AERODYNAMIC DAMPING PREDICTIONS DURING COMPRESSOR SURGE: A NUMERICAL COMPARISON BETWEEN A HALF AND FULL TRANSIENT APPROACH

Kurzfassung

The prediction of the aerodynamic damping during compressor surge is a challenging task, because the flow is continuously evolving along the four surge cycle phases: Pressurization (PR), Flow-Breakdown (FB), Reversed Flow (RF) and Regeneration (RG) and complex flow conditions like shocks and separations occur. Damping predictions with current existing methods typically consist of two steps. In the first step a modified numerical model is used to simulate transient surge cycles. In the second step, damping analyses are performed for multiple timesteps along the surge cycle phases, which are then assumed as quasi-steady. The damping simulation can be performed using nonlinear or linear approaches. If shocks or separations occur, the latter yields inaccuracies in the flow and thus in the damping predictions. A new approach was developed to take into account and improve these inaccuracies. This new method includes the damping prediction within the transient surge simulation. Thus, all surge cycle phases and the continuously evolving flow conditions are considered and nonlinear simulations are performed to account for shocks and separations. The results of this new method are presented and compared to the former method.