The present paper reports a comparison of experimental SPL spectral data related to the tonal noise generated by axial-flow fans.A nine blade rotor has been operated at free discharge conditions and in four geometrica...The present paper reports a comparison of experimental SPL spectral data related to the tonal noise generated by axial-flow fans.A nine blade rotor has been operated at free discharge conditions and in four geometrical configurations in which different kinds of tonal noise generating mechanisms are present:large-scale inlet turbulent structures,tip-gap flow,turbulent wakes,and rotor-stator interaction.The measurements have been taken in a hemi-anechoic chamber at constant rotational speed and,in order to vary the acoustic source strength,during low angular acceleration,linear speed ramps.In order to avoid erroneous quantitative evaluations if the acoustic propagation effects are not considered,the acoustic response functions of the different test configurations have been computed by means of the spectral decomposition method.Then,the properties of the tonal noise generating mechanisms have been studied.To this aim,the constant-Strouhal number SPL,obtained by means of measurements taken during the speed ramps,have been compared with the propagation function.Finally,the analysis of the phase of the acoustic pressure has allowed to distinguish between random and deterministic tonal noise generating mechanisms and to collect information about the presence of important propagation effects.展开更多
为保证对旋风机正风运行性能的同时提高反风运行能力,采用平面叶栅法设计了一台功率55 k W的对旋轴流风机。以C-4翼型为基础,采用CFD方法研究了叶片前缘和尾缘形状变化对对旋风机正反风性能的影响。研究表明:正风整机性能,双头尖叶形风...为保证对旋风机正风运行性能的同时提高反风运行能力,采用平面叶栅法设计了一台功率55 k W的对旋轴流风机。以C-4翼型为基础,采用CFD方法研究了叶片前缘和尾缘形状变化对对旋风机正反风性能的影响。研究表明:正风整机性能,双头尖叶形风机压升和功率明显高于原始翼型,大流量时其内效率高于原始翼型和双头钝叶形,小流量时其内效率低于这2种叶形。双头钝叶形压升和功率略低于原始翼型,内效率略高于原始翼型。反风整机性能,双头尖叶形和双头钝叶形反风全压和功率相差不多,均优于原始翼型,双头钝叶形反风内效率略高于双头尖叶形和原始翼型,原始翼型和双头尖叶形反风内效率接近。正风级性能,两级叶轮级性能变化趋势均与整机类似。反风级性能,双头尖叶形两级反风性能均优于原始翼型。双头钝叶形第一级叶轮性能低于双头尖叶形和原始翼型,第二级叶轮性能优于这2种叶形。可见,大流量时双头尖叶形对旋风机可更好地满足正反风高效运行的目的。展开更多
Half-ducted fan and ducted fan have been designed and numerically analyzed for investigating the radial flow effect on the overall performance and the three dimensional flow field in design. Based on quasi-three dimen...Half-ducted fan and ducted fan have been designed and numerically analyzed for investigating the radial flow effect on the overall performance and the three dimensional flow field in design. Based on quasi-three dimensional flow theory, the meridional flow was calculated by adopting the radial balance equations, while the calculation of the blade to blade flow was obtained by 2D cascade data with the correction by a potential flow theory. Two types of axial flow fan were designed. One is the full ducted case as if it was in the straight pipe and another is the half-ducted case with the radial inflow and outflow. The previous experimental results of authors were used to decide the inclinations of both the inflow and outflow. And the circular arc blade with equal thickness was adopted. The numerical results indicate that both of the designed fans can reach the specified efficiency and also the efficiency surpasses more than 11%. Furthermore, the static pressure characteristic of half-ducted fan is much better than that of ducted fan. In comparison of the three dimensional internal flow of these two fans, the improvement of the flow angle at inlet and outlet, the distributions of velocity in the flow field and the pressure distributions on the blade surfaces can be achieved more successfully in accordance with the design intension on consideration of flow angle in design. The conclusion that half-ducted design with considering radial inflow and outflow is feasible and valid in comparison with ducted design for axial flow fans has been obtained at the end of the paper.展开更多
基金Università di Genova for the financial support to the present work
文摘The present paper reports a comparison of experimental SPL spectral data related to the tonal noise generated by axial-flow fans.A nine blade rotor has been operated at free discharge conditions and in four geometrical configurations in which different kinds of tonal noise generating mechanisms are present:large-scale inlet turbulent structures,tip-gap flow,turbulent wakes,and rotor-stator interaction.The measurements have been taken in a hemi-anechoic chamber at constant rotational speed and,in order to vary the acoustic source strength,during low angular acceleration,linear speed ramps.In order to avoid erroneous quantitative evaluations if the acoustic propagation effects are not considered,the acoustic response functions of the different test configurations have been computed by means of the spectral decomposition method.Then,the properties of the tonal noise generating mechanisms have been studied.To this aim,the constant-Strouhal number SPL,obtained by means of measurements taken during the speed ramps,have been compared with the propagation function.Finally,the analysis of the phase of the acoustic pressure has allowed to distinguish between random and deterministic tonal noise generating mechanisms and to collect information about the presence of important propagation effects.
文摘为保证对旋风机正风运行性能的同时提高反风运行能力,采用平面叶栅法设计了一台功率55 k W的对旋轴流风机。以C-4翼型为基础,采用CFD方法研究了叶片前缘和尾缘形状变化对对旋风机正反风性能的影响。研究表明:正风整机性能,双头尖叶形风机压升和功率明显高于原始翼型,大流量时其内效率高于原始翼型和双头钝叶形,小流量时其内效率低于这2种叶形。双头钝叶形压升和功率略低于原始翼型,内效率略高于原始翼型。反风整机性能,双头尖叶形和双头钝叶形反风全压和功率相差不多,均优于原始翼型,双头钝叶形反风内效率略高于双头尖叶形和原始翼型,原始翼型和双头尖叶形反风内效率接近。正风级性能,两级叶轮级性能变化趋势均与整机类似。反风级性能,双头尖叶形两级反风性能均优于原始翼型。双头钝叶形第一级叶轮性能低于双头尖叶形和原始翼型,第二级叶轮性能优于这2种叶形。可见,大流量时双头尖叶形对旋风机可更好地满足正反风高效运行的目的。
文摘Half-ducted fan and ducted fan have been designed and numerically analyzed for investigating the radial flow effect on the overall performance and the three dimensional flow field in design. Based on quasi-three dimensional flow theory, the meridional flow was calculated by adopting the radial balance equations, while the calculation of the blade to blade flow was obtained by 2D cascade data with the correction by a potential flow theory. Two types of axial flow fan were designed. One is the full ducted case as if it was in the straight pipe and another is the half-ducted case with the radial inflow and outflow. The previous experimental results of authors were used to decide the inclinations of both the inflow and outflow. And the circular arc blade with equal thickness was adopted. The numerical results indicate that both of the designed fans can reach the specified efficiency and also the efficiency surpasses more than 11%. Furthermore, the static pressure characteristic of half-ducted fan is much better than that of ducted fan. In comparison of the three dimensional internal flow of these two fans, the improvement of the flow angle at inlet and outlet, the distributions of velocity in the flow field and the pressure distributions on the blade surfaces can be achieved more successfully in accordance with the design intension on consideration of flow angle in design. The conclusion that half-ducted design with considering radial inflow and outflow is feasible and valid in comparison with ducted design for axial flow fans has been obtained at the end of the paper.
