14th European Conference on Turbomachinery Fluid dynamics & Thermodynamics
In the scope of this publication, the unsteady pressure fluctuations measured by fast-response transducers mounted within a linear low-pressure turbine cascade are compared to simulation results provided by a Harmonic Balance solver based on a formulation in the frequency domain. The unsteady measurement data in combination with numerical results based on a conventional time-marching solution process are used to evaluate the capability of the Harmonic Balance solver to predict the transient pressure fluctuations exciting the investigated stator vane. The dominant source of unsteadiness in the investigated cascade flow is induced by the application of a wake generator located upstream of the measured low pressure turbine cascade. Wakes of an upstream rotor are generated by rotating cylindrical steel bars at a prescribed rotational speed that refer to a frequency of f ~ 500 Hz. The numerical results indicate that the pressure fluctuations acting on the vane's pressure side and the front part of its suction side are dominated by the wake induced velocity deficit. The excitation at the rear part of the suction side is essentially driven by the presence of an open separation bubble and is therefore highly dependent on the unsteady behaviour of turbulence. For both time and frequency domain methods, the impact of turbulence is considered by the application of Wilcox' k-ω two equation model in combination with a correlation based transition model. In order to increase the stability of the investigated frequency domain solver, a developed Lanczos-type filter method is applied if the unsteadiness of the underlying turbulence model is taken into account. Furthermore, the benefit of the applied filter method compared to an approach neglecting unsteady turbulence phenomena is discussed in order to judge its benefit in the context of an aerodynamic design process.