Department of Mechanical Engineering

Buoyancy-induced flow and heat transfer inside compressor rotors project

A combined experimental, theoretical and computational study aiming to understand buoyancy-induced flow and heat transfer inside compressor rotors.

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, it is necessary to determine the radial growth of the compressor discs; this in turn requires the calculation of the transient temperatures of the discs, which involves the calculation of the heat transfer coefficients.

Inside the cavity between co-rotating compressor discs the flow is buoyancy-induced and this creates a strongly conjugate problem: the heat transfer coefficients depend on the temperature distribution of the discs, and the disc temperature depends on the heat transfer coefficients.

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

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, and there are many unanswered questions in the published literature. These aim to be answered through an integrated experimental, theoretical and computational programme of research being undertaken collaboratively between the University of Bath (experiments and theory), the University of Surrey (computational fluid dynamics) and Rolls-Royce plc.

schematic-showing-the-TRC-compressor-drum-test-facilityThe Turbomachinery Research Centre at Bath is constructing an engine-representative rotating-disc rig that models the flow in a high-pressure aero-engine compressor, matching engine-representative fluid dynamic conditions in terms of the Rossby, Reynolds and Grashof numbers.

The test facility will be specifically designed to collect data to inform a theoretical model (recently developed at Bath) and for the validation of CFD conducted at Surrey.

Not only will this research help to understand buoyancy-induced rotating flows, it will also lead to the development of computational fluid dynamics codes and theoretical models that can be used by the entire gas turbine community.