The performance of a centrifugal impeller is predicted under steady ideal axial inlet conditions. The operational range is given in terms of load and flow coefficient and polytropic efficiency. The flow field at the exit of the impeller is analyzed to show how it deteriorates while moving close to the stall limit of the characteristic curve. The effect of a strong inlet distortion obtained by intentionally altering the geometry of an inlet volute on the impeller is analyzed. The investigation is carried out for two different distortions, without and with pre swirl, and for two pressure ratios, close to the design point and close to the stall limit of the operational range. The effect of the distortion is analyzed by both a quasi-steady and unsteady approaches. The first method, while faster, is found to give results in partial disagreement with the fully unsteady analysis and is therefore abandoned. The impeller under unsteady distorted inlet is found to have degraded performances in terms of efficiency and load factor, but the overall operational range seems not be significantly affected by the fluctuations of inlet total pressure and angles.

A three-dimensional transonic turbine stage is computed by means of a numerical simulation tool. The simulation accounts for the coolant ejection from the stator blade and for the tip leakage of the rotor blade. The stator and rotor rows interact via a mixing plane, which allows the stage to be computed in a steady manner. The analysis is focused on the matching of the stator and rotor mass flow rates. The computations proved that the mixing plane approach allows the stator and rotor mass flow rates to be balanced with a careful choice of the stator-rotor static pressure interface. At the same time, the pitch averaged distribution of the transported quantities at the interface for the stator and rotor may differ slightly, together with the value of the static pressure at the hub.

The performance of a transonic axial turbine stage, representative of a wide class of aeroengines, is computed by a Navier-Stokes solver with a three-equation turbulence model. The stator blade has a coolant ejection slot on the pressure side close to the trailing edge. The stator-rotor interaction is modelled by a mixing plane approach. The tangential mixing strategy is discussed and analysed in terms of area or mass averaging. The computational results are compared with an experimental data set, which includes all the relevant quantities necessary to describe the stage. Both computations and experiments are carried out in four different operating conditions to allow first the effects of changes in Reynolds number and pressure ratio to be assessed and second the sensitivity of the computational model to these changes to be tested. The effect of tip leakage is investigated and CFD is used to help understand the experiments. The predictions compare favourably with experiments for most of the relevant parameters and prove the validity of the simple and fast computational model.

No abstract

No abstract