Jet Disintegration Research Articles

Effect Chain Analysis of Supercritical Fuel Disintegration Processes Using an LES-based Entropy Generation Analysis

ABSTRACT In this work, a large eddy simulation (LES) technique combined with entropy generation analysis (EGA) is employed in order to investigate the complex physics of fuel injection under supercritical conditions. In particular, physical processes that are relevant for the fuel breakup and mixing are identified and their effects on the overall disintegration process are quantified. Thereby, it turned out that (1) a chain of four consecutive physical processes (shearing, separation, pseudo-boiling, and turbulent mixing) drive the overall jet disintegration, (2) entropy is primarily generated due to thermal energy conversion processes including pseudo-boiling rather than hydrodynamics, and (3) LES technique combined with EGA proved to be a promising approach for effect chain analyses, not only for simple flows, but also for those with complex thermodynamic properties like supercritical fuel injection. Based on these findings, a physical model of the disintegration process of a cryogenic jet flow injected at supercritical conditions is proposed.

Disintegration of diminutive liquid helium jets in vacuum

The phenomenon of liquid jets disintegrating into droplets has attracted the attention of researchers for more than 200 years. An overwhelming fraction of these studies considered classical viscous liquid jets issuing into ambient atmospheric gases, such as air. Here, we present an optical shadowgraphy study of the disintegration of a cryogenic liquid helium jet produced with a 5 µm diameter nozzle into vacuum. The physical properties of liquid helium, such as its density, surface tension, and viscosity, change dramatically as the jet flows through the nozzle and evaporatively cools in vacuum, eventually reaching the superfluid state. In this study, we demonstrate that, at different stagnation pressures and temperatures, droplet formation may involve spraying, capillary breakup, jet branching, and/or flashing and cavitation. The average droplet sizes produced in this work range from 3.4 × 1012 to 6.5 × 1012 helium atoms or 6.7-8.3 µm in diameter. This paper also reports on the distributions of sizes and shapes of the resulting droplets.

Simulation of Elliptical Liquid Jet Primary Breakup In Supersonic Crossflow

The study of elliptical liquid jets in supersonic flow in a Mach 2.0 is performed numerically. The primary breakup process of the elliptical liquid jet is simulated for a Weber number 223, liquid/gas flux momentum 4.0. The aspect ratios of elliptical geometries are set to be 0.25, 0.5, 1, 2, and 5. The results show a remarkable difference in liquid jet disintegration morphology at different aspect ratios. Under supersonic crossflow conditions, the elliptical liquid jet shows more breakup characteristics than the round liquid jet. As the aspect ratio grows, the penetration depth decreases. The elliptical liquid jet with AR=0.25 has the largest penetration depth in all cases. Moreover, the round jet has a maximum spreading angle of 50.2°. The changing trends of the column breakup length both x direction and y direction are similar. The elliptical jet at a lower aspect ratio has a shorter breakup length due to the narrower windward area. The liquid jet has a pair of larger horseshoe vortex structure and a wider wake region at a higher aspect ratio. Two pairs of reversal vortex pairs with obvious characteristics can be observed in all the simulations.

Transient modes in a swirl jet of superheated water

Experimental studies of boiling-up in a jet of superheated water have been carried out in the presence of a passive swirler during a discharge through a short cylindrical nozzle. The evolution of the jet disintegration of a boiling-up liquid has been traced under changes of thermodynamic parameters (temperature, pressure) along the saturation line. The characteristic structures and shapes of the jet corresponding to different modes of boiling-up have been identified. In a swirl jet 1 / f - fluctuations have been detected at both for low and for high superheats. The loss of the jet stability of superheated water under conditions of explosive boiling-up has been noted.

Effect of pulsating water jet disintegration on hardness and elasticity modulus of austenitic stainless steel AISI 304L

The presented article is focused on the evaluation of mechanical properties of stainless steel disintegrated using an ultrasonically modulated pulsating water jet. The experimental procedure was performed using a nozzle with a circular orifice with an equivalent diameter of 1.6 mm. The mechanical properties evaluation was based on indentation elasticity modulus Ep and nano hardness H, which were measured using nanoindentation technique. Influence of ultrasonic power and plunger pressure change on disintegrated material was evaluated. Changes in mechanical properties in dependence on distance from the disintegrated surface were evaluated. Elasticity modulus and nano hardness change were observed below and on the sides of the disintegrated surfaces. Measurements were performed until the distance of 930 μm. The indentation was carried in three series of 10 indents with 100 μm spacing located below the affected area, next to the affected area and in the unaffected material. Results of experimental testing show changes of nano hardness (generally an appreciable decrease) and elasticity modulus (limited increase) of material under and to the side of the newly created surface.

Jet disintegration in supercritical environments

A N2 jet was injected into quiescent ambient N2. The jet temperature was measured by four T-type thermocouples: one inside the injector and three at downstream positions (0.9d, 10.6d, and 28.1d, respectively; here, d is the inner diameter of the jet). The density was also measured downstream to 15d using two-dimensional Raman scattering with a pulse stretcher. Normally, our observations were consistent with expectations according to classical mixing theory; however, within a certain injection temperature range, there was no constant density region inside the jet core, and the jet temperature was measured to decrease. To explain this behavior of the jet, we considered three effects: classical mixing, thermal disintegration, and relaxation from high to low pressures. The absence of jet potential core can be explained by both thermal disintegration and relaxation, while the decrease of the temperature could be explained only by relaxation.

Coherent Capillary Wave Structure Revealed by ISS Experiments for Spontaneous Nozzle Jet Disintegration

A series of International Space Station (ISS) experiments were conducted to observe the disintegration feature of a water jet issued from an orifice/nozzle into atmospheric air. The purpose was to validate our proposal that any laminar liquid jet can spontaneously disintegrate by its own self-destabilizing loop formed along the jet. This paper reports the experiment results focusing on a water jet issued from a nozzle with a radius 0.4 mm and length 120 mm, in which the parabolic velocity profile relaxes toward that of a plug flow along the jet. As predicted in our proposal, the nozzle jet had a two-valued breakup distance in a certain jet issue speed range and exhibited hysteresis behaviors, indicating that the jet disintegration state is determined by past jet disintegration history. Analyses of video images suggest the establishment of a coherent capillary wave structure in the steady jet disintegration state. New fundamental theories were developed to examine the underlying physics involved. The short-length breakup mode was confirmed to essentially follow the same self-destabilizing mechanism as that of the plug flow jet, in which the upstream propagating capillary wave produced by the release of surface energy due to jet tip contraction or nonlinear unstable wave growth is reflected at the orifice, and becomes the unstable wave responsible for jet disintegration. In the long-length breakup mode, the velocity profile relaxation plays a role equivalent to an orifice and the average nozzle jet length is expressed as the sum of the velocity profile relaxation length and average orifice jet length at large jet issue speeds. This paper focuses on the coherent capillary wave structure of long-length breakup mode.

Explosive boiling-up in a swirl jet of superheated ethanol

Based on the knowledge of the kinetics of liquid vaporization under conditions of high and attainable superheats, experimental data on the atomization of a jet of boiling ethanol at various speeds of a flow swirl are discussed. It has been stated that under conditions of low superheats and boiling-up on solitary non-interacting heterogeneous sites, the rotation of the flow is considered to be the decisive factor in the atomization process. At high superheats and the realization of the mechanism of intense heterogeneous vaporization, the effect of boiling-up on the jet disintegration becomes dominant. When establishing conditions for explosive boiling-up (homogeneous nucleation) under attainable superheats, a complete jet breakup was observed both without a swirl and at low swirl speeds. With an increase in the swirl speed, the temperature range of the breakup narrowed. With a strong swirl the breakup disappeared completely. In the initial states of ethanol close to the thermodynamic critical point, the jet shape was similar to a gas one with or without a swirl. The 1/f fluctuations revealed were caused by oscillations (nutation) of the precessional motion of the jet. They indicate a possibility of large-scale outbursts in the jet.

Morphological classification of disintegration behavior of viscoelastic simulant gel propellant in coaxial streams

In this study, the spray structure of simulant gel propellant was analyzed morphologically and qualitatively to understand the basic characteristics of the gelled jet disintegration process in a shear coaxial environment. Categorization of breakup process was conducted based on the water jet breakup theory with generalized Reynolds number of the Herschel–Bulkley model and aerodynamic Weber number. Similar breakup types and disintegration process comparable to Newtonian fluids were depicted. However, the disintegration development was relatively slow compared to Newtonian cases, and the spray structures were quite different especially in fiber-type breakup due to its inherent viscosity change and viscoelastic properties. In the case of gel propellant, a strong Reynolds number dependency was observed under a certain critical value of the generalized Reynolds number, whereas beyond this value, breakup regime can be categorized with only the Weber number as in Newtonian cases. The border of Reynolds number dependency was shown at approximately $$\text{Re}_{\text{gen}} = 200$$ for all simulant gel contents cases considered in this study. The Weber number ranges for the three breakup modes (Rayleigh type, membrane type and fiber type) were found, and a new breakup mode showing a more intricate gel disintegration than the Newtonian one is proposed. .

Determination of parameters of the compelled capillary disintegration of liquid jets

The technique of the automated precision parameters diagnostics of the compelled capillary disintegration of liquid jet is developed for the solution of heat-physical problems of receiving the stable monodisperse drop streams. The analysis of the images received from two digital cameras, located at the angle ninety degrees to each other is the basic of this procedure. One of cameras fixes the image of a drop flow in plane X, another - in plane Y. The minimum time of storing images is ∼0.1 microsecond. By means of specially developed software in the “on line” mode it is possible to process images and to determine the following parameters: jets speed, drops speed, jets length, jets diameter and drops diameter. Testing on objects with the known geometrical sizes confirmed working capacity and efficiency of the technique and the software. The relative error of parameters determination does not exceed 0.5% for jets with length of several millimeters. The developed technique and the software allow to increase the accuracy and reliability of parameters determination of compelled capillary disintegration of liquid jets and drop streams and expand possibilities of parameters control of setups for receiving monodisperse streams.

Liquid jet breakup behind a pylon in supersonic flow

The thin pylon has been found to be one of the most promising hypermixers, offering enhanced mixing of fuel with minimum pressure loss. In the present study, the effect of pylon height and the angled injection on the liquid jet breakup and its effect on atomization in a free stream of Mach 1.71 has been studied experimentally. Acetone is used as the liquid medium to characterize the liquid jet injection in supersonic flow. Acetone is injected into the flow in the transverse direction behind the pylon at different mass flow rates for 3 different pylon geometries and 3 angled injection cases. The height of the pylon is varied (17.32 mm, 10 mm, 6 mm) and the injection angle is such that it impinges against the pylon wall at three different angles of 30°, 45° and 60° while maintaining the other geometrical features to be the same. The study includes Schlieren imaging to find the effect of liquid injection and Pylon on the compressible flow field, and Shadowgraphy visualization was employed to evaluate the jet disintegration and atomization; Mie Scattering visualization techniques were used for evaluating the lateral spread of liquid jet spray. Mathematical techniques such as temporal variance, POD and DMD are used to analyze the temporal behavior of the jet spread. It is observed that the pylon height not only increases the penetration height but also has a significant effect on the jet breakup and atomization. The shear layer also plays a major role in jet atomization and penetration height. Angled injection case was observed to perform better than transverse injection in terms of penetration height and jet spread.

Cooling of streams of hydrogen and deuterium in relation to units for receiving cryogenic monodisperse targets

The purpose of work is development of the model and carrying out numerical calculations of cooling of thin jets from hydrogen and deuterium as applicable to installations for receiving cryogenic monodisperse targets. For this purpose the model of the expiration of a cryogenic jet to the low pressure area is created, the change of surface temperature and an internal jet part at different external parameters with respect to time is investigated through numerical solutions in PHOENICS software. Dependences of temperature change of liquid jets from hydrogen and deuterium along jet surface and on radius depending on jet diameter, speed, initial jet temperature and pressure in the working chamber of installations for receiving cryogenic monodisperse targets are carried out. The basic possibility of creation of high-speed cryogenic monodisperse targets is shown. According to calculations, at input of thin liquid jets of hydrogen or deuterium with a speed up to 100 m/s in the working chamber with low pressure, jets at distance up to 1 mm do not manage to freeze and can be broken into monodisperse drops. Drops are cooled and become granules due to evaporation. The developed model, the program for determination of parameters of steady monodisperse disintegration of liquid cryogenic jets and results of numerical calculations can be used during creation of installations for receiving high-speed cryogenic monodisperse targets.

Atomization of a Sheet Jet of Superheated Water Using a Passive Swirler

In this paper, an experimental study of boiling-up of a superheated water jet at an outflow through a short slit nozzle into the atmosphere in the presence of a passive swirler (twisted tape, wire winding) has been carried out in order to affect and control the jet behavior. The evolution of jet disintegration with increasing liquid superheat during the outflow both from the saturation line and at a fixed initial pressure has been traced. The characteristic structures and shapes of the flow have been identified. The relationship between the jet shape and various mechanisms of vaporization has been noted. For small superheats when outflowing from the saturation line, both unswirling jet shapes and swirling jet ones have looked the same. When a liquid outflows at a fixed initial pressure, a more structured parabolic jet profile with a decreasing opening angle is observed when the pressure increases. The differences have been revealed at moderate superheats, when the parabolic jet profile has been replaced by a trapezoidal jet one with increasing temperature along the isobars. It has been established that in the case of attainable superheats, the intensive process of boiling-up plays the main role in the flow formation. In this case the jet shape remained unchanged at outflows both from the saturation line and from the isobars. In the experiments conducted, manifestations of the two-phase jet instability, which have been in experiments with a passive swirler for a short cylindrical nozzle have not been observed.

Numerical simulation of the growth and interaction of vapour bubbles in superheated liquid jets

Operating fluids for steering and propulsion of orbital manoeuvring systems are to be changed from toxic substances to environmentally less harmful alternatives. Liquid oxygen (LOX) can be used as oxidizer but the near vacuum conditions of outer space lead to a fast expansion into a superheated state when LOX is injected into the combustion chamber. The disintegration of the liquid jet is driven by bubble nucleation and growth, which is called flash boiling. These processes typically occur at small length and time scales and need to be modelled in macroscopic simulations of the entire combustion chamber. The goal of the present work is a quantification of bubble growth rates and bubble-bubble interactions that can be used to improve the existing submodels needed for full-scale simulations of the entire thruster. We use direct numerical simulations (DNS) of bubble clusters and compare the resulting growth rates to standard models for single bubble growth. The DNS solver is based on a discontinuous Galerkin approach and combined to a level-set equation to transport the interface between liquid and vapour. A modified HLLC Riemann solver accounts for the phase transfer. The computations show that vapour bubbles grow more slowly in the center of a jet than at its surface. The bubble radii exponentially decrease with distance from the liquid jet interface and growth rates are reduced by more than 70% in the center of the jet such that their volumetric expansion can be neglected for the computation of the jet expansion. The reduced growth can be associated with the interactions of the pressure fields surrounding the bubbles as the liquid pressure increases due to bubble growth and evaporation. The degree of superheat is locally reduced and bubbles grow at a smaller rate. The growth rates of individual bubbles can be parameterised with the local degree superheat, which may serve as a potential sub-scale model. These findings hold for various operating conditions that are characteristic for LOX flash evaporation under vacuum conditions.

On-line measurement and monitoring of pulsating saline and water jet disintegration of bone cement with frequency 20 kHz

This paper deals with performance analysis of disintegration of polymethylmethacrylate using pulsating liquids jet with different density with frequency 20 kHz using condition monitoring. The influence of the liquid on the cutting depth was studied by using contactless measurement device MicroProf, FRT. The cutting depths were compared to studies that used a continuous water jet to assess the volume flow reduction. On-line condition measurement was used for controlling the disintegration process without compromising the structural integrity of neighbouring materials. With a flow rate of 0.54 l/min, a maximum disintegration depth of 1.3 mm and material removal of 0.4 mm3 was obtained using physiological saline and 1.1 mm and 0.2 mm3 for water. Continuous jets required approximately 1.0 l/min to reach similar cutting depths. Hence, a pulsating liquid jet enhances the cutting capacity with reduced flow rate. Signal strength for individual pressures 7–10 MPa is not significant, but signal increases during significant bone cement removal. The results open new avenues for research a minimally invasive and non-thermal technique for on-line controlled processes for medical purposes.

A numerical study on jet characteristics under different supercritical conditions for engine applications

Fuel injection is one of the key factors that influence the energy conversion efficiency and emission level of engines. In this study, supercritical injection and mixing under different conditions were investigated using large eddy simulation method. Real-fluid thermodynamic models based on the Peng-Robinson equation of state, including the volume-translation method, were established, and the adjusted pressure implicit split operator algorithm was developed to handle solution instability due to thermodynamic nonidealities. Density variations, potential core lengths, spreading rate, and turbulent velocity fluctuations were analyzed. The effects of injection temperature and ambient pressure on supercritical jet disintegration were studied. The results show that both high injection temperature and elevated ambient pressure can facilitate jet mixing, and the potential core length and spreading rate are sensitive to the injection temperature near pseudo-boiling point. The pseudo-boiling process, which results in a large density gradient and isobaric heat capacity in the jet surface, delays the shrinkage of the radial boundary of the potential core and leads to small spreading angles of jets. The turbulent velocity fluctuations reveal significant anisotropy in the mixing layer of supercritical jets, and a large density gradient resulting from pseudo-boiling behavior damps radial turbulent velocity fluctuations at the surface of jets.

Single vapour bubble growth under flash boiling conditions using a modified HLLC Riemann solver

Common fuel-oxidizer combinations in orbital manoeuvring systems consist of toxic substances but will be replaced in the future. Liquid oxygen (LOX) is one potential oxidizer but it rapidly superheats under the initial low-pressure conditions in the combustion chamber. Bubble nucleation and growth dominate the efficient disintegration of the liquid jet, which is called flash boiling. An investigation of the small scale bubble dynamics will help to improve existing models for the break-up of the LOX jet and the mixing with the fuel. Direct numerical simulations (DNS) can be used to analyse the underlying processes if the solver handles phase transition effects at extreme ambient conditions. In this paper we use a fully compressible discontinuous Galerkin solver combined to a level-set equation and to a modified HLLC Riemann solver. The main goal of our investigation is to assess closure conditions for the mass transfer models which accurately represent the physics of vapour bubble growth. We couple three models for the estimation of vaporisation mass fluxes to the interface Riemann solver. The Hertz-Knudsen relation and a kinetic relation predict the volumetric expansion well but cannot represent the instantaneous mass flux. A sub-grid scale heat flux model predicts the mass flux qualitatively better but the volumetric bubble expansion matches only at late time intervals. The dependency of the calibrated coefficients on the physical conditions is similar for the different vaporisation models.

Influence of a Perpendicular Electrostatic Field on Aerodynamic-Force-Induced Primary Disintegration of a Thin Plane Jet of Dielectric Liquid

The disintegration of a plane nonconductive jet of a high-permittivity liquid has been studied. The jet moves with constant velocity in a gas that is quiescent at infinity in the presence of a perpendicular electrostatic field. Initially, the boundaries of the jet are parallel to each other. Its thickness is much smaller than the capillary constant. The gas density has been included into the list of governing parameters. The case has been considered when aerodynamic forces arising from wave disturbance of the gas–liquid interface make a greater contribution to the dynamics of the liquid than capillary forces. It has been shown that when the jet is aerodynamically unstable, the application of a perpendicular electric field with moderate intensity considerably decreases fragments of the jet after disintegration.

Full-length visualisation of liquid oxygen disintegration in a single injector sub-scale rocket combustor

This work presents results of an effort to create an extended experimental database for the validation of numerical tools for high pressure oxygen-hydrogen rocket combustion. A sub-scale thrust chamber has been operated at nine load points covering both sub- and supercritical chamber pressures with respect to the thermodynamic critical pressure of oxygen. Liquid oxygen and gaseous hydrogen were injected through a single, shear coaxial injector element at temperatures of around 120 K and 130 K, respectively. High-speed optical diagnostics were implemented to visualise the flow field along the full length of the combustion chamber. This work presents the analysis of shadowgraph imaging for characterising the disintegration of the liquid oxygen jet. The large imaging data sets are reduced to polynomial profiles of shadowgraph intensity which are intended to provide a more direct means of comparison with similarly reduced numerical results. Comparing half-lengths of these profiles across operating conditions show clear groupings of load points by combustion chamber pressure and mixture ratio. All load points appear to collapse to an inverse dependence of length on impulse flux ratio.

Влияние перпендикулярного электростатического поля на вызванный аэродинамическими силами первичный распад тонкой плоской струи жидкого диэлектрика

AbstractThe disintegration of a plane nonconductive jet of a high-permittivity liquid has been studied. The jet moves with constant velocity in a gas that is quiescent at infinity in the presence of a perpendicular electrostatic field. Initially, the boundaries of the jet are parallel to each other. Its thickness is much smaller than the capillary constant. The gas density has been included into the list of governing parameters. The case has been considered when aerodynamic forces arising from wave disturbance of the gas–liquid interface make a greater contribution to the dynamics of the liquid than capillary forces. It has been shown that when the jet is aerodynamically unstable, the application of a perpendicular electric field with moderate intensity considerably decreases fragments of the jet after disintegration.