The object of this study is to investigate the effect of Prandtl number in heat transfer phenomena of turbulent boundary layer with various external forces by means of direct numerical simulation (DNS). In this study, DNS of turbulent boundary layer with an adverse pressure gradient (APG) or a buoyancy is carried out under conditions of three different Prandtl number. In the boundary layer of thermal field which develops in the entrance region due to the boundary condition of wall, the effect of Prandtl number is clearly observed in all cases, though the thermal boundary layer is not fully developed. However, in the case of lower Prandtl number, the effects of APG or buoyancy cannot be much seen. As for the boundary layer of velocity field, it can be slightly observed the effect of Prandtl number due to the undeveloped thermal boundary layer. Therefore, DNSs of this study reveal characteristics and structures of turbulent boundary layer with various external forces in various Prandtl number.
Flow accelerated corrosion (FAC) is one of the causes for wall thinning mechanisms in carbon steel pipes. Prediction of geometry factor is the key elements for estimation of FAC. Geometry factor is defined as the ratio of wall mass transfer coefficient in the piping systems such as elbow to that in a straight pipe. In order to simulate the mass transfer coefficient, we adopt the analogy between mass transfer and heat transfer. In this study, geometry factor of the elbow pipe is computed by using large eddy simulation (LES) for various Prandtl number and Reynolds number. When Prandtl number is close to unity, geometry factor changes depending on Prandtl number. However, as Prandtl number increases sufficiently, geometry factor becomes independent of Prandtl number. As the Reynolds number increases, geometry factor of the INSS elbow decreases, with reduction of the area in which large geometry factor is observed.