Numerical simulations on flow and heat transfer in turbine cascade and tip clearance over shrouded blades.

摘要

A three-dimensional solver based on AF (Approximate Factorization) method and Baldwin-Lomax algebraic turbulence model is developed to deal with the three-dimensional transonic turbulent flow in a turbine cascade. The calculation results show that: (1) there are complex three-dimensional vortices existing in the wake flow downstream of the blade trailing edge, which interact with the main flow to dissipate the secondary flow and with the boundary layer on the end-wall to result in high heat transfer region on the end-wall; (2) the Baldwin-Lomax turbulence model lacks the ability to predict the heat transfer in the transition and laminar region, but valid in the turbulent region; (3) the upward pressure gradient near the end-wall on the suction side and the pressure difference between the pressure side and the suction side are the “driving forces” for the secondary flow to emerge and develop in the passage; the secondary flows interact with the boundary layer on the end-wall and enhance the heat transfer in the local regions; the secondary flow dissipation mechanism in transonic flow is different from that in subsonic flow; (4) it is possible to control the secondary flow by an appropriate blade geometric design and end-wall contouring.; In order to minimize the blade tip clearance loss, a new kind of labyrinth seal, the staggered labyrinth seal with case recessing, is developed. The presented staggered labyrinth seal is found through the study to be more efficient than the typical one. The staggered labyrinth seal arrangement can reduce the highest load imposed on seal tooth. The numerical simulation results show that: the leakage flow-rate is dominated the pressure drop and the minimum clearance space in the passage; the space between two seal teeth has a little influence on the total mass flow rate but influences the flow pattern and the dissipation mechanism in the seal space; the leakage flow rate increases as the wall temperature decreases; swirl flow has little effect on the change of the flow pattern in the axial-radial plane, but affects the turbulence dissipation in the channel.