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.

The impact of gas turbine compressor rotor bow on aircraft operations

“…Ongoing research into the rotor bow phenomenon by Smith and Neely (37)(38)(39)(40)(41) has investigated a range of potential driving parameters, including rotor length, rotor thermal mass, internal geometry, initial rotor temperature, ambient conditions and installation design. Smith and Neely (40) have developed an approach for investigating rotor thermal bow using 3D unsteady CHT CFD simulations coupled one-way with FEA of fundamental geometries/analogues, as shown in Fig. 4.…”

“…4), can restrict convective heat transfer within the rotor and thus dampen the thermal gradient, reducing the thermal bow. While these preliminary studies (37)(38)(39)(40)(41) did not yet represent a comprehensive breakdown of the phenomenon and its driving parameters, they did provide a useful basis for later work. These results were subsequently used by the authors to develop a robust Plackett-Burman (43) screening test, followed by a more targeted quasi-random sampling study (43) .…”

“…The third general preliminary finding, and that most relevant to engine designers, was that the geometry of the compressor rotor and case will unsurprisingly influence the thermal and structural response and thus can strongly affect thermal bow behaviour (40) . For example, as illustrated by Fig.…”

“…4), can restrict convective heat transfer within the rotor and thus dampen the thermal gradient, reducing the thermal bow.

Figure 7. Influence of geometry on rotor bow behaviour (40) .

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Prediction of the thermal bow of rotor based on the measured displacement and temperature

“…The numerical simulation is widely applied to unveil the mechanism of the rotor thermal bow of aeroengine. With the commercial packages, it is convenient to investigate the effects of the rotor geometry, 6,7 the case and the integration design, 6,8 the blades and vanes, 9 and the operation of the aeroengine before shutdown, 10 on the rotor thermal bow by numerical simulation. Numerical simulation is an effective method to study the thermal bow of aeroengine qualitatively, while the quantitative research on this problem still requires experimental test.…”