Design of heat transfer instrumentation to be applied at the wind tunnel for rotating cascades at DLR, Göttingen

Kurzfassung

Due to the raising turbine entrance temperatures, a detailed knowledge of the heat transfer distribution on the affected areas is necessary. The shroud, a part of the casing which is especially affected by the hot combustion gases, has been excluded so far from research, due to the absence of proper measurement techniques. The AG-Turbo program 2.4.11A aims to measure the heat transfer coefficient at the shroud. Therefore new measurement techniques have to be developed. The experiments will be carried out in the Institute of Propulsion Technology at the DLR Göttingen. The first part of the report is addressed to a detailed literature survey, in order to summarise the major fluid-dynamical structures which cause the increased heat transfer coefficient present at the shroud. The influence of the main operating parameters such as the pressure ratio, rotational speed and Reynolds number on the heat transfer rate is discussed. In the second part of the report various heat-transfer measurement methods are appraised with regard on their usability in the Rotating Cascade Wind Tunnel at the DLR Göttingen. Three methods are chosen to be appropriate for an installation in the wind tunnel. The first method is based on the combination of an electrical heater and a net of thermocouples. The second method is a marginally elevated hot-wire which allows accurate unsteady measurements. The influence of the vicinity of the wall to the hot-wire on both the steady and unsteady response is discussed in great detail in the report. The third method presented is a commercial heat flux sensor which allows heat transfer measurements with response times smaller than 10 microseconds.