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New omega vortex identification method

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Science China(Physics,Mechanics & Astronomy) 2016年第8期59卷 56-64页

作者： ChaoQun Liu YiQian Wang Yong Yang ZhiWei Duan department of Mathematics University of Texas at Arlington department of aerodynamics Nanjing University of Aeronautics and Astronautics School of Aerospace Engineering Tsinghua University

A new vortex identification criterion called W-method is proposed based on the ideas that vorticity overtakes deformation in *** comparison with other vortex identification methods like Q-criterion and λ_2-method is conducted and the advantages of the new method can be summarized as follows:(1) the method is able to capture vortex well and very easy to perform;(2) the physical meaning of W is clear while the interpretations of iso-surface values of Q and λ_2 chosen to visualize vortices are obscure;(3)being different from Q and λ_2 iso-surface visualization which requires wildly various thresholds to capture the vortex structure properly, W is pretty universal and does not need much adjustment in different cases and the iso-surfaces of W=0.52 can always capture the vortices properly in all the cases at different time steps, which we investigated;(4) both strong and weak vortices can be captured well simultaneously while improper Q and λ_2 threshold may lead to strong vortex capture while weak vortices are lost or weak vortices are captured but strong vortices are smeared;(5) W=0.52 is a quantity to approximately define the vortex boundary. Note that, to calculate W, the length and velocity must be used in the non-dimensional form. From our direct numerical simulation, it is found that the vorticity direction is very different from the vortex rotation direction in general 3-D vortical flow,the Helmholtz velocity decomposition is reviewed and vorticity is proposed to be further decomposed to vortical vorticity and non-vortical vorticity.

关键词： vorticity vortex vortex identification turbulence

ANovel Immersed Boundary Method Implemented by Imposing Reconstructed Velocity on Virtual Boundary

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Advances in Applied Mathematics and Mechanics 2021年第1期13卷 83-100页

作者： Jingyang Wang Chunhua Zhou department of aerodynamics Nanjing University of Aeronautics and AstronauticsNanjingJiangsu 210016China

In this paper,a novel immersed boundary method is presented for simulating incompressible flows governed by Navier-Stokes equations.A virtual boundary is formed by the cell edges(for two-dimensional cases)in the vicinity of the immersed *** the domain with the virtual boundary,the governing equations can be solved in the conventional *** velocity is imposed on the virtual boundary,which is determined via the interpolation along the direction normal to the wall and in conjunction with the no-slip condition for the actual ***”freshly cleared nodes”on the virtual boundary encountered in moving-boundary problems,pressure at the previous time step is reconstructed by solving the local simplified momentum *** the test case for an analytical solution,the local accuracy of pressure is verified to be of the second *** order to further validate the present method,various flows over the stationary and/or moving circular cylinder and NACA0012 airfoil have been *** obtained results agree well with the available numerical or experimental data in the published literatures.

关键词： Immersed boundary method boundary condition convergence rate solution reconstruction.

Physics of multiple level hairpin vortex structures in turbulence

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Science China(Physics,Mechanics & Astronomy) 2016年第2期59卷 91-101页

作者： Yi Qian Wang Hassan Al-Dujaly Yong Hua Yan Ning Zhao Chao Qun Liu department of aerodynamics Nanjing University of Aeronautics and Astronautics Nanjing 210016 China department of Mathematics University of Texas at Arlington Arlington 76019 USA

Previous experimental and numerical studies have revealed that the hairpin vortex is a basic flow element of transitional boundary layer. The hairpin vortex is believed to have legs, necks and a ring head. Based on our DNS study, the legs and the ring head are generated separately by different mechanisms. The legs function like an engine to generate low speed zones by rotation, create shear layers with surrounding high speed neighbor fluids, and further cause vortex ring formation through shear layer instability. In addition, the ring head is Ω-shaped and separated from quasi-streamwise legs from the beginning. Contrary to the classical concept of ＂vortex breakdown＂, we believe transition from laminar flow to turbulence is a ＂buildup＂ process of multiple level vortical structures. The vortex tings of first level hairpins are mostly responsible for positive spikes, which cause new vorticity rollup, second level vortex leg formation and finally smaller second level vortex ring generation. The third and lower level vortices are generated following the same mechanism. In this paper, the physical process from A-vortex to mul- ti-level hairpin vortices is described in detail.

关键词： hairpin vortex vortex buildup multiple level vortices flow transition

Development of a Balanced Adaptive Time‑Stepping Strategy Based on an Implicit JFNK‑DG Compressible Flow Solver

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Communications on Applied Mathematics and Computation 2022年第2期4卷 728-757页

作者： Yu Pan Zhen‑Guo Yan Joaquim Peiró Spencer J.Sherwin department of Aeronautics Imperial College LondonLondonUK State Key Laboratory of aerodynamics China Aerodynamics Research and Development CenterMianyang 621000SichuanChina

A balanced adaptive time-stepping strategy is implemented in an implicit discontinuous Galerkin solver to guarantee the temporal accuracy of unsteady simulations.A proper relation between the spatial,temporal and iterative errors generated within one time step is *** an estimate of temporal and spatial error using an embedded RungeKutta scheme and a higher order spatial discretization,an adaptive time-stepping strategy is proposed based on the idea that the time step should be the maximum without obviously infuencing the total error of the *** designed adaptive time-stepping strategy is then tested in various types of problems including isentropic vortex convection,steady-state fow past a fat plate,Taylor-Green vortex and turbulent fow over a circular cylinder at Re=*** results indicate that the adaptive time-stepping strategy can maintain that the discretization error is dominated by the spatial error and relatively high efciency is obtained for unsteady and steady,well-resolved and under-resolved simulations.

关键词： Adaptive time-stepping Unsteady simulations High order Discontinuous Galerkin Implicit time integration

Drag Reduction Effect for Hypersonic Lifting-Body Vehicle with Counterflowing Jet

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Transactions of Nanjing University of Aeronautics and Astronautics 2018年第5期35卷 789-799页

作者： Dong Hao Deng Fan Xie Feng Geng Xi Cheng Keming College of Aerospace Engineering Nanjing University of Aeronautics and Astronautics General Control department Space Transportation Technology CO.Ltd. Hypervelocity aerodynamics Institute China Aerodynamics Research and Development Center

This study takes the novel approach of using a counterflowing jet positioned on the nose of a lifting-body vehicle to explore its drag reduction effect at a range of angles of *** studies are conducted at a freestream Mach number of 8 in standard atmospheric conditions corresponding to the altitude of 40 *** effects of jet pressure ratio and flying angles of attack on drag reduction of the model are systematically *** the reverse thrust generated from the counterflowing jet,the drag on the nose at hypersonic speeds could be reduced up to 66%.The maximum lift-to-drag ratio of the model is obtained at 6°;meanwhile,the counterflowing jet produces a drag reduction of 8.8%for the whole *** addition to the nose,the counterflowing jet influences the drag by increasing the pressure drag of the model and reducing the skin friction drag of the first cone within 8°.The results show that the potential of the counterflowing jet as a means of active flow control for drag reduction is significant in the engineering application on hypersonic lifting-body vehicles.

关键词： hypersonic lifting-body counterflowing jet drag numerical simulation

Accurate attitude estimation of HB2 standard model based on QNCF in hypersonic wind tunnel test

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Chinese Journal of Aeronautics 2020年第1期33卷 64-72页

作者： Haotian YANG Bin ZHOU Qi WEI Xiong WANG Xiaobin XU Rong ZHANG department of Precision Instrument Tsinghua UniversityBeijing 100084China Xi’an Research Institute of High Technology Xi’an 710025China Hypervelocity aerodynamics Institute China Aerodynamics Research and Development CenterMianyang 621000China

The accuracy of the HB2 standard model attitude measurement has an important impact on the hypersonic wind tunnel data *** limited size of the model and the existence of external vibrations make it challenging to obtain real-time reliable attitude *** reduce the influence of attitude errors on test results,this paper proposes a Quaternion Nonlinear Complementary Filter(QNCF)attitude determination algorithm based on Microelectromechanical Inertial Measurement Unit(MEMS-IMU).Firstly,the threshold-based PI control strategy is adopted to eliminate noise effect according to the Acceleration Magnitude Detector(AMD).Then,the flexible quaternion method is updated to carry out attitude estimation which is operational and easy to be embedded in the Field Programmable Gate Array(FPGA).Finally,a high-precision three-axis turntable test and a hypersonic wind tunnel test are *** results show that the pitchroll attitude errors are within 0.05°and 0.08°in the high-precision three-axis turntable test in a calculation time of 100 s respectively,and the attitude error is within 0.3°after the elastic angle correction in the hypersonic wind tunnel *** proposed method can provide accurate real-time attitude reference for the analysis of the actual movement of the model,exhibiting certain engineering application value with robustness and simplicity.

关键词： Attitude determination MEMS Nonlinear complementary filter Quaternion Wind tunnel test

Quantum Optical Description of Radiation by a Two-Level System in Strong Laser Fields

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Chinese Physics Letters 2023年第5期40卷 20-24页

作者：彭朝阳胡华雨赵增秀袁建民 department of Physics National University of Defense TechnologyChangsha 410073China department of Physics Graduate School of China Academy of Engineering PhysicsBeijing 100193China Hypervelocity aerodynamics Institute China Aerodynamics Research and Development CenterMianyang 621000China

We develop a quantum optical description of radiation from a two-level system(TLS)in strong laser fields,which provides a clear insight into the final states of the TLS and the harmonics *** is shown that there are two emission channels:the Rayleigh-like channel and the Raman-like channel,which correspond to the TLS ending up in the ground state and excited state after the emission,*** numerical result shows that the harmonics are mainly produced by the Rayleigh-like *** addition,according to the coherence of emission among the emitters,the radiation is divided into coherent parts that result from the semi-classical dipole oscillation and incoherent parts that result from the quantum fluctuations of the dipole *** the weak field limits,the Rayleigh-like channel corresponds to the coherent parts,and the Raman-like channel corresponds to the incoherent ***,in strong laser fields,both channels contribute to coherent and incoherent radiation,and how much they contribute depends on the final *** manipulating the laser field,we can make the Rayleigh-like channel produce either coherent or incoherent radiation.

关键词： coherent harmonics dipole

A simplified method for calculating spectral emission of nonequilibrium air plasmas in hypersonic shock-layers

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Advances in aerodynamics 2021年第1期3卷 272-280页

作者： Xin He Cheng Gao Tao Jiang department of Physics National University of Defense TechnologyChangsha 410073China Computational aerodynamics Institute China Aerodynamics Research and Development CenterMianyang 621000China.

A simplified method for calculating the spectral emission of nonequilibrium air plasmas is *** order to obtain the nonequilibrium energy level populations,the nonequilibrium coefficients are introduced into the Saha-Boltzmann *** nonequilibrium coefficients are calculated by using several significant radiative *** approach to the determination of nonequilibrium electronic energy level populations of diatomic molecules is also *** on the method,spectral emission of atoms and molecules in a typical air plasma cell is *** results reveal that there is a significant difference between the nonequilibrium and equilibrium *** apply the method to the nonequilibrium AVCO R-156 *** agreement with the NEQAIR code and the measured data is shown,indicating that the method is reasonable and has good accuracy.

关键词： Spectral emission Nonequilibrium Air plasma Hypersonic

Evaluation of Turbulence Models in Predicting Hypersonic and Subsonic Base Flows Using Grid Adaptation Techniques

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Chinese Journal of Aeronautics 2012年第3期25卷 325-334页

作者： YOU Yancheng BUANGA Bjorn HANNEMANN Volker LUDEKE Heinrich Institute of aerodynamics and Flow Technology German Aerospace Center (DLR) Braunschweig 38108 Germam Institute of aerodynamics and Flow Technology German Aerospace Center (DLR) Gottingen 37073 Germany department of Aeronautics Xiamen University Xiamen 361005 China

The flows behind the base of a generic rocket, at both hypersonic and subsonic flow conditions, are numerically studied. The main concerns are addressed to the evaluation of turbulence models and the using of grid adaptation techniques. The investigation focuses on two configurations, related to hypersonic and subsonic experiments. The applicability tests of different turbu- lence models are conducted on the level of two-equation models calculating the steady state solution of the Reynolds-averaged Navier-Stokes（RANS） equations. All used models, the original Wilcox k-co, the Menter shear-stress transport （SST） and the ex- plicit algebraic Reynolds stress model（EARSM） formulation, predict an asymmetric base flow in both cases caused by the support of the models. A comparison with preliminary experimental results indicates a preference for the SST and EARSM results over the results from the older k-co model. Sensitivity studies show no significant influence of the grid topology or the location of the laminar to turbulent transition on the base flow field, but a strong influence of even small angles of attack is reported from the related experiments.

关键词： base flows turbulence models steady calculation grid adaptation numerical simulation