Design and Experimental Validation of a Ducted Counter-rotating Axial-flow Fans System
Résumé
An experimental study on counter-rotating axial-flow fans was carried out. The fans of diameter D = 375 mm were designed using an inverse method. In particular, the system is designed to have a pure axial discharge flow. The counter-rotating fans operate in a ducted-flow configuration and the overall performances are measured in a normalized test bench. The rotation rate of each fan is independently controlled. The axial spacing between the fans can vary from 10 to 150 mm. The results show that the efficiency is strongly increased compared to a conventional rotor or to a rotor-stator stage. The effects of varying the rotation rates ratio on the overall performances are studied and show that the system has a very flexible use, with a large patch of high efficient operating points in the parameter space. Measurements of wall pressure fluctuations in between the two rotors are also performed. They give hints on the overall machine noise and on the flow structure. For small axial spacings there is a strong interaction between the front rotor wake and the rear rotor induced flow that lead to very rich spectra and high levels for the casing pressure fluctuations. The increase of axial spacing from 10 to 150 mm causes only a small decrease of the efficiency and strongly modifies the shape of the spectra and the azimuthal correlations of the pressure fluctuations.
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