The focus of the present study is to understand the effect of Rayleigh number on a high Rossby number flow in a high  
pressure compressor (HPC) inter-disk cavity. The Rayleigh number here is defined as the ratio of the centrifugal buoyancy-  
induced force to the viscous force and the Rossby number characterizes the strength of the axial bore flow with respect to the  
rotation of the cavity. These cavities form between the compressor disks of a gas turbine engine and they are an integral part  
of the internal air cooling system. The fluid flow inside these cavities and induced heat transfer rate from the disks affect the  
clearance between the blades and the casing of an HPC. Thus, it is crucial to understand the flow physics inside these cavities to enhance the operational efficiency and safety of a gas turbine engine.

In this study, we perform highly resolved large eddy simulations by using a standard wall-adapting local eddy-viscosity  
model to account for the sub-grid stresses for the two Rayleigh numbers of 1.34 × 10^8^ and 2.84 × 10^8^ at a fixed Rossby number of 4.5. The simulations are performed using a compressible Navier–Stokes solver with a fourth-order accurate finite-difference discretization scheme in the radial and axial directions and a Fourier spectral method in the azimuthal direction. For the time integration, a fourth-order accurate Runge–Kutta scheme is used.

The results show a flow structure dominated by a toroidal vortex in the inner region of the cavity that extends in the radial  
direction to approximately 40% of the cavity height. In the remaining outer region of the cavity, radial flares are observed  
which are responsible for thermal mixing and heat transfer from the side disks. The azimuthal velocity of the flow is observed  
to be higher than the local disk speed in the toroidal vortex region and decelerated in the outer region to a velocity lower than  
the local disk speed. In the outer region, the flow is observed to move radially outwards by a constant thickness boundary layer formed on the side disks and to move radially inwards through the central core region of the cavity. Only a subtle difference is observed in the percentage of bore flow entering the cavity for the two Rayleigh numbers. However, a significant enhancement in the intensity of the radial flares is observed in the outer region of the cavity for the high Rayleigh number case. The near shroud region is mostly dominated by the centrifugal buoyancy-induced flow and Rayleigh–Bénard type of streaks are observed for both the Rayleigh numbers. Detailed analysis of flow structure and comparison for both the Rayleigh numbers will follow in the full paper.


Large Eddy Simulations of High Rossby Number Flow in the High Pressure Compressor Inter-Disk Cavity

Division / Sponsor:
International Gas Turbine Institute (IGTI)

Paper Proceedings: https://asmedigitalcollection.asme.org/GT/GT2020/volume/84058

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