Gao Zheng-hong

Robust Design of Supercritical Wing Aerodynamic Optimization Considering Fuselage Interfering

Abstract Robust optimization approach for aerodynamic design has been developed and applied to supercritical wing aerodynamic design. The aerodynamic robust optimization design system consists of genetic optimization algorithm, improved back propagation (BP) neural network and deformation grid technology. In this article, the BP neural network has been improved in two major aspects to enhance the training speed and precision. Uniformity sampling is adopted to generate samples which will be used to establish surrogate model. The testing results show that the prediction precision of the improved BP neural network is reliable. On the assumption that the law of Mach number obeys normal distribution, supercritical wing configuration considering fuselage interfering of a certain aerobus has been taken as a typical example, and five design sections and twist angles have been optimized. The results show that the optimized wing, which considers robust design, has better aerodynamic characteristics. Whats more, the intensity of shock wave has been reduced.

A High-speed Nature Laminar Flow Airfoil and Its Experimental Study in Wind Tunnel with Nonintrusive Measurement Technique

Abstract This article deals with an experimental study on the aerodynamic characteristics of a low-drag high-speed nature laminar flow (NLF) airfoil for business airplanes in the TST27 wind tunnel at Delft University of Technology, the Netherlands. In this experiment, in an attempt to reduce the errors of measurement and improve its accuracy in high-speed flight, some nonintrusive measurement techniques, such as the quantitative infrared thermography (IRT), the digital particle imaging velocimetry (PIV), and the shadowgraphy, are applied to obtain precise data about transition locations, separation on trailing edges, and lift/drag characteristics. The experimental results reveal that, in the high-speed flight, small angles of attack are helpful in retaining long laminar flows, preventing the vortex at the trailing edge from moving forward and thus imparting the airfoil and the high-lift and low-drag characteristics. The comparison of the measured results to the calculated ones proves the acceptability of the airfoil and its aerodynamic characteristics satisfying the design requirements.

An Efficient Algorithm for Calculating Aircraft RCS Based on the Geometrical Characteristics

Abstract Taking into account the influences of scatterer geometrical shapes on induced currents, an algorithm, termed the sparse-matrix method (SMM), is proposed to calculate radar cross section (RCS) of aircraft configuration. Based on the geometrical characteristics and the method of moment (MOM), the SMM points out that the strong current coupling zone could be predefined according to the shape of scatterers. Two geometrical parameters, the surface curvature and the electrical space between the field position and source position, are deducted to distinguish the dominant current coupling. Then the strong current coupling is computed to construct an impedance matrix having sparse nature, which is solved to compute RCS. The efficiency and feasibility of the SMM are demonstrated by computing elec-tromagnetic scattering of some kinds of shapes such as a cone-sphere with a gap, a bi-arc column and a stealth aircraft configuration. The numerical results show that: (1) the accuracy of SMM is satisfied, as compared with MOM, and the computational time it spends is only about 8% of the MOM; (2) with the electrical space considered, making another allowance for the surface curvature can reduce the computation time by 9.5%.

UNCONDITIONAL STABLE SOLUTIONS OF THE EULER EQUATIONS FOR TWO-. AND THREE-D WINGS IN ARBITRARY MOTION

The work presented here shows the unsteady inviscid results obtained for the two-and three-dimensional wings which are in rigid and flexible oscillations.The results are generated by a finite volume Euler method. It is based on the Runge-Kutta time stepping scheme developed by Jameson et al.. To increase the time step which is limited by the stability of Runge-Kutta scheme, the implicit residual smoothing which is modified by using variable coefficients to prevent the loss of flow physics for the unsteady flows is engaged in the calculations. With this unconditional stable solver the unsteady flows about the wings in arbitrary motion can be received efficiently.The two- and three-dimensional rectangular wings which are in rigid and flexible pitching oscillations in the transonic flow are investigated here, some of the computational results are compared with the experimental data. The influence of the reduced frequency for the two kinds of the wings are researched. All the results given in this work are reasonable.

Research on the hysteresis properties of unsteady aerodynamics about the oscillating wings

In the work, it is shown the numerical investigations about the unsteady inviscid results obtained for the pitching oscillating wings at different angles of attack. The results are obtained by solving the unsteady Euler equations in a bodyfitted coordinate system. It is based on the four-stage runge-Kutta time stepping scheme. Meanwhile to increase the time step that is limited by Courant limit (CFL), the implicit residual smoothing with local variable parameters is used. As a result, the unsteady aerodynamics about a rectangular wing and a delta wing, which are oscillated in pitching with different frequencies, are shown in this paper. The properties of the unsteady aerodynamics in these cases are researched here.

Robust design of transonic laminar wingbody configuration based on direct manipulated FFD technique

The geometric shape is not directly manipulated by free-form deformation (FFD) technique. A high level FFD control volume is always adopted in the refined aerodynamic design. The direct manipulated free-form deformation (DFFD) technique is developed in this paper to improve the shortcomings of the FFD technique. This method adopt a parameter identification technique which can identify the disturbance quantities and convert them into displacement values on the FFD control lattices. The DFFD technique can accomplish refined aerodynamic shape design using less design variables. The visual impression is much better than the traditional FFD technology, and the number of the design variables is not increased with using of the high level FFD control volume. The robust design system is established by DFFD technique, multi-groups collaboration particle swarm optimization (MCPSO) and adaptive sampling algorithm, combined with quaternion mesh deforming technique and the numerical simulation of boundary layer transition based on γ - Re θt transition model. A transonic laminar wing body is optimized by this system. The design results show that not only a wide range of laminar flow area is maintained, but also the development of shock is controlled.

Refined aerodynamic design optimization of a wing with small aspect ratio

For aerodynamic design of figher wings with the feature of small aspect ratio, the plat shape, camber-twist and thickness modification are mainly concerned and refined design of the airfoil is neglected. Therefore, Euler equation combined with boundary layer is the main technique to calculate the aerodynamic characteristics. Taking a typical fighter wing as an example, Euler equation and RANS equation are respectively utilized to calculate the flow field of the figher wing. From the result, the flow details cannot be captured by Euler equation which reveals that Euler equation is not qualified for refined design of figher wing. Airfoil aerodynamic design optimization is carried out and it is inferred that the results of airfoil design does not hold in small aspect ratio wing. Therefore, for small aspect ratio wing, airfoil design optimization must be conducted in 3-D circumstance. A 3-D aerodynamic design optimization frame is built which consists of FFD parameterization method, robust mesh deformation technique, Kriging surrogate model and PSO optimization algorithm. Employing the optimization frame, a single objective design is carried out at transonic state and a multi objective design is conducted at transonic/supersonic states. Aerodynamic characteristics are greatly improved from the design results.

Computation of field structure and aerodynamic characteristics of delta wings at high angles of attack

A numerical investigation of the structure of the vortical flowfield over delta wings at high angles of attack in longitudinal and with small sideslip angle is presented. Three-dimensional Navier-Stokes numerical simulations were carried out to predict the complex leeward-side flowfield characteristics that are dominated by the effect of the breakdown of the leading-edge vortices. The methods that analyze the flowfield structure quantitatively were given by using flowfield data from the computational results. In the region before the vortex breakdown, the vortex axes are approximated as being straight line. As the angle of attack increases, the vortex axes are closer to the root chord, and farther away from the wing surface. Along the vortex axes, as the adverse pressure gradients occur, the axial velocity decreases, that is, λ is negative, so the vortex is unstable, and it is possible to breakdown. The occurrence of the breakdown results in the instability of lateral motion for a delta wing, and the lateral moment diverges after a small perturbation occurs at high angles of attack. However, after a critical angle of attack is reached, the vortices breakdown completely at the wing apex, and the instability resulting from the vortex breakdown disappears.

Unsteady transonic aerodynamic loadings on the airfoil caused by heaving, pitching oscillations and control surface

An implicit upwind finite volume solver for the Euler equations using the improved flux-splitting method is established and used to calculate the transonic flow past the airfoils with heaving, pitching oscillations and the control surface. Results are given for the NACA64A-10 airfoil which is in harmonic heaving and pitching oscillation and with the control surface in the transonic flow field. Some computational results are compared with the experiment data and the good agreements are shown in the paper.