Noise reduction for centrifugal fan with non-isometric forward-swept blade impeller

To reduce the noise of the T9-19No.4A centrifugal fan, whose impeller has equidistant forward-swept blades, two new impellers with different blade spacing were designed and an experimental study was conducted. Both the fan’s aerodynamic performance and noise were measured when the two redesigned impellers were compared with the original ones. The test results are discussed in detail and the effect of the noise reduction method for a centrifugal fan using impellers with non-isometric forward-swept blades was analyzed, which can serve as a reference for researches on reduction of fan noise. __________ Translated from Fluid Machinery, 2007, 35(9): 1–4, 37 [译自: 流体机械]     

Noise reduction for centrifugal fan with non-isometric forward-swept blade impeller

To reduce the noise of the T9-19No.4A centrifugal fan, whose impeller has equidistant forward-swept blades, two new impellers with different blade spacing were designed and an experimental study was conducted. Both the fan’s aerodynamic performance and noise were measured when the two redesigned impellers were compared with the original ones. The test results are discussed in detail and the effect of the noise reduction method for a centrifugal fan using impellers with non-isometric forward-swept blades was analyzed, which can serve as a reference for researches on reduction of fan noise.     

Research on performance of centrifugal pump with different-type open impeller

To investigate the influence of impeller type on the performance and inner flow of centrifugal pump, the numeri- cal simulation and experimental research were carried out on the same centrifugal pump with straight-blade and curved-blade open impeller. Based on SIMPLEC algorithm, time-averaged N-S equation and the standard k-e turbulence model, the numerical results are obtained. The pressure distribution in the different type impellers is uniform, while the low pressure area in straight-blade inlet is larger. The vortexes in the passage of impeller exist in both cases. Relative to curved-blade impeller, there are larger vortexes in most of the flow passages except the passage near the tongue in straight-blade impeller. Also some small backflow regions are found at the blade inlet of two impellers. The characteristic curves achieved by numerical simulation basieaUy agree with those by experiment, and straight-blade open impeller centrifugal pump has a better hydraulic performance.     

Investigation of a miniature centrifugal fan

A centrifugal fan was designed with a matching centrifugal volute flow channel in order to investigate a numerical simulation with prototype manufacturing, and to compare with experimental results. The fan configuration was developed according to a fan-design theorem. A model P-60 turbojet engine compressor blade design was adopted for the fan aerodynamic analysis and design. The results were verified using the STAR-CD code. Also, based on the findings, a miniature centrifugal fan was designed and manufactured using a CNC five axes machine. The P–Q performance curves were tested using an AMCA standard 210-85 test chamber apparatus. From the numerical analysis results, the pressure on the suction and pressure surfaces will increase gradually from the inlet to one-half the distance of the hub’s camber line, however, it will increase more rapidly afterwards. In addition, stress-concentration phenomenon occurred at the tip of the suction and pressure surfaces. In other words, the tip was more prone to damage when the fan was operated. Experiments show that the designed fan maximum flow rate Q and static pressure P were 32% and 59%, respectively, which were lower than the commercial fan data at 2000 rpm rotational speed. However, when the rotational speed was increased to 4000 rpm, the maximum flow rate Q and static pressure P were increased to 38% and 82%. This study concluded that a centrifugal fan’s static pressure at high rotational speed is higher than that of an axial-flow fan. Therefore, a centrifugal fan should be chosen if high static pressure cooling or blowing is required. This advanced research investigation is to build up the capabilities of design, analysis, manufacturing, and measurement of a centrifugal fan with an outer diameter smaller than 10 cm.     

Cooling of a permanent magnet electric motor with a centrifugal impeller

This paper presents a thermal fluid analysis on the air cooling of a permanent magnet electric motor with a centrifugal impeller. A numerical model is developed for the heat transfer and fluid flow process. The flow rates of the cooling air are also experimentally measured. The agreement between the numerical model prediction and experimental data is reasonably good. Detailed structures of the cooling flow are presented. Convection heat transfer on the surface of the armature is quantified. Comments on the application of the motor architecture are given. Design modifications are proposed for performance improvements.     

发电机冷却离心风机的三维数值分析

针对发电机冷却离心风机的特点,采用计算流体动力学的方法对其在设计工况时的整机内部流场进行了数值模拟,揭示了其内部流场的基本特征,重点探讨了在数值模拟过程中各种网格的优缺点及构建整台离心风机的几何实体和划分网格中的一些技巧。通过对数值计算结果然后处理,可以比较直观地得到风扇内部流动的一些重要特点,为进一步对风扇进行优化设计提供指导。     

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.     

Numerical simulation of flow in centrifugal pump with complex impeller

Based on the Navier-Stokes equations and the Spalart-Allmaras turbulence model, three dimensional turbulent flow fields in centrifugal pump with long-mid-short blade complex impeller are calculated and analyzed numerically. The relative velocity and pressure distributions in the flowpart are obtained. It is found that the flow in the passage of the complex impeller is unsymmetrical due to the joint action between volute and impeller. The back-flow region is at inlet of long-blade suction side, near middle part of long-blade pressure side and outlet of short-blade suction side. The flow near volute throat is affected greatly by volute. The relative velocity is large and it is easy to bring back flow at outlet of the complex impeller near volute throat. The static and total pressure rise uniformly from inlet to outlet in the impeller. At impeller outlet, the pressure periodically decreases from pressure side to suction side, and then the static pressure sharply rise near the throat. The experimental results show that the back flow in the impeller has an important influence on the performance of pump.     

Experimental study on a centrifugal pump with an open impeller during startup period

Transient performance of fluid machinery during transient operating periods,such as startup and stopping,has been drawn more attentions recently due to the growing engineering needs.In this paper,the transient behavior of a prototype centrifugal pump with an open impeller during rapid startup period is studied experimentally.The variations of the rotational speed,flow rate,head,and shaft power during rapid startup period are recorded in experiments at different discharge valve openings.In addition,the non-dimensional flow rate and head are also used to analyze the transient behavior.The research result shows that the rise characteristic of the rotational speed is not basically changed by working points,while mainly depends on the startup characteristics of the driving motor.Compared with the rapid rise of the rotational speed,the flow rate rises slowly in the initial stage of startup.Moreover,the flow rate lags behind the rotational speed to rise to final stable value,and the delay becomes more severe with the increase of the discharge valve opening.The shaft power impact phenomenon generally exists in the process of startup.The non-dimensional analysis shows that the non-dimensional head is very high at the very beginning of startup,and quickly falls to the minimum,then gradually rises to final stable value,while the non-dimensional flow rate always shows the rise tendency during whole startup period.In conclusion,it is found from the non-dimensional results that the quasi-steady analysis is unable to accurately assess the transient flow during startup period.     

Comparison of flow characteristics of enlarged blood pump models with different impeller design

In earlier studies, a 5:1 enlarged pump model of the Kyoto-NTN Magnetically Suspended Centrifugal Blood Pump has been constructed and the gap pressure and wall shear stress have been measured. With the satisfactory results obtained and also as air was the medium used in the previous investigations, another 5:1 enlarged pump model using water as the medium was thus designed and constructed. Five different impeller blade profile designs are used in the present study. By varying (1) the design of the blade profiles i.e. forward, radial and backward, (2) the number of blades used and (3) the rotating speeds, the flow characteristics of the pump are investigated. It is found that the impeller with the higher number of blades used with the forward and straight blade profiles have the best performance.     

Investigation of the flow in the impeller side clearances of a centrifugal pump with volute casing

The paper is concerned with the fluid flow in the impeller side clearances of a centrifugal pump with volute cas-ing.The flow conditions in these small axial gaps are of significant importance for a number of effects such as disk friction,leakage losses or hydraulic axial thrust to name but a few.In the investigated single stage pump,the flow pattern in the volute turns out to be asymmetric even at design flow rate.To gain a detailed insight into the flow structure,numerical simulations of the complete pump including the impeller side clearances are accom-plished.Additionally,the hydraulic head and the radial pressure distributions in the impeller side clearances are measured and compared with the numerical results.Two configurations of the impeller,either with or without balancing holes,are examined.Moreover,three different operating points,i.e.:design point,part load or overload conditions are considered.In addition,analytical calculations are accomplished to determine the pressure distri-butions in the impeller side clearances.If accurate boundary conditions are available,the 1D flow models used in this paper can provide reasonable results for the radial static pressure distribution in the impeller side clearances.Furthermore,a counter rotating wake region develops in the rear impeller side clearances in absence of balancing holes which severely affects the inflow and outflow conditions of the cavity in circumferential direction.     

配内燃机车离心风机的设计改型

利用商业软件Fluent对配内燃机车离心风机内部气流的流动情况进行了数值模拟。模拟结果与实验结果对比表明,两者能够较好的吻合,误差在5％以下。在此基础上,对风机内部的流场分布,尤其是沿叶高方向气流的流动情况进行了分析,找到了导致风机效率较低的原因,并有针对性地对风机进行了改型。改型后的模拟结果显示,风机的效率提高了6％左右,效率提升较为明显。     

Investigation on centrifugal impeller in an axial-radial combined compressor with inlet distortion

Assembling an axial rotor and a stator at centrifugal compressor upstream to build an axial-radial combined compressor could achieve high pressure ratio and efficiency by appropriate size augment.Then upstream potential flow and wake effect appear at centrifugal impeller inlet.In this paper,the axial-radial compressor is unsteadily simulated by three-dimensional Reynolds averaged Navier-Stokes equations with uniform and circumferential distorted total pressure inlet condition to investigate upstream effect on radial rotor.The results show that spanwise nonuniform total pressure distribution is generated and radial and circumferential combined distortion is formed at centrifugal rotor inlet.The upstream stator wake deflects to rotor rotation direction and decreases with blade span increases.Circumferential distortion causes different separated flow formations at different pitch positions.The tip leakage vortex is suppressed in centrifugal blade passages.Under distorted inlet condition,flow direction of centrifugal impeller leading edge upstream varies evidently near hub and shroud but varies slightly at mid-span.In addition,compressor stage inlet distortion produces remarkable effect on blade loading of centrifugal blade both along chordwise and pitchwise.     

甲醛生产装置离心风机的废热利用

针对甲醛装置离心风机产生的废热,提出改变冷却介质及部分修改可加以利用。通过对改造前后进行对比分析,说明在一定条件下利用化工低温废热是可行的。经改造实践证明,冷却介质改变后,离心风机废热不但得到利用,同时产生一定经济效益,而且风机运行更加稳定连续,具有一定的推广应用价值。     

Prediction of dynamic and aerodynamic characteristics of the centrifugal fan with forward curved blades

The main aim of this paper is determine the centrifugal fan with forward curved blades aerodynamic characteris- tics based on numerical modeling. Three variants of geometry were investigated. The first, basic ＂A＂ variant con- tains 12 blades. The geometry of second ＂B＂ variant contains 12 blades and 12 semi-blades with optimal length [1]. The third, control variant ＂C＂ contains 24 blades without semi-blades. Numerical calculations were per- formed by CFD Ansys. Another aim of this paper is to compare results of the numerical simulation with results of approximate numerical procedure. Applied approximate numerical procedure [2] is designated to determine char- acteristics of the turbulent flow in the bladed space of a centrifugal-flow fan impeller. This numerical method is an extension of the hydro-dynamical cascade theory for incompressible and inviscid fluid flow. Paper also par- tially compares results from the numerical simulation and results from the experimental investigation. Acoustic phenomena observed during experiment, during numerical simulation manifested as deterioration of the calcula- tion stability, residuals oscillation and thus also as a flow field oscillation. Pressure pulsations are evaluated by using frequency analysis for each variant and working condition.     

离心泵叶轮内流场数值模拟及分析

基于计算流体力学,对离心泵叶轮内部流场进行了数值模拟。采用有限体积中心格式、时间推进解法以及N-S方程计算。得到了叶轮压力分布等值线、叶轮相对速度矢量以及二次流分布,并进行详尽的分析,揭示了叶轮内部流动情况,为优化叶轮设计提供了理论依据和技术保障。     

我国小型离心风机研究发展综述

介绍了离心风机的工作原理和结构。根据离心风机的结构,回顾了近年来国内关于提高离心风机效率,降低其噪声的研究现状。分析了我国离心风机水平较低原因。在今后的研究中应利用数值模拟方法,多因素考虑离心风机内流场特征,发展产学研相结合的生产模式,提高我国风机生产质量。     

CFB锅炉大型离心式风机调速装置的选择

介绍了CFB锅炉大型离心式风机调速装置选择的必要性,并对不同的调速方式在适用性、经济性方面进行了比较.作为实例,介绍了广州石化465t/hCFB锅炉引风机的选择过程.     

Influence of tip clearance on performance of a contra-rotating fan

Influences of tip clearance on the tip flow and associated loss mechanism in a contra-rotating axial flow fan has been studied in the paper, based on three dimensional numerical results. The results with different tip clearance are compared in terms of stage efficiency, relative total pressure loss coefficient, flow angle. It is found that the efficiency of the contra-rotating fan changes almost linearly with increment of the tip clearance, however, efficiency of the rear rotor is observed to decrease more dramatically than that of the forward rotor given same tip clearance variation. The analysis on the flow structure indicates that the tip region flow field is qualitatively similar in both rotors. However, with the same clearance value, the leakage flow in the rear rotor is effected by a tip leakage vortex of greater intensity caused by relative loading levels and the inter rotor interaction.