Supersonic Chemical Oxygen-iodine Laser Research Articles

Numerical investigation of the boundary layer separation in chemical oxygen iodine laser

Large eddy simulation is carried out to model the flow process in a supersonic chemical oxygen iodine laser. Unlike the common approaches relying on the tensor representation theory only, the model in the present work is an explicit anisotropy-resolving algebraic Subgrid-scale scalar flux formulation. With an accuracy in capturing the unsteady flow behaviours in the laser. Boundary layer separation initiated by the adverse pressure gradient is identified using Large Eddy Simulation. To quantify the influences of flow boundary layer on the laser performance, the fluid computations coupled with a physical optics loaded cavity model is developed. It has been found that boundary layer separation has a profound effect on the laser outputs due to the introduced shock waves. The F factor of the output beam decreases to 10% of the original one when the boundary transit into turbulence for the setup depicted in the paper. Because the pressure is always greater on the downstream of the boundary layer, there will always be a tendency of boundary separation in the laser. The results inspire designs of the laser to apply positive/passive control methods avoiding the boundary layer perturbation.

Comparison of one- and three-dimensional computational fluid dynamics models of the supersonic chemical oxygen–iodine laser

A simple one-dimensional (1D) computational fluid dynamics (CFD) model of the chemical oxygen iodine laser (COIL) with supersonic mixing is compared with three-dimensional (3D) CFD models and with experimental measurements of the COIL parameters. Dependence of the gain, iodine dissociation fraction and temperature at the resonator optical axis and of the output lasing power on the iodine flow rate predicted by the 1D model is in good agreement with that found using 3D models and experimental results. Hence the 1D model can be used instead of much more complicated 3D models for estimates of the working parameters of supersonic COILs.

超音速化学氧碘激光器能量提取对流场影响的数值研究

超音速化学氧碘激光器能量提取对流场影响的数值研究

Scalable chemical oxygen — iodine laser

The problem of scaling chemical oxygen — iodine lasers (COILs) is discussed. The results of experimental study of a twisted-aerosol singlet oxygen generator meeting the COIL scalabilityrequirements are presented. The energy characteristics of a supersonic COIL with singlet oxygen and iodine mixing in parallel flows are also experimentally studied. The output power of ∼7.5 kW,corresponding to a specific power of 230 W cm-2, is achieved. The maximum chemical efficiency of the COIL is ∼30%.

Study of Different Nozzle Configurations for Supersonic COIL System

Supersonic chemical oxygen iodine laser (SCOIL) hasrecently proved itscapabilities against projectile targets such as missiles and rockets in the tests performed with ABL system. It is primarily a chemical based gas laser system involving extensive gas dynamics for achieving lasing action. COIL (l= 1.315 mm) is conducive for both defenseand industrial applications and the beam is optical fibre compatible. One of the chief components of a SCOIL device is the supersonic nozzle system which not only produces the desired cavity conditions in terms of Mach number and cavity pressure but is also responsible for efficient mixing of lasing [I2 + N2] and pumping media [O2 (1Dg) + N2]. The supersonic nozzle to a large extent controls the pressure recovery potential of the laser system and thereby the system volume. The present study discusses the performance of three nozzle configurations viz, slit, advanced/ ejector and winglet nozzle. The comparisons have been made in terms.

超音速化学氧碘激光器内流动与光能提取耦合仿真

超音速化学氧碘激光器内流动与光能提取耦合仿真

Comparing modeling and measurements of the output power in chemical oxygen-iodine lasers: A stringent test of I2 dissociation mechanisms

A parametric study of the output power of supersonic chemical oxygen-iodine lasers (COILs) is carried out, applying a kinetic-fluid dynamics model calculations as well as an analytical model and comparing the results to experimental studies. The I(2) dissociation mechanism recently suggested by Azyazov et al. [J. Chem. Phys. 130, 104306 (2009)], which was previously used for comparison of model calculations to measurements of the small signal gain [K. Waichman et al., J. Appl. Phys. 106, 063108 (2009)], is applied here for a similar, but more sensitive, comparison of the laser output power. The dependence of the power on iodine flow rate and on mirror transmission is studied for low and high pressure COILs, respectively. Good agreement between the calculated and measured power is obtained for both low and high pressure COILs only when the processes suggested by Azyazov et al. are included in the calculations. This is different from the situation for the gain where for high pressure COILs, the calculated values were insensitive to the assumed dissociation mechanism, although for low pressure the measurements were reproduced only by applying the Azyazov et al. mechanism. We believe that the results of the present work strongly support the application of this mechanism for modeling the COIL operation.

Mixing in a supersonic COIL laser: influence of trip jets

We present an experimental study of a supersonic nozzle with supersonic iodine injection. This nozzle simulates Chemical Oxygen Iodine Laser (COIL) flow conditions with non-reacting, cold flows. During the experiments, we used a laser sheet near 565 nm to excite fluorescence in iodine, which we imaged with an intensified and gated CCD camera. We captured streamwise and semi-spanwise (oblique-view) images, with fluorescence revealing the material injected into the flow. We identified the flow structures in the images, and produced quantitative characterizations of the flow morphology and of the mixing between the primary and injected flow. We considered four injection scenarios. The first scenario includes a single injector positioned downstream of the nozzle throat. To enhance the mixing between the flows, trip jets are placed in the wake of the single jet. The sonic trip jets, significantly smaller than the primary supersonic iodine jet, are intended to destabilize the counter-rotating vortex pair (CRVP) of the primary jet. We compare three different trip jet configurations for their ability to enhance mixing between the oxygen and iodine flows.

Pressure recovery studies on a supersonic COIL with central ejector configuration

A chemical oxygen–iodine laser (COIL) is an electronic transition, low pressure, high throughput system. The field use of this laser demands the development of suitable pressure recovery systems. Ejector based pressure recovery systems form a potent alternative for open cycle COIL operation. The two possible configurations of motive gas injection in ejectors are peripheral and central. The present paper focuses on the investigation of a central injection low pressure ejector operated with a small scale supersonic COIL (SCOIL). The ejector handles a motive flow of nearly 120 g s −1 and an entrained laser flow of nearly 3 g s −1. The predicted geometry using integral methods has been validated numerically by employing Fluent 6.1 software in a 2-d axisymmetric viscous turbulent flow formulation. The numerical predictions have been experimentally validated, which indicate a pressure recovery of 63 Torr at design conditions. The results also show that the recovered pressure improves to 75 Torr for an off-design condition of higher motive flow rate.

Kinetic-fluid dynamics modeling of I2 dissociation in supersonic chemical oxygen-iodine lasers

The mechanism of I2 dissociation in supersonic chemical oxygen-iodine lasers (COILs) is studied applying kinetic-fluid dynamics modeling, where pathways involving the excited species I2(X Σ1g+,10≤v<25), I2(X Σ1g+,25≤v≤47), I2(A′ Π32u), I2(A Π31u), O2(X Σ3g−,v), O2(a Δ1g,v), O2(b Σ1g+,v), and I(P21/2) as intermediate reactants are included. The gist of the model is adding the first reactant and reducing the contribution of the second as compared to previous models. These changes, recently suggested by Azyazov, et al. [J. Chem. Phys. 130, 104306 (2009)], significantly improve the agreement with the measurements of the gain in a low pressure supersonic COIL for all I2 flow rates that have been tested in the experiments. In particular, the lack of agreement for high I2 flow rates, which was encountered in previous models, has been eliminated in the present model. It is suggested that future modeling of the COIL operation should take into account the proposed contribution of the above mentioned reactants.

Supersonic diffuser for pressure recovery in SCOIL system

Classical supersonic chemical oxygen iodine laser (SCOIL) systems operate under a low total pressure of nearly 18 Torr (2400 Pa) with cavity pressure being in the range 3 Torr (400 Pa) and Mach number of 1.7. These systems handle high flow rates and hence an efficient supersonic diffuser (SD) is a critical first step towards an open-cycle operation, which may be followed by a multi-stage ejector system. The present study discusses the various aspects in the design of a supersonic diffuser for a twin 10 kW COIL module source which employs flow rates of 100 gs −1 in each module. The results of computational studies based on 3-D, viscos compressible flow, k– ε turbulence formulation for the supersonic diffuser geometry have also been discussed. The experimental results from a single-module test of the supersonic diffuser show that a total recovered pressure of nearly 7 Torr is achieved at the diffuser exit.

Modeling of the gain and temperature in high pressure, ejector type chemical oxygen-iodine lasers and comparison to experiments

The results of three-dimensional computational fluid dynamics model calculations are compared to available experimental results [V. D. Nikolaev et al., IEEE J. Quantum Electron. 38, 421 (2002)]. It is shown that the model is applicable to high pressure, ejector type chemical oxygen-iodine laser (COIL), reasonably reproducing the measured gain, temperature, static pressure, and gas velocity. A previous model, which included I2(A′Π32u), I2(AΠ31u), and O2(aΔ1g,v) as significant intermediates in the dissociation of I2 [K. Waichman et al., J. Appl. Phys. 102, 013108 (2007)], reproduced the measured gain and temperature of a low pressure supersonic COIL. The previous model is complemented here by adding the effects of turbulence, which play an important role in high pressure COILs.

Numerical study on the performance of nozzle flow for supersonic chemical oxygen–iodine lasers

Laser performance is greatly dependent on its operating conditions due to the strong coupling among multi-physics such as gas-dynamics, chemical reaction kinetics and optics in the mixing nozzle of COIL. In this paper, 3D CFD technology is used to simulate the mixing and reactive flow of subsonic cross jet scheme at different conditions. Results obtained show that the jet penetration depth plays a dominant role in the spatial distribution of small signal gains. In the case of over-penetration, unsteady flow structures are induced by impinging between the opposing jets. The optimum spatial distribution of the chemical performance cannot be obtained even if the full penetration condition is achieved through the subsonic transverse jet mixing scheme in the COIL nozzle flow.

Application of profiled ejector in chemical lasers

Recently, the use of profiled ejectors based on constant rate of momentum change [I.W. Eames, Applied Thermal Engineering 22 (2002) 121] along the mixing chamber has been proposed for enhancing the recovery ratio across an ejector stage by minimizing shock losses for application in ejector based refrigeration system. Such ejectors can achieve pressure recovery ratio in excess of 150, thus making the system a compact one. Chemical lasers in general and chemical oxygen-iodine laser (COIL) in particular fall in the high power lasers category and find numerous applications in defense and industry. However, these lasers have not been exploited fully because these require pressure recovery systems for their operation and as such the practical systems are extremely voluminous and bulky. The profiled ejectors find direct applications in these lasers and thus can make the system extremely compact. The conventional supersonic COIL systems operate at a typical stagnation pressure of nearly 20 torr and a cavity static pressure of approximately 3 torr, which are amongst the lowest in the class of chemical lasers. Thus, a low-pressure operation of the laser system demands a high capacity vacuum system. Alternatively, efficient ejector based pressure recovery system has been utilized for achieving direct atmospheric exhaust of the lasing medium. However, a minimum of two-stage conventional supersonic ejectors need to be employed for the operation of the laser system. Multiple stages of the ejector are essential on account of the stagnation pressure loss occurring across a normal shock at the exit of the mixing chamber in each ejector stage. The present study presents a general treatment on the design of a profiled ejector for the case of dissimilar motive and suction fluids that are typical of these lasers. Also, determinations for the increase in recovery ratio for various conditions of entrainment ratio over the conventional ejectors have also been presented. Finally, a computational study using McCormack’s method for Euler system of equations has been carried out to numerically validate the analytical studies for a peripheral air ejector system suitable for a 500 W class COIL employing a flow rate of ∼3 gm/s with an entrainment ratio of 0.025. It has been concluded that a single-stage profiled ejector is sufficient to achieve atmospheric pressure recovery even in the low-pressure systems.

Active-medium inhomogeneities and optical quality of radiation of supersonic chemical oxygen—iodine lasers

Optical inhomogeneities of the active medium of a supersonic chemical oxygen—iodine laser (COIL) and their effect on the radiation parameters are studied in the case when an unstable resonator is used. Classification of optical inhomogeneities and the main factors affecting the quality of COIL radiation are considered. The results of numerical simulation of a three-dimensional gas-dynamic active medium and an unstable optical resonator in the diffraction approximation are presented. The constraints in the fabrication of large-scale COILs associated with a deterioration of the optical quality of radiation are determined.

Toward understanding the dissociation of I2 in chemical oxygen-iodine lasers: Combined experimental and theoretical studies

The dissociation of I2 molecules at the optical axis of a supersonic chemical oxygen-iodine laser (COIL) was studied via detailed measurements and three-dimensional computational fluid dynamics calculations. The measurements, briefly reported in a recent paper [Rybalkin et al., Appl. Phys. Lett. 89, 021115 (2006)] and reanalyzed in detail here, revealed that the number N of consumed O2(aΔg1) molecules per dissociated I2 molecule depends on the experimental conditions: it is 4.5±0.4 for typical conditions and I2 densities applied for optimal operation of the COIL but increases at lower I2 densities. Comparing the measurements and the calculations enabled critical examination of previously proposed dissociation mechanisms and suggestion of a mechanism consistent with the experimental and theoretical results obtained in a supersonic COIL for the gain, temperature, I2 dissociation fraction, and N at the optical axis. The suggested mechanism combines the recent scheme of Azyazov and Heaven [AIAA J. 44, 1593 (2006)], where I2(A′Π2u3), I2(AΠ1u3), and O2(aΔg1,v) are significant dissociation intermediates, with the “standard” chain branching mechanism of Heidner III et al. [J. Phys. Chem. 87, 2348 (1983)], involving I(P1∕22) and I2(XΣg+1,v).

Computation of streamwise vorticity in a compressible flow of a winglet nozzle-based COIL device

Chemical oxygen iodine laser (COIL) is a high-power laser with potential applications in both military as well as in the industry. COIL is the only chemical laser based on electronic transition with a wavelength of 1.315 μm, which falls in the near-infrared (IR) range. Thus, COIL beam can also be transported via optical fibers for remote applications such as dismantling of nuclear reactors. The efficiency of a supersonic COIL is essentially a function of mixing specially in systems employing cross-stream injection of the secondary lasing ( I 2) flow in supersonic regime into the primary pumping (O 2 1Δ g) flow. Streamwise vorticity has been proven to be among the most effective manner of enhancing mixing and has been utilized in jet engines for thrust augmentation, noise reduction, supersonic combustion, etc. Therefore, a computational study of the generation of streamwise vorticity in the supersonic flow field of a COIL device employing a winglet nozzle with various delta wing angles of 5°, 10°, and 22.5° has been carried out. The study predicts a typical Mach number of approximately 1.75 for all the winglet geometries. The analysis also confirms that the winglet geometry doubles up both as a nozzle and as a vortex generator. The region of maximum turbulence and fully developed streamwise vortices is observed to occur close to the exit, at x/ λ of 0.5, of the winglets making it the most suitable region for secondary flow injection for achieving efficient mixing. The predicted length scale of the scalloped mixer formed by the winglet nozzle is 4 λ. Also, the winglet nozzle with 10° lobe angle is most suitable from the point of view of mixing developing cross-stream velocity of 120 m/s with acceptable pressure drop of 0.7 Torr. The winglet geometry with 5° lobe angle is associated with a low cross-stream velocity of 60 m/s, whereas the one with 22.5° lobe angle is associated with a large static and total pressure drop of 1.87 and 9.37 Torr, respectively, making both the geometries unsuitable for COIL systems. The experimental validation shows a close agreement with the computationally predicted values. The studies for the most suitable 10° lobe angle geometry show an observed Mach number of 1.72 with an improved mixing efficiency of 74% due to the occurrence of predicted streamwise vortices in the flow.

Power enhancement in chemical oxygen-iodine lasers by iodine predissociation via corona/glow discharge

The gain and power in a supersonic chemical oxygen-iodine laser (COIL) are enhanced by applying dc corona/glow discharge in the transonic section of the secondary flow in the supersonic nozzle, dissociating I2 prior to its mixing with O2(Δ1). The loss of O2(Δ1) consumed for dissociation is thus reduced, and the consequent dissociation rate downstream of the discharge increases, resulting in up to 80% power enhancement. The implication of this method for COILs operating beyond the specific conditions reported here is assessed.

Numerical Analysis of the Flowfield in a Supersonic Coil with an Interleaved Jet Configuration and its Effect on the Gain Distribution

In a supersonic chemical oxygen-iodine laser (COIL) operating without primary buffer gas, the features of flowfield have significant effects on the Laser efficiency and beam quality. In this paper three-dimensional, multispecies, chemically reactive CFD technology was used to study the flowfield in mixing nozzle implemented with a supersonic interleaving jet configuration. The features of the flowfield as well as its effect on the spatial distribution of small signal gain were analyzed.

高マッハ数ランプノズルを用いた超音速流ヨウ素レーザーの数値シミュレーション

The adoption of three types of nozzle contours, the ramp nozzle, symmetric ramp nozzle, and symmetric swept-ramp nozzle, in chemical oxygen-iodine lasers with supersonic ejector-nozzle banks is examined by simulating the mixing and reacting flow fields numerically. 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 induced downstream of the base region of the nozzle array are enhanced with decreasing the length ls of diverging region in I2 nozzle. However, the optimum ls which results in a high small signal gain coefficient exists for each nozzle contour, since the mixing depends also on the size and location of the streamwise vortex. Therefore, the symmetric swept-ramp nozzle which produces strong streamwise vortices even with rather large ls is most preferable among the proposed nozzle contours. The pitot pressure in the mixing region obtained in the present calculation is approximately 10kPa which is ten times higher than that of conventional supersonic flow chemical oxygen-iodine lasers.