Effects of bending-torsional duct-induced swirl distortion on aerodynamic performance of a centrifugal compressor

A turbocharger compressor working in commercial vehicles,especially in some passenger cars,often works together with some pipes with complicated geometry as an air intake system,due to limit of available space in internal combustion engine compartments.These pipes may generate various distortions of physical parameters of the air at the inlet of the compressor and therefore the compressor aerodynamic performance deteriorates.Sometimes,the turbocharging engine fails to work at some operation points.This paper investigates the effects of various swirl distortions induced by different bending-torsional intake ducts on the aerodynamic performance of a turbocharger compressor by both 3D numerical simulations and experimental measurements.It was found that at the outlet of the pipes the different inlet ducts can generate different swirl distortions,twin vortices and bulk-like vortices with different rotating directions.Among them,the bulk-like vortices not only affect seriously the pressure distribution in the impeller domain,but also significantly deteriorate the compressor performance,especially at high flow rate region.And the rotating direction of the bulk-like vortices is also closely associated with the efficiency penalty.Besides the efficiency,the transient flow rate through a single impeller channel,or the asymmetric mass flow crossing the whole impeller,can be influenced by two disturbances.One is from the upstream bending-torsional ducts;other one is from the downstream volute.     

串列叶栅前后排叶片周向相对位置对离心压气机性能的影响

串列叶栅前后排叶片相对位置对串列扩压器的性能有重要影响.根据离心叶轮出口气流参数设计了一离心式串列叶栅扩压器,并利用数值模拟方法在前、后排叶栅周向相对位置分别为10%、20%、30%、40%、50%、60%、70%、80%和90%时对离心压气机级进行了计算和分析,研究周向相对位置变化对离心压气机性能的影响以及作用机理.数值模拟结果表明:随着前后排叶栅周向相对位置变化,后排叶栅前缘滞止高压区相对前排叶栅的位置发生了变化,影响了前排叶栅压力面的压力分布,从而改变了前排叶栅压力分布及大小;当前后排叶栅周向相对位置为30%时,扩压器性能达到最佳,使压气机总压比和等熵效率最大,稳定工作范围增大;前后排叶栅所形成的渐缩通道可抑制后排叶栅吸力面边界层的分离.     

The change of the inlet geometry of a centrifugal compressor stage and its influence on the compressor performance

The impact on the compressor performance is important for designing the inlet pipe of the centrifugal compressor of a vehicle turbocharger with different inlet pipes. First, an experiment was performed to determine the compressor performance from three cases: a straight inlet pipe, a long bent inlet pipe and a short bent inlet pipe. Next, dynamic sensors were installed in key positions to collect the sign of the unsteady pressure of the centrifugal compressor. Combined with the results of numerical simulations, the total pressure distortion in the pipes, the pressure distributions on the blades and the pressure variability in the diffuser are studied in detail. The results can be summarized as follows: a bent pipe results in an inlet distortion to the compressor, which leads to performance degradation, and the effect is more apparent as the mass flow rate increases. The distortion induced by the bent inlet is not only influenced by the distance between the outlet of the bent section and the leading edge of the impeller but also by the impeller rotation. The flow fields in the centrifugal impeller and the diffuser are influenced by a coupling effect produced by the upstream inlet distortion and the downstream blocking effect from the volute tongue. If the inlet geometry is changed, the distributions and the fluctuation intensities of the static pressure on the main blade surface of the centrifugal impeller and in the diffuser are changed accordingly.     

Numerical investigation of aerodynamic performance influenced by circumferentially pre-swirling coming flow on the crossover and de-swirling cascade of a multistage centrifugal compressor

Numerical investigation is implemented on aerodynamic performance inside the crossover and de-swirling cascade of a multistage centrifugal compressor. The emphasis is put on the aerodynamic performance influenced by the circumferentially pre-swirling coming flow. The results indicate that flow separation occurs inside the crossover, and the separation area may be changed with different circumferentially pre-swirling coming flow. Decreased pre-swirling intensity of the coming flow may effectively restrain the flow separation and make the outflow from the crossover more uniform, which helps to improve the aerodynamic performance of the successive de-swirling cascade. The flow inside the de-swirling cascade is a non-uniform swirling flow with large separation. The complex secondary flow occurs along the main flow and experiences a process of generating, developing, dissipating and collapsing. __________ Translated from Power Engineering, 2007, 27(1): 24–28, 49 [译自: 动力工程]     

Effect of high negative incidence on the performance of a centrifugal compressor stage with conventional vaned diffusers

Three vaned diffusers, designed to have high negative incidence (-8°) at the design operating point, are studied experimentally. The overall performance (efficiency and pressure ratio) are measured at three rotational speeds, and flow angles before and after the diffuser are measured at the design rotational speed and with three mass flow rates. The results are compared to corresponding results of the original vaneless diffuser design. Attention is paid to the performance at lower mass flows than the design mass flow. The results show that it is possible to improve the performance at mass flows lower than the design mass flow with a vaned diffuser designed with high negative incidence. However, with the vaned diffusers, the compressor still stalls at higher mass flow rates than with the vaneless one. The flow angle distributions after the diffuser are more uniform with the vaned diffusers.     

Design and Prototyping of Micro Centrifugal Compressor

In order to establish the design methodology of ultra micro centrifugal compressor, which is the most important component of ultra micro gas turbine unit, a 10 times of the final target size model was designed, prototyped and tested. The problems to be solved for downsizing were examined and 2-dimensional impeller was chosen as the first model due to its productivity. The conventional ID prediction method, CFD and the inverse design were attempted. The prototyped compressor was driven by using a turbocharger and the performance characteristics were measured.     

离心压缩机无叶扩压器的改进新方法

研究了某高压比离心压缩机无叶扩压器的性能,提出在无叶扩压器轮盘侧加装一定高度机翼型导叶的改进方法。结果表明,这种扩压器可以改善其内部流动,提高自身的压力恢复系数和效率,从而改善离心压缩机的整级性能。     

Unsteady pressure measurements in a high-speed centrifugal compressor

This paper presents the unsteady data acquisition system used to measure the pressure field in high speed compressors. Details and electronic sketches are given for the conditioners developed in-house that have been used to amplify and to filter the pressure signal with the aim of acquiring data up to 150 kHz. A discussion of the experimental results carried out in a centrifugal compressor is proposed. Through different processing of the pressure signals and a comparison with URANS simulations, the excitation of the pressure transducers by the pressure waves generated by shock waves that occur between the impeller and the diffuser is highlighted. The levels of pressure fluctuations measured when entering into surge are also presented and reveal very repetitive behaviour of the flow instabilities.     

Investigation of a centrifugal compressor and study of the area ratio and TIP clearance effects on performance

In this research, the centrifugal compressor of a turbocharger is investigated experimentally and numerically. Performance characteristics of the compressor were obtained experimentally by measurements of rotor speed and flow parameters at the inlet and outlet of the compressor. Three dimensional flow field in the impeller and dif- fuser was analyzed numerically using a full Navier-Stokes program with SST turbulence model. The performance characteristics of the compressor were obtained numerically, which were then compared with the experimental results. The comparison shows good agreement. Furthermore, the effect of area ratio and tip clearance on the performance parameters and flow field was stud- ied numerically. The impeller area ratio was changed by cutting the impeller exit axial width from an initial value of 4.1 mm to a final value of 5.1 mm, resulting in an area ratio from 0.792 to 0.965. For the rotor with exit axial width of 4.6 mm, performance was investigated for tip clearance of 0.0, 0.5 and 1.0 mm. Results of this simula- tion at design point showed that the compressor pressure ratio peaked at an area ratio of 0.792 while the effi- ciency peaked at a higher value of area ratio of 0.878. Also the increment of the tip clearance from 0 to 1 mm resulted in 20 percent efficiency decrease.     

Effects of Diffuser Vane Geometry on Interaction Noise Generated from a Centrifugal Compressor

The characteristics of interaction tone noise radiated from a centrifugal compressor with a vaned diffuser are discussed by experiments, including visualization techniques using the oil-film method. Research attention is paid to the leading edge geometries of the diffuser vanes that are deeply related to the generation mechanism of the interaction tone noise. The compressor-radiated noise can be reduced by several decibels by setting some clearances in both the hub and shroud surfaces of the diffuser wall along with some decline in the pressure-rise coefficient. Since the decline turned out to be caused by the flow impingement and also by the secondary flow within the diffuser passages, several new types of diffuser vane geometries which do not detract from both the performance and noise level are developed and utilized for the experiments. The presented diffuser vane geometries will offer a few basic guidelines for the diffuser vane design.     

Effects of airfoil-probe tubes on the flow field of a compressor cascade

To explore the effects of airfoil-probe tubes and its installment position on the flow field of the compressor cascade,and find out the mechanism that how the airfoil-probes affect the aerodynamic characteristics of the compressor cascade,this paper performed both numerical and experimental works on the same compressor cascade.The experiment mainly focused on the cases of low Mach number (Ma =0.1),and cases with different Mach numbers (0.1,0.3,0.7) and different incidence angles (-5,0,5) are investigated by the numerical method.The case without the airfoil-probe tube was referenced as the baseline,and other three cases with the airfoil-probe tubes installed in different chordwis positions (30％,50％,70％ of the chord length) were studied.The diameter of the airfoil-probe tube is 3ram,which is configured as 300％ amplification of some particular airfoil-probe according to the geometrical similarity principle.The results show that the airfoil-probe tubes have a negative influence on the flow capacity of the cascade at all investigation points.The separations and the large scale streamwise vortices that induced by the airfoil-probe tube on the pressure side cause most the losses at the high Mach number.The influence of the airfoil-probe tube on the flow field in the vicinity of the pressure side surface is local separation at the low Mach number.The airfoil-probe tubes also have a clearly effect on the leakage flow.It decreases the mass flow of the leakage flow and weakens the intensity of the leakage vortex,but enlarges the influence area.The total pressure loss of the case that the tube is installed at the half chordwise position is generally lower than other cases especially at the high Mach number,it can even decrease the losses compared with the basic case.     

Aerodynamic performance and noise characteristics of a centrifugal compressor with modified vaned diffusers

Improvement of aerodynamic performance and reduction of interaction tone noise of a centrifugal compressorwith vaned diffusers are discussed by experiments and visualization techniques using a colored oil-film method.The focus of the research is concentrated on the leading edge shape of diffuser vanes that are deeply related to thegeneration mechanism of the interaction tone noise.The compressor-radiated noise can be reduced by more thanten decibels by using modified diffuser vanes which have 3-D tapered shapes on both pressure and suction sur-faces of the leading edge.Furthermore,by adopting the proposed modified diffuser vanes,the secondary flowwhich is considered to be an obstruction of diffuser pressure recovery can be suppressed,and also the pressuredecrease observed in the throat part of the diffuser flow passage is reducible.Thus,the proposed diffuser vanesshow a favorable result for both noise and the aerodynamic performance of the centrifugal compressor,and offera few basic guidelines for the diffuser vane design.     

Performance analysis of a centrifugal compressor with variable inlet guide vanes

The flow in a centrifugal compressor stage with variable inlet guide vanes (VIGVs) is investigated by numerical simulation in this paper. Analysis of the performance curves and relative velocity vectograms indicates that performance curves shift toward small flow domain when VIGVs turn positively, and toward large flow domain when VIGVs turn negatively. Stage efficiency drops quickly after work condition enters a small flow domain through the peak efficiency point. Under the circumstance of large setting angles of the guide vanes, there exist obvious flow separations in guide vane passages within wide flow ranges, and back flow regions can be located at the front of splitter suction surfaces under large flow conditions, while under the condition of small flow, flow separations occur on suction surfaces of long blades. __________ Translated from Journal of Power Engineering, 2006, 26(6): 804–807 [译自: 动力工程]     

离心式压气机叶片的造型和加工方法

首先分析了离心式压气机工作轮的结构特点,指出随着新的排放标准的逐步实施,米勒定时和可变喷嘴等技术的应用已成为未来的发展方向,直纹曲面径向叶型在离心式压气机未来的发展中将有用武之地。进而针对直纹曲面径向叶型,给出了通过导线构造叶片曲面的造型方法。针对叶片的数控加工方法,提出利用非线性方程组的数值计算方法进行精铣叶片的刀具加工轨迹的求解方法。     

Design and prototyping of micro centrifugal compressor for ultra micro gas turbine

In order to establish the design methodology of an ultra micro centrifugal compressor, which is the most important component of an ultra micro gas turbine unit, a 10 times size of the final target compressor (impeller outer diameter 40 mm, corrected rotational speed 220,000 r/min) was designed. The problems to be solved for downsizing were examined and a 2-dimensional impeller was chosen as the first model due to its productivity. The conventional ID prediction method and CFD were used. The prototyped compressor was tested by using cold air at the reduced speed of 110,000 r/min. Following to the 10 times model, a 5 times size of the final target model having fully 3-dimensional shape (impeller outer diameter 20mm, corrected rotational speed 500,000 r/min) was designed and tested by using hot gas at the reduced speed of 250,000 r/min.     

Investigation of surge behavior in a micro centrifugal compressor

This paper reports the experimental and theoretical study of the surge occurred in prototyping an ultra micro centrifugal compressor. As the first step, the 10 times size model of an ultra micro centrifugal compressor having the 40 mm outer diameter was designed and manufactured. The detailed experimental investigations for the transient behavior of surge with several different values of B parameter were carried out. The experimental results during the surge were compared with those obtained by the non-linear lumped parameter theory in order to validate the effectiveness of the theoretical surge model for the micro centrifugal compressor. As a result, the quite different behavior of the surge appeared for the different values of B both in the experiment and in the analysis.     

Detailed analysis of the flow in the inducer of a transonic centrifugal compressor

Numerical and experimental investigations were conducted in a transonic centrifugal compressor stage composed of a backswept splittered unshrouded impeller and a vaned diffuser. A detailed analysis of the flow in the inducer (i.e. the entry zone of the impeller between the main blade leading edge and the splitter blade leading edge) is proposed from choke to surge. Steady and unsteady simulations were performed using the code elsA, which uses a multi-domain approach on structured meshes and solves the compressible RANS equations, associated with a two-equation turbulence model k-l in the rotating frame of reference. The 1MW LMFA-ECL test rig was used for carrying out the tests in the compressor stage. Unsteady pressure measurements up to 150 kHz and Laser Doppler Anemometry measurements were performed in the inducer. A good agreement is obtained between the experimental and numerical data even if an over dissipation is noticed in the numerical results. The change in flow pattern from choke to surge is mainly due to a change in the tip leakage flow trajectory which straightens, leading to a flow blockage of an individual passage near shroud. A spectral analysis shows that only the blade passing frequency and its harmonics compose the various spectra obtained from choke to surge.     

Use of partially shrouded impeller in a small centrifugal compressor

Numerical analysis is conducted for the 3-dimensional impeller and vaneless diffuser of a small centrifugal com- pressor. The influence of impeller tip clearance on the flow field of the impeller is investigated. Detailed investigation on the leaking flow across the tip clearance of the impeller shows that the leaking flow rate is higher near the exit of the impeller than that near the inlet of the impeller. Based on this phenomenon, a new partially shrouded impeller is designed. The impeller is shrouded near the exit of the impeller. Numerical results show that the secondary flow region becomes smaller at the exit of the impeller. Better performance is achieved than that with the unshrouded impeller.     

Experimental Analysis of the Rotor Stator Interaction Within a High Pressure Centrifugal Compressor

IntroductionThe t1ow field in a multi-row compressor is three-dimensional, turbu1ent, viscous and inherently unsteady.That makes it truly a challenging flow to understand,measure and compute. Attempts are made to increase theunderstanding of the flow in a multi-row environment,notabIy regarding the flow field unsteadiness due to therotor-stator interactions. Several works have beenpublished conceming the mu1ti-stage unsteadycomputational techniques which involve vallous kinds ofhypothesis. Th…     

Computational and experimental study of an industrial centrifugal compressor volute

IntrotctionThe overall performance of a centrifugal compressoris a combination of the dueller, diffuser, and voluteperformances. Each component has to be designedcarefully in order tO' minimize the losses and maximizethe efficiency. In this paper, a centrifugal compressorvolute (or spiral) is stUdied numerically, and the CFDresults are compared with measured data.A volute is used to collect the flow from a vaned orvaneless diffuser and to gUide it Ollt of the compressor.The volute geometry…