Experimental and numerical studies of fluid-structure interaction in flow-induced vibration problems

This thesis aims to validate a boundary element numerical method (BEM) and use it to investigate fluid-structure interaction problems occurring in turbomachines, especially problems arising from rotorstator pairs. Before applying this BEM technique to treat stator blade vibration in a rotor-stator pair, a comprehensive study was carried out to validate it. The procedure involved careful experimental work to measure the structural response, the use of the Particle Image Velocimetry (PIV) technique to measure the wake flow and the use of a finite-element numerical method to calculate the whole flow field in order to determine the vortex shedding pattern and to provide calculations that take into account viscous and turbulence effects. The measured and calculated wake pattern was used as input to the BEM for prediction of the structural response. Thus configured, the inviscid flow assumption made in the BEM can also be verified.; Originally, the BEM was developed to analyze different kinds of two-dimensional flow-induced vibration problems due to vortex/blade interactions and has not been formally validated. In this thesis, the BEM is formally validated using recently measured vortex-induced unsteady aerodynamic response and blade vibration data. Three problems were examined and they included the case of single-blade single-vortex interaction, single-blade single vortex-street interaction and single-blade dual vortex-street interaction. In the single-blade single-vortex interaction case, the blade was modelled as rigid; therefore, the response of the structure was purely aerodynamic. The trend of the calculated variation of blade lift coefficient with the horizontal miss distance of the convected vortex compares well with known experimental data.; An experiment of a coupled elastic cylinder/blade system was carried out to model the Karman-vortex-street/blade interaction. In the experiment, a circular cylinder placed upstream in tandem with an elastic blade was used to generate the Karman-vortex-street. A NACA0012 airfoil with a constant cross-section along its span was used to model the blade, which was exposed to an oncoming Karman-vortex-street. In order to determine the vortex spacing correctly, three different methods were employed. The first method involved the use of PIV to measure the vorticity distribution in the wake flow, the second method was to use the Karman vortex street theory to calculate the wake properties, and the third method was to interpret the vortex spacing from existing flow visualization data at about the same Reynolds number. All three techniques yielded comparable results in terms of the vortex spacing thus determined. (Abstract shortened by UMI.)...