Distribution of Film-Cooling Effectiveness on a Turbine Endwall Measured Using the Ammonia and Diazo Technique

Abstract

The distribution of adiabatic film-cooling effectiveness on the endwall of a large-scale low-speed linear turbine cascade has been measured using a new technique. This technique is based on an established surface-flow visualisation technique, and makes use of the reaction between ammonia gas and a diazo surface coating. A new method of calibration has been developed to relate the result of the reaction to surface concentration of coolant. Using the analogy that exists between heat and mass transfer the distribution of film-cooling effectiveness can then be determined. The complete representation of the film-cooling effectiveness distribution provided by the technique reveals the interaction between the coolant ejected from the endwall and the secondary flow in the turbine blade passage. Over- and under-cooled regions on the endwall are identified, illustrating the need to take these interactions into account in the design process. Modifications to the cooling configuration examined in this paper are proposed as a result of the application of the ammonia and diazo technique.

Heat transfer and film-cooling for the endwall of a first stage turbine vane

“…Detailed endwall film cooling results have been conducted by Friedrichs et al [24][25][26] and Knost and Thole [27,28]. The results of the studies by Friedrichs et al indicated a strong influence of the secondary flows on the film cooling and an influence of the film-cooling on the secondary flows.…”

Film cooling effectiveness distribution of cylindrical hole injections at different locations on a vane endwall

“…Region 1-4 separated by red lines have been pointed out by Friedrich et al [11] as distinct regions requiring individual cooling hole placements. However, the division of these four regions only represents the influence of horseshoe vortex, passage vortex and secondary flow on endwall cooling design.…”

Film cooling of a contoured endwall nozzle vane through fan-shaped holes

“…In the blade to blade plane, each row has a compound angle equal to the mean flow angle at mid span. This setting was the same used in the planar endwall investigation (Barigozzi et al, 2006), originally chosen in agreement with Friedrichs et al, 1996. Air at ambient temperature (or slightly heated with a density ratio DR = 0.95) was blown as cooling flow. The influence of density ratio on film cooling performance is well documented in the open literature (Hah et al, 2000).…”