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ABSTRACT
Effective cooling techniques are required urgently because of high thermal loads on the blade tip region. The 180° turning bend is recognized to perform well in heat transfer on a blade tip. The thermal fluid-solid coupling models of the internal tip region with pin-fin-dimples/protrusions are established in the present paper. The local flow characteristics near the 180° turning bend, average Nu/Nu0, and the friction loss on the impingement surfaces are obtained. The local flow field near the tip surface is influenced by the 180° turning bend, where the fluid impingement, cross-flow convection and deflection of the secondary flow exist. The average Nu of dimple/protrusion structures is increased by 3.2%-31.5% comparing to that of a smooth case. After arranging pin-fin-dimple/protrusion, the average Nu is increased to 31.2%-127.3%, much higher than dimple/protrusion structures. Furthermore, the arrangement of pin-fin-dimple/protrusion brings no significant increase in the friction, which indicates an efficient heat transfer structure with little resistance.
Nomenclature
| Dh = | = | hydraulic diameter |
| Dp = | = | pin-fin diameter |
| D = | = | dimple/protrusion diameter |
| f = | = | friction factor |
| H = | = | inlet height of the channel |
| k = | = | turbulent kinetic energy |
| L1 = | = | length of the channel |
| L2 = | = | width of the channel |
| L3 = | = | clearance width of the turning bend |
| Nu = | = | Nusselt number |
| Nu/Nu0 = | = | heat transfer enhancement factor |
| Ph = | = | longitudinal spacing of dimple/protrusion |
| Pw = | = | lateral spacing of dimple/protrusion |
| q″ = | = | surface heat flux |
| Re = | = | Reynolds number |
| T = | = | temperature |
| W = | = | inlet width of the channel |
| y+ = | = | nondimensional grid spacing at the wall |
| δ = | = | dimple/protrusion depth |
| Δp = | = | pressure drop |
| ε = | = | rate of energy dissipation |
| λ = | = | fluid thermal conductivity |
| μ = | = | fluid dynamic viscosity |
| ρ = | = | fluid density |
| ω = | = | specific dissipation rate |
| Subscripts | = | |
| f = | = | fluid |
| w = | = | wall |
Nomenclature
| Dh = | = | hydraulic diameter |
| Dp = | = | pin-fin diameter |
| D = | = | dimple/protrusion diameter |
| f = | = | friction factor |
| H = | = | inlet height of the channel |
| k = | = | turbulent kinetic energy |
| L1 = | = | length of the channel |
| L2 = | = | width of the channel |
| L3 = | = | clearance width of the turning bend |
| Nu = | = | Nusselt number |
| Nu/Nu0 = | = | heat transfer enhancement factor |
| Ph = | = | longitudinal spacing of dimple/protrusion |
| Pw = | = | lateral spacing of dimple/protrusion |
| q″ = | = | surface heat flux |
| Re = | = | Reynolds number |
| T = | = | temperature |
| W = | = | inlet width of the channel |
| y+ = | = | nondimensional grid spacing at the wall |
| δ = | = | dimple/protrusion depth |
| Δp = | = | pressure drop |
| ε = | = | rate of energy dissipation |
| λ = | = | fluid thermal conductivity |
| μ = | = | fluid dynamic viscosity |
| ρ = | = | fluid density |
| ω = | = | specific dissipation rate |
| Subscripts | = | |
| f = | = | fluid |
| w = | = | wall |