The Experts below are selected from a list of 258 Experts worldwide ranked by ideXlab platform

Emily S C Ching - One of the best experts on this subject based on the ideXlab platform.

  • Thermal Boundary Layer equation for turbulent rayleigh benard convection
    Physical Review Letters, 2015
    Co-Authors: Olga Shishkina, Susanne Horn, S R Wagner, Emily S C Ching
    Abstract:

    We report a new Thermal Boundary Layer equation for turbulent Rayleigh-Benard convection for Prandtl number Pr>1 that takes into account the effect of turbulent fluctuations. These fluctuations are neglected in existing equations, which are based on steady-state and laminar assumptions. Using this new equation, we derive analytically the mean temperature profiles in two limits: (a) Pr≳1 and (b) Pr≫1. These two theoretical predictions are in excellent agreement with the results of our direct numerical simulations for Pr=4.38 (water) and Pr=2547.9 (glycerol), respectively.

Ambrish Pandey - One of the best experts on this subject based on the ideXlab platform.

Andre Thess - One of the best experts on this subject based on the ideXlab platform.

  • structure of the Thermal Boundary Layer for turbulent rayleigh benard convection of air in a long rectangular enclosure
    Physical Review E, 2007
    Co-Authors: Anna Maystrenko, Christian Resagk, Andre Thess
    Abstract:

    Measurements of the temperature distribution were performed in the upper (cold) Boundary Layer of a rectangular Rayleigh-Benard cell with aspect ratios Gamma(x) = 5 and Gamma(y) = 1 using air with Prandtl number Pr = 0.71 as the working fluid. The range of investigated Rayleigh numbers was from Ra approximately 6 x 10(7) to Ra approximately 6 x 10(8), and the measurements were taken at two different positions with the purpose of understanding the variation of the properties of the Thermal Boundary Layer along the cell. We present profiles of the mean temperature, rms temperature fluctuations, skewness, and kurtosis as a function of the distance from the cooling plate from which we extract scaling exponents and Boundary Layer thicknesses. Whereas most of these quantities are found to depend monotonically on the Rayleigh number for the peripheral measurement position, their values at the central measurement position exhibit a high degree of variability. These observations indicate that the properties of the Thermal Boundary Layer in large-aspect-ratio convection can have strong spatial variations.

Olga Shishkina - One of the best experts on this subject based on the ideXlab platform.

  • Thermal Boundary Layer equation for turbulent rayleigh benard convection
    Physical Review Letters, 2015
    Co-Authors: Olga Shishkina, Susanne Horn, S R Wagner, Emily S C Ching
    Abstract:

    We report a new Thermal Boundary Layer equation for turbulent Rayleigh-Benard convection for Prandtl number Pr>1 that takes into account the effect of turbulent fluctuations. These fluctuations are neglected in existing equations, which are based on steady-state and laminar assumptions. Using this new equation, we derive analytically the mean temperature profiles in two limits: (a) Pr≳1 and (b) Pr≫1. These two theoretical predictions are in excellent agreement with the results of our direct numerical simulations for Pr=4.38 (water) and Pr=2547.9 (glycerol), respectively.

Talal Yusaf - One of the best experts on this subject based on the ideXlab platform.

  • Simulation of Instantaneous Heat Transfer in Spark Ignition Internal Combustion Engines: Unsteady Thermal Boundary Layer Modeling
    Journal of Engineering for Gas Turbines and Power, 2010
    Co-Authors: David R. Buttsworth, Abdalla Agrira, Ray Malpress, Talal Yusaf
    Abstract:

    Simulation of internal combustion engine heat transfer using low-dimensional thermodynamic modeling often relies on quasisteady heat transfer correlations. However, unsteady Thermal Boundary Layer modeling could make a useful contribution because of the inherent unsteadiness of the internal combustion engine environment. Previous formulations of the unsteady energy equations for internal combustion engine Thermal Boundary Layer modeling appear to imply that it is necessary to adopt the restrictive assumption that isentropic processes occur in the gas external to the Thermal Boundary Layer. Such restrictions are not required and we have investigated if unsteady modeling can improve the simulation of crank-resolved heat transfer. A modest degree of success is reported for the present modeling, which relies on a constant effective turbulent Thermal conductivity. Improvement in the unsteady Thermal Boundary Layer simulations is expected in the future when the temporal and spatial variations in effective turbulent conductivity are correctly modeled.

  • Instantaneous heat flux simulation of S.I. engines: comparison of unsteady Thermal Boundary Layer modelling with experimental data
    2009 3rd International Conference on Energy and Environment (ICEE), 2009
    Co-Authors: Abdalla Agrira, David R. Buttsworth, Talal Yusaf
    Abstract:

    Due to the inherently unsteady environment of the internal combustion engine, unsteady Thermal Boundary Layer modelling could make a useful contribution. Instantaneous heat flux measurements in three different spark ignition internal combustion engines were simulated using a quasi-one dimensional engine simulation program developed in Matlab. Simulation parameters were tuned within reasonable limits until good agreement between the simulated and measured pressure was achieved. The heat flux simulated using Annand's model agreed with the experimental data to some degree, particularly when an averaging process was applied over the simulated unburned and burned zones. However, the agreement between the measured heat flux and the unsteady Thermal Boundary Layer model was less satisfactory. Implementing a model for turbulent Thermal conductivity in the unsteady Thermal Boundary Layer is expected to improve the simulated heat flux results.

  • Simulation of Instantaneous Heat Transfer in Spark Ignition Internal Combustion Engines: Unsteady Thermal Boundary Layer Modelling
    ASME 2009 Internal Combustion Engine Division Fall Technical Conference, 2009
    Co-Authors: David R. Buttsworth, Abdalla Agrira, Ray Malpress, Talal Yusaf
    Abstract:

    Simulation of internal combustion engine heat transfer using low-dimensional thermodynamic modelling often relies on quasi-steady heat transfer correlations. However, unsteady Thermal Boundary Layer modelling could make a useful contribution because of the inherent unsteadiness of the internal combustion engine environment. Previous formulations of the unsteady energy equations for internal combustion engine Thermal Boundary Layer modelling appear to imply that it is necessary to adopt the restrictive assumption that isentropic processes occur in the gas external to the Thermal Boundary Layer. Such restrictions are not required and we have investigated if unsteady modelling can improve the simulation of crank-resolved heat transfer. A modest degree of success is reported for the present modelling which relies on a constant effective turbulent Thermal conductivity. Improvement in the unsteady Thermal Boundary Layer simulations is expected in future when the temporal and spatial variation in effective turbulent conductivity is correctly modelled.