Unsteady Macro-Structures from Large-Eddy Simulation of Industrial Turbopump Turbine Cavity

Abstract

Large-scale dynamics of high Reynolds industrial rotor/stator cavities is poorly understood today, although it remains critical in determining operating margins for many devices. For space applications, the unsteady pressure phenomena of turbopumps called “pressure bands” depend on geometrical and thermal parameters. Today, such dangerous operating modes are not captured by computational fluid dynamics: the present primary goal is to investigate the ability of large-eddy simulation to accurately reproduce such flows and their sensitivity in terms of large-scale motions and spectral content. After validation of large-eddy simulation based on two geometries and thermalizations, we show that large-eddy simulation reproduces the spectral content overhaul triggered by the change of thermalization. The second objective is a study of the activity recorded in the different cases to improve our understanding of the pressure bands phenomena. To do so, dynamic modal decomposition reveals that the dynamics of the flow is driven by some atomic modes of which the combination explains the oscillatory signals registered by pointwise probes. These modes form macrostructures occupying the interdisk space and are at the origin of the large-scale flow dynamics. Finally, they are observed to significantly differ depending on the configuration, confirming the dependency of pressure bands phenomena on the operating condition and geometrical parameters.