Flow visualization and hot-wire measurement techniques were combined to investigate the influence of the size and number of tabs on jet flow field and vortex structure generation mechanism. Streamwise vortices generat...Flow visualization and hot-wire measurement techniques were combined to investigate the influence of the size and number of tabs on jet flow field and vortex structure generation mechanism. Streamwise vortices generated by the tabs of different sizes and numbers were observed from the flow visualization images. Combined with flow visualization, hot-wire measurement gave a quantitative insight of the effect of various tabbed jet flows. Instantaneous two-component velocity signals (longitudinal and transverse velocity components) at different cross sections along radius direction and streamwise direction with different tabbed jet nozzles were measured using hot-wire anemometer. Average flow field parameters of tabbed jet flow such as mean velocity, tur-bulence intensity, vorticity were analyzed and the effects of tabs with different sizes and numbers were compared with that of circular no-tab jet flow. It is revealed that the generation of a series of counter-rotating quasi-streamwise vortices, azimuthal vortices and double-row azi-muthal vortex are the reasons for mixing enhancement of tabbed turbulent jet flow.展开更多
Micro-rockets for propulsion of small spacecrafts exhibit significant differences with regard to their macroscale counterparts,mainly caused by the role of the viscous dissipation and heat transfer processes in the mi...Micro-rockets for propulsion of small spacecrafts exhibit significant differences with regard to their macroscale counterparts,mainly caused by the role of the viscous dissipation and heat transfer processes in the micron-sized scale.The goal of this work is to simulate the transient operation of a micro-rocket to investigate the effects of viscous heating on the flow and performance for four configurations of the expanding gas and wafer material.The modelling follows a multiphysics approach that solves the fluid and solid regions fully coupled.A contin- uum-based description that incorporates the effects of gas rarefaction through the micro-nozzle,viscous dissipa- tion and heat transfer at the solid-gas interface is presented.Non-equilibrium is addressed with the implementa- tion of a 2nd-order slip-model for the velocity and temperature at the walls.The results stress that solid-fluid cou- pling exerts a strong influence on the flowfield and performance as well as the effect of the wafer during the first instants of the transient in micro-rockets made of low and high thermal conductivity materials.展开更多
An experimental study is presented for the mixing of one-and dual-line heated jets injected at 60° angle with x-axis into a cold crossflow in a rectangular channel.Measurements of the mean temperature,velocity,an...An experimental study is presented for the mixing of one-and dual-line heated jets injected at 60° angle with x-axis into a cold crossflow in a rectangular channel.Measurements of the mean temperature,velocity,and turbulence intensity together with the flow visualization were performed.Self-similar forms for the dimensionless vertical temperature profiles were found.Parametric variations characterizing the mixing processes of the temperature and velocity fields were examined and correlated in terms of the momentum flux ratio and downstream distance.Results show that both the thermal and velocity penetration depths increase with increasing momentum flux ratio and downstream distance.The turbulence intensity is strong within the region of jet half-width,and the maximum value occurs at a point close to the jet velocity trajectory.展开更多
A hybrid rocket can be used in various applications and is an attractive propulsion system. However, serious erosion of nozzles is common in motor firing operations, which could restrict the application of hybrid rock...A hybrid rocket can be used in various applications and is an attractive propulsion system. However, serious erosion of nozzles is common in motor firing operations, which could restrict the application of hybrid rocket motors. Usually, the serious erosion is attributed to the high concentration of oxidizing species in hybrid motors, while the details of flowfields in the motors are not paid special attention to. In this paper, first the thermochemical erosion of C/C nozzle is simulated coupled with the flowfields in a 98% H2O2/hydroxyl-terminated polybutadiene（HTPB） hybrid rocket motor. The simulation is made on a typical axisymmetric motor, including a pre-combustion chamber, an aft-combustion chamber and nozzle structures. Thermochemica reactions of H2 O, CO2, OH, O and O2 with C are taken into account. Second, the change of flowfields due to fuel regression during motor firing operations is considered. Nozzle erosion in different flowfields is evaluated. Third, the results of nozzle erosion in the coupled simulation are compared with those under uniform and chemical equilibrium flow and motor firing test results. The results of simulation and firing tests indicate that the thermochemical erosion of nozzles in hybrid motors should be calculated coupled with flowfields in the motor. In uniform and chemical equilibrium flowfields, the erosion rate is overestimated. The diffusion flame in hybrid motors protects the nozzle surface from the injected oxidizer and high temperature products in flowfields, leading to a relatively fuel-rich environment above the nozzle. The influence of OH and the geometry of motor should also be considered in the evaluation of nozzle erosion in hybrid motors.展开更多
基金National Natural Science Foundation of China (No.10472081)Program for New Century Excellent Talents in Universities of Minis-try of Education of China and Plan of Tianjin Science and Technology Development (No.06TXTJJC13800)
文摘Flow visualization and hot-wire measurement techniques were combined to investigate the influence of the size and number of tabs on jet flow field and vortex structure generation mechanism. Streamwise vortices generated by the tabs of different sizes and numbers were observed from the flow visualization images. Combined with flow visualization, hot-wire measurement gave a quantitative insight of the effect of various tabbed jet flows. Instantaneous two-component velocity signals (longitudinal and transverse velocity components) at different cross sections along radius direction and streamwise direction with different tabbed jet nozzles were measured using hot-wire anemometer. Average flow field parameters of tabbed jet flow such as mean velocity, tur-bulence intensity, vorticity were analyzed and the effects of tabs with different sizes and numbers were compared with that of circular no-tab jet flow. It is revealed that the generation of a series of counter-rotating quasi-streamwise vortices, azimuthal vortices and double-row azi-muthal vortex are the reasons for mixing enhancement of tabbed turbulent jet flow.
基金as part of the micropropulsion activities in the Small Satellites Programme,funded by the Spanish Ministry of Defence
文摘Micro-rockets for propulsion of small spacecrafts exhibit significant differences with regard to their macroscale counterparts,mainly caused by the role of the viscous dissipation and heat transfer processes in the micron-sized scale.The goal of this work is to simulate the transient operation of a micro-rocket to investigate the effects of viscous heating on the flow and performance for four configurations of the expanding gas and wafer material.The modelling follows a multiphysics approach that solves the fluid and solid regions fully coupled.A contin- uum-based description that incorporates the effects of gas rarefaction through the micro-nozzle,viscous dissipa- tion and heat transfer at the solid-gas interface is presented.Non-equilibrium is addressed with the implementa- tion of a 2nd-order slip-model for the velocity and temperature at the walls.The results stress that solid-fluid cou- pling exerts a strong influence on the flowfield and performance as well as the effect of the wafer during the first instants of the transient in micro-rockets made of low and high thermal conductivity materials.
基金Partial support of this work by the Science and Technology Coordination Council in Defence in Taiwan under Grants CS 79-0210-D110-03
文摘An experimental study is presented for the mixing of one-and dual-line heated jets injected at 60° angle with x-axis into a cold crossflow in a rectangular channel.Measurements of the mean temperature,velocity,and turbulence intensity together with the flow visualization were performed.Self-similar forms for the dimensionless vertical temperature profiles were found.Parametric variations characterizing the mixing processes of the temperature and velocity fields were examined and correlated in terms of the momentum flux ratio and downstream distance.Results show that both the thermal and velocity penetration depths increase with increasing momentum flux ratio and downstream distance.The turbulence intensity is strong within the region of jet half-width,and the maximum value occurs at a point close to the jet velocity trajectory.
文摘A hybrid rocket can be used in various applications and is an attractive propulsion system. However, serious erosion of nozzles is common in motor firing operations, which could restrict the application of hybrid rocket motors. Usually, the serious erosion is attributed to the high concentration of oxidizing species in hybrid motors, while the details of flowfields in the motors are not paid special attention to. In this paper, first the thermochemical erosion of C/C nozzle is simulated coupled with the flowfields in a 98% H2O2/hydroxyl-terminated polybutadiene（HTPB） hybrid rocket motor. The simulation is made on a typical axisymmetric motor, including a pre-combustion chamber, an aft-combustion chamber and nozzle structures. Thermochemica reactions of H2 O, CO2, OH, O and O2 with C are taken into account. Second, the change of flowfields due to fuel regression during motor firing operations is considered. Nozzle erosion in different flowfields is evaluated. Third, the results of nozzle erosion in the coupled simulation are compared with those under uniform and chemical equilibrium flow and motor firing test results. The results of simulation and firing tests indicate that the thermochemical erosion of nozzles in hybrid motors should be calculated coupled with flowfields in the motor. In uniform and chemical equilibrium flowfields, the erosion rate is overestimated. The diffusion flame in hybrid motors protects the nozzle surface from the injected oxidizer and high temperature products in flowfields, leading to a relatively fuel-rich environment above the nozzle. The influence of OH and the geometry of motor should also be considered in the evaluation of nozzle erosion in hybrid motors.
