Strength estimation for disk of projected microtubine

Microturbine unit designed in SUSU uses radial gas turbine for driving electrical generator. The turbine is small size (turbine wheel diameter 150 mm), high speed (65,000 rpm for rated operation), and should have reliably long lifetime (60,000 hours). Operation of the turbine includes both long stationary periods and numerous transients on startup, shutdown, power changes due to changes in the load on the electric generator. Strength ensuring at such conditions requires an analysis of long-time durability and cycle life. Long-term strength assessment was made taking into account the redistribution of stresses on stationary regime due to creep. The assumption that the creep strain is sufficient for the desired stresses redistribution allows usage of the limit equilibrium theory static approach that within the FEM corresponds to calculation with ideal elastic-plastic schematization material where ultimate stress corresponds to the limit long-term strength. The paper contains available input data analysis and results of the calculations. It is shown that one of the proposed wheel design provides the required safety factor value. The calculations allow also to evaluate the possible fracture mechanisms for subsequent safety analysis at emergency situations. Preliminary evaluation of stresses on transient conditions is also performed. It is shown that the inertial forces at rapid turbine start-up does not limit the turbine strength. However thermal stresses in hypothetical case of instantaneous fuel supply change from zero up to full one limit allowed durability by 200 “start-stop” cycles only, which indicates the need for a relaxed start regime.