Time-Accurate CFD Analysis of a Centrifugal Compressor

2012

In this paper, the flow inside a small modified centrifugal compressor with a vaned diffuser used in an automotive turbocharger application was simulated. It has been known that the performance of the centrifugal compressor depends on the interaction between the compressor impeller and the vaned diffuser. The modified compressor comprises two splitters, which are not extended to the leading edge. If the splitters extend to the leading edge, it would produce a sufficient blockage to cause choking at high speed. This research aimed to study and simulate the effect of a vaned diffuser on the performance of a modified turbocharger compressor. The simulation was undertaken using CFD analysis to predict the aerodynamic flow field and characteristics. The mesh generator of a CFD code was used to generate a polyhedral mesh. Steady state analysis was carried out for the stage with the mixing plane approach. According to the results of the simulation, the vaned diffuser flow is characterized by a subsonic flow and there is no choking in between impellers exit and vane inlet. It was also observed that the outlet diffuser velocity is lower than outlet impeller velocity. At the outlet of the vaned diffuser, the total pressure was found to decrease, and the static pressure increase.

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

2008

In this paper a three dimensional viscous flow field in a Centrifugal Impeller with backswept and lean has been numerically analyzed using a commercial code (FLUENT) to understand the physics of complex real flow phenomena. The study was taken to investigate the flow interaction13; between impeller and vane diffuser for three different setting angles. It was shown at design point the13; flow at the exit of the impeller is uniform and the classical jet wake pattern is absent. At the intermediate13; plane between impeller inlet and exit and within vane diffuser channel the flow behaves like a potential13; flow. The stage analysis carried out using mixing plane formulation for three diffuser settings provided13; the optimum diffuser setting angle for maximum stage efficiency.

EPJ Web of Conferences

The article deals with a description of results from research and development of a radial compressor stage. The experimental compressor and used numerical models are briefly described. In the first part, the comparisons of characteristics obtained experimentally and by numerical simulations for stage with vaneless diffuser are described. In the second part, the results for stage with vanned diffuser are presented. The results are relevant for next studies in research and development process.

Volume 1: Turbomachinery, 1998

International Journal of Rotating Machinery, 2005

To reduce vibration and noise level, the impeller and diffuser blade numbers inside an industrial compressor are typically chosen without common divisors. The shapes of volutes or collectors in these compressors are also not axis-symmetric. When impeller blades pass these asymmetric structures, the flow field in the compressor is time-dependent and three-dimensional. To obtain a fundamental physical understanding of these three-dimensional unsteady flow fields and assess their impact on the compressor performance, the flow field inside the compressors needs to be studied as a whole to include asymmetric and unsteady interaction between the compressor components. In the current study, a unified three-dimensional numerical model was built for a transonic centrifugal compressor including impeller, diffusers, and volute. HFC 134a was used as the working fluid. The thermodynamic and transport properties of the refrigerant gas were modeled by the Martin-Hou equation of state and power law...

2014

In order to obtain more power from the engine, a new and larger turbocharger is being used. This paper is the culmination of the complete fundamental study of air flow physics. The purpose of this project is to analyze a centrifugal compressor in a turbocharger system of a diesel engine. Turbochargers are extensively used throughout the automobile industries as they can enhance the output of an internal combustion (IC) engine without the need to increase its cylinder capacity. This paper deals with the computational fluids dynamics analysis of flow in high speed turbocharger.

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.

International Journal of Turbo and Jet Engines, 2003

This paper presents the development of a numerical algorithm for the computation of axial thrust load on a centrifugal compressor. An unstructured flow solver has been developed for the computation of a hybrid, structured and unstructured grid. The computational domain of the impeller has been discretized using a structured mesh, while the computational domain on the back side of the wheel has been discretized using an unstructured mesh. The two grids are merged and a median dual-mesh is generated. The Navier-Stokes equations are discretized using a finite volume method. Roe's fluxdifference scheme is used for inviscid fluxes and directional derivatives along edges are used for viscous fluxes. The gradients at the mesh vertices are calculated using the Least-squares method. An explicit scheme is used for time integration. Convergence is accelerated using a local time-step and implicit residual smoothing. The results of the numerical simulation include the axial thrust load of the centrifugal compressor. In addition, details of the leakage flow are presented. Nomenclature A Jacobian matrix c Speed of sound Cp Specific heat at constant pressure Ε Source term e Total internal energy per unit volume F Flux vector G Non-convective part of the flux vector Η Total internal enthalpy per unit mass i Unit vector in the ^-direction j Unit vector in they-direction k Unit vector in the z-direction k Kinetic energy of turbulent fluctuations per unit mass k(i)

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.

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.

Journal of Mechanics, 2013

ABSTRACTThis paper is a numerical simulation that was made in the three-dimensional flow, carried out in a modified centrifugal compressor, having vaned diffuser stage, used as an auto-motive turbo charger. Moreover, the performance of the centrifugal compressor was dependent on the proper matching between compressor impeller and vaned diffuser, influencing significantly surge and the efficiency of centrifugal compressor stages. In addition, a modified compressor impeller, coupled with vane and vaneless diffuser, has been found to have similar internal flow patterns for both the vaneless and vaned diffuser design. The vaned diffuser effect has been paid particular attention in terms of better analysis where the diffuser was designed for high sub-sonic inlet conditions. Another aim of this research was to study and simulate the effect of vaned diffuser on the performance of a centrifugal compressor. The simulation was undertaken by using a commercial software, the so-called ANSYS CFX...

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 + ...

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.

An enhanced framework for various turbulence models study is exercised in a rotating and curved flow channels present in the centrifugal compressor of a micro gas turbine. This study is to evaluate the suitable turbulence model which asses the close behaviour of the internal flows obtaining in the present geometry since as it is believed from the previous research a turbulence model plays a major role in disparity between various approaches (i.e. Experimental, Analytical and Numerical). Presently a steady state numerical analysis is carried out by using Navier-Strokes equations coupled with standard k-ε, Realizable k-ε and k-kl-ω models were used in simulating the flow field around the geometry by means of commercial software ANSYS 15.0. On accumulation of curvature correction and compressibility effects to the corresponding models shows good match in numerical predictions of density profiles, Mach number profiles, Pressure profiles, temperature profiles etc. Overall Realizable k-ε model shows good agreement rather to standard k-ε, k-kl-ω models for the present geometry.