The use of ultrasonic sensors has varied applications, but the sensor operation frequency limits the operating distance. An easy way to increase this distance is to couple a mechanical element （horn）, but it is nece...The use of ultrasonic sensors has varied applications, but the sensor operation frequency limits the operating distance. An easy way to increase this distance is to couple a mechanical element （horn）, but it is necessary to characterize this technique. In this paper the results obtained in a study of the behaviour of mechanical elements coupled to an ultrasonic sensor using finite element techniques are presented. These results have been obtained using Comsol Multiphysics modelling. Also, the effect caused by the sensor size on the radiation acoustic pressure has also been evaluated. In other way, in this paper it is presented the results obtained in the laboratory measurements. First, it is studied the influence of a straight horn attached to the ultrasonic sensor. Later, it is presented the variation in the sound pressure on the radiation axis when the sensor varies its size. In the final part of the paper, the experimental validation of the simulations is presented.展开更多
The pintle injector used for a liquid rocket engine is a newly re-attracted injection system famous for its wide throttle ability with high efficiency. The pintle injector has many variations with complex inner struct...The pintle injector used for a liquid rocket engine is a newly re-attracted injection system famous for its wide throttle ability with high efficiency. The pintle injector has many variations with complex inner structures due to its moving parts. In order to study the rotating flow near the injector tip, which was observed from the cold flow experiment using water and air, a numerical simulation was adopted and a verification of the numerical model was later conducted. For the verification process, three types of experimental data including velocity distributions of gas flows, spray angles and liquid distribution were all compared using simulated results. The numerical simulation was performed using a commercial simulation program with the Eulerian multiphase model and axisymmetric two dimensional grids. The maximum and minimum velocities of gas were within the acceptable range of agreement, however, the spray angles experienced up to 25% error when the momentum ratios were increased. The spray density distributions were quantitatively measured and had good agreement. As a result of this study, it was concluded that the simulation method was properly constructed to study specific flow characteristics of the pintle injector despite having the limitations of two dimensional and coarse grids.展开更多
Today, the most commonly used bi-directional airfoil in hydraulic machinery is the S-shaped airfoil(SA). A new bi-directional airfoil, obtained by lowering the bent airfoil camber and thickening the bone line bi-direc...Today, the most commonly used bi-directional airfoil in hydraulic machinery is the S-shaped airfoil(SA). A new bi-directional airfoil, obtained by lowering the bent airfoil camber and thickening the bone line bi-directionally, is proposed. Two bi-directional axial flow pumps, with the SA blades and the arc airfoil(AA) blades, respectively, were designed to verify the applicability of this airfoil. By comparing the hydraulic performances of the two pumps obtained from the experiments, and the cavitation performance and flow field of the two pumps obtained from numerical simulations, it was found that AA blades can improve both the hydraulic and cavitation performances under a low flow rate and near the best efficiency flow point(BEP), whether in forward or reverse operation for the bi-directional axial-flow pump. Furthermore, the hydraulic performance of the AA blade pump declines sharply in a large flow rate compared to that of the SA blade pump. The location and composition of the inhomogeneous flows inside the impellers of the two pumps are similar. However, the SA blades work on fluid, mainly at the front half of the blades, which is a distinctive feature from the AA blades and may be a universal phenomenon in all SA-type blades.展开更多
This paper describes the development of a miniature pump having an impeller with an exit diameter of 24 mm supported with the motor rotor by a fluid dynamic beating. Tests verify that the miniature pump is stable and ...This paper describes the development of a miniature pump having an impeller with an exit diameter of 24 mm supported with the motor rotor by a fluid dynamic beating. Tests verify that the miniature pump is stable and quiet for rotational speeds larger than 4000 rain-1. The three-dimensional turbulent flow in the entire pump flow passage and the laminar flow in the fluid dynamic bearing were then simulated numerically. The average pump performance was well predicted by the simulations. Both the tests and the simulations show that there is no obvious Reynolds effect for the miniature pump within the tested range of rotational speeds. The numerical results also show that the beating capacity of the fluid dynamic bearing increases with the pump rotor rotational speed and the eccentricity ratio of the journal to the bushing. This pump is very compact, so it is a prom- ising device for surgical use.展开更多
文摘The use of ultrasonic sensors has varied applications, but the sensor operation frequency limits the operating distance. An easy way to increase this distance is to couple a mechanical element （horn）, but it is necessary to characterize this technique. In this paper the results obtained in a study of the behaviour of mechanical elements coupled to an ultrasonic sensor using finite element techniques are presented. These results have been obtained using Comsol Multiphysics modelling. Also, the effect caused by the sensor size on the radiation acoustic pressure has also been evaluated. In other way, in this paper it is presented the results obtained in the laboratory measurements. First, it is studied the influence of a straight horn attached to the ultrasonic sensor. Later, it is presented the variation in the sound pressure on the radiation axis when the sensor varies its size. In the final part of the paper, the experimental validation of the simulations is presented.
基金supported by Advanced Research Center Program(NRF-2013R1A5A1073861)through the National Research Foundation of Korea(NRF)grant funded by the Korea government(MSIP)contracted through Advanced Space Propulsion Research Center at Seoul National University
文摘The pintle injector used for a liquid rocket engine is a newly re-attracted injection system famous for its wide throttle ability with high efficiency. The pintle injector has many variations with complex inner structures due to its moving parts. In order to study the rotating flow near the injector tip, which was observed from the cold flow experiment using water and air, a numerical simulation was adopted and a verification of the numerical model was later conducted. For the verification process, three types of experimental data including velocity distributions of gas flows, spray angles and liquid distribution were all compared using simulated results. The numerical simulation was performed using a commercial simulation program with the Eulerian multiphase model and axisymmetric two dimensional grids. The maximum and minimum velocities of gas were within the acceptable range of agreement, however, the spray angles experienced up to 25% error when the momentum ratios were increased. The spray density distributions were quantitatively measured and had good agreement. As a result of this study, it was concluded that the simulation method was properly constructed to study specific flow characteristics of the pintle injector despite having the limitations of two dimensional and coarse grids.
基金supported by the Production,Education and Scientific Research Program of the Baoshan District,Shanghai City(Grant No.CXY2012-12)
文摘Today, the most commonly used bi-directional airfoil in hydraulic machinery is the S-shaped airfoil(SA). A new bi-directional airfoil, obtained by lowering the bent airfoil camber and thickening the bone line bi-directionally, is proposed. Two bi-directional axial flow pumps, with the SA blades and the arc airfoil(AA) blades, respectively, were designed to verify the applicability of this airfoil. By comparing the hydraulic performances of the two pumps obtained from the experiments, and the cavitation performance and flow field of the two pumps obtained from numerical simulations, it was found that AA blades can improve both the hydraulic and cavitation performances under a low flow rate and near the best efficiency flow point(BEP), whether in forward or reverse operation for the bi-directional axial-flow pump. Furthermore, the hydraulic performance of the AA blade pump declines sharply in a large flow rate compared to that of the SA blade pump. The location and composition of the inhomogeneous flows inside the impellers of the two pumps are similar. However, the SA blades work on fluid, mainly at the front half of the blades, which is a distinctive feature from the AA blades and may be a universal phenomenon in all SA-type blades.
基金supported by the National Natural Science Foundation of China (Grant No. 50976061)State Key Laboratory for Hydroscience and Hydraulic Engineering, Tsinghua University (Grant No. 2010-ZY-4)Tsinghua-Yuyuan Medical Fund and the Ministry of Science and Technol-ogy of China (Grant No. 2008KR0441)
文摘This paper describes the development of a miniature pump having an impeller with an exit diameter of 24 mm supported with the motor rotor by a fluid dynamic beating. Tests verify that the miniature pump is stable and quiet for rotational speeds larger than 4000 rain-1. The three-dimensional turbulent flow in the entire pump flow passage and the laminar flow in the fluid dynamic bearing were then simulated numerically. The average pump performance was well predicted by the simulations. Both the tests and the simulations show that there is no obvious Reynolds effect for the miniature pump within the tested range of rotational speeds. The numerical results also show that the beating capacity of the fluid dynamic bearing increases with the pump rotor rotational speed and the eccentricity ratio of the journal to the bushing. This pump is very compact, so it is a prom- ising device for surgical use.
