The interactions between turbulence and flames in premixed reacting flows are studied for a broad range of intensities by analyzing scalar (reactant mass-fraction) gradient, vorticity, strain rate fields. analysis is based on fully compressible, three-dimensional numerical simulations H2-air combustion an unconfined domain. For low intensities, flame reconstruction method the gradient shows that internal structure similar to laminar flame, while magnitudes vorticity suppressed heat release...

Large eddy simulations of the Craik‐Leibovich equations are used to assess effect misaligned Stokes drift and wind direction on Langmuir cells in ocean mixed layer. Misalignments from 0° 135° examined turbulence structures evident all cases. The is modeled using a broadband empirical spectrum, cases with without Coriolis effect, waves, an initial layer examined. expected scaling for vertical velocity variance recovered aligned adapted here adjusted projects friction (aligned stress) into...

Abstract The interactions between boundary layer turbulence, including Langmuir and submesoscale processes in the oceanic mixed are described using large-eddy simulations of spindown a temperature front presence eddies, winds, waves. solve surface-wave-averaged Boussinesq equations with Stokes drift wave forcing at resolution that is sufficiently fine to capture small-scale turbulence. A simulation without also performed for comparison. Spatial spectral properties temperature, velocity,...

Turbulent premixed combustion involves simultaneous and mutually interacting fluid, chemical, transport phenomena spanning a wide range of spatial temporal scales. Many practical devices – such as gas turbine combustors, afterburners, ramjets operate with turbulent flows that contain length time scales smaller than those associated flame propagation. This paper reviews current knowledge understanding flames at "highly turbulent" conditions, including the effects turbulence on turbulence. At...

Abstract Ocean tracers such as carbon dioxide, nutrients, plankton, and oil advect, diffuse, react primarily in the oceanic mixed layer where air‐sea gas exchange occurs light is plentiful for photosynthesis. There can be substantial heterogeneity spatial distributions of these due to turbulent stirring, particularly submesoscale range partly geostrophic fronts eddies small‐scale three‐dimensional turbulence are simultaneously active. In this study, a large eddy simulation spanning...

Spectral kinetic energy transfer by advective processes in turbulent premixed reacting flows is examined using data from a direct numerical simulation of statistically planar flame. Two-dimensional turbulence kinetic-energy spectra conditioned on the planar-averaged reactant mass fraction are computed through flame brush and variations connected to terms spectral transport equation. Conditional show that small-scale motions suppressed burnt combustion products, while content mean flow...

Abstract. Using adjoint optimization and three-dimensional steady-state Reynolds-averaged Navier–Stokes (RANS) simulations, we present a new gradient-based approach for optimally siting wind turbines within utility-scale plants. By solving the equations of flow model, gradients needed are found at cost that is independent number control variables, thereby permitting large plants with many turbine locations. Moreover, compared to common superimposing prescribed wake deficits onto linearized...

Abstract This paper provides a detailed analysis of momentum, angular vorticity, and energy budgets submesoscale front undergoing frontogenesis driven by an upper‐ocean, eddy field in Large Eddy Simulation (LES). The LES solves the wave‐averaged, or Craik‐Leibovich, equations order to account for Stokes forces that result from interactions between nonbreaking surface waves currents, resolves both eddies boundary layer turbulence down 4.9 m × 1.25 grid scales. It is found differs traditional...

Local and nonlocal contributions to the total strain rate tensor S(ij) at any point x in a flow are formulated from an expansion of vorticity field local spherical neighborhood radius R centered on x. The resulting exact expression allows (background) S(ij)(B)(x) be obtained S(ij)(x). In turbulent flows, where naturally concentrates into relatively compact structures, this alignment with most extensional principal axis background evaluated. vicinity vortical structure, required corresponding...

Intermittency in premixed reacting flows is studied using numerical simulations of flames at a range turbulence intensities. The are modeled simplified reaction mechanism that represents stoichiometric H2-air mixture. associated with high probabilities large fluctuations flow quantities, and these can have substantial effects on the evolution structure flames. characterized here probability density functions (pdfs) moments local enstrophy, pseudo-dissipation rate (strain magnitude), scalar...

Abstract. Turbines in wind power plants experience significant losses when wakes from upstream turbines affect the energy production of downstream turbines. A promising plant-level control strategy to reduce these is wake steering, where are yawed direct away However, there uncertainties many aspects steering problem. For example, infield sensors do not give perfect information, and inflow plant complex difficult forecast with available even over short time periods. Here, we formulate solve...

A direct Biot-Savart integration is used to decompose the strain rate into its local and nonlocal constituents, allowing vorticity alignment with eigenvectors be investigated. These tensor constituents are evaluated in a turbulent flow using data from highly resolved numerical simulations. While aligns preferentially intermediate eigenvector of combined rate, as has been observed previously, present results, for first time, clearly show that most extensional rate. This, turn, reveals...

Natural climate variations in the United States wind resource are assessed by using cyclostationary empirical orthogonal functions (CSEOFs) to decompose reanalysis data. Compared approaches that average signals or assume stationarity of on interannual time scales, CSEOF analysis isolates variability associated with specific oscillations, as well their modulation from year year. Contributions speed modulated annual cycle (MAC) and El Niño-Southern Oscillation (ENSO) quantified, information...

A three-dimensional wavelet multi-resolution analysis of direct numerical simulations a turbulent premixed flame is performed in order to investigate the spatially localized spectral transfer kinetic energy across scales vicinity front. formulation developed that addresses compressible dynamics space. The basis enables examination local spectra, along with inter-scale and subfilter-scale (SFS) cumulative fluxes scale cutoff, all quantities being available either unconditioned or conditioned...

The effects of initial stratification on single-mode Rayleigh-Taylor instability are examined using fully compressible wavelet-based direct numerical simulations. Such instabilities widespread and found in inertial confinement fusion, supernova ignition fronts, x-ray bursts, geophysics.

Abstract Combustor turbulence in a gas turbine engine greatly influences the efficiency of downstream high pressure stage. Here we use multi-fidelity computational optimization methodology to modify geometry non-reacting combustor simulator such that properties are optimized at combustor-turbine interface. We size, orientation, and positioning primary dilution jets minimize intensity exit while demonstrating negligible or favorable changes loss mixing characteristics combustor. The is...

From consideration of turbulence anisotropy dynamics due to spatial or temporal variations in the mean strain rate, a new Reynolds stress closure for nonequilibrium effects turbulent flows has been developed. This closure, formally derived from transport equation, results an effective rate tensor that accounts history which subjected. In contrast prior models have sought address via changes eddy viscosity, present approach fundamental relation between and tensor. The time-local form can be...

Abstract Local dissipation-scale distributions and high-order statistics of the energy dissipation rate are examined in turbulent channel flow using very high-resolution direct numerical simulations at Reynolds numbers ${\mathit{Re}}_{\tau } = 180$ , $381$ $590$ . For sufficiently large $ moments bulk agree with those homogeneous isotropic turbulence, including only a weak Reynolds-number dependence both finest largest scales. Systematic, but -independent, variations arise as wall is...

Abstract The effects of climate oscillations on spatial and temporal variations in wildland fire potential the continental U.S. are examined from 1979 to 2015 using cyclostationary empirical orthogonal functions (CSEOFs). CSEOF analysis isolates associated with modulated annual cycle El Niño–Southern Oscillation (ENSO). results show that, early summer, is reduced southwest during Niño but increased northwest, opposite trends for La Niña. In late southwest. Relative mean, largest impacts ENSO...

A new approach to turbulence closure is presented that eliminates the need specify a predefined model and instead provides for fully adaptive, self-optimizing, autonomic closures. The in sense simulation itself determines optimal local, instantaneous relation between any unclosed term resolved quantities through solution of nonlinear, nonparametric system identification problem. This allows freely adapt varying nonlocal, nonequilibrium, other characteristics flow. Even simple implementation...