Contraction Nozzle Research Articles

Prediction of gas-solid nozzle performance based on CFD and response surface methodology

In this work, structural parameters and performance prediction of fan nozzles for powder spraying are investigated. Computational Fluid Dynamics (CFD) was used to simulate the working process of the grooved fan nozzle. A Box-Behnken experimental model was developed to analyze the effects of the structural parameters on the nozzle air flow stability and working performance, taking the nozzle structural parameter contraction angle (α), the ratio of outlet to inlet diameter (d/D), the ratio of outlet diameter to length (L2/d), and the half angle of the “V”– shaped groove (β). The air flow stability and working performance of nozzle were evaluated through coefficient of variation (Cv) and standard deviation (SD). Using multiple regression analysis, the prediction model of Cv and SD on the structural parameters is established. It was obtained that: with the increase of the diameter and length of the nozzle outlet, the spray angle of the nozzle decreases. As the “V”– shaped groove angle increases, the powder spray angle decreases. The effects of structural parameters on Cv are d/D, α, β, and L2/d in ascending order, and on SD are d/D, α, β, and L2/d in ascending order. In addition, the influence of the interaction of each structural parameter on Cv and SD was obtained. This study can provide a reference for the design and structural optimization of fan nozzles for powder spraying.

Evaluation of influence of wall roughness on wall turbulence using LES simulation with MSGD model for liquid Li flow inside two-staged contraction nozzle

ABSTRACT Liquid lithium (Li) jet is planned as a beam target in fusion neutron sources (FNSs), such as IFMIF, A-FNS and IFMIF-DONES. For the safety and the efficiency of such FNSs, the high-speed Li jet need to be kept stable. For investigation of the detailed flow pattern inside the Li jet, numerical approaches using CFD simulation have been required to evaluate it because of its opacity. As one of issues about the inner flow structure, the influence of wall roughness on the vortex structure and surface variation is concerned in long-term operation of actual FNSs. In our previous simulation, in order to consider wall roughness in LES simulation, MSGD model was adopted to ANSYS Fluent using User-Defined Function, and CFD simulation in a simple parallel plate flow was conducted to confirm the performance of MSGD model. In this study, firstly, MSGD model was verified by LES simulation of Li flowing on smooth and rough plates. After that, LES simulation with MSGD model for two-staged contraction nozzle, installed into Li loop of Osaka University, was conducted. It was found that MSGD model was valid and spectrum of velocity in roughness wall cases clearly had different behavior from that in smooth wall case.

Nitrous Oxide/Ethanol Cylindrical Rotating Detonation Engine for Sounding Rocket Space Flight

There are few experimental studies on rotating detonation engines (RDEs) with liquid propellants. This study reveals the static thrust performance of a cylindrical RDE with ethanol and liquid nitrous oxide as propellants under atmospheric pressure. This RDE had an inner diameter of 40 mm, a maximum combustor length of 230 mm, a nozzle contraction ratio of 1.7, and a nozzle expansion ratio of 9.1. Nineteen experiments were conducted at total mass flow rates of 184–210 g/s, mixture ratios of 3.6–5.9, and combustion pressures of 0.35–0.46 MPa, resulting in a maximum detonation velocity of 1840 m/s (approximately 80% of the theoretical detonation velocity, 2251 m/s), maximum thrust at sea level of 294 N, and maximum specific impulse at sea level of 148 s. In addition, the maximum characteristic exhaust velocity, c*, was 1716 m/s, which was 99% of the theoretical value. The characteristic length of the combustion chamber at this time was 0.15 m. Since conventional rocket combustion requires 1.57 m to achieve the same c* efficiency, this study shows that detonation combustion can reduce the combustor size by 88%.

Auto-ejection of liquid from a nozzle.

Auto-ejection of liquid is an important process in engineering applications, and is also very complicated since it involves interface moving, deforming, and jet breaking up. In this work, a theoretical velocity of meniscus at nozzle exit is first derived, which can be used to analyze the critical condition for auto-ejection of liquid. Then a consistent and conservative axisymmetric lattice Boltzmann (LB) method is proposed to study the auto-ejection process of liquid jet from a nozzle. We test the LB model by conducting some simulations, and find that the numerical results agree well with the theoretical and experimental data. We further consider the effects of contraction ratio, length ratio, contact angle, and nozzle structure on the auto-ejection, and observe some distinct phenomena during the ejection process, including the deformation of meniscus, capillary necking, and droplet pinch off. Finally, the results reported in the present work may play an instructive role on the design of droplet ejectors and the understanding of jetting dynamics in microgravity environment.

Super-cooled droplet impact and ice accretion on an aircraft engine nacelle lip

This manuscript concentrated on the icing phenomenon on the lips of an engine nacelle. Numerical simulation was employed to establish the airflow, supercooled droplet impact, and engine nacelle ice accretion models. The study investigated the airflow field near the lip, the characteristics of supercooled droplet impact, and the ice accretion near the lip under different flight conditions. The computational results indicated that due to the effects of nozzle contraction and flow extraction, a low-pressure, high-velocity, and low-temperature region appeared on the inner side of the lip, leading to ice accretion on the nearby wall. The maximum collection efficiency on the lip surface at 20, 000 ft was slightly higher than that at 10, 000 ft, with a maximum value of approximately 0.6. In the computed conditions of this study, as the flight altitude and Mach number increased, the ice thickness on the lip surface increased and the ice spread inward, posing a significant risk of ingestion after detachment.

Energy-saving discharge needle shape for electrohydrodynamic airflow generation

Electrohydrodynamics (EHD) is a way to produce low energy-consuming airflow without moving components. The basis of airflow by EHD is corona discharge. A way to generate corona discharge is done, among others, via needle-type emitter electrodes whose shape and arrangement play a crucial role in the effectiveness of the discharge. Until now, the needle shape was chosen somewhat arbitrarily, although it impacts the energy consumption of the EHD process. We lack systematic studies on the impact of needle shape on the EHD discharge process and associated airflow to help engineers and scientists choose the best shape. This in-silico study screens the impact of the needle shape parameters on EHD performance in terms of electrical power consumption and airflow generation. The study aims to find the ideal EHD needle shape for unrestricted and confined flow. For this purpose, we test three different geometrical configurations. The first configuration is a free-flow single-needle configuration. The second configuration adds a dielectric nearby, which represents a needle enclosure. Lastly, a configuration including a dielectric and a converging nozzle is examined. All studies use a 2D-axisymmetric, fully automatized EHD physics-based model. The first set of parametric studies explores the inherent geometrical properties of the needle shape, like tip radii (10–250 μm), needle cone angle (10–70°), and needle diameters (0.5–2 mm). The second set of parametric studies investigates the operation conditions, such as the emitter-collector distance (10–40 mm), the nozzle contraction ratio (0.04–1), and the operating voltage (6–32 kV). The results of the free-flow configuration show qualitative agreement with experiments on existing needle products. The ideal energy-saving needle shape for free flow configuration features a short conical tip length (i.e., a large angle ≥30°), a diameter of 2 mm, and a needle rip radius of 100 μm. The situation changes when a dielectric is present, and a sharp angle of 10° is favorable to reduce energy consumption. Since a dielectric inverts the optimal needle shape, it makes sense to customize it for a particular application in EHD airflow generation. We provide performance maps that can be used as design charts. This study is a guideline to optimize EHD devices further to reduce energy consumption and increase airflow speed.

High-order optimization of bicubic parametric convergent curves for carbon capture nozzles in hydrogen-rich fuel

Supersonic condensation separation is a potential environmentally-friendly hydrogen purification and CO2 capture technology. Among them, the nozzle contraction structure is essential in creating conditions conducive to CO2 condensation. In this study, the H2–CO2 binary condensate flow model based on the condensation dynamics theory was used to predict the influence of the contraction curve on the condensation parameters. Furthermore, this paper proposed a combined high-order curve correction method based on the standard Bicubic parametric curve and summarized the universal formula of the High-order correction curve (HOCC). Furthermore, the influence law of the correction exponent and quantile location on the hydrogen-rich fuel gas decarburization performance was further obtained through numerical calculation. After two-stage optimization, the HOCC n = 7 xm = 0.35 structure can improve the decarburization performance of the supersonic purification device by 7.44%. Moreover, the H2–CO2 condensate flow will not flow separation in the nozzle.

Analysis on the radial structure of rotating detonation wave in a hollow combustor

This experimental study discusses the radial structure of the rotating detonation wave (RDW) in a hollow chamber. The head chamber wall could be fabricated with quartz glass for high-speed visualizations or metal cover for high-frequency pressure measurement. The entire radial-stratified reaction zone was directly and continuously captured. The wall-attached bright zone indicated that the main reaction zone propagated along the chamber wall, but some deflagration was still observed in the inner zone. Based on the phase-averaged CH* chemiluminescence image, the radial thickness of the reaction zone was determined to be about 15–20 mm. The diminishing pressure peaks and deteriorating waveforms of the high-frequency pressure signals proved that the intensity of shock waves decreased along the chamber radius. The structure of RDW was reconstructed using radially distributed pressure sensors. Due to the compression effect of the concave chamber wall, a Mach reflection of detonation wave might occur. The detonation wave was connected to a diffracted shock, which stretched in the radial direction with decreasing intensity. The central angles calculated with the time-difference analysis demonstrated that the entire RDW bent forward in the inner zone of the chamber. Moreover, the radial thickness of the reaction zone and the curvature of shock waves increased with decreasing nozzle contraction ratio, which mainly attributed to the increasing expansion effect. This study demonstrated the distribution of reaction zone and the radial structures of shock waves for the RDW in a hollow combustor, contributing to the exploration of the flow and combustion process in a rotating detonation engine.

Experiments and simulations of surface cleaning for a gas-liquid two-phase jet.

In this study, a new cleaning method for the gas-mixed water jet is proposed. The pulsation characteristics of the gas -liquid two-phase jet and the influences of parameters on the cleaning effect were analyzed by performing simulations and experiments. The results showed that the impact pressure fluctuated and was much higher than the inlet pressure. With a continuous increase in the standoff distance, the impact pressure first decreased slowly and then decreased significantly, while the diameter and depth of the crater first increased and then decreased. The optimal standoff distance for a desirable impact effect was 10 mm. With the increase in gas concentration, the impact pressure became higher for gas concentrations of less than 8%, while the impact pressure decreased for the gas concentration of more than 8%. A higher impact pressure along with a fiercer jet pulsation resulted when the flow rate became larger. Accordingly, the diameter and depth of impact crater became enlarged. The impact pressure first increased and then decreased with the increase of nozzle contraction angle. Moreover, the optimal value of such an angle was 140°. This study provides fundamental and practical guidance to further improve the application of gas-mixed water jet cleaning technology.

Impact of combustion chamber wall heat loss on the energy, exergy, ecology, NOx emission based performance and multiobjective optimization of the precooled scimitar engine

In this paper, the impact of the combustion chamber wall heat loss on the performance of the hydrogen-fueled precooled combined cycle Scimitar engine is investigated. Overall and exergy efficiencies, coefficient of ecological performance and coefficient of emission based ecological performance (CEEP) are considered as the performance indicators to analyze the effects of wall heat loss flux, chamber length, chamber contraction area ratio, throat area and nozzle convergent half angle. A multiobjective optimization is carried out to find the optimum values of hydrogen and air mass flow rates, cruise speed and altitude and core nozzle outlet area. It is found that a wall heat loss flux of 10 MW/m2 decreases the overall efficiency by 1.1% and causes an increase of 2 kJ/gNOx in CEEP. Multiobjective optimization revealed that increasing the hydrogen mass flow rate, decreasing the cruise speed and air mass flow rate improve the overall performance while the optimum values of cruise altitude and core nozzle outlet area are 23 km and 4.94 m2, respectively. The optimized design has a 20.35% better emission performance than the base design with a compromise of a 3.38% reduction in the overall efficiency.

Flow–structure interaction of a starting jet through a flexible circular nozzle

In the present study, the flow–structure interaction of a starting jet through a flexible nozzle is experimentally investigated, with a focus on the optimal flexibility for thrust generation. Water slug is impulsively accelerated through a cylindrical nozzle, fabricated with silicone rubber of varying flexibility. In general, the flexible nozzle modifies the vortical structure of the jet and augments the thrust of the starting jet. The measurement of nozzle surface deformation revealed that a back-and-forth wave propagation on the nozzle surface is responsible for the jet-vortex evolution augmenting the thrust generation. Combining the hydrodynamic conservation equations and the linearized shell theory, we also formulated the governing equations, dominated by two relevant dimensionless parameters: the effective acceleration time of the jet ( $\varPi _0$ ) and the effective nozzle stiffness ( $\varPi _1$ ). Asymptotic analysis of the equation showed that the dimensionless wave speed ( $\hat {c}$ ) is expressed as $\hat {c}=(\varPi _{0}^{2}\varPi _{1}/2)^{0.5}$ , and the jet momentum is maximized at $\hat {c}=\hat {c}_{crit}$ ( $\simeq 3.0$ ), the condition at which the release of elastic energy stored during nozzle contraction to the jet is synchronized with the instant of termination of jet acceleration. While $\hat {c}=\hat {c}_{crit}$ , the achievable maximum jet velocity decreases with the effective acceleration time of the jet ( $\varPi _0$ ), which is attributed to the reduced speed of the surface wave by the flow inside the nozzle.

Study on the Influence Rule of High-Pressure Water Jet Nozzle Parameters on the Effect of Hydraulic Slotting

In order to get the appropriate nozzle parameters, numerical simulation and field tests are used to investigate the influence of high-pressure water jet nozzle parameters on the effect of hydraulic slotting. A nozzle model is created by using FLUENT software. For different nozzle contraction angles, outlet diameters, and straight column section lengths, the distribution rules of the velocity of the water jet and dynamic pressure on the central and vertical axes are obtained, and the parameters for the best nozzle effect are determined. The relationship between the nozzle contraction angle gradient, the inlet water pressure, and the nozzle outlet water velocity is discovered. A mathematical model of the nozzle outlet water velocity of the water jet is established. The depth, width, and volume of the hole generated by the nozzle impact are employed as indications for inquiry, and field measurements are used to derive the results of nozzle geometry parameter optimization. The field tests validate the numerical simulation conclusions, and the results have theoretical and practical guidance for hydraulic slotting in coal mines and get the appropriate nozzle parameters specially.

Tomographic Absorption Spectroscopy for H2O Transport in a Laminar Jet with Inverse Concentration Gradient.

We report a tomographic absorption spectroscopy (TAS) study of water vapor transport in a laminar jet issuing into the ambient. The jet was generated using compressed dry air that was straightened by a honeycomb and a smooth contraction nozzle. A TAS scheme using the water vapor in the ambient as absorbing species and the absorption line near 1368.598 nm was proposed to study the H2O transport in the laminar jet with an inverse concentration gradient. One-dimensional tomography was conducted at various heights above the nozzle, and the results were validated by the predictions from computational fluid dynamics (CFD) simulations. Particularly, the variations in the concentration gradient in the shear layer at different heights were captured. The 2D distribution of water concentration in the dry laminar jet was obtained experimentally. The present study shows that TAS has great potential in the research of mass transfer and scalar field of gaseous flows.

Design of Wind Nozzle for Nozzle Augmented Wind Turbine

In some countries, wind turbines are designed to operate at relatively high speeds to be appropriately efficient, limiting the use of wind turbines in urban areas with low wind speeds. Thus, innovation is needed to enhance the possibility of wind energy use within the range of low speeds. In order to increase the electrical power of the wind turbines, the velocity of the wind blowing on the wind turbine, is the most important factor that has to increase. In this paper it has been recommended that contraction nozzles could be applied between Wind Turbines and wind-way to provide the wind through themselves with more velocity. The main objective of this research is to optimize the nozzle design for vertical axis wind turbine (VAWT). Specifically, this study investigates the effect of wind velocity on different shapes of nozzle to develop the suitable nozzle for the wind turbine. For that purpose, the ideologies of contraction nozzle have been studied. Different nozzle design concepts were developed and the wind speed for each design is simulated.

Continuous rotating detonation engine fueled by ammonia

As a carbon-free fuel, ammonia has attracted increasing interests while the corresponding utilizations are still limited. In this paper, ammonia-oxygen continuous rotating detonation (CRD) was firstly proposed and realized in the hollow chamber with Laval nozzle. The formation process and propagation characteristics were investigated through pressure measurement and optical observation. The CRD wave formation time increased with the nozzle contraction ratio, which was mainly attributed to the slower injection recovery process under the higher chamber pressure. The operation range was large, and the CRD wave propagated in single-wave mode with the velocity of 1806 m/s in the chosen test. The propagation velocity did not increase continuously as the equivalence ratio increased, which could be attributed to the changeable reaction mechanisms and the slow heat release of ammonia. The coupling of ammonia injection and CRD wave propagation was analyzed under both supersonic and subsonic injection conditions. The synchronous fluctuations of the pressure in ammonia plenum and the intensity of detonation waves proved that the coupling was very tight under subsonic injection condition. This paper was beneficial to the improvement of the detonation theory, and it provided an efficient approach to the utilization of ammonia.

Nozzle Contraction Effect on the Performance of the Generator of Periodic Pulsed Jets

Nozzle Contraction Effect on the Performance of the Generator of Periodic Pulsed Jets

Research on performance optimization of gas–liquid ejector in multiphase mixed transportation device

ABSTRACT In the process of oil and gas extraction, a system that uses a pump and reversing mechanism to achieve high-efficiency export of gas–liquid mixture is devised. A gas–liquid ejector is fitted in the front of the device to boost pressure inside the tank in order to store more gas in the tank under a given volume. To meet the working conditions of gas–liquid high-efficiency transport device and obtain a larger outlet pressure and better ejection performance, this paper investigates the effect of outlet pressure, ratio of throat inlet area to nozzle outlet area and nozzle contraction angle on the ejection performance of gas–liquid ejector, and simulations using the computational fluid dynamics approach. At the same time, an experiment platform is built for testing. The research findings show that the ejection gas flow rate and ejection ratio of gas–liquid ejector decrease with the increase of the outlet pressure; as the ratio of throat inlet area to nozzle outlet area increases, the ejection gas flow rate and the ejection ratio of gas–liquid ejector increase first and then decrease. Different nozzle diameters correspond to different optimal area ratios; under the specified working parameters, with the increase of the nozzle contraction angle, the ejection gas flow rate and injection ratio of the gas–liquid ejector increase first and then decrease, and there is an optimal nozzle contraction angle.

Effects of the nozzle contraction angle on particle flow behaviors in a gas-particle two-phase jet

The particle dynamics of a conical jet with different contraction angles (the cone angle of the contraction wall, α = 20°, 40°, 60°, 80°) were investigated using particle image velocimetry (PIV) and optical fiber probes. The axial and radial distributions of particle-phase velocity and concentration were measured within a confined chamber at the mass loading ratio mp = 0.3–3.3 and jet Reynolds number Re = 11,843–104,497. Due to the nozzle contraction effect, the particle dynamics of conical jet are significant differences from the pipe jet and the smooth contraction jet. In the axial direction, there is a strong slip velocity between two phases near the nozzle exit (x/D = 0–6), which leads to the occurrence of particle acceleration. In the radial direction, the particles preferentially converge towards the centerline, forming the particle contraction, which intensifies the momentum transfer from the axial to radial direction and thus increases the particle dispersion. The particle acceleration and contraction are more pronounced with the increase of contraction angle. Furthermore, the order of the velocity decay rate and the spreading rate for different contraction angles are 40° > 80° > 60° > 20°. The nozzle contraction angle of 40° shows the best entrainment and mixing characteristics. In addition, the particles contraction near the nozzle exit as well as the particles accumulation in the wall region (r/R = 0.83–1.00) increase the non-uniformity of particle concentration.

On a three-dimensional investigation of airfoil turbulence-impingement noise and its reduction by leading-edge tubercles

The present work addresses the turbulence-impingement noise of an airfoil and its reduction by a wavy cut of the leading edge, referred to as serrations or tubercles. It is primarily aimed at completing existing experimental databases for both straight-edge and serrated airfoils, by measurements also performed off the mid-span plane on a portion of sphere, in an open-jet anechoic wind tunnel. The three-dimensional investigation is a required condition for further applications in rotating-blade noise modeling. The turbulence is generated by a grid placed upstream of the nozzle contraction. An almost monotonically increasing reduction is found with increasing frequency, in a wide frequency range for which turbulence-impingement noise dominates, for all radiation directions. This extends observations reported in previous studies in the midspan plane only. The straight-edge results are also used to validate an analytical prediction model in a three-dimensional context. This part includes a novel correction method to account for sound refraction through the shear layers of the nozzle jet, leading to a remarkably good agreement of predictions with measurements even at shallow observer angles where the effect of the jet shear layers is significant and needs to be accounted for.

Grid Generated Turbulence for Aeroacoustic Facility

A preliminary version of this paper was presented at the AIAA Aviation 2020 forum (Paper 2020-2525).This paper provides an insight into the grid generated turbulence for aeroacoustic studies. Several passive grids of square bars were tested in the open-jet aeroacoustic facility at the University of Bristol. The geometric properties of the grids and their position within the tunnel contraction nozzle were varied to quantify their influence on the average and statistical flow properties as well as the generated self-noise. Moreover, case studies involving turbulence interaction noise generation with a NACA0012 airfoil and cylinder were conducted. Turbulence intensity, integral length scale, and the anisotropy of the flow generated by each grid were characterized by hot-wire measurements, and the associated far-field noise was measured by a far-field microphone array. The grid turbulence results show that the downstream evolution of the turbulence intensity and integral length scale was comparable to results of closed test-section wind-tunnel studies for the first hydraulic diameter downstream of the contraction nozzle exit. However, beyond the first hydraulic diameter, the turbulence intensity plateaus and the integral length scales show rapid growth. Moreover, the results show that grids positioned closest to the contraction nozzle exit produced turbulence closest to isotropy with high levels of turbulence intensity, but the measured noise spectra suffered from the contamination from the grids self-noise. The grids located farthest from the contraction nozzle exit performed best in terms of noise contamination and could generate almost the same level of turbulence properties as the grids closest to the contraction nozzle exit.