Experimental and numerical investigation of the flow and heat transfer in conical Swirl Cooling Chambers

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The main goals in the development of industrial gas turbines and aero-gas turbines are the reduction of fuel consumption as well as the drastic reduction of pollutant emissions. This can be achieved, for example, by increasing the thermal efficiency of the gas turbine with the help of an increase in the process temperature. However, the increased combustion chamber temperature and the increased turbine inlet temperature are today already well above the melting temperature of the blade material, which makes it necessary to develop efficient turbine blade internal cooling strategies. Currently, various internal cooling concepts are being investigated in detail, such as ribbed channels, pin fins, impingement jets, dimples and cyclone cooling chambers. Cyclone cooling (swirl cooling or vortex tubes) are characterized by very high heat transfer rates. In the first funding period (FP1) of this project, vortex tubes with convergent tube cross-sections in the flow direction were investigated both experimentally and numerically. Here, a very good agreement between measurement results, such as the heat transfer measured with the transient liquid crystal technique and Detached Delayed Eddy Simulations (DDES) could be achieved. In addition, stability effects play an important role in heat and mass transfer processes. Therefore, the stability of the flow in the vortex tube was investigated using various stability criteria, with a focus on the stability criterion by Marsik, which is based on the second law of thermodynamics. In the current proposal for the second funding period (FP2), the investigations are now to be extended to cyclone cooling chambers with diverging cross-sections in the main flow direction. Due to the widening cross-sectional area in the direction of the flow, the swirl and the resulting detachment areas are significantly influenced. The flow is, thus, destabilized in a targeted manner. It is expected that the shaping will lead to higher heat transfer rates. Analogous to FP1, the flow and the heat transfer in the divergent cyclone cooling chambers will be investigated numerically by means of DDES and experimentally by means of PIV and the transient liquid crystal method. Furthermore, stability investigations for this geometry will again be carried out based on the second law of thermodynamics. At the end of the project, after six years, there will be detailed knowledge about the influence of convergent and divergent cross-sectional flows in swirl cooling chambers. This understanding of the very complex flow and heat transfer in convergent and divergent vortex tubes should help to successfully use such cooling systems for blade cooling in the future, for example in new types of gas turbine blades.