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The airfoil on modern fighters needs large positive moment to maintain longitudinal trim in addition to good aerodynamic and stealth performance. The novel design requirements would increase the likelihood of multimodality in design space. To address this issue, this paper uses parallel niching method to identify the existence and possible sources of multimodality in the aerodynamic and stealth shape optimizations based on a symmetrical airfoil. To isolate the instances of space multimodality, several subproblems are studied by varying the number and range of design variables, as well as positive moment constraints, respectively. The results demonstrate that the occurrences of multimodality in aerodynamic design space are highly related to positive moment constraint and ranges of design variables. Additionally, it’s found that some local minimums in aerodynamic space are very close to that of stealth space, indicating that the there’s not that large conflict between aerodynamic and stealth design under certain circumstances. This discovery may appeal a new approach of aerodynamic/stealth design of aircraft.

The ever-increasing demands for risk-free, resource-efficient and environment-friendly air vehicles motivate the development of advanced design methodology. As a particularly promising design methodology considering uncertainties, robust aerodynamic design optimization (RADO) is capable of providing robust and reliable aerodynamic configuration and reducing cost under probable uncertainties in the flight envelop and all life cycle of air vehicle. However, the major challenges including high computational cost with increasing dimensionality of uncertainty and complex RADO procedure hinder the wider application of RADO. In this paper, the complete RADO procedure, i.e., uncertainty modeling, establishment of uncertainty quantification approach as well as robust optimization subject to reliability constraints under uncertainty, is elaborated. Systematic reviews of RADO methodology including uncertainty modeling methods, comprehensive uncertainty quantification approaches, and robust optimization methods are provided. Further, this paper presents a brief survey of the main applications of RADO in the aerodynamic design of transonic flow and natural-laminar-flow, and discusses the application prospects of RADO methodology for air vehicles. The detailed statement of the paper indicates the intention, i.e., to present the state of the art in RADO methodology, to highlight the key techniques and primary challenges in RADO, and to provide the beneficial directions for future researches.

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.

Different from the traditional helicopter, there would be a severe interaction between rotor and fuselage with canard and horizontal tail during hovering for canard rotor wing (CRW) aircraft. The un-steady RANS (URANS) equations discretized on overset grid are solved in this paper to simulate this kind of aerodynamic interaction. A UH60-A rotor hovering case is used to validate the numerical method. Subsequently, the numerical method is employed on two configurations, i.e., Isolated rotor configuration and Full CRW configuration under numerous collective pitch angle. The force and moment coefficients for different parts with respect to different collective pitch angles are obtained. The result shows that downwash of rotor has a stronger impact on fuselage than canard wing and horizontal tail. Compared with isolated rotor, fuselage with canard wing and horizontal tail has a slight impact on the trust and torque of the rotor in full CRW aircraft configuration.

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. What's more, the intensity of shock wave has been reduced.

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.

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.

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.