Numerical and experimental investigation on aerodynamic performance of small axial flow fan with hollow blade root

To reduce the influence of adverse flow conditions at the fan hub and improve fan aerodynamic performance,a modification of conventional axial fan blades with numerical and experimental investigation is presented.Hollow blade root is manufactured near the hub.The numerical and experimental results show that hollow blade root has some effect on the static performance.Static pressure of the modified fan is generally the same with that of the datum fan,while,the efficiency curve of the modified fan has a different trend with that of the datum fan.The highest efficiency of the modified fan is 10% greater than that of the datum fan.The orthogonal experimental results of fan noise show that hollow blade root is a feasible method of reducing fan noise,and the maximum value of noise reduction is about 2 dB.The factors affecting the noise reduction of hollow blade root are in the order of importance as follows: hollow blade margin,hollow blade height and hollow blade width.The much smoother pressure distribution of the modified fan than that of the datum fan is the main mechanism of noise reduction of hollow blade root.The research results will provide the proof of the parameter optimization and the structure design for high performance and low noise small axial fans.     

Effect of inlet guide vanes on the performance of small axial flow fan

Effects of the inlet guide vanes on the static characteristics, aerodynamic noise and internal flow characteristics of a small axial flow fan are studied in this work. The inlet guide vanes with different outlet angle are designed,which are mounted on the casing and located at the upstream of the impeller of the prototype fan. Both steady and unsteady flow simulations are performed. The steady flow is simulated by the calculations of Navier-Stokes equations coupled with RNG k-epsilon turbulence model, while the unsteady flow is computed with large eddy simulation. According to the theoretical analysis, the inlet guide vanes with outlet angle of 60° are regarded as the optimal inlet guide vanes. The static characteristic experiment is carried out in a standard test rig and the aerodynamic noise is tested in a semi-anechoic room. Then, performances of the fan with optimal inlet guide vanes are compared with those of the prototype fan. The results show that there is reasonable agreement between the simulation results and the experimental data. It is found that the static characteristics of small axial flow fan is improved obviously after installing the optimal inlet guide vanes. Meanwhile, the optimal inlet guide vanes have effect on reducing noise at the near field, but have little effect on the noise at the far field.     

Numerical simulation of air flow field in high-pressure fan with splitter blades

For a deeper understanding of the flow characteristics in the high-pressure centrifugal blower of a fan of Model 9–26 with splitter blades, a three dimensional (3-D) numerical simulation of air flows in the fan was conducted with FLUENT software. The standard k-ε turbulent model and unstructured grids were used. The computational fluid dynamics (CFD) results showed that the performance of a fan could be improved by adding the splitter blades in the channel among the leaf blades. Under operational conditions, with the presence of splitter blades, the air flow rate of the fan increased about 5% and the total pressure at the outlet of the fan increased about 10% on average. It was also found that the length of the splitter blades affected the air flow and pressure drop. There is an optimal value for the length. The simulation results provide helpful information for improving the fan performance. __________ Translated from Fluid Machinery, 2007, 35(10): 29–32 [译自:流体机械]     

Effect of the uneven circumferential blade space on the performance of small axial flow fan

Effects of the uneven circumferential blade space on static characteristics and aerodynamic noise of a small axial flow fan are studied in this work.The blade angle modulation is adopted to design a series of unequally spaced fans,which have different maximum of modulation angular displacement.The steady flow is simulated by the calculations of Navier-Stokes equations coupled with RNG k-epsilon turbulence model,while the unsteady flow is computed with large eddy simulation.According to theoretical analysis,a fan with a maximum of modulation angular displacement of 6° is regarded as the optimal unequally spaced fan.The experiment of static characteristic is carried out in a standard wind tunnel and the aerodynamic noise of both fans is tested in a semi-anechoic room.Then,performances of the optimal unequally spaced fan are compared with those of the prototype fan.The results show that there is reasonable agreement between the simulation results and the experimental data.It is found that the discrete noise of the optimal unequally spaced fan is lower than that of the prototype fan at the near field monitoring point.This can be explained that the total pressure fluctuation of the optimal unequally spaced fan is much more regular than that of the prototype fan.     

Effects of rotor structure on performance of small size axial flow fans

Small size axial flow fans are used as a cooling component for computers,electronic equipment and other electronic components.With the increasing power of electrical equipment,the demand for lower noise and higher ventilation of cooling fan is also increasing.Traditional methods of improving ventilation by raising the fan’s rotation speed causes a decrease in efficiency and an increase in noise.In this paper,different structures of fans were simulated,and as a result,the counter-rotating fan can achieve higher pressure,efficiency and facilitate ventilation in a smaller space.Furthermore,some other conclusions are as follows:(1) Higher pressure rise can be obtained by a counter-rotating fan than by the two-stage rotor fan in the same axial length.Meanwhile,the counter-rotating fan has a broader work scope.(2) The main noise type of the counter-rotating fan is rotating noise;the small peak pulse caused by vortex noise mainly due to the eddy current produced by small eddies.(3) When the distance of counter-rotating fans is smaller than 2 times the chord,the greater distance the greater total pressure of the circum-averages and along the axial direction,the total pressure begin to decline until the distance is three times the chord,so there is an optimal distance between rotors.The simulation results are of important significance to the quantitative analysis and optimization design of the counter-rotating fan.     

Numerical analysis of aerodynamic noise radiated from cross flow fan

The flow field in a cross flow fan was simulated by solving the 2-D unsteady Reynolds-averaged Navier-Stokes equations. The calculated pressure fluctuations of the blades, the vortex wall, and the rear wall were then used as noise sources to calculate the sound field. The Ffowcs Williams-Hawkings (FW-H) equation was employed to predict the noise field caused by these sources. The predictions show that the rear wall and the vortex wall sources contribute significantly to the total noise and that both the predicted aerodynamic performance and noise agree well with the experimental results. __________ Translated from J Tsinghua Univ (Sci & Tech), 2007, 47(2): 236–239 [译自: 清华大学学报(自然科学版)]     

Unsteady flow condition of contra-rotating small-sized axial fan

Small-sized axial fans are used as air cooler for electric equipments.But there is a strong demand for higher power of fans according to the increase of quantity of heat from electric devices.Therefore,higher rotational speed design is conducted,although,it causes the deterioration of efficiency and the increase of noise.Then,the adoption of contra-rotating rotors for the small-sized axial fan is proposed for the improvement of performance.In the case of contra-rotating rotors,it is necessary to design the rotor considering the unsteady flow condition of each front and rear rotor.In the present paper,the fan performance of the contra-rotating small-sized axial fan with 100mm diameter at a designed and a partial flow rates is shown,and the unsteady flow conditions at the inlet and the outlet of each front and rear rotor are clarified with unsteady numerical results.Furthermore,the relation between the performance and the unsteady flow condition of the contra-rotating small-sized axial fan is discussed and the methods to improve the performance are considered.     

Factors affecting small axial cooling fan performance

Many factors such as outer diameter,hub ratio,blade numbers,shape and stagger angle affect the performance of small cooling fans.A small cooling fan was simulated using CFD software for three blade stagger angles (30.5°,37.5°,44.5°)and obtained the internal flow field and the static characteristics.Research indicated that the stagger angle has an obvious effect on the static characteristics of a fan.For flow rates below 0.0104 m3/s,total pressure is the greatest when the stagger angle is 37.5°;flow rates higher than 0.0104 m3/s,the total pressure is greatest when the stagger angle is 44.5° For the same flow rates,the velocity at inlet of pressure surface increases with increasing stagger angle,but the change of velocity on the suction surface is very small.For one model,vortices and the speed of revolution surfaces decrease with tip clearance increasing.But for other three models,increasing the stagger angle,the vortex intensity and speed of revolution surfaces at same height tip clearance increases,simultaneously,the position of vortex offset from the top of the rotor blade to the suction surface.     

Unsteady internal flow conditions of mini-centrifugal pump with splitter blades

Mini centrifugal pumps having a diameter smaller than 100mm are employed in many fields. But the design method for the mini centrifugal pump is not established because the internal flow condition for these small-sized fluid machines is not clarified and conventional theory is not suitable for small-sized pumps. Therefore, mini centrifugal pumps with simple structure were investigated by this research. Splitter blades were adopted in this research to improve the performance and the internal flow condition of mini centrifugal pump which had large blade outlet angle. The original impeller without the splitter blades and the impeller with the splitter blades were prepared for experiment. The performance tests are conducted with these rotors in order to investigate the effect of the splitter blades on performance and internal flow condition of mini centrifugal pump. On the other hand, a three dimensional unsteady numerical flow analysis was conducted to investigate the change of the internal flow according to the rotor rotation. It is clarified from the experimental results that the performance of the mini centrifugal pump is improved by the splitter blades. The blade-to-blade low velocity region was suppressed in the case with the splitter blades. In addition to that, the unsteady flows near the volute casing tongue were suppressed due to the splitter blades. In the present paper, the performance of the mini centrifugal pump is shown and the unsteady flow condition is clarified with the results of the numerical flow analysis. Furthermore, the effects of the splitter blades on the performance and the unsteady internal flow condition are investigated.     

Effect of inlet box on performance of axial flow fans

Numerical investigations on 3D flow fields in an axial flow fan with and without an inlet box have been extensively conducted, focusing on the variation of fan performance caused by the internal flow fields and the velocity evenness at the exit of the inlet box. It is interesting to find that although the inlet box is well designed in accordance with basic design principles, there is a flow separation region in it. Furthermore, this flow separation and the resulting uneven velocity distribution at the exit lead to some decrease in the efficiency and an increase in the total pressure rise of the fan. This research shows that the inlet box needs further improvement and such a check on the flow fields is of value for the design of inlet boxes. __________ Translated from Journal of Engineering Thermophysics, 2007, 28 (Suppl.1): 161–164 [译自: 工程热物理学报]     

Numerical investigation on the flow field of an axial flow fan in a direct air‐cooled condenser for a large power plant

The flow field of an axial fan in a direct air‐cooled condenser for a large power plant is modeled numerically. In order to improve the efficiency of heat exchange of the air‐cooled condenser, methods of increasing the rotational velocity of the fan and laying out the guide blade at the outlet of the fan are adopted. Results show that increasing the rotational velocity of the fan can effectively increase the flux of the fan, and can improve the efficiency of an air‐cooled condenser; laying out the guide blade at the fan outlet can ameliorate the flow field in an A‐flame. This causes the rotational kinetic energy to change into static pressure at the fan outlet, so the ability of the heat exchange of the air‐cooled condenser is improved. © 2012 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library (wileyonlinelibrary.com/journal/htj). DOI 10.1002/htj.21027     

Numerical simulation of air flow field in high-pressure fan with splitter blades

For a deeper understanding of the flow characteristics in the high-pressure centrifugal blower of a fan of Model 9-26 with splitter blades, a three dimensional (3-D) numerical simulation of air flows in the fan was conducted with FLUENT software. The standard k-? turbulent model and unstructured grids were used. The computational fluid dynamics (CFD) results showed that the performance of a fan could be improved by adding the splitter blades in the channel among the leaf blades. Under operational conditions, with the presence of splitter blades, the air flow rate of the fan increased about 5% and the total pressure at the outlet of the fan increased about 10% on average. It was also found that the length of the splitter blades affected the air flow and pressure drop. There is an optimal value for the length. The simulation results provide helpful information for improving the fan performance.     

Performance and flow condition of small-sized axial fan and adoption of contra-rotating rotors

Small-sized axial fans are used as air coolers for electric equipments. But there is a strong demand for higher power of fans according to the increase of quantity of heat from electric devices. Therefore, higher rotational speed design is conducted, although it causes the deterioration of the efficiency and the increase of noise. Then the adoption of contra-rotating rotors for the small-sized axial fan is proposed for the improvement of the performance. In the present paper, the performance and the internal flow condition of the small-sized axial fan are shown as a first step of the research for the contra-rotating small-sized axial fan and the important points to apply contra-rotating rotors to the small-sized axial fan are discussed. Furthermore, the numerical flow analysis is conducted to investigate the performance of the contra-rotating small-sized axial fan and internal flow conditions and pressure distributions are clarified and the effect of contra-rotating rotors is considered.     

具有较强气动性能的风力发电机叶片研究

利用流体分析软件Fluent对NACA4415与SD7043两种常见翼型进行流场模拟,从外形特征分析两者的气动性能差异,进一步利用翼型分析软件profili的翼型设计功能,结合两种翼型的长处,设计出新的翼型,并对新翼型与原有翼型在升阻特性上的差异进行分析,对比发现新翼型气动性能更优。最后利用新翼型基于Solidworks设计出一款小型风力发电机叶片。     

Effects of a kind of non-smooth blade on the unsteady flow field at the exit of an axial fan

An experimental investigation of effects of a kind of streamwise-grooved blade on the unsteady flow field at an exit of an axial-flow fan was performed. The flow field at 25% chord downstream from the trailing edge at hub was measured using a fast-response five-hole pressure probe at different mass-flow conditions. The unsteady flow of the grooved blades was compared with that of the smooth blades. The measurement results indicate that： （1） the grooved blades restrain the velocity fluctuation and the pressure fluctuation by modulating the blade boundary layers, which contributes to the flow loss reduction in the hub region and in the rotor wake region at the design condition; （2） the stream-wise grooves play an important role in restraining the radial migration in the blade boundary layer and abating the tip flow mixing, which contributes to the flow loss reduction in the tip region at the design condition; （3） at the near stall condition, the grooved surface can not reduce the flow loss, even increase the loss nearby when the separation happens in the blade boundary layer.     

Flow fields with tip leakage vortex in a small axial cooling fan

In order to improve the fan characteristics, especially efficiency and noise level of a small axial cooling fan with a large tip clearance, the internal flow measurements with tip leakage vortex were carried out at fan rotor outlet us- ing an I-type hot-wire probe. The probe was set toward two directions, parallel and normal to the meridional plane of test fan, and the two directional velocity components were measured. From the result of fan test it was found that the test fan didn＇t have the unstable characteristic with a positive gradient on its pressure - flow-rate curve. From the results of velocity measurement it was observed that the tip leakage vortex exited at maximum efficiency flow-rate and large flow-rate conditions. However, at small flow-rate conditions the tip leakage vortex was not observed and it was found that the flow field were enlarged toward radial outwards     

Effects of a kind of non-smooth blade on the performance of an axial fan

This paper presents an experimental investigation of effects of a kind of streamwise-grooved blade on theperformance of an axial-flow fan.The flow field at 25% chord downstream from the trailing edge at hub wasmeasured using a 5-hole pressure probe at different mass-flow conditions.The fan performance of the grooveblades was compared with that of the smooth blades.The measurement results indicate that:(1)the non-smoothblades increase mass flow of the fan at the same throttle conditions except a near stall condition;(2)thenon-smooth blades reduce the relative total pressure loss in the rotor passage and increase the fan's total pressurerise at the test mass-flow conditions except the near stall condition;(3)Negative benefits are obtained at a nearstall condition when the smooth blades are replaced by the non-smooth ones.The fan mass flow decreases 0.9%while the total-pressure rise decreases 2.4% at the near stall condition.     

Measurement and analysis of tip clearance unsteady flow spectrum in axial-flow fan rotor

The dynamic pressure measurement device and test technology are described in this study. The tip clearance unsteady flow development from the inlet to the outlet of an axial-flow rotor was revealed by analyzing pressure frequency spectrum acquired from measuring the unsteady pressure field of the tip endwall. The experiment provides test basis for thoroughly understanding the tip clearance unsteady flow and building interaction models of tip clearance flow and main flow. __________ Translated from Compressor, Blower & Fan Technology, 2007, (5): 12–15 [译自: 风机技术]     

分流叶片进口直径对离心泵空化特性影响

为探究分流叶片对离心泵空化性能的影响,以IS80-50-200模型泵为研究对象,在模型泵上设计添加了3种不同进口直径分流叶片,利用CFD软件对离心泵进行全流道三维定常湍流空化数值模拟,分析不同汽蚀余量对离心泵空化特性和叶轮内部流场的影响,探究叶轮空化初生和发展规律。结果表明:添加分流叶片后,泵的扬程、效率均有一定程度的提高,且分流叶片的进口直径对扬程和效率的影响不大;泵的H-Q曲线驼峰减弱;泵的抗空化性能均有提高。在研究的水力模型中,当离心泵短叶片进口直径为0.8D2时,泵的抗空化性能最好。添加分流叶片后,长叶片两侧压差减小,叶轮进口处的低压区范围变小,有利于提高泵的抗空化能力。     

高速离心风机变工况模拟及轴向力预测研究

利用CFD模拟软件ANSYS-CFX,对某单机高速离心风机进行了设计转速下的变工况数值模拟,选用sst湍流模型进行多工况计算,得到了较为详细的离心风机内流场数据。对传统经验公式法及纯CFD积分方法计算的风机轴向力进行了比较分析。计算结果表明风机在变工况运行过程中的轴向力变化较大。准确预测轴向力对高速风机的稳定运行及推力轴承选择具有重要意义,为今后高速离心风机产品结构设计和轴向力预测研究提供一定的参考和指导。