Visualization of dilute hydrogen jet flame in air flow

The structure of hydrogen jet flame diluted by CO₂ in air flow is studied by various visualization techniques, such as schlieren, direct photograph, tracer injection and reactive Mie scattering method, which allow understanding of the influence of CO₂ on the characteristics of the hydrogen jet flame. The experimental result indicates that the flame structure consists of laminar fuel jet and surrounding reaction zone near the nozzle exit. When the CO2 fraction is increased, the width of the fuel jet grows and the reaction zone is reduced in size. These observations are further confirmed by quantitative measurements of temperature and velocity fields in the flame, which are evaluated by thermocouple and particle image velocimetry (PIV), respectively. These results indicate that the flame temperature is decreased and the flow rate of the fuel jet is increased by the influence of diluents, which are due to the reduced calorific value and larger density of fuel, respectively.     

Interaction of shock waves with a jet wake during gas injection into supersonic stream

In the present paper, we report the results of an experimental study of the interaction region of a planar compression shock produced by a wedge in stream with the wake formed behind a cocurrent gas jet (H₂, air, or Ar) injected into the flow. Depending on the gas jet parameters, three modes of interaction could be distinguished: a strong interaction, observed when the flow velocity in the wake was subsonic; a moderate interaction, observed when a subsonic flow region, bounded by a shock of almost conical shape, formed in the vicinity of the compression shock; and a neutral interaction. Three-dimensional non-stationary Euler equations were solved to numerically examine the interaction of an axisymmetric jet with an oblique shock wave. The obtained interaction regimes were found to be in a reasonable agreement with experimental data.     

Microwave streamer discharge in a supersonic air flow

Data are presented from experiments on the ignition of a pulsed, triggered microwave streamer discharge at the focus of a cm-band TEM wave in an immersed supersonic air jet. It is shown experimentally that for velocities of the air in the jet up to 500 m/s, the structure of the discharge remains qualitatively unchanged and retains its streamer character. The finite size of the transverse cross section of the jet determines some features of the discharge. Zh. Tekh. Fiz. 69, 14–18 (November 1999)     

Effects of the injector geometry on a sonic jet into a supersonic crossflow

Large-eddy simulation of a sonic injection from circular and elliptic injectors into a supersonic crossflow has been performed.The effects of injector geometry on various fundamental mechanisms dictating the intricate flow phenomena including shock/jet interaction,jet shear layer vortices and their evolution,jet penetration properties and the relevant turbulence behaviors have been studied systematically.As a jet issuing transversely into a supersonic crossflow,salient three-dimensional shock and vortical structures,such as bow,separation and barrel shocks,Mach disk,horseshoe vortex,jet shear layer vortices and vortex pairs,are induced.The shock structures exhibit considerable deformations in the circular injection,while their fluctuation becomes smaller in the elliptic injection.The jet shear layer vortices are generated at the jet periphery and their evolution characteristics are analyzed through tracing the centroid of these coherent structures.It is found that the jet from the elliptic injector spreads rapidly in the spanwise direction but suffers a reduction in the transverse penetration compared to the circular injection case.The turbulent fluctuations are amplified because of the jet/crossflow interaction.The vertical Reynolds normal stress is enhanced in the downstream of the jet because of the upwash velocity induced by the counter-rotating vortex pair.     

Longitudinal DC electric discharge in a supersonic air flow

A longitudinal dc electric discharge in a submerged high-pressure supersonic air jet is described. Photographs of the discharge are provided. The experimental voltage across the discharge gap and the discharge current are given for two resistances of the resistor that limits the discharge current over a certain range of the discharge channel length along the air flow. The current-voltage discharge characteristic is provided at a constant discharge length. The main discharge characteristics are obtained from a comparison of the experimental and theoretical results calculated on the basis of the simplest model.     

超声喷流氩氢混合团簇特性研究

利用瑞利散射方法研究了超声喷流Ar-CH4混合团簇和超声喷流Ar-H2混合团簇的特性.通过测量不同混合比例和不同背压下所形成混合团簇的散射信号发现,当用Ar气和CH4的混合气体进行超声喷流时很容易形成Ar-CH4混合团簇,当Ar气含量为50%时混合团簇尺度最大且大于相同气压下纯Ar团簇尺度和纯CH4团簇尺度.实验发现,与纯H2团簇只能在低温条件下获得不同,常温下即可形成Ar-H2混合团簇,实现了常温下含氢团簇的获取,从而有效降低了制备成本.在H2含量大于40%时混合团簇开始形成并在60%时达到最大尺度.含氢(氘)混合团簇在氢(氘)团簇的基础上引入了更重的异核Ar元素,在激光氘团簇聚变实验中它将进一步加速氘离子从而获得更高的能量,并具有更高的中子产额和聚变效率.     

Visualization of secondary flow choking phenomena in a supersonic air ejector

The present study deals with the visualization of the air flow inside a supersonic ejector. Our attention is more precisely focused on the choked flow phenomenon which occurs along the mixing chamber of the secondary nozzle and which can be visualized by CFD. Laser tomography visualizations are used to validate the CFD model. The evolution of flow configuration in the ejector with the primary stagnation pressure is examined both in the case of zero secondary flow and in the case of free entrainment of induced air.     

Effect of high temperatures on the combustion of hydrogen in a supersonic flow

The results of experiments on studying the effect of temperature on the character of burnout and emission characteristics of a hydrogen flow symmetrically injected into a supersonic air flow are presented. The combustion of hydrogen in the supersonic flow at 1500–3000 K is demonstrated to be affected by dissociation and recombination. This manifests itself through an increase in the OH emission intensity by 40% upon 1.5–2.0-fold temperature rise starting from 1500 K.     

Deeply undercritical microwave discharge excited by the field of a quasi-optical electromagnetic beam in a supersonic air jet

Electric discharge in a supersonic air jet is studied. It is ignited in a linearly polarized quasi-optical microwave electromagnetic beam the initial field intensity of which is much lower than the breakdown level. Electric breakdown is initiated by a tubular electromagnetic vibrator, one end of which has spikes and is covered by a quartz tube. Atmospheric air enters into a low-pressure working chamber through the inner channel of the vibrator. As a result, an immersed supersonic air jet forms in the chamber at the outlet from the quartz tube. A microwave discharge ignited in this jet is “attached” to aft spikes of the vibrator. The energy deposit into the discharge plasma and the effective area of energy interaction between the discharge and excited microwave field are estimated from the temperature and stagnation pressure distributions in the wake of the discharge.     

Combustion characteristics in a supersonic combustor with hydrogen injection upstream of cavity flameholder

Combustion characteristics in a supersonic combustor with hydrogen injection upstream of a cavity flameholder were investigated both experimentally and numerically. The combustion was observed to be stabilized in the cavity mode around the shear layer via a dynamic balance and then spread into the main stream in the region around the jet centerplane where the flow was decelerated and turned to the main stream, supplying a favorable condition for the combustion to spread. The combustion spreading from the cavity shear layer to the main stream seemed to be dominated not only by the traditional diffusion process but also by the convection process associated with the extended recirculation flows resulting from the heat release and the interaction between the jet and the cavity shear layer. Therefore, the cavity-stabilized combustion appeared to be a strongly coupled process of flow and heat release around the cavity flameholder.     

Regularities of the interaction of hydrogen jets during combustion in a supersonic high-temperature flow

The efficiency of combustion in a supersonic high-temperature flow at spread and local hydrogen feed is considered. Similarities and distinctions of combustion in open and confined space were examined with consideration given to the effect of gasdynamic structures typical of supersonic air jets.     

Gas flow from a supersonic nozzle with screen into vacuum

The backflow formation under gas outflow from the supersonic nozzle into vacuum was studied in detail both experimentally and numerically. Possibilities of backflow control (minimization) by using the gas-dynamic protective devices (screens) mounted at the nozzle outlet were discussed. It was shown that certain screen configurations can increase the backflow instead of decreasing it.     

Numerical simulations of shock-wave interaction with a boundary layer in the plane supersonic flows with jet injection

A supersonic air flow in a plane channel with a transverse turbulent jet of hydrogen injected through a slot on the bottom wall is simulated. The algorithm for solving the Favre-averaged Navier-Stokes equations for the flow of a perfect multispecies gas on the basis of the WENO scheme is proposed. The main attention is paid to the interaction of the shock-wave structure with the boundary layers on the upper and lower duct walls under the conditions of an internal turbulent flow. Namely, a detailed study of the structure of the flow is done, and separation and mixing depending on the jet slot width are investigated. It is found that in addition to well-known shock-wave structures produced by the interaction of the free stream with the transverse jet and the bow shock interaction with the boundary layers near the walls, an additional system of shock waves and the flow separation arise on the bottom wall downstream at some distance from the jet. The comparison with the experimental data is performed.     

Numerical simulation of an energy deposition zone in quiescent air and in a supersonic flow under the conditions of interaction with a normal shock

The potential of using the Euler equations to numerically simulate the evolution of localized energy deposition zones interacting with a normal shock in quiescent air and in a supersonic channel flow is demonstrated. Simulation results are compared with available experimental data for an optical discharge in quiescent air and with results calculated for a supersonic flow using the Navier-Stokes equations with allowance for real gas effects. The possibility of predicting gasdynamic effects using the T- and q-models of energy deposition for perfect gas is justified. The variation of the gasdynamic structure and flow parameters near an energy deposition zone developing in a quiescent medium and interacting with a normal shock is analyzed in detail for different energy deposition powers.     

A PIV study of a supersonic impinging jet

The characteristics of supersonic impinging jets are investigated using Particle Image Velocimetry (PIV). The purpose of the experiments is to understand the jet induced forces on STOVL aircraft while hovering close to the ground. For this purpose, a large diameter circular plate was attached at the nozzle exit. The oscillations of the impinging jet generated due to a feedback loop are captured in the PIV images. The instantaneous velocity field measurements are used to describe flow characteristics of the impinging jet. The important flow features such as oscillating shock waves, slipstream shear layers and large scale structures are captured clearly by the PIV. The presence of large scale structures in the impinging jet induced high entrainment velocity in the near hydrodynamic field, which resulted in lift plate suction pressures. A passive control device is used to interfere with the acoustic waves travelling in the ambient medium to suppress the feedback loop. As a consequence, the large scale vortical structures disappeared completely leading to a corresponding reduction in the entrainment.     

Stereoscopic PIV measurements of a screeching supersonic jet

The effect of acoustic feed back on global flow response is illustrated through an example of a rectangular screeching jet operating at a nominal Mach number of 1.69. Using a stereoscopic Particle Image Velocimetry, the detailed flow characteristics within a screeching cycle are obtained with fidelity. To resolve the “bias” errors inherent with standard PIV image processing technique, a novel mesh-free and high spatial resolution scheme is implemented to yield accurate velocity measurements in a complex three-dimensional supersonic flow. The axis-switching phenomenon that arises due to unusual mixing enhancement in the minor axis plane of a rectangular jet is vividly displayed. Strong streamwise vortex structure in the jet shear layers, enhanced by the inherent instability of the shear layer, is reported.     

Implementation of air injection into the turbulent boundary layer of aircraft wing using external pressurized flow

The possibility of using the injection of air into the incompressible turbulent boundary layer of an axisymmetric wing through a finely perforated area provided on the wing surface was studied. The air blowing was implemented via the supply of external pressurized flow through a permeable leading edge of the wing. It is shown that, with the blowing section located on the “flat” side of the wing, only an insignificant reduction in airfoil drag could be achieved. Simultaneously, the data obtained show that there exists a possibility of raising the lift-drag ratio due to a more appropriate choice of blowing-section location in the rarefaction region of the flow.