PSI - Issue 73

Vladimira Michalcova et al. / Procedia Structural Integrity 73 (2025) 106–111 Author name / Structural Integrity Procedia 00 (2025) 000–000

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2

the heat transfer in mixed velocity-thermal boundary layers. There are presented the results of testing a wall element placed on a heated plate in a climatic wind tunnel under realistic weather conditions. The paper outlines detailed measurements of velocity and temperature profiles in order to ensure a comprehensive evaluation of heat exchange mechanisms and fluid motion. Similar issues of heat transfer, particularly the boundary layer flow over heated plates, is solved in (Incropera & DeWitt, 1996). The experimental determination of Convective Heat Transfer Coefficient (CHTC) under various scenarios, including changes in the solid surface´s orientation, its roughness, the velocity and temperature of the fluid flow, and the surfaces own temperature, is used for the validation of Computational Fluid Dynamics (CFD) simulations. Deep understanding of the dynamics in convective heat transfer processes is in (Mahgoub, 2013) , there is an investigation on forced convection over flat plates within porous media composed of varying materials. Full-scale evaluations on building exteriors is done by (Zheng et al., 2024), who focus on the dynamic changes in heat flow and the impact of building porosity on heat transfer. General CHTC applications for building energy simulation tools is expanded by (Montazeri & Blocken, 2018). (Awol et al., 2020) uses CFD simulations to understand the impact of CHTCs on building energy consumption and to estimate external CHTCs in urban-like settings. (Shishkina & Wagner, 2011) modelled the influence of wall roughness on heat transfer in thermal convection. In (Blocken et al., 2009) there was applied 3D steady RANS CFD simulations of forced convective heat transfer at the facades of a low-rise cubic building are performed to determine CHTC. (Defraeye et al., 2010) used Steady Reynolds-Averaged Navier-Stokes CFD to evaluate the forced convective heat transfer at the surfaces of a cube immersed in a turbulent boundary layer, for applications in atmospheric boundary layer (ABL) wind flow around surface-mounted obstacles such as buildings. 2. Description of the task This numerical study is performed using CFD codes in the Ansys Fluent 2023 R2 software. Incompressible non isothermal flow is modelled for two variants of air velocity. The input parameters are listed in Table 1. Their values are set so that validation with experimental data is possible (Kočí et al., 2025), where the surface temperature of the wall of the heated structural element T w was measured and determined based on the conduction heat transfer through the entire heated element. During the experiment, in both variants of the air velocity, the structural element was placed on a plate heated to 80 °C and the conduction heat transfer through the structural element was monitored. The surface temperature of the wall of the warm element T wi was taken for this presented task. For this reason, T wi is different in both calculation variants (Table 1).

Table 1. Input parameters for both velocity variants.

Variant 1

Variant 2

Air velocity

u 1 = 0.82 m.s -1

2 = 2.25 m.s

-1

u

Turbulence intensity Initial air temperature

i u = 1 %

i u = 1 %

T 0 = 20.5 °C T w1 = 55.5 °C   T 01 = 35 °C 

T 0 = 20.5 °C T w2 = 49.5 °C   T 02 = 29 °C 

Surface temperature of the wall of heated element T w Initial temperature difference ∆ � = � − �

The computational mesh has dimensions of 7×1 m. The scheme is shown in Fig. 1. Due to the high gradients of the monitored quantities, the mesh is formed with a boundary layer along the entire length of the bottom wall. The heated planar structural element has a length of 0.4 m. Three points are marked on the element, which are visible in the figure. Above them, vertical velocity and temperature profiles are evaluated. Horizontal temperature profiles are also recorded at different heights above the element wall.