DNS of turbulent channel flow with inclined, continuous and segmented V-shaped turbulators

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Lucena-Jiménez, John A.
Embargoed Until
Leonardi, Stefano
College of Engineering
Department of Mechanical Engineering
Degree Level
The cooling system of the gas turbine blades plays a critical role in increasing the thermal efficiency and power output of advanced gas turbine engines. In fact, by increasing the heat transfer, the turbine blade can resist to an impinging fluid with higher temperature. Roughness elements (turbulators) are usually placed on the walls of the internal channels of a turbine blade to enhance the heat transfer. Direct numerical simulations are carried out to study the turbulent flow in a square channel with continuous V- shaped turbulators on one wall and segmented V-shaped square ribs on two walls. The geometrical parameters are k/h = 0.25, w/k = 3, 5,α = 45, 60, 75 and G/H = 0.2, where k is the rib height, w the pitch, h the channel half height, α the angle in degrees with respect to the flow direction and G the gap size (segmented V-shape only). Numerical results show that the heat transfer is 9% higher while the drag is 10% lower for the segmented V-shaped configuration (w/k = 3,α = 45), when compared with that for continuous V-shaped turbulators. The drag reduction is due to the fact that turbulators have less surface perpendicular to the flow direction, and as a consequence, the form drag decreases. The heat transfer enhancement is caused by a change in the flow structure inside the cavity due to the stream through the gap. When the turbulators are placed on one wall only, the drag and heat transfer are, respectively, 3.00 and 3.04 less than that in continuous V-shaped turbulators. By varying the angle of the turbulators with respect to the flow direction, higher heat transfer and drag is found for α = 60 (w/k = 5).

El sistema de enfriamiento de las aspas de una turbina de gas tiene un rol critico en la eficiencia termal de la misma. Si se incrementa la transferencia de calor en una turbina de gas, esta puede resistir flujo más caliente. Para incrementar la trasferencia de calor en estas aspas, se colocan rugosidades en las paredes de los canales de enfriamiento internos. Simulaciones numéricas directas fueron realizadas para estudiar el flujo turbulento en un canal con rugosidad en forma de V continua en una pared y rugosidad de forma segmentada en las dos paredes. Los parámetros del estudio son k/h = 0.25, w/k = 3, 5, α = 45, 60, 75 y G/H = 0.2, donde k es la altura del elemento, w la distancia entre los elementos, h la altura del canal y G el tamaño del hueco (solo para el elemento segmentado). Se encontró que la rugosidad segmentada en forma de V promueve un aumento de 9% en la transferencia de calor y una reducción de 10% del arrastre total cuando se compara con los valores de la rugosidad continua en forma de V. El arrastre reduce debido a la reducción de área normal al flujo y la transferencia de calor aumenta debido a cambios en la estructura de flujo dentro de la cavidad (espacio entre los elementos rugosos). Por otra parte la transferencia de calor y el arrastre es 3 veces menos cuando se colocan los elementos rugosos en una sola pared. Cuando se varía el ángulo, la mayor cantidad de transferencia y arrastre de calor ocurre para α = 45 (w/k = 5).
Lucena-Jiménez, J. A. (2011). DNS of turbulent channel flow with inclined, continuous and segmented V-shaped turbulators [Thesis]. Retrieved from