Numerical Investigation of the Effect of Different Back Sweep Angle and Exducer Width on the Impeller Outlet Flow Pattern of a Centrifugal Compressor With Vaneless Diffuser (original) (raw)
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La Houille Blanche, 2015
The paper presents the analysis of the performance and the internal flow behaviour in the vaned diffuser of a radial flow pump using PIV (particles image velocimetry) technique, pressure probe traverses and numerical simulations. PIV measurements have been performed at different hub to shroud planes inside one diffuser channel passage for a given rotational speed and various flow rates. For each operating condition, PIV measurements have been made for different angular positions of the impeller. Probe traverses have also been performed using a 3 holes pressure probe from hub to shroud diffuser width at different radial locations in between the two diffuser geometrical throats. The numerical simulations were realized with the two commercial codes: i-Star CCM+ 8.02.011 (RANS (Reynolds Averaged Navier Stokes) turbulence model, frozen rotor and unsteady calculations), ii-CFX 10.0 (turbulence modelled with DES model (Detached Eddy Simulation) combining RANS with LES (Large Eddy Simulation), unsteady calculations). Comparisons between numerical (fully unsteady calculations) and experimental results are presented and discussed for two flow rates. In this respect, the effects of fluid leakage due to the gap between the rotating and fixed part of the pump model are analysed and discussed.
Design and optimization of meridional profiles for the impeller of centrifugal compressors
Journal of Mechanical Science and Technology, 2017
An impeller design for radial flow compressors is addressed in several text books. According to practiced methods, the overall dimensions and properties of an impeller can be determined using basic aerodynamic and thermodynamic relations. However, the values of several parameters and geometric details have not been strictly assigned. Hence, the experience and empirical relations of designers are important. The impeller meridional profile is an important detail that has a significant influence on the performance of the impeller. Generally, circular arc curves are implemented for this purpose. In this study, the effect of using elliptic curves is studied and compared with circular curves. An experimentally validated numerical code is used for this investigation. Two different compressors are studied to formulate the conclusion. Results show that elliptic curves can be a better initial choice for hub and shroud profiles compared with the commonly used circular arc. Smoother direction change with less secondary flow and related loss are identified as the improvement cause.
Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science, 2016
A steady state simulation procedure is proposed to capture localized flow reversal inside of a centrifugal compressor vaneless diffuser. The procedure was performed on 12 compressor stages of varying geometry for speed lines of 13,100, 19,240, and 21,870 r/min. The simulations were run for all points from choke to surge including the experimentally determined rotating stall onset point. The experimental data and geometry were provided by Solar Turbines Inc. San Diego, CA. It was found possible to capture localized flow reversal inside of a vaneless diffuser using a steady state simulation. The results showed that using a geometric parameter, comparing the diffuser width, b4, to the impeller blade pitch distance, dpitch, it could be determined whether or not a steady state simulation could capture localized flow reversal. For values of b4/dpitch beneath 0.152 flow reversal could not be captured. But, for values of b4/dpitch above 0.177 localized flow reversal was captured. For values...
Flow analysis in centrifugal compressor vaneless diffusers
Journal of Scientific & Industrial Research, 2008
Flow computations have been performed in vaneless diffuser (diam, 1 m), in low speed backswept centrifugal compressor using finite volume method (FVM), coupled with Standard k-ε turbulent model by solving on commercial package FLUENT assuming steady, incompressible flow condition with design flow-rate in Navier-Stokes equations. Mean velocities and pressure have been computed on eight planes through the diffuser. Flow field at diffuser entry clearly shows impeller jet-wake flow pattern and the blade wakes. Passage wake is located on shroud side of diffuser and mixes out slowly as flow moves through diffuser. On the other hand, blade wakes distort and mix out rapidly in diffuser. Contours of turbulent kinetic energy are also presented on each of the diffuser stations, from which regions of turbulent mixing are identified. Close agreement was observed between numerical simulation and experimental results.
Investigations inside a vaned diffuser of a centrifugal pump at low flowrates
IOP conference series, 2016
This paper focuses on the unsteady flow behaviour inside the vaned diffuser of a radial flow pump model, operating at partial flowrates (0.387Q i , 0.584Q i and 0.766Q i where Q i is the impeller design flowrate).The effects of the leakage flows are taken into account in the analysis. PIV measurements have been performed at different hub to shroud planes inside one diffuser channel passage for a given speed of rotation, for several flowrates and different angular impeller positions. The performances and the static pressure rise of the diffuser were also measured using a three-holes probe in the same experimental conditions. The unsteady numerical simulations were carried out with Star CCM+ 10.02 code with and without leakage flow. The PIV measurements showed a high unsteadiness at very low flowrate which was confirmed by the numerical calculations. In previous studies it has been shown that the global performances, as the efficiencies are in good agreement between calculations and measurements. In this paper, a joint analysis of measurements and numerical calculations is proposed to improve the understanding of the flow behaviour in a vaned diffuser. Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.
The internal flow investigation of a centrifugal pump
This paper provides the results of a detailed flow investigation within a centrifugal pump equipped with a vaned diffuser. The measurements made with a laser-Doppler velocimeter were carried out at the impeller design point. In a previous paper concerning the same machine, El Hajem (1998) found a jet-wake structure developing at the impeller exit. During the actual study, measurements were obtained in the impeller and the diffuser at different measuring planes relative to the diffuser vanes. Results are presented as animations reconstituting a temporal evolution of the flow at the diffuser inlet. Unsteady velocity measurements obtained in phase with the impeller angular position gave access to the flow inside the impeller channels where three sections were explored. For each section, results were obtained as a function of the position of impeller blades relative to the diffuser vanes. Thus time resolved details of the flow could be examined for a better understanding of the complex unsteady flow existing between the two interacting blade rows. The analysis of the impeller flow field indicates the presence of a complex, unsteady and periodic flow. It is organised in a jet-wake structure. The wake is characterised by low relative velocities and is localised in the suction side/shroud corner. At this flow rate, it seems that presence of the vanes has only a limited effect on the impeller flow structure, except when the blades suction side are facing the diffuser vanes. At the impeller discharge, the time-resolved sequences show that the mixing process of the unsteady and periodic flow leaving the impeller is affected by the presence of the diffuser. At the leading edge, at the suction side of diffuser vanes, the flow is rapidly mixed. Whereas, when approaching the diffuser throat, the flow still shows its periodic character observed at the impeller outlet. This indicates that the diffuser is subject to unsteady inlet conditions that can alter its performances.