Session: 35-18 Turbine Methods 2

Paper Number: 101108

101108 - Efficient Unsteady Simulations of Multistage Turbines Using a Flexible Frequency-Domain Approach 

In turbomachinery systems, the relative motion of adjacent blade rows makes the flow motion unsteady and periodic by nature. The numerical treatment of such a spatial and temporal periodicity can be done using either the time-domain or the frequency-domain approaches. Among the last decades, the latter methods have been greatly developed. Their capability to accurately and efficiently represent the unsteady interactions between consecutives blade rows has been demonstrated in single and multi-stage configurations. Nonetheless, most of the methods can only handle perturbations originating from one blade row to the next one. A few studies have demonstrated the capabilities of the frequency-domain approaches to deal with clocking effects of consecutive rotor or stator blades.

Nonlinear Harmonic method (NLH) is a frequency-domain approach that is now widely used by the turbomachinery industry. Compared to other frequency-domain approaches, this method can easily deal with multiple blade-passing frequencies as sources of perturbation. The aim of this article is to present further improvements of the method that allow to include more flexibility in the selection of perturbations that are of interest for the turbomachinery designer. The selected perturbations and the number of harmonics that are used to represent the signal are now inferred from a post-processing of a steady simulation using the state-of-the-art mixing plane approach. The entropy signal at the rotor/stator interface is used to characterize the downstream traveling information, whereas the static pressure is used for the upstream traveling signal. To validate this new harmonic selection, the method has been applied to the TATEF one-stage turbine and compared to a classical time-domain approach. The same level of accuracy can be obtained at a significantly reduced computing cost. In that configuration the number of relevant harmonics is more important to represent the wake than to treat the potential effect. But the latter is of crucial importance to accurately represent the pressure distribution along the guide vane.

Furthermore, the NLH method has been extended to make a perturbation travel across more than one and a half stage. This is of particular interest for turbine applications to investigate the influence of the hot streaks originating from the combustion chamber into the turbine. This has been applied to the 2.5 stage turbine of the KJ66 micro aero-engine. It shows that the hot streak not only have an influence in the high-pressure stages but also on the low-pressure region of the turbine. Indeed, the computed maximum temperature along the low-pressure nozzle blade is about 300 K higher than the one produced by a steady mixing-plane approach.

Presenting Author: Benoit Tartinville Cadence Design Systems

Presenting Author Biography: Benoit Tartinville is an engineer in fluid dynamics and has a PhD thesis from the Universite catholique de Louvain (Belgium). He has joined Numeca in 2001 and has participated in the development of numerous features in the commercial CFD software Fine/Turbo. His main domains of interest are turbulence/transition, unsteady frequency domain methods. He he now working for Cadence Design Systems in turbomachinery CFD.

Authors:

Benoît Tartinville Cadence Design Systems
Stéphane Vilmin Cadence Design Systems