Direct Numerical Simulation (DNS) of fully developed velocity and passive scalar temperature fields in two-dimensional turbulent channel flow was coupled with the unsteady conduction in the idealized slab heated with constant volumetric heat source. Similar geometry can be found in some experimental nuclear reactors with fuel in the form of parallel slabs. Beside streamwise and spanwise directions, periodicity of the computational domain was assumed also in the wall-normal direction. Simulations were performed at constant friction Reynolds number 180 and Prandtl number 1, and with various geometrical and material properties of the heated slab. Due to the periodicity, the same Reynolds number and the same flow direction is assumed on both sides of the slab. Results of the simulations predict penetration of the turbulent temperature fluctuations into the solid wall. For thick slab, temperature fluctuations from both sides of the slab do not interfere. As the slab gets thinner, fluctuations from both sides interfere and tend to a finite value as the slab thickness limits toward zero. However, due to the non-coherent turbulent flows on each side of the slab, thermal fluctuations of the zero-thickness slab are actually lower than in the case of the zero-thickness wall heated by the same turbulent flow on one side but cooled by the constant heat flux boundary condition on the other side. Results of the present study can serve as benchmarks for less accurate mathematical models used to predict temperature fluctuations and thermal fatigue in realistic conditions.
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