{'fraction_non_alphanumeric': 0.020015396458814474, 'fraction_numerical': 0.0, 'mean_word_length': 4.777777777777778, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Detection of aerodynamic noise sources in low-speed axial fans with tip end-plates

Abstract This article reports on the use of modified blade-tip configurations designed with a view to passive noise control in low-speed fans for compact cooling units. The addition of end-plates at the tip of a datum fan blade is shown to have a positive influence on the fan's rotor-only aero-acoustic signature. The aerodynamic effects of the modified blade tips are experimentally tested in a fully ducted configuration in the near field and far field using a correlation technique. The nature of the flow mechanisms in the blade-tip region are correlated with the specific end-plate design features and their role in the creation of overall acoustic emissions is clarified. The noise emitted by the fans is analysed in terms of coherent vortex structures, tip-leakage flow, and noise sources. Differences in human perception of the noise emitted to the environment are also investigated using a dot-pattern visualization. The study concludes that the modified tip configurations have a marked effect on tip-leakage vortex formation by altering the near-wall fluid paths on blade surfaces. The reduction in rotor noise emission is correlated with the control of tip-leakage flows produced by the tip end-plates.