Influence of Meridional Width on Head-Curve Instability and Pump Performances

  • The present study deals with the cause of head-curve instability and the influence of impeller-outlet and diffuser-inlet width on pump performances. Experiments and Computational Fluid Dynamics (CFD) simulations were carried out on a 4-stage model pump. Three impellers and diffusers with different meridional-widths were designed for a specific speed around 30 [m\(^3\)/s, m, rpm]. Overall-performance curves, stage-head curves, inlet recirculation in the 1\(^{st}\) stage, internal-head curves in the 2\(^{nd}\) stage and pressure profiles in the impeller side room were measured with 29 pressure sensors. Pressure pulsations were recorded at various positions in the multistage pump. When the pump ran at the onset of the instability, an excessive head-loss was detected in the inlet triangular section of the diffuser. The pressure profiles in the side room and flow patterns in the impeller showed a sudden shift of flow recirculation at the impeller outlet across the span. According to [1, 2], this flow phenomenon is called flow pattern switching. The abrupt movement of outlet recirculation across the span produced a large momentum-exchange between streamlines and a massive mixing-loss in the inlet triangular section. This was considered the main cause of the instability. As the meridional-width increased, flow recirculation at the impeller outlet was intensified, giving a higher head and power at shut-off. In contrast, the onset of the instability did not vary systematically with the meridional width. Diffuser rotating-stall was detected at \(f/f_n\) = 0.029 when the pump with the largest width ran at the onset of the instability. Even though all three designs generated a head-curve instability, the rotating stall appeared only in the largest meridional-width. The uncertainty in the CFD prediction of pressure pulsations was evaluated. The discrepancy between measured and calculated values was largely dependent on the sampling location and operating points.
Author:Joohyen Kim
URN (permanent link):urn:nbn:de:hbz:386-kluedo-63891
Advisor:Martin Böhle
Document Type:Doctoral Thesis
Language of publication:English
Publication Date:2021/06/02
Year of Publication:2021
Publishing Institute:Technische Universität Kaiserslautern
Granting Institute:Technische Universität Kaiserslautern
Acceptance Date of the Thesis:2021/04/30
Date of the Publication (Server):2021/06/07
Number of page:XX, 115
Faculties / Organisational entities:Fachbereich Maschinenbau und Verfahrenstechnik
DDC-Cassification:6 Technik, Medizin, angewandte Wissenschaften / 620 Ingenieurwissenschaften und Maschinenbau
Licence (German):Creative Commons 4.0 - Namensnennung, nicht kommerziell, keine Bearbeitung (CC BY-NC-ND 4.0)