Effects of inlet velocity profile on flow and heat transfer in the entrance region of a ribbed channel

Due to a complex channel structure, the coolant flow supplied to the internal cooling passage of a gas turbine blade shows an asymmetrical pattern rather than a fully developed or uniform distribution. In this study, the effect of the non-uniform inlet velocity profile of the coolant on the flow and heat transfer in a ribbed channel was investigated using the numerical analysis method. Four inlet velocity profiles were applied to a stationary ribbed channel and three Reynolds numbers of 10,000, 20,000 and 30,000 were considered. The hydraulic diameter of the channel was 24 mm and the rib installation angle was 60°. The rib height-to-hydraulic-diameter ratio (e/D_h) and the rib-pitch-to-height-ratio (P/e) were 0.125 and 10, respectively. Numerical analysis results showed that in the entrance region, the location and shape of the reattachment and the recirculation region were altered by the local velocity distribution caused by the different inlet velocity profiles. Therefore, the distribution and the strength of the vorticity in the channel were changed, and the local heat transfer coefficient and pressure drop in the channel were affected by the inlet velocity profile. The overall heat transfer coefficients for all cases showed similar values, however, the fully developed flow profile resulted in the highest thermal performance factor due to the lowest value of friction factor.