DNS Study of Effects of Suddenly-Vanishing Wall Heating in Turbulent Boundary Layer

摘要

The objective of this study is to investigate a thermal field in the turbulent boundary layer by means of direct numerical simulation (DNS), in which the wall heating has suddenly vanished in the downstream region, i.e., the wall is heated by a constant temperature condition followed by an adiabatic condition. The DNS of spatially developing boundary layers with heat transfer using the generation of turbulent inflow data method has been conducted. In this study, two types of flow field with heat transfer are investigated via DNS. One is a turbulent boundary layer along flat plate, and the other is a turbulent boundary layer over the forward-facing step. In both cases, constant temperature wall followed by adiabatic wall condition is adopted. In particular, the turbulent heat transfer phenomena around suddenly-changing wall thermal condition are revealed. In the case of forward-facing step flow, since the adiabatic wall thermal condition is applied on the step, a peculiar phenomenon is observed in comparison with the case of flat plate. DNS results clearly show the statistics and structure of turbulent heat transfer in a constant temperature wall followed by an adiabatic wall. Also, DNS clearly shows the wall-limiting behaviour of turbulence in thermal field whose index number with reference to the distance from the wall changes due to the modification of wall thermal conditions, which may be useful for the turbulence modelling.