Hot Jet Research Articles

Statistical properties of Hα jets in the polar coronal hole and their implications in coronal activities

Context. Dynamic features such as chromospheric jets, transition region network jets, coronal plumes, and coronal jets are abundant in the network regions of polar coronal holes on the Sun. Aims. We investigate the relationship between chromospheric jets and coronal activities, such as coronal plumes and jets. Methods. We analyzed observations of a polar coronal hole including the filtergrams taken by the New Vacuum Solar Telescope at the Hα − 0.6 Å to study the Hα jets, as well as the Atmospheric Imaging Assembly 171 Å images to follow the evolution of coronal activities. Results. The Hα jets are persistent in the network regions, with only some regions (denoted as R1–R5) rooted in discernible coronal plumes. With an automated method, we identified and tracked 1320 Hα jets in the network regions. We find that the average lifetime, height, and ascending speed of the Hα jets are 75.38 s, 2.67 Mm, 65.60 km s−1, respectively. The Hα jets rooted in R1–R5 are higher and faster than those in the others. We also find that propagating disturbances (PDs) in coronal plumes have a close connection with the Hα jets. The speeds of 28 out of 29 Hα jets associated with PDs are ≳50 km s−1. In the case of a coronal jet, we find that the speeds in both the coronal jet and the Hα jet are over 150 km s−1, suggesting that both cool and hot jets can be coupled. Conclusions. Based on our analyses, it is evident that more dynamic Hα jets could release their energy to the corona, which might be the result of a Kelvin-Helmholtz instability developing or that of small-scale magnetic activities. We suggest that chromospheric jets, transition region network jets, and ray-like features in the corona are coherent phenomena that serve as important vehicles for cycling energy and mass in the solar atmosphere.

Numerical simulation on radiation effect of hypersonic vehicle's hot gas jet

Numerical simulation on radiation effect of hypersonic vehicle's hot gas jet

Особенности динамики струйного потока, генерируемого при поверхностном кипении жидкости на лазерном нагревателе

It was experimentally found that hot submerged jets appeared at laser induced nucleation boiling near the tip optical fiber placed in water exponentially decrease the velocity with the increasing of laser power (heat flux). This result was obtained for closed cylindrical cuvette where hot jets collided with walls slipped the cuvette boundary and transfer the heat. Obtained result is necessary to take into account at precise laser induced surface cleaning inside the closed volumes, for development of medical technologies of laser therapy of pathologically changed vessels, cysts, and for other applications.

Features of dynamics of a jet flow generated on a laser heater by surface boiling of liquid

It was experimentally found that speeds of hot submerged jets appearing in case of laser induced nucleation boiling of water near the tip of optical fiber submerged in water decrease exponentially with increasing laser power (heat flux). This result was obtained for a closed cylindrical cuvette where hot jets collided with walls and slipped the cuvette boundary transferring heat to it. The obtained result is to be taken into account in performing precise laser-induced surface cleaning inside confined volumes, in developing medical technologies for laser therapy of pathologically changed vessels or cysts, and in other applications. Keywords: laser radiation, submerged jet, boiling, bubbles, cavity, heat transfer.

Numerical simulation of the submerged hot jet propagation in a bounded domain with obstacles

Numerical simulation of the submerged hot jet propagation in a bounded domain with obstacles

CFD PREDICTION OF THE TRAJECTORY OF HOT EXHAUST FROM THE FUNNEL OF A NAVAL SHIP IN THE PRESENCE OF SHIP SUPERSTRUCTURE

The superstructure of a modern naval ship is fitted with multitude of sensors for electronic surveillance, weapon discharge, navigation, communication and varieties of deck handling equipment. Locating these electronic equipment/sensors and its integration on board is of paramount importance to achieve optimal operational performance of the naval vessel. Among the many problems in locating these sensors (like stability, EMC EMI etc.,), the presence of entrapped hot gases from the ship exhaust affects the functioning of these electronics. Hence the prediction of temperature profile and trajectories of the ship exhaust plume from the funnel around the superstructure during the design stage is a mandatory requirement for positioning the sensors on superstructure. This trajectory prediction is not amenable to theoretical analysis or empirical calculation procedures in the modern warship superstructure. Experimental and CFD studies conducted on ship superstructure are the only reliable tools that are available to estimate temperature field as well as to study the exhaust smoke superstructure interaction on ships. This paper presents the CFD simulation of the published results for two cases, namely hot jet in a cross flow and hot exhaust with a cross flow on a generic frigate. Simulations have been made using k-ɛ turbulence model with different values of turbulent Schmidt number. It has been observed that temperature field is predicted with reasonable accuracy with turbulent Schmidt number of 0.2.

Solar jets observed with the Interface Region Imaging Spectrograph (IRIS)

Solar jets are impulsive, collimated plasma ejections that are triggered by magnetic reconnection. They are observed for many decades in various temperatures and wavelengths, therefore their kinematic characteristics, such as velocity and recurrence, have been extensively studied. Nevertheless, the high spatial resolution of the Interface Region Imaging Spectrograph (IRIS) launched in 2013 allowed us to make a step forward in the understanding of the relationship between surges and hot jets. In this paper we report on several results of recent studies of jets observed by IRIS. Cool and hot plasma have been detected with ejections of cool blobs having a speed reaching 300 km s−1 during the impulsive phase of jet formation and slow velocity surges surrounding hot jets after the reconnection phase. Plasma characteristics of solar jets, such as the emission measure, temperature, and density have been quantified. A multi-layer atmosphere at the reconnection site based on observed IRIS spectra has been proposed. IRIS evidenced bidirectional flows at reconnection sites, and tilt along the spectra which were interpreted as the signature of twist in jets. The search of possible sites for reconnection could be achieved by the analysis of magnetic topology. Combining Solar Dynamics Observatory/Helioseismic Magnetic Imager (SDO/HMI) vector magnetograms and IRIS observations, it was found that reconnection site could be located at null points in the corona as well as in bald patch regions low in the photosphere. In one case study a magnetic sketch could explain the initiation of a jet starting in a bald patch transformed to a current sheet in a dynamical way, and the transfer of twist from a flux rope to the jet during the magnetic reconnection process.

Experimental study of the ignition of lean methane/air mixtures using inductive and NRPD ignition systems in the pre-chamber and turbulent jet ignition in the main chamber

The optimization of the combustion process in spark ignition engines has led to novel strategies to ignite lean and low reactivity mixtures, such as the application of turbulent jet ignition and Nanosecond Repetitively Pulsed Discharge (NRPD) ignition systems and Turbulent Jet Ignition (TJI). In the present experimental work, an optically accessible setup was used to investigate the ignition occurrence and early flame development in the pre-chamber and subsequent main chamber ignition of methane/air mixtures at density conditions relevant to engine application. Two schlieren setups coupled with fast recording cameras allow the visualization of both the pre-chamber and main chamber.NRPD ignition with different pulse patterns in terms of pulse number and repetition frequency is applied in the pre-chamber. Conventional inductive ignition and NRPD-assisted ignition are compared for the first time in terms of flame development in the pre-chamber and hot jet ignition in main chamber. The effect of different air to fuel ratios is assessed in both laminar and turbulent pre-chamber conditions.Results show that while NRPD is always advantageous when compared to standard inductive ignition, the higher amount of energy added by increasing the number of pulses only affects the ignition success in very lean conditions, thus showing that increased energy is not the main governing mechanism for successful ignition. Irrespectively of the initial conditions (laminar or turbulent) in the pre-chamber, it is shown that an optimum jet velocity exists that ensures increased ignition probability in the main chamber, thus suggesting that mixing plays a major role in main chamber ignition. The combination of both techniques, NRPD and TJI, allowed assessing the optimum conditions in terms of number and frequency of NRPD pulses for a reliable ignition in lean conditions.

Effect of Local Turbulent Structures on the Hot Jet in Transitional Flow

Turbulent parts localized in flow direction may arise in a pipe with transitional regime of the stable laminar Poiseuille flow. A key condition for occurrence of such structures is a pipe with rather long length relative to its diameter. Our paper presents numerical modelling of the hot air jet flowing from the long pipe into the cold open volume at Re=2426. The modelling was performed in OpenFOAM software on the basis of the large eddy simulation (LES) method. The WALE (Wall-adapting local eddy-viscosity) model was used for closure of Navier-Stokes equations on subgrid scales. We demonstrated that local turbulent structures have a weak effect on the hot jet at flowing into the cold open volume.

Hot Jets in the Solar Corona: Creating a Catalogue of Events Based on Multi-Instrumental Observations

Hot Jets in the Solar Corona: Creating a Catalogue of Events Based on Multi-Instrumental Observations

Modeling the conjugate problem of heat transfer at hot jet impingement onto a cooled surface

The paper solves the problem of thermal conductivity inside a flat plate under the impact of a hot jet of nitrogen impinging from one side and cooled by a gas flow from the other side. In this formulation of the problem, there may be local maxima and minima of the temperature inside the plate, caused by an uneven distribution of heat fluxes along the plate.

Anti-icing hot air jet heat transfer augmentation employing inner channels

Many approaches exist today that employ hot-air from aircraft compressor bleed for anti-icing critical aircraft surfaces. This paper introduces and numerically analyzes the novel application of an inner or etched channel to augment heat transfer from a hot-air jet impinging on a curved surface representing the inner surface of an aircraft wing’s leading edge or slat. The study shows that proper positioning, geometry, and flow characteristics of a channel along the inner surface of the leading edge can significantly enhance heat transfer, boost the anti-icing system performance, and greatly enhance flight safety during critical icing weather conditions. Commercially available CFD software, ANSYS Fluent is used to model and analyze the effect of different geometric and flow parameters typical of those found in small to medium category commercial transport aircraft to help determine the optimum arrangement. These parameters include: (1) jet nozzle height-to-slot diameter ratios from 4 to 8, (2) channel width-to-slot diameter ratios from 0.4 to 1.8, and (3) inner-channel inlet location angles from 10° to 60°. Each configuration resulting from a combination of the above parameters was simulated at Reynolds numbers based on jet-slot diameter of 30,000, 60,000, and 90,000. Empirical relations based on available experimental data are used to validate the results. The main findings of the study reveal that the jet height-to-slot diameter ratio of 6, inner channel height-to-slot diameter ratios of 1.8, and inner-channel inlet angular locations of 10° combination resulted in the highest heat transfer at all Reynolds number as well as higher at increased Reynold numbers.

Diagnostics of Parameters of Hot Jets in the Solar Corona in Time Series of Images

Diagnostics of Parameters of Hot Jets in the Solar Corona in Time Series of Images

Tracking the evolution of the accretion flow in MAXI J1820+070 during its hard state with the JED-SAD model

Context. X-ray binaries in outburst typically show two canonical X-ray spectral states (i.e., hard and soft states), as well as different intermediate states, in which the physical properties of the accretion flow are known to change. However, the truncation of the optically thick disk and the geometry of the optically thin accretion flow (corona) in the hard state are still debated. Recently, the JED-SAD paradigm has been proposed for black hole X-ray binaries, aimed at addressing the topic of accretion and ejection and their interplay in these systems. According to this model, the accretion flow is composed of an outer standard Shakura-Sunyaev disk (SAD) and an inner hot jet emitting disk (JED). The JED produces both hard X-ray emission, effectively playing the role of the hot corona, and radio jets. The disruption of the JED at the transition to the soft state coincides with the quenching of the jet. Aims. In this paper we use the JED-SAD model to describe the evolution of the accretion flow in the black hole transient MAXI J1820+070 during its hard and hard-intermediate states. Unlike the previous applications of this model, the Compton reflection component has been taken into account. Methods. We use eight broadband X-ray spectra, including NuSTAR, NICER, and the Neil Gehrels Swift Observatory data, providing a total spectral coverage of 0.8–190 keV. The data were directly fitted with the JED-SAD model. We performed the procedure twice, considering two different values for the innermost stable circular orbit (ISCO): 4 RG (a* = 0.55) and 2 RG (a* = 0.95). Results. Our results suggest that the optically thick disk (the SAD) does not extend down to the ISCO in any of the considered epochs. In particular, assuming RISCO = 4 RG, as the system evolves toward the transitional hard-intermediate state, we find an inner radius within a range of ∼60 RG in the first observation down to ∼30 RG in the last one. The decrease of the inner edge of the SAD is accompanied by an increase in the mass-accretion rate. However, when we assume RISCO = 2 we find that the mass accretion rate remains constant and the evolution of the accretion flow is driven by the decrease in the sonic Mach number mS, which is unexpected. In all hard–intermediate state observations, two reflection components, characterized by different values of ionization, are required to adequately explain the data. These components likely originate from different regions of the SAD. Conclusions. The analysis performed provides a coherent physical evolution of the accretion flow in the hard and hard-intermediate states and supports a truncated disk scenario. We show that a flared outer disk could, in principle, explain the double reflection component. The odd results obtained for RISCO = 2 RG can also be considered as further evidence that MAXI J1820+070 harbors a moderately spinning black hole, as suggested in other works.

Numerical analysis of the effect of hot dent infusion jet on the fluid flow and heat transfer rate through the microchannel in the presence of external magnetic field

Numerical analysis of the effect of hot dent infusion jet on the fluid flow and heat transfer rate through the microchannel in the presence of external magnetic field

Study on drying characters of a thin cotton fabric under uneven radial heating by the hot air jet

It is important to understand the characteristics of hot-air drying of cotton fabrics for the structure design and process optimization of the drying equipment. A transient heat and moisture transfer model of the thin porous cotton fabric is established, in which the uneven heating on the textile surface caused by the hot air jet was considered. The effects of environmental air temperature and relative humidity, initial moisture content, hot air temperature, and velocity at the nozzle outlet on the drying characters were studied via this model. Results show that the temperature of the constant rate drying period at various points on the fabric is different due to the uneven heat input, which is higher at the center part of the fabric and lower away from the center of the fabric. The drying time is very non-uniform on the fabric surface especially when the hot air for drying and the environmental air have a large temperature difference. The environmental air humidity also has great influence on the drying time. The drying time of fabric increases by more than two times as the environmental air humidity rises from 5% to 30%. During the drying process, increasing hot air temperature is more conducive to improve the drying efficiency than increasing hot air velocity. The drying time decreases 19% only when the hot air velocity doubled, meaning that increasing hot air velocity cannot improve drying rate effectively. Moreover, experiments were conducted and results show that the experimental results coincided with the simulated ones well.

Generalized Acoustic Analogy Modeling of Hot Jet Noise

A generalized acoustic analogy model is implemented for the hot and cold static high-speed jet cases corresponding to conditions of the Strategic Investment in Low-carbon Engine Technology (SILOET) experiment performed by QinetiQ. The model is statistical and based on the covariance of fluctuating Reynolds stresses and enthalpy source terms in accordance with Goldstein’s theory. These quantities are obtained from a solution of the validated large-eddy simulation accelerated on graphics processing units. The covariance of fluctuating enthalpy terms is represented by the Khavaran and Bridges model, which involves the velocity autocorrelation function and temperature gradient in the jet. The velocity autocorrelation function and the covariance of fluctuating Reynolds stresses are approximated by an analytical Gaussian-exponential function. The input parameters of the acoustic model include single-point quantities such as the time-averaged local streamwise velocity, sound speed, temperature, vorticity magnitude, turbulent kinetic energy, and dissipation rate. Modeling choices for the acoustic length and time scales based on either the turbulent kinetic energy dissipation rate or mean flow vorticity are discussed. In each case, the model involves two dimensionless parameters associated with the acoustic correlation length and time scale. These two parameters are calibrated based on the far-field noise data at 90° observer angle. The sensitivity of the calibration coefficients to the jet type, cold versus hot, is investigated. Furthermore, the same acoustic model without recalibration is applied for far-field noise predictions of two NASA Small Hot Jet Acoustic Rig jets for acoustic Mach numbers 0.5 and 0.9. To probe the sensitivity of the acoustic model to the input flow data, Reynolds-averaged Navier–Stokes solutions of the same jet cases are considered along with the large-eddy-simulation solutions. The comparison of the predicted far-field noise spectra with the experiment is discussed in each case.

An Integrated Approach of Simulation, Modeling and Computer-aided Design of Hot Abrasive Jet Machining Setup

In the past few decades, sophisticated machining industries have rapidly improved in order to achieve the required shape of a part within a specific time while also not affecting material properties. Accuracy of machined components in all industries is important. In the case of subassemblies of components, geometrical accuracy of hole is vital. The researchers updated their machinery from time to time from this perspective. In the machining process, environment and time are the vital parameters that are mainly affected, so in this case, the design of experiments that are very useful in the machining region needs to be considered to overcome these challenges. This study aims to analyze the fabrication of hot abrasive jet machining (HAJMing) with different abrasive temperatures using fluidized bed system as well as accomplishment of cutting performance in hot-abrasive jet machining concerning target surface erosion. Additionally, this research study accomplishes the experimental study and computational fluid dynamics (CFD) technique for erosive footprint prediction extent in HAJMing constraints on target surface for intricately shaped tapered holes generation. The use of hot abrasives in the HAJM process has demonstrated an interest in improving cutting performance for material erosion. Moreover, this proposed experimental work contains the manufacturing, design and fabrication of hot abrasive jet machine (HAJM) using commercially available hardware and software. So, the components are manufactured indigenously as per the designed parameters for the purpose of improving the machining performance. Simulation for material erosion mechanism of HAJMing is used to obtain the nature of produced workpiece profile. Additionally, FB-HAJMing also deals with the sustainability assessment under environmental-friendly hot abrasive-assisted machining conditions.

A predictive model for the industrial air-impingement drying of resin impregnated paper

Industrial drying lines of resin-impregnated paper are formed by contiguous furnaces where hot air jets impinge on the surface of the moving paper sheet. The number of production parameters that conditions the process is very high, making the final drying prediction, and the optimal adjustment of the production parameters, very complex tasks. A novel numerical tool for the fast prediction of this industrial drying is presented. The model, obtained from local mass and energy equations for the paper sheet, and fed with results from three-dimensional computational fluid dynamic simulations and thermo-gravimetric tests, determines the evolution of the paper weight along the line for any given combination of production parameters: paper velocity, furnaces air temperatures and mass flows, among others. The model is validated in an industrial line with 11 furnaces, 2 impregnation stages, and more than 150 adjustable operational input parameters, leading to relative errors in the predicted paper temperature evolution and final paper weight of less than 7% and 1%, respectively. Likewise, the model coupling with an optimization tool is also presented to show its capabilities on selecting the best production parameters for prescribed conditions, making the model a useful tool in the framework of the increasingly relevant role of mathematical models in industry.

Numerical simulation of the shear stress produced by the hot metal jet on the blast furnace runner

During steel casting process a jet of molten metal runs out of the blast furnace hearth and strikes the runner. The continuous impact of hot fluids causes significant damage to its surface, which is made of refractory concrete. In particular, the initial impact on the dry runner is expected to be critical. This work deals with the analysis of the mechanical impact on the runner through the numerical simulation of the process. We propose an incompressible turbulent isothermal Navier-Stokes model, where turbulence is modelled considering two k−ω models (standard and SST). The interface dynamics is described by applying the Volume of Fluid (VOF) method, while the surface tension vector is provided by the Continuum Surface model (CSF). Their numerical results are performed in 2D. A comparative analysis of the most suitable transient turbulent multiphase model is presented by simulating benchmark physical experiments. The shear stress arising from the impact of the jet on the runner is also analyzed. An improvement of the classical analytical expression given in [1] is proposed. Both, the chosen turbulence model, and the formulas to compute the shear stress are validated using two benchmark laboratory tests and three numerical experiments. Numerical results are given for the impact of the jet on the dry runner of the blast furnace.