The continuous improvement in thermal efficiency of gas turbines is primarily achieved by increasing the turbine inlet temperatures without, however, affecting the thermal stability and the fatigue strength of the blades which must be guaranteed for their entire service life. The precise analysis of secondary air systems is therefore of crucial importance for the design of gas turbines.

Stationary and rotating passages constitute important elements of secondary air systems, and this paper focuses on the calculation of the characteristics of fluid flow through stationary and rotating passages (or bores) as a function of passage length, asymmetric inflow (i.e. crossflow at the inlet) and inlet edge geometry (i.e. rounded or sharp–edged inlets). A simple physical model is developed on the basis of the simple and thoroughly investigated passage flow. The model is then matched to a large number of test results taken from the literature. The result is a versatile tool for calculating flow losses in rotating and stationary passages.

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