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Zhang Y.,Northwestern Polytechnical University | Xu J.,Beihang University | Bai J.,Northwestern Polytechnical University | Hua J.,Chinese Aeronautics Establishment
Lixue Xuebao/Chinese Journal of Theoretical and Applied Mechanics | Year: 2014

Transition is a chief obstacle for high-accuracy prediction of drag. The γ-θ transition model proposed by Menter and Langtry increases the adaptability by inducing vorticity Reynolds number and intermittency factor, but there are lots of empirical formulae that cannot be told the lodgments of theory. The dissipation term of kinetic energy can be sufficiently constructed with the first and second order correlations of velocity. Transition phenomena can be caught by adding some dissipation terms into the turbulent kinetic energy equation. The method is tested by a natural transition and two bypass transition test cases. The results approve that this method can be applied in engineering turbulence flows simulation.

Liu Y.,Northwest University, China | Bai J.-Q.,Northwest University, China | Hua J.,Chinese Aeronautics Establishment | Huang J.-T.,Northwest University, China | Huang J.-T.,China Aerodynamics Research And Development Center
Jisuan Lixue Xuebao/Chinese Journal of Computational Mechanics | Year: 2014

An approach to CFD/CSD non-linear coupling based on radial basis functions (RBF) interpolation technology is established, which is based on the Navier-Stokes (N-S) equations of unstructured hybrid grid and the method of structure flexibility coefficient matrix, and is used to analyze the non-linear aeroelasticity of flexible aircraft with high aspect ratio. Steady flow is simulated by the method of time correlation, which calculates unsteady equations for long time to get the solutions of steady N-S equations. The structure equations are solved at every time step. Because CSD analysis spends much less time than CFD solver, so the non-linear computation aeroelasticity method just takes the time of the calculation of unsteady equations to complete the whole process of aeroelasticity. Considering that the flexible aircraft with high aspect ratio is geometric non-linear, an approximate nonlinear method is used in CSD analysis. The RBF interpolation technology is easy to realize, accurate to exchange data and saving time, so it is applied to exchange flexible deformation aerodynamic loads with the principle of virtual power. The mesh motion method based on RBF interpolation method is established instead of re-meshing, which can be used in moving the hybrid mesh of tetrahedron and triangular prism mesh etc, that can make the computation of boundary accurate. The aeroelasticity of M6 wing, DLR-F6 wing body and a wing of aero-transport are simulated. And results show that the approach to nonlinear computational aeroelasticity based on RBF interpolation method is feasible, accurate and efficient.

Bai J.,Northwestern Polytechnical University | Zhang Y.,Northwestern Polytechnical University | Xu J.,Beihang University | Hua J.,Chinese Aeronautics Establishment
Hangkong Xuebao/Acta Aeronautica et Astronautica Sinica | Year: 2014

In order to enhance the predictive precision of the influence of Reynolds stress constitutive relation on non-equilibrium turbulent flow and preserve computational efficiency as well, a turbulent kinetic energy k based one-equation (KDO) turbulence model is proposed in this paper. The basic idea of the turbulence model is to recalibrate the original Bradshaw assumption results using the flat plate direct numerical simulation (DNS) data, which makes the local turbulence kinetic energy adaptively adjustable according to the local flow conditions. Meanwhile, the turbulence dissipation rate equation in the standard k-ε model is modeled by using the algebraic type and then a one-equation turbulence model has been completely constructed. The results of test cases showed that the KDO turbulence model could acceptably reflect the log-law. In the cases RAE-2822, ONERA-M6 and DLR-F6 with shock waves or component interferences, the KDO turbulence model is able to control the augmentations and decay of turbulence kinetic energy. Furthermore, comparing with the Spalart-Allmaras and Menter k-ω shear stress transport (SST) models, the KDO turbulence model evidently improved the calculation results.

Bai J.,Northwestern Polytechnical University | Zhang Y.,Northwestern Polytechnical University | Hua J.,Chinese Aeronautics Establishment
Hangkong Xuebao/Acta Aeronautica et Astronautica Sinica | Year: 2013

To improve the calculation precision of the original shear stress transport (SST) two-equation turbulence model, the filter factor of the large eddy simulation (LES) and SST formula are combined. The computation zone is splitted by the filter factor, through which a stable flow near the wall is controlled by the turbulence model while the flow far from the wall is simulated by LES. The advantage of this method in comparison with the classic hybrid RANS/LES methods is that the filter can be chosen without depending on grid scale, resulting in a decrease of the probability of grid induced separation. The deep stall of NACA0021 airfoil is simulated by using the filter SST, unsteady Reynolds-averaged Navier-Stokes (URANS) and SST-DES. The simulation result demonstrates that the impulse in the separated region can be effectively activated by the filter SST method. The phenomenon shows the three dimension characteristics of separation. Meanwhile, the result of the test case is more precise than that obtained by the URANS method and it matches well with the result obtained by experiment.

Liu Y.,Northwest University, China | Bai J.-Q.,Northwest University, China | Hua J.,Chinese Aeronautics Establishment
Applied Mechanics and Materials | Year: 2013

The influence of structural elastic deformation on the aerodynamic characterisitcs of large transport aircraft has been researched. A method of static aeroelasticity based on multi-block structural grid of high aspect ratio wing has been established, and then a design method of jig-shape is developed. The technology of RBF interpolation is used to exchange the data of CFD/CSD. Based on RBF&Delaunay technology, a mesh motion method is developed to make the design process less time-consuming, which can be applied to large deformation of multi-block structural grid. The static aeroelastic deformation of a wing-body of large transport aircraft is analyzed. Then the wing-body's jig-shape is designed. Compared the aerodynamic characteristics between design cruise shape and target cruise shape, it shows that the aerodynamic characteristics of design cruise shape is almost equal to target cruise shape and the design process of jig-shape is feasible. © (2013) Trans Tech Publications, Switzerland.

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