Figure 17. Amplitude of pressure fluctuations for main harmonics vs. inter-distance
CONCLUSION
The aerodynamic characteristics of a high-speed high-reaction pre-whirl axial fan stage are determined. The variation of axial inter-distance has revealed an optimum spacing allowing for the majority of wake diffusing and mixing and subsequently reaching a maximum aerodynamic efficiency. The steady flow simulations have shown that the model of frozen IGV/rotor interface has a weak influence on the average flows and the pseudo interactions. Better results, including RSI, are obtained from the unsteady flow simulation based on the frozen-rotor interface. Time mode analysis of pressure fluctuations has permitted the determination of different frequencies and the prevailing modes of a lobed structure of pressure waves. The amplitudes of pressure fluctuations and harmonics are shown to vary significantly depending on the monitor locations and also on the axial inter-distance. It is clear that IGV/rotor interactions are influenced by this distance, and the potential interaction propagating upstream and downstream of blade-row prevails more for the small inter-distances. Accordingly, an optimum distance has been identified which to maximizes the efficiency and minimize static pressure fluctuations which in turn may alleviate the levels of vibration and noise. More details about the vortical structures involvement in RSI studies requires adopting LES simulation but this is still requiring powerful computing resources.