Rectangular Nozzle Research Articles

Numerical simulation for axis switching of pulsating jet issued from rectangular nozzle at low Reynolds number

Axis switching of a jet ejected from a rectangular nozzle affects flow mixing characteristics. To elucidate such a mixing mechanism, the axis switching and vortex structure deformation should be investigated in detail. This study performed a numerical analysis of the axis switching of a pulsating jet ejected from a rectangular nozzle at a low Reynolds number. At all aspect ratios, a rectangular vortex ring similar to the shape of the nozzle cross-section is periodically shed downstream, and the side of the vortex ring deforms into a hairpin shape downstream. A vortex pair is generated inside the vortex ring downstream of the nozzle corner. When the aspect ratio is AR = 1.0, the vortex pair consists of symmetrical vortices, while as AR increases, the asymmetry of the vortex pair enlarges. At AR = 1.0, regeneration of a vortex ring occurs downstream. For AR = 2.0, alternately on the long and short sides of the nozzle, an upstream vortex ring overtakes a downstream vortex ring. Regardless of AR, downstream near the nozzle, as the vortex pair existing inside the vortex ring distorts the vortex ring, the positions of the side and corner of the vortex ring exchange, resulting in a 45° axis switching. For AR > 1.0, further downstream, the hairpin part of the vortex ring on the long side develops away from the jet center compared to the short side, causing a 90° axis switching. As a result, high turbulence occurs over a wide area, strengthening the mixing action. As AR increases, intensive interference between the vortex rings on the upstream and downstream sides diffuses the vortices downstream. Then, as turbulence by the diffused vortices widely occurs, the mixing effect is further strengthened.

Aerodynamic sealing using a segmented recirculating horizontal air curtain for buoyancy-driven flows in doorways

Dealing with buoyancy-driven flow to reduce infiltration heat is challenging for buildings such as cold storages where the indoor-outdoor temperature differences are significant. In this study, a segmented recirculating horizontal air curtain (SRHAC) is proposed to respond to the vertical thermal buoyancy profile in doorways and recover the cold air entrained by the air curtain. Specifically, SRHAC is a planar turbulent impingement jet discharged through a vertically mounted rectangular nozzle. The discharge nozzle is divided into segments and the return vent recirculates the discharged air to the rear of the discharge nozzle. In this study, the aerodynamic sealing performance of the SRHAC is investigated by considering structural, operational, and ambient parameters. Orthogonal analysis reveals the flow rate, nozzle width, and discharge angle as significant factors affecting the thermal separation efficiency of the SRHAC. Increasing the flow rate and decreasing the nozzle width leads to an increase in the jet momentum flux, thereby enhancing the thermal separation efficiency, with a maximum efficiency of 75.9 %. Setting the discharge parameters in the three sections along the height improves the thermal separation efficiency by 16.5% points. The maximum efficiencies of two-, three-, and five-segment air curtains are 83.6 %, 87.3 %, and 90.3 %, respectively. The separation efficiency of the SRHAC remains relatively stable even when the indoor-outdoor temperature difference varies between 32 and 57 K. These results establish that the SRHAC is an efficient energy-saving device, with the ratio of reduced infiltration load to energy consumption as high as 110.9.

Direct numerical simulation of turbulent jet in regular waves: A comparison between circular and non-circular cross-sections

Direct numerical simulations of circular and non-circular jets (square and rectangular) when released into regular waves are performed and reported in this article. In case of a rectangular jet, two different orientations of the nozzle have been simulated i.e major axis parallel (case 1) and perpendicular (case 2) to wave advancement direction. An analysis of the leading vortex ring reveals that axis switching in a rectangular jet takes place irrespective of nozzle orientation with respect to wave advancement direction. The axis switching is absent in the square jet. Further, the roll-up frequency of the non-circular jets is found less than the circular jet. Also, the roll-up frequency is independent of the orientation of the rectangular jet with respect to the wave direction. The braid region shows that the number of counter-rotating pairs are four for all the cases, however, the lateral jets are three for circular, square and case 1 of rectangular jets. The lateral jets in case 2 of the rectangular jet remain four due to change in orientation of the lateral jets owing to change in the nozzle orientation. The time-averaged quantities suggest increased mixing and entrainment in the rectangular jet as compared to circular jet. The highest mixing and shortest potential core are observed in case 2 of the rectangular jet. Therefore, for better mixing, the rectangular nozzle should be placed in the ocean outfall such that its major axis remains perpendicular to the direction of wave advancement.

Prediction of the bead profile for wide-band laser cladding via hybrid model of mathematics and thermal simulation

Wide-band laser cladding has high deposition rate and low dilution due to the large laser spot and rectangular powder nozzle. A mathematical model was proposed to predict the track cross-section profile for wide-band laser cladding. The melt pool morphology and powder spatial concentration were taken into consideration to improve the accuracy of the model. Thermal field simulation was carried out to study the melt pool evaluation with process parameters, while infrared images were used to verify the simulation fidelity. Powder stream photographs were taken via a CCD (charge coupled device) camera to obtain the powder spot size. Single and multi-track cladding experiments were conducted, and calculated contours of the model coincide well with the experimental results. Simulated and measured melt pool width and length agree with in 2.16% and 2.36% of error, respectively. The error of predicted cross section area is less than 9.35%. The model also has good ability to predict the powder efficiency and morphology of the cladding layer.

The effect of cant angle on the sound production of mutually inclined rectangular supersonic jets

Rectangular nozzle geometries offer a number of benefits over their axisymmetric counterparts, particularly for military aviation. Among these benefits are altered thermal and noise signatures, ease of airframe integration, and simpler thrust vectoring. Many next-generation tactical aircraft concepts employ two rectangular jets in close proximity. These jets can couple together, producing high-amplitude acoustic tones that are deleterious to aircraft structure. In this work, we take a combined experimental and theoretical approach to examine the effect of cant angle (i.e., mutual inclination angle) on the jets' proclivity to couple. We employ modal decomposition of flow visualization data alongside resonance predictions based on linear stability theory to explore the degree to which mutual inclination can suppress resonance.

Robust generation of monodisperse droplets using a microfluidic step emulsification device with triangular nozzle

AbstractIn this work, the droplet generation process in the microfluidic step emulsification chip with a triangular nozzle (SE‐T) was investigated in the combination of visualization experiment and numerical simulation, through a comparison with a rectangular nozzle (SE‐R). The flow regimes, including dripping, dripping‐jetting transition, and jetting, were observed in the SE‐T, among which the dripping is the preferred flow regime to generate monodispersed droplet with corresponding C.V. (coefficient of variation) of the droplet size smaller than 1.9%. Compared with the SE‐R, the larger space and expanding structure of the triangular nozzle in the SE‐T enhance the wall wetting effects, which induces earlier appearance and accelerates shrinking of the neck. As a result, the SE‐T exhibits more robust droplet performance under the dripping regime, which produces the droplets with nearly unchanged size and higher monodispersity, especially little related to the variations of surfactant concentrations and dispersed phase flow rates.

Influence of nozzle geometry on screech instability closure

The effect of nozzle exit geometry on the triadic interactions between convective Kelvin–Helmholtz instabilities and the quasi-steady shock structure of supersonic jets is discussed in this study. A circular and rectangular nozzle with an aspect ratio (AR) of 2 were evaluated using results from near field acoustics and high-speed Schlieren images. The study investigated different types of screech instabilities in both nozzle configurations, including the multimode instability in rectangular jets. The near field acoustic measurements showed comparable trends in screech staging in both nozzle configurations. The Schlieren results revealed that the standing waves in the jet near field were influenced by the oscillation mode of the jets. The study also explored a new technique of noise visualization from Schlieren images based on near field acoustics and temporal Fourier decomposition. Spatial Fourier decomposition demonstrated that the resonance closure mechanism across both nozzle configurations was dependent on the relative influence of the first two shock cells. Comparisons between the AR 2 and AR 9 jet showed that jet aspect ratio can significantly affect the energy distribution from the triadic interactions.

Conceptions and Feasibility Study of Fiber Orientation in the Melt as Part of a Completely Circular Recycling Concept for Fiber-Reinforced Thermoplastics

Fiber-reinforced thermoplastics are an important construction material for lightweight applications. The increasing use of especially glass fiber-reinforced plastics leads to growing amounts of not recyclable composite materials, which is commonly disposed of by landfilling. Hence, there is a need for a recycling concept for glass-fiber-reinforced plastics that enables their complete reuse over many recycling cycles. In this paper, such a recycling concept is presented, which is based on the idea of melting the whole glass-fiber-reinforced component without prior size reduction. The fiber-reinforced melt will be pressed through a nozzle in order to achieve a strand with highly oriented fibers that can then be applied in new components via a tape-like laying process. The feasibility of the recycling concept is proved in this paper. Therefore, investigations on the reorientation of fibers in the melt by pressing through a rectangular nozzle have been carried out with different nozzle diameters, shear rates and melt temperatures. The investigations result in a stable process, which enables an increase in fiber orientation of about 37% up to a mean fiber orientation of 67% in the flow direction. These findings are independent of the initial fiber orientation.

Mechanisms of Plasma Actuators Controlling High-Aspect-Ratio Rectangular Jet Width for Automobile Air Conditioning Systems

High-aspect-ratio (HAR) rectangular jets have attracted attention in automobile air conditioning (A/C) systems and turbulent jet applications owing to their excellent air delivery and mixing and attractive interior design. Active flow control (AFC) of rectangular jets using plasma actuators (PAs) has proven to be a promising technique because the actuator is simple, has low energy consumption, and can create flow features without interference. This research aims to understand the interaction between PAs and flow from a HAR rectangular nozzle using hot-wire anemometry, particle image velocimetry, and theoretical studies. Understanding how PAs affect the flow is beneficial for designing air vents to fit automobile A/C systems and various engineering applications by recreating the flow features with other AFC techniques and actuators. The combination of periodic excitation and vectoring effects transfers the flow’s mean energy to organized structures—known as spanwise vortexes—as large as 6 mm. The interaction between these coherent structures and the dissipative environment compresses the vortexes, resulting in the flow converging on the spanwise–streamwise (X–Z) plane and diverging on the transverse–streamwise (X–Y) plane. HAR rectangular jet flow features controlled by PAs can be predicted for specific cases by calculating the Strouhal number based on PA operating parameters.

Experimental study on the flow characteristics during liquid nitrogen leakage

ABSTRACT The accidental leakage from tanks and pipelines is one of the main risks in cryogenic superheated liquid storage and transportation. To investigate the effects of superheat degree and jet pressure on the leakage characteristics, the corresponding liquid nitrogen (LN2) leakage experiments were carried out under different conditions. In this study, a rectangular nozzle ( 1 mm × 3 mm ) was applied to imitate the crack in typical release scenarios. The dynamic evolution process of jet pattern was also investigated. Three jet patterns including the mechanical breakup jet, the partially flashing jet, and the fully flashing jet were identified in the stable stage. The results indicate that the jet angle rises with the increase of superheat degree. At high superheat degree, the jet pressure presents a more significant influence on the jet angle. While the superheat degree decreases, its influence on the jet angle reduces. The leakage mass flow rate declines with the increase of superheat degree and rises with the increase of jet pressure. Furthermore, a new discharge coefficient correlation suitable for superheated LN2 leakage is developed, and its prediction error is within±3.8%. The new correlation is a good tool to predict the mass flow rate during LN2 leakage process.

Ground Tests of Rectangular Nozzle with Noise Reduction Devices on Aircraft

Ground Tests of Rectangular Nozzle with Noise Reduction Devices on Aircraft

Ground Tests of Rectangular Nozzle with Noise Reduction Devices on Aircraft

The importance of jet noise for prospective supersonic transport (SST) in takeoff and climb modes dictates the need to develop methods for reducing jet noise and their subsequent validation in large- and full-scale tests. This paper presents the results of Russia’s first ground acoustic tests of a rectangular nozzle with a noise suppression system, installed on a subsonic aircraft engine to demonstrate the technology. The authors studied a rectangular beveled nozzle with an ejector and screens—elements of the SST airframe. The test results were compared for three nozzle geometries: a round nozzle corresponding to measurements for the original engine without modifications, a rectangular nozzle without screens, and a rectangular nozzle with screens. It was found that when the rectangular nozzle without screens is used, there two opposite effects occur: noise amplification compared to the round nozzle for angles of observation close to the jet axis, and noise attenuation at angles of observation close to the fan rotation plane. Installing screens increases noise up to 5 dB in the low-frequency region below 150 Hz and reduces noise by 2 dB for frequencies higher than 250 Hz. Estimation of community noise in the EPNL metric showed that this rectangular nozzle with the noise suppression system has the effect of reducing community noise in comparison with the baseline round nozzle.

Improving Homogeneity of 3D-Printed Cementitious Material Distribution for Radial Toolpath

The 3D cementitious material printing method is an extrusion-based additive manufacturing strategy in which cementitious materials are extruded through a dynamic nozzle system to form filaments. Despite its ability to fabricate structures with high complexity and efficiency, the uneven material distribution during the extrusion and deposition process is often encountered when a radial toolpath is introduced. This limits the design freedom and printing parameters that can be utilized during radial toolpath printing. Here, we report a facile strategy to overcome the existing challenges of cementitious material non-homogeneity by rationally developing new nozzle geometries that passively compensate the differential deposition rate encountered in conventional rectangular nozzles. Using two-phase numerical study, we showed that our strategy has the potential of achieving a homogeneous mass distribution even when the nozzle travel speed is unfavorably high, while filament from a rectangular nozzle remains highly non-homogenous. The material distribution unevenness can be reduced from 1.35 to 1.23 and to 0.98 after adopting trapezoid and gaussian nozzles, indicating improvements of 34.3% and 94.2%, respectively. This work not only outlines the methodology for improving the quality of corner/curved features in 3DCMP, but also introduces a new strategy which can be adopted for other extrusion-based fabrication techniques with high material inertia.

Effect of internal geometry on supersonic jet noise

The current study discusses the experimental results of the effect of two types of nozzle internal geometries. The first configuration uses a common inlet that diverges the flow into two separate channels that feed twin rectangular nozzles, and the second configuration has the plug flow type system with twin rectangular nozzles drawing air from a common plenum. The nozzles are converging diverging type with design Mach number of 1.5. Flow conditions encompassing overexpanded, design, and underexpanded conditions are tested with acoustic data collected in the farfield and nearfield domains. High-speed Schlieren imaging is used to visualize the effect of internal geometry on the development of the jet shock cell structure and twin jet interaction. The variations in the Overall Sound Pressure Level (OASPL), frequency spectra, and jet phase coupling are used to quantify the effect of the internal geometries. This is supplemented by Spectral Proper Orthogonal Decomposition (SPOD) results obtained from the Schlieren images to quantify the variations in flow development.

Multi-mode instability interactions in twin jet configurations

Twin jet configurations are prone to a wide range of interactions due to flow instabilities driven by jet self-excitation and cross-excitation of one jet on another. These instability modes and associated phases are sensitive to many parameters chief among which is the exit profile of the nozzle. Extensive studies on Twin Circular nozzles and Large Aspect Ratio (AR) Twin rectangular nozzles have shown various mode coupling but, not much is known about twin jets with moderate aspect ratios (AR < 3). This study aims to understand the effect of the exit nozzle geometry on the generation of flow instabilities by comparing a Twin Rectangular nozzle (AR 2) to a Twin Square nozzle (AR 1) with identical design parameters through experimental analysis. High speed Schlieren imaging is coupled with Particle Image Velocimetry (PIV) to explore both qualitative (internal shock cell structure) and quantitative aspects (flow vorticity and turbulence) of these jets. Near field and far field acoustics are also studied to provide a wholistic understanding of the effect of mode coupling exhibited by these jets. Generation and propagation mechanisms of multi-mode instabilities which effect both nozzle orientations are also studied through Spatial and Temporal Fourier analysis.

Flow and surface loading induced by a supersonic jet over an aft deck

Aircraft designs may include an engine that exhausts over the upper fuselage of the aircraft. This design has many benefits including reduced noise below the aircraft. However, the scrubbing of the high-speed turbulent jet flow over the fuselage has the potential to cause structural fatigue. This paper describes a joint experimental/computational study of the surface pressure fluctuations induced by the supersonic jet flow. The model configuration consists of a rectangular convergent-divergent nozzle that exhausts over a flat plate. The plate is a continuation of the lower lip of the nozzle. Pressure measurements are made at several locations on the plate surface. In addition, schlieren visualization is used to identify the jet's shock cell structure. Numerical simulations are performed using Large Eddy Simulation (LES). Results are compared between the simulations and the experiments. The importance of shock turbulent boundary layer interaction to the surface loading is identified.

Direct-connect supersonic nozzle design considering the effect of combustion

The effect of the chemical reaction that occurs in the flow of the supersonic nozzle is investigated to design a circular to rectangular shape transition nozzle for a rocket-type vitiated air heater. A simple method of assigning the specific heat ratio for the supersonic nozzle design is suggested. By using the specific heat ratio calculated by the one-dimensional chemical equilibrium analysis, it is confirmed applicable up to Mach 6.0 nozzle with the upstream total temperature which does not cause chemical dissociation. It is found that the effect of the species dissociation and recombination is very slight therefore it becomes negligible at a total temperature less than at which the chemical dissociation takes place. Also, regardless of the scale of the supersonic nozzle, the change in the nozzle performance due to the energy conversion is negligible. Therefore, it becomes applicable to most of the range for the direct-connect type supersonic nozzles. The designed supersonic nozzle with the approximated specific heat ratio for the direct-connect supersonic combustion experiment was confirmed to have an error of less than 1 percent. Based on this design method, the flow characteristic induced by the shape transition is reviewed in a three-dimensional simulation.

Acoustic Characteristics of Rectangular Hypersonic Mixer Ejector

JAXA is currently studying the pre-cooled turbojet engine (PCTJ) to be installed in a hypersonic transport. As a device to reduce exhaust noise at takeoff, a mixer-ejector that is applicable to a rectangular hypersonic nozzle having a complicated geometry with an external ramp has been proposed and tested. The ejector introduces the low-speed secondary flow into the high-speed main jet and reduces the exhaust velocity by mixing. As a result, the mean jet velocity decreases and the jet noise decreases. A 1%-scale mixer-ejector was fabricated, and the mixing process between the main jet and the secondary flow was visualized using Mie scattering of water droplets. The direct relationship between the degree of mixing and the amount of noise reduction was investigated.

Effect of Ratio of Divergent to Parallel Length in Rectangular Cross Section Nozzle and Particle Size on Spray Pattern of Copper Coating by High Pressure Cold Spray

Effect of Ratio of Divergent to Parallel Length in Rectangular Cross Section Nozzle and Particle Size on Spray Pattern of Copper Coating by High Pressure Cold Spray

Influence of nozzle geometry on torch parameters during gas combustion

In this paper, when performing and analyzing the series of calculated results of the analysis of the sides of a rectangular nozzle for the parameters of a turbulent free air jet and a flame of a propane-butane mixture based on three-dimensional parabolic Navier-Stokes bonds for multicomponent reacting jets. To estimate the turbulent viscosity, differential equations of the kinetic and dissipation of the kinetic energy of turbulence are observed with refined empirical constants that are acceptable in turbulent combustion, as in the calculations, the initial values of the kinetic energy of turbulence did not exceed 5% of the dimensionless velocity of the main jet. It was found that when an air jet flows out of a nozzle with an aspect ratio of (1:2) and (1:4) in the initial sections of the jet, its shape behaves like an ellipse and, with the distance, it turns into a round one, with dimensionless, x greater or equal to 20 for the nozzle (1:2) and x greater or equal to 30 for (1:4), and for this variant there is again a transition to an elliptical shape. Studies of the diffusion combustion of a propane-butane mixture flowing out of a rectangular nozzle with an aspect ratio of (1:2) and (1:4) showed that with the ratio of the speed of the oxidizer to fuel mu, the flame length increases when mu between 0 and 0.164, and then, with an increase of mu more than 0.41, the torch length is shortened. The axial distributions of the momentum flux density with the aspect ratio (1:4), the jet core is shortened by 2÷2.5 times, compared with the aspect ratio (1:2) with the other parameters unchanged. Setting the tangential velocity at the mouth of the nozzle (ω=6.1 m/s) leads to a decrease in the torch length by 11% compared to its value equal to zero.