Zhang Hanxin

Investigation on Weighted Compact Fifth-order Nonlinear Scheme and Applications to Complex Flow

The Fourier analysis and applications of Weighted Compact Fifth-order Nonlinear Scheme, which is called as WCNS-E-5, are presented in this paper. Using weighted technique, the nonlinear adaptive solver automatically chooses the locally smoothest stencil, hence avoiding crossing discontinuities in the interpolations at cell-edges as much as possible. As one of the high-order WCNS developed before, WCNS-E-5 is of fifth-order accuracy in smooth region and third-order accuracy in the vicinity of discontinuities. By Fourier analysis the features of WCNS-E-5 are discussed in terms of dissipative and dispersive errors, the resolving efficiency and the multi-dimensional phase speed anisotropy in smooth regions. The analytical results show that WCNS-E-5 has better characteristics than EUW-5 in terms of dispersive and dissipative errors, and it also has the higher resolving efficiency than EUW-5 and e

Physical analysis and numerical simulation for the dynamic behaviour of vehicles in pitching oscillations or rocking motions

Analytical methods of nonlinear dynamics and numerical simulations for the coupling equations of Navier-Stokes and flight mechanics are used to study the dynamic behaviour of pitching motions of reentry capsules with the variation of Mach number, and rocking motions of swept wings with the variation of angle of attack. Conditions under which the dynamic instability, Hopf bifurcation and saddle-node bifurcation occur are obtained. The node-saddle-node topological structure in the phase portrait, i.e. the state of bi-attractors (attracting basins) is described. The evolving process of dynamic behaviour and flow fields are given. The theories are compared with some numerical simulations conducted by the authors. Besides, some verifiable experimental results are cited. The agreement between them is very well.

NND schemes and numerical simulation of axial symmetric free jet flows

Through a study on one-dimensional Navier-Stokes equations, it was found that the spurious oscillations occuring near shock waves with finite difference equations are related to the dispersion term in the corresponding modified differential equations. If the sign of dispersion coefficient is properly adjusted so that the sign changes across shock waves, the undesirable oscillations can be totally suppressed. Based on this finding, the non-oscillatory, containing no free parameters and dissipative shheme (NND scheme) is developed. This scheme is one of “TVD”. The axisymmetric free jet flows are simulated numerically using this scheme. The results obtained by the present scheme are compared with the experimental picture. It is shown that the agreement is very good, and that this scheme has advantages of high resolution for capturing shocks and contact discontinuities.

Advances in the study of separated flows

This paper consists of three parts. The first deals with the separation conditions for three dimensional steady viscous separated flows, in which the behaviour of separated flow described by Navier-Stokes equations and boundary layer equations is studied. The second part involves an application of differential topology to qualitative analysis of flow fields. Here the distribution rule of singular points on the separation line is studied. The last part discusses the numerical method solving Navier-Stokes equations for separated flows. The obtained computational results are analysed by the above mentioned theories and methods.

New problems of aerodynamics

Aerodynamics is a branch of mechanics, and is also one of the foundations of aero-space technology. Starting from 1930’s, it gradually separate itself from the traditional fluid mechanics. With the development of aero-space technology, the development of aerodynamics is very fast. In many countries, especially in big countries, the manpower and material resources devoted to aerodynamics is the biggest among all branches of fluid mechanics and even among the whole field of mechanics. In fact, aerodynamics has already had its own comprehensive system of knowledge. But recently, the R&D of the technology for near space flying vehicles, which would fly at the height of 40–70 km with the speed of 5–20 times of sound speed, has draw more and more attention. The flight height, combined with the flight speed, is new to us. So people would ask, if there is relevant new and important area of aerodynamics needs to be explored, and what would be its key scientific problem. In this paper, we would try to answer this question.

A Finite Element/Finite Volume Mixed Solver and Applications on Heat Flux Prediction

A finite element/finite volume mixed solver is presented. A discontinuous Galerkin (DG) finite element (FE) solver is used near the boundary layers to capture the viscous effects, whereas a finite volume (FV) solver is adopted in the outer field to save CPU time and store memory. The mixed solver is validated with several hypersonic cases. The computational results show good agreements with experimental data, and the comparison on CPU time and memory demonstrates the higher efficiency than that of the pure FE solver.