Supersonic Flow Chemical Oxygen-iodine Laser Research Articles

Numerical Simulation of Q-Switched Supersonic Flow Chemical Oxygen-Iodine Laser by Solving Time-Dependent Paraxial Wave Equation

The quality and power of an extracted beam from a Q-switched supersonic flow chemical oxygen-iodine laser have been investigated by numerical simulation. The flow system adopted in this study is the throat-mixing system proposed in a previous paper. Three-dimensional calculation for optics is coupled with one-dimensional calculation for gas flow including chemical reactions. Both geometric and wave optics are calculated and compared to assess the effects of diffraction. Wave optics is calculated with a time-dependent paraxial wave equation. The results indicate that wave and geometric optics are qualitatively similar in the time-dependent behavior of beam power. Quantitatively, it is found that diffraction reduces the extracted power by 9%. It is also found from the spreading half-angle of the beam for wave optics that the beam quality at a maximum power is equivalent to that of a plane wave; however, it is lower than that of continuous extraction.

Numerical Simulation of Throat-mixing System for Supersonic Flow Chemical Oxygen-Iodine Laser.

Throat-mixing systems are proposed and assessed for the supersonic flow chemical oxygen-iodine laser (S-COIL). Three-dimensional, numerical simulation solving the governing equations of compressible gas flows together with chemical kinetics has been made for investigating the characteristics of the mixing condition and chemical reactions. The compressible Navier-Stokes equations and a chemical kinetic model encompassing 21 chemical reactions and 10 chemical species are solved by means of a full-implicit finite difference method. Two types of nozzles, a blade- and cylinder-type nozzles are adopted. The results show satisfactorily high values of the small signal gain coefficient G. The proposed throat-mixing system shows higher efficiency than the parallel mixing system. The blade-type nozzle is found to give 44% higher peak value of G than that of the parallel mixing system. It is also noted that the cylinder-type nozzle has superior ability than the parallel mixing system, in spite of its exceedingly simple structure.

412 波動光学による超音速流よう素レーザのQスイッチ出力計算(G.S.2 機器開発・モデル)

412 波動光学による超音速流よう素レーザのQスイッチ出力計算(G.S.2 機器開発・モデル)

Characteristics of Radiation from a Q-Switched Supersonic Flow Chemical Oxygen-Iodine Laser.

The flow and optical fields of a Q-switched supersonic flow chemical oxygen-iodine laser are simulated by solving simultaneously the gas flow model coupled with the precise chemical kinetic model and the geometric optical model. The effects of hyperfine relaxation and velocity cross relaxation for iodine atoms and nonuniformity of the three-dimensional flow field on power extraction are investigated. The results show that the peak power under the influence of hyperfine relaxation and velocity cross relaxation, which is normalized by the corresponding continuous wave value, is 15. This value agrees fairly well with previously reported experimental results of Q-switched chemical oxygen-iodine laser operations. The peak power of pulse in the three-dimensional flow field is considerably small compared to that in the equivalent one-dimensional flow field and the pulse is widened roughly twice due to insufficient mixing, shock waves, expansion waves and wakes.

Characteristics of Radiation from a Supersonic Flow Chemical Oxygen-Iodine Laser.

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 O 2 ( 1 Δ) and I 2 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.

Effects of Wall Catalysis on the Reacting Zone Structure of a Supersonic Flow Chemical Oxygen-Iodine Laser.

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.

Three-Dimensional Mixing/Reacting Zone Structure in a Supersonic Flow Chemical Oxygen-Iodine Laser.

The flow field of a supersonic 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 I 2 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.

Effects of Water Vapor Condensation on the Performance of Supersonic Flow Chemical Oxygen-Iodine Laser.

Water vapor is produced in the singlet oxygen generator of a supersonic flow chemical oxygen-iodine laser as an undesirable by-product. Since the water vapor deactivates the excited iodine atoms very efficiently, it is removed using a water vapor trap before the singlet oxygen is mixed with the iodine. However, part of the water vapor passes through the trap, mixes with the iodine and expands through the supersonic nozzle. In the present study, a condensation model is proposed and the effect of the water vapor condensation due to the supersonic expansion is simulated numerically assuming that the mixing takes place instantaneously and the flow is one-dimensional. The condensation causes a reduction in water vapor concentration and, in this respect, the deactivation of the excited iodine atoms is suppressed. However, the latent heat released into the flow greatly suppresses the cooling in the supersonic expansion. As a result, the small signal gain coefficient is lowered considerably. However, the scattering and the absorption of the laser beam by the water droplets are negligibly small compared to the amplification.

A210 SCOIL装置内流れ場の3次元数値計算による可視化

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.

Theoretical Analysis on Supersonic Flow Chemical Oxygen-Iodine Laser Performances Using an Instantaneous Mixing Assumption.

Numerical simulation of a supersonic flow chemical oxygen-iodine laser is performed and its gain characteristics are studied. It is assumed that the flow is quasi-one-dimensional and the O2-I2 mixing takes place instantaneously at the iodine injector. The numerical results clearly show that the gas cooling by the supersonic expansion is very effective in obtaining high gain. It is shown that a small signal gain coefficient of 1.5∼2 m<-1> is attained downstream of the nozzle exit. It is also shown, however, that the temperature rise due to the chemical reactions which persist in the flow is quite detrimental to the laser performance.

Aerodynamic Characteristics of a Supersonic Flow Chemical Oxygen-Iodine Laser. Starting Characteristics of Supersonic Flow at Low Reynolds Number.

Starting characteristics of a supersonic flow are investigated experimentally in the low Reynolds number range of interest for supersonic flow chemical oxygen-iodine lasers. It is shown that the supersonic flow cannot be started in the test section of constant cross-sectional area at low Reynolds number due to the unacceptale pressure loss, even though a second throat is not utilized. The supersonic flow can be stared at higher Reynolds number with a reasonable pressure ratio which is predicted by the normal shock theory. However, the Mach number in the test section decreases rapidly along the flow due to the presence of thick boundary layers. The use of the diverging test section resuls in a lower critical Reynolds number for starting the supersonic flow and lowers the temperature, although a considerably high pressure ratio is required.