The Richtmyer-Meshkov instability ofa ‘V＇ shaped air/helium gaseous interface subjected to a weak shock wave is experimentally studied. A soap film technique is adopted to create a ‘V＇ shaped interface with accura...The Richtmyer-Meshkov instability ofa ‘V＇ shaped air/helium gaseous interface subjected to a weak shock wave is experimentally studied. A soap film technique is adopted to create a ‘V＇ shaped interface with accurate initial conditions. Five kinds of ‘V＇ shaped interfaces with different vertex angles are formed to highlight the effects of initial conditions on the flow characteristics. The results show that a spike is generated after the shock impact, and grows constantly with time. As the vertex angle increases, vortices generated on the interface become less noticeable, and the spike develops less pronouncedly. The linear growth rate of interface width after compression phase is estimated by a linear model and a revised linear model, and the latter is proven to be more effective for the interface with high initial amplitudes. The linear growth rate of interface width is, for the first time in a heavy/light interface configuration, found to be a non-monotonous function of the initial perturbation amplitude-wavelength ratio.展开更多
Laser-induced spark ignition of hydrogen-oxygen-argon mixtures was experimen- tally investigated using a Q-swiched Nd:YAG laser to break down the gas at 532 nm. The laser-based high-speed schlieren system was employed...Laser-induced spark ignition of hydrogen-oxygen-argon mixtures was experimen- tally investigated using a Q-swiched Nd:YAG laser to break down the gas at 532 nm. The laser-based high-speed schlieren system was employed to record flame front evolution for the gas mixtures with different initial pressure or laser output energy or argon dilution. The results show that the breakdown of the gas leads to the generation of ellipsoidal plasma. The rarefaction waves create the toroidal rings at the leading and trailing edges of the plasma, which provides a reasonable explana- tion for inward wrinkle of the plasma and the resultant flame. The toroidal rings at leading edge decays more rapidly and a gas lobe is generated that moves towards the laser. The hot gas in the plasma induces the generation of the spark kernel. Affected by the very weak shock wave or compression waves reflected off the wall, the initial laminar flame decelerates. The arc flame front interactions with the wall, reversed shock wave or compression waves, rarefaction waves, etc. induce the transition from laminar flame to turbulent one. These induce the transition from laminar flame to turbulent flame. For stoichiometric hydrogen-oxygen mixtures diluted by 76.92% argon at an initial pressure of 53.33 kPa, the minimum output energy of the laser is 15 mJ for successful laser-induced spark ignition. With in- creasing initial pressure or the output energy of the laser, or decreasing argon di- lution, the speed of the flame front increases.展开更多
基金supported by the National Natural Science Foundation of China(U1530103,11302219,and 11272308)
文摘The Richtmyer-Meshkov instability ofa ‘V＇ shaped air/helium gaseous interface subjected to a weak shock wave is experimentally studied. A soap film technique is adopted to create a ‘V＇ shaped interface with accurate initial conditions. Five kinds of ‘V＇ shaped interfaces with different vertex angles are formed to highlight the effects of initial conditions on the flow characteristics. The results show that a spike is generated after the shock impact, and grows constantly with time. As the vertex angle increases, vortices generated on the interface become less noticeable, and the spike develops less pronouncedly. The linear growth rate of interface width after compression phase is estimated by a linear model and a revised linear model, and the latter is proven to be more effective for the interface with high initial amplitudes. The linear growth rate of interface width is, for the first time in a heavy/light interface configuration, found to be a non-monotonous function of the initial perturbation amplitude-wavelength ratio.
文摘Laser-induced spark ignition of hydrogen-oxygen-argon mixtures was experimen- tally investigated using a Q-swiched Nd:YAG laser to break down the gas at 532 nm. The laser-based high-speed schlieren system was employed to record flame front evolution for the gas mixtures with different initial pressure or laser output energy or argon dilution. The results show that the breakdown of the gas leads to the generation of ellipsoidal plasma. The rarefaction waves create the toroidal rings at the leading and trailing edges of the plasma, which provides a reasonable explana- tion for inward wrinkle of the plasma and the resultant flame. The toroidal rings at leading edge decays more rapidly and a gas lobe is generated that moves towards the laser. The hot gas in the plasma induces the generation of the spark kernel. Affected by the very weak shock wave or compression waves reflected off the wall, the initial laminar flame decelerates. The arc flame front interactions with the wall, reversed shock wave or compression waves, rarefaction waves, etc. induce the transition from laminar flame to turbulent one. These induce the transition from laminar flame to turbulent flame. For stoichiometric hydrogen-oxygen mixtures diluted by 76.92% argon at an initial pressure of 53.33 kPa, the minimum output energy of the laser is 15 mJ for successful laser-induced spark ignition. With in- creasing initial pressure or the output energy of the laser, or decreasing argon di- lution, the speed of the flame front increases.
