Bulletin of the American Physical Society
67th Annual Meeting of the APS Division of Fluid Dynamics
Volume 59, Number 20
Sunday–Tuesday, November 23–25, 2014; San Francisco, California
Session H33: Turbulent Multiphase Flows |
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Chair: Antonio Ferrante, University of Washington Room: 2022 |
Monday, November 24, 2014 10:30AM - 10:43AM |
H33.00001: Exploration of turbulence/surface tension interaction through direct numerical simulation Jeremy McCaslin, Olivier Desjardins Two canonical multiphase flows are constructed that provide a platform for a statistical description of surface tension effects on a surrounding turbulent flow field. In the first flow, short-time behavior is studied by inserting an initially flat interface into a triply periodic box of decaying homogeneous isotropic turbulence (HIT). Long-time behavior is studied in the second flow by inserting a randomly distributed interface into forced HIT. Simulations are performed for a variety of turbulent Reynolds and Weber numbers, including an infinite Weber number (no surface tension), on mesh sizes ranging from $256^3$ to $1024^3$. The interaction between fluid inertia and the surface tension force is isolated by utilizing unity density and viscosity ratios. The probability density function of principal curvature and global interface statistics are presented and discussed, highlighting the importance of the Kolmogorov critical radius on the spatial scales of interfacial corrugations that form. A spectral analysis of energy transfer is conducted, shedding light on the role played by surface tension in this process. [Preview Abstract] |
Monday, November 24, 2014 10:43AM - 10:56AM |
H33.00002: Direct numerical simulation of interfacial wave generation in turbulent gas-liquid flows in horizontal channels Bryce Campbell, Kelli Hendrickson, Yuming Liu, Hariprasad Subramani For gas-liquid flows through pipes and channels, a flow regime (referred to as slug flow) may occur when waves form at the interface of a stratified flow and grow until they bridge the pipe diameter trapping large elongated gas bubbles within the liquid. Slug formation is often accompanied by strong nonlinear wave-wave interactions, wave breaking, and gas entrainment. This work numerically investigates the fully nonlinear interfacial evolution of a two-phase density/viscosity stratified flow through a horizontal channel. A Navier-Stokes flow solver coupled with a conservative volume-of-fluid algorithm is use to carry out high resolution three-dimensional simulations of a turbulent gas flowing over laminar (or turbulent) liquid layers. The analysis of such flows over a range of gas and liquid Reynolds numbers permits the characterization of the interfacial stresses and turbulent flow statistics allowing for the development of physics-based models that approximate the coupled interfacial-turbulent interactions and supplement the heuristic models built into existing industrial slug simulators. [Preview Abstract] |
Monday, November 24, 2014 10:56AM - 11:09AM |
H33.00003: Phase segregation in multiphase turbulent channel flow Federico Bianco, Alfredo Soldati The phase segregation of a rapidly quenched mixture (namely spinodal decomposition) is numerically investigated. A phase field approach is considered. Direct numerical simulation of the coupled Navier-Stokes and Cahn-Hilliard equations is performed with spectral accuracy and focus has been put on domain growth scaling laws, in a wide range of regimes. The numerical method has been first validated against well known results of literature, then spinodal decomposition in a turbulent bounded flow (channel flow) has been considered. As for homogeneous isotropic case, turbulent fluctuations suppress the segregation process when surface tension at the interfaces is relatively low (namely low Weber number regimes). For these regimes, segregated domains size reaches a statistically steady state due to mixing and break-up phenomena. In contrast with homogenous and isotropic turbulence, the presence of mean shear, leads to a typical domain size that show a wall-distance dependence. Finally, preliminary results on the effects to the drag forces at the wall, due to phase segregation, have been discussed. [Preview Abstract] |
Monday, November 24, 2014 11:09AM - 11:22AM |
H33.00004: Destabilization of a liquid-gas interface at supercritical pressure Guilhem Lacaze, Anthony Ruiz, Joseph Oefelein To improve efficiency, advanced propulsion systems are operated at high pressure. In many cases the pressure exceeds the critical pressure of the fuel and oxidizer, which leads to radical changes in mixing. Even though this transition is understood theoretically, many important questions remain. One is the impact of the strong interfacial density-gradient on destabilization of the shear layer. At these conditions, experimental imaging techniques fail to provide the resolution required for detailed analysis of the flow structures. In this work, we use Large Eddy Simulation to study these structures in a three-dimensional turbulent mixing layer at a Reynolds number of 500,000. A splitter separates streams of liquid oxygen and gaseous hydrogen. In the last decade, similar conditions have been studied using two-dimensional computational domains. This work is the first attempt to simulate a three-dimensional flow at these conditions with this level of resolution. Simulation results provide new insights on the destabilization processes of the liquid interface. Dynamic instabilities leading to turbulence are enhanced by inhomogeneities in density through baroclinic effects and high shear in the interfacial region. [Preview Abstract] |
Monday, November 24, 2014 11:22AM - 11:35AM |
H33.00005: Modulation of isotropic turbulence by deformable droplets of Taylor lengthscale size Michael Dodd, Antonino Ferrante We investigate the effects of finite-size deformable droplets on decaying isotropic turbulence via direct numerical simulation (DNS). DNS is performed using the two-fluid pressure-correction method by Dodd and Ferrante [\emph{J. Comput. Phys.} \textbf{273} (2014) 416--434] coupled with the volume of fluid method by Baraldi et al. [\emph{Comput. \& Fluids} \textbf{96} (2014) 322--337]. We fully-resolve the flow around and inside 3130 droplets of Taylor lengthscale size, resulting in a droplet volume fraction of 0.05. The initial Taylor lengthscale Reynolds number is Re$_{\lambda0}=75$, and the computational mesh has $1024^3$ grid points. We analyze the effects on turbulence modulation of varying the droplet- to carrier-fluid viscosity ratio ($1 \leq \mu_d/\mu_c \leq 100$) and the droplet Weber number based on the r.m.s velocity of turbulence ($0.1 \leq \mathrm{We}_{rms} \leq 5$). We discuss how varying these parameters affects the turbulence kinetic energy budget, and explain the physical mechanisms for such modulation. [Preview Abstract] |
Monday, November 24, 2014 11:35AM - 11:48AM |
H33.00006: Coalescence and break-up of large droplets in turbulent channel flow Luca Scarbolo, Federico Bianco, Alfredo Soldati The behaviour of large, deformable and coalescing droplets, released in a turbulent channel flow, has been numerically investigated with a Phase Field approach; focus has been put on droplet-droplet interactions and droplet fragmentation, enhanced by turbulent fluctuations. Two different dynamics of the dispersed phase may be observed depending on the Weber number ($We$). For small $We$ surface tension balances turbulent shear; slightly deformed droplets, transported by the carrying fluid, may only coalesce. The analysis of the droplet pair distance shows that the geometrical separation of the droplets is a leading factor for the coalescence regime determination. On the contrary, if $We$ is larger than a critical value, a dynamic equilibrium between coalescences and breakups is shown. In this regime, in line with seminal work of Hinze (1955) and recent numerical simulations of Perlekar et al. (2012), $We$ controls the critical stable diameter of droplets as well as the average distance between droplet pairs. [Preview Abstract] |
Monday, November 24, 2014 11:48AM - 12:01PM |
H33.00007: Multiphase turbulence modeling of the flow in the wake of a transom stern Kelli Hendrickson, Sankha Banerjee, Dick Yue The objective of this effort is to develop and assess multiphase turbulence closure models for incompressible highly variable density turbulent (IHVDT) flows such as the two-phase flow in the wake of a transom stern. These flows, which have an Atwood number $At=(\rho_{2} - \rho_{1})/(\rho_{2} + \rho_{1})\approx 1$, are characterized by significant turbulent mass flux for which there is little guidance in turbulence closure modeling for both the momentum and the scalar transport. In this work, high-resolution numerical simulations are performed on the wake of a canonical transom stern at large scales using conservative Volume-of-Fluid (cVOF) and implicit Large Eddy Simulation (iLES). Boundary Data Immersion Method (BDIM) is used to simulate the dry transom stern wake region at three different Froude numbers and two different effective viscosities. Analysis of the simulation results for the turbulent anisotropy, turbulent kinetic energy and turbulent mass flux budget, as well as \emph{a priori} closure model testing will be presented. [Preview Abstract] |
Monday, November 24, 2014 12:01PM - 12:14PM |
H33.00008: The Effect of Nose Shape on Water-Entry Cavity Formation Jeremy Ellis, Tadd Truscott We examine the effect of nose shape and wetting angle on the threshold velocity at which an underwater cavity will form in the wake of a slender axisymmetric rigid body. The study covers a range of Reynolds numbers ($1E4 |
Monday, November 24, 2014 12:14PM - 12:27PM |
H33.00009: Growth of gravity-capillary waves in countercurrent air/water turbulent flow Francesco Zonta, Alfredo Soldati, Miguel Onorato Mass, momentum and energy transport phenomena through a deformable air-water interface are important in many geophysical processes and industrial applications. In this study we use Direct Numerical Simulations (DNS) to explore the dynamics of countercurrent air/water flow. The motion of the air/water interface is computed by solving an advection equation for the interface vertical elevation (boundary fitted method). At each time step, the physical domain is mapped into a rectangular domain using a nonorthogonal transformation. Continuity and Navier-Stokes equations are first solved separately in each domain, then coupled (velocity/stress) at the interface. DNS are performed in the Weber, Froude and Reynolds number (We,Fr,Re) parameter space. Regardless of Re, Fr and We, the process of wave generation is driven by surface tension and follows a universal scaling ($t^{2/5}$). Later in time, the waves growth rate differs depending on the value of Fr,We: for small capillary waves, we don not observe substantial changes from $t^{2/5}$ law; for larger and longer waves (gravity waves) we observe a faster growth rate. We also derive simple phenomenological models to explain our results. [Preview Abstract] |
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