Heat transfer and pressure loss in swirl tubes with one and multiple tangential jets pertinent to gas turbine internal cooling

Abstract

This paper presents a comparative experimental and numerical study of heat transfer and pressure loss characteristics in swirl tubes with one (S1) and five (S5) tangential inlet jets, respectively. Transient liquid crystal thermography has been used in the experiments to obtain detailed local and globally averaged heat transfer data in the swirl tubes with the two different inlet jet configurations. Comparisons of the experimental data for the heat transfer and pressure loss characteristics of the swirl tubes are analyzed under equal mass flow rates and under equal inlet jet Reynolds numbers, respectively. With equal overall mass flow rates in the two configurations the experiments showed that the heat transfer patterns of the swirl tube S1 are substantially different from those of the swirl tube S5. The swirl tube S1 shows significantly higher heat transfer and pressure loss than the swirl tube S5. The heat transfer in the swirl tube S1 reaches peak values under the inlet jet and then continuously decreases to the end of the tube, while the heat transfer in the swirl tube S5 is increased under each inlet jet along the tube length. The swirl tube S5 shows a more uniform heat transfer pattern than the swirl tube S1 along the tube length. However, under equal inlet jet Reynolds numbers, the globally averaged heat transfer of swirl tube S5 is higher than that of swirl tube S1 over the whole tube length. The heat transfer of the swirl tube S5 can be regarded as a combination of repeated heat transfer patterns along the tube, each of which is dominated by a single jet induced swirling flow over a shorter tube length between the jets. The cross flow does not show detrimental effects on the heat transfer of the downstream inlet jets in the swirl tube S5. In support of the experiments, three-dimensional numerical computations are presented to provide more insight into the flow structure in the swirl tubes.