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Copyright of Basic Sciences Journal of Textile Universities / Fangzhi Gaoxiao Jichu Kexue Xuebao is the property of Basic Sciences Journal of Textile Universities and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Helicopters have been playing an increasingly important role in military and civilian activities. The review of helicopter noise reduction is needed to be updated, because new technologies are constantly emerging. Firstly, the mechanism and propagation properties of the rotor (tail rotor) noise are described, and the co‑axial rigid rotor high‑speed helicopter and the tilting rotor are introduced. There are complicated aerodynamic or acoustic interaction in two new configuration helicopters. Secondly, the progress of helicopter flight noise measurement, as the verification approach for low noise design technologies, is demonstrated. Then, the design technologies for silent helicopters are summarized. The passive noise reduction strategies have been intensively implemented, and reduced helicopter radiated noise level greatly. The strategies of variable rotor speed and low noise trajectory are gradually maturing. However, the active control technologies are in the laboratory stage, and need further research on driving devices and control parameters et al. The final part summarizes the state of art for low noise control strategies in helicopters, and outlooks the development trend. [ABSTRACT FROM AUTHOR]

Copyright of Chinese Journal of Liquid Crystal & Displays is the property of Chinese Journal of Liquid Crystal & Displays and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The CFD method with moving overset grid scheme is used to simulate the flow-field of a tilt-rotor aircraft during helicopter mode and conversion mode in small forward velocity flight. The wakes from different flight conditions are investigated and their effects on the horizontal tail are explored. In helicopter mode, when the aircraft is in hover or small forward velocity flight（≤4 m/s）, the rotor wakes, which form fountain flow effects due to the presence of wing, focus in the vicinity of wing and have few effects on the horizontal tail. With the increase of forward velocity, a pair of stream-wise vortexes called fountain vortexes, which dominates the flow around the horizontal tail, is formed by the interaction between the fountain flow and the freestream. When the forward velocity is further enlarged (≥16 m/s), the edge vortexes of rotor wakes move downstream and have significant effects on the horizontal tail. The fountain vortexes are generated from the upper surface of wing; the edge vortexes are from the edge of rotor disc. Although their production mechanisms are different, both the fountain vortexes and edge vortexes cause an upwash near the horizontal tail, and therefore a pitch down moment for the aircraft. In addition, the edge vortexes of rotor wakes are weakened and the pitch down moment is reduced, with the flight condition changing from helicopter mode to fixed-wing mode. [ABSTRACT FROM AUTHOR]

Copyright of Chinese Journal of Liquid Crystal & Displays is the property of Chinese Journal of Liquid Crystal & Displays and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Imaging Science & Photochemistry is the property of Imaging Science & Photochemistry Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Basic Sciences Journal of Textile Universities / Fangzhi Gaoxiao Jichu Kexue Xuebao is the property of Basic Sciences Journal of Textile Universities and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This definition takes the direction of the vorticity into account and can accelerate the the transition from Reynolds-averaged Navier-Stokes (R A N S) region to large-eddy-simulafoon (LES) region. A n isolated jet w k h Mach number of 0.9 and Reynolds number of 1.1 m i l o n based on the nozzle daameter js simulated. The flow quantities and nojse from two meshes are compared. The two meshes both provide reasonable results, but the results from the hne mesh are closer to the measurements. Beside nojse from iive integral surfaces of dense mesh are compared. It js proved that the numerical methods are competent to predict jet-noise. W h e n the freest ream Mach number increases to 0.2, the length of potendal core increases and the turbulent kinedc energy (T K E) and the and the far-field nojse decrease. The changes of of far-field nojse due to Hight velodty by our simulations are similar to the measurements. Tlis method can be extended to predict llgght velodty effects on jet nojse. [ABSTRACT FROM AUTHOR]

Copyright of Basic Sciences Journal of Textile Universities / Fangzhi Gaoxiao Jichu Kexue Xuebao is the property of Basic Sciences Journal of Textile Universities and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)