Flow features and thermal stress evaluation in turbulent mixing flows

摘要

The present paper depicts a numerical study of flow and thermal features in T-junctions with circular cross-section. The numerical simulation is based on the experimental validated wall-resolved Large-Eddy Simulation method. The Reynolds number in the warm main pipe flow covers a range of Re_m = 27000 to Re_m= 134000 and the temperature difference of the mixing fluids is up to △T = 249 K. The location of maximum fluctuations does not change due to a nearly identical flow pattern type in all simulations. This condition allows the investigation of the flow evolution, mixing process and heat transfer for the same thermal flow pattern type. The numerical simulations are coupled with the heat conduction in the structure due to the thermal fluid-structure-interaction. Further, this study offers a deeper insight into the hidden physics of turbulent mixing flows and the transport as well as damping of thermal fluctuations in the near-wall fluid/solid region. Our study considers also thermal stress analysis by Finite-Element Method by utilizing the wall temperature distribution of previously performed numerical simulations. Therefore, fatigue damage is evaluated based on the stress received from the Finite-Element analysis. The results show that the highest Reynolds number case corresponds to the highest flux intensity and turbulence. This affects the flow field and the thermal features in the core flow and the transport of fluctuations close to the wall. The locations with peak fluctuation intensity in the fluid generates also high fluctuating temperature areas in the structure. The finite element analysis demonstrates that the highest temperature difference case leads to the highest alternating stress intensity which has potential for thermal fatigue. The generated maximal alternating stress is coupled with the flow conditions of the mixing fluids. With an increasing Reynolds number of the main and branch pipe flow as well as temperature difference raises also the resulting maximum alternating stress intensity.