Jong Keun Shin

Elliptic relaxation second moment closure for the turbulent heat fluxes

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.

Numerical analysis of turbulent flow and heat transfer in a square sectioned U-bend duct by elliptic-blending second moment closure

A second moment turbulence closure using the elliptic-blending equation is introduced to analyze the turbulence and heat transfer in a square sectioned U-bend duct flow. The turbulent heat flux model based on the elliptic concept satisfies the near-wall balance between viscous diffusion, viscous dissipation and temperature-pressure gradient correlation, and also has the characteristics of approaching its respective conventional high Reynolds number model far away from the wall. Also, the traditional GGDH heat flux model is compared with the present elliptic concept-based heat flux model. The turbulent heat flux models are closely linked to the ellipticblending second moment closure which is used for the prediction of Reynolds stresses. The predicted results show their reasonable agreement with experimental data for a square sectioned U-bend duct flow field adopted in the present study.

Elliptic-blending second-moment turbulence closure using an algebraic anisotropic dissipation rate tensor model

This study describes the amendment of an algebraic anisotropic dissipation rate model (ADRM) and its application to various turbulent flows to test the models performance. Modeling anisotropies for the turbulence dissipation rate is considered by an analysis of the exact transport equation for the dissipation rate tensor. The second-moment closure, which is based on the explicit amended ADRM, is proposed and it is closely linked to the elliptic-blending model that is used for the prediction of Reynolds stresses.To develop and calibrate the present elliptic-blending second-moment closure that uses the amended ADRM, firstly, the distributions of both the mean velocity and Reynolds stress are solved for flows in a fully developed non-rotating channel and a straight square duct. And then, the fully developed turbulent flows in a rotating channel and a rotating straight square duct are predicted to test the ability of the explicit amended ADRM that is combined with the rotation effect.The prediction results are directly compared with the DNS and the large-eddy simulation (LES) to assess the performance of the new model predictions and to show their reasonable agreement with the DNS and LES data for all the flow fields that are analyzed for the present study.