NDLI: Unsteady Numerical Simulations of the Flow Related to the Unstable Energy-Discharge Characteristic of a Medium Specific Speed Double Suction Pump

Content Provider	The American Society of Mechanical Engineers (ASME) Digital Collection
Author	Braun, Olivier Avellan, Francois Dupont, Philippe
Copyright Year	2007
Abstract	Regions of positive slope in the pressure-discharge characteristics can result in a reduction or even lack of damping of system instabilities. They are therefore one of the major concerns in design and operation of centrifugal pumps as they are limiting the admissible operating range. The considered preliminary hydraulic design of an industrial double suction pump of medium specific speed ν = 0.410 (0.205 per impeller side) shows a marked saddle in the energy-discharge characteristic associated to a sudden drop of efficiency versus discharge at part load. Unsteady RANS type flow simulations are performed using hexahedral meshes with 2.5 million nodes to model the inlet casing, the shrouded double sided impeller with 2 × 7 blades, the diffuser with 12 blades and the volute. In unsteady solution monitoring, low frequency (below blade passing frequencies) phenomena are noticed. Therefore, simulation times of up to 10 impeller revolutions at each flow rate are requested to achieve statistically steady behavior of the flow judged on global performance numbers and circumferential flow rate distribution. The numerical simulations emphasize a drop in the characteristic, though at a lower flow rate than found on the test rig. It is shown to be associated to a one-sided separation in the diffuser, further leading to an unbalanced flow rate distribution of about 10% of flow rate between both sides of the impeller. There is a region of hysteresis, where both configurations with balanced and unbalanced flow rate distributions can be obtained for the same global flow rate. The asymmetric flow distribution leads to asymmetric velocity profiles at the impeller-diffuser interface which results in a strongly vortical flow in the diffuser channels, where an important amount of energy is dissipated in regions of increased viscous and turbulent shear.
Sponsorship	Fluids Engineering Division
Starting Page	971
Ending Page	977
Page Count	7
File Format	PDF
ISBN	0791842894
DOI	10.1115/FEDSM2007-37550
e-ISBN	0791838056
Volume Number	Volume 2: Fora, Parts A and B
Conference Proceedings	ASME/JSME 2007 5th Joint Fluids Engineering Conference
Language	English
Publisher Date	2007-07-30
Publisher Place	San Diego, California, USA
Access Restriction	Subscribed
Subject Keyword	Damping Suction pumps Turbulence Computer simulation Blades Centrifugal pumps Separation (technology) Flow (dynamics) Pressure Stress Design Flow simulation Simulation Reynolds-averaged navier–stokes equations Impellers Diffusers Vortex flow Shear (mechanics)
Content Type	Text
Resource Type	Article

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