Correlations of the Convective Heat Transfer in Annular Channels With Rotating Inner Cylinder

Abstract

In the internal air system of gas turbine engines or generators, a large variety of different types of annular channels with rotating cylinders are found. Even though the geometry is very simple, the flow field in such channels can be completely three-dimensional and also unsteady. From the literature it is well-known, that the basic two-dimensional flow field breaks up into a pattern of counter-rotating vortices, as soon as the critical speed of the inner cylinder is exceeded. The presence of a superimposed axial flow leads to a helical shape of the vortex pairs, which are moving through the channel. For the designer of cooling air systems there are several open questions. Does the formation of a Taylor-vortex flow field significantly affect the convective heat transfer behaviour of the channel flow? Is there a stability problem even for high axial Reynolds-numbers and where is the location of the stability boundary? After all, the general influence of rotation on the heat transfer characteristics has to be known. By the results of flow field and heat transfer measurements, the impact of rotation and the additional influence of Taylor-vortex formation on the heat transfer characteristics in annular channels with axial throughflow will be discussed. The flow field was investigated by time-dependant LDA-measurements, which revealed detailed information about the flow conditions. By a spectral analysis of the measured data, the different flow regimes could be identified. Based on these results, the heat transfer from the hot gas to the rotating inner shaft was determined with a steady-state method. Thus, the influence of the different physical phenomena such as rotation with and without Taylor-vortex formation or the flow development could be separated and quantified. Finally, correlations of the measured results were derived for technical applications.

Investigation into Taylor-Couette-Poiseuille flow heat transfer for supercritical carbon dioxide turbomachinery

“…However, for axial Reynolds numbers above 1500 the effect is reversed. Similar results have been observed in the experiments by Jakoby et al [4].…”

“…It was found that the critical Taylor number had the form seen in Equation 2.10 for low axial Reynolds numbers and radius ratios close Contrary to this, Yamada [59] determined that there was in fact a transition zone between flow regimes. The existence of a transition area between the two flows was confirmed experimentally by Jakoby et al [4].…”

“…These results for comparing the effect annular gap height (or radius ratio) on the transition and stabilization of Taylor vortices appear contradictory between Kaye and Elgar [57], Jakoby et al [4] and those of Martin and Hasoon [60] and Di Prima and Pridor [61]. However, these difference may be caused by a second geometric parameter, length ratio (Γ).…”

“…The efficiency and performance characteristics of gas turbine engines depend on the turbine inlet temperature and the pressure ratio of the working cycle. Turbine inlet temperatures already exceed the maximum operating limits of even super alloys [4]. Therefore, turbine units require an efficient cooling system for the various temperature sensitive components.…”

“…Cooling air mass flow had to be raised significantly in past years in order to ensure there is sufficient heat transferred from the turbine as operating temperatures increased. Currently, some cooling mass flows can reach 20% of the cycle main flow which then indicates that cooling systems play a key role in overall efficiency of the cycle [4]. Obtaining better understanding of the heat transfer present in the cooling regions of the turbine will ensure that the cooling system is efficient and utilizing minimum cooling mass flow.…”