Abstract
In this paper, experimental testing of flutter and numerical simulations using a commercial code ANSYS CFX and an in-house code TRAF are performed on an oscillating linear cascade of turbine blades installed in a subsonic test rig. Bending and torsional motions of the blades are investigated in a travelling wave mode approach. In each numerical approach, a rig geometry model with a different level of complexity is used. Good agreement between the numerical simulations and experiments is achieved using both approaches and benefits and drawbacks of each technique are commented in this paper. It is demonstrated that both used computational techniques are adequate to predict turbine blade flutter. It is concluded that validated numerical tools can provide a better insight of flutter phenomena of operationally flexible steam turbine last stage blades.
Highlights
With the increase of steam turbine operational flexibility, the risk of asynchronous blade vibrations induced by flow becomes higher and higher and may lead to undesired failures of last stage blades (LSBs)
Experimental testing of flutter and numerical simulations using a commercial code ANSYS CFX and an in-house code TRAF are performed on an oscillating linear cascade of turbine blades installed in a subsonic test rig
Two different numerical methods were applied for the flutter assessment of blade cascade: a commercial code ANSYS CFX and an in-house code TRAF
Summary
With the increase of steam turbine operational flexibility, the risk of asynchronous blade vibrations induced by flow becomes higher and higher and may lead to undesired failures of last stage blades (LSBs). As the validation is not possible in industrial environments (real turbines) controlled flutter tests on simplified experimental models must be used Such an experimental rig has been built at the Department of Power System Engineering at the University of West Bohemia (UWB) where the unsteady aerodynamic forces and moments in the oscillating turbine blade cascade can be investigated. The code validation has been extended to compressor blades and steam turbine rows [4, 5] so that the actual design process includes an extensive use of these methods to achieve a free flutter design [6] Such methodologies are usually classified in time-linearized, harmonic balance and non-linear approaches both in frequency and time domain and require high quality experimental data for the validation and tuning, especially in off-design conditions. The stability results are evaluated by aerodynamic work which describes the exchange of energy between blade and flow [7, 8]
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