Nozzle Flow Research Articles

The application of the state-of-the-art turbulence models in the OpenFOAM CFD codes and the validation for different flow control cases in the continuous casting process

Computational fluid dynamics (CFD) is an established approach to study flow behaviour. Despite advances in mathematical numerical modelling in recent decades, accurately predicting the turbulent flow behaviour of steel using CFD remains a challenge. In the continuous casting process, two main flow control systems are employed to transfer liquid steel from the tundish to the mould, namely stopper control and slide gate control. In additional to these two main flow control systems, the casting nozzle geometries, casting rate, and casting mould dimensions vary considerably, and this complexity makes it difficult to precisely simulate turbulent flow in the casting channel. In this paper, examples are presented showing how different turbulence models influence the simulation results, using the latest version of the open source CFD simulation software OpenFOAM. Prior to the CFD modelling, RHI Magnesita's water modelling facilities in Leoben (Austria) were used to validate the state-of-the-art turbulence models selected for a particular casting nozzle geometry and flow control system.

Impact of Fine Water Mist Curtains on Fire Safety in Historic Buildings: A Case Study of Foshan Historical and Cultural District, Guangdong Province, China

ABSTRACT To address inadequate fire separation distances in historical buildings leading to extensive fire spread, practical research employing Fire Dynamics Simulator (FDS) was conducted. The study involved simulating a historical and cultural block in Foshan City to analyze variations in heat flux density and temperatures within a 5-meter radius of windows under fire powers of 1.5 MW, 6 MW, and 10 MW, with window openings at 10%, 25%, and 50%, respectively. The aim was to preserve the original architectural integrity without modifying existing fire separations. Augmentation of fire protection through the implementation of a fine water mist water curtain between buildings was proposed, and its efficacy in smoke and heat insulation was evaluated. Results indicate that, at 1.5 MW fire power, adjacent structures remain relatively secure with current fire separations. However, at 6 MW and 10 MW, fire spread to neighboring buildings was significant regardless of window opening area. Implementation of the water curtain with a nozzle flow coefficient (K) of 80, typical for standard coverage area sprinkler nozzles, and a spacing of 0.8 m, proved effective in enhancing smoke and heat insulation while also offering cost efficiencies. Optimal results were achieved with an average droplet size of 200 µm and nozzle pressure set at 6.0 MPa, corresponding to a nozzle flow rate of 615 L/min. These findings provide valuable insights for drafting specifications for the adaptive reuse of historical buildings and deploying fine water mist water curtains in confined spaces.

New insights of heat transfer in pistons and nozzles flow of graphene-transformer oil nanofluid: A differential transform method

This work aims to study heat transfer analysis in a squeezing flow problem of nanofluid. The flow between pistons and nozzles in an automobile engine is one industrial application where the knowledge of the squeezing flow plays a crucial role. The applied magnetic field has a longitudinal inclined angle that ranges from zero to ninety degrees. In addition, viscous dissipation, chemical reaction, and suction injection are taken into consideration. Graphene nanoparticles with transformer oil are considered for Tiwari-Das Model. The transformed system of nonlinear ODEs is solved using the differential transform method. The numerical findings of the skin friction coefficient, the Nusselt and the Sherwood numbers are assessed with previously available works for accuracy. The graphical findings for relevant parameters of all profiles are analyzed. It becomes apparent that the velocity and heat transfer in compressing flows are significantly influenced by the angle of the inclination of the magnetic field. The temperature of the nanofluid and the rate of the heat transfer are both improved in the existence of the viscous-dissipation and thermophoresis. The findings show that the temperature rises with increased Prandtl and Eckert numbers. Furthermore, when Brownian movements of nanoparticles take place, the rate of mass transfer decreases.

Multiscale simulation of spray and mixture formation for a coaxial atomizer

Coaxial atomization is an established atomization strategy for many stationary combustion systems. While modeling spray formation in coaxial atomization is challenging due to the existence of a wide range of length and time scales, typical models introduce a substantial uncertainty for Euler–Lagrange simulations of the actual application, e.g., a spray flame. To reduce uncertainties, a recently proposed multiscale approach is adopted for simulations of realistic applications in this work. The multiscale approach uses three one-way coupled simulation domainss that cover the internal nozzle flow, the interfacial flow of the near-field, and the dispersed flow of the far-field. The capabilities of the approach are explored by applying it to a standardized non-reacting experiment from the flame spray pyrolysis research community. In order to assess the relevance for application simulations, results are discussed in the context of mixture formation. The results are compared against shadowgraphy images of the near-field and measured droplet statistics in the far-field. It is found that the multiscale approach is capable of providing similarly accurate droplet statistics as experiments or models derived from them. In addition, it is found that the breakup dynamics in the near-field introduce substantial mixture fraction fluctuations. These fluctuations are only included because of the deterministic coupling of the multiscale approach and are typically neglected in conventional approaches.

End-to-End Differentiable Model for Optimization of Rocket-Powered Vehicles Including Plume Radiant Emission

This paper proposes an end-to-end differentiable model for infrared radiant emission for low-altitude exhaust plumes. Considering plume radiant emission during the design phase is important for ensuring vehicle design constraints and objectives can be met while accounting for the coupling of plume radiant emission with other aspects of vehicle design. The model is suitable for computational frameworks using automatic differentiation or gradient-based optimizers—such as CasADi and AeroSandbox—which enable direct optimization of solid rocket-powered vehicle design with constraints on plume radiant emission. It consists of six submodels of different coupled physical phenomena: chamber thermodynamic equilibrium, motor internal ballistics, isentropic nozzle flow, plume flow field, afterburning kinetics, and radiative transfer. The combined model shows reasonable agreement for several different rocket-powered vehicles. The use of the model is demonstrated in an example case study for optimizing a low-thrust, transonic, rocket-powered aircraft concept.

玉米植保无人机离心喷施系统设计与雾滴分布特性试验

Aiming at the problems of spraying pole-type plant protection machines difficult to get down to the field after row closure of maize in the middle and late stages, uneven droplet distribution of pressure nozzle-type plant protection drone, and difficult to change the droplet particle size, this paper designed a UAV centrifugal spraying system for maize planting protection through the designed centrifugal nozzle combined with a plant protection drone. A single nozzle parameter test was carried out to study the relationship between nozzle speed, flow rate and droplet size. The variable parameter flow rate is set in the range of 300 ml ~ 1000 mL / min, and the nozzle rotation speed is set in the range of 8000 ~ 18000 r / min gradient change. The test results show that the droplet size is related to the liquid supply flow rate and the nozzle rotation speed. According to the theory of optimal biological particle size, the centrifugal nozzle parameter is determined to select the liquid supply flow rate of 1000 mL / min and the nozzle rotation speed of 14000 r / min. The droplet distribution characteristics test under the actual operating conditions was carried out with this parameter, and the important index parameters such as droplet size, droplet density and coverage rate were analyzed to characterize the UAV aerial spraying operation. The experimental results show that the flight speed of the UAV has an important effect on the droplet deposition parameters, which significantly affects the droplet coverage, droplet density and deposition amount of the bottom layer of maize, and the droplet coverage and the droplet deposition amount of each sampling layer tends to decrease with the increase of flight speed, and the coefficient of variation (CV) value of the centrifugal spraying system was the smallest at the flight speed of 1.5m/s, and the effect of droplet deposition was the most uniform. at a flight speed of 1.5m/s. The effect of droplet deposition is the most uniform. This study can provide a reference basis for the optimization of parameters and the correct use of centrifugal plant protection UAV in the middle and late stage plant protection operations of tall crops such as maize.

Cavitating bubbly flow of non-Newtonian second grade fluid through nozzles: Application of reduction of cavitation damage and noise

This research is focused on studying the behavior of bubbles in one-dimensional nozzle flows. The study delves into the complex flow of cavitating bubbles within geometries of varying cross-sectional areas, using a second-grade fluid. The cavitation phenomenon poses a potential threat, as it can harm surfaces upon bubble collapse or interaction with adjacent boundaries. Thus, the proposed model unveils the intricate behavior of cavitating bubbles in response to nozzle shape and fluid properties. The governing equations are first modeled using the Rayleigh–Plesset equation along with continuity and momentum equations for bubbly liquids. They are then simplified and nondimensionalized to solve by means of the RK method. The influence of several nondimensional parameters, including the Reynolds number, fluid parameter, cavitation number and the number of bubbles, on the flow behavior of second-grade fluid through various channels is illustrated using graphs. To validate the results, the Newtonian formulation was applied in the current setting, and it was found that the obtained results matched the available literature. Also, critical values of void fractions for the radius of the bubble are presented. The non-Newtonian properties of the fluid are observed a significant outcome for the reduction of cavitation damage and noise.

Physics-data fusion for digital metering of gas-liquid two-phase flow in oil nozzles

Oil well production metering is an important basis for assessing resource reserves and production capacity. Existing metering methods require high investment and involve significant implementation difficulties and high computational costs. A new method of multiphase flow metering method was proposed by combining the fluctuation of pressure drop and temperature difference generated after throttling through the oil nozzle. The throttling equation coupling differential pressure, flow rate and gas fraction was derived. By regulating the gas and liquid superficial velocity, we carried out the experimental test for true nozzle aperture of 10 mm in the loop system, covering various flow patterns. In addition, the deep neural network was constructed for inversion prediction of mass gas fraction. The proposed flow metering equation has an adaptable gas mass fraction range of 0 to 100%, unaffected by the variations in flow patterns, gas-liquid velocities, and system pressure changes. The metering errors of gas mass fraction and mass flow rate is below ±10%. The proposed metering method only relies on the existing temperature and pressure measurement system in the gathering and transportation system, and no additional measuring devices are required. It can be widely used in oil filed production to realize the virtual metering.

Optimization of Operational Parameters of Plant Protection UAV.

The operational parameters of plant protection unmanned aerial vehicles (UAVs) significantly impact spraying effectiveness, but the underlying mechanism remains unclear. This paper conducted a full factorial experiment with varying flight speeds, heights, and nozzle flow rates to collect parameter space data. Using the Kriging surrogate model, we characterized this parameter space and subsequently optimized the average deposition rate and coefficient of variation by employing a variable crossover (mutation) probability multi-objective genetic algorithm. In the obtained Pareto front, the average sedimentation rate is no less than 46%, with a maximum of 56.08%, and the CV coefficient is no more than 13.91%, with a minimum of only 8.42%. These optimized parameters enhance both the average deposition rate and spraying uniformity compared to experimental data. By employing these optimized parameters in practical applications, a balance between the maximum average deposition rate and minimum coefficient of variation can be achieved during UAV spraying, thereby reducing pesticide usage, promoting sustainable agriculture, and mitigating instances of missed spraying and re-spraying.

Computation of Unsteady Swirling Flows in Nozzles and Pipes by Applying a New Locally Implicit Godunov-Type Scheme

Computation of Unsteady Swirling Flows in Nozzles and Pipes by Applying a New Locally Implicit Godunov-Type Scheme

Gravitational decoupling and aerodynamics: black holes and analog gravity in a jet propulsion lab

A connection is established between transonic sound waves propagating along a de Laval nozzle and quasinormal modes emitted from hairy black holes obtained with the gravitational decoupling method applied to the Reissner–Nordström geometry. Aerodynamical features provide an analogue setup to test experimentally perturbations of fluid flows in a de Laval nozzle producing quasinormal modes. In particular, nozzle shape, pressure, Mach number, temperature, density, and thrust coefficient profiles are determined as functions of the black hole parameters for several multipole numbers. The black hole quasinormal mode frequencies are also investigated for different overtones, evaluating the quality factor of the nozzle.

Kinetic Simulation of Nozzle Flow in a Micronewton-Class Cold Gas Thruster

Many scientific space missions need highly precise attitude and orbit control or ultrafine drag compensation, which relies on the variable-thrust propulsion technology operating at the micronewton level. Cold gas thruster (CGT) is a very promising solution, mainly because of its high reliability. One of the keys to the success of micronewton variable-thrust CGT is to understand the flow in its nozzle, whose configuration is much more complex than traditional CGT nozzles. This paper applies kinetic-based multiscale models to investigate the gas flow in the complex nozzle of a micronewton variable-thrust CGT. The simulations reveal that the flow simultaneously experiences all kinds of regimes from continuum to free molecular. The continuum breakdown is likely to occur near the throat region due to large gradients of flow variables and in the expander due to low gas density. Frictional choking is observed, and the nozzle length can be optimized to improve the thruster performance. Nozzle performance measures such as thrust, discharge coefficient, and thrust efficiency are found to change only with the throat Knudsen number Knt. The performance curves can be divided into two sections at Knt≃0.1, and thereby an empirical piecewise formula for thrust prediction is proposed.

Carbon dioxide separation from natural gas using a supersonic nozzle

Carbon Dioxide (CO2) is often released in the process of natural gases and is one of greenhouse gases that are being treated as the most troublesome environmental issues. One of the promising ways to economically remove CO2 in natural gas processes is to use the technology of supersonic separation that makes use of non-equilibrium condensation in supersonic swirling flows in convergent-divergent nozzle using wet outlet. In the present study, the mixture of Methane (CH4) and CO2 was considered as natural gas. Two-dimensional convergent–divergent nozzle was employed to produce supersonic swirling flow with non-equilibrium condensation. The Peng–Robinson real gas model was used for the mixture gas. A nucleation equation and a droplet growth equation were incorporated into the governing equations of the compressible Navier–Stokes with the k-ω turbulence closure. The predicted results were verified and validated with existing experimental data. The convergent–divergent nozzle was varied to investigate its effect on the non-equilibrium condensation of CO2 in the mixture flow. The Technique for Order of Preference by Similarity to Ideal Solution method was applied to achieve the optimum case with amounts of wetness (the mass fraction of liquid CO2 to the summation of the mass fraction of liquid and vapor CO2 at the outlet of the nozzle) and kinetic energy. Three locations of wet outlets for the optimum case were analyzed. The results show that an increase in the divergent angle of the nozzle, swirling intensity, and inlet supply pressure results in more nucleation of CO2. However, the enhancement of mole fractions of CO2 decreases the nucleation rate and wetness. The exit wetness from wet outlets was increased with increasing distance from the throat.

OPTIMISATION OF A NEEM OIL BASED MINIMUM QUANTITY LUBRICATING (MQL) SYSTEM PARAMETERS FOR THE ORTHOGONAL MACHINING OF MILD STEEL

Cutting tools experience early failure and dimensional variation due to the high temperature developed during machining. Conventional cutting fluid applications do not successfully remove heat because they do not reach the chip-tool contact. Operators on the work floor may experience the adverse side effects of cutting fluids, such as skin and respiratory issues. As a result, a different lubricating method is necessary for machining without harming the tool-workpiece, which would also be advantageous for health and the economy. This research aims to develop and evaluate the efficiency and optimization of minimal use of Neem seed oils as lubrication for the Taguchi L9 array-based design for machining of mild steel. The Taguchi optimization technique was used to examine the impact of the neem oil based Minimum quantity lubrication (MQL) system (with flow rate, air pressure and nozzle diameter as factors) on the workpiece temperature and chip thickness ratio at cutting speeds of 260 rpm and 470 rpm. The outcome demonstrated that optimal settings at 260 rpm were a flow rate of 50 ml/hr, air pressure of 1.5 bars, and nozzle diameter of 0.8 mm for workpiece temperature, and a flow rate of 100 ml/hr, air pressure of 1 bar, and nozzle diameter of 0.8 mm for chip thickness ratio. At 470 rpm, optimal settings for workpiece temperature were a flow rate of 50 ml/hr, air pressure of 1.5 bars, and nozzle diameter of 0.5 mm, while chip thickness ratio optimization indicated a flow rate of 100 ml/hr, air pressure of 1 bar, and nozzle diameter of 0.5 mm.

Numerical investigation of annular expansion-deflection nozzle flow under varying backpressure changing rate

The characteristics of flow and thrust evolution of an annular Expansion-Deflection (ED) nozzle are numerically investigated under varying backpressure changing rates during ascending and descending trajectories. The objective is to test the sensitivity of unsteady behaviors of shock waves in the ED nozzle to backpressure changing rate, and to further elucidate the thrust evolution mechanism and mode transition hysteresis. The movement of shock reflection points on the nozzle wall follows two flow mechanisms, namely, shock self-excited oscillations and rapid backpressure changes. A low backpressure changing rate enables shock self-excited oscillations, leading to a reciprocating motion of the shock waves accompanied by thrust oscillations, while a high backpressure changing rate suppresses the shock self-excited oscillations, leading to a unidirectional motion of the wave system on the nozzle shroud wall. A criterion for distinguishing ED nozzle operation modes is proposed, which relies on the loading inflection points of the nozzle pintle base and exhibits a fast and user-friendly feature. A dual-wake mode hysteresis region is defined to quantify the hysteresis in nozzle mode transition, with the span of the region decreasing as the backpressure changing rate slows down. The present work helps in understanding the unsteady flow mechanism and thrust evolution in ED nozzles.

Influence of Double-Ducted Serpentine Nozzle Configurations on the Interaction Characteristics between the External and Nozzle Flow of Aircraft

To clarify the influence of the serpentine nozzle configurations on the flow characteristics and aerodynamic performance of aircraft, the flow features and aerodynamic performances of the double-ducted serpentine nozzles with different aspect ratios (AR), length–diameter ratios (LDR) and shielding ratios (SR) are numerically investigated. The results show that the asymmetric nozzle flow occurs due to the curved profile of serpentine nozzles, and a local accelerating effect exists at the S-bend, causing the increase in wall shear stress. The unilateral unsymmetrical expansion of the tail jet in the upward direction interacts with the separated external flow of the afterbody, forming an obvious cross-shock wave and shear layer structure. The surface pressure of the afterbody increases along the external flow direction, and decreases sharply in the separation point of the boundary layer. With the increase in AR and LDR, the local accelerating effect of the nozzle flow weakens, while with the increase in SR, the accelerating effect increases. The total pressure recovery coefficient, flow coefficient and axial thrust coefficient all decrease with the increase in AR, LDR, and SR. The thrust vector angle decreases with the increase in AR but is less affected by LDR and SR.

Cavitation Phenomenon and Spray Atomization in Different Types of Diesel Engine Nozzles: A Systematic Review

<div>The high-pressure common rail fuel injection system for diesel engines is one of the core technologies that need to be addressed in the automobile industry. The control of the internal flow in multi-hole injector nozzles is the key to achieve accurate control of the fuel injection and spray process. There are various types of research on cavitation phenomena currently conducted on various types of test benches, but there is no conclusive discussion. Therefore, it is to summarize these studies in order to identify the highlights of existing studies and point out their shortcomings. This article compares and analyzes the developing patterns of cavitation phenomena on four test benches through literature review and has obtained rich research data on these four types of nozzles, but they still have their own shortcomings at the same time, even with numerical simulation. Based on this, the article has conducted a detailed and critical discussion on the current research situation and completed a summary. Specifically, it mainly involves four geometry parameters, two dynamic factors, and three fuel physical property parameters. The discussion conducted can contribute to the future development of cavitation models, further improving the energy-saving and -reducing emission reduction of diesel engines.</div>

Predictive modeling of flow characteristics in supersonic separators using machine learning

In the pursuit of cleaner energy sources, pre-processing fuel streams is crucial before distribution. Challenges arise during this process, leading to operational issues and diminished transmission efficiency. Among different technologies, supersonic separators are the ones that separate undesired components from the main gas stream more effectively. Precise forecasting of nozzle flow rate and shockwave location at a low cost can markedly enhance the efficiency of manufacturing and rating. In this research, the one-dimensional method has been developed to solve flow equations simultaneously by implementing equations of state. CFD has been used for the verification of the developed model, and the effect of different equations of state is investigated. Results show that the one-dimensional model significantly reduces the calculation time. Different EOSs result in up to 2.0 % and 3.5 % variation in the prediction of shock location and the mass flow rate, respectively.A machine learning methodology is employed to predict the location of shockwaves and the choked flow rate at an even lower cost. A dataset of 160 entries, generated using Peng Robinson's EOS, serves as the basis for this analysis. Prediction tasks are executed using Random Forest, k-nearest Neighbors, and Multilayer Perceptron models. While all three models demonstrate proficiency in data interpolation with R2 scores up to 0.9962 and 0.9951 for the shockwave location and mass flow rate, respectively, discerning their performance in extrapolation appears contingent on the specific case. In the case of extrapolation, Multilayer Perceptron and k-Nearest Neighbors show better match to one-dimensional results.

Non-Intrusive Frequency Measurements With Laser Shadowgraphy And Event-Based Schlieren Imaging Of Bluff Body Wakes In Compressible Flow

Event-based imaging is an emerging technology in thermodynamics and fluid dynamics. In this work, we are leveraging an event-based camera with a conventional schlieren set-up to investigate the vortex shedding dynamics behind a blunt central injector in a transonic nozzle flow. We offer different methods to evaluate the data stream of the event-based camera. Standard Fourier methods are not directly applicable to this data due to a non-constant time step. Therefore, the data needs to be treated with special care. Clusters of on- and off-events alternate and show the periodic nature of the wake. Using a clustering algorithm on the event groups also provides an estimation of vortex shedding frequency. These results are compared with laser shadowgraphy, a second novel method to measure the vortex shedding frequency in the wake. Both approaches to measuring the vortex shedding frequency are agreeing with each other within 1%. They each offer a simple set-up with comparatively low cost for their high temporal resolution.

Experimental investigation on the effects of complex pressure gradients on the film cooling effectiveness of a serpentine nozzle

Serpentine nozzles more easily deform and damage due to high-temperature airflow because of their multi-bend channel configuration. Therefore, film cooling technologies should be applied to serpentine nozzles. Complex pressure gradients in serpentine nozzles lead to different film cooling characteristics from combustion chambers, turbine blades, and other exhaust systems. This study experimentally investigated the effects of complex pressure gradients and film hole inclination angles on a serpentine nozzle’s film cooling effectiveness (FCE) using pressure-sensitive paint (PSP). The flow mechanisms were obtained via numerical simulations. The experimental nozzle design needs to consider the needs of PSP observations and the normal flow of serpentine nozzles. However, the complex structure of serpentine nozzles makes those increasingly difficult. The studied pressure gradients include the pressure gradient mutation (PGM), strong adverse pressure gradient (SAPG), weak adverse pressure gradient (WAPG), and favorable pressure gradient (FPG). The results show that complex pressure gradients change the coolant coverage and adhesion and may induce a recirculation zone in the SAPG region. This affects the development of the vortex construction and leads to different FCE distributions. The FCE under the effects of the PGM is the largest, followed by the SAPG, WAPG, and FPG. A larger inclination angle weakens the coolant adhesion but may enhance its downstream and lateral flow treads. This is coupled with the effects of complex pressure gradients, where larger inclination angles bring better film cooling effects in some cases. After accounting for the four blowing ratios, the area-averaged FCEs under the effects of the SAPG, WAPG, and FPG are 28.9 %, 42.8 %, and 52.3 % lower than that under the PGM, respectively. The area-averaged FCEs under the conditions α = 45° and 60° are 6.6 % and 10 % lower than that under α = 30°.