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1
Kozlov, Viktor, Genrich Grek, Oleg Korobeinichev, Yuriy Litvinenko, and Andrey Shmakov. "Influence Of Initial Conditions At The Micro Nozzle Exit On Hydrogen Diffusion Combustion." Siberian Journal of Physics 11, no. 3 (2016): 34–45. http://dx.doi.org/10.54362/1818-7919-2016-11-3-34-45.
Testo completoAbstract (sommario):
The purpose of the given work will consist in an experimental study of influence of initial conditions at the micro nozzle exit on hydrogen diffusion combustion. It is shown, that the mean velocity profile and presence/absence of a heatcapacious material at the nozzle exit play an essential role on a flame structure and process of a round hydrogen microjet combustion. Velocity ranges of existence of a round hydrogen microjet diffusion combustion, flame separation and «bottleneck flame» region for a case of a top – hat mean velocity profile at the nozzle and two cases of a parabolic mean velocity profile with presence/absence of a heatcapacious material at the nozzle exit are found. Dependences of the «bottleneck flame» region size from a hydrogen microjet efflux velocity for case of a top – hat mean velocity profile at the nozzle and two cases of a parabolic mean velocity profile with presence/absence of a heatcapacious material at the nozzle exit are shown. Decrements of reduction of the «bottleneck flame» region size with growth of the hydrogen microjet efflux velocity for three situations of changes of initial conditions at the nozzle exit are determined.
2
Lepicovsky, J. "An Experimental Investigation of Nozzle-Exit Boundary Layers of Highly Heated Free Jets." Journal of Turbomachinery 114, no. 2 (1992): 469–75. http://dx.doi.org/10.1115/1.2929167.
Testo completoAbstract (sommario):
An experimental investigation of the effects of nozzle operating conditions on the development of nozzle-exit boundary layers of highly heated air free jets is reported in this paper. The total pressure measurements in the nozzle-exit boundary layer were obtained at a range of jet Mach numbers from 0.1 to 0.97 and jet total temperatures up to 900 K. The analysis of results shows that the nozzle-exit laminar boundary-layer development depends only on the nozzle-exit Reynolds number. For the nozzle-exit turbulent boundary layer, however, it appears that the effects of the jet total temperature on the boundary-layer integral characteristics are independent from the effect of the nozzle-exit Reynolds number. This surprising finding has not yet been reported. Further, laminar boundary-layer profiles were compared with the Pohlhausen solution for a flat-wall converging channel and an acceptable agreement was found only for low Reynolds numbers. For turbulent boundary layers, the dependence of the shape factor on relative Mach numbers at a distance of one momentum thickness from the nozzle wall resembles Spence’s prediction. Finally, the calculated total pressure loss coefficient was found to depend on the nozzle-exit Reynolds number for the laminar nozzle-exit boundary layer, while for the turbulent exit boundary layer this coefficient appears to be constant.
3
Chen, Hongjie, Bingxu Chen, Zhizhou Xu, Jing Ge, Honghua Chen, and Zhaoqi Zhong. "A Thermodynamic Model for Performance Prediction of an Ejector with an Adjustable Nozzle Exit Position." Processes 13, no. 3 (2025): 879. https://doi.org/10.3390/pr13030879.
Testo completoAbstract (sommario):
Improving the efficiency of ejectors during off-design operations can be effectively achieved through the automatic adjustment of the nozzle exit position (NXP). A thermodynamic model for predicting the performance of an ejector with an adjustable nozzle position is proposed and validated. The key factors influencing the optimal nozzle exit position under variable operating conditions are analyzed using the model. The dimensionless optimal nozzle exit position (DONXP) of the ejector is fitted as a function of these key factors, and a nozzle exit position adjustment scheme for variable operating conditions is further derived. The proposed model has maximum errors in the entrainment ratio, critical back pressure, and nozzle exit position within ±10.70%, ±7%, and ±15.85%, respectively. When the area ratio increases, with the transition point located in the mixing chamber, the increase rates of the DONXP are within 0.068~0.195 for the R245fa, R600a, R141b, and R134a ejectors. However, when the transition point is located before the entrance of the mixing chamber, the increase rates are within 0.0009~0.0034. When the area ratio is fixed, the larger the expansion ratio, the smaller the DONXP. The DONXP can be fitted according to different cases where the turning point is located either before or after the entrance of the mixing chamber, to meet the demand for automatic adjustment of the nozzle exit position.
4
Fontaine, Ryan A., Gregory S. Elliott, Joanna M. Austin, and Jonathan B. Freund. "Very near-nozzle shear-layer turbulence and jet noise." Journal of Fluid Mechanics 770 (March 27, 2015): 27–51. http://dx.doi.org/10.1017/jfm.2015.119.
Testo completoAbstract (sommario):
One of the principal challenges in the prediction and design of low-noise nozzles is accounting for the near-nozzle turbulent mixing layers at the high Reynolds numbers of engineering conditions. Even large-eddy simulation is a challenge because the locally largest scales are so small relative to the nozzle diameter. Model-scale experiments likewise typically have relatively thick near-nozzle shear layers, which potentially hampers their applicability to high-Reynolds-number design. To quantify the sensitivity of the far-field sound to nozzle turbulent-shear-layer conditions, a family of diameter $D$ nozzles is studied in which the exit turbulent boundary layer momentum thickness is varied from $0.0042D$ up to $0.021D$ for otherwise identical flow conditions. Measurements include particle image velocimetry (PIV) to within $0.04D$ of the exit plane and far-field acoustic spectra. The influence of the initial turbulent-shear-layer thickness is pronounced, though it is less significant than the well-known sensitivity of the far-field sound to laminar versus turbulent shear-layer exit conditions. For thicker shear layers, the nominally missing region, where the corresponding thinner shear layer would develop, leads to the noise difference. The nozzle-exit momentum thickness successfully scales the high-frequency radiated sound for nozzles of different sizes and exhaust conditions. Yet, despite this success, the detailed turbulence statistics show distinct signatures of the different nozzle boundary layers from the different nozzles. Still, the different nozzle shear-layer thicknesses and shapes have a similar downstream development, which is consistent with a linear stability analysis of the measured velocity profiles.
5
Wang, P. C., and J. J. McGuirk. "Validation of a large eddy simulation methodology for accelerated nozzle flows." Aeronautical Journal 124, no. 1277 (2020): 1070–98. http://dx.doi.org/10.1017/aer.2020.12.
Testo completoAbstract (sommario):
ABSTRACTPrediction of aeroengine exhaust plume near-field development requires knowledge of velocity and turbulence distributions at nozzle exit. The high Reynolds number nozzle inlet boundary layers of engineering practice are fully turbulent, but acceleration can induce re-laminarisation. Thus, to reproduce nozzle exit conditions accurately, large eddy simulation (LES) for plume prediction must be capable of capturing re-laminarisation and any subsequent boundary layer recovery. Validation is essential to establish a credible LES methodology, but previous studies have suffered from lack of nozzle inlet/exit measurements in the test cases selected. Validation data were here taken from an experiment on a convergent round nozzle with a parallel exit extension to allow boundary layer recovery. LES inlet condition generation applied a rescaling/recycling method (R2M), whose performance was validated against measurements of first and second moment statistics as well as the turbulence integral length scale. Simulations employed two sub-grid-scale (SGS) models; these produced similar predictions up to the end of the nozzle convergent section, but marked differences appeared for the nozzle exit turbulence field. The Smagorinsky model predicted much lower turbulence levels than measured, whereas the Piomelli and Geurts model revealed the presence of a small separation region at the convergence/parallel section corner, which led to higher exit turbulence and much better agreement with measured data.
6
Mokni, Amèni, Jamel Kechiche, Hatem Mhiri, Georges Le Palec, and Philippe Bournot. "Numerical Study of the Inlet Conditions Influence on Laminar Plane Wall Jets." Defect and Diffusion Forum 273-276 (February 2008): 406–12. http://dx.doi.org/10.4028/www.scientific.net/ddf.273-276.406.
Testo completoAbstract (sommario):
In this paper, we present a numerical investigation of a laminar isothermal plane two dimensional wall jets. Special attention has been paid to the effect of the inlet conditions at the nozzle exit on the flow thermal characteristics in forced convection regime. Two velocities profiles at the nozzle exit are used: uniform profile and parabolic profile. The system of equations governing the studied configuration is solved with a finite difference scheme and an implicit scheme, for numerical stability we use a staggered non uniform grid. The obtained results show, first, that the inlet conditions affect the flow in the immediate neighbourhood of the nozzle (core region) in which the flow is governed mainly by the inertias forces. At the established region the results become independent of the flow inlet conditions.
7
Huh, Kang Y., Eunju Lee, and Jaye Koo. "DIESEL SPRAY ATOMIZATION MODEL CONSIDERING NOZZLE EXIT TURBULENCE CONDITIONS." Atomization and Sprays 8, no. 4 (1998): 453–69. http://dx.doi.org/10.1615/atomizspr.v8.i4.60.
Testo completo
8
Liu, Fuhai, Songchao Lu, Sibao Zeng, Rong Zhu, Guangsheng Wei, and Kai Dong. "Flow Field of Supersonic Oxygen Jet Generated by Various Wear Lengths at the Laval Nozzle Exit." Coatings 14, no. 11 (2024): 1444. http://dx.doi.org/10.3390/coatings14111444.
Testo completoAbstract (sommario):
As a main apparatus, the oxygen lance is used to deliver the oxygen element and transfer kinetic energy into the molten bath in the steelmaking process. However, the Laval nozzle exit would be gradually worn out during the service life, which suppresses the performance of the oxygen lance. This paper investigated three different wear length (Lw) conditions at the exit of the Laval nozzle through numerical simulations and high-temperature experiments with various oxygen flow rates. The result showed that the entrainment of the ambient gas was the key factor of the wear phenomenon for the Laval nozzle exit. The maximum total temperature of the gas phase at the Laval nozzle exit formed by the Lw of 0 mm, 2 mm, and 4 mm were 300 K, 959 K, and 1700 K, respectively. Thus, by increasing the Lw value, the total temperature of the gas phase was rapidly improved at the exit of the Laval nozzle, which further accelerated the wear phenomenon at the exit of the Laval nozzle. Besides, axial velocities at the end of the potential core formed by the Lw of 0 mm, 2 mm, and 4 mm were 483.7 m/s, 480.0 m/s, and 478.7 m/s, respectively. As a result, the wear phenomenon reduced the impaction ability of the oxygen jet, which suppressed the impaction depth and radius, resulting in a smaller droplet generation rate.
9
Liu, Meng, and Yufeng Duan. "Predicting the Liquid Film Thickness and Droplet–Gas Flow in Effervescent Atomization: Influence of Operating Conditions and Fluid Viscosity." International Journal of Chemical Reactor Engineering 11, no. 1 (2013): 393–405. http://dx.doi.org/10.1515/ijcre-2013-0073.
Testo completoAbstract (sommario):
Abstract The droplet–gas flow in effervescent atomization was simulated using a comprehensive numerical model. Liquid film thicknesses in the nozzle exit orifice and droplet size distribution at the downstream of spray were calculated. The thickness of liquid film in the nozzle exit orifice increased and approached the droplet size in the primary atomization, as the air–liquid ratio increased. The primary breakup model can accurately predict the Sauter mean diameter in the primary atomization when gas–liquid two-phase flow belongs to the annular flow in the nozzle exit orifice. The viscosity of fluid had minimal influence on the liquid film thickness for spray with fluids, the viscosity of which is significantly greater than that of water. Droplet size initially decreased and then increased along the axial distance because of the secondary atomization and droplet coalescence at the downstream of spray.
10
Kim1, H.-D., J.-H. Kim, K.-A. Park, T. Setoguchi, and S. Matsuo. "Study of the effects of unsteady downstream conditions on the gas flow through a critical nozzle." Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science 218, no. 10 (2004): 1163–73. http://dx.doi.org/10.1243/0954406042369053.
Testo completoAbstract (sommario):
The present study addresses a computational result of unsteady gas flow through a critical nozzle. The axisymmetric unsteady compressible Navier-Stokes equations are solved using a finite volume method that makes use of the second-order upwind scheme for spatial derivatives and the multi-stage Runge-Kutta integral scheme for time derivatives. The steady solutions of the governing equation system are validated with the previous experimental data to ensure that the present computational method is valid to predict the critical nozzle flows. In order to simulate the effects of back-pressure fluctuations on the critical nozzle flows, an excited pressure oscillation with an amplitude and frequency is assumed downstream of the exit of the critical nozzle. The results obtained show that, for low Reynolds numbers, the unsteady effects of the pressure fluctuations can propagate upstream of the throat of the critical nozzle, thus giving rise to the applicable fluctuations in mass flow rate through the critical nozzle, while, for high Reynolds numbers, the pressure signals occurring at the exit of the critical nozzle do not propagate upstream beyond the nozzle throat. For a low Reynolds number, it is found that the sonic line near the throat of the critical nozzle markedly fluctuates with time, providing an important mechanism for pressure signals to propagate upstream of the nozzle throat, even in choked flow conditions. The present study is the first investigation to clarify the unsteady effects on the critical nozzle flows.
11
Menon, Pranav. "Investigation of Variation in the Performance of an Electro Thermal Thruster with Aerospike Nozzle." Advanced Engineering Forum 16 (April 2016): 91–103. http://dx.doi.org/10.4028/www.scientific.net/aef.16.91.
Testo completoAbstract (sommario):
One of the most recently developed modes of propulsion is electric propulsion. The commonly used chemical propulsion systems have the advantage of a high Specific Impulse as compared to that of ion propulsion systems. However, owing to the efficacy of ion propulsion systems, it is considered the future of space exploration.Electro thermal thrusters produce thrust by using electrical fields to force hot plasma out of the nozzle with certain exit velocity. The plasma’s exit velocity and the system’s thrust capacity, as of now, are insufficient for space travel to be conducted within a reasonable time. I intend to study the possibility of improving the thruster’s performance by using an aerospike nozzle as an exit nozzle which meets the conditions required for the thruster to function appropriately. I shall be studying the plasma plume exit velocity variation with respect to the nozzles used. Also, a thermal analysis will be conducted in order to find the correct material for the nozzle.
12
Laitón, Sergio Nicolas Pachón, João Felipe de Araujo Martos, Israel da Silveira Rego, George Santos Marinho, and Paulo Gilberto de Paula Toro. "Experimental Study of Single Expansion Ramp Nozzle Performance Using Pitot Pressure and Static Pressure Measurements." International Journal of Aerospace Engineering 2019 (February 27, 2019): 1–11. http://dx.doi.org/10.1155/2019/7478129.
Testo completoAbstract (sommario):
In order to overcome the drag at hypersonic speed, hypersonic flight vehicles require a high level of integration between the airframe and the propulsion system. Propulsion system based on scramjet engine needs a close interaction between its aerodynamics and stability. Hypersonic vehicle nozzles which are responsible for generating most of the thrust generally are fused with the vehicle afterbody influencing the thrust efficiency and vehicle stability. Single expansion ramp nozzles (SERN) produce enough thrust necessary to hypersonic flight and are the subject of analysis of this work. Flow expansion within a nozzle is naturally 3D phenomena; however, the use of side walls controls the expansion approximating it to a 2D flow confined. An experimental study of nozzle performance traditionally uses the stagnation conditions and the area ratio of the diverging section of the tunnel for approaching the combustor exit conditions. In this work, a complete hypersonic vehicle based on scramjet propulsion is installed in the test section of a hypersonic shock tunnel. Therefore, the SERN inlet conditions are the real conditions from the combustor exit. The performance of a SERN is evaluated experimentally under real conditions obtained from the combustor exit. To quantify the SERN performance parameters such as thrust, axial thrust coefficient Cfx and lift L are investigated and evaluated. The generated thrust was determined from both static and pitot pressure measurements considering the installation of side walls to approximate 2D flow. Measurements obtained by a rake show that the flow at the nozzle exit is not symmetric. Pitot and pressure measurements inside the combustion chamber show nonuniform flow condition as expected due to side wall compression and boundary layer. The total axial thrust for the nozzle obtained with the side wall is slightly higher than without it. Static pressure measurements at the centerline of the nozzle show that the residence time of the flow in the expansion section is short enough and the flow of the central region of the nozzle is not altered by the lateral expansion when nozzle configuration does not include side walls.
13
Mitruka, Jatin, Pranav Kumar Singh, and E. Rathakrishnan. "Exit Geometry Effect on Jet Mixing." Applied Mechanics and Materials 598 (July 2014): 151–55. http://dx.doi.org/10.4028/www.scientific.net/amm.598.151.
Testo completoAbstract (sommario):
An elliptical nozzle of 3:1 aspect ratio (AR) issuing a Mach 1.5 jet has been used to investigate its mixing promoting efficiency under over-expanded and under-expanded conditions at the nozzle exit. Azimuthal asymmetry of the elliptical shape is interpreted as a benefit to the mixing process, which is significantly enhanced in comparison to an equivalent circular jet under identical conditions. The elliptical jet decays faster than its circular counterpart throughout the jet field. It is found that continuous variation in the size of the mixing promoting vortices shed from the nozzle exit, as a result of its azimuthal asymmetry, is responsible for faster decay of elliptical jet. The visualization of elliptic jet corroborates the fact that the waves prevailing in the elliptical jet are significantly weaker than those in the circular jet.
14
Jeon, Yongseok, Hoon Kim, Jae Hwan Ahn, and Sanghoon Kim. "Effects of Nozzle Exit Position on Condenser Outlet Split Ejector-Based R600a Household Refrigeration Cycle." Energies 13, no. 19 (2020): 5160. http://dx.doi.org/10.3390/en13195160.
Testo completoAbstract (sommario):
The objective of this study is to investigate the performance characteristics of a small-sized R600a household refrigeration system that adopts a condenser outlet split (COS) ejector cycle under various operating and ejector geometry conditions. The coefficient of performance and pressure lifting ratio of the COS ejector cycle were analyzed and measured by varying the entrainment ratio, compressor speed, and nozzle exit position. The optimum nozzle exit position in the COS ejector cycle adopted to achieve the maximum cycle performance was proposed as a function of the compressor speed and entrainment ratio. The optimum nozzle exit position was 0 mm when the entrainment ratio and compressor speed were low, and it increased as the entrainment ratio and compressor speed increased owing to the associated internal pressure drop in the suction section.
15
Vinod, G., S. Renjith, and V. Thaddeus Basker. "Thermo Structural Analysis of Carbon-Carbon Nozzle Exit Cone for Rocket Cryo Engines." Applied Mechanics and Materials 877 (February 2018): 320–26. http://dx.doi.org/10.4028/www.scientific.net/amm.877.320.
Testo completoAbstract (sommario):
Launch and space vehicle structures are required to be extremely weight efficient. The need to achieve the performance required for the engine in the upper stage of a launch vehicle, increase the payload capacity drives rocket engine manufacturers to seek higher thrust level, specific impulse and thrust to weight ratio. The use of high temperature C-C composite materials is an efficient way to reach these objectives by allowing use of high expansion ratio. Nozzle extensions benefiting of the outstanding thermal, mechanical and fatigue resistance of these materials to decrease mass and featuring high temperature margins. A three-directionally reinforced (3D) carbon-carbon (c-c) material nozzle exit cone is selected for the current study. C-C composite exit nozzle must possess excellent stability and strength under extreme conditions for a specified amount of time. Carbon-carbon composites are appropriate materials for applications that require high specific strength at elevated temperatures. The paper describes the thermo structural analysis of a typical c/c nozzle exit cone.
16
Choi, Myeung Hwan, Yoojin Oh, and Sungwoo Park. "Investigation of Spray Characteristics for Detonability: A Study on Liquid Fuel Injector and Nozzle Design." Aerospace 11, no. 6 (2024): 421. http://dx.doi.org/10.3390/aerospace11060421.
Testo completoAbstract (sommario):
Detonation engines are gaining prominence as next-generation propulsion systems that can significantly enhance the efficiency of existing engines. This study focuses on developing an injector utilizing liquid fuel and a gas oxidizer for application in detonation engines. In order to better understand the spray characteristics suitable for the pulse detonation engine (PDE) system, an injector was fabricated by varying the Venturi nozzle exit diameter ratio and the geometric features of the fuel injection hole. Analysis of high-speed camera images revealed that the Venturi nozzle exit diameter ratio plays a crucial role in determining the characteristics of air-assist or air-blast atomization. Under the conditions of an exit diameter ratio of Re/Ri = 1.0, the formation of a liquid film at the exit was observed, and it was identified that the film’s length is influenced by the geometric characteristics of the fuel injection hole. The effect of the fuel injection hole and Venturi nozzle exit diameter ratio on SMD was analyzed by using droplet diameter measurement. The derived empirical correlation indicates that the atomization mechanism varies depending on the Venturi nozzle exit diameter ratio, and it also affects the distribution of SMD. The characteristics of the proposed injector, its influence on SMD, and its velocity, provide essential groundwork and data for the design of detonation engines employing liquid fuel.
17
V. Kozlov, Grigory, Genrich R. Grek, Aleksandr M. Sorokin, and Yuriy A. Litvinenko. "Influence of Initial Conditions at Nozzle Section on Flow Structure and Instability of Plane Jet." Siberian Journal of Physics 3, no. 3 (2008): 14–33. http://dx.doi.org/10.54362/1818-7919-2008-3-3-14-33.
Testo completoAbstract (sommario):
Experimental data concerning the influence of initial conditions at the nozzle exit on the structure and development characteristics of plane jet are reported. Features in the development of laminar and turbu-lent round jets emanating from variously elongated nozzles at identical Reynolds numbers are revealed. Smoke visualization pictures obtained for jets formed under different initial conditions (with different distributions of mean and pulsating flow velocities at the nozzle exit), influence of acoustic and interac-tion of streaky structures with vortex trail of laminar plane jet are discussed. It is established that, the laminar and turbulent jet on an output of the plane channel of Hagen-Poiseuille undergoes sine wave os-cillations, as a single whole. It is established that, the symmetric mode of instability of a laminar plane jet are suppressed asymmetrical. It is shown that, interaction of the streaky structures generated on one side of plane nozzle, with vortices of a laminar plane jet with a parabolic velocity profile leads to appearance of Λ- or Ω-vortices on vortices of a vortex trail, on the right as well as on the left side of the nozzle.
18
Bruce Ralphin Rose, J., and J. Veni Grace. "Performance analysis of lobed nozzle ejectors for high altitude simulation of rocket engines." International Journal of Modeling, Simulation, and Scientific Computing 05, no. 04 (2014): 1450019. http://dx.doi.org/10.1142/s1793962314500196.
Testo completoAbstract (sommario):
Ejectors are used in high altitude testing of rocket engines to create vacuum for simulating the engine test in vacuum conditions. The performance of an ejector plays a vital role in creating vacuum at the exit of the engine nozzle and the nozzle design exit pressure at the time of ignition. Consequently, the performance of ejectors has to be improved to reduce the consumption of active fluid. In this investigation, the performance of an ejector has been improved by changing the exit shear plane of the nozzle. Conventionally, conical nozzles are used for creating the required momentum. Lobes of 4 no's, 6 no's and 8 numbers for an equivalent area ratio = 5.88 are used to increase the shear area. The influence of shear plane variation in the suction pressure is studied by a detailed CFD analysis.
19
Anil Hemanth, Varada, and U. S. Jyothi. "CFD Analysis of a Solid Propellant Retro Rocket Motor using Ansys Fluent." E3S Web of Conferences 184 (2020): 01054. http://dx.doi.org/10.1051/e3sconf/202018401054.
Testo completoAbstract (sommario):
A Solid propellant Retro Rocket Motor with a C-D Nozzle is analyzed using Ansys Fluent 17.1 .Steady State analysis of a retro rocket motor has been done for Viscous models like Inviscid and k-ɛ (Realizable) with air and gas as working fluids. The dimensions and the boundary conditions of the nozzle are kept consistent for both the viscous models to compare the exit parameters to theoretical values obtained by using one dimensional equations. The results obtained shows that the exit temperature of the nozzle in Inviscid viscous model is higher than theoretical value by 2.2% and for k-ɛ viscous model it is higher by 5.4% with gas as working fluid.
20
Wen, Kui, Min Liu, Kesong Zhou, et al. "The Influence of Anode Inner Contour on Atmospheric DC Plasma Spraying Process." Advances in Materials Science and Engineering 2017 (2017): 1–12. http://dx.doi.org/10.1155/2017/2084363.
Testo completoAbstract (sommario):
In thermal plasma spraying process, anode nozzle is one of the most important components of plasma torch. Its inner contour controls the characteristics of plasma arc/jet, determining the motion and heating behaviors of the in-flight particles and hence influencing the coating quality. In this study, the effects of anode inner contour, standard cylindrical nozzle, and cone-shaped Laval nozzle with conical shape diverging exit (CSL nozzle) on the arc voltage, net power, thermal efficiency, plasma jet characteristics, in-flight particle behaviors, and coating properties have been systematically investigated under atmospheric plasma spraying conditions. The results show that the cylindrical nozzle has a higher arc voltage, net power, and thermal efficiency, as well as the higher plasma temperature and velocity at the torch exit, while the CSL nozzle has a higher measured temperature of plasma jet. The variation trends of the plasma jet characteristics for the two nozzles are comparable under various spraying parameters. The in-flight particle with smaller velocity of CSL nozzle has a higher measured temperature and melting fraction. As a result, the coating density and adhesive strength of CSL nozzle are lower than those of cylindrical nozzle, but the deposition efficiency is greatly improved.
21
Ghazwani, Hassan A., Afrasyab Khan, Pavel Alexanrovich Taranenko, et al. "Hydrodynamics of Direct Contact Condensation Process in Desuperheater." Fluids 7, no. 9 (2022): 313. http://dx.doi.org/10.3390/fluids7090313.
Testo completoAbstract (sommario):
Due to global environmental conditions, the focus of household heating has shifted from fossil fuels towards environmentally friendly and renewable energy sources. Desuperheaters have attracted attention as a domestic provision involving steam-induced direct contact condensation (DCC)to warm the water. The present study is an attempt to investigate the hydrodynamics in the desuperheater vessel experimentally, namely, when the pressurized pulsating steam is injected into the vessel, where the steam jet interacts co-currently with the slow-moving water. Flow visualization showed a circulation region when the pulsating steam was injected into the slow-moving water, and the peaked vorticity corresponded to the steam injection duration of 10–60 s. Sevenhot film anemometers (HFAs) were traversed axially and radially to determine the velocity fluctuations at 0–20 cm from the steam’s nozzle exit. Vortical structures indicated the entrainment of the steam with the surrounding moving water. The circulation regions were thus exhibited in relation to the steam’s injection durations as well as the downstream axial distances of 2 and 15 cm from the nozzle exit, which showed that the core local circulation at 2 cm downstream of the nozzle exit lost 75–79% of its circulation at 15 cm downstream of the nozzle exit.
22
Forster, M., and R. Steijl. "Design study of Coanda devices for transonic circulation control." Aeronautical Journal 121, no. 1243 (2017): 1368–91. http://dx.doi.org/10.1017/aer.2017.65.
Testo completoAbstract (sommario):
ABSTRACTCirculation control via blowing over Coanda surfaces at transonic freestream Mach numbers is investigated using numerical simulations. The performance and sensitivity of several circulation control devices applied to a supercritical aerofoil are assessed. Different Coanda devices were studied to assess the effect of Coanda radius-to-slot height ratio, nozzle shape and Coanda surfaces with a step. The range of operating conditions for which a supersonic Coanda jet remained attached at transonic freestream conditions were extended by increasing the radius of curvature at the slot exit for Coanda devices with a converging nozzle. Additional improvements were found by reducing the strength of shock boundary-layer interactions on the Coanda surface by expanding the jet flow using a converging-diverging nozzle and also by introducing a step between the Coanda surface and the nozzle exit. The performance when using a converging-diverging nozzle can be matched using a simple stepped Coanda device. It is shown that circulation control has the potential to match the performance of traditional control surfaces during regimes of attached flow at transonic speeds, up to an equivalent aileron deflection angle of 10°. In addition, lift augmentation ratios ΔCl/Cμof over 100 were achieved.
23
Stevens, J., Y. Pan, and B. W. Webb. "Effect of Nozzle Configuration on Transport in the Stagnation Zone of Axisymmetric, Impinging Free-Surface Liquid Jets: Part 1—Turbulent Flow Structure." Journal of Heat Transfer 114, no. 4 (1992): 874–79. http://dx.doi.org/10.1115/1.2911895.
Testo completoAbstract (sommario):
This study characterized the mean and fluctuating parts of the radial component of the local velocity in the stagnation region of an impinging, free-surface liquid jet striking a smooth flat plate. Four different nozzle exit conditions were studied, including fully developed pipe flow, a contoured nozzle, and turbulence-damped and -undamped sharp-edged orifices. Liquid jet Reynolds numbers in the range 30,000 to 55,000 were investigated. Velocities were measured using laser-Doppler velocimetry. Mean velocities were found to vary nearly linearly with radial location, with the slope of the line being a function of distance from the impingement plate. Dimensionless mean velocity gradients, of relevance to the heat transfer, were found to be a strong function of nozzle type, but roughly independent of jet Reynolds number for a given nozzle type. Turbulence levels were also found to be strongly influenced by the nozzle exit condition. Local heat transfer data corresponding to the flow structure measurements presented here are reported in Part 2 of this study.
24
BOGEY, C., and C. BAILLY. "Influence of nozzle-exit boundary-layer conditions on the flow and acoustic fields of initially laminar jets." Journal of Fluid Mechanics 663 (November 4, 2010): 507–38. http://dx.doi.org/10.1017/s0022112010003605.
Testo completoAbstract (sommario):
Round jets originating from a pipe nozzle are computed by large-eddy simulations (LES) to investigate the effects of the nozzle-exit conditions on the flow and sound fields of initially laminar jets. The jets are at Mach number 0.9 and Reynolds number 105, and exhibit exit boundary layers characterized by Blasius velocity profiles, maximum root-mean-square (r.m.s.) axial velocity fluctuations between 0.2 and 1.9% of the jet velocity, and momentum thicknesses varying from 0.003 to 0.023 times the jet radius. The far-field noise is determined from the LES data on a cylindrical surface by solving the acoustic equations. Jets with a thinner boundary layer develop earlier but at a slower rate, yielding longer potential cores and lower centreline turbulent intensities. Adding random pressure disturbances of low magnitude in the nozzle also increases the potential core length and reduces peak r.m.s. radial velocity fluctuations in the shear layer. In all the jets, the shear-layer transition is dominated by vortex rolling-ups and pairings, which generate strong additional acoustic components, but also amplify the downstream-dominant low-frequency noise component when the exit boundary layer is thick. The introduction of inlet noise however results in weaker pairings, thus spectacularly reducing their contributions to the sound field. This high sensitivity to the initial conditions is in good agreement with experimental observations.
25
Li, Li, Zhi Hui Shi, and Tsutomu Saito. "A Survey of Fluidic Thrust Vectoring Nozzle by Numerical Analysis." Applied Mechanics and Materials 423-426 (September 2013): 1685–88. http://dx.doi.org/10.4028/www.scientific.net/amm.423-426.1685.
Testo completoAbstract (sommario):
Numerical investigations are conducted to simulate the flow field of a 2D converging-diverging nozzle, for fluidic thrust vectoring. The numerical simulation of nozzle flow is carried out with Navier-Stokes equations model. Simulations are done with different primary and secondary jet conditions. The numerical results show that the smaller of the distance between secondary jet and exit, the larger is the thrust deflection angle. As the injection pressure ratio increases, the deflection angle increases followed on the premise of not far between secondary jet port and exit. The parameters play important roles on thrust vectoring capability.
26
Nanduri, Madhusarathi, David G. Taggart, and Thomas J. Kim. "A Study of Nozzle Wear in Abrasive Entrained Water Jetting Environment." Journal of Tribology 122, no. 2 (1999): 465–71. http://dx.doi.org/10.1115/1.555383.
Testo completoAbstract (sommario):
Parameters that influence nozzle wear in abrasive water jetting environment are identified and classified. Regular and accelerated wear test procedures are developed to study wear under actual and simulated conditions, respectively. In addition to exit diameter growth, nozzle weight loss and bore profiles are shown to better characterize and explain the wear phenomenon. The effect of nozzle geometry on wear is investigated by means of the developed test procedures and measures of wear. [S0742-4787(00)00202-2]
27
Brès, Guillaume A., Peter Jordan, Vincent Jaunet, et al. "Importance of the nozzle-exit boundary-layer state in subsonic turbulent jets." Journal of Fluid Mechanics 851 (July 19, 2018): 83–124. http://dx.doi.org/10.1017/jfm.2018.476.
Testo completoAbstract (sommario):
To investigate the effects of the nozzle-exit conditions on jet flow and sound fields, large-eddy simulations of an isothermal Mach 0.9 jet issued from a convergent-straight nozzle are performed at a diameter-based Reynolds number of $1\times 10^{6}$. The simulations feature near-wall adaptive mesh refinement, synthetic turbulence and wall modelling inside the nozzle. This leads to fully turbulent nozzle-exit boundary layers and results in significant improvements for the flow field and sound predictions compared with those obtained from the typical approach based on laminar flow in the nozzle. The far-field pressure spectra for the turbulent jet match companion experimental measurements, which use a boundary-layer trip to ensure a turbulent nozzle-exit boundary layer to within 0.5 dB for all relevant angles and frequencies. By contrast, the initially laminar jet results in greater high-frequency noise. For both initially laminar and turbulent jets, decomposition of the radiated noise into azimuthal Fourier modes is performed, and the results show similar azimuthal characteristics for the two jets. The axisymmetric mode is the dominant source of sound at the peak radiation angles and frequencies. The first three azimuthal modes recover more than 97 % of the total acoustic energy at these angles and more than 65 % (i.e. error less than 2 dB) for all angles. For the main azimuthal modes, linear stability analysis of the near-nozzle mean-velocity profiles is conducted in both jets. The analysis suggests that the differences in radiated noise between the initially laminar and turbulent jets are related to the differences in growth rate of the Kelvin–Helmholtz mode in the near-nozzle region.
28
De Chant, L. J. "Subsonic Elector Nozzle Limiting Flow Conditions." Journal of Engineering for Gas Turbines and Power 125, no. 3 (2003): 851–54. http://dx.doi.org/10.1115/1.1581890.
Testo completoAbstract (sommario):
This paper describes an analytical method used to provide information concerning limiting flows for subsonic ejector nozzles. Three potential limiting flows have been identified and modeled using reduced control volume based analysis: (1) incipient reverse flow into the secondary inlet, (2) choked flow in the secondary inlet, and (3) choked flow in the exit mixing stream. Comparison of the methods developed here with the classical control volume portion of an ejector nozzle code have been performed and show good agreement. As such, it is concluded, that within the scope of one-dimensional control-volume based computations, that the methods developed here provide an efficient tool to help delimit the design space acceptable for ejector operation.
29
Elangovan, S., and E. Rathakrishnan. "Studies on high speed jets from nozzles with internal grooves." Aeronautical Journal 108, no. 1079 (2004): 43–50. http://dx.doi.org/10.1017/s000192400000498x.
Testo completoAbstract (sommario):
Experiments were carried out on jets issuing from circular nozzles with grooved exits and the results compared with those of the plain nozzle. The plain nozzle had an exit diameter of 10mm. Because of the introduction of semi-circular grooves at the exit, the effective or equivalent diameter of the grooved nozzles was 10·44mm. The groove lengths were varied as 3, 5 and 8mm. The nozzles were operated at fully expanded sonic and underexpanded exit conditions. The corresponding fully expanded Mach numbers were 1·0 and 1·41. The shock cell structure of the underexpanded jets from grooved nozzles appeared to be weaker than that of the plain nozzle, as indicated by lesser amplitudes of the cyclic variation of the Pitot pressure. The iso-Mach contours indicate that the jet spread along the grooved plane is significantly higher than that along the ungrooved plane. Off-centre peaks were observed in the mean pressure profile of underexpanded jets from grooved nozzles. They were probably due to the streamwise vortices shed from the grooves.
30
Ternova, K. V. "Effect of the length of truncated nozzle with a tip on its thrust characteristics." Technical mechanics 2022, no. 4 (2022): 26–34. http://dx.doi.org/10.15407/itm2022.04.026.
Testo completoAbstract (sommario):
Nowadays, for solving new problems, rocket engine nozzle developers are increasingly turning to non- traditional nozzle configurations that differ from the classic Laval one. A relatively new line in the design of supersonic nozzles is the development of the so-called bell-shaped nozzle, which, unlike the classical Laval nozzle, has a larger angle of entry into the supersonic part of the nozzle. In this case, dual bell nozzles, which have two flow expansion sections in their supersonic part, are considered. However, the effect of the length ratio of the two flow expansion sections of a truncated nozzle on its characteristics has not yet been studied. The goal of this work is to determine the effect of the length of the upstream conical supersonic section on the static pressure distribution in the nozzle and its thrust characteristics with the shape of the bell-shaped tip kept unchanged. The nozzle characteristics were studied using the ANSYS Fluent computing package. It was shown that the flow patterns in the nozzle (velocity fields) change with the length of the conical part upstream of the tip and the underexpansion degree. Under terrestrial conditions (Pн = 1 bar), all variants show a developed separation zone that starts from the corner point where the tip is connected to the conical part. In this case, the pressure on the nozzle wall is nearly equal to the ambient pressure. At a large flow underexpansion degree (P0 = 300 bar) and in low-pressure conditions conditions (Pн =0.1 bar), the flow in the tip is adjacent to the wall. At a large flow underexpansion degree, the pressure in the nozzle increases from the corner point to the tip exit, and the pressure at the tip exit increases with decreasing tip length. The nozzle thrust coefficient decreases with increasing flow underexpansion degree, and it reaches a constant value after the flow becomes adjacent to the tip wall downstream of the corner point where the tip is connected to the nozzle. At high flow underexpansion degrees, the nozzle thrust coefficient is higher for a nozzle with a longer conical part. The calculated results are in good agreement with experimental data on nozzles of this type.
31
Ihnatiev, O. D., N. S. Pryadko, G. O. Strelnikov, and K. V. Ternova. "Gas flow in a truncated Laval nozzle with a bell-shaped tip." Technical mechanics 2022, no. 2 (2022): 39–46. http://dx.doi.org/10.15407/itm2022.02.039.
Testo completoAbstract (sommario):
Flow in a truncated supersonic Laval nozzle with a bell-shaped tip (“bell”) is investigated. This nozzle configuration can be used in tight layouts of multistage rockets of short length with improved energy-mass characteristics. Similar types of nozzles were developed at the Institute of Technical Mechanics of the National Academy of Sciences and the State Space Agency of Ukraine in the 1990s. Using approximate methods, the parameters of variously configured truncated nozzles were calculated, and their models were made. Some of the models were blown with cold air, and their characteristics were measured. Shadow patterns of gas flow downstream of the nozzle and soot-oil patterns of streamlines on the nozzle wall were obtained. These results were used in the formulation of this work. In this work, a numerical study with the ANSYS package was carried out for gas flow in a truncated Laval nozzle with a spherical tip. For this nozzle configuration, its model was blown with cold air. The calculated results were verified by comparing the velocity distribution in the gas flow downstream of the nozzle exit with the experimental shadow patterns. An additional confirmation of the correctness of the calculated results was a comparison of the flow downstream of a streamline-profiled Laval nozzle with the underexpanded flow pattern downstream of the nozzle exit in the first “cask” (up to the Mach disk) studied in detail. The same initial data and initial conditions that give the best results in terms of verifiability were chosen in both cases. The study of flow in a truncated supersonic nozzle showed the following results. Downstream of the corner exit point of the truncated section of a Laval nozzle, flow separation is observed where the gas flow enters the “bell”. The separation is retained as the pressure upstream of the nozzle increases up to a certain critical (for a given tip type) value of the underexpansion ratio, after which (with a further increase in the underexpansion ratio) the flow attaches to the nozzle wall and remains attached with a further increase in the pressure upstream of the nozzle. The impulse response of a truncated nozzle with a bell-shaped tip is lower than that of a streamline-profiled Laval nozzle of the same geometric expansion ratio.
32
Stufflebeam, J. H., D. W. Kendrick, W. A. Sowa, and T. S. Snyder. "Quantifying Fuel/Air Unmixedness in Premixing Nozzles Using an Acetone Fluorescence Technique." Journal of Engineering for Gas Turbines and Power 124, no. 1 (1999): 39–45. http://dx.doi.org/10.1115/1.1396840.
Testo completoAbstract (sommario):
The ability of a lean-premixed combustion system to minimize emissions while maintaining combustion stability over the operating curve relies upon how well the fuel nozzle premixes the fuel and air. As the level of premixing increases, NOx emissions at a given flame temperature decrease until a perfectly premixed condition is achieved. The objective of this paper is to quantify the level of premixing achieved by a premixing nozzle using an acetone fluorescence technique and determine its relationship to NOx emissions and combustion stability. The technique of using acetone fluorescence has been used as a fast and quantitative diagnostic to map the fuel-air distribution. This technique has been applied to the development of a lean premixing nozzle to measure the fuel air distribution at the fuel nozzle exit plane. In this study, the fuel air distribution is presented as two-dimensional images. The average fuel/air ratio and the standard deviation are calculated at various annular regions to determine the distribution as a function of radius. A single unmixedness parameter (σ/μ) over the entire annulus is also calculated to allow relative ranking of the various fuel nozzle configurations. The fluorescence data is acquired for various nozzle hardware configurations in an atmospheric test facility. Fuel and air flow conditions are determined by scaling engine conditions to cold flow conditions and matching the fuel to air momentum ratio at the fuel injection site. Measured fuel/air distributions, six mm downstream of the nozzle exit plane, from the acetone fluorescence technique are correlated to emissions and acoustic measurements made at full pressure and temperature conditions in a single-nozzle test rig. The paper includes a description of the acetone fluorescence technique, the method for optimizing the fuel/air distribution through changes to the main gas fuel injection array, and correlations made between the fuel/air distribution, nozzle geometry, power setting, emissions, and combustor acoustics.
33
Riani, Novi Indah, Syamsuri Syamsuri, and Rungky Rianata Pratama. "Simulasi Numerik Aliran Melewati Nozzle Pada Ejector Converging – Diverging Dengan Variasi Diameter Exit Nozzle." R.E.M. (Rekayasa Energi Manufaktur) Jurnal 2, no. 1 (2017): 19. http://dx.doi.org/10.21070/r.e.m.v2i1.796.
Testo completoAbstract (sommario):
In the process of cooling or refrigeration, are required components where capable to flow the fluid to create a cycle of the cooling process. Among some of the vapor compression systems, the usage of ejector is the simplest system. Ejector has three main parts: primary nozzle, mixing chamber and diffuser. Various experiments of steam ejectors developed to increase the value of the COP. Entrainment ratio directly affects to the COP value generated by the system, where the geometric shapes and operating conditions in the steam ejector will affect to the value entrainment ratio. This research was carried out numerical simulations using CFD commercial software with k-epsilon to predict flow phenomena which passes through the ejector nozzle in the ejector converging-diverging which varying exit diameters 3.5 mm; 4mm; 5 mm; and 5.5 mm. Respectively the simulation results showed exit nozzle steam ejector that the smallest diameter of 3.5 mm give the optimum performance because it provide the highest speed of fluidity. While the state of vacuum in mixing chamber increase, it cause the secondary mass flow higher as well as the value of the entrainment ratio.
34
Sukesan, Manu K., and Shine S. R. "Effect of back pressure and divergent section contours on aerodynamic mixture separation using convergent–divergent micronozzles." AIP Advances 12, no. 8 (2022): 085207. http://dx.doi.org/10.1063/5.0097772.
Testo completoAbstract (sommario):
A numerical investigation of the aerodynamic separation associated with converging–diverging two-dimensional planar micronozzles is reported. The impact of divergent section shapes such as linear, bell, and trumpet, the effect of different back pressure conditions, and the associated flow and separation features are studied. Simulations used the direct simulation Monte Carlo method and are validated with the available experimental data. The lateral separation effect is found to be influenced by the nozzle divergent section shape. The separation performance of micronozzles of different throat sizes indicates the dependence of the exit Kn on separation performance. The bell shape of the divergent section produced higher flow alignment, a thicker subsonic layer, more reduction in exit velocity, and lower separation performance than linear and trumpet shapes. The divergent section with a trumpet shape is preferred for higher species separation performance. The back pressure conditions at the exit of the nozzle are found to play a significant role in the curvature of streamlines and flow characteristics, which may play a vital role in mixture separation performance.
35
Tuladhar, Upendra, Sang-Hyun Ahn, Dae-Won Cho, et al. "Analysis of Gas Flow Dynamics in Thermal Cut Kerf Using a Numerical and Experimental Approach for Nozzle Selection." Processes 10, no. 10 (2022): 1951. http://dx.doi.org/10.3390/pr10101951.
Testo completoAbstract (sommario):
Consistency in gas flow behavior under various operating conditions is expected for uniform cutting performance in the thermal cutting process. The slope of the cut front in the kerf slot of a sample cutting material varies with the operating condition which affects the gas flow pattern. Therefore, how the nozzle exit diameter and the slope of the cut front effects gas flow behavior has been studied using the Reynolds averaged Navier–Stokes (RANS) based k–ω turbulence model. Convergent–straight-type nozzles with exit diameters φexit of 1.5 mm, 2 mm and 2.5 mm were used to study the flow patterns through the kerf slots of variable cut front slopes. The numerical simulation results were then compared with the results obtained from the Schlieren experiments. In addition, image processing was performed in the Schlieren images for clear visualization and precise comparison of the numerical and experimental data. The results confirm that a nozzle with an exit diameter of 2 mm shows a higher consistency in flow behavior in variable operating conditions.
36
Seyed-Yagoobi, J., V. Narayanan, and R. H. Page. "Comparison of Heat Transfer Characteristics of Radial Jet Reattachment Nozzle to In-Line Impinging Jet Nozzle." Journal of Heat Transfer 120, no. 2 (1998): 335–41. http://dx.doi.org/10.1115/1.2824253.
Testo completoAbstract (sommario):
The heat transfer characteristics of three submerged radial jet reattachment (RJR) nozzles with exit angles of +45, 0, and −10 deg are compared to the heat transfer characteristics of a conventional submerged in-line jet (ILJ) nozzle. The nozzles are compared at their favorable spacing from the impingement surface. The comparisons are based on two criteria: (1) identical fluid flow power, and (2) identical peak pressure exerted on the impingement surface. The local and area-averaged Nusselt numbers are presented. Experiments were conducted for two different flow power conditions. Comparison under identical flow power indicates that significant enhancements in local and comparable enhancements in area-averaged Nusselt numbers can be achieved with the RJR nozzles over the conventional ILJ nozzle while being able to control the net force exerted on the impingement surface. The comparison between the ILJ and RJR nozzles on the basis of the same peak pressure exerted on the impingement surface indicates that the zero degree exit angle RJR nozzle heat transfer characteristics are superior to the ILJ nozzle.
37
Weightman, Joel L., Omid Amili, Damon Honnery, Daniel Edgington-Mitchell, and Julio Soria. "Nozzle external geometry as a boundary condition for the azimuthal mode selection in an impinging underexpanded jet." Journal of Fluid Mechanics 862 (January 11, 2019): 421–48. http://dx.doi.org/10.1017/jfm.2018.957.
Testo completoAbstract (sommario):
The role of the external boundary conditions of the nozzle surface on the azimuthal mode selection of impinging supersonic jets is demonstrated for the first time. Jets emanating from thin- and infinite-lipped nozzles at a nozzle pressure ratio of $3.4$ and plate spacing of $5.0D$, where $D$ is the nozzle exit diameter, are investigated using high resolution particle image velocimetry (PIV) and acoustic measurements. Proper orthogonal decomposition is applied to the PIV fields and a difference in dominant instability mode is found. To investigate possible explanations for the change in instability mode, additional nozzle external boundary conditions are investigated, including the addition of acoustic dampening foam. A difference in acoustic feedback path is suggested to be the cause for the change in dominant azimuthal modes between the flows. This is due to the thin-lip case containing a feedback path that is concluded to be closed exclusively by a reflection from the nozzle base surface, rather than directly to the nozzle lip. The ability of the flow to form a feedback path that maximises the impingement tone gain is discussed with consideration of the numerous acoustic feedback paths possible for the given nozzle external boundary conditions.
38
Nasire, Najim, Mehdi Jadidi, and Ali Dolatabadi. "Numerical Analysis of Cold Spray Process for Creation of Pin Fin Geometries." Applied Sciences 14, no. 23 (2024): 11147. http://dx.doi.org/10.3390/app142311147.
Testo completoAbstract (sommario):
A numerical study was performed to analyze the particle deposition of a cold spray process for the preparation of nickel electrocatalysts used in the Hydrogen Evolution Reaction (HER). The study focused on the creation of fin-shaped geometries with an optimal porosity on the electrode surface using a mask located between the nozzle exit and the substrate. Computational Fluid Dynamics (CFD) was performed on a three-dimensional high-pressure nozzle, with nickel powder used as the injection feedstock. The behavior of particles was effectively modeled through a two-way coupled Eulerian–Lagrangian approach. As per the parametric study, four masks of varying wire thicknesses and opening sizes were investigated. The masks were placed at 4 mm increments from the nozzle exit, with the substrate placed at standoff distances (SODs) of 10 mm and 20 mm. To capture the effects of the gas inlet operating conditions, two different nozzle inlet conditions were analyzed (2 MPa and 400 °C, 4 MPa and 800 °C). It was found that the nozzle inlet operating condition had the most significant impact, as it relates to the particle velocity and powder deposition. The high-pressure operating condition resulted in a deposition efficiency (DE) greater than 99.9% for all the test cases, with nearly all the impacted particles depositing on the substrate. For the medium-pressure operating condition, the DE increased linearly as the mask SOD was increased, due to the increase in the particle velocity upon impact.
39
Chen, W. L., W. H. Huang, and W. H. Lai. "Investigation of flow characteristics of various-aspect-ratio rectangular nozzles with an aft deck." Shock Waves 34, no. 6 (2024): 527–38. https://doi.org/10.1007/s00193-024-01188-z.
Testo completoAbstract (sommario):
AbstractThis study presents an experimental and numerical investigation to characterize the plume pattern of a high-aspect-ratio rectangular convergent/divergent nozzle with an aft deck in under-expanded conditions. The function of an aft deck is to shield the infrared signal of an exhaust plume at its strongest intensity located at the immediate downstream region of the nozzle exit. However, this practice may cause undesirable plume deflection, which needs to be reduced as much as possible. The nozzle pressure ratios ranged from 2 to 4, and the effect of the nozzle exit aspect ratio was examined using wall static pressure measurements and schlieren visualization for cold flows. The experimental setup involved a 3D-printed aft deck nozzle made of acrylonitrile butadiene styrene material, which underwent surface smoothing using acetone vapor. Numerical simulations were conducted using the commercial STARCCM$$^{\mathrm {+}}$$ + software to analyze static pressure ratio variations at the aft deck. The investigation revealed that a nozzle pressure ratio of 3 induced a downward plume deflection at aspect ratio values of 6.77 and 7.54, while an increased aspect ratio of 8.35 resulted in the horizontal ejection of the plume. Moreover, at an aspect ratio of 8.35, the plume was ejected horizontally for nozzle pressure ratios ranging from 2 to 4. At a nozzle pressure ratio of 4, the flow separated from the deck without reattaching, and the plume moved horizontally with minimal deflection. The findings suggest that a combination of a high aspect ratio and sufficiently high nozzle pressure ratio can effectively reduce plume deflection.
40
Ihnatiev, O. D., N. S. Pryadko, G. O. Strelnikov, and K. V. Ternova. "Thrust characteristics of a truncated Laval nozzle with a bell-shaped tip." Technical mechanics 2022, no. 3 (2022): 35–46. http://dx.doi.org/10.15407/itm2022.03.035.
Testo completoAbstract (sommario):
This paper presents the results of a thrust performance study of an unconventionally shaped supersonic nozzle in the form of a truncated Laval nozzle with a bell-shaped tip. This nozzle shape may be used in the development of compact layouts of multistage rockets. The study was carried out using the ANSYS software package in a 3D formulation. The methodological approaches to the numerical calculation of a complex separated gas flow used in this study were verified in a previous study of the flow pattern in similar nozzle. Some results of exact calculations were compared with the results of experimental studies carried out at the Institute of Technical mechanics of the National Academy of Sciences of Ukraine and the State Space Agency of Ukraine for a model of a similar truncated nozzle with a bell-shaped tip blown with a cold air. This study detailed the features of the separated gas flow in a spherical tip connected (at the corner point) to a truncated supersonic Laval nozzle of conical shape. It was found that the pattern of the separated flow in the tip depends on the nozzle flow expansion degree (nozzle inlet pressure). At a relatively low nozzle inlet pressure, a developed separation zone is observed in the nozzle tip (between the jet boundary and the nozzle wall) with a subsonic flow from the external environment, which forms an almost constant static pressure from the tip inlet cross-section to the tip exit. At a nozzle inlet pressure at which the free boundary of the jet flowing from the truncated nozzle adjoins the nozzle wall, the static pressure in the tip varies almost linearly along the tip length from the corner point with the minimum pressure to the tip exit. The dependence of the thrust of a tipped nozzle on the nozzle inlet pressure is nonlinear. As the pressure upstream of the nozzle increases (or the ambient pressure decreases), the effect of the external environment on the tipped-nozzle thrust diminishes. It is shown that under "terrestrial conditions" the thrust of a truncated nozzle with a tip exceeds the thrust of a profiled nozzle with the same geometric expansion degree (due to the atmosphere “entering” the tip). Under "vacuum” conditions, the former is 8% less than the latter.
41
Kozlov, V. V., A. V. Dovgal, M. V. Litvinenko, Yu A. Litvinenko, and A. G. Shmakov. "DIFFUSION COMBUSTION OF A HYDROGEN MICROJET, OUTFLOWING FROM A CURVLINEAR CHANNEL." Доклады Российской академии наук. Физика, технические науки 513, no. 1 (2023): 72–75. http://dx.doi.org/10.31857/s2686740023060123.
Testo completoAbstract (sommario):
The presented work examines the combustion of a hydrogen microjet flowing from a curved channel with a round micronozzle. Jet flows that are generated using rectilinear and curved channels differ in that in the second case, Dean vortices make a noticeable contribution to the formation of the jet and its combustion. The interaction of the latter with Kelvin–Helmholtz vortices, the formation of which is typical for flows with a velocity shift, causes changes in combustion characteristics. They include spatial distortions of the laminar flame zone near the nozzle exit, the area of turbulent combustion downstream, as well as the turbulent flame in the conditions of its separation from the nozzle exit and the cessation of laminar combustion in the initial section of the flow. The results of these studies provide an opportunity to better understand the combustion features of hydrogen microjets under conditions of their hydrodynamic instability.
42
Trabold, T. A., and N. T. Obot. "Evaporation of Water With Single and Multiple Impinging Air Jets." Journal of Heat Transfer 113, no. 3 (1991): 696–704. http://dx.doi.org/10.1115/1.2910620.
Testo completoAbstract (sommario):
An experimental investigation of impingement water evaporation under a single jet and arrays of circular jets was made. The parametric study included the effects of jet Reynolds number and standoff spacing for both single and multiple jets, as well as surface-to-nozzle diameter ratio and fractional nozzle open area for single and multiple jets, respectively. The nozzle exit temperature of the air jet, about the same as that of the laboratory, was 3–6° C higher than that of the evaporating water. Predictive equations are provided for mass transfer coefficient in terms of the flow and geometric conditions.
43
Hutli, Ezddin, Salem Abouali, Ben Hucine, Mohamed Mansour, Milos Nedeljkovic, and Vojislav Ilic. "Influences of hydrodynamic conditions, nozzle geometry on appearance of high submerged cavitating jets." Thermal Science 17, no. 4 (2013): 1139–49. http://dx.doi.org/10.2298/tsci120925045h.
Testo completoAbstract (sommario):
Based on visualization results of highly-submerged cavitating water jet obtained with digital camera, the influences of related parameters such as: injection pressure, nozzle diameter and geometry, nozzle mounting (for convergent / divergent flow), cavitation number and exit jet velocity, were investigated. In addition, the influence of visualization system position was also studied. All the parameters have been found to be of strong influence on the jet appearance and performance. Both hydro-dynamical and geometrical parameters are playing the main role in behavior and intensity of cavitation phenomenon produced by cavitating jet generator. Based on our considerable previous experience in working with cavitating jet generator, the working conditions were chosen in order to obtain measurable phenomenon.
44
Daubner, Tomas, Jens Kizhofer, and Mircea Dinulescu. "Experimental investigation of five parallel plane jets with variation of Reynolds number and outlet conditions." EPJ Web of Conferences 180 (2018): 02018. http://dx.doi.org/10.1051/epjconf/201818002018.
Testo completoAbstract (sommario):
This article describes an experimental investigation in the near field of five parallel plane jets. The study applies 2D Particle Image Velocimetry (PIV) for ventilated and unventilated jets, where ventilated means exiting into a duct with expansion ratio 3.5 and unventilated means exiting to the free atmosphere. Results are presented for Reynolds numbers 1408, 5857 and 10510. The Reynolds number is calculated for the middle channel and is based on the height of the nozzle (channel) equivalent diameter 2h. All characteristic regions of the methodology to describe multiple interacting jets are observed by the PIV measurements - converging, merging and combined. Each of the five parallel channels has an aspect ratio of 25 defined as nozzle width (w) to height (h). The channels have a length of 185 times the channel height guaranteeing a fully developed velocity profile at the exit from the channel. Spacing between the single plane jets is 3 times the channel height. The near field of multiple mixing jets is depended on outlet nozzle geometry. Blunt geometry of the nozzle was chosen (sudden contraction).
45
Knowles, K., and L. Kirkham. "Inverted-profile coaxial jet flows relevant to Astovl applications." Aeronautical Journal 102, no. 1017 (1998): 377–84. http://dx.doi.org/10.1017/s0001924000065155.
Testo completoAbstract (sommario):
AbstractAn experimental investigation has been performed into the free jet and wall jet characteristics of high pressure ratio coaxial jets operating with inverted velocity profiles and impinging onto a ground plane. Pitot-static probes have been used to record free jet properties at various distances from the jet exit plane, and wall jet properties of the impinging jets at various radial positions. Jet properties such as velocity decay and spreading rates were calculated and compared to published literature. Wall jet development was investigated and recorded. Inner and outer nozzle pressure ratio (NPR) were altered to give a range of jet exit conditions. The results obtained showed variations in the wall jet properties as jet exit conditions were altered, but wall jet self-similarity was found and varying either nozzle height above the ground plane or NPR did not alter this. Free jet data showed large variations in behaviour with changes in NPR. The inverted profile jets behaved similarly to annular jets, showing similar characteristics. Inner jet pressurisation was observed for inverted profile jets and also significant acceleration of the flow from the inner, lower NPR, jet when this was subcritical.
46
Ternova, K. V. "Effect of the tip geometry of a truncated supersonic nozzle on its characteristics." Technical mechanics 2023, no. 2 (2023): 32–40. http://dx.doi.org/10.15407/itm2023.02.032.
Testo completoAbstract (sommario):
Truncated nozzles are used for tight packing of the rocket engine. Such nozzles have a profiled tip to maximize the filling of space and reduce the overall weight. This paper is concerned with the study the effect of the tip geometry of a truncated supersonic nozzle on its characteristics. The features of the gas flow at different initial pressures and different environmental conditions in the supersonic area of a nozzle with a bell-shaped tip of different lengths are considered. The flow inside the nozzle followed by the jet outflow into the surrounding space was simulated. The flow simulation for tips at sea level showed a similar structure of the Mach number isolines, and the only difference was in the intensity of the vortex structure near the tip wall. As the pressure at the nozzle inlet increases, the length of the first “barrel” increases proportionally, and the vortex structure near the tip walls decreases. For the upper atmosphere, the flow pattern is different. The supersonic flow in the nozzle does not undergo separation, and therefore there are no vortex structures from the external environment. The flow downstream of the tip exit deflects from the axis through the angle determined by the Prandtl–Meier flow at the corner point of the tip exit, and the shape of the first “barrel” is distorted by a hanging shock. An analysis of the obtained results shows that the ambient pressure downstream the nozzle exit significantly affects the flow pattern in the nozzle. It is established that the thrust coefficient of both circuits at sea level decreases with increasing pressure at the nozzle inlet, which is explained by a decrease in the effect of the ambient pressure on the tip wall. In the upper atmosphere, the flow is adjacent to the tip wall, and the thrust coefficient for nozzles of different lengths has almost the same constant value at different inlet pressures. It is shown that a decrease in the length of the nozzle, all other geometrical dimensions of the nozzle being equal, does not significantly affect the impulse characteristics.
47
Ranjan, Abhash, Mrinal Kaushik, Dipankar Deb, Vlad Muresan, and Mihaela Unguresan. "Assessment of Short Rectangular-Tab Actuation of Supersonic Jet Mixing." Actuators 9, no. 3 (2020): 72. http://dx.doi.org/10.3390/act9030072.
Testo completoAbstract (sommario):
This work explores the extent of jet mixing for a supersonic jet coming out of a Mach 1.8 convergent-divergent nozzle, controlled with two short rectangular vortex-generating actuators located diametrically opposite to each other with an emphasis on numerical methodology. The blockage ratio offered by the tabs is around 0.05. The numerical investigations were carried out by using a commercial computational fluid dynamics (CFD) package and all the simulations were performed by employing steady Reynolds-averaged Navier–Stokes equations and shear-stress transport k−ω turbulence model on a three-dimensional computational space for more accuracy. The numerical calculations are administered at nozzle pressure ratios (NPRs) of 4, 5, 6, 7 and 8, covering the overexpanded, the correctly expanded and the underexpanded conditions. The centerline pressure decay and the pressure profiles are plotted for both uncontrolled and the controlled jets. Numerical schlieren images are used to capture the barrel shock, the expansion fans and the Mach waves present in the flow field. Mach contours are also delineated at varying NPRs indicating the number of shock cells, their length and the variation of the shock cell structure and strength, to substantiate the prominent findings. The outcomes of this research are observed to be in sensible concurrence with the demonstrated exploratory findings. A reduction in the jet core length of 75% is attained with small vortex-generating actuators, compared to an uncontrolled jet, corresponding to nozzle pressure ratio 5. It was also seen that the controlled jet gets bifurcated downstream of the nozzle exit at a distance of about 5 D, where D is the nozzle exit diameter. Furthermore, it was fascinating to observe that the jet spread increases downstream of the nozzle exit for the controlled jet, as compared to the uncontrolled jet at any given NPR.
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Kang, Jun Seok, and Chi Young Lee. "Investigation on Effects of Water Mist Characteristics According to Axial Position on Thermal Radiation Attenuation Performance." Fire Science and Engineering 36, no. 3 (2022): 11–18. http://dx.doi.org/10.7731/kifse.32592e18.
Testo completoAbstract (sommario):
In this study, the effects of water mist characteristics according to the axial position on thermal radiation attenuation performance were experimentally investigated using the single-fluid nozzle. Under the water flow rate conditions of 200∼350 g/min, the thermal radiation attenuation performance was measured at the axial position (i.e., downstream direction of water mist from nozzle exit) of 200∼1000 mm. In addition, during the discharge of water mist, the water supply pressure and droplet size of water mist were measured and the water mist was visualized. As a result, with an increase in the water flow rate, the thermal radiation attenuation performance was improved. Overall, the attenuation rate was measured to be 12.4∼30.1%. In the axial position of 200∼400 mm, with an increase in the axial distance from the nozzle exit, the thermal radiation attenuation performance was improved. This may be because the effect of improvement of the thermal radiation attenuation performance by an increase in the spray width is predominant over the effect of reduction in it by an increase in the droplet size. In addition, in the axial position of 400∼1000 mm, with an increase in the axial distance from the nozzle exit, the thermal radiation attenuation performance was reduced. This is because the droplet size of water mist increases and spray width is narrowed. Based on this study, it was confirmed that the water mist characteristics according to the axial position and thermal radiation attenuation performance are closely correlated.
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Ghazwani, Hassan Ali, Khairuddin Sanaullah, and Afrasyab Khan. "Hydrodynamics of Supersonic Steam Jets Injected into Cross-Flowing Water." Fluids 8, no. 9 (2023): 250. http://dx.doi.org/10.3390/fluids8090250.
Testo completoAbstract (sommario):
High-speed gas/vapour jets injected into a cross-moving sonic liquid signifies a vital phenomenon which bears useful applications in environmental and energy processes. In the present experimental study, a pulsating jet of supersonic steam was injected into cross-flowing water. Circulation zones of opposite vorticity owing to the interaction between the steam jet and cross-water flow were found. However, a large circulation appeared in front of the nozzle exit. Also, most small circulation regions were observed at higher water-flow rates (>2 m3/s). Among the prime mixing variables (i.e., turbulence kinetic energy (TKE) and Reynolds shear stress (RSS)), the RSS estimations backed a small diffusive phenomenon within a region far from the nozzle exit. Further information extracted from the PIV images indicated the existence of Kelvin–Helmholtz (KH) instabilities. The counter-rotating vortex pairs (CVPs) appeared to be significant in the region close to the nozzle exit, and they exhibited leeward side folds. Moreover, the effects of the operating conditions on the pressure recovery and mixing efficiency as well as the penetration and the separation height were evaluated to determine the optimisation of the phenomenon. By applying extreme difference analysis, the mixing efficiency was found as the most influential parameter.
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Chen, J. L., M. Wells, and J. Creehan. "Primary Atomization and Spray Analysis of Compound Nozzle Gasoline Injectors." Journal of Engineering for Gas Turbines and Power 120, no. 1 (1998): 237–43. http://dx.doi.org/10.1115/1.2818082.
Testo completoAbstract (sommario):
This work addresses primary atomization modeling, multidimensional spray prediction, and flow characteristics of compound nozzle gasoline injectors. Compound nozzles are designed to improve the gasoline spray quality by increasing turbulence at the injector exit. Under the typical operating conditions of 270-1015 kPa, spray atomization in the compound nozzle gasoline injectors is mainly due to primary atomization where the flow turbulence and the surface tension are the dominant factors. A primary atomization model has been developed to predict the mean droplet size far downstream by taking into account the effect of turbulent intensity at the injector exit. Two multidimensional spray codes, KIVA-2 and STAR-CD, originally developed for high-pressure diesel injection, are employed for the lower-pressure gasoline injection. A separate CFD analysis was performed on the complex internal flows of the compound nozzles to obtain the initial and boundary conditions for the spray codes. The TAB breakup model used in KIVA-2 adequately facilitates the atomization process in the gasoline injection.