TIP LEAKAGE EFFECTS ON FLOW FIELD OF A CENTRIFUGAL COMPRESSOR (original) (raw)
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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.
EFFECT OF TIP CLEARANCE ON A CENTRIFUGAL COMPRESSOR
Computational analysis of low speed centrifugal compressor is carried out with finite volume method using ANSYS-CFX software. Centrifugal compressor impeller with three values of clearances i.e., 0%, 2% and 5% of blade height at trailing edge are examined at five flow coefficients f=0.28, 0.34, 0.42 (design value), 0.48 and 0.52. The effect of tip clearance on static pressure from inlet to outlet of the compressor is analyzed. The drop in static pressure with 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. Performance reduction with tip clearance is observed. Total pressure and velocity at outlet are analysed for five flow coefficients
EFFECT OF TIP CLEARANCE ON PERFORMANCE OF A CENTRIFUGAL COMPRESSOR
The centrifugal compressor is to study the effect of tip clearance on the performance characteristics and the wall static pressure for a different flow co-efficient. The method of testing the compressor is run at a constant speed at 2000rpm. The tip clearance is varied by using spacers. The volume flow rate is varied with the help of throttling device to conduct the performance test. The performance characteristic of the centrifugal compressor showing the variation of discharge pressure with volume flow rate is plotted. Obtaining the performance characteristics showing the variation of discharge pressure with volume flow rate for different tip clearance, viz. =2.2%, 4%, 6.1% and 7.9%. Measurement of periodic pressure at various tip clearance viz. =2.2%, 4%, 6.1% and 7.9%. For each tip clearance pressure measured in radial location of impeller at 6 positions for different flow co efficient values. Five flow coefficients viz., ф =0.40, =0.34 (both above design flow), =0.28 (near design flow), =0.21=0.18 (both below design flow) and four values of non-dimensional tip clearance viz., =2.2%, 4%, 6.1% and 7.9%, are chosen for experimental work. The objective of the research work is to measure the periodic variation static pressure on the casing over the rotor at different values of tip clearance and flow coefficients. With the availability of these data, it is possible to improve the tip clearance flow in centrifugal compressor.
Numerical Simulation of a Centrifugal Compressor
In this paper, the tip clearance effects on flow field of a low speed centrifugal compressor without and with partial shroud (PS) fitted on to the rotor blade tip at three values of tip clearance, viz. = 2.2%, 5.1% and 7.9% of rotor blade height at the exit at three flow coefficients, namely, = 0.18, 0.28, and 0.34, was studied. Based on the theory of computational fluid dynamics (CFD), performance curves and parameter distributions of the compressor were obtained from the 3-D numerical simulation by using ANSYS CFX 15.0. 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.
Losses and blade tip clearance for a centrifugal compressor
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 %.
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.
NUMERICAL SIMULATION ON PERFORMANCE OF A LOW SPEED CENTRIFUGAL COMPRESSOR
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
Enhancing the surge margin of a Centrifugal Compressor with different Blade Tip Geometry
— The reliability operation for small fuel cells and hybrid fuel cell with gas turbine requires centrifugal compressor surge prevention. This study concerns a high speed centrifugal compressor stage with different blade tip geometries. The investigations were performed with unsteady three-dimensional, compressible flow simulations. A novel parameterization method has been developed to alter the tip geometry of an impeller blade. Different tip geometries are investigated includes flat tip blade, main blade winglet, main and splitter blade winglet and finally pressure side grooved tip. The performance and internal flow results are presented at surge, design and near choke points. The conclusion is that the tip geometry has a significant effect on the compressor performance and the operation stability at lower flow rates. The pressure ratio and surge margin for the blades with winglet have been improved, and decreased for the grooved tip geometry. More uniform flow at impeller outlet with winglet blade. The use of winglet tip displaces the tip leakage vortex away from the blade and weakening the impingement effect. The winglet tip reduces the aerodynamic losses by unloading the tip section, reducing the leakage flow rate and turning the leakage flow in a more stream wise direction.
International Journal of Heat and Fluid Flow, 2015
CFD has become an essential tool for researchers to analyze centrifugal compressors. Tip leakage flow is usually considered one of the main mechanisms that dictate compressor flow field and stability. However, it is a common practice to rely on CAD tip clearance, even though the gap between blades and shroud changes when compressor is running. In this paper, sensitivity of centrifugal compressor flow field and noise prediction to tip clearance ratio is investigated. 3D CFD simulations are performed with three different tip clearance ratios in accordance to expected operating values, extracted from shaft motion measurements and FEM predictions of temperature and rotational deformation. Near-surge operating conditions are simulated with URANS and DES. DES shows superior performance for acoustic predictions. Cases with reduced tip clearance present higher pressure ratio and isentropic efficiency, but no significant changes in compressor acoustic signature are found when varying clearance. In this working point, tip clearance is immersed in a region of strongly swirling backflow. Therefore, tip leakage cannot establish any coherent noise source mechanism.