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University of Bath

Buoyancy-induced flow and heat transfer inside compressor rotors

This project combines experiment, computation and theory to generate a fundamental understanding of buoyancy-induced rotating flow.

A challenging problem for designers

Modern high-pressure aero-engine compressors present a challenging problem for designers. The higher the pressure ratio, the smaller the blades become. And the size of the clearance between the blades and casing has an increasing effect on the compressor performance and stability. To calculate and control these small clearances for transient and steady conditions, we need to determine the radial growth of the compressor discs. This requires us to calculate the transient temperatures of the discs and calculate the heat transfer coefficients.

The flow inside the cavity between co-rotating compressor discs is buoyancy-induced. This creates a conjugate problem. The heat transfer coefficients depend on the temperature distribution of the discs. And the disc temperature depends on the heat transfer coefficients.

Furthermore, Coriolis forces in the rotating fluid create cyclonic and anti-cyclonic circulations inside the cavity. As such flows are three-dimensional, unsteady and unstable, it is difficult to measure the heat transfer from the discs to the air.

Answering rotating flow problems in gas turbines

Buoyancy-induced flow in a rotating cavity is one of the most difficult rotating flow problems in gas turbines. There are many unanswered questions in literature published to date. We aim to answer these through integrated experimental. theoretical and computational research. This collaborative project brings together:

  • University of Bath (experiments and theory)
  • University of Surrey (computational and fluid dynamics)
  • Rolls-Royce plc

Our Centre is constructing an engine-representative rotating-disc rig that models the flow in a high-pressure aero-engine compressor. This matches engine-representative fluid dynamic conditions in terms of the Rossby, Reynolds and Grashof numbers.

We are designing the test facility to collect data to inform a recently developed theoretical model. It will also validate computational fluid dynamics conducted at Surrey.

This research will help the gas turbine community understand buoyancy-induced rotating flows better. And it will lead to the development of computational fluid dynamics code and theoretical models.