Bonilla-Alicea, Ricardo J.

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    Reynolds averaged and large eddy simulations of the turbulent flow in a channel with inclined and V-shaped turbulators on the walls
    (2012-07) Bonilla-Alicea, Ricardo J.; Leonardi, Stefano; College of Engineering; Díaz, Rubén; Gutierrez, Gustavo; Department of Mechanical Engineering; Colón, Silvestre
    Turbine inlet air temperatures may exceed the melting points of the turbine blade material. Proper cooling processes increase turbine blade durability as well as the engine efficiency by allowing higher combustion temperatures and compression ratios. Artificial roughness elements are placed inside the cooling ducts of turbine blades to enhance the heat transfer characteristics of the cooling duct, making the turbine blade more resistant to incoming hot gases. Reynolds Averaged Navier Stokes (RANS) are carried out to study the turbulent flow inside a square channel with transverse ribs and V-shaped Turbulators on both walls. A parametric study has been performed varying the inclination angle of the ribs α = 900, 750, 600, and 450 degrees with respect to the streamwise flow direction while the pitch to height ratio remains constant at p/e=15. The height of the ribs is e/h=0.1 where h is the channel’s half height. The objective is to find the configuration leading to the maximum heat transfer with the lowest drag. Transverse square bars on the wall induce a spanwise vortex while for V-shaped turbulators a vortex inclined with respect to the streamwise direction can be observed. These vortices increase the heat and mass transfer between the wall and the overlying flow without a significant increase in wetted area. The main mechanism is based on two strong ejections at the sidewalls of the channel and one inward stream of fluid at the center of the channel. This mechanism redistributes the kinetic energy in the spanwise and normal directions, determining a more isotropic flow. The roughness on the wall increases the total drag of the square channel due to the pressure drag component. Most of the drag is due to the pressure contribution, the friction being negligible. The V-shaped turbulators present a higher form drag when compared to the transverse ribs because of the increase pressure difference(∆P) between the leading and trailing edge of the roughness geometry. Large Eddy Simulation (LES) of the case presenting the maximum heat transfer is being performed. The results obtained with the LES simulation showed an increase in the heat transfer characteristics of the channel when compared with the RANS simulations.