The aims of this work are to achieve a better understanding of thermal fluxes around a multi-perforated plate and obtain correlations for heat transfer coefficient on the hot as well as cold side and in a perforation. A 3-dimensional, RANS, conjugate simulation and an adiabatic one are performed for different aerothermal conditions already studied experimentally. Convective heat flux, wall temperature and adiabatic temperature are averaged on a periodic pattern around each hole. A mean heat transfer coefficient is calculated based on these quantities and correlations are deduced for this coefficient. Such results as fluid temperature rise in a perforation or the contribution of flux in the perforations to the whole cooling flux are also given in this article.
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
Effusion cooling is one of the most widespread system used to cool combustion chamber liners nowadays: it is efficient, cheap and light. Effusion cooling consists of drilling thousands of submillimetric holes into the combustor wall in order to cool it down from inside the holes and create a cooling film inside the combustor protecting it from the hot gases. Effusion cooling has long time been very challenging for combustor simulations because it involves lengthscales 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 effusion cooling has long been inaccessible, and has generated the studies presented in this paper. This study will focus on the effusion cooling holes discharge coefficient evaluation as a function of numerous aerothermal and design parameters. Many attempts to describe aerodynamically effusion have occurred, mainly based on experiments exploring few of the parameters mentioned above. But none of these studies tried to elaborate a model able to handle most of them. This is the purpose of this study which will set up a 3D model able to describe finely the physical phenomena involved in combustor effusion cooling holes and the influence of the design parameters available to combustor engineers on these phenomena. The strategy 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 wide range of effusion cooling design parameters such as hole diameter, orientation, shape, etc. . . on the effective cross section. 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. A preliminary study allowed to select the parameters which were both the least known and the most influential on the effusion hole mass flowrate according to literature, preexisting numerical and experimental databases. More than 60 new CFD simulations have been performed and show the influence of each effusion cooling design parameter taken separately: effusion holes inclination, orientation and taper angle. A mesh sensitivity study has been performed in order to validate the numerical approach. Then, the analysis of both the preexisting data and this new numerical database showed that some of the design parameters have strong effects and coupled influences on the mass flow rate through the holes. On the other hand, some other parameters could be easily described by simple models or even neglected. This study concludes by quantifying the improvement of a proprietary effective cross section correlation of effusion cooled walls, based on the analysis mentioned in this study.
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