Film Cooling With Compound Angle Holes: Adiabatic Effectiveness

Abstract

The introduction of Lean Burn concept as basic Low-N O x scheme for future aero-engines is heavily affecting the aero-thermal design of combustors. A great amount of air is admitted through the injection system with relevant swirl components, producing very complex flow structures (recirculations, vortex breakdown) for flame stabilization. As a consequence a reduced quantity of air is available for liner cooling, pushing the adoption of high effectiveness cooling schemes. Effusion cooling represents one of the first choices due to its low weight and a relatively easy manufacturability. Liner metal temperature is kept low by the combined protective effect of coolant film, heat removal inside holes and an improved cold-side convection. In lean burn systems the evolution of film protection can be heavily influenced by the swirl flow interaction with combustor walls. The subject of this work is to investigate the effects of the realistic flow field of a lean burn injector on the adiabatic film cooling effectiveness on an effusion cooled combustor liner. A dedicated three-sector rig was designed with the aim of measuring film effectiveness with Pressure Sensitive Paint technique. Three effusion cooling geometries with different inclination angles were tested at various levels of pressure drops across the perforation, resulting in different blowing ratio values. It was also taken into consideration several flow rate levels of starter film realized by spent dome cooling air, injected through a dedicated plain slot. The analysis of film effectiveness measurements were supported by flow field investigation in the near wall region carried out by means of Particle Image Velocimetry. Results pointed out the relevant impact of combustor flow field on the adiabatic film cooling effectiveness as well as a significant role of the inclination angle, recommending a careful revision of standard design practices based on one dimensional flow assumption and suggesting possible holes arrangement optimization.

Internal Wall-Jet Film Cooling with Straight Cylindrical Holes

“…Such changes with blowing ratio convince possibilities of different flow patterns of the coolant immediately downstream of injection. These results are qualitatively consistent with the observations made by Schmidt et al [37] and Bell et al [38] for compound angle coolant injection on a flat plate.…”

Film Cooling Effectiveness From a Single Scaled-Up Fan-Shaped Hole: A CFD Simulation of Adiabatic and Conjugate Heat Transfer Models

“…Schmidt et al [4] and Sen et al [5] presented two companion papers in which the effect of adding a 15° forward diffusion exit to a streamwise oriented hole was investigated. They found that the exit diffused film hole demonstrated better spread of adiabatic effectiveness than the cylindrical counterpart.…”

Turbine Blade Film Cooling Using PSP Technique

“…Compound angled configurations are also found to resist to lift-off more than simple angled configurations, as reported by Ligrani et al (1994b) and Ekkad et al (1997). Using shaped film cooling holes (with a fan shaped diffuser on the blade surface) results in a smaller tendency to lift off due to the reduction in momentum due to the increase cross sectional area for the coolant, as reported by Schmidt et al (1996) and Gritsch et al (1998).…”