Nozzle Operating Conditions Research Articles

The Research on Self-Excited Oscillating Jet Cleaning Technology

Abstract Self-oscillating nozzles have gained wide popularity due to their ability to generate powerful impact forces, long-range projection, and concentrated, stable jets in applications such as water-jet drilling and rust removal. However, the nozzle’s efficient operation relies heavily on specific structural designs and operational parameters, which necessitates further indepth research. By studying the characteristics of self-excited oscillating pulse cavitation jet within the nozzle cavity structure. Analyzing the evolution characteristics of internal flow field. Solving optimization problems in a targeted manner. The purpose of this study is to reveal the resonance principle behind the self-excited oscillation of nozzle. It also explores the regularities of the effects that the cavity diameter has on jet performance, ultimately seeking to find the optimal configuration of nozzle structure and operating conditions.

On the Water Jet Quality at Part-Load Operation of Pelton turbines

Abstract Pelton turbines with multiple nozzles are characterised by their excellent performance over a wide operating range of mass flow rates. Thus, Pelton turbine manifolds must also be designed to deliver good flow quality to the nozzles at part-load operating conditions to accomplish the expectations. A reduced number of nozzles are opened at low mass flow rate operating conditions, where the choice of the open nozzles depends on the water jet quality generated at the individual nozzles. We investigate the flow phenomena occurring in the manifold with the operation of a reduced nozzle number employing numerical simulations to analyse beneficial nozzle opening selections. The turbulent two-phase flow is predicted by the Volume-Of-Fluid (VOF) approach and the k–ω SST turbulence closure model. Different nozzle operating scenarios are simulated, and the implications on the water jet quality, i.e. deviation and shape deformation, are reported. The results show that the free water jet quality criteria can change drastically at individual nozzle operating conditions because of the velocity changes at the branch line junctions.

Effect of Y-jet nozzle geometry and operating conditions on spray characteristics and atomizer efficiency

The investigation and optimization of the atomizer nozzle design are paramount for an efficient atomization performance. Motivated by internal mixing atomizers used in FCC-reactors in the oil industry, the present work aims to improve the gas-liquid mixing process promoted by a specific design of the Y-jet nozzle by investigating the impact of key geometric parameters. The performance assessment is conducted by investigating the internal mixing chamber pressure, high-speed images of the spray, and the analysis of droplet size and velocity spatial distributions. The investigation considers industrially representative operating conditions as opposed to the lower mass flow rates typically employed in lab-scale investigations. The geometry variation considers the length and opening angle of the internal mixing chamber, as well as the impingement angle between the gas and the liquid jets inside the atomizer nozzle. A particular geometric characteristic of the utilized nozzles is the mixing-chamber conical geometry, distinguishing them from conventional cylindrical geometries. The impact of the nozzle geometry and operation parameters on atomization efficiency and spray homogeneity are the main outcomes of this approach. Overall, nozzles with shorter mixing chambers promote more efficient atomization combined with small droplet sizes and a more homogeneous spray.

Study on the Cooling Effect of Double-Layer Spray Greenhouse

Greenhouses provide suitable environmental conditions for plant growth. Double-layer plastic greenhouses are often used in many regions to ensure normal crop growth during winter since single-layer plastic greenhouses have poor insulation. However, during summer, the high insulation of double-layer plastic greenhouses, combined with excessive external solar radiation, can cause high temperatures inside the greenhouse that are not suitable for plant growth and require cooling. In this study, we propose a double-layer spray greenhouse using a high-pressure spraying system that is placed inside the double film that allows for additional cooling capacity during the summer in order to sustain plant growth. A greenhouse platform test was set up to investigate the optimum operating conditions for the nozzles and to explore changes in greenhouse microclimate under different nozzle operating conditions. The results show that (1) the cooling rate increases with increasing water supply pressure, nozzle diameter and spraying time, and the humidification rate is consistent with the change in the rate of cooling. (2) The optimal condition for cooling in this experiment is achieved with a 120° double nozzle with a nozzle diameter of 0.30 mm, a water supply pressure of 6 MPa, and a spraying time of 15 min, which can reduce the temperature by up to 5.36 °C and serve as a reference for the summer cooling of the double-layer greenhouse.

Three issues on nozzle thrust performance in cold-to-hot correlation considering variable specific heat effect

A high-temperature effect is crucial in cold-to-hot correlation for thrust nozzles to employ experimental data of cold flow to predict the real flight performance of hot gas. The high-temperature nozzle flow behaves beyond the classical gas dynamics and restricts the feasibility of cold-flow experiments, and it becomes more severe due to the species transformation from cold air to hot gas when safety and cost are considered. For an in-depth awareness, this work refines three fundamental issues regarding the high-temperature variable specific heat effect on nozzle flow characteristics. A comprehensive analysis is performed from theory to applications. First, the flow properties of calorically perfect gas (CPG) and thermally perfect gas (TPG) are distinguished and connected via the basic flow equations. One-dimensional flow theory is extended by the generalized stagnation–static gas functions for TPG. The unanticipated intersections within pressure are discovered, which could produce substantial perplexities in nozzle performance determinations. Second, the pros and cons of two homologous nozzle thrust coefficients are clarified on application objects, definition methods, and solution manners. It is proved that temperature has no influence on thrust coefficients for CPG, while the variable specific heat effect might induce three types of false-positive thrust coefficients, to make flow state unidentified, and further shake the baseline of nozzle performance. Third, for the aggravated variable specific heat effect in cold-to-hot correlation from air to hot gas, two methods are proposed with reliable verifications to solve this issue through introducing a novel concept of relative nozzle operating conditions.

Influence of operating conditions on the optimal nozzle exit position for vapor ejector

Vapor ejector cooling systems have attracted a lot of interest in the last 25 years, given that their electrical consumption is much lower than that of conventional refrigeration systems. However, ejector systems have suffered from a low coefficient of performance. Among ejector design parameters, the nozzle exit position (NXP) has a strong impact on system performance, but so far, limited and contradicting observations in terms of its optimal value have been reported in different literary works. In this work, a large-sized and well instrumented experimental setup was used to determine the impact of the nozzle geometry and operating conditions on the optimal NXP values. The results showed that the optimal NXP values were significantly impacted by the ejector nozzle geometry and the critical entrainment ratio (ωcrit), however the primary, secondary and outlet pressures had negligible effect. Up to four optimal NXP values were observed over the tested NXP range. This number was found to increase with the critical entrainment ratio, with two optimal NXP values for ωcrit < 0.25 and four optimal NXP values for ωcrit > 0.4. Proper adjustment of the NXP value increased the entrainment ratio by >34%. For the first time, the wall pressure along the constant area section of the ejector was used to study the optimal NXP values. This led to a new finding: while the critical entrainment ratio was going from peaks to valleys along the NXP range, the wall pressure at the inlet of the constant area section varied inversely, this pressure being at a minimal value when NXP is close to an optimal value. It was also observed that the critical compression ratio decreased at higher NXP values. This work is the first to show that the optimal NXP is linked to the critical entrainment ratio, which provides an explanation to the contradictory observations reported in the literature regarding the impact of operating pressures on the optimal NXP values. Finally, this is the first study that shows the importance of adjusting the NXP whenever operating conditions are modified or a different ejector is used.

A Design Method for Low-Pressure Venturi Nozzles

The purpose of this work is to provide empirical design models for low-pressure, subsonic Venturi nozzles. Experimentally validated simulations were used to determine the effect of nozzle geometry and operating conditions on the suction ratio (ratio of suction mass flow rate to motive mass flow rate) of low-pressure, subsonic Venturi nozzles, over a wide range of geometries and operating conditions, through a parametric study. The results of the parametric study were used to develop seven empirical models, each with a different range of applicability or calculating a different indicator of nozzle performance (i.e., suction ratio, momentum ratio, or dynamic pressure ratio), of the Venturi nozzles using a constrained multi-variable global optimization method. Of the seven empirical models, the best models were found to be those for low- (less than one) and high-suction ratios (greater than one), with mean absolute percentage errors of 5% and 18%, respectively. These empirical models provide a design tool for subsonic, low-pressure Venturi nozzles that is more than an order of magnitude more accurate than a governing equation approach or conventional flow head calculations. These newly-developed empirical models can be applied for initial nozzle design when precise suction ratios are required.

On the fluidic behavior of an over-expanded planar plug nozzle under lateral confinement

The present work aims to study the fluidic behavior on lateral confinement by placing sidewalls on the planar plug nozzle through experiments. This study involves two cases of nozzle pressure ratio (NPR = 3, 6), which correspond to over-expanded nozzle operating conditions. Steady-state pressure measurements, together with schlieren and surface oil flow visualization, reveal the presence of over-expansion shock and subsequent interaction and modification of the flow field on the plug surface. The flow remains attached to the plug surface for NPR = 3; whereas for NPR = 6, a separated flow field with a recirculation bubble is observed. Spectral analysis of the unsteady pressure signals illustrates a clear difference between the attached and the separated flow. Besides, other flow features with a distinct temporal mode associated with and without lateral confinement are observed. The absence of lateral confinement reduces the intensity of low-frequency unsteadiness; however, on the contrary, the interaction region is relatively reduced under lateral confinement.

Numerical Modelling of Internal Flow in Water Mist Injectors: Effect of Nozzle Geometry and Operating Conditions

Water mist fire fighting has achieved a well established position in fire protection for industrial and civil applications. The performances of water mist nozzles, largely used in water mist production, are deeply influenced by the internal nozzle flow characteristics and CFD modelling is a powerful tool to analyse them in details. The paper focuses on the numerical investigation of the internal flow in pressure swirl injectors for water mist applications. 3D large eddy simulations based on the Volume-Of-Fluid methodology have been implemented. The flow is assumed to be incompressible and under isothermal non-reacting conditions. Validation of the model against available experimental data is performed with satisfactory results. The effect of internal nozzle geometry on the injector behaviour is investigated by modifying the inclined swirling channels (five configurations) and the injection pressure in the range 5 to 320 bar. The effect of the size of cylindrical and conical swirl chambers are also independently investigated. Three different flow regimes can be distinguished as a function of imposed swirl and injection pressure and a map is reported to clarify the effect of these parameters. When a stable hollow cone spray is formed the mass flow rate fluctuations are < 5%, corresponding to a discharge coefficient between 0.34 and 0.50. When no air core is present in the discharge hole, mass flow rate fluctuations as high as 16% are observed, which correspond to discharge coefficient as high as 0.7. A detailed quantification of in-nozzle characteristics, like swirl number and momentum flux distribution along the nozzle and lamella thickness in the discharge hole, is reported and discussed, with particular emphasis on stability and transient behaviour of the atomiser internal flow, which represents the main novelty of the present study.

Experimental investigation of jet noise from a high BPR dual-stream jet in a static model-scale test

The noise characteristics of a dual-stream jet of bypass ratios greater than 10 were investigated in response to area ratio, nozzle-operating conditions, installation effect, and chevron effect. The key conclusions were as follows. (1) The area ratio impacted the noise by up to 3 dB at aft angles and at mid-frequency for heated conditions. (2) The spectral variation due to the change of primary stream parameters was constant at low Strouhal numbers and diminished at high Strouhal numbers. (3) The impact of the secondary stream pressure was described by the scaling law of single-stream jets for unheated conditions. The flow parameters of other jets were required to describe the spectra of Strouhal numbers between 0.2 and 2.0, based on the secondary jet for heated conditions. (4) The installed jet noise was quantified for various wing configurations and was more pronounced at forward angles. (5) The chevron nozzle reduced overall noise by up to 4 dB, though it became less attractive when installed. The quantified information is expected to improve the estimation of noise from a dual-stream jet of high bypass ratios.

A model-scale test on noise from single-stream nozzle exhaust geometries in static conditions

A model-scale test with single-stream nozzle exhaust geometries was carried out at the anechoic chamber of Beihang University in Beijing, China. The spectral characteristics are investigated, and the effects of the following parametric variations are reported in this paper: impact of nozzle operating conditions on spectra; impact of the presence of a plug; and effectiveness of chevron configurations for noise mitigation. The measurement shows that the change of pressure values has more impact on spectra than the change of temperature values. The spectral change due to pressure is shown at all band numbers for unheated conditions whereas it is more pronounced at high-frequency ranges for heated conditions. An impact of the presence of a plug is also clearly observed. The reduction of noise is moderate up to band number of 35, and becomes more significant at higher band numbers. It is observed that chevron nozzles are more efficient at high pressure and temperature values. It is expected that the quantified analysis will be used to develop an empirical model of single jet noise, which will be the baseline for the development of prediction of noise from turbofan engines of high bypass ratios.

Comparison of Near-Nozzle Spray Performance of Gas-to-Liquid and Jet A-1 Fuels Using Shadowgraph and Phase Doppler Anemometry

The gas-to-liquid (GTL) fuel, a liquid fuel synthesized from natural gas through Fischer–Tropsch process, exhibits better combustion and, in turn, lower emission characteristics than the conventional jet fuels. However, the GTL fuel has different fuel properties than those of regular jet fuels, which could potentially affect its atomization and combustion aspects. The objective of the present work is to investigate the near-nozzle atomization characteristics of GTL fuel and compare them with those of the conventional Jet A-1 fuel. The spray experiments are conducted at different nozzle operating conditions under standard ambient conditions. The near-nozzle macroscopic spray characteristics are determined from the shadowgraph images. Near the nozzle exit, a thorough statistical analysis shows that the liquid sheet dynamics of GTL fuel is different from that of Jet A-1 fuel. However, further downstream, the microscopic spray characteristics of GTL fuel are comparable to those of the Jet A-1 fuel.

Unsteady velocity measurements of model-scale supersonic exhaust jets in military-relevant configurations

Of the utmost importance is the need to better understand the high temperature, high velocity flow fields generated by military tactical aircraft during “run up” and take-off that gives rise to extremely hazardous conditions for personnel and equipment within the vicinity of the aircraft. The present study aims to fill the need for high frequency, two velocity component measurements throughout the flow fields produced by university-scale supersonic jets exhausting from nozzles in configurations relevant to practical, full-scale application. Specifically, this work focuses on studying the supersonic jets operating in two basic configurations: horizontal, free jets and jets impinging normal to a ground plane reminiscent of current short-takeoff and vertical landing aircraft. Experiments are conducted at nozzle operating conditions similar to those of full-scale aircraft. Both mean velocities and turbulence components are measured in both flow fields using a laser Doppler velocimeter. Axial components of the mean flow and turbulence are measured in the free jet. In the single impinging jet flow field two-component mean velocity and turbulence components are measured in the jet plume, impingement region, and outwash flow. Free jet velocity measurements show good consistency with 50% increase in jet Reynolds number. Turbulence intensities up to 15% of the mean jet exit velocity are observed at the nozzle exit plane. Laser Doppler measurements in the outwash of an impinging jet show turbulent fluctuations produce unsteady velocities well above the mean value. Two-component impinging jet unsteady velocity spectra show a distinct peak at the same frequency as the impingement tone observed in prior impinging jet acoustic field measurements.

Modelling of the spray drying process for particle design

Spray drying is widely applied in many industries, such as the pharmaceutical, food, detergents, polymers, to convert liquids in solid particles. However, it still requires continuous innovation in order to provide more sophisticated particles, which are difficult to design by using only empirical approaches. In this context, a steady-state mathematical model for a co-current spray dryer is developed to give a more phenomenological insight in the production of inhalable particles. The model includes mass, energy and momentum balances for both particulate and gaseous phases. Particularly, and as a model inhalable compound, ciprofloxacin hydrochloride (CIP) aqueous solutions are studied. Several experimental data, obtained in a Mini-Spray Dryer B-290, BÜCHI, were available. In addition, droplet size measurements were carried out by using laser diffraction. The effect of the binary nozzle operating conditions on the mean droplet size was analyzed and a correlation to predict the mean Sauter diameter was established. The experimental data are used to fit and validate the proposed model. The validated model is used to perform parametric studies in order to evaluate the effect of the main process variables on the final product properties (e.g., particle size and density, powder moisture content) and to track key powder attributes for pulmonary administration.

On flow regime inside plain-orifice nozzle

The plain-orifice is the most common type of atomizer. The flow regime inside plain-orifice nozzle has a tremendous effect on the external spray. At present, the judgement method of the flow pattern is not uniform. The purpose of this study is to numerically investigate the relationship between the change of flow pattern, the ratio of nozzle length and nozzle diameter (L/d), the ratio of nozzle radius of the entrance and nozzle diameter (r/d) in plain-orifice nozzle. The computational fluid dynamics (CFD) code FLUENT was used to perform the numerical simulation of the cavitating flow and hydraulic flip in the nozzles. In this paper, the relationship between the change of flow pattern, r/d and L/d was obtained, and the relation curves between L/d and r/d were plotted, and a new model of flow pattern was obtained. The model established in this paper is more accurate than the empirical model to judge the change of flow pattern. The new model is helpful to modify the existing empirical model. According to the relationship, the researcher can use the method of reasonably adjusting the relationship between the nozzle structure and operating conditions to avoid the generation of hydraulic flip, and to get better atomization effect.

Zonal Detached Eddy Simulations of a Dual-Stream Jet: Turbulence Rate Sensitivity

This paper investigates the effect of turbulence injection using the random flow generation technique at the inlet boundaries of the core and fan channels of a dual-stream nozzle with an external plug. The objective is to reproduce the turbulence rate at the center of the nozzle ducts’ exhaust. The nozzle design and operating conditions are typically those of an aircraft engine at cruise, although the external flow is not simulated. The paper focuses on the effects of the nozzle exhaust turbulence characteristics, namely turbulent length scales and turbulent rate, on the jet flow prediction and the mixing-layer development. The results are discussed in terms of Reynolds-averaged data and spectral content. Turbulence injection over the whole height of the nozzle ducts accelerates the Reynolds-averaged Navier–Stokes to large-eddy simulation transition in both external and internal mixing layers, which is in better agreement with the experimental results. The transition length is further reduced when the injected turbulent ratio is higher but also when the injected turbulent length scale is smaller. Of interest, the shock-cell positioning in the fan jet is also improved using random flow generation, which emphasizes the importance of accounting for upstream turbulence for this type of simulation.

Passive scalar mixing studies to identify the mixing length in a supersonic confined jet

Supersonic jet with a co-flow, closely bounded by walls is known as supersonic confined jet. Supersonic confined jet is encountered in practical devices like the supersonic ejector. Mixing of the primary and the secondary fluid inside the confined passage is complex. From a design perspective, it is necessary to have an accurate knowledge of the mixing length (L-MIX). Tracers that do not actively participate in the flow behavior but rather mark the fluids such that they faithfully follow the fluid motion are known as passive scalars. Passive scalars help in the understanding the progression of mixing amidst interacting flows. In this work, we have performed passive scalar mixing studies in a supersonic confined jet for different operating conditions using an existing low area ratio (AR = 3.7) rectangular supersonic gaseous ejector. Air is used as the working fluid in both the primary and the secondary flow. The design Mach number of the primary flow nozzle (M-PD = 1.5-3.0) and the total pressure of the primary flow (P-OP = 4.89-9.89 bar) are varied during the experiments. Using the planar laser-induced fluorescence (PLIF) technique and acetone as the passive scalar, L-MIX is determined. A 266 nm Nd-YAG laser with a repetition rate of 8 Hz is used to excite the acetone molecules in the flow field, and the emitted fluorescence is captured by an ICCD camera. A new method is proposed to study the passive scalar distribution from the acetone PLIF images through digital image processing. Spatial Scalar Fluctuations Intensity (SSFI or psi ) is a parameter defined at every transverse section along the flow direction. Based on the variation of psi along the jet, the location of L-MIX can be identified. L-MIX is defined as the length from the supersonic nozzle exit where psi first attains a value of 0.05. For the first time, L-MIX is quantified in a supersonic confined jet. L-MIX values are observed to be in the range of 3H to 6H for the cases under study, where H is the height of the confined passage. The behavior of L-MIX is closely dependent on the nozzle operating conditions. The values of L-MIX are found to be reduced by 17.67% for the over-expanded flows and increased by 15.76% for the under-expanded flows from the perfectly expanded condition. This study also provides other supersonic confined jet characteristics like the potential core length (L-PC) and the shock cell spacing (S-x) of the primary supersonic jet. Compared to the supersonic free jet, values of L-PC and S-x are found to be different in the supersonic confined jet.

Experimental investigation on the near flow field of dual stream nozzles

An experimental investigation was carried out to investigate the effect of beveling of primary nozzle exit in the near field of a dual stream nozzle flow. Two exit geometry configurations of primary stream nozzle viz., (a) circular (b) bevel along with one exit geometry of the secondary stream-circular, were studied. Experiments were carried out at both subsonic and supersonic primary nozzle operating conditions Mp=0.96 and 1.2. The secondary nozzle exit Mach number was maintained at 0.65 and 0.85 respectively to maintain the velocity ratio of 0.7 between the primary and secondary jet. The by-pass ratio for this investigation is maintained at 2.0. Flow visualization using retro-reflective shadowgraph technique was used for the qualitative visualization of the near flow field at the Mach number of 1.2. The mean and turbulent quantities in near flow field were obtained using particle image Velocimetry (2D-PIV). The flow visualization and PIV investigations show significant change in mean and turbulent quantities brought about in the near field due to the beveling of the primary nozzle. PIV results show increase in the potential core length and reduction in turbulence levels in the potential core by the secondary flow regardless of the jet exit geometry. A differential trend is seen in the shear layer growth and the turbulence characteristics between the shorter and longer lips sides of the beveled nozzle. In the dual stream configurations, bevel nozzle shows lower Reynolds stress values than the circular one except in the shorter lip side at the larger downstream locations.

Zonal Detached-Eddy Simulations of a Dual-Stream Jet

This paper presents a study using zonal detached-eddy simulation to simulate the flow of a dual-stream nozzle. The nozzle design and operating conditions are typically those of an aircraft engine at cruise, although the external flow speed is not simulated. The paper focuses on the effects on the mixing-layer development and the shock-cell positioning of a low dissipative spatial scheme, as well as the interest of a subgrid length scale based on local vorticity, in the frame of mode 1 and mode 2 of a zonal detached-eddy simulation. Reynolds-averaged data are discussed in terms of mean and fluctuating quantities. Results are compared with experimental data. The dependency on the numerical scheme is demonstrated, and the advantage of the subgrid length scale based on the local vorticity is confirmed, especially for the development of the core mixing layer, which is triggered by small velocity differences. A spectral analysis of the fluctuating aerodynamic field is performed, and the salient results concerning the physics of shear layers and the interactions between shocks and mixing layers are compared with those provided in the literature. Eventually, the “automatic” mode of the zonal detached-eddy simulation (mode 2) is investigated and is found to provide similar results to the user-defined mode.

On the Numerical and Experimental Study of Spray Cooling

The spraying of an impinging jet is an effective way to cool heated surfaces. The objective of this study is to develop a numerical model to predict the heat transfer with phase change between a hot plate surface and a two-phase impinging jet. Different two-phase modeling approaches (Lagrangian and Eulerian methods) are compared. The influence of the spray nozzle operating conditions and of the distance between the nozzle exit and the surface impact is analyzed. The numerical results are compared with measurements obtained on an experimental test bench. The confrontation numerical/experimental is carried out by comparing the distribution of temperature at the surface of the plate and the heat transfer coefficient. This comparison shows that it is the Eulerian model which seems most capable to take into account the evaporation of the droplets in contact with the heated plate. However, the simulation performed with this model show a strong dependence of the results to the turbulence model used.