2D and 3D numerical investigation of flow and combined natural-forced convection from a triangular cylinder with radius corners in cross flow

In this study, two and three dimensional numerical investigation of unsteady mixed (forced and free) convection heat transfer and fluid flow over a horizontal triangular cylinder with rounded corners is carried out. The cylinders are equilateral triangles side length D are equilateral in shape, and the fluid flow is assumed to be laminar (50≤Re≤250) and Richardson numbers are varied in the range 0≤Ri≤2. The effects of fluid type, corner rounding and cylinder configurations on flow and heat transfer are investigated. Three cases of corner rounding (radius ratios) are investigated; r=d/D=0.05, 0.1 and 0.15. Three cylinder configurations are examined; a triangular cylinder sitting on its flat surface (Case 1, =0), a flat face of the cylinder facing the flow (Case 2, =30), and a corner of the cylinder facing the flow (Case 3, =90). Air (Pr=0.7) and water (Pr=7), which have a wide range of applications, were preferred as working fluids. The numerical solution is carried out using Fluent 2020® software, based on the finite volume method. Validation and comparison with the sharp-edged cylinder data in the literature are made for Cases 1 and 2 in terms of flow, for Case 3 in terms of flow and heat transfer. The effects of rounding ratio, cylinder configurations, Prandtl, Reynolds and Richardson numbers on quantitative parameters such as resistance/lift coefficients, Strouhal and mean Nusselt numbers are presented in tables and graphs. The qualitative results such as development of the thermal and velocity boundary layers, development of the wakes at the rear of the cylinder are visualized in terms of isotherms, isovorticity and streamlines plots. It is observed that the orientation of cylinders (position), corner rounding and the fluid type do have effect on the flow and heat transfer characteristics. It is found that while corner rounding does not have significant effect on the Strouhal and mean Nusselt numbers, the drag and the lift coefficients can be significantly altered due to corner rounding and cylinder orientations. The flow is two-dimensional until a certain Reynolds number, then it passes into a three-dimensional flow. Since this value is around Re=180 for Case 1 and r=0.15, three-dimensional analyzes are performed for Re=200 and 250 values and the results are given comparatively with two-dimensional flow analyses. It is seen that 3D and 2D results diverge as the Reynolds number increases. Using nonlinear regression, correlations with r2>0.999 for flow and heat transfer characteristics were developed.