In this paper, the effects of turbulence on sound generation and velocity fluctuations due to pressure waves in a large subsonic wind tunnel are studied. A trip strip located at different positions in the contraction ...In this paper, the effects of turbulence on sound generation and velocity fluctuations due to pressure waves in a large subsonic wind tunnel are studied. A trip strip located at different positions in the contraction part or at one position in the diffuser of a large wind tunnel is used to investigate the aforementioned phenomenon, and the results indicate that the trip strip has significant effects on sound reduction. The lowest turbulence intensity and sound are obtained from a trip strip with a diameter of 0.91 mm located either at X/L = 0.79 or at X/L = 0.115 in the wide portion of the contraction. Furthermore, the effect of monopole, dipole and quadrupole sources of aerodynamic noise at different velocities is investigated, and it is demonstrated that the contribution of the monopole is dominant, while the shares due to the dipole and quadrupole remain less important. In addition, it is found that the sound waves have a modest impact on the measured longitudinal turbulence and are generated essentially by eddies.展开更多
To investigate the convective heat transfer of nanofluids, experiments were performed using silver-water nanofluids under laminar, transition and turbulent flow regimes in a horizontal 4.3 mm inner-diameter tube-in-tu...To investigate the convective heat transfer of nanofluids, experiments were performed using silver-water nanofluids under laminar, transition and turbulent flow regimes in a horizontal 4.3 mm inner-diameter tube-in-tube counter-current heat transfer test section. The volume concentration of the nanoparticles varied from 0.3% to 0.9% in steps of 0.3%, and the effects of thermo-physical properties, inlet temperature, volume concentration, and mass flow rate on heat transfer coefficient were investigated. Experiments showed that the suspended nanoparticles remarkably increased the convective heat transfer coefficient, by as much as 28.7% and 69.3% for 0.3% and 0.9% of silver content, respectively. Based on the experimental results a correlation was developed to predict the Nusselt number of the silver-water nanofluid, with ＋10% agreement between experiments and prediction.展开更多
This article presents an improved computational fluid dynamics （CFD）-synthesis method to predict dynamic distortion. A steady-state flow field is derived from a CFD solution, through which are acquired total pressur...This article presents an improved computational fluid dynamics （CFD）-synthesis method to predict dynamic distortion. A steady-state flow field is derived from a CFD solution, through which are acquired total pressure, density, turbulence kinetic energy and others in steady-state at an aerodynamic interface plane （AIP）. Back-propagation artificial neural network （BP ANN） is used to find out the relationship between the measured flight turbulence and the CFD-computed turbulence parameters. The dynamic pressure is obtained by incorporating CFD-found total steady-state pressure with fluctuating pressure. Finally, the dynamic distortion is predicted by means of the synthesized dynamic pressure. The fairly good agreement between the computed inlet surface pressure and the flight test data bears out the reliability of CFD solution used in this article. To validate the proposed method, six sets of flight test data are used and the results show that the predicted dynamic distortion is well in line with the distortion displayed in flight tests. An examination of the traditional method is also accomplished and the comparison also shows that the proposed method is superior to the traditional one in higher consistency with flight test data.展开更多
基金supported by the Iranian Aircraft Manufacturing (HESA) company,Bureau of Aircraft Design
文摘In this paper, the effects of turbulence on sound generation and velocity fluctuations due to pressure waves in a large subsonic wind tunnel are studied. A trip strip located at different positions in the contraction part or at one position in the diffuser of a large wind tunnel is used to investigate the aforementioned phenomenon, and the results indicate that the trip strip has significant effects on sound reduction. The lowest turbulence intensity and sound are obtained from a trip strip with a diameter of 0.91 mm located either at X/L = 0.79 or at X/L = 0.115 in the wide portion of the contraction. Furthermore, the effect of monopole, dipole and quadrupole sources of aerodynamic noise at different velocities is investigated, and it is demonstrated that the contribution of the monopole is dominant, while the shares due to the dipole and quadrupole remain less important. In addition, it is found that the sound waves have a modest impact on the measured longitudinal turbulence and are generated essentially by eddies.
基金King Mongkut’s University of Technology Thonburi, the Thailand Research Fund, the Office of the Higher Education Commissionthe National Research University Project
文摘To investigate the convective heat transfer of nanofluids, experiments were performed using silver-water nanofluids under laminar, transition and turbulent flow regimes in a horizontal 4.3 mm inner-diameter tube-in-tube counter-current heat transfer test section. The volume concentration of the nanoparticles varied from 0.3% to 0.9% in steps of 0.3%, and the effects of thermo-physical properties, inlet temperature, volume concentration, and mass flow rate on heat transfer coefficient were investigated. Experiments showed that the suspended nanoparticles remarkably increased the convective heat transfer coefficient, by as much as 28.7% and 69.3% for 0.3% and 0.9% of silver content, respectively. Based on the experimental results a correlation was developed to predict the Nusselt number of the silver-water nanofluid, with ＋10% agreement between experiments and prediction.
文摘This article presents an improved computational fluid dynamics （CFD）-synthesis method to predict dynamic distortion. A steady-state flow field is derived from a CFD solution, through which are acquired total pressure, density, turbulence kinetic energy and others in steady-state at an aerodynamic interface plane （AIP）. Back-propagation artificial neural network （BP ANN） is used to find out the relationship between the measured flight turbulence and the CFD-computed turbulence parameters. The dynamic pressure is obtained by incorporating CFD-found total steady-state pressure with fluctuating pressure. Finally, the dynamic distortion is predicted by means of the synthesized dynamic pressure. The fairly good agreement between the computed inlet surface pressure and the flight test data bears out the reliability of CFD solution used in this article. To validate the proposed method, six sets of flight test data are used and the results show that the predicted dynamic distortion is well in line with the distortion displayed in flight tests. An examination of the traditional method is also accomplished and the comparison also shows that the proposed method is superior to the traditional one in higher consistency with flight test data.
