Nozzle Edge Research Articles

Design Method of a Modular Shape-Transition Nozzle for an Axisymmetric Scramjet-Powered Vehicle

For a hypersonic vehicle powered by modular scramjet, integration of the airframe with the engine is critical to generating positive net thrust. In this study, a design method that combines the ideas of streamline tracing and trimming is generalized to design the modular shape-transition nozzle for integrating with the axisymmetric vehicle after-body. As an example, the design of a modular shape-transition nozzle with three modules for an axisymmetric vehicle is presented, and the computational fluid dynamics (CFD) approach is adopted to obtain the detailed flowfield and performance of the modular nozzle. Smooth expansion of the burner-exits gas along the flow direction is involved in the modular nozzle. The flow interactions between any two module exhausts, as well as the flow interaction of the modular jet with the external freestream, are all appearing at the trailing edge of the modular nozzle. Moreover, the modular nozzle produces a net thrust coefficient of 0.8536 and an integrated thrust coefficient of 0.7896 for the vehicle. The mixing of the modular nozzle jet with the freestream is enhanced with the trimming of the separate nozzle module, an approach which can reduce the infrared radiation signal.

Investigation of fluidic thrust vectoring for scramjets

Fluidic thrust vectoring (FTV) offers a novel approach to aerodynamic control, circumventing some of the issues associated with mechanical systems. One method is shock vector control which involves injecting a fluid into the exhaust nozzle of an engine to redirect the gases and thus, produce a control force. An experimental model which incorporated FTV was designed and tested at Mach 6 in the Oxford high density tunnel (HDT). The model was a simplified two-dimensional scramjet geometry with two different configurations to compare an internal and external exhaust nozzle. The FTV injection system consisted of a slot at the rear edge of the exhaust nozzle fed from an internal plenum. In the experimental campaign, a range of gas injection pressures and free stream stagnation pressures were tested to assess the effectiveness of both configurations. Two new measurement methods were successfully implemented in the HDT: pressure sensitive paint and a 6-axis load cell. The FTV system has been shown to be effective with observable increases in lift and pitching moment. A linear relation between the injection pressure ratio and the control forces could be observed for both configurations.Graphical abstract

Effect of various configurations of swirl generator system on the hydrothermal performance of the flat-plate solar collector

This is a numerical study that analysis the heat extraction potential of solar collector tubes by assembling a couple of nozzles at the sealed end of the pipe to make swirl flow. Swirl flow intensifies the turbulence rate which augments heat transfer by ruffling the boundary layer. To this end, several decisive factors including nozzle angle (A: 30°, 45°, 60°, 90°), tube diameter (D: 20 mm, 50 mm), nozzle edge size (N: 6.25, 12.5, 25 mm (for D50) and N: 2.5, 5, 10 mm (for D20)), and mass flow rate (M: 0.1, 0.5, 1 kg/s (for D50) and M: 0.04, 0.2, 0.4 kg/s (for D20)) were considered. Results demonstrated that all of the models of class ''A…/D20/N…/M…“ had higher heat extraction potential but lower friction factor compared with ”A…/D50/N…/M…“. Maximum and minimum values of heat flux extractions are 2113390 W/m2 and 59239 W/m2 that were obtained by ”A60/D20/N2.5/M0.4″ and “A30/D50/N25/M0.1″. The created friction factor by class ”A…/D50/N…/M…“ is higher than class ''A…/D20/N…/M…”. The highest friction factor is 3.51 (''A90/D20/N2.5/M0.04″) and the lowest friction factor is 0.019 (“A30/D20/N2.5/M0.2″). Overall, for all cases, class ”A…/D50/N…/M…“ bear the higher TPF compared with class ”A…/D50/N…/M…“ so that the greatest and lowest values of TPF are 5.09 and 0.49 achieved by ”A30/D50/N6.25/M1″ and “A90/D20/N5/M0.4″, respectively.

Long Range Optical Distance Sensors for Liquid Metal Free Surface Detection

For the demonstration of fusion power plant technology, DEMO dedicated materials are necessary to cope with the harsh environment of high energy neutrons. For this purpose, the international neutron irradiation facility for fusion materials IFMIF/DEMO Oriented Neutron Source (DONES) is planned to be built in Granda, Spain. In the DONES facility, a deuteron beam hitting the lithium target produces a high energy neutron flux. Due to the high-power density, the windowless target is a free surface liquid lithium flow in a duct with a concave backplate. In order to keep the heat released by the beam within the liquid lithium and to avoid its intrusion in the backplate, a stable configuration of the free surface flow with a setpoint layer thickness of 25 ± 1 mm is crucial. In particular, stable wave structures, so called wakes, which occur from accumulated impurities at the nozzle edge, can cause a critical local decrease in the layer thickness of more than 1 mm. Therefore, it is necessary to better understand the nature of these wakes and to be able to monitor the surface profile to shut down the beam in case of a critical thickness loss, but to avoid unintended shutdowns. In the context of this work, currently available optical sensors were tested on their capability of detecting a specular liquid metal surface at measurement distances of several meters. After an initial selection, two optical sensors were further considered. Experiments with the liquid metal alloy GaInSn and simulations with the software Blender of the selected optical sensors for their capability of measuring distances of liquid metal were conducted. The results showed a significant dependency of the measurement results on the waviness of the liquid metal surface. Nevertheless, it was possible to resolve the wavy liquid metal surface with a sufficient resolution to detect critical wake structures.

Flow Feature in Supersonic Non-Isobaric Jet near the Nozzle Edge

Using the example of studying the supersonic underexpanded jet initial section, the issue of interpreting the experimental visualization data and Pitot pressure measurement data using the results of numerical calculations (2d RANS k-ω SST) is discussed. It is shown that the gradient S-shaped feature of the gas-dynamic structure near the nozzle exit, observed in the form of a barrel shock, is a characteristic that separates the expansion and compression regions, and downstream is transformed into a barrel shock. It has been established that the reason for the observed S-shaped curvature of this feature is the axisymmetric nature of the jet flow.

Reimann Brake Ramp for planar flow casting processes and analysis of ribbon gluing

Planar flow casting is a rapid solidification process used to manufacture thin, metallic ribbons, and foil. Liquid metal is forced through a nozzle against a heat-sink wheel, and it rapidly solidifies into thin ribbons. A puddle of molten metal, held by surface tension, forms between the nozzle and wheel. This study examines a well-defined periodic surface defect called herringbone (HB), which is commonly produced when casting zirconium based alloys. The presence of this defect is related to processing conditions and puddle dynamics. Its formation has been correlated with the pinning of the liquid puddle at the nozzle edge. Here, the uniformity of thickness along a ribbon was successfully controlled (over a length of 50 m) using the Reimann Brake Ramp, which reduces the wheel speed at the start of the cast. For the alloy used in this study, the variation in the dimensionless thickness parameter, τ/G, with the Euler number (Eu=ΔP/ρU2) at assigned values of B/G followed an allometric scaling, with an exponent value close to the theoretical value of 1/3. Furthermore, the nozzle inclination was related to the ribbon thickness, τ, and the ribbon quality. Moreover, a newly developed automatized melt spinner permitted monitoring and controlling of the process parameters, elucidating the gluing phenomenon of the ribbon observed during the starting phase. The ribbon gluing was influenced by the puddle geometry, the recirculation in the puddle, and later, to the ribbon cooling rate. Within these results, high-quality ribbons with control thickness over a considerable length are achieved.

Gravity impact on inverted conical flame stability and dynamics

The paper studies experimentally the stability of an inverted conical plane-symmetrical premixed methane-air flame under normal and reversed gravity. The conical flame is stabilized by a thin transverse rod. Flow velocity is varied within the range of 1–8 m/s, fuel equivalence ratio— within the range of 0.8–1.4. It is shown that such a flame could be both V-shaped (attached only to the stabilization rod) and M-shaped (attached both to nozzle edge and stabilization rod) depending on the set of conditions. The transition between two modes is studied experimentally under normal and reversed gravity. The hysteresis properties for the M–V and V–M transitions under the normal gravity conditions and their absence under the reverse gravity ones are reported. The most unstable flames are observed under reversed gravity at the maximum burning velocity (φ ≈ 1.1 ±). For such conditions, periodical oscillations between M-shaped and V-shaped flames occur over a wide range of velocities. In the experiments under reverse gravity, the V shape prevails over the M shape. It is found that a reverse flow exists above the stabilizer at any velocity under normal gravity and at high velocities (>5 m/s) under reverse gravity. In both cases, a linear increase in the longitudinal size of the vortex zone with increasing velocity is observed. It is concluded that gravity noticeably contributes to rich flames stability.

Resolvent-based modelling of coherent structures in a turbulent jet flame using a passive flame approach

Motivated by the recent success in finding coherent structures in turbulent flows and describing their noise emission using the Resolvent Analysis (RA), the method is applied to a turbulent jet flame at Re=15,000 and a corresponding non-reacting flow to investigate their axisymmetric dynamics. The RA, which in this study assumes a passive flame and neglects compressibility effects, is based on the governing equations linearized around the temporal mean state. It is validated against Spectral Proper Orthogonal Decomposition (SPOD) obtained from time-resolved snapshots. Both the temporal mean state and the snapshots are obtained by Large Eddy Simulation (LES). The SPOD reveals that an axisymmetric, convective Kelvin–Helmholtz (KH) instability is the dominant hydrodynamic mechanism in the jet flame within a narrow frequency band and incorporates up to 40% of the turbulent kinetic energy. Results show that the RA is capable of reproducing the mode shapes seen in the SPOD. The RA furthermore allows to address the origin of these hydrodynamic structures: While the corresponding KH mode in a non-reacting turbulent jet flow is most sensitive to perturbations in the nozzle boundary layer, the same dominant mode in the turbulent Bunsen flame is most receptive to perturbations in the region between the nozzle edge and the annular pilot burner. The results suggest that the strong density gradients in this region initiate perturbations in the baroclinic torque, which are feeding the KH mode. Finally, a linear stability analysis proves that the high sensitivity of the KH structure is due to resonance with stable linear eigenmodes, which explains its high energy content. By applying the RA to a turbulent reacting flow, this study opens up a new pathway in analyzing the role of hydrodynamic structures in reacting flows.

Wake Shape and Height Profile Measurements in a Concave Open Channel Flow regarding the Target in DONES

Wakes appearing downstream of disturbances on the surface of a water flow in a concave open channel were examined experimentally. The investigated channel geometry was similar to the liquid lithium target in DONES (Demonstration fusion power plant Oriented NEutron Source). The objective of the measurements was to analyze the effect of a disturbance on the downstream layer thickness. For measuring the height profiles in the channel, an optical measurement system based on laser triangulation was developed. It was shown that the wake of the undisturbed flow emerged from the nozzle corner, which was in accordance with analytical solutions. For sufficiently large disturbances at the nozzle edge, the height profiles located downstream showed symmetrical minima and maxima on both sides of the disturbance. The wake depth strongly depended on the diameter and penetration depth of the disturbance, as well as the circumferential position in the channel, which yields to a critical wake depth of one millimeter for the lithium target in DONES.

Direct Numerical Simulation of Bubble Formation Through a Submerged “Flute” With Experimental Validation

Abstract Direct numerical simulation (DNS) is often used to uncover and highlight physical phenomena that are not properly resolved using other computational fluid dynamics methods due to shortcuts taken in the latter to cheapen computational cost. In this work, we use DNS along with interface tracking to take an in-depth look at bubble formation, departure, and ascent through water. To form the bubbles, air is injected through a novel orifice geometry not unlike that of a flute submerged underwater, which introduces phenomena that are not typically brought to light in conventional orifice studies. For example, our single-phase simulations show a significant leaning effect, wherein pressure accumulating at the trailing nozzle edges leads to asymmetric discharge through the nozzle hole and an upward bias in the flow in the rest of the pipe. In our two-phase simulations, this effect is masked by the surface tension of the bubble sitting on the nozzle, but it can still be seen following departure events. After bubble departure, we observe the bubbles converge toward an ellipsoidal shape, which has been validated by experiments. As the bubbles rise, we note that local variations in the vertical velocity cause the bubble edges to flap slightly, oscillating between relatively low and high velocities at the edges.

Inducing swirl flow inside the pipes of flat-plate solar collector by using multiple nozzles for enhancing thermal performance

In this numerical study, an attempt has been made to improve the thermal performance of the flat-plate solar collector (FPSC) by inducing the swirl flow inside the tube by the considered nozzles. To this end, the effect of the number of circumferential nozzles and their inclination angles was taken into the account. The considered number of nozzles was "single", ''dual'', ''triple'', and ''quad''. For each of the said cases, the inclination angle of nozzles was taken 30°, 45°, 60°, and 90° (A30, A45, A60, A90). Moreover, the mass flow rate of single-nozzle pipe was considered 0.2 kg/s, 1 kg/s, and 2 kg/s. To analyze all of the cases under identical conditions, the said mass flow rates were distributed equally among all of the nozzles (for ''dual'', ''triple'', and ''quad''). All of the characteristics were defined in a form of "A…-D…-N…-M…'' where ''A…'', "D…", "N…", and "M…" stand for angle of injection, diameter of pipe, nozzle cross-section edge, and mass flow rate, respectively. Numerical simulation (3-dimensional) of the system was performed by Finite Volume Method (FVM). The turbulence nature of flow was simulated by the k-omega SST (shear stress transport) turbulent model. Results showed that the "single-nozzle'' swirl generator had the highest thermal performance factor (TPF) so that for all cases its values were greater than unit. Mass flow rate growth increases Nu, heat extraction rate, and kinetic energy rate (KER) while drops friction factor and outlet temperature. Increment of injection angle increases outlet temperature and friction factor and reduces KER. The maximum and minimum values of TPF are 4.19 and 0.44 which belong to "single; A30-D50-N12.5-M0.2" and "quad; A90-D50-N12.5-M0.5", respectively.

Investigation of Pobeda furnace bubbling zone physics using cold modeling method. Message 1. Investigation of fluid and gas dynamics of bubbling using a side-blowing gas-protected lance

Pobeda furnace operation was studied in the Archimedes criteria range from 5 to 60 using the cold modeling method to determine fluid and gas dynamics of bubbling using a side-blowing gas-protected lance. A transparent reactor of the laboratory setup was made on a scale of 1 : 10. Cylindrical lance nozzle diameter was 5 mm, annular space was 1 mm and angle to the horizontal in the reactor working position was 12°. It is shown that air interaction with water at its excessive pressure of 105 N/m2 occurs in the form of a pulsating stream in a cyclical pattern with the different maximum torch size amplitude and the time required to achieve it. Dynamic borders of the primary near-nozzle zone were determined depending on the Archimedes criterion value for separate and cooperative gas flow through the lance shell and central channel in the stream straight-line development area (lmin ≤ I ≥ lmax). Dynamic head of torch pulsation at extremum points varies in the range of 6,00 • 10-5÷8,26 • 10-4 Pa. Empirical equations for stream length in straight-line and full stream development areas and liquid release height were obtained depending on the Archimedes criterion value. An intermediate layer of ejected liquid was found between circular and cylindrical submerged streams. Cooperative axial gas flow is maintained at identical Archimedes criteria of air supply to the shell and central channel for the values Arsh = Arc = 25 at a distance of 0.0094—0.0116 m from the nozzle edge. As a result of research conducted it should be assumed that there is no interaction of blast oxygen from the central channel of the double -flow lance with surrounding melt at a distance of 9—11 cm from the Pobeda furnace lining.

Inverted conical methane/air flame shape transformation under acoustic excitation

An inverted conical plane-symmetrical premixed methane–air flame under acoustic excitation was investigated experimentally. The flame was a conical one stabilized by a thin transverse rod. The Reynolds numbers were varied within 400–3000, and the fuel equivalence ratios were 0.8–1.4. Such a flame can take the shape of two fundamentally different types: M—when the flame front attaches both to the nozzle edge and stabilization rod; V—only to the stabilization rod. The transition conditions from one front configuration to another (M–V and V–M) were studied under various excitation parameters. Acoustic disturbances with a frequency of up to 420 Hz and an amplitude of longitudinal velocity pulsations up to 10% of the mean flow velocity excited the flame. New experimental data were obtained on the conditions corresponding to the M–V and V–M transitions. Qualitative and quantitative parameters of the hysteresis effect at which M–V and V–M transitions are realized, similar to the case of swirling flames, were revealed. The frequencies at which the acoustics most strongly affects the M–V and V–M transitions conditions were found. The hysteresis deterioration for M–V and V–M transitions was shown for the first time. It was noted that the conditions for the hysteresis deterioration are close to the theoretical frequency of the descent of vortices from the nozzle edge. The local maxima of the characteristic Strouhal numbers corresponding to the features of the minimum divergence of the flow velocities at the M–V and V–M transitions were determined.

Optimization of printing parameters of 3D-printed continuous glass fiber reinforced polylactic acid composites

A novel 3D printing strategy for continuous glass fiber reinforced polylactic acid (CGF/PLA) composites was proposed. CGF/PLA filament was prepared by a melting impregnation device, and then CGF/PLA filament was directly supplied to the self-modified 3D printing device. The impregnation process was optimized systematically, and the fiber content reached up to 45 wt%. A specific compatibilizer was used and the amount of compatibilizer was optimized to enhance the interfacial bonding between fiber and polymer. The effects of printing parameters such as nozzle diameter, edge width, layer thickness, printing speed and temperature on the mechanical properties and microstructure of the final printed products were studied. The flexural strength and flexural modulus of the printed products reached 312 MPa and 21.5 GPa, respectively. The fabrication strategies proposed in this study can provide a low-cost and high-strength method for the industrial application of 3D printed continuous fiber reinforced thermoplastic composites.

Kinetics of the WC particles motion in liquid steel during laser surface modification*

ABSTRACT Laser surface modification of steel with tungsten carbide (WC) particles provides significant wear-resistance increasing. At the same time, it is important to achieve a uniform distribution of reinforcing particles over the depth of the created composite layer. To find out the possibility of the particles of different sizes application and to determine the allowable ranges of parameters of the coaxial to the laser beam powder injection, the calculations of the kinetics of penetration of WC particles into the molten surface of a sample made of carbon steel were carried out. It was shown that WC spherical particles with a diameter of about 50–150 µm, which are the most suitable for this application, could be injected into the entire depth of the molten part of the steel matrix if their speed of movement from the nozzle edge is from 6 m/s. All of them must reach the boundaries of the molten pool, and its shape determines their distribution throughout the depth. This provides the possibility to achieve uniform hardening throughout the depth by varying the parameters of laser radiation.

МЕТОДИКА РАСЧЕТА СТРУЙНЫХ АППАРАТОВ, ИСПОЛЬЗУЕМЫХ В ГИДРОМЕХАНИЗАЦИИ

Purpose: to develop a methodology for calculating jet devices used in hydromechanization for the development of soils and cleaning reservoirs from sediments using the results of our own research and the theoretical and empirical dependences presented in the literature. Materials and Methods: on the example of a diagram of an annular two-surface jet ejectors with increased energy characteristics, a method has been developed and the calculation of the relative and actual geometric and hydraulic parameters of its elements is shown for use as a suction tip on suction dredgers at the necessity to increase the suction height and development depth of centrifugal dredgers. Results. Based on the initial data (the values of the hydraulic resistance coefficients of the inlet section, diffuser, nozzle, the distance from the nozzle edge to the beginning of the mixing chamber, mixer, operating parameters of the pump – pump head and flow rate, pipeline diameters), the pulp density in the suction nozzle, the weight coefficient of ejection, geometric characteristic, relative optimum head, actual heads of the jet apparatus and pump-blower, volumetric total flow, volumetric consistency of the pulp in the suction pipeline, performance over the ground, actual dimensions. Conclusions: the developed methodology will allow calculating the optimal dimensions of jet enjector of a new design and developing a design for the suction tip of a suction dredger for various in pressure, flow rate and development depth of operational options for removing bottom sediments in water bodies.

Моделирование интенсивного теплосилового воздействия газовой среды для испытаний образцов в широком диапазоне параметров

The results of the work extend the available range of the parameters of gas acting on the samples of materials and coatings being tested under intense heat and power loads to study their properties and resource characteristics under stationary and pulsed exposure. A feature of the conditions proposed in this work for testing samples, distinguishing them from most common existing methods, is the simultaneous impact of a high temperature flux and high-pressure flow on the sample surface, the possibility of obtaining an oxidizing or reducing medium with different chemical compositions, as well as a pulsed cyclic effect on a material sample. The high performance of the experimental setup allows for up to 10 sample tests per day. To perform the research of the samples, a supersonic gas jet with nominal mode regimes was modeled. The jet was generated by gas dynamics facility through carbohydrate and oxygen mixture combustion and flow acceleration in Laval nozzle. Test sample can be positioned under various angles relative to the jet axis and on the desired distance from the nozzle edge. If necessary, the sample can be provided with measurement devices allowing measurements of temperature, heat flow and pressure. In order to provide a calibrated effect on the samples, the fields of jet parameters were studied using calibration plates provided with surface pressure sensors and thermocouples for determining heat fluxes. As a result, parameter fields of pressure, heat fluxes, pressure gradients, and friction stresses on the surface of samples were obtained depending on samples orientation and gas jet thermodynamic properties. Considering these field of parameters, tests can be performed to study the properties of materials. Metal and composite materials can be used as test samples as well as samples for testing the durability of coatings, multi-layer structures and protective fabric materials.

Investigation of the flow phenomena in high-pressure water jet nozzles

High-pressure water jets are often used as a tool for cleaning, cutting or for modification of the surface morphology. The nozzle design has a considerable influence on cavitation and wear effects as well as on the nature of the exiting jets. Different applications are affected by different flow regimes, such as cavitation or hydraulic-flip, which depend on the radius of the nozzle edge.In this work, the turbulent two-phase flow within two different nozzle types is analyzed using Computational Fluid Dynamics. The focus was to establish a relationship between the geometry of these nozzles and the flow phenomena as well as between wall shear stress and the wear, which leads to the change of the water jet shape and reduces the lifetime of high-pressure nozzles. The performed variation of the nozzle edge from sharp to round showed a significant influence on the maximum wall shear stress and cavitation. Additionally, the inner surface of used nozzles was investigated with Scanning Electron Microscope. Numerous marks of erosion were found at the nozzle edge. For the validation, the volumetric flow rate through the nozzles was measured at different inlet pressures and compared with the simulation results, which showed a good agreement.

Ablation-Dominated Arcs in CO2 Atmosphere—Part II: Molecule Emission and Absorption

Molecule radiation can be used as a tool to study colder regions in switching arc plasmas like arc fringes in contact to walls and ranges around current zero (CZ). This is demonstrated in the present study for the first time for the case of ablation-dominated high-current arcs as key elements of self-blast circuit breakers. The arc in a model circuit breaker (MCB) in CO2 with and an arc in a long nozzle under ambient conditions with peak currents between 5 and 10 kA were studied by emission and absorption spectroscopy in the visible spectral range. The nozzle material was polytetrafluoroethylene (PTFE) in both cases. Imaging spectroscopy was carried out either with high-speed cameras or with intensified CCD cameras. A pulsed high-intensity Xe lamp was applied as a background radiator for the broad-band absorption spectroscopy. Emission of Swan bands from carbon dimers was observed at the edge of nozzles only or across the whole nozzle radius with highest intensity in the arc center, depending on current and nozzle geometry. Furthermore, absorption of C2 Swan bands and CuF bands were found with the arc plasma serving as background radiator. After CZ, only CuF was detected in absorption experiments.

Accuracy of the pneumatic follower for the wooden surface quality assessment

Wooden or wood-plastic composite surfaces are often valued for their aesthetic appearance and the quality of the surface. Independent from the technology, the surface features may be assessed using typical roughness parameters. In this paper, a pneumatic non-contact method is proposed. Despite certain limitations in surface characteristics measurement, air gauges proved to be a good tool for wooden surfaces, much cheaper than the laser profilometers. In the current research, a novel non-contact air gauge was combined with a slider to eliminate the influence of the asperities of higher order (waviness) and to protect the wooden surface from being damaged by the measuring nozzle. The measurement signal was used to control a follower that kept constant distance between the surface and the nozzle edge. The measuring speed was set at 0.8 mm/s, and the back-pressure was measured with accuracy of 0.01 kPa with real time acquisition. A series of measurements was taken, and the results were compared with the ones obtained from Perthen S8P profilometer (contact measurement) and WYKO NT 1100 interferometer microscope.