Abstract

The results of a simulation of the three-dimensional unsteady viscous flow in a highly loaded last stage of an axial flow low pressure turbine are presented. The focus in the flow analysis is on the temporal fluctuations of the rotor lift and the resulting unsteady forces and torques acting on the rotor blading. In the lower 50 % of the rotor span the stator exit flow is transonic and strong interaction effects between the stator and the rotor potentials can be observed. The resulting temporal fluctuations of the static pressure on the rotor blades amount to a maximum of more than 4O% of the time-mean value, In the region between 20 and 4O% of the span where the unsteady interaction effects are maximal, complex shock motion patterns are found. The unsteady static pressure is integrated along the chord and over the surface of the rotor blade to yield the unsteady distributed loads, forces, and torques, respectively. These quantities are analysed both in time and the frequency domain. It is found that the first harmonic of the blade passing frequency of the driving torque amounts to 6.3 % of the time-mean value. The second harmonic still amounts to 3.4Y%.