CFD prediction of flutter of turbine blades and comparison with an experimental test case

Abstract

Abstract. Last stage blades are a key element of steam turbines and in many ways determine the turbine configuration alongside with the overall turbine performance. The total efficiency of the low pressure turbine section can be increased by extending the last stage blades. The design process of such long blades involves a flutter analysis using CFD tools which have to be validated by measurements in test facilities under various operating conditions. Experimental data obtained from a subsonic wind tunnel with an oscillating turbine blade cascade, which is available at the Department of Power System Engineering at the University of West Bohemia, was compared with simulations in ANSYS CFX currently used in the Doosan Škoda Power. The paper provides a brief summary of experimental rig description, CFD tool setup and the results for the case of a travelling wave mode with the pure torsion motion of amplitude of 0.5°, Ma = 0.2, reduced frequency of 0.38 and angle of attack +5°.

Enhanced Flutter Test Rig for a Transonic Flow in a Linear Turbine Blade Cascade and Numerical Data Validation

“…6. All solver setups are defined according to simulations in [12][13][14][15]; the flow field is modelled as viscous and fully turbulent. The ideal gas law is used to describe the thermodynamic properties of the flow.…”

“…One of the major advantages of this setup over the available testing facilities is that coupled bending-torsion modes can be easily achieved [10,11]. Before the test rig enhancement, measurements in the controlled flutter test rig were carried out on subsonic flow field cases, and datasets were exploited for CFD validations [12][13][14][15], where a close match between the experimental data and the numerical results was achieved. In addition, a calculating procedure for a flutter prediction based on the commercial code ANSYS CFX was also developed to be used during the preliminary design phase in Doosan Skoda Power [16].…”

Experimental and Numerical Study of Controlled Flutter Testing in a Linear Turbine Blade Cascade

“…6. This model has been simplified for numerical simulations based on detailed CFD investigations [12]. Final computational domains for steady-state and unsteady simulations are shown in Fig.…”

“…The total time duration of unsteady simulations was specified using the total number of periods per run. It was investigated that 6 periods per run were sufficient enough to calculate the required aerodynamic work [7,12]. To quantify convergence criteria of steadystate simulations, the residual values were used where the RMS (root mean square) residual type was chosen and 1 • 10 −5 residual target value was defined.…”