Nano-second pulse surface dielectric barrier discharge (NS-SDBD) has been a topic of great interest in the field of flow control for high speed and high Reynolds number. The recent development tendency of NS-SDBD plasma flow control is reviewed in this paper. The relevant literature of pneumatic excitation mechanism, phenomenon reveal and flow control mechanism is summarized based on experimental investigations and numerical simulations. The key scientific issues of NS-SDBD research are the mechanism of the electric field excitation-aerodynamic induction and the application of flow control. Multiple time scales and multi-physics coupling are the major difficulties of the study. The numerical algorithm and experimental method are generally used for solution of multi-time scale and multi-physics coupling issues. The breakthrough of the key scientific issues contributes to the optimization criteria for the design of the actuator and its control system.

The development of lattice gas model to discrete Boltzmann method is briefly introduced for modeling multiphase complex fluid systems. Based on the basic principles of statistical physics, the Boltzmann equation is given through the idea of coarse-grained modeling. The physical images of progressively refined measurements contained in the Chapman-Enskog multi-scale expansion method are analyzed, and the basic principles and main steps of Discrete Boltzmann Modeling (DBM) are given. The applications of discrete Boltzmann in phase separation, combustion and hydrodynamic instability systems are briefly reviewed. For the kinetic modeling of multiphase complex fluid systems, the key techniques are the introduction of intermolecular forces and the contribution of chemical reactions. The introduction of tracer particles of different colors makes it possible to determine the source of material particles in the mixing process under the framework of single-fluid theory. The structure formed by the distribution of tracer particles in their velocity space contains rich flow field information, which opens a new perspective for the study of complex flow field. In the case of multi-media, the correspondence between discrete Boltzmann modeling and Kinetic Macro Modeling (KMM) is one-to-several, where KMM means that to derive the macroscopic model equations from kinetic theory. As the degree of non-equilibrium of the system deepens, the complexity of discrete Boltzmann modeling and simulation increases more slowly than that of KMM and simulation. As a coarse-grained physical modeling method, discrete Boltzmann selects a perspective to study a set of kinetic properties of the system according to research requirements, so it is required that the kinetic moments describing this set of properties maintain their values in the process of model simplification. It provides a convenient and effective way to investigate the mesoscale situations where continuum modeling fails or physical functions are insufficient and molecular dynamics method is unable to do so due to the limited applicable scale.

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 Re_θ=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.

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.

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.