Direct Numerical Simulations of Flows with Phase Change

AbstractDirect Numerical Simulations (DNS) of multiphase flows, where every continuum length and time scale are fully resolved, currently allow us to simulate flows of considerable complexity, such as the motion of several hundred bubbles or drops in turbulent flows, for sufficiently long time so that meaningful statistical quantities can be obtained. Additional physical processes such as heat transfer and phase change have also been included, although only for relatively small systems so far. After reviewing briefly recent studies of bubbles in turbulent channel flows, we discuss simulations of flows with phase change, focusing on bubble generation by boiling. The addition of new physics often results in new length and time scales that are shorter and faster than the dominant flow scales. Similarly, very small features such as thin films, filaments, and drops can also arise during coalescence and breakup of fluid blobs. The geometry of these features is usually simple, since surface tension effects are strong and inertia effects are relatively small and in isolation these features are often well described by analytical or semi-analytical models. Recent efforts to embed analytical and semi-analytical models to capture such features, in combination with direct numerical simulations of the rest of the flow, are discussed. We conclude by a short discussion of the use of DNS data for closure laws for model equations for the large scale flow

Azimuthal asymmetries in single polarized proton-proton Drell-Yan processes

We study the azimuthal asymmetries in proton-proton Drell-Yan processes with one incident proton being transversely or longitudinally polarized. We consider particularly the asymmetries contributed by the leading-twist chiral-odd quark distributions. We analyze the asymmetries with $\sin(2\phi+\phi_S)$ and $\sin(2\phi-\phi_S)$ modulations in transverse single polarized $p^\uparrow p$ Drell-Yan and $\sin2\phi$ asymmetries in longitudinal single polarized $p^\rightarrow p$ Drell-Yan at RHIC, J-PARC, E906 (Fermi Lab) and NICA (JINR). We show that the measurements of the asymmetries in those facilities can provide valuable information of the chiral-odd structure of the nucleon both in the valence and sea regions.Comment: 12 latex pages, 7 figures. Final version to appear in PR

Multiphase turbulence mechanisms identification from consistent analysis of direct numerical simulation data

Direct Numerical Simulation (DNS) serves as an irreplaceable tool to probe the complexities of multiphase flow and identify turbulent mechanisms that elude conventional experimental measurement techniques. The insights unlocked via its careful analysis can be used to guide the formulation and development of turbulence models used in multiphase computational fluid dynamics simulations of nuclear reactor applications. Here, we perform statistical analyses of DNS bubbly flow data generated by Bolotnov (Reτ= 400) and Lu–Tryggvason (Reτ= 150), examining single-point statistics of mean and turbulent liquid properties, turbulent kinetic energy budgets, and two-point correlations in space and time. Deformability of the bubble interface is shown to have a dramatic impact on the liquid turbulent stresses and energy budgets. A reduction in temporal and spatial correlations for the streamwise turbulent stress (uu) is also observed at wall-normal distances of y+= 15, y/δ = 0.5, and y/δ = 1.0. These observations motivate the need for adaptation of length and time scales for bubble-induced turbulence models and serve as guidelines for future analyses of DNS bubbly flow data. Keywords: Budget Equations, Bubble-Induced Turbulence, DNS, M&C2017, Multiphase CFDUnited States. Department of Energy. Naval Reactors Division (Rickover Fellowship Program in Nuclear Engineering

AJK2011-04004 MULTISCALE ISSUES IN DNS OF MULTIPHASE FLOWS

ABSTRACT In direct numerical simulations (DNS) of multiphase flows it is frequently found that features much smaller than the "dominant" flow scales emerge. Those features consist of thin films, filaments, drops, and boundary layers, and usually surface tension is strong so the geometry is simple. Inertia effects are also small so the flow is simple and often there is a clear separation of scales between those features and the rest of the flow. Thus it is often possible to describe the evolution of this flow by analytical models. Here we discuss two examples of the use of analytical models to account for small-scale features in DNS of multiphase flows. For the flow in the film beneath a drop sliding down a sloping wall we capture the evolution of films that are too thin to be accurately resolved using a grid that is sufficient for the rest of the flow by a thin film model. The other example is the mass transfer from a gas bubbly rising in a liquid. Since diffusion of mass is much slower than the diffusion of momentum, the mass transfer boundary layer is very thin and can be captured by a simple boundary layer model. INTRODUCTION The development of direct numerical simulations (DNS) over the last decade and a half or so is perhaps the biggest new development in studies of multiphase flows and such simulations are already starting to have a major impact. As their use has increased, it has become clear that in many situations the formation of small-scale features such as thin films or drops requires excessive (and often unachievable) resolution. Here we discuss the development of a general strategy to include multi-scale description of small-scale phenomenon in numerical simulations of the dynamics of multiphase flows. The approach is based on the observation that many small-scale features (films, threads, boundary layers

Changes of serum high mobility group box 1 and soluble triggering receptor expressed on myeloid cells-1 in patients with multiple injuries and their prognostic significance

Objective·To detect the serum levels of high mobility group box 1 (HMGB1) and soluble triggering receptor expressed on myeloid cells-1 (sTREM-1) in patients with multiple injuries at different time points, and to analyze their correlation with disease severity, complications and prognosis.Methods·Ninety-two patients with multiple injuries admitted to the Department of Emergency Medicine of the Suzhou Ninth People′s Hospital from December 2020 to December 2022 were selected. According to the injury severity scores of the patients at admission, the patients were divided into light injury group (n=24), grave injury group (n=58) and severe injury group (n=10). According to whether there was multiple organ dysfunction syndrome (MODS) after admission, the patients were divided into MODS group (n=20) and non-MODS group (n=72). According to the outcome within 28 d after trauma, the patients were divided into death group (n=13) and survival group (n=79). Inflammatory factor indicators in venous blood of patients after admission were detected. Enzyme linked immunosorbent assay (ELISA) was used to detect the serum HMGB1 and sTREM-1 levels at 24 h, 72 h and 7 d after trauma, and the differences of serum HMGB1 and sTREM-1 levels among different groups were analyzed. Multiple Logistic regression was used to analyze the influencing factors of adverse outcomes in patients with multiple injuries. The receiver operating characteristic (ROC) curve was used to evaluate the predictive value of HMGB1 and sTREM-1 for adverse outcomes.Results·The levels of HMGB1 and sTREM-1 in the grave injury and severe injury groups were significantly higher than those in the light injury group (P<0.05). The levels of HMGB1 at 72 h and 7 d, and sTREM-1 at 24 h and 72 h in the severe injury group were significantly higher than those in the grave injury group (P<0.05). There was a positive correlation between HMGB1 and sTREM-1 levels at various time points (r=0.645, r=0.942, r=0.722; all P<0.05). The levels of HMGB1 at 72 h and 7 d, and sTREM-1 at 24 h and 72 h in the MODS group were significantly higher than those in the non-MODS group (all P<0.05). The levels of HMGB1 at 72 h and 7 d, and sTREM-1 at 24 h and 72 h in the death group were significantly higher than those in the survival group (all P<0.05). Logistic regression analysis showed that HMGB1 at 7 d, admission time and hypersensitive C-reactive protein (hs-CRP) were independent factors of adverse outcomes in patients with multiple injuries (all P<0.05). The ROC curve showed that the area under the curve of HMGB1 for predicting poor prognosis at 7 days after trauma was 0.890, the sensitivity was 83.5%, and the specificity was 92.3%.Conclusion·The levels of HMGB1 and sTREM-1 are correlated with MODS and survival outcomes in patients with multiple injuries at different time points after trauma, and HMGB1 at 7 d after trauma is an independent factor affecting adverse outcomes in patients with multiple injuries

Three-dimensional parton distribution functions g1Tg_{1T} and h1L⊥h_{1L}^\perp in the polarized proton-antiproton Drell-Yan process

We present predictions of the unweighted and weighted double spin asymmetries related to the transversal helicity distribution $g_{1T}$ and the longitudinal transversity distribution $h_{1L}^\perp$, two of eight leading-twist transverse momentum dependent parton distributions (TMDs) or three-dimensional parton distribution functions (3dPDFs), in the polarized proton-antiproton Drell-Yan process at typical kinematics on the Facility for Antiproton and Ion Research (FAIR). We conclude that FAIR is ideal to access the new 3dPDFs towards a detailed picture of the nucleon structure.Comment: 6 latex pages, 5 figures, version for publication in EPJ