RESUMO

The effects of freestream turbulence on the turbulent combined-convection boundary layer, which is created by imposing an aiding freestream to a turbulent natural-convection boundary layer along a vertical plate have been experimentally investigated. Using an active turbulence grid, the high level turbulence involved in the freestream was generated. The measured heat transfer rates and turbulent quantities show the turbulent heat transfer characteristics markedly changes with an increase in the freestream turbulence. When the freestream turbulence level is extremely low, the rapid decreases in heat transfer rate due to the transition location to turbulence moving downstream with a weak freestream occur. As the freestream turbulence level arises, the laminar region of combined convection is drastically shortened. Simultaneously, the dependence of freestream velocity on the heat transfer rate appreciably diminishes, and the heat transfer rate of combined convection increases with the freestream turbulence. In addition, it is found that turbulent characteristics in the boundary layer strongly depend on the lengthscale of freestream turbulence.