Water jet thruster, which is a marine system that creates a jet of water for propulsion, has several advantages such as low noise, good anti-cavitation characteristics and maneuvering characteristics. The reaction thr...Water jet thruster, which is a marine system that creates a jet of water for propulsion, has several advantages such as low noise, good anti-cavitation characteristics and maneuvering characteristics. The reaction thrust characteristics of water jet for conical nozzles directly determine the speed of autonomous underwater vehicles (AUV). Theoretical, numerical and experimental studies have been, carried out to investigate the effects of the nozzle geometries as well as inlet conditions on the reaction thrust of water jet in this paper. The experimental results show that: 1) the reaction thrust is proportional to inlet pressure, the square of flow rate and 2/3 power exponent of input power; 2) the diameter of cylinder column for conical nozzle has great influence on the reaction thrust characteristics; 3) the best values of the half cone angle and the cylinder column length exist to make the reaction thrust coefficient to reach the maximum under the same inlet conditions. Those provide a basis for nozzles design and have significant value, especially for developing high performance and efficiency water jet propulsion unit.展开更多
Clear knowledge on the reaction thrust of water jet is valuable for better design of water jet propulsion system. In this paper, theoretical, numerical and experimental studies were carried out to investigate the effe...Clear knowledge on the reaction thrust of water jet is valuable for better design of water jet propulsion system. In this paper, theoretical, numerical and experimental studies were carried out to investigate the effects of the nozzle geometry as-well as the inlet conditions on the reaction thrust of water jet. Comparison analyses reveal that the reaction thrust has a direct proportional relationship with the product of the inlet pressure, the square of flow rate and two-thirds power exponent of the input power. The results also indicate that the diameter of the cylinder column for the conical nozzle has great influence on the reaction thrust characteristics. In addition, the best values of the half cone angle and the cylinder column length exist to make the reaction thrust reach its maximum under the same inlet conditions.展开更多
The cow-nosed ray is studied as natural sample of a flapping-foil robotic fish.Body structure, motion discipline, and dynamicfoil deformation of cow-nosed ray are analyzed.Based on the analysis results, a robotic fish...The cow-nosed ray is studied as natural sample of a flapping-foil robotic fish.Body structure, motion discipline, and dynamicfoil deformation of cow-nosed ray are analyzed.Based on the analysis results, a robotic fish imitating cow-nosed ray,named Robo-ray Ⅱ, mainly composed of soft body, flexible ribs and pneumatic artificial muscles, is developed.Structure andswimming morphology of the robotic prototype are as that of a normal cow-nosed ray in nature.Key propulsion parameters ofRobo-ray Ⅱ at normal conditions, including the St Number at linear swimming, thrust coefficient at towing are studied throughexperiments.The suitable driving parameters are confirmed considering the efficiency and swimming velocity.Swimmingvelocity of 0.16 m·s’and thrust coefficient of 0.56 in maximum are achieved in experiments.展开更多
The use of biomimetic tandem flapping foils for ships and underwater vehicles is considered as a unique and interesting concept in the area of marine propulsion. The flapping wings can be used as a thrust producing, s...The use of biomimetic tandem flapping foils for ships and underwater vehicles is considered as a unique and interesting concept in the area of marine propulsion. The flapping wings can be used as a thrust producing, stabilizer and control devices which has both propulsion and maneuvering applications for marine vehicles. In the present study, the hydrodynamic per- formance of a pair of flexible flapping foils resembling penguin flippers is studied. A ship model of 3 m in length is fitted with a pair of counter flapping foils at its bottom mid-ship region. Model tests are carried out in a towing tank to estimate the propulsive performance of flapping foils in bollard and self propulsion modes. The same tests are performed in a numerical environment using a Computational Fluid Dynamics (CFD) software. The numerical and experimental results show reasonably good agreement in both bollard pull and self propulsion trials. The numerical studies are carried out on flexible flapping hydrofoil in unsteady conditions using moving unstructured grids. The efficiency and force coefficients of the flexible flapping foils are determined and presented as a function of Strouhal number.展开更多
Conical plug nozzle and truncated conical plug nozzle are advanced rocket nozzles suitable for use as altitude compensating nozzles.In this study flow through the conical plug and truncated conical plug nozzles are nu...Conical plug nozzle and truncated conical plug nozzle are advanced rocket nozzles suitable for use as altitude compensating nozzles.In this study flow through the conical plug and truncated conical plug nozzles are numerically simulated to first validate with experimental data and then to compare the performance when a base bleed is introduced.The numerical analysis has considered two-dimensional axisymmetric models.Reynolds-averaged NavierStokes equations are solved with two equation shear stress transport k-ω turbulence model.For the validation of the plug nozzle,flow features and wall pressure along the length of the nozzle is taken for different nozzle pressure ratios.For the validation of truncated plug nozzle,flow features and base pressures at various nozzle pressure ratios are compared.The base bleed is taken as 2%of the inlet mass flow rate.The comparison of results shows that the introduction of base bleed helps to compensate for the loss of thrust due to conical plug nozzle truncation.展开更多
基金supported by the National Natural Science Foundation of China(Grant No.50775081)the National High Technology Research and Development Program of China(863 Program,Grant No.2006AA09Z238)
文摘Water jet thruster, which is a marine system that creates a jet of water for propulsion, has several advantages such as low noise, good anti-cavitation characteristics and maneuvering characteristics. The reaction thrust characteristics of water jet for conical nozzles directly determine the speed of autonomous underwater vehicles (AUV). Theoretical, numerical and experimental studies have been, carried out to investigate the effects of the nozzle geometries as well as inlet conditions on the reaction thrust of water jet in this paper. The experimental results show that: 1) the reaction thrust is proportional to inlet pressure, the square of flow rate and 2/3 power exponent of input power; 2) the diameter of cylinder column for conical nozzle has great influence on the reaction thrust characteristics; 3) the best values of the half cone angle and the cylinder column length exist to make the reaction thrust coefficient to reach the maximum under the same inlet conditions. Those provide a basis for nozzles design and have significant value, especially for developing high performance and efficiency water jet propulsion unit.
基金supported by the National Natural Science Foundation of China (Grant No.50375056)the National High-Technology Research and Development Program of China (Grant No.2006AA09Z238)
文摘Clear knowledge on the reaction thrust of water jet is valuable for better design of water jet propulsion system. In this paper, theoretical, numerical and experimental studies were carried out to investigate the effects of the nozzle geometry as-well as the inlet conditions on the reaction thrust of water jet. Comparison analyses reveal that the reaction thrust has a direct proportional relationship with the product of the inlet pressure, the square of flow rate and two-thirds power exponent of the input power. The results also indicate that the diameter of the cylinder column for the conical nozzle has great influence on the reaction thrust characteristics. In addition, the best values of the half cone angle and the cylinder column length exist to make the reaction thrust reach its maximum under the same inlet conditions.
基金supported by the National High Technology Research and Development Program of China(863 Program)Program for New Century Excellent Talents in University
文摘The cow-nosed ray is studied as natural sample of a flapping-foil robotic fish.Body structure, motion discipline, and dynamicfoil deformation of cow-nosed ray are analyzed.Based on the analysis results, a robotic fish imitating cow-nosed ray,named Robo-ray Ⅱ, mainly composed of soft body, flexible ribs and pneumatic artificial muscles, is developed.Structure andswimming morphology of the robotic prototype are as that of a normal cow-nosed ray in nature.Key propulsion parameters ofRobo-ray Ⅱ at normal conditions, including the St Number at linear swimming, thrust coefficient at towing are studied throughexperiments.The suitable driving parameters are confirmed considering the efficiency and swimming velocity.Swimmingvelocity of 0.16 m·s’and thrust coefficient of 0.56 in maximum are achieved in experiments.
文摘The use of biomimetic tandem flapping foils for ships and underwater vehicles is considered as a unique and interesting concept in the area of marine propulsion. The flapping wings can be used as a thrust producing, stabilizer and control devices which has both propulsion and maneuvering applications for marine vehicles. In the present study, the hydrodynamic per- formance of a pair of flexible flapping foils resembling penguin flippers is studied. A ship model of 3 m in length is fitted with a pair of counter flapping foils at its bottom mid-ship region. Model tests are carried out in a towing tank to estimate the propulsive performance of flapping foils in bollard and self propulsion modes. The same tests are performed in a numerical environment using a Computational Fluid Dynamics (CFD) software. The numerical and experimental results show reasonably good agreement in both bollard pull and self propulsion trials. The numerical studies are carried out on flexible flapping hydrofoil in unsteady conditions using moving unstructured grids. The efficiency and force coefficients of the flexible flapping foils are determined and presented as a function of Strouhal number.
文摘Conical plug nozzle and truncated conical plug nozzle are advanced rocket nozzles suitable for use as altitude compensating nozzles.In this study flow through the conical plug and truncated conical plug nozzles are numerically simulated to first validate with experimental data and then to compare the performance when a base bleed is introduced.The numerical analysis has considered two-dimensional axisymmetric models.Reynolds-averaged NavierStokes equations are solved with two equation shear stress transport k-ω turbulence model.For the validation of the plug nozzle,flow features and wall pressure along the length of the nozzle is taken for different nozzle pressure ratios.For the validation of truncated plug nozzle,flow features and base pressures at various nozzle pressure ratios are compared.The base bleed is taken as 2%of the inlet mass flow rate.The comparison of results shows that the introduction of base bleed helps to compensate for the loss of thrust due to conical plug nozzle truncation.