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Real fluids near the critical point in isotropic turbulence
KTH, Skolan för teknikvetenskap (SCI), Mekanik, Fysiokemisk strömningsmekanik.
KTH, Skolan för teknikvetenskap (SCI), Mekanik, Fysiokemisk strömningsmekanik.ORCID-id: 0000-0003-2830-0454
University of Washington, USA.
KTH, Skolan för teknikvetenskap (SCI), Mekanik, Fysiokemisk strömningsmekanik.ORCID-id: 0000-0003-3336-1462
(engelsk)Inngår i: Physics of fluids, ISSN 1070-6631, E-ISSN 1089-7666Artikkel i tidsskrift, Editorial material (Fagfellevurdert) In press
Abstract [en]

We investigate the behavior of a uid near the critical point by using numerical simulations of weakly compressible three-dimensional isotropic turbulence. Much has been done for a turbulent ow with an ideal gas. The primary focus of this work is to analyze uctuations of thermodynamic variables (pressure, density and temperature) when a non-ideal Equation Of State (EOS) is considered. In order to do so, a hybrid lattice Boltzmann scheme is applied to solve the momentum and energy equations. Previously unreported phenomena are revealed as the temperature approaches the critical point. These phenomena include increased uctuations in pressure, density and temperature, followed by changes in their respective probability density functions (PDFs). Unlike the ideal EOS case, signicant dierences in the thermodynamic properties are also observed when the Reynolds number is increased. We also address issues related to the spectral behavior and scaling of density, pressure, temperature and kinetic energy.

HSV kategori
Identifikatorer
URN: urn:nbn:se:kth:diva-183483OAI: oai:DiVA.org:kth-183483DiVA, id: diva2:911699
Forskningsfinansiär
Swedish Research Council, 2010-3938Swedish Research Council, 2011-5355
Merknad

QP 2016

Tilgjengelig fra: 2016-03-14 Laget: 2016-03-14 Sist oppdatert: 2017-11-30bibliografisk kontrollert
Inngår i avhandling
1. Phase change, surface tension and turbulence in real fluids
Åpne denne publikasjonen i ny fane eller vindu >>Phase change, surface tension and turbulence in real fluids
2016 (engelsk)Doktoravhandling, med artikler (Annet vitenskapelig)
Abstract [en]

Sprays are extensively used in industry, especially for fuels in internal combustion and gas turbine engines. An optimal fuel/air mixture prior to combustion is desired for these applications, leading to greater efficiency and minimal levels of emissions. The optimization depends on details regarding the different breakups, evaporation and mixing processes. Besides, one should take into consideration that these different steps depend on physical properties of the gas and fuel, such as density, viscosity, heat conductivity and surface tension.

In this thesis the phase change and surface tension of a droplet for different flow conditions are studied by means of numerical simulations.This work is part of a larger effort aiming to developing models for sprays in turbulent flows. We are especially interested in the atomization regime, where the liquid breakup causes the formation of droplet sizes much smaller than the jet diameter. The behavior of these small droplets is important to shed more light on how to achieve the homogeneity of the gas-fuel mixture as well as that it directly contributes to the development of large-eddy simulation (LES) models.

The numerical approach is a challenging process as one must take into account the transport of heat, mass and momentum for a multiphase flow. We choose a lattice Boltzmann method (LBM) due to its convenient mesoscopic natureto simulate interfacial flows. A non-ideal equation of state is used to control the phase change according to local thermodynamic properties. We analyze the droplet and surrounding vapor for a hydrocarbon fuel close to the critical point. Under forced convection, the droplet evaporation rate is seen to depend on the vapor temperatureand Reynolds number, where oscillatory flows can be observed. Marangoni forces are also present and drivethe droplet internal circulation once the temperature difference at the droplet surface becomes significant.In isotropic turbulence, the vapor phase shows increasing fluctuations of the thermodynamic variables oncethe fluid approaches the critical point. The droplet dynamics is also investigated under turbulent conditions, where the presence of coherent structures with strong shear layers affects the mass transfer between the liquid-vapor flow, showing also a correlation with the droplet deformation. Here, the surface tension and droplet size play a major role and are analyzed in detail.

sted, utgiver, år, opplag, sider
Stockholm: KTH Royal Institute of Technology, 2016. s. xiv, 53
Serie
TRITA-MEK, ISSN 0348-467X ; 2016:02
HSV kategori
Forskningsprogram
Teknisk mekanik
Identifikatorer
urn:nbn:se:kth:diva-183487 (URN)978-91-7595-895-8 (ISBN)
Disputas
2016-04-07, Kollegiesalen, Brinellvägen 8, KTH, Stockholm, 10:15 (engelsk)
Opponent
Veileder
Forskningsfinansiär
Swedish Research Council, 2010-3938Swedish Research Council, 2011-5355
Merknad

QC 20160314

Tilgjengelig fra: 2016-03-14 Laget: 2016-03-14 Sist oppdatert: 2016-03-14bibliografisk kontrollert

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Do-Quang, MinhAmberg, Gustav

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