A virtual laboratory for the classroom as well as for distance education on World Wide Web is presented making use of the various FEM software packages for the numerical calculation of electromagnetic field problems developed at IGTE. For creating interactive educational examples, the HTMLformat specification was chosen. The interaction between the HTML document and the FEM software is performed by the widespread Tool Command Language (TCL).
In order to achieve the ACARE targets regarding reduction of emissions, it is essential to reduce fuel consumption drastically. Reducing engine weight is supporting this target and one option to reduce weight is to reduce the overall engine length (shorter shafts, nacelle). However, to achieve a reduction in engine length, the spacing between stator and rotor can be minimised, thus changing the rotor blade excitation. Related to the axial spacing, a number of excitation mechanisms with respect to the rotor blading must already be considered during the design process. Based on these facts several setups have been investigated at different engine relevant operating points and axial spacing between the stator and rotor in the subsonic test turbine facility (STTF-AAAI) at the Institute for Thermal Turbomachinery and Machine Dynamics at Graz University of Technology. In order to avoid upstream effects of supporting struts, these struts are located far downstream of the stage which is under investigation. For rotor blade vibration measurements, a novel telemetry system in combination with strain gauges is applied. To the best of the author’s knowledge, the present paper is the first report of blade vibration measurements within a rotating system in the area of low pressure turbines under engine relevant operating conditions. In addition, aerodynamic measurements including unsteady flow measurements have been conducted, but will not be presented in this paper. By analysing the flow field, aerodynamic excitation mechanisms can be identified and assigned to the blade vibration. However, this is not presented in this paper. Within this paper, the flow fields are analysed in both upstream and downstream of the turbine stage, visualised for two axial gaps and then compared to the forced response of the blading. Detailed structural dynamic investigations show critical modes during the operation which are identified by the telemetry measurements as well. Finally the influence of the axial spacing regarding the rotor blade excitation and vibration can be elaborated and is prepared to get a better understanding of basic mechanisms. The paper shows that reducing axial spacing is a promising option for reducing engine weight, but aeroelasticity must be carefully taken into account.
Cracks were found in the roots of steam turbine blades of the third blade row (LA-2) of the low-pressure turbine during revision works in a coal-fired power plant. Metallographic examinations reveal pitting corrosion sites, branched cracks, and local plastic deformation at the root of the first load bearing flank radius. The fracture surface was analyzed using light microscopy and scanning electron microscopy (SEM). Finite element (FE) simulations were performed in order to qualitatively represent the stress peak positions on the blade root.
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