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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 |
| 3 | Mode transition and oscillation suppression in supersonic cavity flow显示文摘Supersonic flows past two-dimensional cavities with/without control are investigated by the direct numerical simulation(DNS). For an uncontrolled cavity, as the thickness of the boundary layer declines, transition of the dominant mode from the steady mode to the Rossiter Ⅱ mode and then to the Rossiter Ⅲ mode is observed due to the change of vortex-corner interactions. Meanwhile, a low frequency mode appears. However, the wake mode observed in a subsonic cavity flow is absent in the current simulation.The oscillation frequencies obtained from a global dynamic mode decomposition(DMD)approach are consistent with the local power spectral density(PSD) analysis. The dominant mode transition is clearly shown by the dynamic modes obtained from the DMD. A passive control technique of substituting the cavity trailing edge with a quarter-circle is studied. As the effective cavity length increases, the dominant mode transition from the Rossiter Ⅱ mode to the Rossiter Ⅲ mode occurs. With the control, the pressure oscillations are reduced significantly. The interaction of the shear layer and the recirculation zone is greatly weakened, combined with weaker shear layer instability, responsible for the suppression of pressure oscillations. Moreover, active control using steady subsonic mass injection upstream of a cavity leading edge can stabilize the flow. | Chao ZHANG Zhenhua WAN Dejun SUN | 2016 | Applied Mathematics and Mechanics(English Edition)2016，37，7： | 3 |
| 4 | In vitro comparison of the hemocompatibility of diamond-like carbon and carbon nitride coatings with different atomic percentages of N显示文摘Carbon nitride (CNx) and diamond-like carbon (DLC) coatings were prepared by dc magnetron sputtering at room temperature. Different partial pressures of N2 were used to synthesize CNx to evaluate the relationship between the atomic percentage of nitrogen and hemocompatibility. Auger electron spectroscopy and atomic force microscopy indicated atomic percentages of N of 0.12 and 0.22 and that the CNx coatings were smooth. An in vitro study of the hemocompatibility of the coatings revealed that both CNx coatings had better anticoagulant properties and lower platelet adhesion than DLC. Compared with CN0.12, the CN0.22 coating showed longer dynamic clotting time (about 42 min), static clotting time (23.6 min) and recalcification time (45.6 s), as well as lower platelet adhesion (102 cells μm 2), aggregation, and activation. The presence of nitrogen in the CNx coatings induced their enhanced hemocompatibility compared with DLC. | ZHAO MengLi LI DeJun ZHANG YiTeng GUO MeiXian DENG XiangYun GU HanQing WAN RongXin | 2012 | Science China(Life Sciences)2012，55，4： | 3 |
| 5 | Bifurcations in penetrative Rayleigh-Be′nard convection in a cylindrical container显示文摘The bifurcations of penetrative Rayleigh-B′enard convection in cylindrical containers are studied by the linear stability analysis(LSA) combined with the direct numerical simulation(DNS) method. The working ?uid is cold water near 4?C, where the Prandtl number P r is 11.57, and the aspect ratio(radius/height) of the cylinder ranges from 0.66 to 2. It is found that the critical Rayleigh number increases with the increase in the density inversion parameter θ_m. The relationship between the normalized critical Rayleigh number(Rac(θ_m)/Rac(0)) and θ_m is formulated, which is in good agreement with the stability results within a large range of θ_m. The aspect ratio has a minor effect on Rac(θ_m)/Rac(0). The bifurcation processes based on the axisymmetric solutions are also investigated. The results show that the onset of axisymmetric convection occurs through a trans-critical bifurcation due to the top-bottom symmetry breaking of the present system.Moreover, two kinds of qualitatively different steady axisymmetric solutions are identi?ed. | Chuanshi SUN Shuang LIU Qi WANG Zhenhua WAN Dejun SUN | 2019 | Applied Mathematics and Mechanics(English Edition)2019，40，5： | 2 |
| 6 | Model reduction for supersonic cavity flow using proper orthogonal decomposition(POD)and Galerkin projection显示文摘The reduced-order model(ROM) for the two-dimensional supersonic cavity flow based on proper orthogonal decomposition(POD) and Galerkin projection is investigated. Presently, popular ROMs in cavity flows are based on an isentropic assumption,valid only for flows at low or moderate Mach numbers. A new ROM is constructed involving primitive variables of the fully compressible Navier-Stokes(N-S) equations, which is suitable for flows at high Mach numbers. Compared with the direct numerical simulation(DNS) results, the proposed model predicts flow dynamics(e.g., dominant frequency and amplitude) accurately for supersonic cavity flows, and is robust. The comparison between the present transient flow fields and those of the DNS shows that the proposed ROM can capture self-sustained oscillations of a shear layer. In addition, the present model reduction method can be easily extended to other supersonic flows. | Chao ZHANG Zhenhua WAN Dejun SUN | 2017 | Applied Mathematics and Mechanics(English Edition)2017，38，5： | 1 |
| 7 | Map Matching in Road Crossings of Urban Canyons Based on Road Traverses and Linear Heading-Change Model Instrumentation and Measurement 显示文摘 | Xiaoguo Zhang Qing Wang Dejun Wan | 2007 | IEEE Transactions2007，56，6： | 1 |
| 8 | A Fast Inertial Alignment Method for Strapdown Inertial Navigation System on Stationary Base显示文摘 | Fang Jiancheng Wan Dejun | 1996 | IEEE Transactions on Aerospace and Electronic Systems1996，32，4： | 1 |
| 9 | Map matching in road crossings of urban canyons based on road traverses and linear-heading-changing model显示文摘 | Zhang Xiaoguo Wang Qing Wan Dejun | 2007 | IEEE Transactions on Instrumentation and Measurement2007，56，6： | 1 |
| 10 | A fast initial alignment method for strapdown inertial navigation system on stationary base显示文摘 | Fang Jiancheng Wan Dejun | 1996 | IEEE Transactions on Aerospace and Electronic Systems1996，32，4： | 1 |
| 11 | A fuzzy neural controller design for ship autopilot显示文摘 | Cheng Qiming Wan Dejun | 1999 | Chinese Journal of Electronics1999，8，4： | 1 |
| 12 | Mode decomposition of a noise suppressed mixing layer显示文摘Noise is generated in a two-dimensional mixing layer due to the growing of instability waves and vortex pairings. The adjoint-based control methodology has shown to be a robust tool to suppress noise radiation. The mode decomposition algorithms such as the compressible version of proper orthogonal decomposition (POD) and dynamic mode decomposition (DMD) are employed to analyze the spatial/spatial-temporal coherent structures for a consecutive data sets of the controlled mixing layer and its uncontrolled counterpart. The analyses of POD indicate that the y-direction body force control mainly modify the most energetic spatial structures, and increase the uniformity of the flow. The analyses of DMD show us prevalent frequencies and corresponding mode structures, and the stability characteristics of each mode can be obtained from DMD-spectrum. The spectral signatures illustrate that a lot of neutral/slightly damping modes emerging in uncontrolled flow within the frequency range (ω < 0.4) are suppressed due to control, relevant spatial-temporal structures are also varied, which is coincident with the change of far-field noise spectra. From the view of mode decomposition, the action of control redistribute the energy for frequency components of ω < 0.4 by weakening nonlinearities and regularizing corresponding dynamic structures in streamwise direction, and thus suppress the noise radiation. Moreover, the PODand DMD-analysis in this study demonstrate that DMD can serve as an important supplement for POD in analyzing a time-resolved physical process. | Zhenhua Wan Haihua Yang Lin Zhou Dejun Sun | 2013 | Theoretical & Applied Mechanics Letters2013，3，4： | 1 |
| 13 | A study on large coherent structures and noise emission in a turbulent round jet显示文摘A moderate Reynolds number,and high subsonic turbulent round jet is investigated by large eddy simulation.The detailed results(e.g.mean flow properties,turbulence intensities,etc.)are validated against the experimental data,and special attention is paid to study motions of coherent structures and their contributions to far-field noise.Eulerian methods(e.g.Q-criteria andλ2criteria)are utilized for visualizing coherent structures directly for instantaneous flow fields,and Lagrangian coherent structures accounting for integral effect are shown via calculating fields of finite time Lyapunov exponents based on bidimensional velocity fields.All visualizations demonstrate that intrusion of three-dimensional vortical structures into jet core occurs intermittently at the end of the potential core,resulting from the breakdown of helical vortex rings in the shear layer.Intermittencies in the shear layer and on the centerline are studied quantitatively,and distinctively different distributions of probability density function are observed.Moreover,the physical sound sources are obtained through a filtering operation of defined sources in Lighthill’s analogy,and their distributions verify that intrusion of vortical structures into the core region serves as important sound sources,in particular for noise at aft angles.The facts that intermittent behaviors are caused by motions of coherent structures and correlated with noise generation imply that to establish reasonable sound sources in active noise production region based on intermittent coherent structures is one of the key issues for far-field noise prediction. | WAN ZhenHua ZHOU Lin SUN DeJun | 2014 | Science China(Physics,Mechanics & Astronomy)2014，57，8： | 1 |
| 14 | Map Matching in RoadCrossings of Urban Canyons Based on Road Traverses and LinearHeading-Change Model显示文摘 | Zhang Xiaoguo Wang Qing Wan Dejun | 2007 | IEEE Transactions on Instrumenta-tion and Measurement2007，56，6： | 1 |
| 15 | A study on large coherent structures and noise emission in a turbulent round jet显示文摘 | WAN Zhenhua ZHOU Lin & SUN Dejun | | SCIENCE CHINA Physics Mechanics & Astronomy 00，，： | 1 |
| 16 | The Regulating Mechanism of Nm23-H1 Gene for FAK Signal Pathway in Human Lung Cancer Cell Line L9981显示文摘Background and objective Lung Cancer is one of the most malignant cancers threatening people’s health and life and one of the most rapid increasing cancers both in morbidity | Dejun KONG Zhilin SUN Yang QIN Wen ZHU Li REN Jun CHEN Sen WEI Zhigang LI Hongyu LIU Haisu WAN Zhi-hao WU Ke XU Qinghua ZHOU | 2009 | 中国肺癌杂志2009，12，6： | 0 |
| 17 | The effects of initial perturbation to mixing-layer noise显示文摘The far-field noise radiated from mixing layers is determined by the near-field flow dynamics which is sensitive to the initial perturbation of instability introduced physically or numerically.This study focuses on the effects of the phase delay in two initial perturbations,one at the fundamental wave number and the other at its subharmonic both calculated from linear instability analysis,on the sound generation in mixing layers.When different phase delaysφ_1 changing from zero to 2πis applied on the fundamental mode,we observe different vortex merging processes(e.g.vortex pairing or tearing).The strong nonlinear interaction in the merging process generates most of the noise from mixing layers.There shows a pattern in a period of 2πfor the response of far-field sound to the change ofφ_1.Similar effects on the dynamics and acoustics can be achieved by adding different phase delaysφ_2 to the subharmonic mode instead,however,the response repeats in a period of onlyπforφ_2.The effects of the combination of different phase delays to other parameters,including the amplitude and wave number for each perturbations,are also investigated.All the results indicate a critical role of nonlinearity in the sound generation mechanism of mixing layers. | Lin Zhou Zhenhua Wan Dejun Sun Mingjun Wei | 2012 | Theoretical & Applied Mechanics Letters2012，2，3： | 0 |
| 18 | Linear stability analysis of supersonic axisymmetric jets显示文摘Stabilities of supersonic jets are examined with different velocities, momentum thicknesses, and core temperatures. Amplification rates of instability waves at inlet are evaluated by linear stability theory(LST). It is found that increased velocity and core temperature would increase amplification rates substantially and such influence varies for different azimuthal wavenumbers. The most unstable modes in thin momentum thickness cases usually have higher frequencies and azimuthal wavenumbers. Mode switching is observed for low azimuthal wavenumbers, but it appears merely in high velocity cases. In addition, the results provided by linear parabolized stability equations show that the mean-flow divergence affects the spatial evolution of instability waves greatly. The most amplified instability waves globally are sometimes found to be different from that given by LST. | Zhenhua Wan Haihua Yang Lin Zhou Dejun Sun | 2014 | Theoretical & Applied Mechanics Letters2014，4，6： | 0 |
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