Reduction of aerodynamic forces on turbine blading by asymmetric layout of struts based on flow interaction between rotor-strut-volute

Abstract

The flows in the power turbine and nonaxisymmetric exhaust volute with struts are closely coupled and inherently unsteady for marine gas turbines, and the flow interactions between them have a significant influence on the rotor and strut blade aerodynamic force characteristics; however, the asymmetric flow interactions have not been taken into account properly in current turbine design approaches. This paper is a continuation of the previous work and aims to clarify effects of different symmetrical and asymmetric layouts of struts on the flow interactions between power turbine and exhaust volute, in an attempt to seek an optimal layout of struts with the objective of making use of the mentioned asymmetric flow interactions to reduce the rotor and strut blade aerodynamic forces. This work was carried out using coupled unsteady simulations with the full annulus computational domain including 76 rotor blades, 9 strut blades, and an exhaust volute. Results show that the level of aerodynamic force at specific frequencies on the power turbine blade surface can be reduced by applying a proper distribution of asymmetric layout of struts; using the asymmetric strut design, although the reduction of the rotor blade aerodynamic force is weak, the strut blade aerodynamic force has been reduced significantly; the asymmetric layout of struts does not improve the overall flow characteristics of turbines very much. The present results indicate that it is possible to reduce vibration and increase blade fatigue life by asymmetric strut designs.