Nozzle Divergence Research Articles

Two-dimensional quasi-double-layers in two-electron-temperature, current-free plasmas

The expansion of a plasma with two disparate electron populations into vacuum and channeled by a divergent magnetic nozzle is analyzed with an axisymmetric model. The purpose is to study the formation and two-dimensional shape of a current-free double-layer in the case when the electric potential steepening can still be treated within the quasineutral approximation. The properties of this quasi-double-layer are investigated in terms of the relative fraction of the high-energy electron population, its radial distribution when injected into the nozzle, and the geometry and intensity of the applied magnetic field. The two-dimensional double layer presents a curved shape, which is dependent on the natural curvature of the equipotential lines in a magnetically expanded plasma and the particular radial distribution of high-energy electrons at injection. The double layer curvature increases the higher the nozzle divergence is, the lower the magnetic strength is, and the more peripherally hot electrons are injected. A central application of the study is the operation of a helicon plasma thruster in space. To this respect, it is shown that the curvature of the double layer does not increment the thrust, it does not modify appreciably the downstream divergence of the plasma beam, but it increases the magnetic-to-pressure thrust ratio. The present study does not attempt to cover current-free double layers involving plasmas with multiple populations of positive ions.

Aerodynamics Numerical Study on Vapor Flowing of the Oil Booster Pump

The pumping power of oil booster pump is the vapor jet stream that determined pump performance. The key importance is the study of vapor flowing characteristics, and also is the method of improvement pump structure and saving energy. The aerodynamics is adopted to study the oil vapor flowing characteristics. The study shows that it should adopted the higher oil boiler pressure in order to increase the density of the oil vapor, and so it can be benefit to pumping gas in 1Pa—10Pa. The nozzle divergence angle and divergence rate also should be increased in order to increase the oil vapor velocity and kinetic energy, and so increased the pumping rate on 0.1Pa. Increasing divergence angle and divergence rate of the first nozzle at constant compression ratio, the upper bottom of jet stream can be moved up, and the eject stream thickness was increased. In other word, increasing the compression ratio at constant eject stream thickness, the oulett pressure was increased. When the pump was operated at higher pressure, it should be decreased compression ratio of first stage. The main pump body was also designed to prominence chamber in order to increase the pumping rate.

The optimization of rough surface supersonic nozzles

In this work, a theoretical optimization study of compressible gases adiabatic flows was conducted for conical nozzles with internal rough surface. A mathematical model was developed for allowing the determination of thrust accounting for nozzle friction and divergence losses. In the first part of the study, it is shown that in rough surface nozzles there are critical values of the nozzle opening half angle, under which, additional increase in gas velocity is not obtained. It is also observed that the minimum nozzle opening half angle value increases as the flow velocity and the nozzle internal surface roughness increase. In the second part of the study, it is shown that there are optimal values of nozzle opening half angle for minimum hydraulic loss across the nozzle, for each combination of the hydraulic resistance caused by the internal surface roughness and the nozzle outlet cross sectional area.

Simulation of interference effects in particle streams following impact with a flat surface: Part II. Parametric study and implications for erosion testing and blast cleaning

In a companion paper [Simulation of interference effects in particle streams following impact with a flat surface. Part I. Theory and analysis, submitted for publication], a computer simulation capable of describing the interference between an incident stream of spheres and those rebounding from a flat surface was presented. In the present paper, the model is used to study the effect of the following parameters on the severity of inter-particle collisions: stream angle of incidence, nozzle divergence angle, incident particle velocity, particle size, particle flux, particle–particle and particle–surface impact parameters, and standoff distance. Useful dimensionless parameters are identified and their significance is characterised using a sensitivity analysis. A detailed parametric study of the most important input parameters revealed that interference effects strongly depend not only on flux, but also on angle of attack, standoff distance, coefficient of restitution between particle and surface, and nozzle to particle radius ratio. It is thus important that a full description of experimental conditions in erosion tests be given. Finally, a series of non-dimensional results was presented that can be used to assess the reduction, due to interference effects, in stream power from that available at the nozzle exit. This can be used to estimate how coverage in shot peening, and erosive power in erosion testing, will be affected by interference effects.

Simulation of interference effects in particle streams following impact with a flat surface: Part I. Theory and analysis

The interference between an incident stream of spheres and those rebounding from a flat surface is described using a computer model. The model was capable of examining the effect of the following parameters on the severity and frequency of inter-particle collisions: stream angle of incidence, nozzle divergence angle, incident particle velocity and flux, particle size, particle–particle and particle–surface impact parameters, and stand-off distance. The collision dynamics for systems consisting in excess of 10 4 particles were obtained. Frictionless inter-particle collisions were assumed, but friction for particles impacting the surface was considered. For all collisions, a coefficient of restitution model of impact behaviour was assumed. Dimensionless parameters used to aid in the presentation of the results were identified, and a companion paper [Simulation of interference effects in particle streams following impact with a flat surface. Part II. Parametric study and implications for erosion testing and blast cleaning, submitted for publication] presents a parametric study of their role in erosion testing and blast cleaning processes.

Thrust-Vectoring Nozzle Performance Modeling

A polytropic analytical equation system for the internal flow of nozzles, inlets, and ducts has been developed through an analysis of the compressible flow equations including the friction and area change driving potentials. These equations are verified through comparison with experimental data and numerical simulations using FLUENT 5.0. The nozzle performance predictions include consideration of the nozzle divergence and surface roughness. It is demonstrated that the analytical model well matches the experimental data after the throat is fully choked. The numerical and analytical results are compared and discussed. Such an analytical model is extremely useful in bridging the gap between accepted empirical parameters such as the friction factor, performance coefficients, and analytical performance modeling. Furthermore, it provides the first analytical model for thrust-vectoring nozzle performance predictions. In aircraft nozzle simulations where empirical data may not be available, this model provides good simulation capability.

Nozzle Performance Modeling

A polytropic analytical equation system for the internal e ow of nozzles and ducts has been developed by a solution to the combined friction/area change compressible e ow equations. Validation of the system is sought through comparison with experimental data and numerical simulations using FLUENT in the prediction of the performances of two conventional axisymmetric nozzles. Analytical performance coefe cient equations have been developed from the polytropic equation system for this purpose. The predictions with consideration of nozzle divergence angle and roughness are presented for the e rst time. It is demonstrated that the analytical model well matches the experimental data after the throat is fully choked. The numerical and analytical results are compared and discussed. Such an analytical model is extremely useful in bridging the gap between accepted empirical parameters, such as the friction factor and performance factors, and analytical performance modeling. In aircraft nozzle simulations, where empirical data may not be available, this model provides more precise simulation capability especially applicable to modern thrust-vectoring nozzles.

Numerical and Experimental Investigations of Supersonic Jets from Sootblower Nozzle.

The present paper describes the numerical as well as the experimental study on the axisymmetric supersonic jet associated with a sootblower nozzle for boiler cleaning. The navier-Stokes equations are solved numerically, and the experimental work is also performed with the low-density wind tunnel. Calculations and experiments both cover the region from the nozzle exit to the downstream distance of 20 times the nozzle exit diameter. The effect of the nozzle divergence angle is discussed by comparing the experiments with calculations, and it is pointed out that, even when the expansion ratio across the nozzle is correct, the regular shock-cell structure appears in the jet for the nozzles with finite divergence angles. Also, the present numerical results on the impact pressures along the jet center-line agree favorably well with those reported by the other researchers.

Parallel electron temperature and density gradients measured in the JET MkI divertor using thermal helium beams

This paper describes the first application of a thermal helium beam diagnostic to a divertor. The helium beam is used to determine spectroscopically the electron temperature and density from the inner and outer strike points up to the X-point, using helium line ratios which are primarily sensitive to electron density and temperature, as reported by Schweer et al. [J. Nucl. Mater. 196–198 (1992) 174]. Measurement of the neutral helium line intensities in the outer divertor target were performed under attached, high recycling and detached plasma conditions in Ohmic and L-mode discharges. An interpretative model has been developed using the DIVIMP code at JET which incorporates the helium injection point, the nozzle divergence and the viewing arrangement of the periscope for a particular equilibrium.

Implementation of a regional pediatric trauma center

This paper describes the first application of a thermal helium beam diagnostic to a divertor. The helium beam is used to determine spectroscopically the electron temperature and density from the inner and outer strike points up to the X-point, using helium line ratios which are primarily sensitive to electron density and temperature, as reported by Schweer et al. [J. Nucl. Mater. 196–198 (1992) 174]. Measurement of the neutral helium line intensities in the outer divertor target were performed under attached, high recycling and detached plasma conditions in Ohmic and L-mode discharges. An interpretative model has been developed using the DIVIMP code at JET which incorporates the helium injection point, the nozzle divergence and the viewing arrangement of the periscope for a particular equilibrium.

Numerical Calculation of Underexpanded Axisymmetric Supersonic Jet. Effects of Nozzle Divergence Angle and Mach Number on Shock Cell Length.

A numerical study of underexpanded axisymmetric supersonic jets is presented. The TVD finite-difference scheme is employed for the numerical calculation of Euler's equations. The numerical results are compared both with results from the theoretical shock cell spacing formula suggested by Tam and with previous experimental results. For nozzles having no divergence angle at the nozzle exit, a good agreement is obtained among the theoretical, experimental and numerical results for pressure ratios across the nozzle until the occurrence of a Mach disk in the jet. For nozzles having a divergence angle at the nozzle exit, the effects of the divergence angle, the nozzle design Mach number and the pressure ratio across the nozzle on the shock cell length are discussed and clarified.

Flow and acoustic features of a supersonic tapered nozzle

The acoustic and flow characteristics of a supersonic tapered jet were measured for free and shrouded flow configurations. Measurements were performed for a full range of pressure ratios including over- and underexpanded and design conditions. The supersonic tapered jet is issued from a converging-diverging nozzle with a 3∶1 rectangular slotted throat and a conical diverging section leading to a circular exit. The jet was compared to circular and rectangular supersonic jets operating at identical conditions. The distinct feature of the jet is the absence of screech tones in the entire range of operation. Its near-field pressure fluctuations have a wide band spectrum in the entire range of measurements, for Mach numbers of 1 to 2.5, for over- and underexpanded conditions. The free jet's spreading rate is nearly constant and similar to the rectangular jet, and in a shroud, the pressure drop it is inducing is linearly proportional to the primary jet Mach number. This behavior persisted in high adverse pressure gradients at overexpanded conditions, and with nozzle divergence angles of up to 35°, no inside flow separation was observed.

Structure of self-field accelerated plasma flows

An analysis is presented of self-field accelerated quasi-one-dimensional plasma flows with zero axial current. When magnetic convection dominates over magnetic diffusion (large magnetic Reynolds number inlet and exit current concentration layers occur, which are analyzed by asymptotic methods to zeroth order in l/Rm. Sonic passage is found in the inlet layer, which largely determines injector conditions. Near magnetosonic conditions prevail at throats or constant-area sections. Performance factors accounting for inlet convergence and nozzle divergence are derived by exploiting the smallness of pressure forces. The effect of finite magnetic Reynolds numbers is seen to be moderate down to Rm 3 for contoured channels, but to Rm s 10 for constant-area channels. Contouring is shown to be effective for control of current and dissipation concentrations.

Some Experiments on Flow Separation in Rocket Nozzles

Flow separation in de Laval nozzles has been investigated experimentally over a range of divergence angles and reservoir pressures us ing compressed air as a working fluid. The results indicate that the onset of separation in such nozzles is governed primarily by the reservoir pressure and the nozzle divergence angle. However, no quantitat ive treatment has been evolved to unify all the existing experimenta l data. Further experimental work, or a more sophisticated interpretation of available facts, is needed to establish a theory for predicting the plane of separation for a nozzle of given geometry operated under specified condit ions.