Supersonic Air Stream Research Articles

Effects of a focused laser pulse for combustion augmentation characteristics in supersonic airstreams

An investigation on effects of a focused laser pulse for combustion enhancement characteristics was conducted for supersonic airstreams with a transverse hydrogen-fuel injection. In order to estimate behaviors of a laser-induced plasma, temporal variations of its emission distribution were measured with an ICCD camera and photodiodes. From these measurements, characteristic time scales of an absorption process of an incident laser pulse and a plasma formation process were also estimated. Numerical simulations using a time-dependant Navier–Stokes equation with finite-rate chemistry were also conducted to elucidate laser-induced ignition and mixing enhancement characteristics in supersonic airstreams with a transverse hydrogen injection. From the results, it was confirmed that, depending on the laser energy density and focal points, radicals, a shock wave, and shock-induced local turbulences were being formed through laser irradiation. Then, recirculation zones with flamelets were induced. Moreover, it was shown that these flamelets were growing in moving upstream and downstream from the focal point up to 1 ms. Consequently, it was shown that laser-induced plasmas could be effective in both combustion reaction and mixing enhancements for the supersonic combustion.

ランプから噴射した２軸超音速旋回噴流の混合

Mixing of twin swirling helium jets injected from a ramp into a supersonic airstream was experimentally investigated to clarify the interaction between the vortices introduced by the ramp and the swirl. The direction and strength of the swirl were changed by replacing cylindrical chambers through which the injectant was introduced to the injector. The direction of the swirl was either same as or opposite to that of the ramp vortex. Helium concentration distributions were measured in three cross sections. The swirl in the same direction brought the injectant to the center plane of the two jets and merged to a single one, while that in the opposite direction kept each jet apart. However, there was no significant difference in the maximum concentration of helium observed in the tests with different directions and strength of the swirl.

超音速燃焼器燃料噴射孔形状の設計問題における最適化と設計情報の知識発見

A Multi-Objective Genetic Algorithm (MOGA) is applied in search of the optimal fuel injector shape in the supersonic combustor. The optimal shape is investigated in terms of rapid mixing of fuel jet and supersonic airstream. Two goals, those are to maximize the jet core height and to minimize the total pressure loss, are adopted for the optimization. The numbers of maximum injector holes are restricted to 1, 2 and 3 during the evolutive process. Pareto fronts under the 2 and 3 maximum holes restriction evolve successfully. Self-Organizing Map (SOM) is applied, in order to realize the role of optimal solutions in actual design, to analysis of structure on design space by means of design database obtained in evolutive process of optimization. The design database is mapped onto the two-dimensional SOM, where design space is successfully visualized. The visualization that clarifies relativity of performance parameters acquires valuable design information.

Numerical study on supersonic combustion with cavity-based fuel injection

The present study describes the numerical investigations concerning the combustion enhancement when a cavity is used for the hydrogen fuel injection through a transverse slot nozzle into a supersonic hot air stream. The cavity is of interest because recirculation flow in cavity would provide a stable flame holding while enhancing the rate of mixing or combustion. Several inclined cavities with various aft wall angle, offset ratio and length are evaluated for reactive flow characteristics. The cavity effect is discussed from a viewpoint of total pressure loss and combustion efficiency. The combustor with cavity is found to enhance mixing and combustion while increasing the pressure loss, compared with the case without cavity. But it is noted that there exists an appropriate length of cavity regarding the combustion efficiency and total pressure loss.

Aeroelastic Dynamic Analysis of a Full F-16 Configuration for Various Flight Conditions

An overview is given of recent advances in a three-field methodology for modeling and solving nonlinear fluid-structure interaction problems, and its application to the prediction of the aeroelastic frequencies and damping coefficients of a full F-16 configuration in various subsonic, transonic, and supersonic airstreams is reported. In this three-field methodology the flow is described by the arbitrary Lagrangian-Eulerian form of the Euler equations, the structure is represented by a detailed finite element model, and the fluid mesh is unstructured, dynamic, and updated by a robust torsional spring analogy method. Simulation results are presented for stabilized, accelerated, low-g, and high-g flight conditions, and correlated with flight-test data. Consequently, the practical feasibility and potential of the described computational-fluid-dynamics-based computational method for the flutter analysis of high-performance aircraft, particularly in the transonic regime, are discussed.

超音速せん断流中の水素ガス初期燃焼への気体分子運動論的アプローチ｀＊１´ 第１報：混合拡散過程

Direct Simulation Monte Carlo (DSMC) method based on the Boltzmann equation, in-cooperating a new reactive inelastic molecular collision model, has been employed to analyze the fuel gas mixing in two-dimensional supersonic shear flow which originates from the meeting at a thin plate (lip) edge of two parallel flows, a supersonic air stream and a sonic hydrogen gas flow. In the present study, the influence of hydrogen gas temperature upon the mixing within the shear layer is clarified. In a companion paper (the 2nd report), the relationship between mixing and chemical reaction will be presented.

多目的遺伝的アルゴリズムを用いた超音速燃焼器燃料噴射口形状の最適化

The optimal fuel injector shape for a supersonic combustor is investigated in terms of rapid mixing of fuel jet and supersonic airstream. A Multi-Objective Genetic Algorithm (MOGA) has been applied to discover the optimal fuel injector shape, and two goals of the optimization are adopted. One is to maximize the jet core height, and the other is to minimize the total pressure loss. The algorithm works well, and the characteristics of the optimized shapes for the fuel injector are understood. The effects of the fuel injector shape, which is derived from the statistical process of the optimized shape, are numerically investigated on the jet core height and total pressure loss.

The effect of injection angle on mixing and flame holding in supersonic combustor

A numerical study on mixing of hydrogen injected into a supersonic air stream has been performed by solving two-dimensional full Navier-Stokes equations. An explicit Harten-Yee Non-MUSCL Modified-flux-type TVD scheme has been used to solve the system of equations, and a zero-equation algebraic turbulence model to calculate the eddy viscosity coefficient. The main objectives of this study are to increase the mixing efficiency and flame holding capability of a supersonic combustor. The performance of combustor has been investigated by varying the hydrogen injection angle made with the direction of air stream considering anti-clockwise direction as positive. The injector position from left boundary, backward-facing step height and the inlet width of air stream are kept constant. The results show that upstream of injector the mixing is dominated by recirculation and in downstream the mixing is dominated by mass concentration of hydrogen. Upstream recirculation is dominant for injecting angle 60° and 90°. Incorporating the various effects, perpendicular injection shows the maximum mixing efficiency and its large upstream recirculation region has a good flame holding capability.

Thermal Response and Ablation Characteristics of Carbon Fiber Reinforced Composite with Novel Silicon Containing Polymer MSP

Polymer composites are widely used for high temperature thermal protection (TPS)materials for spacecraft heat shields, and nozzle liners for solid propellant rocket motors. Newly developed silicon containing polymer, abbreviated MSP (Mitsui Silicon Containing Polymer), possesses high decomposition temperature (500 C), and high char yield (>94% at 1000 C)after pyrolysis. Therefore, the MSP polymer has potential as matrix resin of high performance ablative composites compared with conventional phenolic resins. In this study, thermal performance and ablation characteristics of a carbon composite with the MSP polymer (CF/MSP) were investigated under supersonic plasma air stream. The cold wall heat fluxes ranged from 1.2 to 11.0MW/m2. Conventional carbon fiber phenolic (CF/PR) composite was tested at the similar conditions for direct comparison. The mass loss of the CF/MSP composite was far less than that of the CF/PR composite, which is due to higher char yield and consequent high density of char layer. On the other hand, higher internal temperature was measured in the CF/MSP composite.

Effects of Swirl and Skew Upon Supersonic Wall Jet in Crossflow

The results of an experimental investigation of the effects of swirl and skew on the mixing of a supersonic light gas jet injected from a e at wall into a supersonic airstream are presented. Tests were at nominally equal injectant masse owrate, totalpressure,andinjectornozzleexitstaticpressure. Data includesurveysofcross-sectionalplanes of the e ow for several different cases of swirl and skew using cone static pressure, pitot, stagnation temperature, and gas sampling probes (with gas analysis system ). The results are analyzed to determine mixing efe ciency and lateral motions of the center of the injectant plume. The effect of combined swirl and skew on injectant mixing is to slightly increase mixing in the near e eld of injection, but there is little effect of either swirl or skew on mixing far downstream. Both swirl and skew slightly reduce penetration.

Influence of main flow inlet configuration on mixing and flameholding in transverse injection into supersonic airstream

A numerical study on mixing and combustion of hydrogen transversely injected into a main airstream is performed, by solving two-dimensional full Navier–Stokes equations. The focus of this paper is to study the means of increasing the mixing and combustion efficiencies, and the flameholding capability for supersonic propulsion application by changing the main flow inlet configuration. Accordingly, the following three inlet configurations are considered: (1) A finite parallel flow with backward-facing step; when the main flow enters through a finite-width inlet of wall, the wall under the inlet acts as a backward-facing step. (2) A finite parallel flow without step; although the inlet configuration is identical to Case 1, there is no step under the inlet. (3) The infinite parallel flow; the main flow enters throughout the left boundary. As combustion modeling we have used full chemistry between hydrogen and air consisting of eight species (H 2, O 2, H, O, OH, H 2O, HO 2, H 2O 2) and 19 reactions shown in Table 1. The effects of inlet configurations are evaluated by calculating mixing and combustion efficiencies. The results show that a finite parallel flow with backward-facing step (Case 1) causes the highest penetration and mixing of hydrogen and provides the best flameholding region between the downstream injecting slit and backward-facing step. The effects of high penetration and mixing on combustion, and characteristics of the reacting flowfields are studied. The finite parallel flow configuration (Cases 1 and 2) makes the bow shock steeper and eventually increases the diffusion of hydrogen in the downstream of injecting slit.

203 菱形/円形噴射孔からの音速噴流の超音速流への貫通

203 菱形/円形噴射孔からの音速噴流の超音速流への貫通

Fuel Injection into a Supersonic Airflow by Means of Pylons

The mixing and reaction processes in a scramjet combustion chamber have been experimentally investigated. Hydrogen was injected into a preheatedMach 2.15 airstream by means of pylon-like fuel injectors. The supersonic  ame was stabilized in a purely reaction–kinetical way; i.e., by means of self-ignition. Various pylon designs have been employed to study their in uence on fuel mixing and combustion in the supersonic airstream. Based on the results, an optimized fuel injector has been designed and tested. To assess the reacting  ow, nonintrusive, optical measurement techniques have been employed: the Rayleigh scattering technique to study the injected mixing jets, and the self- uorescence of the OH radical to determine location and intensity of the reaction zones. Additionally, the wall static pressure has been measured.

Supersonic Combustion of Kerosene/H2-Mixtures in a Model Scramjet Combustor

Liquid hydrocarbon supersonic combustion has been experimentally investigated. Kerosene was burnt in a steady. vitiated Mach 2.15 - air flow of a model scramjet combustor. The fuel is injected into the supersonic air stream by means of pylons. The effervescent atomisation method has been employed such that the liquid fuel is injected as a spray. By means of the Mie scattering technique the fuel jet structure was visualised and the evaporation rate estimated. The mechanisms of ignition and combustion of the kerosene/H2-mixture were studied and compared with the case of hydrogen combustion. Combustor ignition limits have been determined. Fuel-specific combustion phenomena are discussed. It was found that for the kerosene combustion a gas dynamic feedback mechanism strongly affects the supersonic combustion process.

Combustion of kerosene in a supersonic stream

Experiments on the organization of the combustion of kerosene in high-enthalpy supersonic air streams is analyzed. The use of promotor additives, as well as improvements in the atomization process, vaporization, and mixing, do not always facilitate efficient combustion development. The existence of a conversion process is found to have a significant effect on the ignition parameters. The burnup intensity can be ensured by adding hydrogen, and the relative position of the fuel injectors is important in that case. The fundamental role of wave structures in determining the length of the combustion zone in the channel is noted. The integral characteristics of combustion for hydrogen and kerosene are compared.

Advanced Mixing Control in Supersonic Airstream with a Wall-Mounted Cavity

Advanced Mixing Control in Supersonic Airstream with a Wall-Mounted Cavity

98/01484 Effects of mixing schemes on kerosene combustion in a supersonic airstream: Owens, M. et al. J. Propul. Power, 1997, 13, (4), 525–531

98/01484 Effects of mixing schemes on kerosene combustion in a supersonic airstream: Owens, M. et al. J. Propul. Power, 1997, 13, (4), 525–531

Nonlinear instabilities leading to rapid mixing and combustion in confined supersonic double-shear-layer flow

Direct numerical simulations conducted in the present study show that a slow fuel gas stream issued between supersonic high-temperature air streams confined in a constant-area channel can mix with air quickly to cause explosive combustion along the following processes: (1) linear flaw instability excitation, (2) eddy formation without shocks, fuel flow acceleration to supersonic speed and enhanced mixing with air, associated with fuel layer meandering, (3) explosive combustion, and (4) thermally choked burnt gas flow. The underlying physics of the supersonic instabilities involved are revealed by interpreting the simulation results in an attempt to find an effective mixing enhancement technique. The basic flow configuration consists of a confined, plane, double shear/mixing layer flow with forcing fluctuations at the inlet. The difference in velocities between inlet air and fuel streams is supersonic. The reflection condition imposed at the walls serves to disturb acoustically the double shear layer flow in such a way that the walls reflect Mach waves radiated from the inlet disturbance. The most unstable wave excited downstream is skew-symmetric with respect to the centerline, thus leading to the meandering of fuel layer accompanied by Karman-vortex-like eddies. A series of instability excitations couples with the fuel layer meandering in a confined flow region, enhances the exchange of momentum and species between the fuel and air streams, thus accelerating the mixture to a supersonic speed within a short distance prior to explosive combustion. The behavior of the flame front resembles that of lifted turbulent-jet flames. Flame flashback, stationary flame front and flame blowout take place, depending on the inlet condition. Their criteria are provided in terms of the Chapman-Jouguet detonation wave speed.

Experimental Studies on Self-Ignition of Hydrogen/Air Supersonic Combustion

Self-ignition tests of a model scramjet combustor were conducted by using parallel sonic injection of gaseous hydrogen from the base of a blade-like strut into a supersonic airstream, The vitiated air was produced by burning H-2, O-2, and air to a stagnation temperature of 1000-2100 K and a stagnation pressure of 0.8-1.6 MPa, The effects of different parameters on the self-ignition limits were analyzed, In addition, the effects of the combustor's different wall configurations on self-ignition limits were specifically studied. It was found that the wall configurations of the combustor had a significant effect on self-ignition limits, which might have variations of 420-840 K deg in stagnation temperature; however, the local static temperature in the recirculation zones for different wall configurations remained the same at approximately 1100 K, It was found that self-ignition could initiate at the exit of the combustor and this can be considered as a weak self-ignition characteristic.

Effects of Mixing Schemes on Kerosene Combustion in a Supersonic Airstream

A study of kerosene combustion in a supersonic vitiated aire ow at Mach 4.75 e ight enthalpy was conducted in direct-connect tests at Mach 1.8 at a stagnation temperature of 1000 K. The effects of shockand vortex-enhanced mixing mechanisms on the combustion efe ciency were evaluated. Also included in this study were the effects of fuel heating and jet penetration. The experimental conditions corresponded to the low end of the hypersonic e ight regime. The following geometric cone gurations were employed: 1) a generic, rearward-facing step, 2 ) a modie ed rearward-facing step with beveled edges to facilitate vortex-enhanced mixing, and 3 ) a rearward-facing wedge (15 or 30 deg) placed downstream of the rearward-facing step to induce shock-enhanced mixing. In all cone gurations, a gaseous hydrogen ‐ pilot jet was injected parallel to the main e ow from the base of the rearward-facing step and the liquid kerosene was injected normal to the main e ow at three or e ve step heights downstream of the step (the step height was 10 mm). Stable kerosene combustion was obtained for a maximum injected kerosene equivalence ratio of 0.86. For efe ciency evaluation, the pilot ‐ hydrogen equivalence ratio was selected between 0.02 ‐ 0.04, while the kerosene equivalence ratio was maintained at 0.325. In all experiments, locally rich stratie ed kerosene combustion took place in a layer close to the injection wall. The wedge e ameholder contributed to an increased kerosene combustion efe ciency by the generation of shock ‐ jet interactions. The beveled-edge step improved far-e eld mixing, thereby reducing the local kerosene equivalence ratio, resulting in the highest kerosene combustion efe ciency among all cone gurations tested. Fuel heating below levels required for e ash vaporization (one-third of the e ash vaporization energy, in this case ) did not contribute to increased combustion efe ciency. On the contrary, this level of heating reduced the fuel density with adverse effects on penetration and mixing.