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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operating temperature [K]. In the other equations, the density is treated as a constant value of the operating density. ( � ) ∙ � ∙ ( � ) (3) The Boussinsq approximation is given by the equation (4): � ∙ (1 − ) (4) This approximation is used for the solution of the equation (3). It can be considered accurate if , which is fulfilled in the given problem. The boundary conditions for numerical simulations are presented in Table 2.

Table 2. Boundary conditions.

Boundary conditions

Type of boundary area

Velocity inlet: T 0 = 20.5 °C, minimal i u = 1 %, constant velocity profile, u 1 = 0.82 m.s -1 , u

Computational area entry

2 = 2.25 m.s

-1

Computational area exit

Pressure outlet, T 0

Bottom, outside of the heated structural element Bottom, wall of the heated structural element

Wall: no slip on the wall, T 0 = 20.5 °C

Wall: no slip on the wall, T w1 = 55.5 °C, T w2 = 49.5 °C Symmetry: no friction on side walls, T 0 = 20.5 °C

Top edge Fluid (air)

Incompressible non-isothermal flow

4. Results and discussion Horizontal temperature profiles at various low distances above the structural element are shown in Fig. 2-3. Since the surface temperature of the sample wall differs in both variants, the horizontal temperature profiles are expressed dimensionlessly as a proportion ∆ � ⁄ , where: ∆ � − is the current temperature difference between the wall of the heated element T w and the air T [°C], ∆ � = � − � is the initial temperature difference between the wall of the heated T w element and the initial air temperature � [°C].

Fig. 2. u 1 = 0.82 m.s -1 , horizontal temperature profiles above a heated structural element expressed by a dimensionless fraction ∆ � ⁄ . Since the influence of buoyancy forces increases at lower speeds, more significant changes in the temperature field occur. The calculation confirmed this fact. The dimensionless expression of the temperature difference in variant 1 is lower (the air heats up more) and its more uniform distribution between the monitored layers is also evident compared to variant 2. It is also worth mentioning the demonstration of the influence of velocity on the effect of buoyancy forces.