Turbine Rotor Generated Forcing Functions for Flow Induced Vibrations

Abstract

A series of experiments are performed to investigate the effect of steady loading on the unsteady aerodynamic gust forcing functions generated by turbine rotor blade rows and the validity of the vortical and potential gust splitting techniques. Both the downstream vortical-potential gusts and, for the first time, the upstream generated potential gust are considered. Note that these upstream gusts are in fact the potential field of the rotor and not the nozzle wakes. This is accomplished by measuring the downstream and upstream unsteady forcing functions generated by the first stage rotor of the low speed research turbine over a range of steady loading levels. These forcing functions are then split into vortical and potential gusts utilizing both the V-Method using only velocity data and the P-Method which also incorporates unsteady static pressure data. The results clearly show an increase in potential effects for the downstream gust forcing functions with increased blade loading. The rotor blade gusts upstream of the first rotor are theoretically purely potential gusts since no vorticity can be conducted upstream. These potential disturbances do not appear to be a function of the blade loading. The results of the linear theory splitting show that both splitting methods have discrepancies in their recombined forcing functions. The V-Method either under or over estimates the unsteady static pressure and has trouble duplicating the phase. The P-Method tends to skew the recombined velocity in the lift force direction. The upstream potential gusts posed a particular problem for the splitting, with neither method able to fully reconcile the measured pressure and velocity perturbations.