![Sample our Engineering & Technology journals, sign in here to start your access, latest two full volumes FREE to you for 14 days]({"type":"image" , "src" : "/sda/5933/TOC-Subject-Sample-2021-Engineering-Tech.jpg"})
Abstract
For modern high-efficiency gas turbines, film cooling is an essential method to protect the turbine blade from the hot gas, and the issue about how to improve the film cooling performance has attracted much attention. This study presents a new design concept used for film cooling in gas turbine to improve the overall cooling effectiveness and better decrease the metal temperature of the blade at the same time. A tree-shaped film cooling structure is considered. To validate the superiority of the proposed structure, a series of numerical simulation cases are conducted at three typical blowing ratios (i.e. 0.5, 0.764, and 0.9). The first case is a film cooling channel with a single film hole with a diameter of 5 mm and it is inclined by α = 45° relative to the mainstream direction and the other three cases are tree-shaped structures with one level, two levels and three levels of bifurcations. Moreover, the same boundary conditions and turbulence model (realizable k–ε) are adopted, and three-dimensional numerical simulations are used for all cases. The computed results show that the higher the blowing ratio, the better is the overall effectiveness downstream the film holes of the tree-shaped structures, whereas the opposite is valid for the case with a single film hole. Additionally, the overall effectiveness of the tree-shaped structures is improved more than 50% compared with Case 1 with a single film hole, and the results also demonstrate that the more levels of the structure, the lower the metal temperatures will be. Therefore, it is indicated that this research will make a contribution to a higher performance gas turbine.
Nomenclature
| Ah | = | cross-section area of film cooling hole |
| Cε1, Cε2 | = | k–ε turbulence model constants |
| d | = | diameter of circular film cooling hole |
| di | = | diameter of the ith level of tree-shaped hole |
| L | = | length of mainstream domain |
| M | = | dimensionless blowing ratio |
| mh | = | mass flow rate through the film hole |
| min,c | = | mass flow rate entering the cooling channel |
| mout,c | = | mass flow rate at outlet of the cooling channel |
| P | = | pressure |
| Pabs | = | standard atmospheric pressure |
| Pk | = | production of turbulence |
| SM | = | momentum source |
| SE | = | energy source |
| Re | = | Reynolds number |
| T | = | temperature |
| Tcw | = | wall temperature |
| Tc | = | coolant flow inlet temperature |
| Tg | = | mainstream inlet temperature |
| u | = | velocity |
| uc | = | inlet velocity of the plenum |
| ug | = | inlet velocity of the main flow channel |
| W | = | width of mainstream domain |
| Greek symbols | ||
| α | = | inclination angle of the film hole |
| ρc | = | secondary flow inlet density |
| ρg | = | mainstream inlet fluid density |
| σk and σε | = | k–ε turbulence model constants |
| μ | = | molecular (dynamic) viscosity |
| μt | = | turbulent viscosity |
| ν | = | kinematic viscosity |
| φsp,av | = | the laterally averaged cooling effectiveness |
| φ | = | overall effectiveness |
Nomenclature
| Ah | = | cross-section area of film cooling hole |
| Cε1, Cε2 | = | k–ε turbulence model constants |
| d | = | diameter of circular film cooling hole |
| di | = | diameter of the ith level of tree-shaped hole |
| L | = | length of mainstream domain |
| M | = | dimensionless blowing ratio |
| mh | = | mass flow rate through the film hole |
| min,c | = | mass flow rate entering the cooling channel |
| mout,c | = | mass flow rate at outlet of the cooling channel |
| P | = | pressure |
| Pabs | = | standard atmospheric pressure |
| Pk | = | production of turbulence |
| SM | = | momentum source |
| SE | = | energy source |
| Re | = | Reynolds number |
| T | = | temperature |
| Tcw | = | wall temperature |
| Tc | = | coolant flow inlet temperature |
| Tg | = | mainstream inlet temperature |
| u | = | velocity |
| uc | = | inlet velocity of the plenum |
| ug | = | inlet velocity of the main flow channel |
| W | = | width of mainstream domain |
| Greek symbols | ||
| α | = | inclination angle of the film hole |
| ρc | = | secondary flow inlet density |
| ρg | = | mainstream inlet fluid density |
| σk and σε | = | k–ε turbulence model constants |
| μ | = | molecular (dynamic) viscosity |
| μt | = | turbulent viscosity |
| ν | = | kinematic viscosity |
| φsp,av | = | the laterally averaged cooling effectiveness |
| φ | = | overall effectiveness |