The mass flow rate measurement using a critical nozzle shows the validity of the inviscid theory, indicating that the discharge coefficient increases and approaches unity as the Reynolds number increases under the ide...The mass flow rate measurement using a critical nozzle shows the validity of the inviscid theory, indicating that the discharge coefficient increases and approaches unity as the Reynolds number increases under the ideal gas law However, when the critical nozzle measures the mass flow rate of a real gas such as hydrogen at a pressure of hundreds bar, the discharge coefficient exceeds unity, and the real gas effects should be taken into account. The present study aims at investigating the flow features of the critical nozzle using high-pressured hydrogen gas. The axisymmetric, compressible Navier-Stokes computation is employed to simulate the critical nozzle flow, and a fully implicit finite volume method is used to discretize the governing equation system. The real gas effects are simulated to consider the intermolecular forces, which account for the possibility of liquefying hydrogen gas. The computational results are compared with past experimental data. It has been found that the coefficient of discharge for real gas can be corrected properly below unity adopting the real gas assumption.展开更多
Due to viscous heating spontaneous ignition of a supersonic flow of premixed combustible gases canoccur in boundary layers. This process is studied numerically for a hydrogen-air mixture in the caseof a laminar bounda...Due to viscous heating spontaneous ignition of a supersonic flow of premixed combustible gases canoccur in boundary layers. This process is studied numerically for a hydrogen-air mixture in the caseof a laminar boundary layer over a flat plate. In a previous study the main structure of the reactingflow was given as well as a first mapping of the ignition conditions versus boundary conditions. In thepresent work computations are performed in order to further specify the controlling mechanisms andparameters of such a boundary layer ignition. We emphasize more precisely i) the elementary stepsof the chemical process which effectively control the ignition n) the unusual role played by the equivalence ratio of the mixture iii) the influence of the Soret effect (species transport due to temperaturegradients).展开更多
文摘The mass flow rate measurement using a critical nozzle shows the validity of the inviscid theory, indicating that the discharge coefficient increases and approaches unity as the Reynolds number increases under the ideal gas law However, when the critical nozzle measures the mass flow rate of a real gas such as hydrogen at a pressure of hundreds bar, the discharge coefficient exceeds unity, and the real gas effects should be taken into account. The present study aims at investigating the flow features of the critical nozzle using high-pressured hydrogen gas. The axisymmetric, compressible Navier-Stokes computation is employed to simulate the critical nozzle flow, and a fully implicit finite volume method is used to discretize the governing equation system. The real gas effects are simulated to consider the intermolecular forces, which account for the possibility of liquefying hydrogen gas. The computational results are compared with past experimental data. It has been found that the coefficient of discharge for real gas can be corrected properly below unity adopting the real gas assumption.
文摘Due to viscous heating spontaneous ignition of a supersonic flow of premixed combustible gases canoccur in boundary layers. This process is studied numerically for a hydrogen-air mixture in the caseof a laminar boundary layer over a flat plate. In a previous study the main structure of the reactingflow was given as well as a first mapping of the ignition conditions versus boundary conditions. In thepresent work computations are performed in order to further specify the controlling mechanisms andparameters of such a boundary layer ignition. We emphasize more precisely i) the elementary stepsof the chemical process which effectively control the ignition n) the unusual role played by the equivalence ratio of the mixture iii) the influence of the Soret effect (species transport due to temperaturegradients).
