The accurate prediction of wall temperatures in modern turbomachines is extremely important as firing temperatures increase to achieve ever higher efficiency. Many factors affect these predictions, including variations in the inlet profile, purge and cooling flows, tip clearances and geometry-specific unsteady flow physics. This paper explores the statistical behavior of gas-side near-wall temperature predictions to demonstrate the prediction uncertainty associated with solution time averaging. Gas-side temperatures have been obtained by time-averaging unsteady CFD solutions of a single-stage commercial HPT rotor. Forced unsteady calculations are performed for a cooled vane and an uncooled rotor with purge cavities. The presence of the vane coolant induces a significant circumferential temperature variation for the flow entering the rotor. For select regions within the rotor passage, this circumferential gradient, combined with the influence of the purge cavities, produces near-wall variations dominated by frequency content lower than blade passing. This content directly affects the uncertainty of the time average. Traditional CFD averaging approaches consider data over a single blade passing or some multiple associated with the blade counts, but often assume start time/position to be immaterial. In this work the variation in predicted average near-wall gas-side temperature at select points in the flow field is explored as both the averaging window (number of blade passings) and the averaging start time are varied. Time histories of gas-side temperature are taken at select near-wall locations around the passage in and away from regions heavily influenced by purge flows. Simulation results are examined for 120 blade passings after an initial transient period. These values are used to identify and discuss regions in this geometry with large predicted average temperature uncertainty. It was found that as the window size is increased the variation in predicted temperatures is reduced everywhere in the flow. Possible unsteadiness sources driving problem areas are discussed and convergence trends for the average temperature of each surface of interest are presented.

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