Investigation of Internal Flow in Centrifugal Pump Diffuser using Laser Doppler Velocimetry (LDV) and Computational Fluid Dynamics

This study was carried out to assess the ability of a computational fluid dynamics (CFD) code to predict the scavenging flow in the cylinder of a two-stroke cycle engine. Predictions were obtained from a CFD simulation of the flow within the cylinder. Due to the apparent sym-metry of the engine port layout, only half of the cylinder volume was modelled. Boundary conditions for the CFD model were obtained from experimentally measured pressure-time histories in the crankcase and exhaust. The two-stroke cycle engine was modified to allow laser Doppler velocimetry (LDV) measurements to be made of the in-cylinder flow. The engine was operated under motoring conditions at 500 r/min with a delivery ratio of 0.7. Although the engine scavenge port layout was geometrically symmetrical, an asymmetrical flow field was identified in the cylinder. As a result of this, a direct comparison of the in-cylinder LDV measured and CFD computed results was not possible. However, LDV and CFD results for the in-cylinder flow are presented to help highlight the dissimilarity between the measured and predicted flow fields. Two-dimensional LDV measurements were made in the cylinder at the transfer ports for a portion of the cycle. A comparison of these LDV measurements with CFD predictions of the in-cylinder velocities at the same locations showed that the CFD model could replicate reasonably well the general trend of the flow. The measured cylinder averaged turbulent kinetic energy was compared with that of the CFD model. The qualitative trend of the overall turbulence generating capacity of the engine was well replicated by the CFD model.

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Flow in a Centrifugal Pump Impeller at Design and Off-Design Conditions—Part I: Particle Image Velocimetry (PIV) and Laser Doppler Velocimetry (LDV) Measurements

Journal of Fluids Engineering ◽

10.1115/1.1524585 ◽

2003 ◽

Vol 125 (1) ◽

pp. 61-72 ◽

Cited By ~ 127

Author(s):

Nicholas Pedersen ◽

Poul S. Larsen ◽

Christian B. Jacobsen

Keyword(s):

Particle Image Velocimetry ◽

Centrifugal Pump ◽

Laser Doppler Velocimetry ◽

Particle Image ◽

Laser Doppler ◽

Doppler Velocimetry ◽

Pump Impeller ◽

Design Load ◽

Image Velocimetry ◽

Centrifugal Pump Impeller

Detailed optical measurements of the flow inside the rotating passages of a six-bladed shrouded centrifugal pump impeller of industrial design have been performed using particle image velocimetry (PIV) and laser Doppler velocimetry (LDV). Results include instantaneous and ensemble averaged PIV velocity vector maps as well as bin-resolved LDV data acquired in the midplane between hub and shroud of the impeller. The flow is surveyed at both design load and at severe off-design conditions. At design load, Q=Qd, the mean field of relative velocity is predominantly vane congruent, showing well-behaved flow with no separation. At quarter-load, Q=0.25Qd, a previously unreported “two-channel” phenomenon consisting of alternate stalled and unstalled passages was observed, with distinct flow congruence between every second of the six passages. A large recirculation cell blocked the inlet to the stalled passage while a strong relative eddy dominated the remaining parts of the passage. The stall phenomenon was steady, nonrotating and not initiated via the interaction with stationary components. The study demonstrates that the PIV technique is efficient in providing reliable and detailed velocity data over a full impeller passage, also in the close vicinity of walls due to the use of fluorescent seeding. A quantitative comparison of blade-to-blade distributions of mean fields obtained by PIV and LDV showed a satisfactory agreement.

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