The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform

Keqing Xia - One of the best experts on this subject based on the ideXlab platform.

  • viscous boundary layer properties in turbulent thermal convection in a cylindrical cell the effect of cell tilting
    Journal of Fluid Mechanics, 2013
    Co-Authors: Ping Wei, Keqing Xia
    Abstract:

    with Re decreases with . The normalized meanHorizontal Velocity profiles measured at the same tilt angle but with different Ra arefound to have an invariant shape. However, for different tilt angles, the shape of thenormalized profiles is different. It is also found that the Reynolds number Re based onthe maximum mean Horizontal Velocity scales with Ra as Re˘Ra

  • viscous boundary layer properties in turbulent thermal convection in a cylindrical cell the effect of cell tilting
    arXiv: Fluid Dynamics, 2012
    Co-Authors: Ping Wei, Keqing Xia
    Abstract:

    We report an experimental study of the properties of the Velocity boundary layer in turbulent Rayleigh-B\'{e}nard convection in a cylindrical cell. The measurements were made at Rayleigh numbers $Ra$ in the range $2.8\times10^{8}Reynolds number $Re$ with an exponent close to that for a Prandtl-Blasius laminar boundary layer, i.e. $\delta_{v} \sim Re^{-0.46\pm0.03}$. For larger tilt angles, the scaling exponent of $\delta_{v}$ with $Re$ decreases with $\theta$. The normalized mean Horizontal Velocity profiles measured at the same tilt angle but with different $Ra$ are found to have an invariant shape. But for different tilt angles, the shape of the normalized profiles is different. It is also found that the Reynolds number $Re$ based on the maximum mean Horizontal Velocity scales with $Ra$ as $Re \sim Ra^{0.43}$ and the Reynolds number $Re_{\sigma}$ based on the maximum rms Velocity scales with $Ra$ as $Re_{\sigma} \sim Ra^{0.55}$, with both exponents do not seem to depend on the tilt angle $\theta$. We also examined the dynamical scaling method proposed bys Zhou and Xia [Phys. Rev. Lett. 104, 104301 (2010)] and found that in both the laboratory and the dynamical frames the mean Velocity profiles show deviations from the theoretical Prandtl-Blasius profile, with the deviations increase with $Ra$. But profiles obtained from dynamical scaling in general have better agreement with the theoretical profile. It is also found that the effectiveness of this method appears to be independent of $Ra$.

Manabu Kanda - One of the best experts on this subject based on the ideXlab platform.

  • organized structure of active turbulence over an array of cubes within the logarithmic layer of atmospheric flow
    Boundary-Layer Meteorology, 2010
    Co-Authors: Atsushi Inagaki, Manabu Kanda
    Abstract:

    We investigate the coherent structure of atmosphere turbulence over very large roughness within a fully rough, high Reynolds number turbulent flow. The Horizontal distributions of coherent turbulence were determined by multipoint measurements of Velocity fluctuations using sonic anemometers in a comprehensive outdoor scale model experiment for urban climate (COSMO). COSMO is made up of 512 cubical obstacles, each 1.5 m on a side, arranged in a rectangular pattern on a flat 50 m × 100 m concrete plate. A total of 15 sets of sonic anemometers were aligned Horizontally within the logarithmic layer above this site. The Velocity fluctuations observed in COSMO were decomposed into active and inactive contributions by applying a spatial-filtering method, and which used a simple moving average along the spanwise direction of the predominant flow as a filter function. The size of the filter should be between the sizes of the active and inactive fluctuations. This method potentially eliminates the considerable portion of low frequency modes included in the Horizontal Velocity fluctuation, while preserving well the Reynolds stress. The structural characteristics of the active turbulence were qualitatively similar to those measured over various surface configurations. Overall, the observed structures of the active turbulence are composed of very large streaks of low momentum fluid elongated in the streamwise direction with some sub-structures included in the streaks. The sub-structures were the main cause of the ejections, which accompany Horizontal vortices. The active motion, including the streaky structures, did not reproduce the lower frequency peak of the bi-modal distribution of the Horizontal Velocity spectra, but reproduced the higher frequency mode that robustly follows inner-layer similarity (i.e. Monin–Obukhov similarity).

  • turbulent flow similarity over an array of cubes in near neutrally stratified atmospheric flow
    Journal of Fluid Mechanics, 2008
    Co-Authors: Atsushi Inagaki, Manabu Kanda
    Abstract:

    The main objective of this study is to examine the robustness of the inner-layer scaling similarity of near-wall turbulence. The turbulent boundary layer of interest is over a very rough surface with a very high Reynolds number and significant outer-layer disturbances. This is not consistent with the canonical turbulent flows studied in laboratories, but it is common in urban areas. The investigation was conducted using the comprehensive outdoor scale model (COSMO) facility. COSMO is composed of a regular array of 1.5 m concrete cubes on a 50 x 100 m 2 flat concrete base. This unique facility allows us to obtain the turbulent dataset within the vertical constant stress region under near-neutral stratification at high Reynolds numbers. The turbulent spectra and the standard deviation of Velocity fluctuations from COSMO were compared with the values obtained over rural and urban surfaces, and in wind-tunnel experiments. The results confirmed that the inner-layer scaling similarity was robust for the wall-normal fluctuations and the Reynolds stress, independent of the roughness types and the outer-layer conditions. The inner-layer scaling similarity failed for the Horizontal Velocity fluctuations owing to the influence of the outer-layer disturbance. The relative importance of outer-layer turbulence to inner-layer-scale eddies in the Horizontal Velocity fluctuations was successfully quantified in terms of the roughness scale normalized by the outer-layer scale.

John Y N Cho - One of the best experts on this subject based on the ideXlab platform.

Erik Lindborg - One of the best experts on this subject based on the ideXlab platform.

Edriss S Titi - One of the best experts on this subject based on the ideXlab platform.

  • global well posedness of the 3d primitive equations with Horizontal viscosity and vertical diffusivity
    Physica D: Nonlinear Phenomena, 2020
    Co-Authors: Chongsheng Cao, Edriss S Titi
    Abstract:

    Abstract In this paper, we consider the 3D primitive equations of oceanic and atmospheric dynamics with only Horizontal eddy viscosities in the Horizontal momentum equations and only vertical diffusivity in the temperature equation. Global well-posedness of strong solutions is established for any initial data such that the initial Horizontal Velocity v 0 ∈ H 2 ( Ω ) and the initial temperature T 0 ∈ H 1 ( Ω ) ∩ L ∞ ( Ω ) with ∇ H T 0 ∈ L q ( Ω ) , for some q ∈ ( 2 , ∞ ) . Moreover, the strong solutions enjoy correspondingly more regularities if the initial temperature belongs to H 2 ( Ω ) . The main difficulties are the absence of the vertical viscosity and the lack of the Horizontal diffusivity, which, interact with each other, thus causing the “ mismatching ” of regularities between the Horizontal momentum and temperature equations. To handle this “mismatching” of regularities, we introduce several auxiliary functions, i.e., η , θ , φ , and ψ in the paper, which are the Horizontal curls or some appropriate combinations of the temperature with the Horizontal divergences of the Horizontal Velocity v or its vertical derivative ∂ z v . To overcome the difficulties caused by the absence of the Horizontal diffusivity, which leads to the requirement of some L t 1 ( W x 1 , ∞ ) -type a priori estimates on v , we decompose the Velocity into the “temperature-independent” and temperature-dependent parts and deal with them in different ways, by using the logarithmic Sobolev inequalities of the Brezis–Gallouet–Wainger and Beale–Kato–Majda types, respectively. Specifically, a logarithmic Sobolev inequality of the limiting type, introduced in our previous work (Cao et al., 2016), is used, and a new logarithmic type Gronwall inequality is exploited.

  • continuous data assimilation for a 2d benard convection system through Horizontal Velocity measurements alone
    Journal of Nonlinear Science, 2017
    Co-Authors: Aseel Farhat, Evelyn Lunasin, Edriss S Titi
    Abstract:

    In this paper we propose a continuous data assimilation (downscaling) algorithm for a two-dimensional Benard convection problem. Specifically we consider the two-dimensional Boussinesq system of a layer of incompressible fluid between two solid Horizontal walls, with no-normal flow and stress-free boundary conditions on the walls, and the fluid is heated from the bottom and cooled from the top. In this algorithm, we incorporate the observables as a feedback (nudging) term in the evolution equation of the Horizontal Velocity. We show that under an appropriate choice of the nudging parameter and the size of the spatial coarse mesh observables, and under the assumption that the observed data are error free, the solution of the proposed algorithm converges at an exponential rate, asymptotically in time, to the unique exact unknown reference solution of the original system, associated with the observed data on the Horizontal component of the Velocity.

  • continuous data assimilation for a 2d b enard convection system through Horizontal Velocity measurements alone
    arXiv: Analysis of PDEs, 2016
    Co-Authors: Aseel Farhat, Evelyn Lunasin, Edriss S Titi
    Abstract:

    In this paper we propose a continuous data assimilation (downscaling) algorithm for a two-dimensional Benard convection problem. Specifically we consider the two-dimensional Boussinesq system of a layer of incompressible fluid between two solid Horizontal walls, with no-normal flow and stress free boundary condition on the walls, and fluid is heated from the bottom and cooled from the top. In this algorithm, we incorporate the observables as a feedback (nudging) term in the evolution equation of the Horizontal Velocity. We show that under an appropriate choice of the nudging parameter and the size of the spatial coarse mesh observables, and under the assumption that the observed data is error free, the solution of the proposed algorithm converges at an exponential rate, asymptotically in time, to the unique exact unknown reference solution of the original system, associated with the observed data on the Horizontal component of the Velocity. Moreover, we note that in the case where the observational measurements are not error free, one can estimate the error between the solution of the algorithm and the exact reference solution of the system in terms of the error in the measurements.