| Summary: | The radius ratio of pre-swirl nozzles to supply holes (r1/r3) has a direct influence on the flow losses generated as well as the temperature drop in the pre-swirl cooling systems used in gas turbine engines. Deciding a proper radius ratio is a significant step for achieving the maximum cooling efficiency. In this paper, the relationship between the temperature drop and entropy increase of the cooling systems is first established theoretically, and from this a novel maximum temperature drop assumption is proposed to give an optimal r1/r3 for the maximum cooling efficiency. To validate this method, the ideal r1/r3 value for a realistic cover-plate pre-swirl system was calculated by this approach, and numerical simulations on five different r1/r3 values of the system were conducted. Static pressure ratio and swirl ratio distributions, entropy production and entropy increase for the five configurations were compared and analyzed. The results show that the cooling performance of a pre-swirl system only depends on the entropy increase in the whole system. For the specific system geometry and design operating conditions investigated, the proposed method and CFD both show that the values of r1/r3 ranging from 0.80–0.96 are the ideal nozzle radial locations, which minimise the wall drag and mixing loss occurred in pre-swirl cavity and rotating supply holes. In this range, the non-dimensional temperature drop is at least 8.6% and 22% higher than those with r1/r3 = 0.72 and 0.64 respectively.
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