Computer-Aided Analysis of Centrifugal Compressors

2016

The Society shall not be responsible for statements or opinions advanced in papers or in die. cussion at meetings of the Society or of Its Divisions or Sections, or printed in its publications. /y ^ Discussion is printed only if the paper is published in an ASME Journal. Papers are available „ ` ® from ASME for fifteen months after the meeting.

The design and off-design performance characteristics of single stage centrifugal compressor consisting of 12 vanes impeller interfacing with 11 vanes diffuser have been studied experimentally and numerically. The impeller has been designed and developed with radial exit, 30o inlet blade angle (with tangent), 77 mm diameter and the discharge volute considering constant mean flow velocity. The performance of the compressor at varying capacity (60 to 120 % of design) by controlling the discharge valve and with the variation of rotating speed (15000 to 35000 rpm) by regulating speed of the coupled gas turbine has been conducted at the recently developed test rig. The numerical simulation has been done by adopting viscous Reynolds Average Navier-Stokes (RANS) equations with and without Coriolis Force & Centrifugal Force in rotating reference frame (impeller) and stationary reference frame (casing) respectively utilizing CFD software Fluent 14. The flow around a single vane of impeller interfacing with single vane of diffuser, the rotational periodicity and sliding mesh at the interfacing zone between rotating impeller and stationery diffuser are considered. Non dimensional performance curves derived from experimental and numerical results are presented and compared. The numerical results are found to match very closely with the experimented data near the design point and deviation is observed at the both side of the designed operating point. Non-uniform pressure profiles towards the impeller exit and strong cross flow from blade to blade are detected at low flow operating conditions. Total pressure, static pressure and velocity distributions at design and off design operation obtained from the CFD results are analysed and presented here.

The present computational investigation deals with performance improvement of a low speed centrifugal compressor by inexpensive partial shroud near the rotor blade tip. Computational study of centrifugal compressor is carried out with finite volume method upwind scheme using ANSYS CFX-15.0 software are carried for four flow coefficients φ=0.12,0.18,0.28 and 0.34 at three values of tip clearance, viz. τ = 2.2%, 5.1% and 7.9% of rotor blade height at the exit. Performance tests are carried out for a total of two configurations. From these measurements, partial shroud is found give best performance. The improvement in the compressor performance may be due to the reduction of tip leakage flows by the small extension of partial shroud (2 mm on the pressure surface side). The axial distribution of static and total pressure coefficient at rotor exit for the four flow coefficients, clearly indicate increase in total pressure in the rotor tip region for the configuration with PS compared to that for the basic configuration (without PS). Similar increase is observed in the static pressure distribution at the rotor exit for the higher values of clearance. The mass averaged total and static pressures at the rotor exit for both configurations at the three values of tip clearances clearly show that partial shrouds are beneficial in improving the pressure rise of the compressor. Notation:-C u = Tangential velocity m = Non-dimensional meridional distance P S = Static pressure P atm = Atmospheric pressure P O = Total pressure R = Non-dimensional radius u 2 = Rotor tip speed = (d 2 N/60) (m/s), x = Non-dimensional axial distance  = Flow coefficient ρ = Density of air (kg/m 3) τ = Tip clearance  o = Total pressure coefficient= 2P o / U2 2  s = Static pressure coefficient= 2P s / U2 2  = Power coefficient

Journal of University of Shanghai for Science and Technology, 2022

This paper is concerned the flow simulation and performance analysis of the Centrifugal Compressor Using CFD-Tool. The complex internal flow of centrifugal compressor can be well analyzed, and the unique design system needs to be developed. It should be early to use the interface and also flexible for input and output. A 3-D flow simulation of turbulent-fluid flow is presented to visualize the flow pattern in-terms of velocity, streamline and pressure distribution on the blade surface are graphically interpreted. The standard K-e turbulence model and the simple model algorithm were chosen for turbulence model and pressure distribution well determined. The simulation was steady Heat transfer and moving reference frame was used to consider the impeller interaction under high resolution. Furthermore, A computational Fluid Dynamics (CFD) 3-D simulation is done to analyze the impeller head and efficiency required of centrifugal compressor. The impeller is rotated for a constant revolution and mass flow rate, in this study initially the geometry of centrifugal compressor impeller is created by an ANSYS Vista CCD, and the Blade modeller done by Bladegen, Finally, CFD analysis was performed in ANSYS CFX using the ANSYS Turbo grid meshing tool. According to the analysis, as the number of impeller blades increases, so does the value of the head and power imparted, as well as the impeller's efficiency.

2014

his paper investigates the development of a preliminary design method for centrifugal compressors. The design process starts with the aerodynamic analysis of the preliminary design and its reliance on empirical rules limiting the main design parameters. The procedure is applied to compressors for pressure ratios of 1.5, 3 and 5 as an example for developing an initial non-dimensional skeleton design. The skeleton diagrams are presented for different exit blade angles ranging from 0° to-60°. The design procedure was carried out for three cases: without prewhirl and with high positive prewhirl of 15° and 30°. Design considerations of mechanical stress for the impeller and minimum inlet relative Mach number are taken into consideration. Diffusion factor limitations have also been considered. Selected design parameters according to economical considerations have been presented for each pressure ratio.

1999

This paper presents the experimental and numerical investigation of an outward volute of rectangular cross section. The investigation is carried out at the level of- stage performance,- volute performance and- detailed flow field study at selected peripheral positions for various operating points.The objective of the investigation was to gain further knowledge about the flow structure and loss mechanism in the volute. Simultaneously with the experimental investigation, a numerical simulation of the flow in the volute was carried out.A 3D Euler-code was used in which a wall friction term and a tuned artificial dissipation term account for viscous effects. A reasonable agreement between the experimental and numerical results is observed. As a result a good and detailed knowledge about the pressure recovery and loss mechanism in the volute is obtained.Copyright © 1999 by ASME

An attempt is made in the present study to investigate the superior turbulence model for simulating three dimensional flows in centrifugal compressor. The strong channelled curvature and intensive rotations prevalent in centrifugal compressor resulting high swirling and secondary flow nictitates choosing appropriate turbulence model for accurate performance predictions. The various turbulence models offered in FLUENT viz Spalart Allmaras (curvature correction), Transition SST (curvature correction), Scaled Adaptive Simulations (Curvature correction with compressibility effect), Reynolds stress model (compressibility effect) were investigated presently for Eckardt Impeller. Reynolds stress model though involves higher computational time was found to be the superior model. It is essential to investigate the onset of surge and choke for completely understanding the performance of a centrifugal compressor. Choking phenomena was observed when the speed reached 16000 rpm with relative Mach number reaching unity in the impeller region. The maximum flow rate at 16000 rpm was 0.4 kg/s per blade and remained constant then 16500 rpm. Surging was founded to initiate when the back pressure has to reach 1.8 bar resulting in zero discharge.

E3S Web of Conferences, 2019

The study presents the simulation results of the viscid gas flow in low flow coefficient centrifugal compressor stages. The problem is solved in a stationary formulation using the Ansys CFX software package. The numerical simulation is carried out on three ultrahigh-pressure model stages; two stages have blades of the classical type impeller and one stage is of the bodily type. The value of the conditional flow coefficient is 0.0063 to 0.015. As part of the study, block-structured design meshes are used for all gas channel elements, with their total number being equaled as 13–15 million. During the calculations a numerical characteristic was validated with the results of tests carried out at the Department of Compressor, Vacuum and Refrigeration Engineering of Peter the Great St. Petersburg Polytechnic University. With an increase of inlet pressure as a result of a numerical study, it was found that for a given mathematical model the disk friction and leakage coefficient (1 + βfr + ...

1992

Detailed measurements of the swirling flow in a centrifugal compressor volute with elliptical cross section are presented. They show important variations of the swirl- and through-flow velocity, total and static pressure distribution at the different volute cross sections and at the diffuser exit. The basic mechanisms defining the complex 3D flow structure are clarified. The different sources of pressure losses have been investigated and used to improve the prediction capability of one dimensional mean streamline analysis correlations. The tangential flow loss model, under decelerating flow conditions, and friction loss model are confirmed. New empirical loss coefficients are proposed for the exit cone loss model and the tangential flow loss model for the case of accelerating flow in the volute.

International Journal of Turbo and Jet Engines, 2003

The performance of different low-Reynolds number turbulence models applied to the simulation of a flow in the NASA low-speed compressor is described. The flow solver utilizes a structured multiblock grid with Cartesian velocity components in a rotating coordinate system. The inviscid fluxes are calculated using Roe's scheme. An implicit solution method is applied and a multigrid cycling is used in order to accelerate the convergence. In this study the Baldwin-Lomax model, Chien's k-ε model and a full Reynolds-stress closure by Speziale et al. are applied. A detailed comparison between the experimental and computational velocity fields and pressure distributions is made.