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Journal of Systems Science & Complexity 2012年第2期25卷 398-409页

作者： jiming yang Yanping CHEN College of Science Hunan Institute of Engineering School of Mathematical Sciences South China Normal University

In order to obtain an expected numerical solution, a fully discrete discontinuous Galerkin method is applied to a kind of reactive transport problems in two dimension. That is to say, the space variable is discretized with the symmetric interior penalty Calerkin method （SIPG）, and the time variable is done with the backward Euler method. Making use of the duality technique, hp approximation properties and the interpolation theory, a residual-type a posteriori error estimation is achieved, which can be used for adaptivity. Compared with the analyses of semi-discretization, the current presentation is more challenging and more significant.

关键词： A posteriori error discontinuous Galerkin duality technique full discretization reactivetransport.

Planar laser scattering visualization of streamwise vortex pairs in a Mach 6 flow

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Chinese Journal of Aeronautics 2023年第1期36卷 166-177页

作者： Yinkai MA Zhufei LI jiming yang Department of Modern Mechanics University of Science and Technology of ChinaHefei 230027China

A series of cross-sectional flow fields of Counterrotating Vortex Pairs(CVPs) generated by a large-scale ramp vortex generator is observed using an ice-cluster-based Planar Laser Scattering(PLS) method in a shock tunnel with a nominal flow Mach number of 6. Combined with a numerical simulation, two streamwise CVPs with opposite rotating directions are identified in the wake flow of the vortex generator with an absence of a boundary layer, namely, a Primary CVP(PCVP) and a Secondary CVP(SCVP). The wake flow is divided into two stages with different features of the PCVP and SCVP. In Stage Ⅰ, the PCVP and SCVP gradually mature, and the flow is relatively stable. In Stage Ⅱ, the PCVP and SCVP depart from each other, and the flow becomes unstable. The profiles of the transverse velocity in the spanwise symmetry plane induced by the PCVP and SCVP do not obey the scaling law of CVPs immersed in the boundary layer. A new scaling law is proposed, in which the transverse distances between adjacent saddle points in the cross-sectional flow field are used as the characteristic lengths for the PCVP and SCVP. After this new scaling procedure, the profiles of transverse velocity induced by the PCVP and SCVP at different streamwise locations collapse well. Moreover, the PLS images show that the mixing between the CVPs and the outside high-momentum flow becomes evident at approximately 5.5 times the height of the vortex generator, which is earlier than that immersed in the boundary layer. These findings enrich the knowledge of CVPs in the hypersonic regime, especially in the absence of the boundary layer.

关键词： Counterrotating vortex pair Hypersonic flow Planar laser scattering Scaling law Shock tunnel

A PRIORI ERROR ESTIMATES OF A COMBINED MIXED FINITE ELEMENT AND DISCONTINUOUS GALERKIN METHOD FOR COMPRESSIBLE MISCIBLE DISPLACEMENT WITH MOLECULAR DIFFUSION AND DISPERSION

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Journal of Computational Mathematics 2011年第1期29卷 91-107页

作者： jiming yang Yanping Chen College of Science Hunan Institute of Engineering Xiangtan 411104 China School of Mathematical Sciences South China Normal University Guangzhou 510631 China

A combined approximation for a kind of compressible miscible displacement problems including molecular diffusion and dispersion in porous media is studied. Mixed finite el- ement method is applied to the ftow equation, and the transport one is solved by the symmetric interior penalty discontinuous Galerkin method （SIPG）. To avoid the inconve- nience of the cut-off operator in [3, 21], some induction hypotheses different from the ones in [6] are used. Based on interpolation projection properties, a priori hp error estimates are obtained. Comparing with the existing error analysis that only deals with the diffusion case, the current work is more complicated and more significant.

关键词： A priori error Mixed finite element Discontinuous Galerkin Compressiblemiscible clisplacement.

A hybrid CFD/characteristics method for fast characterization of hypersonic blunt forebody/inlet flow

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Science China(Physics,Mechanics & Astronomy) 2015年第10期58卷 38-45页

作者： GAO WenZhi LI ZhuFei yang jiming Department of Modern Mechanics University of Science and Technology of China

A hybrid CFD/characteristic method(CCM) was proposed for fast design and evaluation of hypersonic inlet flow with nose bluntness, which targets the combined advantages of CFD and method of characteristics. Both the accuracy and efficiency of the developed CCM were verified reliably, and it was well demonstrated for the external surfaces design of a hypersonic forebody/inlet with nose bluntness. With the help of CCM method, effects of nose bluntness on forebody shock shapes and the flowfield qualities which dominate inlet performance were examined and analyzed on the two-dimensional and axisymmetric configurations. The results showed that blunt effects of a wedge forebody are more substantial than that of related cone cases. For a conical forebody with a properly blunted nose, a recovery of the shock front back to that of corresponding sharp nose is exhibited, accompanied with a gradually fading out of entropy layer effects. Consequently a simplification is thought to be reasonable for an axisymmetric inlet with a proper compression angle, and a blunt nose of limited radius can be idealized as a sharp nose, as the spillage and flow variations at the entrance are negligible, even though the nose scale increases to 10% cowl lip radius. Whereas for two-dimensional inlets, the blunt effects are substantial since not only the inlet capturing/starting capabilities, but also the flow uniformities are obviously degraded.

关键词： hypersonic flow shock wave forebody/inlet flow nose bluntness method of characteristics

Tomography-like flow visualization of a hypersonic inward-turning inlet

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Chinese Journal of Aeronautics 2021年第1期34卷 44-49页

作者： Yiming LI Zhufei LI jiming yang Department of Modern Mechanics University of Science and Technology of ChinaHefei 230027China

The flow field in a typical inward-turning inlet was visualized using the Planar Laser Scattering(PLS)method in a shock tunnel with a nominal Mach number of *** opaque inlet,which is truncated at a series of sections,and the following transparent isolator,are combined to enable the optical access at different streamwise *** sequential PLS images provide a tomography-like flow visualization,which confirm the existence of streamwise Counter-rotating Vortex Pairs(CVPs)in both external and internal flow field of the *** mechanisms of these CVPs are unraveled with the help of a numerical simulation,among which the cowl notch plays an important role in the generation of surface trailing CVPs along the centerline of the ***,the cowl shock sweeps the internal boundary layer towards the body side,which ultimately accumulates low-momentum flow on the body side in forms of a large CVP propagating downstream through the *** CVPs formed in the shape-transition are responsible for the nonuniform flow field of the inward-turning *** study indicates that the V-shaped cowl notch affects the downstream flow significantly and,therefore,should be examined thoroughly in practical applications.

关键词： Counter-rotating Vortex Pair(CVP) Flow visualization Inward-turning inlet Planar Laser Scattering(PLS)method Shock wave

Scaling of interaction lengths for hypersonic shock wave/turbulent boundary layer interactions

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Chinese Journal of Aeronautics 2021年第5期34卷 504-509页

作者： Yuting HONG Zhufei LI jiming yang Department of Modern Mechanics University of Science and Technology of ChinaHefei 230027China

The interaction length induced by Shock Wave/Turbulent Boundary-Layer Interactions(SWTBLIs)in the hypersonic flow was investigated using a scaling analysis,in which the interaction length normalized by the displacement thickness of boundary layer was correlated with a corrected non-dimensional separation criterion across the interaction after accounting for the wall temperature effects.A large number of hypersonic SWTBLIs were compiled to examine the scaling analysis over a wide range of Mach numbers,Reynolds numbers,and wall *** results indicate that the hypersonic SWTBLIs with low Reynolds numbers collapse on the supersonic SWTBLIs,while the hypersonic cases with high Reynolds numbers show a more rapid growth of the interaction length than that with low Reynolds ***,two scaling relationships are identified according to different Reynolds numbers for the hypersonic *** scaling analysis provides valuable guidelines for engineering prediction of the interaction length,and thus,enriches the knowledge of hypersonic SWTBLIs.

关键词： Hypersonic flow Interaction length Scaling laws Separation criterion Shock wave/turbulent boundary layer interactions

A Posteriori Error Estimates of a Combined Mixed Finite Element and Discontinuous Galerkin Method for a Kind of Compressible Miscible Displacement Problems

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Advances in Applied Mathematics and Mechanics 2013年第2期5卷 163-179页

作者： jiming yang Zhiguang Xiong College of Science Hunan Institute of EngineeringXiangtan 411104HunanChina School of Mathematics and Computational Science Hunan University of Science and TechnologyXiangtan 411201HunanChina

Akind of compressiblemiscible displacement problemswhich includemolecular diffusion and dispersion in porous media are *** mixed finite element method is applied to the flow equation,and the transport one is solved by the symmetric interior penalty discontinuous Galerkin *** on a duality argument,employing projection estimates and approximation properties,a posteriori residual-type hp error estimates for the coupled system are presented,which is often used for guiding *** with the error analysis carried out by yang(***,65(7)(2011),pp.781-797),the current work is more complicated and challenging.

关键词： A posteriori error discontinuous Galerkin method compressible miscible displacement mixed finite element duality argument

Effects of trips on the oscillatory flow of an axisymmetric hypersonic inlet with downstream throttle

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Chinese Journal of Aeronautics 2018年第2期31卷 225-236页

作者： Wenzhi GAO Zhufei LI jiming yang Yishan ZENG School of Mechanical Engineering Hefei University of Technology Department of Modern Mechanics University of Science and Technology of China

Experimental investigations are conducted on an axisymmetric hypersonic inlet to evaluate the effects of trips on oscillatory flows. The model exit is throttled with a fixed block to generate oscillatory flows at a freestream Mach number of 6 in a conventional wind tunnel and a shock tunnel. Schlieren imaging and pressure measurements are adopted to record unsteady flow *** indicate that trips with a 1 mm thickness prominently suppress external separations, shorten oscillatory cycles, and modify pressure magnitudes. Trips can reduce the upstream movement ranges of separated shocks from nose regions to locations axially 142 mm downstream. The oscillatory cycles are shortened from 3.75 ms to 3.25 ms and from 4 ms to 3.13 ms in two *** cases generally exhibit higher pressure magnitudes than those of untripped cases, of which the increment is up to 21 times the freestream static pressure for the farthest downstream transducer in the shock tunnel. The effects of trips are related to the streamwise vortexes in wake flows, in which interactions between external separations modify the separated flow patterns and enhance the sustainment of the forebody boundary layers to backpressure. Flow processes causing increments of oscillatory frequencies and pressure magnitudes are analyzed, while the flow mechanisms dominating the processes still need to be clarified in the future.

关键词： Backpressure Flow separations Hypersonic inlets Inlet unstart Oscillatory flow Trips

A facile ionic liquid approach to prepare cellulose fiber with good mechanical properties directly from corn stalks

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Green Energy & Environment 2020年第2期5卷 223-231页

作者： jiming yang Xingmei Lu Yanqiang Zhang Junli Xu Yongqing yang Qing Zhou Beijing Key Laboratory of Ionic Liquids Clean Process CAS Key Laboratory of Green Process and EngineeringState Key Laboratory of Multiphase Complex SystemsInstitute of Process EngineeringChinese Academy of SciencesBeijing100190China School of Chemical Engineering University of Chinese Academy of SciencesBeijing100049China

It is very difficult to directly spin the lignocellulose without *** liquids(ILs)are promising solvent to dissolve lignocellulose to prepare cellulose ***,the degree of cellulose polymerization(DP)is reduced when lignocellulose is dissolved in ILs,and the lignin removal rate is *** elongation at break and tensile strength of the fibers obtained by spinning the lignocellulose dissolved in ILs are *** this paper,preparing cellulose fiber directly from lignocellulose based on dissolving corn stalk via[C4mim]Cl-L-arginine binary system is *** shows that the removal rate of lignin can reach 92.35%and the purity of cellulose can reach 85.32%after corn stalk was dissolved at 150℃C for 11.5 h when the mass fraction of arginine is 2.5%.The elongation at break of fiber reached 10.12%and the tensile strength reached 420 *** is mainly due to the fact that L-arginine not only inhibits the degradation of cellulose but also promotes the *** any pulping or pretreatment,preparing cellulose fibers via direct dissolution and extrusion may provide a simple and effective way to prepare many novel cellulose materials.

关键词： Cellulose fibers Ionic liquids Corn stalks Dissolving Directly spinning

Numerical Investigation of Supersonic Channel Flow with Oscillatory Backpressures

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Advances in Applied Mathematics and Mechanics 2019年第1期11卷 1-23页

作者： Peizhao Sun Nansheng Liu jiming yang Xiyun Lu Department of Modern Mechanics University of Science and Technology of ChinaHefei 230026AnhuiChina

The investigation of supersonic channel flow with periodic oscillatory backpressures at the outlet of the channel was performed using large-eddy simulation for the inlet free-stream Mach number 4 and the Reynolds number approximately 5.2104 based on the height of the *** have been validated carefully against our experimental *** typical backpressures are considered for constant backpressure and both periodic oscillatory backpressures with low and high *** oscillatory backpressure can obviously influence the flow features occurring up to the middle region of the channel for the low frequency case and the downstream region for the high frequency *** differences of phase-averaged quantities at different phases are observed for the low frequency backpressure while the differences are relatively small for the high frequency *** spectral analysis reveals that the flow field experiences a periodic-like evolution of flow structures including shocks and vortices for the low frequency backpressure,resulting in the enhancement of turbulence fluctuations due to the complicated interaction of shocks and vortices.

关键词： Large eddy simulation shock wave turbulent flow