Combustor Effusion Cooling Multiparameter Aerothermal Numerical Analysis
Authors: Savary Nicolas , Cottin Guillaume , Herve Robin 
Published: September 2016

The solid temperature prediction is one of the most widespread type of modelization used in the industry. One reading this study might wonder why there would be readymade solutions for many industries and why they would not fit for combustor wall temperatures calculation. The specificity of state-of-the-art and future combustors is the massive use of effusion cooling for its thermal management. Effusion cooling consists of drilling thousands of sub millimetric holes into the combustor wall in order to cool it from inside the holes and create a cooling film inside the combustor protecting its wall from the hot combustion gases. Effusion cooling has long time been very challenging for combustor simulations because it involves length scales ranging from ½ millimeter (about the size of the effusion holes) to ½ meter (about the diameter of the combustor). That is one of the main reasons for which 3D simulations of an effusion cooled combustor wall temperature has long been inaccessible, and has generated the studies presented in this paper.

This study focuses on setting up a 3D model able to describe finely the physical phenomena involved in combustor effusion cooling and the influence of the design parameters available to combustor engineers on these phenomena. The final goal is to use the knowledge generated in this study to create or improve existing uniform effusion cooling thermal models developed by several teams. The logic which prevails in the setup of the numerical 3D detailed model is to find a compromise between the reliability and the CPU cost of the simulation. Indeed the objective is to study the influence of a very wide range of effusion cooling design parameters such as hole diameter, orientation, pattern, length, etc... on the cooling effectiveness. In addition, for a better understanding of the physical phenomena, all the simulations are performed at the same aerothermal conditions. These aerothermal conditions as blowing ratio, cooling temperature, pressure are not design parameters of effusion cooled walls. They are usually imposed by the gas turbine thermodynamic cycle very early in the development of a new engine.

More than 30 CFD simulations have been performed and show the influence of each effusion cooling design parameter taken separately: effusion holes density, angle with respect to the combustor wall, orientation with respect to the main flow, pattern at a fixed density, and diameter. Some of these simulations have been compared to experimental results in order to validate the global numerical method. Then, the analysis of this design of experiment showed that some of the design parameters have strongly nonlinear effects and coupled influences on the wall cooling and on the aerothermal phenomena involved. On the other hand, the simulations show that the effect of some other parameters could be easily described by simple models or even neglected.

This study concludes by giving a summary of the design parameters influence on the heat transfer factors to be modeled in a full uniform effusion cooling thermal model, taking into account the cooling / heating on the three sides of the wall:

- on the cool side

- inside the effusion holes

- on the hot side, inside the combustor