The Surge Margin of an Axial Compressor: Estimations from Steady State Simulations

Övrigt konferensbidrag, 2017

The present paper reviews past work where numerical simulation results have been compared with experimental data. From this review, the capability of 3D steady state RANS calculations to estimate the surge margin is discussed and it is shown that steady state calculations typically under-estimate the surge margin. Furthermore, different approaches to evaluate and maximize the stable operating range of a compressor from steady state calculations in an optimization process are discussed, with a main focus on a rotor-stator configuration. For validation purposes it is appropriate to compare experimental results with the surge margin calculated using the performance at the last numerically stable operating point. In an optimization process, evaluating and as an objective function maximizing the maximum possible weighted average static pressure recovery of the stage is here discussed to be an appropriate approach to find blade designs with a large stable operating range. As a blade passage reach its diffusing limit, performance quickly deteriorates if the incidence increase further. Compared to the numerical stability limit, the maximum pressure increase is typically more easily evaluated. Finding the last numerically stable operating point may be very time consuming and take a large number of iterations, with the mass flow sometimes showing an asymptotic behavior towards a lower value as iterations progress.