Nozzle Aspect Ratio Research Articles

Advances in predicting surface shape changes of mirror blanks through elliptical nozzle gas jet forming

To facilitate the formation of bifocal aspheric optical surfaces, we present an approach for predicting the surface profile of bifocal aspheric surfaces formed by the gas-liquid interface when an elliptical nozzle gas jet is employed. Through an analysis of the gas flow field morphology emanating from the elliptical nozzle, we inferred the impact of gas jet parameters on the gas-liquid interface surface shape within the core region of the gas jet. By analyzing the variation in the gas flow field morphology emitted from an elliptical nozzle, we deduced the influence patterns of gas jet parameters on the gas-liquid interface surface shape within the gas jet's core region. Theoretical analysis is substantiated by numerical simulations, confirming regular changes in the vertex curvature and conic constant of mirror blanks concerning variations in jet initial velocity and nozzle aspect ratio. A comparison between experimental data and numerical simulation results reveals an average prediction deviation of 0.0083 mm−1 for the vertex curvature and a prediction deviation of 10.7 % for the conic constant, challenging to rectify within numerical simulations. Hence, an empirical model, incorporating jet parameters, is developed based on experimental data to predict the vertex curvature and conic constant of mirror blanks. This model demonstrates an average prediction error of 2.901 × 10−3 mm−1 for the vertex curvature and 7.64 % for the conic constant, surpassing the predictive accuracy of the numerical simulation model.

Experimental study on the change of the orientation of high aspect ratio nozzle slit relative to the airflow

An experimental study to investigate the flow of liquid jet issued from a high aspect ratio nozzle slit into an incoming airflow by changing the orientation angle from the incoming free-stream was performed. A two-dimensional liquid sheet emerged from the narrow slit into the subsonic air crossflow. Different orientation angles between 0 and 90 degrees were studied. High-speed photography and shadowgraphy techniques were utilized to visualize the flow physics. The influence of the slit orientation angle on the flow morphology and the flow regimes of liquid sheets was investigated. Some fluid flow parameters were obtained by analyzing the images. The changes in breakup height of different orientations were measured. A model was offered for the breakup height of the liquid sheet based on the liquid-to-gas momentum ratio, gas Weber number, and a new non-dimensional parameter as a representation of the angle of slit orientation. Also, the defined sheet trajectory for each orientation angle was obtained, and the variations were examined. Empirical correlations for the defined trajectory of the sheet in terms of liquid to gas momentum ratio and gas Weber number for each orientation angle were proposed.

Controlling sonic rectangular jet with nozzle trailing edge modification

Sonic rectangular jet emanating from a convergent nozzle of aspect ratio 2 with modified trailing edge in the form of triangular extension on its widest side is investigated experimentally at different nozzle pressure ratios corresponding to underexpanded states of sonic jet. To assess the impact of trailing edge modification on jet mixing, the sonic rectangular jet from aspect ratio two plain convergent nozzle (without trailing edge modification) is also studied. The centerline pressure decay results at nozzle pressure ratios 2, 3, 4 and 5 confirm the superiority of modified jet (jet from trailing edge modified nozzle) over plain jet from the mixing point of view. At all the pressure ratios, the modified jet possessed shorter core and weaker shock and expansion waves compared to plain jet, which is an outcome of faster mixing of modified jet with ambient fluid. The enhanced mixing caused the modified jet to decay faster than the plain jet. An appreciable core length reduction of about 32% is noticed at pressure ratio of 5. The modified jet experienced increased spread along major axis than along minor axis owing to the restriction offered by the triangular extension on jet spread along minor axis. Thus, the axis switching was absent in modified jet compared to plain jet switching axes at all pressure ratios. The shadowgraph images confirmed the presence of weaker waves in the modified jet. Also, the images confirmed the absence of Mach disk in the modified jet at pressure ratio of 5 compared to plain jet.

Integrated Thermal Management System Concept With Combined Jet Plate, High Porosity Aluminum Foam, and Target Plate for Enhanced Heat Transfer

Abstract An experimental investigation was carried out on high porosity metal foams subjected to array jet impingement with an objective to develop enhanced heat transfer configurations. In this study, we propose an integrated thermal management system (TMS) aimed toward leveraging the conjugate heat transfer capabilities of target plate, metal foam, and the jet plate—all made from aluminum and assembled such that a proper contact between them can be established. Steady-state heat transfer experiments were carried out for 10 and 20 pores per inch (PPI) aluminum foams of 0.93 porosity. Both metal foams were 12.7-mm thick. The normalized jet-to-jet spacing was varied from 2 to 12 times the jet diameter, while the jet diameter was fixed. The ratio of the jet plate thickness and jet diameter (nozzle aspect ratio) was 6.35, which ensured proper development of jets inside the nozzles. Experiments were conducted over a wide range of Reynolds number (based on jet diameter) varied from 100 to 5000. The obtained convective heat transfer coefficient for different configuration was evaluated in context with pressure drop. The analysis of experimental results reveal that large open area ratio jets combined with high porosity metal foams provide highly efficient and high-performance cooling for the investigated range of Reynolds numbers.

Numerical Investigation of the Impact of the Rectangular Nozzle Aspect Ratio On Liquid Jet in Crossflow

Abstract High fidelity simulation is conducted to investigate liquid jet in crossflow, specifically regarding the rectangular nozzle. The influence of aspect ratio (AR) of nozzles on the atomization characteristics of liquid column in the process of primary breakup is explored by the analysis of the flow structure of crossflow and liquid column. The aspect ratio is ranging from 1 to 8. The results indicate that as the increase of aspect ratio, the disturbance of crossflow to the liquid on the sides is weakened. While the thickness of liquid column also gradually decreases, which enables smaller disturbances to promote droplet shedding. Therefore, surface breakup first weakens and then strengthens. In the column breakup process, the increase of aspect ratio causes crossflow to become the main factor affecting column breakup, and the influence of air pressure gradually weakens. This indicates a shift in the mechanism of surface instability from “Rayleigh-Taylor” (R-T) instability to “Kelvin-Helmholtz” (K-H) instability.

Acoustical analysis and optimization design of the hair dryers

Abstract The sound qualities and wind speeds of the four commercial hair dryers (Panasonic, Confu, Flyco, and Philips) were investigated through experimental methods in the present study. The sound qualities included loudness, sharpness, roughness, and fluctuation strength. The experimental results showed that the maximum sound pressure level (SPL) of all hair dryers occurred at about 200 Hz except Flyco hair dryer, which occurred at about 400 Hz. The highest loudness and highest sharpness were found when the hair dryers were set to hot mode and cold mode, respectively. No consistent relationship was found between the effect of room space and SPLs of the hair dryers. The Box–Behnken design method was used to design 13 pieces of oval and rectangular nozzles, and their sound levels and wind speeds were measured. Thereafter, these experimental results were used to derive correlation coefficients between the hair dryer nozzle area, aspect ratio, nozzle length, loudness, and wind speed using the Anova analysis method. Finally, an oval nozzle and a rectangular nozzle with an area of 0.0005 m 2 {}^{2} , an aspect ratio of 1, and nozzle lengths of 0.052 and 0.055 m, respectively, were designed and were tested. These nozzles managed to reduce the sound loudness by 15 and 9.6%, respectively, while maintaining the same level of wind speed.

Study on flow atomization characteristics and structure optimization of swirl nozzle for biodiesel

In this paper, the influence of external conditions and structural parameters on the characteristics of a nozzle flow field is studied, and orthogonal tests have been used to optimize the nozzle structure. The results show that the inlet pressure, nozzle aperture, nozzle outlet aspect ratio, vortex chamber height, and screw core height affect the pressure and velocity distributions of the flow field inside the nozzle. With increasing axial distance, the pressure in the inlet area remains unchanged; however, the pressure gradually decreases inside the screw core region and vortex chamber. Meanwhile, the velocity in the nozzle drainage basin first increases and then decreases. With increasing radial distance, the pressure in the nozzle drainage basin gradually increases, whereas the velocity increases first and then decreases. The velocity contour plot and vector diagram of the nozzle outlet section elucidate the influence of structural parameters on the flow field characteristics inside the nozzle. The nozzle length-to-diameter ratio has the greatest effect on the Sauter mean diameter (SMD). Besides, biodiesel atomization is sequentially affected by the vortex chamber height, screw core height, and nozzle aperture. The best atomization performance of biodiesel is observed at a nozzle aperture of 0.8 mm, nozzle outlet length-to-diameter ratio of 0, vortex chamber height of 5 mm, and screw core height of 4 mm. Compared to the original nozzle, the optimized nozzle increases the atomization cone angle of biodiesel by 30.9% and reduces the SMD by 45.3%.

Experimental investigation of rectangular nozzle aspect ratio effects on high-pressure helium leakage characteristics

High-pressure hydrogen leakage is one of the bottlenecks restricting the development of the hydrogen energy industry. In this study, a high-pressure helium leakage experimental system with stable pressure was built to research the influence of aspect ratio on concentration decay rate and mass flow rate. Similar to the circular nozzle, the centerline helium concentration of the rectangular jet is also inversely proportional to the distance from the nozzle. For the rectangular nozzles with aspect ratio of 1–4, the helium concentration decay rate is consistent with the circular nozzle when the leakage pressure is lower than 6.5 MPa. However, the decay rate is obviously larger for rectangular nozzles with aspect ratio of 10 when the leakage pressure is greater than 5.0 MPa. The aspect ratio has a greater influence on the flow coefficient, which increases with the aspect ratio under the same leakage pressure. To comprehensively consider the effects of nozzle size and shape, a weighted characteristic diameter of equivalent diameter and rectangular width, dc=αde+1−αdw, was proposed in this study. The results indicate that the equivalent diameter has greater impact on the centerline concentration decay rate, while the width of nozzles has substantial influence on the flow coefficient.

Multi-objective optimization design of aerodynamic and infrared characteristics of multi-stream serpentine nozzle

A multi-objective optimization design of multi-stream serpentine nozzle was carried out to improve the aerodynamic performance and reduce the infrared radiation signal. A numerical simulation was carried out to investigate the effects of nozzle pressure ratio (NPR), Aspect ratio (AR) and Ratio of length and diameter (L/D). Computational fluid dynamics (CFD) simulation was employed to study the aerodynamic performance of the multi-stream serpentine nozzle, and the narrow-band method with discrete transfer method were used to calculate its infrared radiation intensity distribution characteristics. A 3-factor, 21-level orthogonal table was designed based on the orthogonal experimental method, and multi-stream serpentine nozzle with different geometrical parameter and operating conditions were designed to obtain the aerodynamic performance and infrared radiation intensity data of each experimental sample point. Radial Basis Function (RBF) neural network and Multi-Objective Particle Swarm Optimization algorithm were used to optimize the geometry and operating conditions with better aerodynamic performance and weaker infrared signal. The result shows that the Pareto solutions obtained by the optimization have good accuracy compared with the numerical simulation results, with an aerodynamic performance error of 0.02% and an infrared radiation intensity error of 0.24%.

A computational analysis of cryogenic hydrogen release under various conditions

Cryogenic liquid hydrogen offers a promising solution for achieving high-density hydrogen storage and efficient on-site distribution. However, the potential hazards associated with hydrogen leakages necessitate thorough investigations. This research aims to model cryogenic hydrogen release from circular and high aspect ratio (HAR) nozzles tested by Sandia. The test conditions cover reservoir pressures and temperatures corresponding to cryogenic hydrogen storage. The study conducts computational simulations using OpenFOAM to examine hydrogen concentration, temperature fields, mass fraction, and temperature distributions, achieving good agreement with the experimental data. To further explore, the study of velocity variations shows a consistent decay rate with room-temperature jets. The numerical data reveals comparable inverse centreline hydrogen mass fractions (0.254 for HAR and 0.26 for circular) and normalised centreline temperature decay rates (0.031 for HAR and 0.032 for circular). The present computational model holds the potential for further analysis of cryogenic hydrogen in large-scale facilities.

The role of nozzle position and channel aspect ratio in thermal management of electronic modules

In this paper, cooling of electronic modules by a series of impinging jets is studied numerically and experimentally. The study investigates the effects of nozzle position (sj/b = 0 − 0.25 − 0.5) and channel aspect ratio (H/Dj = 3 − 4 − 5) on surface temperatures, local and average heat transfer characteristics and flow dynamics. The numerical analyses are conducted using the ANSYS Fluent software, and the numerical results are verified using experimental measurements. The study's findings indicate that the displacement of the nozzles has a notable impact on the location and sizes of the vortex cells around the modules. This alteration influences the rate of convection heat transfer from the modules’ surfaces. It is concluded that increasing the channel aspect ratio leads to a reduction in convective heat transfer. The highest cooling performance is achieved in the scenario where the aspect ratio (H/Dj) is 3 and the dimensionless nozzle position (sj/b) is 0.5. However, in terms of temperature uniformity, this is H/Dj = 3 with sj/b = 0.

Numerical investigation of flow and heat transfer behavior on vortex cooling with an optimal convergent coolant chamber for different nozzle aspect ratio arrangement mode

A computational model including convergent coolant chamber, nozzles and vortex chamber is established. The vortex cooling flow and thermal exchange features are investigated under different nozzle aspect ratio arrangement mode based on an optimal convergent coolant chamber. The nozzle aspect ratio arrangement mode consists of two parts, namely eight nozzle aspect ratio sizes and three kinds of nozzle aspect ratio axial variations. Results indicate that the erosion velocity increases due to the smaller windward area with the increasing nozzle size. The convergent coolant chamber makes the mass flow and pressure increases, the reflux phenomenon appears. And the increasing nozzle size leads to the first increase and then decrease with high pressure and Nusselt number area. For the nozzle aspect ratio arranged from high to low, the airflow stiffness and turbulent kinetic energy at the sixth nozzle are the largest, the thermal transfer feature enhances. For the nozzle aspect ratio arranged from low to high, the airflow impact strength and heat exchange characteristic decreases. But the drag coefficient is minimal that has a positive effect on flow features. The thermal exchange capacity is the highest with the nozzle aspect ratio 2.0. Consequently, this study can provide reference for gas turbine design.

Categorization of iso-pentane flashing spray based on morphology, thermodynamical and mechanical effects

Accidental release of superheated liquids is typically accompanied with hazardous flashing jets. Indeed, flashing jets undergo fragmentation into massive fine droplets, thus forming ideal circumstances for fires and explosion. To gain a deeper understanding of depressurized release, we studied the dynamics of iso-pentane at superheats of 40–80 °C and injection pressures of 0.6–3.0 MPa. The internal flow pattern and external spray morphology are visualized at quasi-steady stage using a high-speed camera. Results show that the flashing patterns can be classified into non-flashing, transitional flashing, and flare flashing arising from the interaction between thermodynamic and mechanical effects. The contribution of thermodynamic effect decreases as mechanical effect intensifies, due to the suppression of bubble nucleation and burst. We propose the index k, based on JaRp = k(WevOh)−1/7, to identify different flashing regions, i.e., k below 211 for non-flashing, k between 212 and 425 for transitional flashing, and k above 425 for flare flashing. Besides, the microscopic characteristics involving droplet velocity and diameter distribution are investigated and a new correlation for drop size is proposed, which is dependent on factors such as nozzle aspect ratio, mechanical force, and thermodynamic force. These findings should help to define policies to decrease the risk associate with flashing jets.

Numerical investigation on spray and flow field characteristics of elliptical nozzle in supersonic crossflow

ABSTRACT It has been suggested that using an elliptical nozzle could enhance the atomization and mixture quality. In order to explore the elliptical liquid jet on spray and flow field characteristics in supersonic airflow, the VOF-Spray one-way coupling model was adopted to study the nozzle exit patterns, size, and velocity distribution of droplets. The research also compared the flow field characteristics in Mach 2.85 air crossflow under the application of different orifices. The numerical results showed that elliptical 4 nozzle (Aspect ratio of 4) had better flow performance than circular nozzle. The cavitation area and turbulent disturbance of elliptical 4 nozzle were mainly concentrated in the major axis direction. The elliptical 4 jet always had a lower penetration depth than circular jet. At the flow range of 0 ~ 50 mm, the penetration depth of elliptical 4 jet is roughly 12% less than that of circular jet. Another finding was that the spanwise extension range of elliptical 4 spray was larger than the circular spray. The spanwise extension range of elliptical 4 spray increased by about 19.4% at most in the flow range of 0 ~ 50 mm. Additionally, the elliptical 4 spray had the smallest Santer Mean Diameter (SMD). The elliptical 4 jet had a 2.9% smaller Santer Mean Diameter than the circular jet. Due to the greater windward surface area of the elliptical 4 orifice, the gas streamwise velocity near the bottom wall was reduced. A reverse vortex pair with distinct characteristics could be observed under the application of elliptical 4 orifice. Furthermore, compared with the circular orifice, the shock wave angle generated by elliptical 4 orifice reduced by 9.7%, and the total pressure recovery coefficient rose by 2.3%.

Numerical investigation on atomization characteristics of sustainable aviation biofuel

It is critical to investigate the atomization features of sustainable aviation biofuel (SAF) to reduce carbon emissions. Fluent software was used to quantitatively simulate the atomization of the fuel. The control variable method was utilized to compare SAF to Chinese aviation fuel RP-3. The volume of fluid model (VOF) and the discrete phase model (DPM) were used to explore the variation law of SAF atomization characteristics in a two-way centrifugal nozzle with a pressure drop of 2–8 MPa and various nozzle configurations. The experimental results suggest that the model is effective. The results demonstrate that when pressure increases, the average diameter of SAF’s Sauter mean diameter reduces from 80 to 23 µm and the spray penetration distance increases from 0.32 to 0.6 m, allowing for more stable fuel combustion. Meanwhile, as the nozzle outlet aspect ratio increases, such as increasing the nozzle diameter from 2.0 to 2.6 mm, the atomization cone angle varies from 60° to 110° and gradually declines, although the average diameter of Sauter only varies minimally within a limited range of 30–40 µm. All of these findings indicate that SAF has good atomization properties and the potential to be used as an aviation fuel.

Influences of nozzle aspect ratio and inlet Reynolds number on flow and heat transfer characteristics for middle double swirl cooling

In this paper, the middle double swirl cooling (M-DSC) models for diverse nozzle aspect ratios (Car) are established for flow and heat transfer behavior research. The k-ω turbulence model and the 3D viscous steady RANS equations are utilized for numerical calculation. The finite volume method and coupled implicit solver are chosen for simulation calculation. Influences of Car values, namely 0.375, 0.67, 1.5, 2.67, 4.17 and 6 on the flow characteristics and thermal performance for the M-DSC are investigated when keeping vortex nozzle inlet area constant. Moreover, the cooling performance for diverse inlet Reynolds numbers 12,500, 22,500, 32,500 and 42,500 is studied with the model owning the optimal Car. Results show that the velocity of the crossflow will increase along in the outlet direction. As Car decreases, the velocity where the jet coolant scours the target will decay more significantly toward the outlet. There are four typical shapes of high heat transfer regions on the target. The uniformity of heat transfer will increase with the growth of Car. When the Car is 4.17, the thermal performance factor is the highest. The flow and heat transfer regulations are almost constant when the inlet Reynolds number is altered.

A Generalized Hydraulic Model for Propulsion Force Calculations in Radial Jet Drilling

Summary Radial jet drilling (RJD) involves drilling several small-diameter lateral holes from a single vertical wellbore to increase reservoir contact and production. RJD system components (diverter, flexible hose, and jetting bit) are conveyed to the target depth using coiled tubing. A high-pressure flexible hose is used in conjunction with a jetting bit to drill holes laterally. Without a rigid drillstring, no axial force can be transferred to the bit as it penetrates the rock. As a result, the bit is propelled by hydraulic means. Thus, in addition to front-jetting nozzles, RJD bits use back-jetting nozzles. Therefore, the rate of penetration (ROP) and maximum hole length (MHL) must be maximized through proper hydraulic optimization. Existing hydraulic models rely on field-measured parameters (discharge coefficient and flow rate ratio) that vary by the bit design to predict the propulsion force, bit hydraulic power, and the maximum lateral hole length. Hence, this study aims to develop a generalized and accurate hydraulic model that does not require field-measured parameters to make predictions. As a result, the new model can be used for optimizing RJD operations by selecting suitable bit designs and lateral hole geometries. This article presents a new RJD hydraulic model that uses a discharge coefficient that varies with the nozzle aspect ratio. The model predicts the propulsion force, differential pressure across the bit, and MHL based on the design of the bit, nozzle, and lateral hole geometries, and flow rate. To verify the model, extensive experiments were conducted with single-nozzle and multi-nozzle jetting bits. The pump pressure was varied while flow rate and propulsion force were recorded during the tests. Model predictions are compared and validated with experimental data. Measured and model-predicted propulsion forces demonstrate a reasonable agreement with a maximum discrepancy of 25%. Once the model has been validated, it is used to perform a parametric study to investigate the influence of various factors on bit performance. According to the parametric study, nozzle and hole diameters, friction factor, and hose density strongly influence bit performance. Furthermore, the diameter of the nozzle has been found to have a significant effect on bit performance parameters (propulsion force, bit hydraulic power, and MHL).

Flow and deformation behaviors of cementitious materials through nozzles with different geometric parameters: Experimental and numerical approaches

Nozzle geometric parameters are important to control the flow and deformation behaviors of printed filament. Choosing the right nozzle geometric parameters before the printing process is critical and requires considerable attention. In this study, nozzles with various geometric characteristics were designed and fabricated. Experiment and computational fluid dynamics (CFD) simulation were used to investigate the flow and deformation behaviour of printing ink via these nozzles. The results indicated that increasing of the area ratio of outlet to inlet AR (Aoutlet/Aintlet) and direction of material deposition θ will reduce the extrusion pressure. Changing the direction of material deposition θ is a critical means for controlling the printing pressure. Increasing of nozzle aspect ratio Ψ (Wn/Hn) and decreasing of direction of material deposition θ will reduces the deformation rate of deposited filament. This study may provide a theoretical guidance for the design and selection of nozzle before printing process.

Aspect ratio and combined installation in fluidic oscillator-crossflow interactions

This paper describes a computational study of fluidic oscillator-crossflow interactions. Fluidic oscillators are high potential active flow control devices, which offer promise for cooling and flow separation. Previous experimental studies have investigated the internal/external flow fields of fluidic oscillators. This improved the understanding of three-dimensional flow fields; however, this has been limited to single aspect ratio nozzles in single variable installations. Research has not analyzed the effects of varying both oscillator parameters and installation conditions. Therefore, the present aim is to enhance flow field understanding by examining three aspect ratio (AR) nozzles in default perpendicular condition and in a “skewed incline” configuration (β = 60°, α = 75°). An unsteady Reynolds averaged Navier Stokes model was validated with prior experimental data and then used to evaluate time-averaged and time-accurate flow fields at three different blowing ratios. Strouhal number analysis uncovers the effectiveness of parametric changes. Internal flow fields are presented, identifying key differences and similarities. External flow field analysis in regard to spreading angles 55°–65° observes greater wall-normal penetration for lower AR oscillators with improved spanwise penetration for larger AR's. The combined installation produces stronger primary vortices, improving penetration along the wall, while inclination keeps vortices close to the wall. Oscillator effectiveness is dependent on the application.

Near Field Decay of Mach 2 Elliptical Jet in the Presence of Tangentially Injected Secondary Swirling Flow

This investigation explores the mixing promoting capability of tangentially injected secondary swirling flow on a Mach 2 elliptical jet issuing from an elliptical nozzle of aspect ratio 2. A detailed three-dimensional numerical analysis was carried out for the combination of different levels of pressure gradient at the nozzle exit and five swirl numbers. Reynolds-Averaged Navier-Stokes equation along with Shear Stress Transport model was solved to predict the flow filed. The presence of secondary swirling flow created large pressure gradient in the direction perpendicular to jet axis, resulting in enhanced mass entrainment leading to high spread of the controlled jet compared to the uncontrolled jet. Also, the secondary jet increased the turbulence level in the flow field for all the cases studied compared to that of free jet case, leading to a reduction in jet core length. The swirl number and the pressure gradient at the nozzle exit is found to have a strong effect on the core length reduction. A maximum of about 70% reduction in core length was achieved for nozzle pressure ratio 4 with secondary flow of swirl number 5.