Showing papers on "Nozzle published in 2013"

Large-eddy simulation of highly underexpanded transient gas jets

Abstract: Large-eddy simulations (LES) based on scale-selective implicit filtering are carried out in order to study the effect of nozzle pressure ratios on the characteristics of highly underexpanded jets. Pressure ratios ranging from 4.5 to 8.5 with Reynolds numbers of the order 75 000–140 000 are considered. The studied configuration agrees well with the classical picture of the structure of highly underexpanded jets. Similarities and differences between simulation and experiments are discussed by comparing the concentration field structures from LES and planar laser induced fluorescence data. The transient stages, leading eventually to the highly underexpanded state, are visualized and investigated in terms of a phase diagram revealing the shock speeds and duration of the transient stages. For the studied nozzle pressure ratio range, the Mach disk dimensions are found to be in good agreement with literature data and experimental observations. It is observed how the nozzle pressure ratio influences the Mach disk width, and thereby the slip line separation, which leads to co-annular jets with inner and outer shear layers at higher pressure ratios. The improved mixing with increasing pressure ratio is demonstrated by the probability density functions of the concentration. The coherent structures downstream of the Mach disk are identified using proper orthogonal decomposition (POD). The structures indicate a helical mode originating from the shear layers of the jet. Despite the relatively low energy content of the dominant POD modes, the frequencies of the POD time coefficients explain the dominant frequencies in the pressure fluctuation spectra.

Solution of the quasi-one-dimensional linearized Euler equations using flow invariants and the Magnus expansion

Abstract: The acoustic and entropy transfer functions of quasi-one-dimensional nozzles are studied analytically for both subsonic and choked flows with and without shock waves. The present analytical study extends both the compact nozzle solution obtained by Marble & Candel (J. Sound Vib., vol. 55, 1977, pp. 225–243) and the effective nozzle length proposed by Stow, Dowling & Hynes (J. Fluid Mech., vol. 467, 2002, pp. 215–239) and by Goh & Morgans (J. Sound Vib., vol. 330, 2011, pp. 5184–5198) to non-zero frequencies for both modulus and phase through an asymptotic expansion of the linearized Euler equations. It also extends the piecewise-linear approximation of the velocity profile in the nozzle proposed by Moase, Brear & Manzie (J. Fluid Mech., vol. 585, 2007, pp. 281–304) to any arbitrary profile or equivalently any nozzle geometry. The equations are written as a function of three variables, namely the dimensionless mass, total temperature and entropy fluctuations, yielding a first-order linear system of differential equations with varying coefficients, which is solved using the Magnus expansion. The solution shows that both the modulus and the phase of the transfer functions of the nozzle have a strong dependence on the frequency. This holds for both choked flows and subsonic converging–diverging nozzles. The method is used to compare two different nozzle geometries with the same inlet and outlet Mach numbers, showing that, even if the compact solution predicts no differences between the transfer functions of the two nozzles, significant differences are found at non-zero frequencies. A parametric study is finally performed to calculate the indirect to direct noise ratio for a model combustor, showing that this ratio decreases at higher frequencies.

Numerical Analysis of Nozzle Material Thermochemical Erosion in Hybrid Rocket Engines

Abstract: Ablative materials are commonly used to protect the nozzle metallic housing and to provide the internal contour to expand the exhaust gases in both solid and hybrid rockets. Because of interaction with hot gas, these materials are chemically eroded during rocket firing, with a resulting nominal performance reduction. The objective of the present work is to study the erosion behavior of graphite nozzles in hybrid engines at different operating conditions and compare results with those obtained for solid motors. A main distinctive feature of hybrid engine operating conditions is, in fact, a greater concentration of oxygen-containing combustion products than solid motors. The adopted approach relies on a validated full Navier–Stokes flow solver coupled with a thermochemical ablation model that takes into account heterogeneous chemical reactions at the nozzle surface, rate of diffusion of the species through the boundary layer, ablation species injection in the boundary layer, heat conduction inside the nozzl...

System for supplying a working fluid to a combustor

Abstract: A system for supplying a working fluid to a combustor includes a fuel nozzle, a combustion chamber 40 downstream from the fuel nozzle, and a flow sleeve 50 that circumferentially surrounds the combustion chamber 40. A plurality of fuel injectors 60 are circumferentially arranged around the flow sleeve 50 to provide fluid communication through the flow sleeve 50 to the combustion chamber 40. A distribution manifold 62 circumferentially surrounds the plurality of fuel injectors 60, and a fluid passage 66 through the flow sleeve 50 and into the distribution manifold 62 provides fluid communication through the flow sleeve 50 to the plurality of fuel injectors 60.

Approaching the theoretical limit of diamagnetic-induced momentum in a rapidly diverging magnetic nozzle.

Abstract: Cross-field diffusion and plasma expansion in a rapidly diverging magnetic nozzle are controlled while maintaining constant plasma production in a contiguously attached radio frequency plasma source. It is demonstrated that the measured electron-diamagnetic-induced axial momentum increases with increasing magnetic field strength to approach the theoretical limit derived using an ideal nozzle approximation. The measured axial momentum exerted onto the axial and radial plasma source boundaries validate the prediction from a maximum electron pressure model on the back wall and from a zero net axial momentum model on the radial wall.

Capsule for beverages

Abstract: A capsule, including: a deformable casing defining a cavity containing an initial product joined to a fluid for making a final product; a nozzle associated with the casing to inject the fluid of a brewing machine, the nozzle having a longitudinal side wall being provided with at least one outflow opening to the cavity, and the nozzle having an end wall provided with a second opening enabling the final product to exit from the cavity.

Process optimization of ultrasonic spray coating of polymer films.

Abstract: In this work we have performed a detailed study of the influence of various parameters on spray coating of polymer films. Our aim is to produce polymer films of uniform thickness (500 nm to 1 μm) and low roughness compared to the film thickness. The coatings are characterized with respect to thickness, roughness (profilometer), and morphology (optical microscopy). Polyvinylpyrrolidone (PVP) is used to do a full factorial design of experiments with selected process parameters such as temperature, distance between spray nozzle and substrate, and speed of the spray nozzle. A mathematical model is developed for statistical analysis which identifies the distance between nozzle and substrate as the most significant parameter. Depending on the drying of the sprayed droplets on the substrate, we define two broad regimes, “dry” and “wet”. The optimum condition of spraying lies in a narrow window between these two regimes, where we obtain a film of desired quality. Both with increasing nozzle-substrate distance and...

The diameter of single, double and triple fluid jet grouting columns: prediction method and field trial results

Abstract: In this paper, a simple expression to predict the average diameter of columns created with single, double and triple fluid jet grouting is proposed considering both the energy of the eroding jet and the resistance of the soil. The injection system (single, double or triple) and the composition of the injected fluids are taken into account on the basis of theoretical analysis of the turbulent diffusion of submerged jets. Instead of separately considering the energy of the air jet shrouding the eroding fluid, a simple parameter is introduced which represents the beneficial effect of air in reducing the energetic dissipation on the jet external surface. In this way, a new expression of the specific kinetic energy of the jet at any distance from the nozzle is proposed, which is a relevant step forward if compared with that at the nozzle or at the pump previously proposed, as it takes into account both the system characteristics and the composition of the eroding jet (either grout or water). In the expression ...

Helicon thruster plasma modeling: Two-dimensional fluid-dynamics and propulsive performances

Abstract: An axisymmetric macroscopic model of the magnetized plasma flow inside the helicon thruster chamber is derived, assuming that the power absorbed from the helicon antenna emission is known. Ionization, confinement, subsonic flows, and production efficiency are discussed in terms of design and operation parameters. Analytical solutions and simple scaling laws for ideal plasma conditions are obtained. The chamber model is then matched with a model of the external magnetic nozzle in order to characterize the whole plasma flow and assess thruster performances. Thermal, electric, and magnetic contributions to thrust are evaluated. The energy balance provides the power conversion between ions and electrons in chamber and nozzle, and the power distribution among beam power, ionization losses, and wall losses. Thruster efficiency is assessed, and the main causes of inefficiency are identified. The thermodynamic behavior of the collisionless electron population in the nozzle is acknowledged to be poorly known and crucial for a complete plasma expansion and good thrust efficiency.

Print head nozzle for use with additive manufacturing system

Abstract: A nozzle (68) for printing three-dimensional parts (52) with an additive manufacturing system (36), the nozzle (68) comprising a nozzle body (78) having an inlet end (80) and a tip end (82) offset longitudinally from the inlet end (80), a tip pipe (86) for extruding a flowable material, an inner ring (90) extending circumferentially around the tip pipe (86) at the outlet end (80), an outer ring (92) extending circumferentially around the inner ring (90), at least one annular recessed groove (94) located circumferentially between the inner ring (90) and the outer ring (92).

Modelling circulation, impulse and kinetic energy of starting jets with non-zero radial velocity

Abstract: The evolution of starting jet circulation, impulse and kinetic energy are derived in terms of kinematics at the entrance boundary of a semi-infinite axisymmetric domain. This analysis is not limited to the case of parallel jet flows; and the effect of non-zero radial velocity is specifically identified. The pressure distribution along the entrance boundary is also derived as it is required for kinetic energy modelling. This is done without reliance on an approximated potential function (i.e. translating flat plate), making it a powerful analytical tool for any axisymmetric jet flow. The pressure model indicates that a non-zero radial velocity is required for any ‘over-pressure’ at the nozzle exit. Jet flows are created from multiple nozzle configurations to validate this model. The jet is illuminated in cross-section, and velocity and vorticity fields are determined using digital particle image velocimetry (DPIV) techniques and circulation, impulse and kinetic energy of the jet are calculated from the DPIV data. A nonzero radial velocity at the entrance boundary has a drastic effect on the final jet. Experimental data showed that a specific configuration resulting in a jet with a converging radial velocity, with a magnitude close to 40 % of the axial velocity at its maximum, attains a final circulation which is 90‐100 % larger than a parallel starting jet with identical volume flux and nozzle diameter, depending on the stroke ratio. The converging jet also attains a final impulse which is 70‐75 % larger than the equivalent parallel jet and a final kinetic energy 105‐135 % larger.

CFD study of a variable area ratio ejector using R600a and R152a refrigerants

Abstract: In the present paper, the numerical results for two 1 kW cooling capacity ejectors with variable primary nozzle geometry are presented using R152a and R600a as working fluids. Working fluids were selected based on the criteria of low environmental impact and good performance in the range of operating conditions adequate for using solar thermal energy as primary heat source. Variable area ratio was achieved by applying a movable spindle at the primary nozzle inlet. Numerical results clearly show that adjusting spindle position resulted in a significant improvement of the entrainment ratio compared to a fixed geometry ejector when the operating conditions were different from design values. This increase in ejector performance was as high as 177% for low condenser pressures. Diagrams are also presented for both refrigerants that can be used to find spindle positions that maximise ejector performance under variable operating conditions.

Comprehensive analysis of laser cladding by means of optical diagnostics and numerical simulation

Abstract: Laser cladding is known as flexible and efficient method for elaboration of diverse protective coatings including functionally graded, multilayered, etc. Robotic laser cladding with coaxial powder injection is often referred to as Direct Metal Deposition (DMD). Development of on-line monitoring and process control, and its integration with DMD machines is a priority task. The objective of the present study is to demonstrate the advantages of comprehensive optical monitoring of DMD technology applying diverse and complementary optical diagnostic tools: pyrometers and infrared camera are applied to measure brightness temperature that is useful to define the shape of molten pool, to control melting/solidification and to avoid thermal decomposition when complex powder blends are used. The CCD-camera based diagnostic tool is useful for a particle-in-flight visualization, for a control of particle jet stability, and for a real-time measurement of particle-in-flight velocity. Numerical simulation of the carrier gas and particle flow in a coaxial nozzle of TRUMPF 505 DMD is carried out. Argon serving as carrier and shielding gas is supplied into an axial and two annular channels of the nozzle. Two-phase jet flowing toward the substrate and particle focusing mechanism are analyzed. Radial distribution of the particle mass flow over the substrate versus conditions of particle collision with nozzle walls is calculated. The developed software is used to analyze peculiarities of the particle heating and melting by the laser beam. This way, trajectories and thermal history are calculated for particles of different size.