No abstract

No abstract

In order to eliminate occurrences of flutter of low pressure turbine blades it is necessary to understand the associated unsteady aerodynamics. For this reason, an experimental and numerical study of controlled flutter (travelling wave mode) in a linear turbine blade cascade oscillating in a torsional as well as translation motion is conducted. Unsteady aerodynamic forces and moments were measured on a subsonic eight-blade turbine cascade rig where central four blades are flexibly mounted each with two degrees of freedom. Thin blades in the cascade represent the tip section of the last stage rotor blades, which defines the turbine overall performance. A commercially available 3D CFD software ANSYS CFX is used to simulate the unsteady aerodynamic loading in the blade cascade. Experimental data and simulations are compared and influence of aerodynamic forces and moments on flutter is analysed.

In low-pressure steam turbines, aerodynamic and structural design of the last stage blades is critical in determining the power plant efficiency. The development of longer last stage blades which are recently over 1 meter in length is an important task for steam turbine manufactures. The design process involves a flutter analysis of last stage blade tip sections where increased unsteady aerodynamic forces and moments might endanger the blade aerodynamic stability. However, numerical design tools must be validated using measurements in test facilities under various operating conditions. In this work, ANSYS CFX is used for flutter prediction of turbine blade tip sections oscillating in a travelling wave mode. Simulations are compared to experimental results obtained from controlled flutter tests in a wind tunnel with a linear cascade of eight turbine blade profiles made of carbon fibre. Central four blades are flexibly mounted each with two degrees of freedom (i.e. bending and torsion motions). Large deflections of thin blade profiles are accounted for the estimation of unsteady aerodynamic forces and moments. A satisfactory agreement between the simulations and experiments is achieved.

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°.