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Prof. Dr. Manolis Gavaises
School of Mathematics, Computer Science and Engineering, City, University of London, London EC1V 0HB, UK

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0 Cavitation
0 Thermodynamics
0 Complex fluids
0 multi-phase flows
0 bubble dynamics

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Cavitation
bubble dynamics
Thermodynamics
multi-phase flows

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Journal article
Published: 23 June 2021 in Applications in Energy and Combustion Science
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Numerical predictions of the fuel heating and cavitation erosion location indicators occurring during the opening and closing periods of the needle valve inside a five-hole common rail Diesel fuel injector are presented. These have been obtained using an explicit density-based solver of the compressible Navier-Stokes (NS) and energy conservation equations; the flow solver is combined with two thermodynamic closure models for the liquid, vapour and vapour-liquid equilibrium (VLE) property variation as function of pressure and temperature. The first is based on tabulated data for a 4-component Diesel fuel surrogate, derived from the Perturbed-Chain, Statistical Associating Fluid Theory (PC-SAFT) Equation of State (EoS), allowing for thermal effects to be quantified. The second thermodynamic closure is based on the widely used barotropic Equation of State (EoS) approximation between density and pressure and neglects viscous heating. The Wall Adapting Local Eddy viscosity (WALE) LES model was used to resolve sub-grid scale turbulence while a cell-based mesh deformation Arbitrary Lagrangian–Eulerian (ALE) formulation is used for modelling the injector's needle valve movement. Model predictions are found in close agreement against 0-D estimates of the temporal variation of the fuel temperature difference between the feed and hole exit during the injection period. Two mechanisms affecting the temperature distribution within the fuel injector have been revealed and quantified. The first is ought to wall friction-induced heating, which may result to local liquid temperature increase up to fuel's boiling point while superheated vapour is formed. At the same time, liquid expansion due to the depressurisation of the injected fuel results to liquid cooling relative to the fuel's feed temperature; this is occurring at the central part of the injection orifice. The spatial and temporal temperature and pressure gradients induce significant variations in the fuel density and viscosity, which in turn, affect the formed coherent vortical flow structures. It is found, in particular, that these affect the locations of cavitation formation and collapse, that may lead to erosion of the surfaces of the needle valve, sac volume and injection holes. Model predictions are compared against corresponding X-ray surface erosion images obtained from injector durability tests, showing good agreement.

ACS Style

Konstantinos Kolovos; Phoevos Koukouvinis; Alvaro Vidal; Manolis Gavaises; Robert M. McDavid. Simulation of transient effects in a fuel injector nozzle using real-fluid thermodynamic closure. Applications in Energy and Combustion Science 2021, 100037 .

AMA Style

Konstantinos Kolovos, Phoevos Koukouvinis, Alvaro Vidal, Manolis Gavaises, Robert M. McDavid. Simulation of transient effects in a fuel injector nozzle using real-fluid thermodynamic closure. Applications in Energy and Combustion Science. 2021; ():100037.

Chicago/Turabian Style

Konstantinos Kolovos; Phoevos Koukouvinis; Alvaro Vidal; Manolis Gavaises; Robert M. McDavid. 2021. "Simulation of transient effects in a fuel injector nozzle using real-fluid thermodynamic closure." Applications in Energy and Combustion Science , no. : 100037.

Journal article
Published: 18 May 2021 in Energies
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An investigation of the fuel heating, vapor formation, and cavitation erosion location patterns inside a five-hole common rail diesel fuel injector, occurring during the early opening period of the needle valve (from 2 μm to 80 μm), discharging at pressures of up to 450 MPa, is presented. Numerical simulations were performed using the explicit density-based solver of the compressible Navier–Stokes (NS) and energy conservation equations. The flow solver was combined with tabulated property data for a four-component diesel fuel surrogate, derived from the perturbed chain statistical associating fluid theory (PC-SAFT) equation of state (EoS), which allowed for a significant amount of the fuel’s physical and transport properties to be quantified. The Wall Adapting Local Eddy viscosity (WALE) Large Eddy Simulation (LES) model was used to resolve sub-grid scale turbulence, while a cell-based mesh deformation arbitrary Lagrangian–Eulerian (ALE) formulation was used for modelling the injector’s needle valve movement. Friction-induced heating was found to increase significantly when decreasing the pressure. At the same time, the Joule–Thomson cooling effect was calculated for up to 25 degrees K for the local fuel temperature drop relative to the fuel’s feed temperature. The extreme injection pressures induced fuel jet velocities in the order of 1100 m/s, affecting the formation of coherent vortical flow structures into the nozzle’s sac volume.

ACS Style

Konstantinos Kolovos; Phoevos Koukouvinis; Robert McDavid; Manolis Gavaises. Transient Cavitation and Friction-Induced Heating Effects of Diesel Fuel during the Needle Valve Early Opening Stages for Discharge Pressures up to 450 MPa. Energies 2021, 14, 2923 .

AMA Style

Konstantinos Kolovos, Phoevos Koukouvinis, Robert McDavid, Manolis Gavaises. Transient Cavitation and Friction-Induced Heating Effects of Diesel Fuel during the Needle Valve Early Opening Stages for Discharge Pressures up to 450 MPa. Energies. 2021; 14 (10):2923.

Chicago/Turabian Style

Konstantinos Kolovos; Phoevos Koukouvinis; Robert McDavid; Manolis Gavaises. 2021. "Transient Cavitation and Friction-Induced Heating Effects of Diesel Fuel during the Needle Valve Early Opening Stages for Discharge Pressures up to 450 MPa." Energies 14, no. 10: 2923.

Journal article
Published: 01 March 2021 in Physics of Fluids
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High-flux synchrotron radiation has been employed in a time-resolved manner to characterize the distinct topology features and dynamics of different cavitation regimes arising in a throttle orifice with an abrupt flow-entry contraction. Radiographs obtained though both x-ray phase-contrast and absorption imaging have been captured at 67 890 frames per second. The flow lies in the turbulent regime (Re = 35 500), while moderate (CN = 2.0) to well-established (CN = 6.0) cavitation conditions were examined encompassing the cloud and vortical cavitation regimes with pertinent transient features, such as cloud-cavity shedding. X-ray phase-contrast imaging, exploiting the shift in the x-ray wave phase during interactions with matter, offers sharp-refractive index gradients in the interface region. Hence, it is suitable for capturing fine morphological fluctuations of transient cavitation structures. Nevertheless, the technique cannot provide information on the quantity of vapor within the orifice. Such data have been obtained utilizing absorption imaging, where beam attenuation is not associated with scattering and refraction events, and hence can be explicitly correlated with the projected vapor thickness in line-of-sight measurements. A combination of the two methods is proposed as it has been found that it is capable of quantifying the vapor content arising in the complex nozzle flow while also faithfully illustrating the dynamics of the highly transient cavitation features.

ACS Style

I. K. Karathanassis; M. Heidari-Koochi; Q. Zhang; J. Hwang; P. Koukouvinis; M. Gavaises. X-ray phase contrast and absorption imaging for the quantification of transient cavitation in high-speed nozzle flows. Physics of Fluids 2021, 33, 032102 .

AMA Style

I. K. Karathanassis, M. Heidari-Koochi, Q. Zhang, J. Hwang, P. Koukouvinis, M. Gavaises. X-ray phase contrast and absorption imaging for the quantification of transient cavitation in high-speed nozzle flows. Physics of Fluids. 2021; 33 (3):032102.

Chicago/Turabian Style

I. K. Karathanassis; M. Heidari-Koochi; Q. Zhang; J. Hwang; P. Koukouvinis; M. Gavaises. 2021. "X-ray phase contrast and absorption imaging for the quantification of transient cavitation in high-speed nozzle flows." Physics of Fluids 33, no. 3: 032102.

Journal article
Published: 20 October 2020 in International Journal of Heat and Mass Transfer
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Immiscible heavy fuel-water (W/HFO) emulsion droplets inside combustion chambers are subjected to explosive boiling and fragmentation due to the different boiling point between the water and the surrounding host fuel. These processes, termed as either puffing or micro-explosion, are investigated with the aid of a CFD model that solves the Navier-Stokes and energy conservation equations alongside with three sets of VoF transport equations resolving the formed interfaces. The model is applied in 2-D axisymmetric configuration and it is valid up to the time instant of HFO droplet initiation of disintegration, referred to as breakup time. Model predictions are obtained for a wide range of pressure, temperature, water droplet surface depth and Weber number; these are then used to calibrate the parameters of a fitting model estimating the initiation breakup time of the W/HFO droplet emulsion with a single embedded water droplet. The model assumes that the breakup time can be split in two distinct temporal stages. The first one is defined by the time needed for the embedded water droplet to heat up and reach a predefined superheat temperature and a vapor bubble to form; while the succeeding stage accounts for the time period of vapor bubble growth, leading eventually to emulsion droplet break up. It is found that the fitting parameters are ±10% accurate in the examined range of We < 220, T < 2000 K, P < 140 bar and δ < 0.15.

ACS Style

Stavros Fostiropoulos; George Strotos; Nikolaos Nikolopoulos; Manolis Gavaises. A simple model for breakup time prediction of water-heavy fuel oil emulsion droplets. International Journal of Heat and Mass Transfer 2020, 164, 120581 .

AMA Style

Stavros Fostiropoulos, George Strotos, Nikolaos Nikolopoulos, Manolis Gavaises. A simple model for breakup time prediction of water-heavy fuel oil emulsion droplets. International Journal of Heat and Mass Transfer. 2020; 164 ():120581.

Chicago/Turabian Style

Stavros Fostiropoulos; George Strotos; Nikolaos Nikolopoulos; Manolis Gavaises. 2020. "A simple model for breakup time prediction of water-heavy fuel oil emulsion droplets." International Journal of Heat and Mass Transfer 164, no. : 120581.

Journal article
Published: 10 August 2020 in Fuel
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Recently, Rokni et al. [1,2] developed entropy-scaling based pseudo-component techniques to predict the viscosity and thermal conductivity of hydrocarbon mixtures and fuels up to high temperature and pressure conditions using only two calculated or measured mixture properties (number average molecular weight and hydrogen-to-carbon ratio). The models are accurate for many hydrocarbon mixtures that do not contain branched compounds (7 and 2% mean absolute percent deviation (MAPD) for viscosity and thermal conductivity, respectively, on average). However, predictions for some hydrocarbon mixtures and fuels containing iso-alkanes are often less accurate (16 and 19% MAPD for viscosity and thermal conductivity, respectively, on average). To improve predictions, it was proposed Rokni et al. [1,2] to fit one model parameter using an experimental reference viscosity or thermal conductivity data point, which may not be ideal if experimental reference data are not available. In order to make these models more practical, this study fits empirical correlations for the model parameters, so that accurate predictions can be made without fitting model parameters. The correlations enable viscosity and thermal conductivity predictions for a wide range of hydrocarbon mixtures and fuels, including those containing branched alkanes, and no longer require input of any experimental reference viscosity or thermal conductivity data. The correlations are temperature (fit to data from 288 to 550 K) and pressure (fit to data from 1 to 4,400 bar) dependent and are functions of average molecular weight, hydrogen-to-carbon ratio, iso-alkane and two-ring saturate concentrations. Viscosity and thermal conductivity predictions were found to improve to within 5 and 2% average MAPD, respectively, relative to experimental data for the hydrocarbon mixtures and fuels considered in this study.

ACS Style

Houman B. Rokni; Joshua D. Moore; Manolis Gavaises. Entropy-scaling based pseudo-component viscosity and thermal conductivity models for hydrocarbon mixtures and fuels containing iso-alkanes and two-ring saturates. Fuel 2020, 283, 118877 .

AMA Style

Houman B. Rokni, Joshua D. Moore, Manolis Gavaises. Entropy-scaling based pseudo-component viscosity and thermal conductivity models for hydrocarbon mixtures and fuels containing iso-alkanes and two-ring saturates. Fuel. 2020; 283 ():118877.

Chicago/Turabian Style

Houman B. Rokni; Joshua D. Moore; Manolis Gavaises. 2020. "Entropy-scaling based pseudo-component viscosity and thermal conductivity models for hydrocarbon mixtures and fuels containing iso-alkanes and two-ring saturates." Fuel 283, no. : 118877.

Journal article
Published: 01 August 2020 in Physics of Fluids
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Cavitating flow dynamics are investigated in an axisymmetric converging–diverging Venturi nozzle. Computational Fluid Dynamics (CFD) results are compared with those from previous experiments. New analysis performed on the quantitative results from both datasets reveals a coherent trend and shows that the simulations and experiments agree well. The CFD results have confirmed the interpretation of the high-speed images of the Venturi flow, which indicated that there are two vapor shedding mechanisms that exist under different running conditions: re-entrant jet and condensation shock. Moreover, they provide further details of the flow mechanisms that cannot be extracted from the experiments. For the first time with this cavitating Venturi nozzle, the re-entrant jet shedding mechanism is reliably achieved in CFD simulations. The condensation shock shedding mechanism is also confirmed, and details of the process are presented. These CFD results compare well with the experimental shadowgraphs, space–time plots, and time-averaged reconstructed computed tomography slices of vapor fraction.

ACS Style

Maxwell Brunhart; Celia Soteriou; Manolis Gavaises; Ioannis Karathanassis; Phoevos Koukouvinis; Saad Jahangir; Christian Poelma. Investigation of cavitation and vapor shedding mechanisms in a Venturi nozzle. Physics of Fluids 2020, 32, 083306 .

AMA Style

Maxwell Brunhart, Celia Soteriou, Manolis Gavaises, Ioannis Karathanassis, Phoevos Koukouvinis, Saad Jahangir, Christian Poelma. Investigation of cavitation and vapor shedding mechanisms in a Venturi nozzle. Physics of Fluids. 2020; 32 (8):083306.

Chicago/Turabian Style

Maxwell Brunhart; Celia Soteriou; Manolis Gavaises; Ioannis Karathanassis; Phoevos Koukouvinis; Saad Jahangir; Christian Poelma. 2020. "Investigation of cavitation and vapor shedding mechanisms in a Venturi nozzle." Physics of Fluids 32, no. 8: 083306.

Journal article
Published: 11 July 2020 in Fuel
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Interfacial tension (IFT) data are reported at temperatures up to 530 K and pressures up to 100 MPa for mixtures of N2 with a highly paraffinic diesel, an ultra-low sulfur diesel, and a highly aromatic diesel. The impact of composition on the IFT is determined by comparing data for each system at the same temperature and pressure calculated from a Tait-like relationship fit to the experimental data. The greatest differences in diesel + N2 IFT values are found near the normal boiling point (Tboil) of each diesel where lower molecular weight diesel components begin to dissolve in the N2-rich vapor phase. IFT data are modeled with density gradient theory (DGT) coupled with the perturbed-chain, statistical associating fluid theory equation of state (EoS). Diesel EoS parameters are calculated using three variations of a pseudo-component technique created from one group contribution (GC) method developed from high-pressure density data and from two other GC methods (S-GC and T-GC) developed from differing sets of pure component vapor pressure and saturated liquid density data. The IFT predictions significantly improve when the DGT influence parameter, cii, is allowed to vary with temperature. The DGT predictions with the B-GC method are in closest agreement with data at temperatures below Tboil, which is attributed to the more accurate representation of liquid phase densities. However, at temperatures above Tboil, where significant amounts of low molecular weight diesel components dissolve in the N2-rich vapor phase, DGT predictions with the S-GC and T-GC methods provide the closest agreement with IFT data.

ACS Style

Aaron J. Rowane; Ashutosh Gupta; Manolis Gavaises; Mark A. McHugh. Experimental and modeling investigations of the interfacial tension of three different diesel + nitrogen mixtures at high pressures and temperatures. Fuel 2020, 280, 118543 .

AMA Style

Aaron J. Rowane, Ashutosh Gupta, Manolis Gavaises, Mark A. McHugh. Experimental and modeling investigations of the interfacial tension of three different diesel + nitrogen mixtures at high pressures and temperatures. Fuel. 2020; 280 ():118543.

Chicago/Turabian Style

Aaron J. Rowane; Ashutosh Gupta; Manolis Gavaises; Mark A. McHugh. 2020. "Experimental and modeling investigations of the interfacial tension of three different diesel + nitrogen mixtures at high pressures and temperatures." Fuel 280, no. : 118543.

Journal article
Published: 17 June 2020 in Fuel
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The heating and explosive boiling leading to fragmentation of immiscible heavy fuel oil-water droplets, termed as W/HFO emulsions, is predicted numerically by solving the incompressible Navier-Stokes and energy equations alongside with a set of three VoF transport equations separating the interface of co-existing HFO, water liquid and water vapour fluid phases. Model predictions suggest that explosive boiling of the water inside the surrounding HFO, ought to their different boiling points, accelerates droplet breakup; this process is termed as either puffing or micro-explosion. In contrast to past studies which predefine the presence of vapor bubbles inside the water droplet, this is predicted here with a phenomenological model based on local temperature and superheat degree. Following their formation, the growth rate of the bubbles is computed with OCASIMAT phase-change algorithm. Moreover, the fuel droplet is simultaneously subjected to convective air flow which further contributes to its deformation. As a result, the performed simulations quantify the relative time scales of the aerodynamic-induced and the emulsion-induced breakup mechanisms. The conditions examined refer to a highly viscous emulsified heavy fuel oil droplet in a gas phase having fixed temperature and pressure equal to 1000 K and 30 bar, respectively. Initially, a benchmark case demonstrates the detailed mechanisms taking place, concluding that droplet fragmentation occurs only at a part of the fuel-air interface, resembling characteristics similar to puffing. Next, a parametric study with Weber number (Oh=0.9,We<200) shows that puffing process can speed up to 10 times the breakup of the droplet relative to aerodynamic breakup.

ACS Style

Stavros Fostiropoulos; George Strotos; Nikolaos Nikolopoulos; Manolis Gavaises. Numerical investigation of heavy fuel oil droplet breakup enhancement with water emulsions. Fuel 2020, 278, 118381 .

AMA Style

Stavros Fostiropoulos, George Strotos, Nikolaos Nikolopoulos, Manolis Gavaises. Numerical investigation of heavy fuel oil droplet breakup enhancement with water emulsions. Fuel. 2020; 278 ():118381.

Chicago/Turabian Style

Stavros Fostiropoulos; George Strotos; Nikolaos Nikolopoulos; Manolis Gavaises. 2020. "Numerical investigation of heavy fuel oil droplet breakup enhancement with water emulsions." Fuel 278, no. : 118381.

Note
Published: 01 June 2020 in Review of Scientific Instruments
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A creative low-cost and compact mechanical device that mimics the rapid closure of the pistol shrimp claw was used to conduct electrochemical experiments, in order to study the effects of hydrodynamic cavitation on the corrosion of aluminum and steel samples. Current–time curves show significant changes associated with local variations in dissolved O2 concentration, cavitation-induced erosion, and changes in the nature of the surface corrosion products.

ACS Style

F. A. Godínez; R. Mayén-Mondragón; J. E. V. Guzmán; O. Chávez; M. Gavaises; R. Montoya. Bioinspired snapping-claw apparatus to study hydrodynamic cavitation effects on the corrosion of metallic samples. Review of Scientific Instruments 2020, 91, 066101 .

AMA Style

F. A. Godínez, R. Mayén-Mondragón, J. E. V. Guzmán, O. Chávez, M. Gavaises, R. Montoya. Bioinspired snapping-claw apparatus to study hydrodynamic cavitation effects on the corrosion of metallic samples. Review of Scientific Instruments. 2020; 91 (6):066101.

Chicago/Turabian Style

F. A. Godínez; R. Mayén-Mondragón; J. E. V. Guzmán; O. Chávez; M. Gavaises; R. Montoya. 2020. "Bioinspired snapping-claw apparatus to study hydrodynamic cavitation effects on the corrosion of metallic samples." Review of Scientific Instruments 91, no. 6: 066101.

Journal article
Published: 29 May 2020 in Fluid Phase Equilibria
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In this study, the PC-SAFT equation of state is used for vapor-liquid equilibrium calculations using as independent variables the mixture composition, density and temperature. The method is based on unconstrained minimisation of the Helmholtz Free energy via a combination of the successive substitution iteration and Newton-Raphson minimisation methods with line-search; the positive definiteness of the Hessian is guaranteed by a modified Cholesky decomposition. The algorithm consists of two stages; initially, the mixture is assumed to be a single-phase and its stability is assessed; in case of being found unstable, a second stage of phase splitting (flash) takes place, in which the pressure of the fluid and compositions of both the liquid and vapor phases are calculated. The reliability of two different methods presented in the existing literature, (i) using mole numbers and (ii) using the logarithm of the equilibrium constants as iterative variables, is evaluated in terms of both iterations and computational time needed to reach convergence, for seven test cases. These include both single and multicomponent Diesel fuel surrogates, known to give incomplete density information when using pressure and temperature as independent variables. Results show that iterating with the logarithm of the equilibrium constants also reproduces this issue, while it requires a smaller number of iterations than using with mole numbers as independent variables. However, the total computational time needed for the latter case is vastly inferior. Pressure and vapor volume fraction fields are discussed for a range of temperatures and densities, apart from the number of iterations needed during the flash calculation stage. A performance comparison is obtained against the Peng-Robinson equation of state, showing similar number of iterations required but a computational time increasing with the number of components. While for a single component PC-SAFT needs around 3 times more CPU time, for 4 components it is 6 times and for a mixture of 8 components it increases up to 14 times. Finally, the method is demonstrated to converge unconditionally for all conditions tested.

ACS Style

Alvaro Vidal; Phoevos Koukouvinis; Manolis Gavaises. Vapor-liquid equilibrium calculations at specified composition, density and temperature with the perturbed chain statistical associating fluid theory (PC-SAFT) equation of state. Fluid Phase Equilibria 2020, 521, 112661 .

AMA Style

Alvaro Vidal, Phoevos Koukouvinis, Manolis Gavaises. Vapor-liquid equilibrium calculations at specified composition, density and temperature with the perturbed chain statistical associating fluid theory (PC-SAFT) equation of state. Fluid Phase Equilibria. 2020; 521 ():112661.

Chicago/Turabian Style

Alvaro Vidal; Phoevos Koukouvinis; Manolis Gavaises. 2020. "Vapor-liquid equilibrium calculations at specified composition, density and temperature with the perturbed chain statistical associating fluid theory (PC-SAFT) equation of state." Fluid Phase Equilibria 521, no. : 112661.

Journal article
Published: 24 April 2020 in Fuel
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The present work investigates the complex phenomena associated with pressure/high temperature dodecane injection for the Engine Combustion Network (ECN) Spray-A case, employing more elaborate thermodynamic closures, to avoid well known deficiencies concerning density and speed of sound prediction using traditional cubic models. A tabulated thermodynamic approach is proposed here, based on log10(p)-T tables, providing very high accuracy across a large range of pressures, spanning from 0 to 2500 bar, with only a small number of interpolation points. The tabulation approach is directly extensible to any thermodynamic model, existing or to be developed in the future. Here NIST REFPROP properties are used, combined with PC-SAFT Vapor-Liquid-Equilibrium to identify the liquid in mixtures penetration, hence avoiding the use of an arbitrary threshold for mass fraction. Identified liquid and vapour penetration are compared against experimental data from the ECN database showing a good agreement, within approximately 3–8% for axial penetration of liquid, 2% for vapor axial penetration and within experimental uncertainty for radial distribution of mass fraction. Analysis of the vortex evolution indicates that driving mechanisms behind the jet break-up are vortex tilting/stretching, then baroclinic torque, leading to Rayleigh-Taylor instabilities, closely followed by vortex dilation and finally viscous effects.

ACS Style

Phoevos Koukouvinis; Alvaro Vidal-Roncero; Carlos Rodriguez; Manolis Gavaises; Lyle Pickett. High pressure/high temperature multiphase simulations of dodecane injection to nitrogen: Application on ECN Spray-A. Fuel 2020, 275, 117871 .

AMA Style

Phoevos Koukouvinis, Alvaro Vidal-Roncero, Carlos Rodriguez, Manolis Gavaises, Lyle Pickett. High pressure/high temperature multiphase simulations of dodecane injection to nitrogen: Application on ECN Spray-A. Fuel. 2020; 275 ():117871.

Chicago/Turabian Style

Phoevos Koukouvinis; Alvaro Vidal-Roncero; Carlos Rodriguez; Manolis Gavaises; Lyle Pickett. 2020. "High pressure/high temperature multiphase simulations of dodecane injection to nitrogen: Application on ECN Spray-A." Fuel 275, no. : 117871.

Journal article
Published: 31 March 2020 in Journal of Fluid Mechanics
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The formation of caustics by inertial particles is distinctive of dispersed flows. Their pressureless nature allows crossing trajectories resulting in singularities that cannot be captured accurately by standard Lagrangian approaches due to their fine spatial scale. A promising method for the investigation of caustics is the Osiptsov method or fully Lagrangian approach (FLA). The FLA has the advantage of identifying caustics, but its applicability is hindered by the occurrence of singularities. We present an original robust framework based on the FLA that provides an explicit expression of the dispersed phase structure that does not degenerate in the vicinity of caustics, using a single representative particle. The FLA is extended to account for the Hessian of the dispersed continuum (DC). It demonstrates the integrability of the FLA number density and allows for the calculation of the number density on a given length scale, retaining the functionality of the FLA. Number density models based on the second-order representation of the DC and on the one-dimensional structure of the particle distribution, that account for the anisotropy of the DC on caustics, are derived and applied for analytical flows. The number density is linked to a finite length scale, needed for the introduction of the FLA to spatially filtered flow fields. Finally, the method is used for the calculation of the interparticle separation on caustics. The identification of the structure of caustics presented in this work paves the way to a robust understanding of the mechanisms of particle accumulation.

ACS Style

Andreas Papoutsakis; Manolis Gavaises. A model for the investigation of the second-order structure of caustic formations in dispersed flows. Journal of Fluid Mechanics 2020, 892, 1 .

AMA Style

Andreas Papoutsakis, Manolis Gavaises. A model for the investigation of the second-order structure of caustic formations in dispersed flows. Journal of Fluid Mechanics. 2020; 892 ():1.

Chicago/Turabian Style

Andreas Papoutsakis; Manolis Gavaises. 2020. "A model for the investigation of the second-order structure of caustic formations in dispersed flows." Journal of Fluid Mechanics 892, no. : 1.

Research article
Published: 26 March 2020 in ACS Omega
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This work investigates the effect of liquid fuel viscosity, as specific by the European Committee for Standardization 2009 (European Norm) for all automotive fuels, on the predicted cavitating flow in micro-orifice flows. The wide range of viscosities allowed leads to a significant variation in orifice nominal Reynolds numbers for the same pressure drop across the orifice. This in turn, is found to affect flow detachment and the formation of large-scale vortices and microscale turbulence. A pressure-based compressible solver is used on the filtered Navier-Stokes equations using the multifluid approach; separate velocity fields are solved for each phase, which share a common pressure. The rates of evaporation and condensation are evaluated with a simplified model based on the Rayleigh-Plesset equation; the coherent structure model is adopted for the subgrid scale modeling in the momentum conservation equation. The test case simulated is a well-reported benchmark throttled flow channel geometry, referred to as "I-channel"; this has allowed for easy optical access for which flow visualization and laser-induced fluorescence measurements allowed for validation of the developed methodology. Despite its simplicity, the I-channel geometry is found to reproduce the most characteristic flow features prevailing in high-speed flows realized in cavitating fuel injectors. Subsequently, the effect of liquid viscosity on integral mass flow, velocity profiles, vapor cavity distribution, and pressure peaks indicating locations prone to cavitation erosion is reported.

ACS Style

Marco Cristofaro; Wilfried Edelbauer; Phoevos Koukouvinis; Manolis Gavaises. Influence of Diesel Fuel Viscosity on Cavitating Throttle Flow Simulations under Erosive Operation Conditions. ACS Omega 2020, 5, 7182 -7192.

AMA Style

Marco Cristofaro, Wilfried Edelbauer, Phoevos Koukouvinis, Manolis Gavaises. Influence of Diesel Fuel Viscosity on Cavitating Throttle Flow Simulations under Erosive Operation Conditions. ACS Omega. 2020; 5 (13):7182-7192.

Chicago/Turabian Style

Marco Cristofaro; Wilfried Edelbauer; Phoevos Koukouvinis; Manolis Gavaises. 2020. "Influence of Diesel Fuel Viscosity on Cavitating Throttle Flow Simulations under Erosive Operation Conditions." ACS Omega 5, no. 13: 7182-7192.

Journal article
Published: 10 March 2020 in Journal of Computational Physics
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A methodology for modelling cavitating flows using a high-order Adaptive Mesh Refinement (AMR) approach based on the Discontinuous Galerkin method (DG) is presented. The AMR implementation used features on-the-fly adaptive mesh refinement for unstructured hybrid meshes. The specific implementation has been developed for the resolution of complex multi-scale phenomena where high accuracy p-adaptive discretisations are combined with an h-adaptive data structure. This approach accommodates the fine spatial resolution for the interface discontinuities and the shock waves observed in compressible cavitating flows. The Tait equation of state is used for the modelling of the liquid phase while an isentropic path is assumed for the liquid/vapour mixture. Second order spatial and a third order non-oscillatory temporal discretisation are used for the integration of the mass and momentum conservation equations, in order to resolve the flow structures responsible for the formation of cavitation bubbles and the resulting compression waves. Assessment of the developed methodology is performed for the one-dimensional advancement of a compressible liquid-vapour interface and the symmetric collapse of a spherical vapour bubble. Following, results obtained with the developed multi-scale modelling AMR approach has revealed a complex bubble collapse mechanism near a rigid wall, providing evidence of processes that have been unknown before due to reduced resolution and dissipative nature of past simulations. The impinging jet accompanying the collapse of a bubble near a wall, was found to induce vortical structures, which result to the formation of a secondary cavitation of a wall-attached bubble at the vicinity of the impingement jet shear layer. At the final stages of the initial bubble collapse, the impinging jet was found to penetrate the centre-line of the wall bubble inducing its partial collapse. This secondary collapse results to a rich spatial structure of shock waves, interacting with the secondary bubbles. Moreover, the calculated pressure level are found to be much higher than those reported from previous methodologies.

ACS Style

Andreas Papoutsakis; Phoevos Koukouvinis; Manolis Gavaises. Solution of cavitating compressible flows using Discontinuous Galerkin discretisation. Journal of Computational Physics 2020, 410, 109377 .

AMA Style

Andreas Papoutsakis, Phoevos Koukouvinis, Manolis Gavaises. Solution of cavitating compressible flows using Discontinuous Galerkin discretisation. Journal of Computational Physics. 2020; 410 ():109377.

Chicago/Turabian Style

Andreas Papoutsakis; Phoevos Koukouvinis; Manolis Gavaises. 2020. "Solution of cavitating compressible flows using Discontinuous Galerkin discretisation." Journal of Computational Physics 410, no. : 109377.

Journal article
Published: 01 March 2020 in Fuel
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ACS Style

Eduardo Gomez Santos; Junmei Shi; Manolis Gavaises; Celia Soteriou; Mark Winterbourn; Wolfgang Bauer. Investigation of cavitation and air entrainment during pilot injection in real-size multi-hole diesel nozzles. Fuel 2020, 263, 1 .

AMA Style

Eduardo Gomez Santos, Junmei Shi, Manolis Gavaises, Celia Soteriou, Mark Winterbourn, Wolfgang Bauer. Investigation of cavitation and air entrainment during pilot injection in real-size multi-hole diesel nozzles. Fuel. 2020; 263 ():1.

Chicago/Turabian Style

Eduardo Gomez Santos; Junmei Shi; Manolis Gavaises; Celia Soteriou; Mark Winterbourn; Wolfgang Bauer. 2020. "Investigation of cavitation and air entrainment during pilot injection in real-size multi-hole diesel nozzles." Fuel 263, no. : 1.

Journal article
Published: 23 January 2020 in Journal of Computational Physics
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A numerical methodology resolving flow complexities arising from the coexistence of both multiscale processes and flow regimes is presented. The methodology employs the compressible Navier-Stokes equations of two interpenetrating fluid media using the two-fluid formulation; this allows for compressibility and slip velocity effects to be considered. On-the-fly criteria switching between a sharp and a diffuse interface within the Eulerian-Eulerian framework along with dynamic interface sharpening is developed, based on an advanced local flow topology detection algorithm. The sharp interface regimes with dimensions larger than the grid size are resolved using the VOF method. For the dispersed flow regime, the methodology incorporates an additional transport equation for the surface-mass fraction (Σ-ϒ) for estimating the interface surface area between the two phases. To depict the advantages of the proposed multiscale two-fluid approach, a high-speed water droplet impact case has been examined and evaluated against new experimental data; these refer to a millimetre size droplet impacting a solid dry smooth surface at a velocity as high as 150 m/s, which corresponds to a Weber number of 7.6×105. Droplet splashing is followed by the formation of highly dispersed secondary cloud of droplets, with sizes ranging from 10 μm close to the wall to less than 1 μm forming at the later stages of droplet fragmentation. Additionally, under the investigated impact conditions, compressibility effects dominate the early stages of droplet splashing. A strong shock wave forms and propagates inside the droplet, where transonic Mach numbers occur; local Mach numbers up to 2.5 are observed for the expelled surrounding gas outside the droplet. Relative velocities between the two fluids are also significant; local values on the tip of the injected water film up to 5 times higher than the initial impact velocity are observed. The proposed numerical approach is found to capture relatively accurately the flow phenomena and provide additional information regarding the produced flow structure dimensions, which is not available from the experiment.

ACS Style

Georgia Nykteri; Phoevos Koukouvinis; Silvestre Roberto Gonzalez Avila; Claus-Dieter Ohl; Manolis Gavaises. A Σ-ϒ two-fluid model with dynamic local topology detection: Application to high-speed droplet impact. Journal of Computational Physics 2020, 408, 109225 .

AMA Style

Georgia Nykteri, Phoevos Koukouvinis, Silvestre Roberto Gonzalez Avila, Claus-Dieter Ohl, Manolis Gavaises. A Σ-ϒ two-fluid model with dynamic local topology detection: Application to high-speed droplet impact. Journal of Computational Physics. 2020; 408 ():109225.

Chicago/Turabian Style

Georgia Nykteri; Phoevos Koukouvinis; Silvestre Roberto Gonzalez Avila; Claus-Dieter Ohl; Manolis Gavaises. 2020. "A Σ-ϒ two-fluid model with dynamic local topology detection: Application to high-speed droplet impact." Journal of Computational Physics 408, no. : 109225.

Journal article
Published: 11 January 2020 in Fuel
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It has been recently speculated that diesel injection into a supercritical air environment at high-pressure, high-temperature (HPHT) conditions results in the diesel + air mixture transitioning into a single supercritical fluid phase. To help resolve this issue we report HPHT isothermal bubble (BP) point data from ~300 to 530 K and pressures to ~160 MPa for three different types of diesel fuels in N2 that is considered a surrogate for air. One of the diesels (Highly Paraffinic, HPF) has a larger paraffinic content relative to the others, another (Highly Aromatic, HAR) has a larger aromatic content relative to the others, and the third is a Ultra-Low Sulfur Diesel (ULSD) that resembles an unfinished commercial diesel. In addition, isothermal, density data are also reported at pressures from the BP to ~165 MPa for mixtures with N2 content ranging from ~3 to 55 wt%. The T, p range of the experimental data are extended with model calculations using the PC-SAFT equation of state (EoS) with pseudo-component parameters for diesel. Both types of diesel + N2 mixture data provide a rational basis for determining values for kij, a binary mixture parameter needed for EoS calculations. Modeling results show that the temperatures predicted for diesel + N2, supercritical fluid behavior can vary significantly depending on the method used to characterize the EoS properties of the complex diesel mixtures. Nevertheless, the predicted critical-mixture curves provide useful insight for interpreting the results from supercritical diesel spray investigations.

ACS Style

Aaron J. Rowane; Ashutosh Gupta; Manolis Gavaises; Mark A. McHugh. Experimental and modeling investigations of the phase behavior and densities of diesel + nitrogen mixtures. Fuel 2020, 265, 117027 .

AMA Style

Aaron J. Rowane, Ashutosh Gupta, Manolis Gavaises, Mark A. McHugh. Experimental and modeling investigations of the phase behavior and densities of diesel + nitrogen mixtures. Fuel. 2020; 265 ():117027.

Chicago/Turabian Style

Aaron J. Rowane; Ashutosh Gupta; Manolis Gavaises; Mark A. McHugh. 2020. "Experimental and modeling investigations of the phase behavior and densities of diesel + nitrogen mixtures." Fuel 265, no. : 117027.

Journal article
Published: 06 December 2019 in Journal of Non-Newtonian Fluid Mechanics
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Viscous oils flowing in the geometrically-complex hydraulic circuits of earth-moving machines are associated with extensive friction losses, thus reducing the fuel efficiency of the vehicles and increasing emissions. The present investigation examines the performance effectiveness of different hydraulic oils, in terms of secondary-flow suppression and pressure-drop reduction. The flow of two non-Newtonian oil compounds, containing poly(alkylmethacrylate) (PMA) and poly(ethylene-co-propylene) (OCP) polymers, respectively, have been comparatively investigated against a base, monograde liquid through Particle Image Velocimetry. An 180° curved-tube layout and a check-valve replica have been selected as representative examples of the hydraulic components comprising the hydraulic circuit. The flow conditions prevailing in the experimental cases are characterized by Reynolds-number values in the range 76–1385. Precursor viscosity measurements with shear rate along with a theoretical analysis conducted using the FENE and PTT models have verified the influence of viscoelasticity and/or shear-thinning on the liquid flow behavior. PIV results have demonstrated that viscoelastic effects setting in due to the OCP additives tend to reduce the magnitude of the secondary flow pattern, commonly known as a Dean-vortex system, arising in the curved geometry by as much as 15% on average compared to the base liquid. A similar flow behavior was also demonstrated in the valve replica layout with reference to the geometry-induced coherent vortical motion in the constriction region, where a vorticity decrease up to 38% was observed for the OCP sample. On the contrary, the flow behavior of the primarily shear-thinning PMA oil was found to be comparable to that of the base oil, hence not presenting significant flow-enhancement characteristics.

ACS Style

I.K. Karathanassis; E. Pashkovski; Milad Heidari Koochi; Hesamaldin Jadidbonab; T. Smith; Manolis Gavaises; C. Bruecker. Non-Newtonian flow of highly-viscous oils in hydraulic components. Journal of Non-Newtonian Fluid Mechanics 2019, 275, 104221 .

AMA Style

I.K. Karathanassis, E. Pashkovski, Milad Heidari Koochi, Hesamaldin Jadidbonab, T. Smith, Manolis Gavaises, C. Bruecker. Non-Newtonian flow of highly-viscous oils in hydraulic components. Journal of Non-Newtonian Fluid Mechanics. 2019; 275 ():104221.

Chicago/Turabian Style

I.K. Karathanassis; E. Pashkovski; Milad Heidari Koochi; Hesamaldin Jadidbonab; T. Smith; Manolis Gavaises; C. Bruecker. 2019. "Non-Newtonian flow of highly-viscous oils in hydraulic components." Journal of Non-Newtonian Fluid Mechanics 275, no. : 104221.

Journal article
Published: 02 November 2019 in Fluid Phase Equilibria
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In this work, we report high-pressure, high-temperature (HPHT) mixture density and T-p isopleth (bubble (BP) and dew (DP) point) data for hexadecane (HXD) + N2 and heptamethylnonane (HMN) + N2 mixtures from ~323 to 523 K and pressures to ~100 MPa. Isothermal, mixture density data for both mixtures are measured in the single–phase region from the BP pressure to ~135 MPa and with ~14–90 mol% N2. A HPHT variable-volume, windowed view cell is used for both density and phase behavior measurements using the synthetic method. Mixture densities are correlated with the modified Tait equation and isothermal BP/DP data are correlated with an Antoine-type equation to allow for reliable interpolation of the data sets. Mixture densities and BP/DP pressures are modeled with the PC-SAFT equation coupled with pure component parameters calculated with two different group contribution methods. Although fairly reasonable predictions of liquid mixture densities are obtained when the binary interaction parameter, kij, is set to zero for both HXD + N2 and HMN + N2 mixtures, a value of kij equal to at least 0.119 is needed for both systems to obtain reasonable predictions of isothermal p-x behavior.

ACS Style

Aaron J. Rowane; Manolis Gavaises; Mark A. McHugh. Vapor-liquid equilibria and mixture densities for 2,2,4,4,6,8,8-heptamethylnonane + N2 and n-hexadecane + N2 binary mixtures up to 535 K and 135 MPa. Fluid Phase Equilibria 2019, 506, 112378 .

AMA Style

Aaron J. Rowane, Manolis Gavaises, Mark A. McHugh. Vapor-liquid equilibria and mixture densities for 2,2,4,4,6,8,8-heptamethylnonane + N2 and n-hexadecane + N2 binary mixtures up to 535 K and 135 MPa. Fluid Phase Equilibria. 2019; 506 ():112378.

Chicago/Turabian Style

Aaron J. Rowane; Manolis Gavaises; Mark A. McHugh. 2019. "Vapor-liquid equilibria and mixture densities for 2,2,4,4,6,8,8-heptamethylnonane + N2 and n-hexadecane + N2 binary mixtures up to 535 K and 135 MPa." Fluid Phase Equilibria 506, no. : 112378.

Research article
Published: 01 November 2019 in Journal of Chemical & Engineering Data
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In this work, a rolling-ball viscometer/densimeter is used to measure high-pressure, high-temperature (HPHT) density and viscosity data from 298.2 to 532.6 K and pressures up to 300.0 MPa for three different diesel fuels. The densities and viscosities have combined expanded uncertainties of 0.6 and 2.5%, respectively, with a coverage factor, k = 2. Two of the diesels contain either a larger paraffinic or a larger aromatic content relative to the others and are standard engine test fuels. The third is an ultralow sulfur diesel that resembles an unfinished commercial diesel. Detailed compositional information is also reported for each diesel that provides a basis for interpreting the impact of composition on density and viscosity at high pressures. Both density and viscosity data are correlated to Tait-type equations with uncertainties of 0.6 and 4.0%, respectively. The Tait equations provide a facile means to compare observed differences in the density–pressure and viscosity–pressure profiles of the three different diesels. Density data are modeled with the perturbed-chain statistical associating fluid theory (PC-SAFT) equation of state (EoS) with pure component parameters calculated representing diesel as a single, pseudo-component only requiring average molecular weight (Mave) and hydrogen-to-carbon ratio (RH/C) as inputs. Viscosity data are modeled reasonably well using entropy scaling coupled with the PC-SAFT EoS and information on the diesel Mave and RH/C. The HPHT viscosity data are also modeled reasonably well with free volume theory with model parameters correlated to Mave and RH/C.

ACS Style

Aaron J. Rowane; Vikrant Mahesh Babu; Houman B. Rokni; Joshua D. Moore; Manolis Gavaises; Michael Wensing; Ashutosh Gupta; Mark A. McHugh. Effect of Composition, Temperature, and Pressure on the Viscosities and Densities of Three Diesel Fuels. Journal of Chemical & Engineering Data 2019, 64, 5529 -5547.

AMA Style

Aaron J. Rowane, Vikrant Mahesh Babu, Houman B. Rokni, Joshua D. Moore, Manolis Gavaises, Michael Wensing, Ashutosh Gupta, Mark A. McHugh. Effect of Composition, Temperature, and Pressure on the Viscosities and Densities of Three Diesel Fuels. Journal of Chemical & Engineering Data. 2019; 64 (12):5529-5547.

Chicago/Turabian Style

Aaron J. Rowane; Vikrant Mahesh Babu; Houman B. Rokni; Joshua D. Moore; Manolis Gavaises; Michael Wensing; Ashutosh Gupta; Mark A. McHugh. 2019. "Effect of Composition, Temperature, and Pressure on the Viscosities and Densities of Three Diesel Fuels." Journal of Chemical & Engineering Data 64, no. 12: 5529-5547.