A numerical and experimental test-bed for low-speed fans

An extensive experimental and numerical database provides detailed information on some transition and noise mechanisms encountered in the low-Reynolds-number flows of low-speed axial fans for the first time. Two different similarly instrumented mock-ups built from the same industrial controlled-diffusion airfoil have allowed the first consistent comparison of wall pressure and near-field velocity statistics on the same geometry with and without rotation in perfect similitude of Mach and Reynolds numbers. The experimental and numerical results on the stationary airfoil constitute the largest unique aeroacoustic data set for airfoil trailing-edge noise characterization including installation effects. A similar experimental aeroacoustic database has been built on the rotating controlled-diffusion blade in the Michigan State University-Automotive Fan Research and Development (MSU-AFRD) test facility for different fan configurations, rotational speeds and flow rates. This yields a unique test-bed for fan code validation. The comparisons between the stationary and rotating airfoils suggest that the wall pressure statistics are hardly influenced by rotation in the trailing-edge region, and that the differences in the velocity statistics in the near-wake are a more energetic wake with smaller velocity deficits and diffusion, and a far-less uniform inviscid region in the rotating case.

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