This thesis focuses on the ingress problem in rotor-stator system in turbines with the primary emphasis on numerical methods.The first part of this dissertation implemented a newly-developed orifice modelfor externally-induced (EI) ingress into a non-commercial one-dimensional (1D)flow network solver. The massflow functions of the EI ingress model are solvedwith an iterative procedure with inner and outer loop iterations. The comparisonof this model against a standard procedure where the fluid exchange is modelledwith multiple branches was in good agreement despite a diverging behaviour at high sealing effectiveness.An extrapolation method was developed to extrapolate the sealing parameterΦmin from one Mach number regime to another. This procedure, which uses thelinear saw-tooth model for EI ingress, showed good agreement with the computed values of Φmin over the investigated subsonic range. It was proposed to use this method to scale the experimentally determined Φmin value obtained at incompressible test rig conditions to a geometric similar engine at compressible conditions.The effect of aerodynamic off-design conditions (varying flow coefficient, CF )and their impact on ingress in rotor-stator systems was investigated with transient CFD computations. Pressure measurements behind the trailing edge of the vane showed a linear variation of the non-dimensional pressure coefficient with flow coefficient. This behaviour was confirmed numerically with theexception of a diverging behaviour with an increase of Cp at low values of CF .This effect could be isolated and associated with the rotor blade at large deviation angles.Various rim-seal concepts were numerically investigated with the intent to minimise the ingress levels in the wheel-space of a high pressure turbine. These concepts were experimentally tested at the ingress facility of the University of Bath and confirmed predicting the ranking order of these seals by the numerical investigation. An optimised rim-seal design was developed from this study which addresses the root cause of the EI ingress by attenuating the tangential pressure variation; the new rim-seal reduced the sealing parameter Φmin by about 40% compared a the baseline case.A numerical study investigated several rotor endwall concepts with the objectiveto minimise the mixing loss associated with the interaction of the egress with themainstream flow. A 3D concept with leading edge feature along with an incorporated egress channel within the endwall reduces not only the interaction loss but also losses associated to secondary flows, (i.e. horse show vortex and cross passage flow), without negatively impacting the ingress levels of the upstream located wheel-space.
|Date of Award||15 Sep 2014|
|Supervisor||Michael Wilson (Supervisor) & Gary Lock (Supervisor)|
- Hot gas ingestion
- Gas Turbines
- Secondary Air Systems