Numerical Analysis of the Primary Breakup Under High-Altitude Relight Conditions Applying the Embedded DNS Approach to a Generic Prefilming Airblast Atomizer

2013 ◽  
Author(s):  
Benjamin Sauer ◽  
Nikolaos Spyrou ◽  
Amsini Sadiki ◽  
Johannes Janicka
Keyword(s):  
Surface Tension ◽  
Boundary Conditions ◽  
High Altitude ◽  
Ambient Pressure ◽  
Planar Geometry ◽  
Slight Variation ◽  
Strong Impact ◽  
Wall Film ◽  
Primary Breakup ◽  
Liquid Wall

The primary breakup under high-altitude relight conditions is investigated in this study where ambient pressure is as low as 0.4 bar and air, fuel and engine parts are as cold as 265 K. The primary breakup is crucial for the fuel atomization. As of today, the phenomena dictating the primary breakup are not fully understood. Direct Numerical Simulations (DNS) of liquid breakup under realistic conditions and geometries are hardly possible. The embedded DNS (eDNS) approach represents a reliable numerical tool to fill this gap. The concept consists of three steps: a geometry simplification, the generation of realistic boundary conditions for the DNS and the DNS of the breakup region. The realistic annular airblast atomizer geometry is simplified to a Y-shaped channel representing a planar geometry. Inside this domain the eDNS is located. The eDNS domain requires the generation of boundary conditions. A Large Eddy Simulation (LES) of the entire Y-shaped channel and a Reynolds-Averaged Navier-Stokes Simulation (RANS) of the liquid wall film are performed prior to the DNS. All parameters are stored transiently on all virtual DNS planes. These variables are then mapped to the DNS. Thus, high-quality boundary conditions are generated. The Volume-of-Fluid (VOF) method is used to solve for the two-phase flow. The results provide a qualitative insight into the primary breakup under realistic high-altitude relight conditions. Instantaneous snapshots in time illustrate the behavior of the liquid wall film along the prefilmer lip and illustrate the breakup process. It is seen that a slight variation of the surface tension force has a strong impact on the appearance of the primary breakup. Case 1 with the surface tension corresponding to kerosene at 293 K indicates large flow structures that are separated from the liquid sheet. By lowering the surface tension related to kerosene at 363 K, the breakup is dominated by numerous small structures and droplets. This study proves the applicability of the eDNS concept for investigating breakup processes as the transient nature of the phase interface behavior can be captured. At this time, the authors only present a qualitative insight which can be explained by the lack of quantitative data. The approach offers the potential of simulating realistic annular highly-swirled airblast atomizer geometries under realistic conditions.

scholarly journals Effect of ambient pressure oscillation on the primary breakup of cylindrical liquid jet spray

2020 ◽  
Vol 12 ◽  
pp. 175682772093555
Author(s):  
Zhen Zhang ◽  
Dong-hyuk Shin
Keyword(s):  
Surface Tension ◽  
Mass Flow Rate ◽  
Flow Rate ◽  
Liquid Surface ◽  
Ambient Pressure ◽  
Pressure Oscillation ◽  
Liquid Jet ◽  
Liquid Surface Tension ◽  
Primary Breakup ◽  
Ambient Gas

The present simulation study investigates the effects of ambient pressure oscillation on cylindrical liquid jet sprays, using the volume of fluid method. The research is motivated by combustion instability in combustion engines, where strong harmonic pressure oscillation can damage internal structures. Oscillating pressure modulates not only the fuel mass flow rate but also the ambient gas density and liquid surface tension, and in liquid sprays, the ambient fluid density and surface tension can have substantial effects on spray breakup. In order to investigate the multiple property changes with ambient pressure oscillation, therefore, a new solver in OpenFOAM is developed. In the solver, liquid mass flow rate, ambient gas density, and liquid surface tension change simultaneously as a result of pressure oscillation. Simulations were conducted at a Reynolds number of 2000 and Weber number over 2000, conditions that are conducive to primary breakup in laminar flows. The simulations show that oscillations in ambient pressure significantly strengthen the surface instability of the liquid ligament, which depends on the surface tension–pressure coefficient, the mean pressure, and the amplitude of oscillation.

A Validated Two-Phase Flow Large Eddy Simulation Methodology

2013 ◽  
Author(s):  
Feng Xiao ◽  
Mehriar Dianat ◽  
James J. McGuirk
Keyword(s):  
Boundary Conditions ◽  
Level Set ◽  
Two Phase Flow ◽  
Local Level ◽  
Density Ratio ◽  
Cross Flow ◽  
Liquid Jet ◽  
Phase Flow ◽  
Two Phase ◽  
Primary Breakup

A robust two-phase flow LES methodology is described, validated and applied to simulate primary breakup of a liquid jet injected into an airstream in either co-flow or cross-flow configuration. A Coupled Level Set and Volume of Fluid method is implemented for accurate capture of interface dynamics. Based on the local Level Set value, fluid density and viscosity fields are treated discontinuously across the interface. In order to cope with high density ratio, an extrapolated liquid velocity field is created and used for discretisation in the vicinity of the interface. Simulations of liquid jets discharged into higher speed airstreams with non-turbulent boundary conditions reveals the presence of regular surface waves. In practical configurations, both air and liquid flows are, however, likely to be turbulent. To account for inflowing turbulent eddies on the liquid jet interface primary breakup requires a methodology for creating physically correlated unsteady LES boundary conditions, which match experimental data as far as possible. The Rescaling/Recycling Method is implemented here to generate realistic turbulent inflows. It is found that liquid rather than gaseous eddies determine the initial interface shape, and the downstream turbulent liquid jet disintegrates much more chaotically than the non-turbulent one. When appropriate turbulent inflows are specified, the liquid jet behaviour in both co-flow and cross-flow configurations is correctly predicted by the current LES methodology, demonstrating its robustness and accuracy in dealing with high liquid/gas density ratio two-phase systems.

scholarly journals Analysis of Diesel Knock for High-Altitude Heavy-Duty Engines Using Optical Rapid Compression Machines

Energies ◽  
2020 ◽  
Vol 13 (12) ◽  
pp. 3080
Author(s):  
Xiangting Wang ◽  
Haiqiao Wei ◽  
Jiaying Pan ◽  
Zhen Hu ◽  
Zeyuan Zheng ◽  
...  
Keyword(s):  
High Altitude ◽  
High Speed ◽  
Ambient Pressure ◽  
Critical Conditions ◽  
Heavy Duty ◽  
Pressure Oscillations ◽  
Spray Impingement ◽  
Rapid Compression ◽  
The Given ◽  
Injection Pressures

In high altitude regions, affected by the low-pressure and low-temperature atmosphere, diesel knock is likely to be encountered in heavy-duty engines operating at low-speed and high-load conditions. Pressure oscillations during diesel knock are commonly captured by pressure transducers, while there is a lack of direct evidence and visualization images, such that its fundamental formation mechanism is still unclear. In this study, optical experiments on diesel knock with destructive pressure oscillations were investigated in an optical rapid compression machine. High-speed direct photography and simultaneous pressure acquisition were synchronically performed, and different injection pressures and ambient pressures were considered. The results show that for the given ambient temperature and pressure, diesel knock becomes prevalent at higher injection pressures where fuel spray impingement becomes enhanced. Higher ambient pressure can reduce the tendency to diesel knock under critical conditions. For the given injection pressure satisfying knocking combustion, knock intensity is decreased as ambient pressure is increased. Further analysis of visualization images shows diesel knock is closely associated with the prolonged ignition delay time due to diesel spray impingement. High-frequency pressure oscillation is caused by the propagation of supersonic reaction-front originating from the second-stage autoignition of mixture. In addition, the oscillation frequencies are obtained through the fast Fourier transform (FFT) analysis.

Inflammability and Electrical Studies of Foams Which may Occur at Altitude by De-Aeration of Aviation Turbine Fuels

1959 ◽  
Vol 63 (586) ◽  
pp. 581-588 ◽  
Author(s):  
B. V. Poulston ◽  
A. Thomas
Keyword(s):  
High Altitude ◽  
Sea Level ◽  
Atmospheric Pressure ◽  
Ambient Pressure ◽  
Electrical Charge ◽  
Air Bubbles ◽  
Electrical Studies ◽  
To Come ◽  
Short Time

Air dissolves in aircraft fuels to an extent directly proportional to the ambient pressure, so that when fuel which has been stored at sea-level atmospheric pressure is taken up to a high altitude, there is a tendency for air to come out of solution. In certain circumstances, which are later described in detail, air bubbles can be liberated very violently from fuels in aircraft tanks at high altitude and a thick foam can form on the surface for a short time.The production of fuel foams by degassing has posed a certain problem; foams, being intimate mixtures of air and fuel, may well be inflammable; furthermore, the rising of air bubbles through fuel can result in the accumulation of electrical charge in the foam giving rise to the possibility of a source of ignition.

Problems related to the tests of resistance and strength of military equipment in reduced atmospheric pressure conditions

2019 ◽  
Vol 124 ◽  
pp. 151-159
Author(s):  
Patryk Płochocki ◽  
Mateusz Makarewicz ◽  
Przemysław Simiński
Keyword(s):  
High Altitude ◽  
Working Conditions ◽  
Atmospheric Pressure ◽  
Ambient Pressure ◽  
Air Transport ◽  
Normative Documents ◽  
Military Equipment ◽  
The Subject

This article is about military equipment research in conditions of reduced atmospheric pressure. Reported cases of equipment damage during work at high altitude or air transport show the need to perform research on phenomena occurring during storage, transport and operation of equipment at a reduced ambient pressure. One of the fragments of the article is devoted to the records contained in normative documents regarding the subject of the study. In addition, an exemplary experiment was made, the purpose of which was to illustrate some of the effects associated with the use of the equipment in the above-mentioned working conditions.

Asymptotic model for the dynamics of curved viscous fibres with surface tension

2009 ◽  
Vol 622 ◽  
pp. 345-369 ◽  
Author(s):  
NICOLE MARHEINEKE ◽  
RAIMUND WEGENER
Keyword(s):  
Surface Tension ◽  
Boundary Conditions ◽  
Capillary Number ◽  
Temporal Evolution ◽  
Slender Body ◽  
Explicit Description ◽  
Asymptotic Model ◽  
Slender Body Theory ◽  
Viscous Transport ◽  
Body Theory

In this paper, we derive and investigate an asymptotic model for the dynamics of curved viscous inertial Newtonian fibres subjected to surface tension, as they occur in rotational spinning processes. Accordingly, we extend the slender body theory of Panda, Marheineke & Wegener (Math. Meth. Appl. Sci., vol. 31, 2008, p. 1153) by including surface tension and deducing boundary conditions for the free end of the fibre. The asymptotic model accounts for the inner viscous transport and places no restrictions on either the motion or the shape of the fibre centreline. Depending on the capillary number, the boundary conditions yield an explicit description for the temporal evolution of the fibre end. We study numerically the behaviour of the fibre as a function of the effects of viscosity, gravity, rotation and surface tension.

scholarly journals Experimental characterization of the COndensation PArticle counting System for high altitude aircraft-borne application

2008 ◽  
Vol 1 (1) ◽  
pp. 321-374 ◽  
Author(s):  
R. Weigel ◽  
M. Hermann ◽  
J. Curtius ◽  
C. Voigt ◽  
S. Walter ◽  
...  
Keyword(s):  
High Altitude ◽  
Ambient Pressure ◽  
Particle Diameter ◽  
The Arctic ◽  
Working Fluid ◽  
Counting System ◽  
Dual Channel ◽  
Particle Counting ◽  
Condensation Particle Counting

Abstract. This study aims at a detailed characterization of an ultra-fine aerosol particle counting system for operation on board the Russian high altitude research aircraft M-55 "Geophysica" (maximum ceiling of 21 km). The COndensation PArticle counting Systems (COPAS) consists of an aerosol inlet and two dual-channel continuous flow Condensation Particle Counters (CPCs). The aerosol inlet, adapted for COPAS measurements on board the M-55 "Geophysica", is described concerning aspiration, transmission, and transport losses. The counting efficiencies of the CPCs using the chlorofluorocarbon FC-43 as the working fluid are studied experimentally at two pressure conditions, 300 hPa and 70 hPa. Three COPAS channels are operated with different temperature differences between the saturator and the condenser block yielding smallest detectable particle sizes (dp50 – as 50% detection "cut off" diameters) of 6 nm, 11 nm, and 15 nm, respectively, at ambient pressure of 70 hPa. The fourth COPAS channel is operated with an aerosol heating line (250°C) for a determination of the non-volatile number of particles. The heating line is experimentally proven to volatilize pure H2SO4-H2O particles for a particle diameter (dp) range of 11 nm<dp<200 nm. Additionally this study includes investigation to exclude auto-nucleation of the working fluid inside the CPCs. An instrumental inter-comparison (cross-correlation) has been performed for several measurement flights and mission flights in the Arctic and the Tropics are discussed. Finally, COPAS measurements are used for an aircraft plume crossing analysis.

Comparison of Atomization Characteristics of Jet A-1 and Alternative Aviation Fuels Using High-Speed Imaging Technique

2019 ◽  
Author(s):  
Manish Kumar ◽  
Srinibas Karmakar
Keyword(s):  
Surface Tension ◽  
High Speed ◽  
Alternative Fuels ◽  
Imaging Technique ◽  
Droplet Formation ◽  
Fuel Properties ◽  
Slight Variation ◽  
High Speed Imaging ◽  
Butyl Butyrate ◽  
Atomization Characteristics

Abstract Environmental pollution from gas turbine engines is becoming a serious concern recently because of the steep growth in the aviation sector globally. Therefore, potential alternative fuels which can partially or fully replace fossil-based jet fuel are getting significant attention. However, the search for suitable candidate fuels which can fulfill the requirement in terms of fuel properties and combustion performance is continuing. The present study deals with an experimental investigation of atomization characteristics of Jet A-1, butanol, and butyl butyrate in quiescent atmospheric air. A high-speed imaging technique has been adopted to make a comparison of ligament breakup characteristics and droplet formation of these alternative biofuels with that of Jet A-1. Various fuel properties, including density, viscosity, and surface tension, are compared. An effort is made to understand how the variation in fuel properties influences the atomization mechanism of each fuel. The surface tension seems to be similar for these three fuels with a slight variation in density. However, there is a significant variation in viscosity. Viscosity appears to play a major role in the difference observed in ligament length and droplet formation. Due to the higher viscosity of butanol, the droplet formation seems to be delayed compared to Jet A-1, whereas the lower viscosity of butyl butyrate promotes faster droplet formation. The effect of blending of these biofuels with Jet A-1 on atomization characteristics will be compared with that of Jet A-1.

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