EisenerZ - Influence of Inflow-Nonuniformieties onto the Excitation of LPTs of Modern Two-Spool Engines

Up to now all test rigs are designed for optimum periodic inlet boundary conditions. That is necessary in order to be able to draw some general conclusions, saving measurement time as well as to compare measurement data with results from simulations. That simulations are usually performed for one periodic sector due to time reasons. However, in an engine under representative operating conditions these ideal periodic boundary conditions are not present, there will always be a variation at the inlet. Normally total pressure and/or total temperature are altered by upstream components. For example the temperature can vary by about 100°C to 200°C along the circumference downstream of the combustion chamber. The following turbine stage especially the rotor blades are then excited and start to vibrate. Also struts in turbine centre frames can produce different wakes, different pressure distributions due to separations. Again, the following low pressure turbine stage is then excited. The excitation will increase the shorter engine components are to safe weight and therefore fuel. With that a significant reduction of emissions can be achieved. An environmental improvement is here coupled to a worsening of the vibration situation of the turbine parts or engine components, respectively. However, we can handle that situation with high quality measurement data gained in high-grade research projects e.g. projects in the framework TAKE OFF. Within that project the influence of these inlet distortions onto the vibration of a turbine rotor will be investigated experimentally and numerically (2 way fluid-structure-interaction). The investigation of that effect clearly separated that project from state-of-the-art projects. The numerical challenge is that the complete circumference has to be modelled and simulated. It is well known that these simulations are very time consuming and computational expensive and therefore a fast and simple calculation tool will be developed in order to estimate the stability margin of the system in a very short time. That tool should then be used in an early design phase of a low pressure turbine.