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Atmospheric air, being also a moist gas, is present as a working medium in various areas of technology, including the areas of airframe aerodynamics and turbomachinery. Issues related to the condensation of water vapor contained in atmospheric air have been intensively studied analytically, experimentally and numerically since the 1950s. An effort is made in this paper to present new, unique and complementary results of the experimental testing of moist air expansion in the de Laval nozzle. The results of the measurements, apart from the static pressure distribution on the nozzle wall and the images obtained using the Schlieren technique, additionally contain information regarding the quantity and quality of the condensate formed due to spontaneous condensation at the transition from the subsonic to the supersonic flow in the nozzle. The liquid phase was identified using the light extinction method (LEM). The experiments were performed for three geometries of convergent–divergent nozzles with different expansion rates of 3000, 2500 and 2000 s−1. It is shown that as the expansion rate increases, the phenomenon of water vapor spontaneous condensation appears closer to the critical cross-section of the nozzle. A study was performed of the impact of the air relative humidity and pollution on the process of condensation of the water vapor contained in the air. As indicated by the results, both these parameters have a significant effect on the flow field and the pressure distribution in the nozzle. The results of the experimental analyses show that in the case of the atmospheric air flow, in addition to the pressure, temperature and velocity, other parameters must also be taken into account as boundary parameters for possible numerical analyses. Omitting information about the air humidity and pollution can lead to incorrect results in numerical simulations of transonic flows of atmospheric air. The presented results of the measurements of the moist air transonic flow field are original and fill the research gap in the field of experimental studies on the phenomenon of water vapor spontaneous condensation. [ABSTRACT FROM AUTHOR]

An experimental study is conducted to determine the effect of chevrons with zero penetration angles at the CD nozzle exit on an emitted noise field. The implication of passive control is to reduce the blockage of the nozzle exit area with minimal engine thrust penalty. The cold air jets issued at design Mach numbers 1.5 and 1.75 from the De Laval nozzles of the circular section were investigated. This passive control eliminates screech tones at the over and ideally expanded conditions at 60° and 90° in the azimuth plane. The acoustic data measurements have also been observed for the chosen jet Mach numbers. The schlieren images reveal the shock cell pattern to eliminate the effect of shock-associated noise levels at supersonic jets. The results show that 10 chevrons with no penetration act as an effective eliminator of screech tone and noise suppression average ∆OASPL value up to 3 dB at Mach number 1.75. [ABSTRACT FROM AUTHOR]

Atmospheric air, being also a moist gas, is present as a working medium in various areas of technology, including the areas of airframe aerodynamics and turbomachinery. Issues related to the condensation of water vapor contained in atmospheric air have been intensively studied analytically, experimentally and numerically since the 1950s. An effort is made in this paper to present new, unique and complementary results of the experimental testing of moist air expansion in the de Laval nozzle. The results of the measurements, apart from the static pressure distribution on the nozzle wall and the images obtained using the Schlieren technique, additionally contain information regarding the quantity and quality of the condensate formed due to spontaneous condensation at the transition from the subsonic to the supersonic flow in the nozzle. The liquid phase was identified using the light extinction method (LEM). The experiments were performed for three geometries of convergent–divergent nozzles with different expansion rates of 3000, 2500 and 2000 s−1. It is shown that as the expansion rate increases, the phenomenon of water vapor spontaneous condensation appears closer to the critical cross-section of the nozzle. A study was performed of the impact of the air relative humidity and pollution on the process of condensation of the water vapor contained in the air. As indicated by the results, both these parameters have a significant effect on the flow field and the pressure distribution in the nozzle. The results of the experimental analyses show that in the case of the atmospheric air flow, in addition to the pressure, temperature and velocity, other parameters must also be taken into account as boundary parameters for possible numerical analyses. Omitting information about the air humidity and pollution can lead to incorrect results in numerical simulations of transonic flows of atmospheric air. The presented results of the measurements of the moist air transonic flow field are original and fill the research gap in the field of experimental studies on the phenomenon of water vapor spontaneous condensation.

For coating deposition and additive manufacturing by cold spray, supersonic de Laval nozzles are traditionally used. The application of other configurations of the prechamber-nozzle units allows for the expansion of the technological capabilities of cold spray. In particular, the use of an ejector nozzle allows utilizing an open-type powder feeder, which does not require maintaining high pressure inside itself. In the present paper, for the first time, the possibility of application of the ejector nozzle under high-pressure cold spray conditions was investigated. A comparative analysis of the main characteristics of copper coatings deposited on aluminum alloy substrates using both the ejector and de Laval nozzles was also performed. It was demonstrated that the coatings obtained using the ejector nozzle are characterized by lower thickness, higher porosity, and similar microhardness as compared to the coatings obtained using de Laval nozzle. This development can be in demand in cases where the use of an open-type powder feeder is necessary to ensure technological simplicity of the cold spraying process. [ABSTRACT FROM AUTHOR]

The study gives a general overview of the CFD-simulated gas flow via the nozzle of a De Laval rocket engine. In CFD software, the mesh is generated using the nozzle’s geometry. In this work, CFD methods are used to compare a number of factors with those derived from classical theory, such as pressure, velocity, temperature, and arear ratios. The results of computational modelling of CFD simulation are comparable to those found from theoretical calculations.

A family of axisymmetric Laval nozzles with a central cylindrical part is considered. The nozzle diffuser with relatively small dimensions ensures stable detonation combustion of kerosene vapor behind an inclined shock front that forms before entering the combustion chamber without auxiliary initiating structures and additional energy supply. Modeling is carried out based on the two-dimensional unsteady Euler equations of motion for axisymmetric flows of a multicomponent gas and a simplified kinetic scheme of chemical transformations. The calculations are performed using a modified numerical scheme by S.K. Godunov of the second order of accuracy in spatial variables. It is shown that effective detonation combustion occurs on the impact of the initiating shock front on the wall of the combustion chamber in the immediate vicinity of the corner point of conjugation with the diffuser. The parameters of a number of nozzles are determined, in which the detonation combustion of kerosene vapor provides high power characteristics with an efficiency of more than 40% in atmospheric air at an altitude of about 40 km at a flight Mach number of M0 = 9. [ABSTRACT FROM AUTHOR]

Laser spectroscopic studies of elements in the heavy actinide and transactinide region help understand the nuclear ground state properties of these heavy systems. Pioneering experiments at GSI, Darmstadt identified the first atomic transitions in the element nobelium. For the purpose of determining nuclear properties in nobelium isotopes with higher precision, a new apparatus for high-resolution laser spectroscopy in a gas-jet called JetRIS is under development. To determine the spectral resolution and the homogeneity of the gas-jet, the laser-induced fluorescence of 164Dy atoms seeded in the jet was studied. Different hypersonic nozzles were investigated for their performance in spectral resolution and efficiency. Under optimal conditions, a spectral linewidth of about 200–250 MHz full width at half maximum and a Mach number of about 7 was achieved, which was evaluated in context of the density profile of the atoms in the gas-jet. [ABSTRACT FROM AUTHOR]

Supersonic gas–solid separation is a new dedusting concept, in which a de Laval nozzle is employed to accelerate a gas laden with solid particles to supersonic speeds. In the present work, a correction for the curved nature of the nozzle walls is implemented in the turbulent boundary layer model. A gas-particle coupled quasi-one-dimensional flow model is established based on an Eulerian–Lagrangian method. Combining the flux vector splitting of gas-phase equations, fifth-order weighted essentially non-oscillatory spatial discretization, and three-step third-order total variation diminishing Runge–Kutta time marching, we create a set of uniformly high-order accurate, stable, and efficient numerical methods. The validation against previous experiments demonstrates the validity and accuracy of the numerical model. The dependence of the flow fields on parameters including particle size and mass loading, nozzle inlet stagnation temperature and pressure, and nozzle expansion angle is numerically computed and analyzed. The results show that the decrease in particle size or mass loading and the increase in inlet stagnation temperature, pressure, or nozzle expansion angle facilitate an increase in exit particle velocity. The increase in particle size, inlet stagnation pressure, or nozzle expansion angle and the decrease in particle mass loading or inlet stagnation temperature increase the exit gas Mach number. In the current parametric study, particle size and mass loading have the largest effects on exit particle velocity and exit gas Mach number, respectively. [ABSTRACT FROM AUTHOR]

We report on the study of ultrafast laser-induced plasma expansion dynamics in a gas microjet. To this purpose, we focused femtosecond laser pulses on a nitrogen jet produced through a homemade De Laval micronozzle. The laser excitation led to plasma generation with a characteristic spectral line emission at 391 nm. By following the emitted signal with a detection system based on an intensified charge-coupled device (ICCD) we captured the two-dimensional spatial evolution of the photo-excited nitrogen ions with a temporal resolution on the nanosecond time scale. We fabricated the micronozzle on a fused silica substrate by femtosecond laser micromachining. This technique enabled high accuracy and three-dimensional capabilities, thus, providing an ideal platform for developing glass-based microfluidic structures for application to plasma physics and ultrafast spectroscopy. [ABSTRACT FROM AUTHOR]

In this paper, we propose asymptotic expansions for the velocity potential and obtain asymptotic equations of gas dynamics for irrotational isentropic flows of an ideal gas: an equation of linear theory, a nonlinear equation for supersonic flows, and a nonlinear transonic equation. We construct some exact particular solutions for the asymptotic nonlinear transonic equation, which takes into account transverse perturbations. Based on a linear asymptotic equation, we examine the dynamic stability of an elastic deformable element of a channel at a subsonic flow rate of a gas or liquid. The study of stability is carried out in a statement corresponding to small perturbations of a homogeneous flow and small deformations of an elastic element, and is based on the construction of a positive definite functional. Sufficient stability conditions are obtained. [ABSTRACT FROM AUTHOR]

In high-speed fluid dynamics, base pressure controls find many engineering applications, such as in the automobile and defense industries. Several studies have been reported on flow control with sudden expansion duct. Passive control was found to be more beneficial in the last four decades and is used in devices such as cavities, ribs, aerospikes, etc., but these need additional control mechanics and objects to control the flow. Therefore, in the last two decades, the active control method has been used via a microjet controller at the base region of the suddenly expanded duct of the convergent–divergent (CD) nozzle to control the flow, which was found to be a cost-efficient and energy-saving method. Hence, in this paper, a systemic literature review is conducted to investigate the research gap by reviewing the exhaustive work on the active control of high-speed aerodynamic flows from the nozzle as the major focus. Additionally, a basic idea about the nozzle and its configuration is discussed, and the passive control method for the control of flow, jet and noise are represented in order to investigate the existing contributions in supersonic speed applications. A critical review of the last two decades considering the challenges and limitations in this field is expressed. As a contribution, some major and minor gaps are introduced, and we plot the research trends in this field. As a result, this review can serve as guidance and an opportunity for scholars who want to use an active control approach via microjets for supersonic flow problems. [ABSTRACT FROM AUTHOR]

Laser spectroscopic studies of elements in the heavy actinide and transactinide region help understand the nuclear ground state properties of these heavy systems. Pioneering experiments at GSI, Darmstadt identified the first atomic transitions in the element nobelium. For the purpose of determining nuclear properties in nobelium isotopes with higher precision, a new apparatus for high-resolution laser spectroscopy in a gas-jet called JetRIS is under development. To determine the spectral resolution and the homogeneity of the gas-jet, the laser-induced fluorescence of 164Dy atoms seeded in the jet was studied. Different hypersonic nozzles were investigated for their performance in spectral resolution and efficiency. Under optimal conditions, a spectral linewidth of about 200–250 MHz full width at half maximum and a Mach number of about 7 was achieved, which was evaluated in context of the density profile of the atoms in the gas-jet.

We report on the study of ultrafast laser-induced plasma expansion dynamics in a gas microjet. To this purpose, we focused femtosecond laser pulses on a nitrogen jet produced through a homemade De Laval micronozzle. The laser excitation led to plasma generation with a characteristic spectral line emission at 391 nm. By following the emitted signal with a detection system based on an intensified charge-coupled device (ICCD) we captured the two-dimensional spatial evolution of the photo-excited nitrogen ions with a temporal resolution on the nanosecond time scale. We fabricated the micronozzle on a fused silica substrate by femtosecond laser micromachining. This technique enabled high accuracy and three-dimensional capabilities, thus, providing an ideal platform for developing glass-based microfluidic structures for application to plasma physics and ultrafast spectroscopy.

The article presents the results of theoretical studies to determine the A/A1(x) function with respect to changes in the flow area of bypass and ball valves of a P40/75 distributor. The optimal shape of the bore of the ball and conoidal valves is analyzed and validated. A theoretical study was performed on the process of landing a ball valve in the seat in terms of the probability of abrasive particles falling between them; the article presents the results of a technical solution to develop a wear-resistant ball valve assembly design using carbide metal ceramics. [ABSTRACT FROM AUTHOR]

In high-speed fluid dynamics, base pressure controls find many engineering applications, such as in the automobile and defense industries. Several studies have been reported on flow control with sudden expansion duct. Passive control was found to be more beneficial in the last four decades and is used in devices such as cavities, ribs, aerospikes, etc., but these need additional control mechanics and objects to control the flow. Therefore, in the last two decades, the active control method has been used via a microjet controller at the base region of the suddenly expanded duct of the convergent–divergent (CD) nozzle to control the flow, which was found to be a cost-efficient and energy-saving method. Hence, in this paper, a systemic literature review is conducted to investigate the research gap by reviewing the exhaustive work on the active control of high-speed aerodynamic flows from the nozzle as the major focus. Additionally, a basic idea about the nozzle and its configuration is discussed, and the passive control method for the control of flow, jet and noise are represented in order to investigate the existing contributions in supersonic speed applications. A critical review of the last two decades considering the challenges and limitations in this field is expressed. As a contribution, some major and minor gaps are introduced, and we plot the research trends in this field. As a result, this review can serve as guidance and an opportunity for scholars who want to use an active control approach via microjets for supersonic flow problems.

Development of a supersonic nozzle with a rectangular cross section for a scramjet model combustor was performed and verified experimentally and numerically. The newly-proposed combined design methodology is easier to use than the other design methodologies when the nozzle exit geometry is the constraint condition because it can get information about the displacement thickness before determining the supersonic nozzle contour. The velocity profile of the numerical simulation and that of LDV measurements are quantitatively in good agreement, which meant that the numerical simulations performed in the present study could quantitatively evaluate the flowfield in the supersonic nozzle and the isolator developed in the present study. The designed supersonic nozzle showed good uniformity of the Mach number and stream angle in the mainstream region at the nozzle exit. Also, the average Mach number in the mainstream region at the nozzle exit plane showed very good agreement with the design Mach number. The influence of airstream total temperature on the Mach number distribution and stream angle distribution in the mainstream region was investigated numerically and was acceptably small, which means that the supersonic nozzle designed in this study can create approximately equivalent supersonic flow in the range of airstream total temperature 300 K - 800 K. Additionally, The mainstream region was found to have a trapezoidal shape with the upper side as the short side and the lower side as the long side. This trapezoidal shape is considered to be caused by the pressure gradient along the side wall, indicating that it is difficult to prevent the mainstream region from growing to trapezoidal shape in case of two dimensional supersonic nozzle with a single contour wall.

Low Pressure Cold Spray process is a relatively new additive technique allowing to create high quality metallic coatings, through the high velocity spraying of particles, on both metallic and non-metallic substrates. The adhesion mechanism of the particles is, to date, not fully understood and the phenomena occurring during long depositions (which are the more interesting for industrial processes) are not known and studied in details. Aiming to fulfill this lack of knowledge, the phenomena occurring during long deposition were studied through both careful experimental evaluations and numerical approach. Particular attention was paid at the working conditions of the De Laval nozzle system which accelerates the particles, a computational fluid dynamics model focusing on both geometrical features and spray behavior was proposed. Micronsized aluminum powders and compressed air as carrier gas were used in this experimentation, numerical simulations are performed to predict the gas flow regime. It has been found that the deposition efficiency tends to decrease due to the critical phenomena occur into the spray nozzle during long time depositions. The sprayed particles tend to stick to the walls of the nozzle and, moreover, shock waves occur inside the nozzle further promoting the particles stick phenomena, making the system inefficient. [ABSTRACT FROM AUTHOR]

Sound waves on a fluid stream, in a de Laval nozzle, are shown to correspond to quasinormal modes emitted by black holes that are physical solutions in a quadratic curvature gravity with cosmological constant. Sound waves patterns in transsonic regimes at a laboratory are employed here to provide experimental data regarding generalized theories of gravity, comprised by the exact de Sitter-like solution and a perturbative solution around the Schwarzschild–de Sitter standard solution as well. Using the classical tests of General Relativity to bound free parameters in these solutions, acoustic perturbations on fluid flows in nozzles are then regarded, to study quasinormal modes of these black holes solutions, providing deviations of the de Laval nozzle cross-sectional area, when compared to the Schwarzschild solution. The fluid sonic point in the nozzle, for sound waves in the fluid, is shown to implement the acoustic event horizon corresponding to quasinormal modes. [ABSTRACT FROM AUTHOR]

The in-gas laser ionization and spectroscopy (IGLIS) technique is used to produce and to investigate short-lived radioactive isotopes at on-line ion beam facilities. In this technique, the nuclear reaction products recoiling out of a thin target are thermalized and neutralized in a high-pressure noble gas, resonantly ionized by the laser beams in a two-step process, and then extracted from the ion source to be finally accelerated and mass separated. Resonant ionization of radioactive species in the supersonic gas jet ensures very high spectral resolution because of essential reduction of broadening mechanisms. To obtain the maximum efficiency and the best spectral resolution, properties of the supersonic jet and the laser beams must be optimized. To perform these studies a new off-line IGLIS laboratory, including a new high-repetition-rate laser system and a dedicated off-line mass separator, has been commissioned. In this article, the specifications of the different components necessary to achieve optimum conditions in laser-spectroscopy studies of radioactive beams using IGLIS are discussed and the results of simulations are presented. [ABSTRACT FROM AUTHOR]

Abstract: New approaches to perform efficient and selective step-wise resonance ionization spectroscopy (RIS) of radioactive atoms in different types of supersonic gas jets are proposed. This novel application results in a major expansion of the in-gas laser ionization and spectroscopy (IGLIS) method developed at KU Leuven. Implementation of resonance ionization in the supersonic gas jet allows to increase the spectral resolution by one order of magnitude in comparison with the currently performed in-gas-cell ionization spectroscopy. Properties of supersonic beams, obtained from the de Laval-, the spike-, and the free jet nozzles that are important for the reduction of the spectral line broadening mechanisms in cold and low density environments are discussed. Requirements for the laser radiation and for the vacuum pumping system are also examined. Finally, first results of high-resolution spectroscopy in the supersonic free jet are presented for the 327.4nm 3d104s 2S1/2→ 3d104p 2P1/2 transition in the stable 63Cu isotope using an amplified single mode laser radiation. [Copyright &y& Elsevier]

This study has focused on numerically exploring the oxygen flow in the convergent-divergent De Laval nozzle. The De Laval nozzle has been commonly used as oxygen outlet at the lance tip in the vacuum oxygen decarburization (VOD) process. The nozzle geometry used in an active VOD plant was investigated by isentropic nozzle theory as well as by numerical modeling. Since an optimal nozzle design is only valid for a certain ambient pressure, one VOD nozzle will be less efficient for a large part of the pressure cycle. Different ambient pressures were used in the calculations that were based on the De Laval nozzle theory. Flow patterns of the oxygen jet under different ambient pressures were studied and the flow information at different positions from the nozzle was analyzed. In addition, the study compared the effects of different ambient temperatures on jet velocity and dynamic pressure. The predictions revealed that the modeling results obtained with the CFD modeling showed incorrect flow expansion, which agreed well with the results from the De Laval theory. Moreover, a little under-expansion is somewhat helpful to improve the dynamic pressure. The jet dynamic pressure and its width for the specific nozzle geometry have also been studied. It has been observed that an altering ambient pressure can influence the jet momentum and its width. In addition, a high ambient temperature has a positive effect on the improvement of the jet dynamic pressure. [ABSTRACT FROM AUTHOR]

Abstract: Liquid metal atomization with De Laval nozzle is not a widely used technique to produce metallic powders. It appears as a versatile process to manufacture different particle sizes according to the processing parameters (gas pressure, melt nozzle diameter, De Laval nozzle diameter, etc.). However, few studies have focused on the understanding of the different stages of the process. During the atomization process two pressure stages can be distinguished: transition time (pressurization time) and stabilized stage (setting pressure). The aim of the work is to study the effect of the operating parameters on the splat diameter during these two stages. Copper (99.9at. %) was atomized using different sets of operating parameters on smooth steel substrates. Different splat shapes and mean equivalent diameters are observed and have shown that they depended on both, the atomization parameters and the atomization time. [ABSTRACT FROM AUTHOR]

Accretion flow on a horizon is supersonic, no matter what the flow angular momentum or the spin of the black hole is. This means that a black hole accretion can always be viewed as a flow in a flat space-time through one or more convergent-divergent ducts. In this paper, we study how the area of cross-sections must vary in order that the flow has the same properties in both systems. We show that the accretion flow experiencing a shock is equivalent to having two ducts connected back-to-back, both with a neck where the flow becomes supersonic. We study the pressure and Mach number variations for corotating, contrarotating flows and flows around a black hole with evolving spin. [ABSTRACT FROM AUTHOR]

direct method for aerodynamic shape optimization based on the use of Bézier spline approximation is proposed. The method is tested as applied to the optimization of the supersonic part of an axisymmetric de Laval nozzle. The optimization results are compared with the exact solution obtained by the control contour method (variational nozzle) and with nozzles constructed using another direct method, namely, local linearization. It is shown that both direct optimization methods can be used on rather coarse grids without degrading the accuracy of the solution. The optimization procedure involves the isoperimetric condition that the surface area of the nozzle is given and fixed, which prevents the use of the control contour method. Optimization with allowance for viscosity is performed using the method. For fairly short maximum possible nozzle lengths in the range of Reynolds numbers under consideration, it is shown that allowance for viscosity does not improve the nozzle shape produced by optimization based on the Euler equations. The role of viscosity is reduced to the determination of an optimal length. [ABSTRACT FROM AUTHOR]

Abstract: In this paper we prove existence, uniqueness and regularity of certain perturbed (subsonic–supersonic) transonic potential flows in a two-dimensional Riemannian manifold with “convergent–divergent” metric, which is an approximate model of the de Laval nozzle in aerodynamics. The result indicates that transonic flows obtained by quasi-one-dimensional flow model in fluid dynamics are stable with respect to the perturbation of the velocity potential function at the entry (i.e., tangential velocity along the entry) of the nozzle. The proof is based upon linear theory of elliptic–hyperbolic mixed type equations in physical space and a nonlinear iteration method. [Copyright &y& Elsevier]

Abstract: Liquid metal atomization using a De Laval nozzle has proven its efficiency in producing fine and narrow sized powders. The modelling work of gas dynamics related to nozzle geometry has led to a better understanding of the effects of the processing parameters. When used during the empting of a crucible, the decrease in the static height of the melt acts on the metal mass flow rate. Moreover, the aspiration due to the negative overpressure formed at the melt nozzle tip depends directly on the atomization pressure. Thus, the gas to metal ratio (GMR) does not increase as fast as the atomization pressure. An experimental study on the particle size distribution in the cross-section of the spray and its evolution during the process has confirmed the unsteadiness of the process. By establishing a model to fit the gas pressure to the mass flow rate evolution, an almost steady state can be reached for the process. This has brought us to reduce the mean particle size and to improve the narrowness of the as-atomized particle size distribution. [Copyright &y& Elsevier]

Black hole accretion is necessarily transonic and the number of physical sonic points depends on the angular momentum of the flow. We study the properties of such a flow by recasting this idea into an engineering problem in which a flow has a subsonic to supersonic transition when it passes through a de Laval nozzle, i.e. a converging and diverging duct in a flat geometry in the presence of sufficient end pressure difference. Particularly interesting is the case of the centrifugal pressure supported standing shock formation inside an accretion flow, because the flow passes through at least two saddle type sonic points, one before and one after the shock. In this case, the duct itself has two minima and a maximum. We study the properties of such a duct as a function of the inflow parameters and classify all possible types of the flow through this composite nozzle. [ABSTRACT FROM AUTHOR]

Abstract: In a companion liquid rocket engine development project, due to the overall weight constraint of the propulsion system, a cavitating venturi is selected to control the liquid fuel and liquid oxidizer mass flow rates. Two cavitating venturis, one for the fuel and the other for the oxidizer, are designed to deliver the desired mass flow rates for a specified operating inlet pressure, temperature, and inlet cross-sectional area. The converging and diverging angles of the venturis are selected from the literature for minimum pressure losses. An experimental setup is designed to verify that the cavitating venturis can deliver the specified flow rates. Two different techniques are used to pressurize the system: in the first method, pressurized nitrogen gas is used, and in the second method, high pressure combustion gases generated from a solid propellant gas generator are used. Transient mass flow rates could not be measured using standard methods due to the short duration of the water tests; instead, average mass flow rates are calculated. The results verify that the designed cavitating venturis can indeed provide the desired mass flow rates. [Copyright &y& Elsevier]

Several designs of high-velocity oxygen fuel (HVOF) thermal spray systems have been created during the last decade. The most advanced systems are now producing coatings comparable in quality to detonation (D-gun) coatings. This paper presents numerical analysis of the interaction of dispersive particles with the carrying gas flow for three different HVOF systems, along with a method to calculate the parameters of sprayed particles that highlights the advantages and limitations of each design. The method includes gas dynamical calculations of the gas flow in an accelerating channel and calculations of the injected par-motion and thermal state (temperature and melted mass fraction). The calculations were performed for particles of tungsten carbide, aluminum oxide, and zirconium oxide with size distributions of 10 to 80 μm. Two conventional types of HVOF systems were considered: those with a supersonic accelerating channel and those with a subsonic accelerating channel (without a de Laval nozzle). A novel design is pro-posed that contains a combined gas dynamical path with functionally separated regions of heating and acceleration. The regularities and distinctions in the behavior of the metallic and ceramic oxide particles are discussed for different jet configurations. The results obtained indicate that it is possible to signifi-cantly affect particle parameters by using the new configuration solutions without creating construction complications. [ABSTRACT FROM AUTHOR]

One method used in spray forming and coating technology involves transonic/supersonic gas-droplet two- phase flows through a de Laval nozzle and subsequent subsonic freejet flow from the nozzle to the sprayed surface. To the first- order approximation, this complex phenomenon can be treated in a quasione-dimensional manner to simulate the entire converging- diverging nozzle flow field (with particle injection at the throat) as well as the plume (freejet) region. The basic numerical technique and computer model solve the steady gas field equations through a conservative variable approach and treat the droplet phase in a Lagrangian manner, with full aerodynamic and energetic coupling between the droplets and the transport gas handled via source terms. These analyses are simple and economical to execute. The one- dimensional models are valuable in constructing algorithms for automated process control. Finally, these one- dimensional models give direction to two- and three- dimensional simulations and serve as a test bed for models based on particle dynamics and energetics. [ABSTRACT FROM AUTHOR]

Factors limiting charge-to-mass ratio achievable for induction-charged aerosol produced in supersonic atomizers are discussed. Experimental investigations performed using supersonic atomizers fitted with de Laval nozzle and concentric induction electrode have demonstrated moderately low electrification levels obtained in case of elevated flow rate of liquid being atomized. It was shown that low charging degree is associated with occurrence of shielding effect. A simplified model of conducting liquid charging process was worked out for the case of atomized liquid cone shielded by an "umbrella" of droplets. Manifestation of the shielding phenomenon and regularities arising from the assumed model has been confirmed experimentally. [ABSTRACT FROM AUTHOR]