The influence of hole size and hence blowing rate on full coverage discrete hole wall cooling for gas turbine combustion chamber applications was investigated. Two temperature conditions were used, firstly a 750K gas temperature and 300K coolant, and secondly a realistic combustor primary zone condition of 2100K flame temperature and 700K coolant. It was shown that a large hole size resulted in a significant improvement in the overall cooling effectiveness due to a reduced film heat transfer coefficient. At high temperature the cooling effectiveness was reduced due to radiative heat transfer from the flame gases. At low coolant flow large temperature increases of the coolant occurred within the wall and approached the transpiration situation.

No abstract

The development of a test facility for investigating full coverage discrete hole wall cooling for gas turbine combustion chamber wall cooling is described. A low temperature test condition of 750K mainstream temperature and 300K coolant temperature was used to investigate the influence of coolant flow rate at a constant cross flow Mach number. Practical combustion conditions of 2100K combustor temperature and 700K coolant temperature are investigated to establish the validity of applying the low temperature results to practical conditions. For both situations a heat balance programme, taking into account the heat transfer within the wall was used to compute the film heat transfer coefficients. The mixing of the coolant air with the mainstream gases was studied through boundary layer temperature and CO2 profiles. It was shown that entrainment of hot flame gases between the injection holes resulted in a very low ‘adiabatic’ film cooling effectiveness.

The influence of hole size and hence blowing rate on full coverage discrete hole wall cooling for gas turbine combustion chamber applications was investigated. Two temperature conditions were used firstly a 750K gas temperature and 300K coolant, and secondly a realistic combustor primary zone conditions of 2100K flame temperature and 700K coolant. It was shown that a large hole size resulted in a significant improvement in the overall cooling effectiveness due to a reduced film heat transfer coefficient. At high temperature the cooling effectiveness was reduced due to radiative heat transfer from the flame gases. At low coolant flow large temperature increases of the coolant occurred within the wall and approached the transpiration situation.

Experimental measurements of the overall cooling effectiveness for full coverage discrete hole effusion cooling are presented for a wide range of practical geometries and for a density ratio between the coolant and combustion gases of 2.5. The influence of the number of holes per unit surface area was investigated at two fixed total hole areas or design pressure losses of 3% and 0.1%, at a relatively low coolant flow rate per unit surface area. Hole configurations suitable for both combustor and turbine blade cooling were investigated with hole sizes from 1.4 to 0.6mm at 3% design pressure loss and 1.3 to 3.3mm at 0.1% design pressure loss. The diameter change at a fixed pressure loss was for a constant total hole area with more holes as the size was reduced. This was shown to increase the cooling effectiveness through improved film cooling. Enlarging the hole size for a fixed number of holes and hence reducing the pressure loss for a fixed coolant mass flow was also shown to improve the cooling effectiveness through better film cooling. Major reductions in current combustor wall cooling flows were demonstrated for some full coverage effusion geometries.