Abstract
Diffuser Rotating Stall (DRS), a fluid instability, often restricts the operational range of diffuser-type centrifugal pumps, requiring countermeasures in industry. Despite various proposed methods for DRS suppression, the optimal approach minimizing pump efficiency reduction remains nonexistent.
In this study, we explored a new DRS suppression method by investigating the mechanism when combining long and short vanes in the vaned diffuser of an industrial pump.
The original vaned diffuser has eight long vanes, with short vanes created by removing the leading edge alternately. Varying short vanes from one to three, we studied the phenomena through experiments and Computational Fluid Dynamics (CFD). Experiments used a closed-loop piping system with a centrifugal pump (specific speed Ns = 138 m3/min, m, rpm = 920 USgpm, ft, rpm). Four pressure sensors in the diffuser passage captured DRS behavior. Incremental valve adjustments from high to low flow (minimum ϕ = 0.002) explored pump performance and DRS occurrence.
Results showed DRS at ϕ = 0.048 for the original diffuser shape, absent at higher flow rates and present at lower ones. With a single short vane, DRS occurred at ϕ = 0.058 without circumferential propagation. Increasing short vanes to two or three prevented DRS until ϕ = 0.010, demonstrating non-symmetric vane effectiveness.
Internal flow analysis using CFD software (Unsteady RANS calculation = URANS) explored time evolution within the diffuser and detailed short vane influences on DRS.
