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Model reduction for supersonic cavity flow using proper orthogonal decomposition(POD)and Galerkin projection

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Applied Mathematics and Mechanics(English Edition) 2017年第5期38卷 723-736页

作者： Chao ZHANG Zhenhua WAN dejun sun Department of Modern Mechanics University of Science and Technology of ChinaHefei 230027China

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.

关键词： supersonic cavity flow reduced-order model (ROM) proper orthogonal decomposition (POD) Galerkin projection

Mode transition and oscillation suppression in supersonic cavity flow

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Applied Mathematics and Mechanics(English Edition) 2016年第7期37卷 941-956页

作者： Chao ZHANG Zhenhua WAN dejun sun Department of Modern Mechanics University of Science and Technology of China

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.

关键词： supersonic cavity flow pressure oscillation mode transition vortex-corner interaction

Bifurcations in penetrative Rayleigh-Be′nard convection in a cylindrical container

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Applied Mathematics and Mechanics(English Edition) 2019年第5期40卷 695-704页

作者： Chuanshi sun Shuang LIU Qi WANG Zhenhua WAN dejun sun Department of Modern Mechanics University of Science and Technology of China

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 ***, two kinds of qualitatively different steady axisymmetric solutions are identi?ed.

关键词： bifurcation convection linear stability analysis (LSA)

A study on large coherent structures and noise emission in a turbulent round jet

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Science China(Physics,Mechanics & Astronomy) 2014年第8期57卷 1552-1562页

作者： WAN ZhenHua ZHOU Lin sun dejun Department of Modern Mechanics University of Science and Technology of China

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 and A2 criteria） 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.

关键词： turbulent round jet coherent structures noise sources

Instabilities and pattern evolution in a vertically heated annulus

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Science China(Physics,Mechanics & Astronomy) 2013年第2期56卷 257-262页

作者： WANG BoFu GUO ZhiWei MA DongJun sun dejun Department of Modern Mechanics University of Science and Technology of China School of Water Resources and Hydropower Engineering Wuhan University School of Aerospace Engineering Georgia Institute of TechnologyAtlantaGeorgia 30332USA

The convection in an annular container with heated bottom,cooled top and insulated side walls are studied by both linear instability analysis and direct numerical *** onset of convection is investigated by linear stability analysis and corresponding pattern selection mechanisms are *** nonlinear evolution of different flow patterns and the convective heat transfer are *** transition to oscillatory flow is also given by stability analysis where the base flow is a steady three dimensional *** stability predictions are in good agreement with the numerical simulations,including both the growth rate and the dimensionless frequency.

关键词： thermal convection flow instability pattern evolution

Instability waves and low-frequency noise radiation in the subsonic chevron jet

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Acta Mechanica Sinica 2018年第3期34卷 421-430页

作者： Lingke Ran Chuangchao Ye Zhenhua Wan Haihua Yang dejun sun Department of Modern Mechanics University of Science and Technology of ChinaHefei 230027China Institute of Applied Physics and Computational Mathematics Beijing 100088China

Spatial instability frequency noise radiation at waves associated with low- 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 down- stream 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.

关键词： Instability waves Chevron jet Wavepacket Far-field noise

Coherent structures and wavepackets in subsonic transitional turbulent jets

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Acta Mechanica Sinica 2017年第1期33卷 10-19页

作者： Haihua Yang Xingchen Zhang Lingke Ran dejun sun Zhenhua Wan Department of Modern Mechanics University of Science and Technology of China Hefei 230027 China

A large eddy simulation (LES) is performed for two subsonic jets with a Reynolds number of , 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 modes have high coherence of near-field pressure for both jets, while the coherence of 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.

关键词： Wavepacket Noise Coherent structure Turbulent jet

Recent advances in switchable surfactants for heavy oil production:A review

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Energy Geoscience 2024年第4期5卷 75-88页

作者： Qi Li Lingfei Liu dejun sun Zhenghe Xu Key Laboratory of Colloid and Interface Chemistry Ministry of EducationSchool of Chemistry and Chemical EngineeringShandong UniversityJinanShandong250100PR China Shenzhen Key Laboratory of Interfacial Science and Engineering of Materials Department of Materials Science and EngineeringSouthern University of Science and TechnologyShenzhenGuangdong518055PR China Key Laboratory of Tertiary Oil Recovery and Oilfield Chemistry PetroChina Dagang Oilfield CompanyTianjin300280PR China

Surfactants are extensively employed in the cold production of heavy ***,producing heavy oil emulsions using conventional surfactants poses a challenge to spontaneous demulsification,necessitating the addition of demulsifiers for oil-water *** inevitably increases the exploitation cost and environmental pollution *** surfactants have garnered much attention due to their dual capabilities of underground heavy oil emulsification and surface *** study focuses on the fundamental working principles and classification of novel switchable surfactants for oil displacement developed in recent *** offers a comprehensive overview of the latest advances in the applications of switchable surfactants in the fields of enhanced oil recovery(EOR),oil sand washing,and oil-water ***,it highlights the existing challenges and future development directions of switchable surfactants for heavy oil recovery.

关键词： Heavy oil Switchable surfactant Cold production Emulsification Demulsification

Linear stability analysis of supersonic axisymmetric jets

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Theoretical & Applied Mechanics Letters 2014年第6期4卷 49-54页

作者： Zhenhua Wan Haihua Yang Lin Zhou dejun sun Department of Modern Mechanics University of Science and Technology of China Institute of Structural Mechanics Chinese Academy of Engineering Physics

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.

关键词： linear stability theory parabolized stability equations axisymmetric jet