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

Fatigue failure of the last three stator rows vanes (S17, EGV1, and EGV2) in the 17 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 380–400 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 the 2D stator cascade system. Three numerical experiments were carried out. The first experiment investigated the flow simulation in the stator cascade 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 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 $f=2200–2300Hz$ than in other investigated cases.