Numerical Simulation of a Centrifugal Compressor

Tip clearance effects on flow field of a low speed centrifugal compressor without and with partial shroud (PS) attached to the rotor blade tip at three values of tip clearance, viz. φ =2.2%, 5.1% and 7.9% of rotor blade height at the exit at three flow coefficients, namely, φ=0.12,0.18 (below design flow coefficient), φ=0.28 (design flow coefficient) and φ=0.34 (above design flow coefficient), is analysed computationally using structured multi block grid with fine grid in the tip clearance region. The paper aims to study several flow characteristics between blade channels using commercial flow solver ANSYS CFX 15.0 based on finite volume techniques. The centrifugal compressor in aerodynamic requirement is that edge velocities along the impeller channel passage surfaces like hub, shroud, pressure and suction surfaces vary smoothly without sudden decelerations, which cause flow separation leading to losses. Using the periodic boundaries and defined flow conditions at inflow / exit flow and blade rotations, the turbulent viscous flow between blade channels are computed. The efficiency related parameters using average quantities, besides flow pattern in terms of velocities, streamlines and pressure distribution on blade surfaces are graphically interpreted. An attempt is also made to study the influence of pressure loads on structural deformations in the chosen blade profile. This paper highlights aero-mechanical features of centrifugal impeller obtained from several numerical simulations, which are expected to provide a sound basis for further investigations.

Journal of Thermal Science, 2008

In this research, the centrifugal compressor of a turbocharger is investigated experimentally and numerically.

INCAS Buletin, 2018

The present paper presents the numerical analysis for a transonic centrifugal compressor using steady state CFD. The blade tip clearance effect over the position of shock waves, tip losses and the performances of the impeller are studied. Numerical simulations have been performed using RANS modelling, with the k-omega SST turbulence model (Shear Stress Transport). Eight cases were taken into consideration for the impeller with the following blade tip clearances values: 0 mm, 0.1 mm, 0.3 mm, 0.4 mm, 0.5mm, 0.7 mm, 1 mm, 2 mm, at the same operating conditions. For the entire stage only seven cases were studied, without the value for 0.1 mm because of its abnormal behaviour, as can be seen in the case of the impeller simulations. Results showed that the position of the shock wave does not change with the increase of the tip clearance. Aerodynamic losses due to shock wave, secondary flow and turbulence can be seen in the polytropic efficiency of the centrifugal impeller and the difference between the two extreme cases is about 3.2 %.

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

The flow in centrifugal compressors is characterized by its stable margin at all speeds of rotation. In this study an experimental measurements are carried out by using slots in the impeller blades at a shroud distance of 30 % from the exit of the blade. It is found that the stable margin is increased due to minimizing the boundary layer growth near the exit part of the blade at off and design speeds, and hence increasing the stable margin in two directions, the first by decreasing the minimum flow rate and surge margin and the second by increasing the maximum mass flow rate. It was found that the surge margin is decreased by 24% and the maximum flow rate is increased by 16.5% and hence, the total stable margin is increased by 60 %. The deriving power of the compressor is decreased due to decreasing the impeller losses. It was found that the losses are decreased from 30-35 % to about 2-3 % at medium speeds. The pressure ratio is not increased at all speeds but the efficiency is incr...

2017

The work addresses an imperious issue of enhancing centrifugal flow compressor performance by modifying the impeller blade design. Recent advancements have reported in enhancement of centrifugal compressor performance by the impeller with extended shroud by 10%. Present work extends to explore the significance geometric and design parametric variation of varying exit blade width and its implications on the compressor performance. Numerical simulations were carried out for the selected cases of extended shroud by 10% along with the width at exit blade width increased by 5% and 10%. The numerical predictions were validated with the compressor theory and matched reasonably well. Results indicates higher static pressure rise with reduced losses and increased efficiency with exit blade width variation. The stagnation pressure distribution increases at exit of diffuser due to rotating vaneless diffuser. The presence of rotating vaneless diffuser yields smooth entry flow profiles, thereby ...

Tip leakage effects on the flow field of a low speed centrifugal compressor is observed computationally using structured multi block grid with fine grid in the tip leakage region. The computational study of centrifugal compressor is carried out without and with a partial shroud on the tip of the blade with finite volume method upwind scheme using ANSYS CFX software. Centrifugal compressor impeller with three values of tip clearances i.e., τ = 2.2%, 5.1% and 7.9% of blade height at trailing edge are examined at four flow coefficients 0.12, 0.18,0.28 and 0.34. The effect of tip clearance on total pressure coefficient and static pressure coefficient from inlet to outlet of the compressor is observed. The drop in static pressure coefficient and total pressure coefficient with the increase in tip clearance is found to be high at the tip of the blade due to high pressure fluid leakage at the tip of the blade. Shifting on the maximum value of non-dimensional tangential velocity towards the hub at the outlet of impeller to increase in clearance is analyzed. The velocity vectors at turbo surface 1.8, velocity contours are analyzed and tangential velocity graphs are plotted.

Applied sciences, 2022

The performance and efficiency of a centrifugal compressor are usually affected by the highly complex 3-dimensional flow structures which develop in the flow field of the compressor. Several experiments and research using numerical analysis have been reported, however, there are still many unknown physical phenomena that need to be studied, in order to optimize the design and improve the efficiency of turbomachines, especially those installed on hydrogen-powered fuel cell electric vehicles (FCEVs). In this study, the 3-dimensional vortex structures were analyzed using the critical-point theory and the probabilistic definitions, for an air supply device mounted on the commercial hydrogen FCEVs. The behavior of the complex 3-dimensional vortex structures at the design flow rate and low flow rate were elucidated. A tip leakage vortex was observed to develop at the leading edge of the main blade at all flow rates, which caused interference to the splitter blade. At 60% of the design flow rate, a vortex breakdown occurred at the tip leakage vortex near the leading edge of the main blade, and a reverse flow at 50% chord length of the main blade’s suction surface. The boundary layer which developed at the leading edge of the main blade’s suction surface at all flow rates led to the creation of a hub separation vortex by interfering with the boundary layer developed at the hub surface as a result of the centrifugal force. In addition, the boundary layer developed at the hub and shroud surface created a horseshoe vortex as it moved downstream and interfered with the leading edge of the main blade and splitter blade. It was confirmed that the behavior of the tip leakage, hub separation, and horseshoe vortex structures determined the aerodynamic performance of the centrifugal compressor. The average pressure difference improved by 1.47% of the entire flow rate after optimizing the compressor design.

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.

유체기계 연구개발 발표회 논문집, 2015

The prediction and design of the aerodynamic performance of a compressor are crucial requirements to properly evaluate the aerodynamic performance and characteristics during preliminary design of a centrifugal compressor because it is not clear to figure out the internal flow property of a compressor including complicated three dimensional turbulent flow. In this study the industrial centrifugal compressor was calculated for variations of mass flow and blade Mach number with 2 cases of different number of diffuser vanes. One of the major cause of the impeller loss is the pressure drop when the operating mass flow rate closes to choking flow coefficient. Momentum transfer and loss characteristics of the impeller are important to understand impeller characteristics. The method was suggested to estimate the impeller performance characteristics.