Numerical Simulation of the Flow Pulsations Origin in Cascades of the Rear Blade Rows in a Gas Turbine Axial Compressor Using Low Calorific Fuel

Abstract

Fatigue failure of the last three stator rows vanes (S17, EGV1 and EGV2) in the seventeen stage gas turbine axial compressor occurred in the power plant where low calorific fuel, syngas, was used. Causes of this dangerous phenomenon were flow pulsations with the frequency of 380 to 400 Hz that were found by the experimental investigation of the duty gas turbine. Mechanism of the flow unsteadiness origin was studied with the help of flow simulations in 2D stator cascade system. Three numerical experiments were carried out. The first experiment investigated the flow simulation in the stator cascades system with a steady undisturbed inlet flow with increased turbulence intensity. Obtained data did not meet the standards of the actual compressor operations. In the remaining two numerical experiments a purposely designed rotor cascade was located in front of the stator cascades. Shedding of vortex structures from the cascade profile surfaces at positive incidence angles is responsible for the flow pulsation origin. The interaction of rotor wakes / stator S17 cascade plays an important role in the investigated phenomenon, as follows from CFD data. Aerodynamic loading of both cascades is equal in the second group of numerical experiments. Computed results were in a good qualitative agreement with the experimental ones. As the flow in rotor cascade was not separated, owing to the different aerodynamic loading of rotor and stator S17 cascades, the vortices shedding in stator cascade S17 had a significantly higher frequency of f = 2200 to 2300 Hz than in other investigated cases.