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Experimental study of the influence of the shape on the spanwise coherence length of the flow over a bluff body

Abstract : The coherence length is a key ingredient in the efficiency of the aeolian tone generated by the flow over a bluffbody, and is often used to extrapolate noise simulations over a short segment of cylinder for comparison with measurements using longer bodies. In the present study, the influence of the cylinder crosssection on the coherence length is studied experimentally in BETI wind tunnel, by hot-wire anemometry of the flow over a circular, a square and two rectangular cylinders, at Reynolds number from 6,000 to 26,000. The coherence length estimation method is first validated for the circular cylinder case, with excellent agreement with values obtained from wall-pressure measurements in the literature. The mean flow is then scanned for the rectangular sections, and the locations of the probes for the spanwise study are based on its topology, such as the position of maximum velocity. This allows fair comparisons between the geometries, while, finally, having no significant influence on the coherence length value. For the square cylinder, the coherence length at the peak frequency is close to, though a little higher than, that of the circular cylinder. For the rectangular cylinders of aspect ratio 2 and 3, coherence lengths up to 25 diameters are measured at the peak frequency. Considering the length of the model and the size of the test-section, these high values leads to the conclusion that the shear-layer flapping is a 2D dynamics.
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Submitted on : Thursday, May 6, 2021 - 8:34:56 PM
Last modification on : Wednesday, November 3, 2021 - 4:56:04 AM
Long-term archiving on: : Saturday, August 7, 2021 - 7:44:32 PM


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Wagner Gonçalves Pinto, Florent Margnat, Camille Noûs. Experimental study of the influence of the shape on the spanwise coherence length of the flow over a bluff body. Forum Acusticum, Dec 2020, Lyon, France. pp.1515-1522, ⟨10.48465/fa.2020.0763⟩. ⟨hal-03215258⟩



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