A throttling experiment for the multi-hole orifice （MO） using water was conducted based on the conclusion of key parameters affecting the MO throttling performance. Testing MOs and standard orifice plates （ SO ） w...A throttling experiment for the multi-hole orifice （MO） using water was conducted based on the conclusion of key parameters affecting the MO throttling performance. Testing MOs and standard orifice plates （ SO ） were designed for the throttling experiment to compare the throttling effect using the equivalent diameter ratio （RED） and diameter ratio （RD ） as key parameters, respectively. Meanwhile, effective metrical conditions were provided for experimental accuracy. The throttling model form was determined according to the theoretical throttling model of SO. Then the unknown parameters involved were identified by experimental data. A good concordance between the modeling computation and experimental results shows a validation of the MO throtting model.展开更多
The T-junction model of engine exhaust manifolds significantly influences the simulation precision of the pressure wave and mass flow rate in the intake and exhaust manifolds of diesel engines. Current studies have fo...The T-junction model of engine exhaust manifolds significantly influences the simulation precision of the pressure wave and mass flow rate in the intake and exhaust manifolds of diesel engines. Current studies have focused on constant pressure models, constant static pressure models and pressure loss models. However, low model precision is a common disadvantage when simulating engine exhaust manifolds, particularly for turbocharged systems. To study the performance of junction flow, a cold wind tunnel experiment with high velocities at the junction of a diesel exhaust manifold is performed, and the variation in the pressure loss in the T-junction under different flow conditions is obtained. Despite the trend of the calculated total pressure loss coefficient, which is obtained by using the original pressure loss model and is the same as that obtained from the experimental results, large differences exist between the calculated and experimental values. Furthermore, the deviation becomes larger as the flow velocity increases. By improving the Vazsonyi formula considering the flow velocity and introducing the distribution function, a modified pressure loss model is established, which is suitable for a higher velocity range. Then, the new model is adopted to solve one-dimensional, unsteady flow in a D6114 turbocharged diesel engine. The calculated values are compared with the measured data, and the result shows that the simulation accuracy of the pressure wave before the turbine is improved by 4.3% with the modified pressure loss model because gas compressibility is considered when the flow velocities are high. The research results provide valuable information for further junction flow research, particularly the correction of the boundary condition in one-dimensional simulation models.展开更多
Pressure losses in flow components are generally characterized either by pressure loss coefficients or by discharge coefficients. The pressure drop for incompressible flow across a screen of fractional free area a is ...Pressure losses in flow components are generally characterized either by pressure loss coefficients or by discharge coefficients. The pressure drop for incompressible flow across a screen of fractional free area a is often calculated from widely used correlation provided in Perry＇s Handbook. This correlation was developed based on experimental work which have covered a wide range of fractional free area （a = 0.14 to 0.79）. The present work aims at validation for a flow in plain square mesh screen with a particular fractional free area （porosity, a） of 0.25 using CFD （Computational Fluid Dynamics） approach. The simulations are carried out for wide range of screen Reynolds number （Re = 0.1 to 105） covering both laminar and turbulent flow regimes. Initial simulations are carried out for incompressible fluid （water） and further extended to compressible fluid （air）. Discharge coefficients obtained from the simulations are compared with experimental values. Effect of compressibility on discharge coefficients is described.展开更多
基金the National Natural Science Foundation of China(Grant No.50578049)
文摘A throttling experiment for the multi-hole orifice （MO） using water was conducted based on the conclusion of key parameters affecting the MO throttling performance. Testing MOs and standard orifice plates （ SO ） were designed for the throttling experiment to compare the throttling effect using the equivalent diameter ratio （RED） and diameter ratio （RD ） as key parameters, respectively. Meanwhile, effective metrical conditions were provided for experimental accuracy. The throttling model form was determined according to the theoretical throttling model of SO. Then the unknown parameters involved were identified by experimental data. A good concordance between the modeling computation and experimental results shows a validation of the MO throtting model.
文摘The T-junction model of engine exhaust manifolds significantly influences the simulation precision of the pressure wave and mass flow rate in the intake and exhaust manifolds of diesel engines. Current studies have focused on constant pressure models, constant static pressure models and pressure loss models. However, low model precision is a common disadvantage when simulating engine exhaust manifolds, particularly for turbocharged systems. To study the performance of junction flow, a cold wind tunnel experiment with high velocities at the junction of a diesel exhaust manifold is performed, and the variation in the pressure loss in the T-junction under different flow conditions is obtained. Despite the trend of the calculated total pressure loss coefficient, which is obtained by using the original pressure loss model and is the same as that obtained from the experimental results, large differences exist between the calculated and experimental values. Furthermore, the deviation becomes larger as the flow velocity increases. By improving the Vazsonyi formula considering the flow velocity and introducing the distribution function, a modified pressure loss model is established, which is suitable for a higher velocity range. Then, the new model is adopted to solve one-dimensional, unsteady flow in a D6114 turbocharged diesel engine. The calculated values are compared with the measured data, and the result shows that the simulation accuracy of the pressure wave before the turbine is improved by 4.3% with the modified pressure loss model because gas compressibility is considered when the flow velocities are high. The research results provide valuable information for further junction flow research, particularly the correction of the boundary condition in one-dimensional simulation models.
文摘Pressure losses in flow components are generally characterized either by pressure loss coefficients or by discharge coefficients. The pressure drop for incompressible flow across a screen of fractional free area a is often calculated from widely used correlation provided in Perry＇s Handbook. This correlation was developed based on experimental work which have covered a wide range of fractional free area （a = 0.14 to 0.79）. The present work aims at validation for a flow in plain square mesh screen with a particular fractional free area （porosity, a） of 0.25 using CFD （Computational Fluid Dynamics） approach. The simulations are carried out for wide range of screen Reynolds number （Re = 0.1 to 105） covering both laminar and turbulent flow regimes. Initial simulations are carried out for incompressible fluid （water） and further extended to compressible fluid （air）. Discharge coefficients obtained from the simulations are compared with experimental values. Effect of compressibility on discharge coefficients is described.
