Investigation of the effect of Reynolds and Prandtl numbers on nusselt number in the flow around curved surfaces

In this study, laminar and turbulent flow were examined numerically on the cylindrical, concave and convex curved surfaces. Effects of Prandtl and Reynolds numbers on Nusselt number for these geometries were investigated. A wide range of Reynolds number between 4x104 and 4x105 was chosen for both laminar and turbulent flow. Air, NH3, mercury, freon, ethylene glycol and motor oil whose Prandtl numbers changing from 0.234 to 3431 were taken as working fluid for the analysis. A new nondimensional parameter (Rr = Rmax/Rmin) was defined changing dimensions of curvature of concave and convex surfaces, and numerical solutions were obtained for three different cases of RrFor numerical analysis ANSYS CFX 11.0 software program was used. Geometry and mesh structure of the models were created in the Workbench package program.Shear Stress Transport (SST) was chosen as turbulent model. This model was compared to standard k-? and k- ? models.Firstly, in order to verify numerical results fluid flow and heat transfer over a cylindrical surface which is widely studied in the literature was investigated for different Reynolds and Prandtl numbers, and the obtained results were compared with literature values. Secondly, the fluid flow and heat transfer over both concave and convex surfaveswhich were rarely studied in the literature were examined for different Reynolds and Prandtl number numerically.The results obtained were presented as velocity, temperature and pressure contours, local and average Nusselt numbers, drag coefficients, wake length. In addition, average Nusselt number correlations ( ) were obtained for different geometrical cases depending on Reynolds and Prandtl numbers.As a result, it is found that with the increase of Re and Pr numbers local and mean Nu numbers increase and with the increase of vertical curvature of geometry local and mean Nu numbers, drag coefficients, the length of wake region increase. It was found that the lower values of mean Nusselt number were obtained in both concave and convex surfaces for Rr = 1, while the highest values of mean Nusselt number were obtained in both concave and convex surfaces for Rr = 4. It was observed that in obtaining correlations for mean Nusselt numbers the effect of Pr number cannot be neglected. It was found that the obtained numerical results for mean Nusselt number have good a agreement for experimental results in the literature. Further, it was observed that at high Reynolds numbers for the flow over both cylindir and convex surfaces mean Nusselt numbers have two different minimum but for the concave surface no any minimum are obtained.