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Instabilities on Nozzle-Wake Loads due to Axial Clearance and Throat Variations in a First Stage Turbine

Abstract A study of flow unsteadiness in a high pressure first stage turbine is presented. The study is based on numerical simulations of nozzle wake using a relative reference frame sliding mesh. Pressure and loads on first stage blades needed for stage efficiency calculation in turbine design are discussed. Excessive wear occurring at engine operating conditions affects the distance between rotating and non-rotating elements by varying throat size and axial clearance. Consequently, force unsteadiness produces changes on cyclic loads amplitude, which modifies the work produced by first stage. Compared against design, increments of throat minimum area lead to maximum total force, while throat area reductions increased pressure unsteadiness across the axial clearance. Also, the amplitude of load on blade increases as axial clearance length reduces. Harmonics of force on blade were used to calibrate a useful life prediction tool for turbine components through FFT analysis.