In this work, the fluid mechanics performance of four different contraction wall shapes has\nbeen studied and compared side-by-side by computational simulation, and the effect of contraction\ncross-sectional shape on the flow uniformity at the contraction exit has been included as well.\nA different contraction wall shape could result in up to an extra 4% pressure drop of a closed-loop\nwind tunnel, and the contraction wall shape has a stronger influence on the pressure loss than the\ncontraction cross-sectional shape. The first and the second derivatives from different wall shape\nequations could provide a hint for qualitatively comparing the flow uniformity at the contraction\nexits. A wind tunnel contraction with an octagonal shape provides not only better fluid mechanics\nperformance than that with a circular or a square cross-sectional shape, but also lower manufacturing\ncosts. Moreover, a smaller blockage ratio within the test section can be achieved by employing an\noctagonal cross-sectional shape instead of a circular cross-sectional shape under the same hydraulic\ndiameter circumstance. A wind tunnel contraction with an octagonal cross-sectional shape is\nrecommended to be a design candidate.
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