Wind energy is one of the most promising renewable energy sources, straight-bladed vertical axis wind turbine(S-VAWT) appears to be particularly promising for the shortage of fossil fuel reserves owing to its distinct...Wind energy is one of the most promising renewable energy sources, straight-bladed vertical axis wind turbine(S-VAWT) appears to be particularly promising for the shortage of fossil fuel reserves owing to its distinct advantages, but suffers from poor self-starting and low power coefficient. Variable-pitch method was recognized as an attractive solution to performance improvement, thus majority efforts had been devoted into blade pitch angle effect on aerodynamic performance. Taken into account the local flow field of S-VAWT, mathematical model was built to analyze the relationship between power outputs and pitch angle. Numerical simulations on static and dynamic performances of blade were carried out and optimized pitch angle along the rotor were presented. Comparative analyses of fixed pitch and variable-pitch S-VAWT were conducted, and a considerable improvement of the performance was obtained by the optimized blade pitch angle, in particular, a relative increase of the power coefficient by more than 19.3%. It is further demonstrated that the self-starting is greatly improved with the optimized blade pitch angle.展开更多
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
基金Project(HEUCF110707)supported by the Fundamental Research Funds for the Central Universities,ChinaProject(E201216)supported by Heilongjiang Natural Science Fund,China
文摘Wind energy is one of the most promising renewable energy sources, straight-bladed vertical axis wind turbine(S-VAWT) appears to be particularly promising for the shortage of fossil fuel reserves owing to its distinct advantages, but suffers from poor self-starting and low power coefficient. Variable-pitch method was recognized as an attractive solution to performance improvement, thus majority efforts had been devoted into blade pitch angle effect on aerodynamic performance. Taken into account the local flow field of S-VAWT, mathematical model was built to analyze the relationship between power outputs and pitch angle. Numerical simulations on static and dynamic performances of blade were carried out and optimized pitch angle along the rotor were presented. Comparative analyses of fixed pitch and variable-pitch S-VAWT were conducted, and a considerable improvement of the performance was obtained by the optimized blade pitch angle, in particular, a relative increase of the power coefficient by more than 19.3%. It is further demonstrated that the self-starting is greatly improved with the optimized blade pitch angle.
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.
