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您的检索式：作者名="Lingke Ran"
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| 1 | Instability waves and low-frequency noise radiation in the subsonic chevron jet显示文摘Spatial instability waves associated with lowfrequency noise radiation at shallow polar angles in the chevron jet are investigated and are compared to the round counterpart. The Reynolds-averaged Navier–Stokes equations are solved to obtain the mean flow fields, which serve as the baseflow for linear stability analysis. The chevron jet has more complicated instability waves than the round jet, where three types of instability modes are identified in the vicinity of the nozzle, corresponding to radial shear, azimuthal shear,and their integrated effect of the baseflow, respectively. The most unstable frequency of all chevron modes and round modes in both jets decrease as the axial location moves downstream. Besides, the azimuthal shear effect related modes are more unstable than radial shear effect related modes at low frequencies. Compared to a round jet, a chevron jet reduces the growth rate of the most unstable modes at downstream locations. Moreover, linearized Euler equations are employed to obtain the beam pattern of pressure generated by spatially evolving instability waves at a dominant low frequency St = 0.3, and the acoustic efficiencies of these linear wavepackets are evaluated for both jets. It is found that the acoustic efficiency of linear wavepacket is able to be reduced greatly in the chevron jet, compared to the round jet. | Lingke Ran Chuangchao Ye Zhenhua Wan Haihua Yang Dejun Sun | 2018 | Acta Mechanica Sinica2018，34，3： | 4 |
| 2 | Coherent structures and wavepackets in subsonic transitional turbulent jets显示文摘A large eddy simulation(LES) is performed for two subsonic jets with a Reynolds number of Re = 105,which have different core temperatures, i.e., the cold and hot jet. The far-field overall sound pressure levels(OASPL)and noise spectra are well validated against previous experimental results. It is found that the OASPL is raised by heating at shallow angles. The most energetic coherent structures are extracted with specified frequencies using the filter based on the frequency domain variant of the snapshot method of proper orthogonal decomposition(POD). The m = 0, 1 modes have high coherence of near-field pressure for both jets, while the coherence of m = 0 modes is enhanced greatly by heating. Based on the coherent structures, spatial wavepackets are educed and the characteristics of growth, saturation and decay are analyzed and compared between the two jets in detail. The results show that heating would enhance the linear growth rate for high frequency components, and nonlinear growth rates for low frequency components in general, which are responsible for higher OASPL in the hot jet. The far-field sound generated by wavepackets is computed using the Kirchhoff extrapolation,which matches well with that of LES at shallow angles.This indicates that the wavepackets associated with coherent structures are dominant sound sources in forced transitional turbulent jets. Additionally, the present POD method is proven to be a robust tool to extract the salient features of the wavepackets in turbulent flows. | Haihua Yang Xingchen Zhang Lingke Ran Dejun Sun Zhenhua Wan | 2017 | Acta Mechanica Sinica2017，33，1： | 4 |
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