抄録
The efficiency index η, (i.e., the ratio between heat transfer enhancement and drag increase from a smooth channel), is discussed in a channel with a delta wing-type vortex generator (VG) installed on the wall in laminar and turbulent flow. In this report, the effect of Prandtl number Pr on η is mainly discussed by use of the equation obtained in the preceding report to estimate various effects on the heat transfer enhancement. From the results of direct numerical simulation, η decreases slightly in the turbulent flow with Pr, while it increases noticeably in the laminar flow. In the laminar flow, since there is no background turbulence in the smooth channel, the fluctuation generated by VG directly enhances the heat transfer, which is greater at high Pr where the thermal diffusion effect is weakened. In addition, the increase of convective heat transfer near the wall has an important effect on the good efficiency. In the turbulent flow, on the other hand, the efficiency index slightly decreases with Pr since the turbulence generated by VG is not strongly dependent on the Prandtl number. The influence of the notched hole beneath the wing is discussed from the numerical results.
