AERODYNAMIC ASPECTS OF ENDWALL FILM-COOLING

This paper describes an investigation of the aerodynamic aspects of en dwall film-cooling in which the flow field downstream of a large-scale low-speed linear turbine cascade has been measured The integrated los ses and locations of secondary flow features with and without endwall film-cooling have been determined for variations of both the coolant s upply pressure and injection location. Together with previous measurem ents of adiabatic film-cooling effectiveness and surface-flow visualiz ation, these results reveal the nature of the interactions between the ejected coolant and the flow in the blade passage. Measured hole mass flows and a constant static pressure mixing analysis, together with t he measured losses, allow the decomposition of the losses into three d istinct entropy generation mechanisms: loss generation within the hole , loss generation due to the mixing of the coolant with the mainstream and change in secondary loss generation in the blade passage. Results show that the loss generation within the coolant holes is substantial and that ejection into regions of low static pressure increases the l oss per unit coolant mass flow. Ejection upstream of the three-dimensi onal separation lines on the endwall changes secondary flow and reduce s its associated losses. The results show that it is necessary to take the three-dimensional nature of the endwall flow into account in the design of endwall film-cooling configurations.