PurposeThe purpose of this paper is to investigate the effect of spanwise shape of the leading edge on unsteady aerodynamic characteristics of wings during forward flapping and gliding flight.Design/methodology/approachA computational fluid dynamics approach was conducted to analyze the flow around airfoils with sinusoidal‐like protuberances at a Reynolds number of 104. Three‐dimensional time‐dependent incompressible Navier‐Stokes equations are numerically solved by using finite volume method. A multigrid mesh method, which was applied to the situation of fluid across the heaving models is used to simulate this type of flow. The simulations are performed for the wavelength between neighbouring peaks of 0.25c and 0.5c. For each wavelength, two heights of the tubercles which are 5 per cent and 10 per cent of the chordwise length of wing, are employed on the leading edge of wings. The aerodynamic forces and flow structure around airfoils are presented and compared in detail. Special attention is paid to investigate the effect of leading‐edge shape on the fluid dynamic forces.FindingsPresent results reveal that the wings with leading‐edge tubercles have an aerodynamic advantage during gliding flight and also have the potential advantages during flapping forward flight.Originality/valueOn the basis of computational study, an improved scenario for flapping wing microaviation vehicle has been originally proposed.

A three-dimensional numerical simulation of a supersonic free-stream at Mach 2.5 over a spherical body with a sonic opposing jet from its stagnation point is carried out by solving the three-dimensional Navier-Stokes equations coupled with the standard k-" turbulence model. It is aimed to investigate the effects of the jet on the drag reduction on the body and the flow field around the body. The influences of the jet pressure, the nozzle size of the jet, and the angle of attack are systematically studied for the purpose. An unsteady oscillatory motion mode and a nearly steady motion mode are identified depending upon the jet total pressure. There exists a critical jet pressure where the flow mode transition from one to the other happens suddenly and this critical pressure value varies approximately linearly with the jet nozzle exit size inversely. For the zero angle of attack, the results show that there exists a maximum overall drag reduction as the jet pressure changes for each jet nozzle size and the maximum overall drag reduction always happens at the unsteady oscillatory motion mode. The main shock in front of the body is pushed backward by the jet and the displacement of the shock decreases with the increase of the angle of attack, and the drag reduction efficiency also decreases with the angle. Regarding to the mode transition, it is found that the drag rises suddenly when the transition happens for the angle of attack smaller than or equal to 5 but it does not result in the rise for the angle larger than 5 . The results show that the maximum overall drag reduction can be reached as high as 32.6% for the cases studied. The present results provide useful information for drag reduction applications using an opposing jet.

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To evaluate the thermal performance of a closed-loop Passive Containment Cooling System (PCCS) based on hot pipe technology under nuclear accidents, the coupled effect of three systems of reactor primary cooling circuit, containment and the PCCS is analyzed under LB-LOCA with SBO and SB-LOCA with SBO with the PCCS started one hour after the accident. The coupled analysis method is that the heat transfer power of PCCS simulated by the LOCUST model and the mass and energy releasing results obtained from the integrated analysis program for serious accidents are the inputs for containment thermal response analysis code. The results showed that in the 0∼10 hours after the accident, the containment pressure is less than the design limit of 5.20bar.a; in the middle and long term of ten more hours after the accident, the containment pressure is less than 3.50bar.a, the integrity of the containment can be ensured and the feasibility of the design of the PCCS in this paper is validated.