The tip vortices and aerodynamics of a NACA0012 wing in the vicinity of the ground were studied in a wind tunnel.The wing tip vortex structures and lift/drag forces were measured by a seven-hole probe and a force bala...The tip vortices and aerodynamics of a NACA0012 wing in the vicinity of the ground were studied in a wind tunnel.The wing tip vortex structures and lift/drag forces were measured by a seven-hole probe and a force balance,respectively.The evolution of the flow structures and aerodynamics with a ground height were analyzed.The vorticity of tip vortices was found to reduce with the decreasing of the ground height,and the position of vortex-core moved gradually to the outboard of the wing tip.Therefore,the down-wash flow induced by the tip vortices was weakened. However,vortex breakdown occurred as the wing lowered to the ground.From the experimental results of aerodynamics,the maximum lift-to-drag ratio was observed when the angle of attack was 2.5°and the ground clearance was 0.2.展开更多
The aim of this study is to identify the influence of the dip angle of a pre-existing macrocrack on the lifetime and ultimate deformation of rock-like material. Prediction of lifetime has been studied for three groups...The aim of this study is to identify the influence of the dip angle of a pre-existing macrocrack on the lifetime and ultimate deformation of rock-like material. Prediction of lifetime has been studied for three groups of specimens under axial static compressive load levels. The specimens were investigated from 65% to 85% of UCS(uniaxial compressive strength) at an interval of 10% of UCS for the groups of specimens with a single modelled open flaw with a dip angle to the loading direction of 30°(first group), at an interval of 5% of UCS increment for the groups of specimens with single(second group), and double sequential open flaws with a dip angle to the loading direction of 60°(third group). This study shows that crack propagation in specimens with a single flaw follows the same sequences. At first, wing cracks appear, and then shear crack develops from the existing wing cracks. Shear cracking is responsible for specimen failure in all three groups. A slip is expected in specimens from the third group which connects two individual modelled open flaws. The moment of the slip is noticed as a characteristic rise in the axial deformation at a constant load level. It is also observed that axial deformation versus time follows the same pattern, irrespective of local geometry. Specimens from the first group exhibit higher axial deformation under different load levels in comparison with the specimens from the second and third groups.展开更多
基金supported by the National Natural Science Foundation of China(11072142)Shanghai Program for Innovative Research Team in Universities
文摘The tip vortices and aerodynamics of a NACA0012 wing in the vicinity of the ground were studied in a wind tunnel.The wing tip vortex structures and lift/drag forces were measured by a seven-hole probe and a force balance,respectively.The evolution of the flow structures and aerodynamics with a ground height were analyzed.The vorticity of tip vortices was found to reduce with the decreasing of the ground height,and the position of vortex-core moved gradually to the outboard of the wing tip.Therefore,the down-wash flow induced by the tip vortices was weakened. However,vortex breakdown occurred as the wing lowered to the ground.From the experimental results of aerodynamics,the maximum lift-to-drag ratio was observed when the angle of attack was 2.5°and the ground clearance was 0.2.
文摘The aim of this study is to identify the influence of the dip angle of a pre-existing macrocrack on the lifetime and ultimate deformation of rock-like material. Prediction of lifetime has been studied for three groups of specimens under axial static compressive load levels. The specimens were investigated from 65% to 85% of UCS(uniaxial compressive strength) at an interval of 10% of UCS for the groups of specimens with a single modelled open flaw with a dip angle to the loading direction of 30°(first group), at an interval of 5% of UCS increment for the groups of specimens with single(second group), and double sequential open flaws with a dip angle to the loading direction of 60°(third group). This study shows that crack propagation in specimens with a single flaw follows the same sequences. At first, wing cracks appear, and then shear crack develops from the existing wing cracks. Shear cracking is responsible for specimen failure in all three groups. A slip is expected in specimens from the third group which connects two individual modelled open flaws. The moment of the slip is noticed as a characteristic rise in the axial deformation at a constant load level. It is also observed that axial deformation versus time follows the same pattern, irrespective of local geometry. Specimens from the first group exhibit higher axial deformation under different load levels in comparison with the specimens from the second and third groups.
