The flow field of a supersonic flow chemical oxygen-iodine laser is simulated by solving the three-dimensional full Navier-Stokes equations, and the dependence of the mixing / reacting zone structure ...and the resulting gain region on the penetration depth of I2 jet into the primary flow of singlet delta oxygen O2(1Δ)is investigated. The effects of wall catalysis are discussed by introducing the surface catalytic efficiency into the wall boundary condition. It is shown that an optimum condition for the secondary I2 jet momentum exists, and that the jet that causes a high gain penetrates the primary flow up to an intermediate depth and does not collide with the counter one. It is also shown that the molar fractions of I(2P1 / 2)and O2(1Δ)are reduced markedly on the fully catalytic wall. The deactivated oxygen molecules are engulfed by the vortices generated behind the I2 jet, leading to the presence of a large amount of unconsumed I2, the reduced formation of I(2P1 / 2)and a large negative gain region in the center of the vortices even far downstream of the nozzle blades. The present study demonstrates the importance of the choice of wall material.
The flow field of a suipersonic flow chemical oxygen-iodine laser is simulated by solving three-dimensional Navier-Stokes equations and the effects of the mixing / reacting zone structure on the ...resulting gain region are studied. It is assumed that the flow is laminar and the water vapor condensation due to the supersonic cooling is ignored. A chemical kinetic model encompassing 21 chemical reactions and 10 chemical species is used to determine the chemical composition of the gas mixture. The present results demonstrate that a pair of contrarotating vortices generated behind the I2 jet greatly enhances the mixing and the simultaneous chemical reaction to produce the excited iodine atom with the singlet oxygen. In the present calculation, the small signal gain coefficient is overestimated to some extent as compared with the experimental one. It is thought that the overestimation is caused by the imperfect chemical kinetic model as well as by ignoring the water vapor condensation and the boundary layers on the upper and lower wall in the present calculation.
Micro-gravity experiment was conducted to observe the instability of a SF6 liquid jet issued into an otherwise quiescent N2 gas at high pressures exceeding the SF6 critical pressure. The liquid, ...which had a near-critical mixing surface, had an extremely small surface tension but a relatively large disparity in liquid-and gas-phase densities. The disintegration process of O(1)-Weber-number liquid jet was successfully observed to reveal the importance of fluid dynamic action in atomization which has been overlooked in past studies. An instability wave which had a wavelength comparable to the jet diameter developed. Droplets disintegrated from the liquid jet made pairs to coalesce, so that the droplet spacing increased downstream.
The flow and optical fields of a supersonic flow chemical oxygen-iodine laser are simulated by solving the three-dimensional Navier-Stokes equations as well as the paraxial wave equation, and the ...laser power extraction characteristics are studied. The present results show that considerable flow nonuniformity remains in the optical resonator. Therefore, the effects of refraction caused by flow nonuniformity on the near-field and far-field patterns of radiative flux, and the laser power are evaluated using an actual nonuniform flow and an equivalent uniform flow. The mixing between O2(1Δ)and I2 in the present condition is fairly satisfactory from the viewpoint of power extraction characteristics. It is also shown that the present simulation overestimates the small signal gain coefficient and the output laser power to some extent. It is thought, however, that the calculation predicts the extremely complicated phenomenon in S-COIL fairly well in spite of the many assumptions used in the present study.
The adoption of a ramp nozzle array in supersonic mixing chemical oxygen-iodine lasers is examined by simulating the mixing and reacting flow fields numerically. Then, the efficiency of the ramps in ...improving the resulting gain region is studied. The compressible Navier-Stokes equations with a detailed chemical kinetic model are solved using a full-implicit finite volume method. The numerical results show that streamwise vortices, which were not anticipated in the previous studies, are induced downstream of the base relief region of the ramp nozzle array and significantly accelerate the mixing and reaction. The contact surface between the reactant streams is stretched very rapidly due to the vortices, resulting in much higher laser performance.
Acoustically excited jet diffusion flame and unburnt jet in quiescent air are investigated experimentally to provide detailed information about combustion characteristics and the jet structure. The ...hydrogen jet diffusion flame and unburnt jet are acoustically excited by monotone sound wave generated by a loud speaker. For the unexcited jet diffusion flame, the hysteresis behavior in the flame lift-off and reattachment, and the sudden increase in lift-off height are observed. Applied the acoustic excitation using a specific range of frequency, the jet velocity at which the transition from laminar to turbulent flame occurs is lowered significantly. Also, the flame shortens its original length and is widened in the incident direction of the sound wave. Furthermore, the flame with branched tip is observed in narrower region of the Strouhal number and the Reynolds number. It is also found out that branching of the unburnt jet is created in a region of lower Strouhal number and lower Reynolds number than the branched tip flame.
This study focuses on the formation mechanism of para-foil canopy. Three types of model wing, which represent each cell of para-foil canopy (a rigid wing with air intake, an inflatable wing and a ...cassette model) were prepared to explore the effects of air intake on inflatable wing formation in wind tunnel experiments. The flow fields both outside and inside of the wings were investigated, together with the process that the flexible wing inflates to form a wing. It was found that the robust nature of canopy is derived from the concaving deformation of the leading edge at small angles of attack, and the enhanced outward suction pressure acting on the leading edge, which are caused by the flexibility of the wing as well as the pressure of air intake in sacrifice of increased drag coefficient.
This study focuses on the formation mechanism of para-foil canopy. Three types of model wing, which represent each cell of para-foil canopy (a rigid wing with air intake, an inflatable wing and a ...cassette model) were prepared to explore the effects of air intake on inflatable wing formation in wind tunnel experiments. The flow fields both outside and inside of the wings were investigated, together with the process that the flexible wing inflates to form a wing. It was found that the robust nature of canopy is derived from the concaving deformation of the leading edge at small angles of attack, and the enhanced outward suction pressure acting on the leading edge, which are caused by the flexibility of the wing as well as the pressure of air intake in sacrifice of increased drag coefficient.
The flow field of a, supersonic flow chemical oxygen-iodine laser is simulated solving three-dimensional Navier-Stokes equations, and the dependence of the mixing/reacting zone structure and the ...resulting gain region on the effective velocity ratio of I2 jet to the primary flow is studied. The I2/He ratio and plenum pressure of the secondary flow are varied in order that the amount of iodine injected into the primary flow is kept constant in each effective velocity ratio. The present results demonstrate that a pair of contrarotating vortices generated behind the I2 jet greatly enhances the mixing and the sumultaneous chemical reaction of I2 and O2(1Δ). It is shown that the optimum condition for the secondary I2 jet momentum exists. The I2 jet which causes the high gain penetrates into the primary flow moderately deeply and does not collide with the counter one.
PDF
