
• Comparative analysis of cavitating flows in two distinct centrifugal pump designs.

Main Results:

• Pump with less backflow showed decreasing cavity volume with flow rate reduction.
• Pump with significant backflow exhibited minimum cavity volume at a specific flow rate, then increased.
• Mass flow gain factors differed significantly; positive values observed in the high backflow pump under specific low-flow, low-cavitation number conditions.
• Backflow was identified as the primary cause for increased cavitation in the inlet tube and positive mass flow gain factors.
• Low-frequency pressure and flow rate fluctuations were observed in the high backflow pump under off-design conditions.

Conclusions:

• Inlet backflow is a critical factor influencing cavitation dynamics and stability in centrifugal pumps.
• The interaction between backflow and main flow can induce cavitation in the inlet tube.
• Backflow is directly linked to positive mass flow gain factors and low-frequency flow instabilities, highlighting its importance for hydraulic system stability.