The Effect of Compressor Shaft Geometry on Shaft Thermal Bow due to Natural Convection

Abstract

This study builds upon previous work by the authors, using a combination of 3D conjugate heat transfer (CHT) computational fluid dynamics (CFD) and finite element analysis (FEA) to characterise the thermal bow behaviour of a simple compressor shaft and case model under natural cooling. As with previous studies by the authors, body temperatures obtained from 3D CHT CFD solutions at set time intervals are transferred to FEA, where the physical distortion associated with the asymmetric thermal load is measured. The current study examines the influence of a range of shaft design parameters on the severity and duration of the shaft deformation. The parameters of interest include shaft length, annulus geometry, degree of shaft ventilation, and shaft internal cavity geometry. Each time the baseline model is modified to analyse the contribution of a parameter, the model is allowed to cool down from representative operational temperatures for a period of 180 minutes, over which time the shaft thermal bow, and shaft-to-case clearance, are measured. The results of this study indicate that the shaft’s thermal bow response and shaft-to-case clearance over time are highly sensitive to changes to its geometry, whereas the change in 180-degree out-of-phase shaft-to-case clearance is more sensitive to the case geometry, rather than the shaft. These results indicate that increasing the length of the shaft, reducing its wall thickness, or introducing a rising-line annulus, will increase the severity of the shaft thermal bow phenomenon; whereas introducing disc geometry inside the shaft will reduce the severity of the bow.