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A fully developed turbulent flow in a concentric annulus, Re = 10,000 , r i / r o = 0.5 , with an inner rotating cylinder in the velocity range N = U ω / U b = 0 ÷ 4 , is studied via a large-eddy simulation. Also, for comparison, simulations by steady-state, unstatiounary RANS k- ω SST (URANS), and Elliptic Blending Model (EBM) were made. The main focus of this study is on the effect of high rotation on the mean flow, turbulence statistics, and vortex structure. Distribution of the tangential velocity and the Reynolds stress tensor change their behaviour at N > 0.5 ∼ 1 . With rotation increases, the production of tangential fluctuation becomes dominant over axial ones and the position of turbulent kinetic energy maximum shifts towards the wall into the buffer zone. URANS and EBM approaches show good agreement with LES in mean flow, turbulent statistics, and integral parameters. The difference in pressure loss prediction between LES and URANS does not exceed 20%, but the average difference is about 11%. The EBM approach underestimates pressure losses up to 9% and on average not more than 5%. Vortex structures are described well by URANS. [ABSTRACT FROM AUTHOR]

Numerical simulations are performed to develop a new heat transfer coefficient correlation applicable to the gas cooler design of a trans-critical carbon dioxide air-conditioner. Thermodynamic and transport properties of the supercritical gas cooling process change dramatically and significantly vary heat transfer coefficients to be much different from those of single or two phase flows. In the present study, the elliptic blending second moment turbulent closure precisely reflecting the effects of these thermo-physical property variations on the turbulent heat transfer is employed to model the Reynolds stresses and turbulent heat fluxes in the momentum and energy equations. Computational results related to the development of turbulent heat transfer during in-duct cooling of supercritical carbon dioxide were used to establish a new heat transfer coefficient correlation that would be widely applicable to a gas cooler design involving turbulent heat transfer of supercritical carbon dioxide in square cross-sectional duct flows. [ABSTRACT FROM AUTHOR]

This study describes the development of near-wall second moment turbulent heat flux model and its application to various turbulent flows with heat transfer to test the performance of the model. The second moment models for turbulent heat fluxes based on the elliptic concept are proposed and closely linked to the elliptic blending model, which is used for the prediction of Reynolds stresses. The new models satisfy the near-wall balance between viscous diffusion, viscous dissipation and pressure-temperature gradient correlation, and also have the characteristics of approaching their respective conventional high Reynolds number model far away from the wall. On the other hand, the traditional heat flux model using the wall-normal vector expression in the wall-reflection model is tested in the present study with the new unit wall-normal vector formulation that appears in the elliptic blending model. To develop and calibrate the new heat flux models, firstly, the distributions of the mean temperature and the scalar flux in a fully developed non-rotating channel flow are solved by the present models in constant wall temperature difference boundary condition. And then, the fully developed rotating channel and square duct flows with heat transfer and the wall bounded turbulent flows with buoyancy are simulated by the new elliptic concept models to show their applicability to the complex flows. The results of prediction are directly compared to the DNS and the LES to assess the performance of new model predictions and show the reasonable agreement with the DNS and the LES data for all the flow fields adopted in the present study. [ABSTRACT FROM AUTHOR]