Development of a test facility for experimental investigation of fluid-structure interaction

Sammanfattning: Fluid-structure interaction phenomena are strongly related to the loading appearing on many energy converting components introducing limitations for improving their efficiency. The term “fluid-structure interaction” includes many phenomena with the “shock wave – boundary layer interaction” being one of the most important. This interaction is commonly met in turbomachines where the flow can accelerate enough to become compressible and can cause separation of the boundary layer formed on the structural components of the machine. This results to fluctuating loading on the structure which can lead to its failure due to High Cycle Fatigue (HCF).A vibrating structure in compressible flow can become unstable depending on the sign of the aerodynamic damping that the flow has on the structure. Although the mechanism that causes a structure to become unstable is known, the limits of the stability region are not yet possible to predict with reasonable accuracy. It is therefore necessary to investigate the underlying mechanism of fluid-structure interaction by means of experimental and numerical studies for providing prediction tools regarding the stability change.The present work aims at developing an experimental facility to be used for investigating fluid-structure interaction. The experimental setup is based on the concept of a simplified aeroelastic test case bringing into focus the area of interaction between an oscillating shock wave and a turbulent boundary layer. This work is based on previous research campaigns using the same generic experimental concept but takes the investigation further to higher and so far unexplored reduced frequencies. The experimental setup has been validated regarding its suitability to meet the research objectives by running vibration tests at an initial stage without the effect of flow.The results from the experimental validation of the facility have shown that the design objectives are met. Specifically the vibration response of the test object concerning vibration amplitude and vibration mode shape is desirable; the vibration amplitude is in the range of 0.5mm and the mode shape remains below the 2nd throughout the targeted frequency range (0-250Hz). This makes the facility suitable for simplified investigation of fluid-structure interaction, bringing the shock foot region into focus.Having validated the facility performing vibration tests without flow, tests with flow is the next step to take place. Since the vibration response of the test object has been investigated in detail, tests with flow will reveal the influence of fluidstructure interaction on the dynamic response of the test object. Similarly, the influence of this interaction on the flow side can be assessed by monitoring the flow parameters. As a first step for performing this investigation, the design study and the validation results for the experimental setup are presented in this work.