A Computational Study of Temperature-Driven Low Engine Order Forced Response in High Pressure Turbines

This paper reports the results of computational studies of the effect of combustor exit temperature distortions on low engine order (LEO) forced response of a high pressure turbine (HPT). Forced response of this kind occurs at frequencies below the stator vane passing frequency (SVPF) and can be a major cause of high cycle fatigue in turbines due to its tendency to excite fundamental modes of vibration. This paper investigates the extent through which temperature distortions act as a forcing stimulus in HPT rotor rows, through measuring unsteady pressure and modal force magnitude recorded from full annulus unsteady simulations of the MT1 stage: a low temperature, unshrouded, HPT rig. Rotor relative incidence angle variations are shown to be the key mechanism through which temperature acts as a forcer in HPT rotor rows while temperature-driven forced response is shown to be dependent on the magnitude of the modal content of the upstream temperature waves. These findings are used to build a reduced domain tool for blocked burner forced response prediction, which is shown to be accurate to a root mean squared (RMS) error of 2.66%, far beyond the current accepted standard for forcing prediction of this kind.