The Effect of Boundary Layer Changes Due to Transient Heat Transfer on the Performance of an Axial-Flow Air Compressor

During transient operation of a gas turbine there are significant heat transfers between the fluid stream and the blades of the compressor and turbine. At the end of a rapid deceleration from maximum speed to idling speed, heat transfer to the compressor blade boundary layers may cause sufficient disturbance to delay any immediate re-acceleration. As a first estimate in one severe case - at altitude in an aircraft engine of compression ratio 20 - the surge margin prior to the re-acceleration is reduced by about 40% due to boundary layer effects, and by a further 25% due to “bulk” heat transfer.