Cooling Air Temperature Reduction in a Direct Transfer Preswirl System

Abstract

This paper describes an experimental study of the cooling efficiency of a preswirl rotor-stator system equipped with a small number of preswirl nozzles of circular shape, located on a radius equal to that of the receiver disk holes. In the direct transfer cooling air system, total air temperatures were measured in the relative frame, i.e., inside the receiver holes by means of small total temperature probes for different throughflow rates, rotational Reynolds numbers and swirl ratios. The experimental data were compared with a simple theoretical model which predicts air temperatures in an “ideal” preswirl system. This comparison served to quantify the efficiency of this cooling scheme. In a subsequent one-dimensional analysis which took into account flow data obtained in an earlier experimental study by the same authors, two different mechanisms responsible for the elevated cooling air temperatures were determined. The new model considers in addition to the observed reduction of swirl due to viscous drag on the stator and mixing inside the rotor-stator cavity, the work put in by the rotor at high disk rotational Reynolds numbers and low cooling air flow rates.