Qing Zhang

To investigate the flow mechanism of feather-like rough airfoils based on swift wings, computational simulations were employed to explore their overall aerodynamic characteristics in comparison to equivalent smooth airfoils. The study focused on angles of attack ranging from 0° to 20° at low Reynolds numbers. The results reveal that the rough airfoil exhibits higher lift and lower drag compared to the smooth airfoil at moderate angles of attack ranging from 6° to 10°, resulting in significantly improved aerodynamic efficiency. Notably, at an angle of attack of 8°, the aerodynamic efficiency is increased by 19%. However, at angles of attack smaller than 6°, the increase in drag outweighs the increase in lift, leading to lower aerodynamic efficiency for the rough airfoil. Conversely, when the angle of attack exceeds 16°, both airfoils experience separated flow-dominated flow fields, resulting in comparable effective aerodynamic shapes and similar aerodynamic efficiencies. Furthermore, the study found that increasing the Reynolds number results in greater pressure differences in the flow field, leading to higher aerodynamic efficiency. These preliminary conclusions are valuable for elucidating the flight mechanisms of bird-feather-like wings and can inform the design or morphing design of bio-inspired micro aerial vehicles in the near future.

Skin corrugation and tandem configuration are two distinct features that characterize the flow around dragonfly wings. In contrast to the smooth airfoil and single pair of wings of conventional airplanes, corrugated surfaces and tandem wings influence aerodynamics both locally and globally. In this article, several kinds of doubly- tandem wing configurations were designed, then computational investigations based on wind tunnel experiments were conducted to investigate the aerodynamic characteristics of these models. Computational simulations using in-house codes were carried out with a freestream velocity of 20 m/s at an angle of attack from −4° to 16°. Based on these computational results, the effects of airfoil thickness, surface waviness and hindwing decalage on aerodynamic characteristics were compared and presented quantitatively. Final results demonstrate that a tandem wing configuration could eliminate separation close to the trailing edge at angles of attack 8°~10°, or delay the trailing edge separation at angles of attack greater than 10°. Thus, the aerodynamic efficiency of tandem configurations could provide significant improvement compared to configurations with a single wing. The greatest percentage of aerodynamic efficiency improvement for a tandem thick configuration compared to a single thick configuration is 1376% at angle of attack 0°. Surface waviness will stall at a lower angle of attack, but will gain some aerodynamic benefit from the standing separated flow. Hindwing decalage has obvious lift enhancement for the tandem configuration. Therefore, it is concluded that the tandem configuration is attractive and promising for MAVs with flexible structures in the near future.

The flow structures and surface pressure distributions on corrugated airfoils significantly differed from those on a conventional, smooth airfoil. An unsteady, two-dimensional computational simulation was carried out to investigate the flow behavior and associated aerodynamic performance of a group of corrugated airfoils with different levels of waviness at angles of attack from 0° to 20° with an interval of 2° at a low Reynolds number regime (Re = 1.2 × 10⁵) and were quantitatively compared with those of its smooth counterpart. Time-averaged aerodynamic coefficients demonstrated that the corrugated airfoils have a lower lift and higher drag because of trapped vortices in the corrugations. The pressure drag of the corrugated airfoils was greater than that of the smooth airfoil. In contrast, the viscous drag of the corrugated airfoils was smaller than that of the smooth airfoil because the recirculation generated in the corrugation could reduce the viscous drag. The averaged velocity gradient in the boundary layer showed that the thickness of the boundary layer increased significantly for the corrugated airfoils because of recirculating flow caused by the small-standing vortices trapped in the valley of corrugations. The smoother the corrugated surface, the closer the aerodynamic characteristics are to those of the smooth airfoil.

Effects of the aeroelasticity on the performance of the hypersonic inlet have been investigated numerically in this study. The aeroelasticity has been simulated using the coupled computational fluid dynamics/computational structural dynamics method, which is solved by the in-house code. The unsteady Reynolds-averaged Navier–Stokes equations have been solved in the computational fluid dynamics simulation, and the modal method has been adopted in the computational structural dynamics simulation. Two cases have been utilized to validate the numerical method. Finally, the aeroelasticity has been simulated for inlet plate with different thicknesses. The effects of aeroelasticity on performance parameters and flow structure have been discussed in detail. The results show that the generalized displacements present the “beat” phenomenon in the time domain. The power spectral density of the generalized displacements implies that the aeroelastic instability is mainly caused by the coupling between the fourth- and fifth-order modes. The time-average flow rate coefficient and pressure rise ratio increase relative to the initial value, while the total pressure recovery coefficient decreases. The fluctuation amplitude of the flow rate coefficient is small, while that of the total pressure recovery coefficient and pressure rise ratio are relatively large. Besides, the phases of the three performance parameters are greatly different. Furthermore, the aeroelasticity has significant effect on the shock wave structure especially at the exit of the inlet.

Optimization of aerodynamic shapes using numerical methods has always been of engineering interest. This paper presents a highly efficient aerodynamic optimization method for hypersonic wings based on local piston theory. The objective of the optimization is to improve the aerodynamic characteristics of original airfoils or wings generated from NACA0012 while satisfying constraints on structure requirements. In the optimization procedure, a genetic algorithm is employed for optimum search, the Hicks–Henne bump function is used for airfoil geometrical modification, and local piston theory is used for unsteady pressure perturbations caused by geometrical modification from the baseline. Because unsteady pressure perturbations at supersonic or hypersonic conditions could be calculated by local piston theory based on initial flowfield results in the optimum searching process, only one steady-state solution without any use of moving or deforming grids is required. Therefore, the optimization method described in this paper is an extremely efficient technique that combines the advantages of steady computational fluid dynamics and the local piston theory and thus has very low computational cost in an optimum search process. Optimization results of airfoils and wings, including single and multipoint optimization for a flat wing without any sweep, and backswept wing, demonstrate the effectiveness and efficiency of the aerodynamic optimization method for hypersonic wings.

In this paper, the effect of the aerodynamic heating on shaft and the connection between the shaft and the body on areothermoelasticity for hypersonic all moving control surface is studied. A loosely coupled framework on aerothermoelastic stability boundary calculation for hypersonic vehicles is developed. Firstly, based on the computational fluid dynamics (CFD) technology, Navier-Stokes equation is solved to get the thermal environment. Then transient heat transfer of structure is analyzed. After that structural mode is analyzed under the effect of structure's thermal stress caused by temperature gradient and material property decrease caused by high temperature. Then structural mode is interpolated to the aerodynamic grids. Finally, Euler equation is solved to get flow parameters, and based on CFD local piston theory, aerothermoelasticity is analyzed in state space. The results show that: the heat transfer process and temperature distribution of the shaft structure are influenced obviously by the effect of the aerodynamic heating on shaft and the connection between the shaft and the body, and natural frequency and flutter characteristics are affected significantly, too. For the model in this paper, the effect of the aerodynamic heating on shaft and the connection between the shaft and the body on aeroelastic stability boundary is 8.31% and 6.87%, respectively.

Aerodynamic optimization by numerical methods has always been of engineering interest with the great advancement of computers. This paper presents a highly efficient aerodynamic optimization method for hypersonic airfoil based on local piston theory. In the optimization procedure, local piston theory has been employed for unsteady pressure perturbations caused by geometrical modification from the baseline. Because unsteady pressure perturbations at hypersonic conditions could be calculated by local piston theory based on initial flow field results in the optimum searching process, only one steady-state solution is required. Therefore, the optimization method described in this paper is an extremely efficient technique which combines the advantages of steady CFD and the local piston theory and thus with zero-computational cost in optimum search process. In order to investigate the applicability of local piston theory on aerodynamic prediction for blunt leading edge shape, single-objective and multi-objective optimizations for NACA0008 at various Mach numbers have been conducted with the objective to improve the lift-to-drag ratio and moment coefficient, and the optimization results have been validated by CFD and it is concluded that the optimization method based on local piston theory could be used in a wide Mach range while keeping a satisfactory efficiency and accuracy, therefore it can be employed for hypersonic airfoil optimization in the process of initial design in the engineering application.

Activated cement with the characters of low water demand and high activity was made with Portland cement clinker and dehydrate-gypsum and liquid superplasticizer which were used as grinding additive in the grinding process. Three states of grinding effect exist with correspondence of different dosages of super-plasticizer: the optimal grinding aid dosage, the critical dosage, and the supercritical dosage. First, under the condition of the optimal grinding effect, the activated cement had the maximum strength with little dosage of super-plasticizer and small effect on the performance of activated cement; second, within the critical dosage, the strength of activated cement was similar to the common cement, more super-plasticizer were held and the performance of cement was obviously improved; third, within the supercritical dosage, the strength of activated cement was reduced, but it can accommodate much super-plasticizer, and had a remarkable influence on the performance of cement. The experiment also shows that different properties of low water demand activated cement can be made with admixture of different concentrations of super-plasticizer. Within the allowed limit, use more admixtures was in compile with green environmental protection concept, improve the durability of concrete, and resolve the problem of compatibility between common cement and super-plasticizer, and offered technical support in the produce of commercial concrete by directly use of Portland cement clinker.