Abstract
In this work, the fluid mechanics performance of four different contraction wall shapes has been studied and compared side-by-side by computational simulation, and the effect of contraction cross-sectional shape on the flow uniformity at the contraction exit has been included as well. A different contraction wall shape could result in up to an extra 4% pressure drop of a closed-loop wind tunnel, and the contraction wall shape has a stronger influence on the pressure loss than the contraction cross-sectional shape. The first and the second derivatives from different wall shape equations could provide a hint for qualitatively comparing the flow uniformity at the contraction exits. A wind tunnel contraction with an octagonal shape provides not only better fluid mechanics performance than that with a circular or a square cross-sectional shape, but also lower manufacturing costs. Moreover, a smaller blockage ratio within the test section can be achieved by employing an octagonal cross-sectional shape instead of a circular cross-sectional shape under the same hydraulic diameter circumstance. A wind tunnel contraction with an octagonal cross-sectional shape is recommended to be a design candidate.
Highlights
In the fields of fluid mechanics research, full/scaled model testing, and airspeed calibration, wind tunnel has a critical role
Both ISO 17713-1 and ASTM D5096-02 request that the flow uniformity and the turbulence intensity should be smaller than 1% difference in transversal velocity profile and less than 1% within the test section of a wind tunnel, respectively
In the field of airspeed calibration or metrology, the testing environments are commonly provided by wind tunnels, the homogeneity among wind tunnels makes people confident that the world activities are sharing a common perception of quantity measurement
Summary
In the fields of fluid mechanics research, full/scaled model testing, and airspeed calibration, wind tunnel has a critical role. Documents recommend that a wind tunnel facility should be used to calibrate or to test the performance of a rotating anemometer Both ISO 17713-1 and ASTM D5096-02 request that the flow uniformity and the turbulence intensity should be smaller than 1% difference in transversal velocity profile and less than 1% within the test section of a wind tunnel, respectively. The present work aims to establish a benchmark for investigating the fluid mechanics performance in terms of pressure drop along a contraction, exit flow uniformity, and boundary layer thickness from different contraction wall shapes which have not been studied and compared side-by-side together. Another unclear issue is the cross-sectional shape of a contraction. The fluid mechanics performance will be compared for three different common cross-sectional shapes, namely, circle, square, and octagon, in the present work
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