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

Abstract

Modern efficient and robust steam turbines must be designed for large operating ranges and run at off-design conditions and high backpressures. Therefore, there is a danger that in some operating conditions, last-stage rotor blades can suffer from self-excited vibration (flutter), leading to severe failures of rotor blades or turbine units. In order to avoid this, the design of aerodynamically stable last stage rotor blades became a major topic for all steam turbine manufacturers and a validated numerical model for flutter prediction during the blade preliminary design phase is required. As flutter measurement is impossible in real turbines, controlled flutter tests on simplified experimental models must be used. However, experimental flutter testing facilities are rare. This paper reports on a flutter test rig enhancement to transonic flow and numerical data validation of aerodynamic stability in a linear turbine blade cascade. Aerodynamic forces and moments are estimated for different boundary conditions at pure bending, pure torsion and combined modes. The results are compared to numerical simulations performed using commercial code ANSYS CFX. Good agreement between the experiment and the numerical simulations proved a successful validation of the numerical tool.