The vortices merging in a turbulent boundary layer of a rectangular channel were experimental studied with a moving single-frame and long-exposure (MSFLE) imaging method which is a Lagrangian-type measurement technique. The process of vortices merging was studied in the streamwise-normal plane with Reθ=97~194. During the experiments, the measurement system moved at a constant speed that is similar to the moving velocity of measured vortex to record continually the moving of vortices with long exposure time. An image processing algorithm based on skeleton extraction was employed to process the images of the flow field for obtaining the velocity of vortices and the flow field. The Liutex theory was adopted to process the flow field for characterizing the intensity of vortex structure. The study shows that the MSFLE imaging method is a cost effective method. It can intuitively show the spatiotemporal evolution of vortex and surrounding flow field in a turbulent boundary layer with a Lagrangian-perspective. The MSFLE image method combined with Liutex vortex recognition algorithm can be applied to the visualization and quantification of vortex structure in the channel turbulent boundary layer. The vortices merging most possibly occur in a pair of adjacent co-rotating vortices with the basically equal intensity and size. During the process of merging, the intensity of these two vortices changes in the opposite direction. Moreover, a new generated vortex has the same rotation direction as the two merging vortices and its size and intensity are about the sum of the two merging vortices at the initial merging.
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CFD has been playing a more and more important role in aeronautics and astronautics as a critical tool of modern aircraft design and aerodynamics research. On the contrary, the improvement of key theories such as physical modelling and numerical scheme is developing slowly. Therefore, the paper focus on applications of CFD in aeronautics and astronautics from the perspectives of turbulence models, transition models, flux schemes and high order schemes, for which state-of-art achievements and challenges are discussed. For turbulence models, the development status and characteristics of the common linear viscosity models are reviewed with emphasis on their drawbacks. More complicated Reynolds stress models are also analyzed. For transition models, the low Reynolds number models, intermittency transition models and laminar kinetic energy models, focusing on the development, construction method and applicable scope of different models. For flux schemes, the upwind flux is mainly considered, reviewing the status of these methods for solving the problems of shock anomaly, overheating, all-speed simulation and multi-dimensional flow. For high order schemes, the WENO and DG methods are focused on, with review and comments on accuracy, temporal integration, shock capturing and costs. Finally, a brief conclusion and suggestions on future development are presented.
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Some recent studies on multi-scale properties of compressible turbulence conducted by the authors' group are reviewed. By multi-process decomposition methods, multi-scale properties of the solenoidal component, the dilatational component, the pseudo-sound mode, the acoustic mode, and the entropy modes of velocity and thermodynamic variables in compressible turbulence are studied. In addition, the scaling behaviors of spectra of velocity and thermodynamic variables in various situations of different compressibility are summarized. Inter-scale transfers of kinetic energy and thermodynamic variables are studied by filtering method, with the emphasis on the effects of compressibility on the inter-scale transfer of the dilatational component of kinetic energy. The compressible effects are stronger in compressible homogeneous shear turbulence. Mach number scaling behaviors of compressible kinetic energy and compressible dissipation rate are similar but have larger magnitudes as compared to those in compressible homogeneous isotropic turbulence. Distributions of eigenvalues of the strain rate tensor and the local flow topologies are more sensitive to the change of turbulent Mach number. For compressible isotropic turbulence in vibrational nonequilibrium, the vibrational relaxation between the translational-rotational and vibrational modes of internal energy results in the deviation between gradients of density and vibrational temperature, which further weakens the effect of compressibility on vibrational rate. Heat release through chemical reactions can greatly enhance compression and expansion motions and result in the increase of spectra of dilatational velocity components and thermodynamic variables at all length scales. The kinetic energy and its dissipation appear to be independent of the turbulent Mach number.
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The rarefaction effects arise when the mean free path of gas molecules is comparable to the characteristic flow length. Compared to monatomic gas, the dynamics of rarefied molecular gas, which consists of two or more atoms in one gas molecule, is more complicated, due to the additional non-equilibrium effects in the rotational and vibrational motions. As the major constituent in the atmosphere of Earth and Mars, rarefied molecular gas dynamics has strong applications in aerospace science, micro-electro-mechanical system, shale gas extraction, and so on. However, the corresponding models and simulation methods are not sophisticated. Starting from the monatomic gas and the Boltzmann equation, we review the development of the kinetic modeling of rarefied gas and the essential connection between the transport coefficients and relaxation processes. Then, we focus on the relaxation process and transport coefficients of molecular gas, and introduce typical kinetic models with the systematic assessment of their accuracy. Meanwhile, we discuss the defect of direct simulation Monte Carlo method in the modeling of rarefied molecular gas, i.e., it cannot specify the thermal relaxation rates (hence cannot recover the thermal conductivities) when the bulk viscosity is determined. Finally, we use the Wu model to quantify the uncertainties, and discuss how to reduce or even eliminate the uncertainties based on the data from the molecular dynamics simulation and Rayleigh-Brillouin scattering experiment. This present article is instructive for the modeling of rarefied gas flows involving chemical reactions.
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The vortices merging in a turbulent boundary layer of a rectangular channel were experimental studied with a moving single-frame and long-exposure (MSFLE) imaging method which is a Lagrangian-type measurement technique. The process of vortices merging was studied in the streamwise-normal plane with Reθ=97~194. During the experiments, the measurement system moved at a constant speed that is similar to the moving velocity of measured vortex to record continually the moving of vortices with long exposure time. An image processing algorithm based on skeleton extraction was employed to process the images of the flow field for obtaining the velocity of vortices and the flow field. The Liutex theory was adopted to process the flow field for characterizing the intensity of vortex structure. The study shows that the MSFLE imaging method is a cost effective method. It can intuitively show the spatiotemporal evolution of vortex and surrounding flow field in a turbulent boundary layer with a Lagrangian-perspective. The MSFLE image method combined with Liutex vortex recognition algorithm can be applied to the visualization and quantification of vortex structure in the channel turbulent boundary layer. The vortices merging most possibly occur in a pair of adjacent co-rotating vortices with the basically equal intensity and size. During the process of merging, the intensity of these two vortices changes in the opposite direction. Moreover, a new generated vortex has the same rotation direction as the two merging vortices and its size and intensity are about the sum of the two merging vortices at the initial merging.
More>
CFD has been playing a more and more important role in aeronautics and astronautics as a critical tool of modern aircraft design and aerodynamics research. On the contrary, the improvement of key theories such as physical modelling and numerical scheme is developing slowly. Therefore, the paper focus on applications of CFD in aeronautics and astronautics from the perspectives of turbulence models, transition models, flux schemes and high order schemes, for which state-of-art achievements and challenges are discussed. For turbulence models, the development status and characteristics of the common linear viscosity models are reviewed with emphasis on their drawbacks. More complicated Reynolds stress models are also analyzed. For transition models, the low Reynolds number models, intermittency transition models and laminar kinetic energy models, focusing on the development, construction method and applicable scope of different models. For flux schemes, the upwind flux is mainly considered, reviewing the status of these methods for solving the problems of shock anomaly, overheating, all-speed simulation and multi-dimensional flow. For high order schemes, the WENO and DG methods are focused on, with review and comments on accuracy, temporal integration, shock capturing and costs. Finally, a brief conclusion and suggestions on future development are presented.
More>Founding time：1980Periodical Monthly
Editor-in-Chief：Tang Zhi Gong
Competent Authorities:：China Aerodynamics Research and Development Center
Sponsored by：Computational Aerodynamics Institute of CARDC
ISSN 0258-1825CN 51-1192/TK
Acta Aerodynamica Sinica Indexed by COAJ
2024-12-05The First Meeting of the 7th Editorial Board of Acta Aerodynamic Sinica was held in Chengdu
2023-02-07Notice on Changing Acta Aerodynamica Sinica to a Monthly Publication
2022-10-28Warm congratulations to our editor in chief Tang Zhigong on his election as an academician of the Chinese Academy of Sciences
2021-11-18Supported by: Beijing Renhe Information Technology Co., Ltd.
