Abstract
ABSTRACTStrong secondary flow generated by ribbed channel and U-shaped bend is the key for forced convection performance and energy dissipation in U-shaped cooling passage. This investigation studies the coupling of nine different rib orientation and the 180-degree bend on overall friction loss and forced convection in the U-shaped passage by ANSYS CFX commercial CFD package when Re = 30000. The comprehensive evolution of secondary flow is visualized by vortex core method and colored by turbulence kinetic energy. The qualitative results show that the Nu ratio and overall pressure loss in the downstream passage (Passage 2) is highly affected by the upstream geometry. The N-type rib orientation in Passage 1 delivers more disturbance energy into Passage 2 where P-type rib orientation can reduce the momentum loss of the upstream secondary flows and pressure loss. Based on the understanding of interaction of secondary flow near the bend, modified bend geometry is proposed with 9% thermal performance gain over the existent optimized rib orientation. This investigation suggests vortex core method is a promising visualization tool for the flow control and optimization in U-shaped cooling channel with angled ribs.
Highlights
In order to achieve desirable performance at high temperature, the blades of modern gas turbines must be protected by the film cooling method and cooled internally by the compulsive convection
Homogenous wall temperature boundary is more representative for the engine blade cooling channel and adapted as the wall boundary condition in this numerical study. Both homogeneous temperature and heat flux wall boundary conditions are evaluated for the modified NP case, it is found the impact of different boundary conditions on the secondary flow structure and Nu distribution is negligible
The influence of rib orientation in a U-shaped channel on local heat transfer and friction loss has been numerically investigated by the vortex core method
Summary
In order to achieve desirable performance at high temperature, the blades of modern gas turbines must be protected by the film cooling method and cooled internally by the compulsive convection. The investigation by Lei, Li, Han, Zhang, and Moon (2013) indicates that the guide vane between the two straight channels enhances the downstream heat convection strength and reduces the friction loss in the whole passage. In order to optimize the cooling performance of multiple-pass channel, visualization of secondary flows generation and interaction is indispensable to understand the coupling effect of rib orientation and U-turn on friction loss and cooling performance. The flow structure visualization and thermal performance analysis method could provide guidance and direction to enhance forced convection and reduce energy dissipation by optimizing the secondary flow in the U-shaped channel, leading to a balance in cooling performance and friction loss
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