Numerical and experimental researches on contraction boundary correction for pilot aeroacoustic wind tunnel

On the basis of the master curve of boundary layer displacement thickness for low speed wind tunnel contraction obtained from numerical research,the distribution of the displace-ment thicknessδ* for the pilot aeroacoustic wind tunnel(PAWT)’s contraction is derived.Ac-cordingly,we redesigned the contraction contour,gave the deviation after correction,fabricated the test article,and conducted the numerical simulation and experimental study.The numerical results show that,although the boundary layer of the contraction was very thin and the maxi-mumδ* was only 0 .5% or so of the test section hydraulic diameter,the correction effect was re-markable.After the correction,for both open and closed test sections,the dynamic pressure non-uniformity was reduced,the flow-deviation angle decreased,and the flow field quality was im-proved.At the contraction exit,the near wall velocity was overshoot due to the reverse pressure gradient.But after entering the straightness section,the dynamic pressure non-uniformity and the flow angle decreased sharply.After the contraction,there is a straight section whose length is 1 6 .7% of contraction,which is very helpful for improving the flowfield quality.Using mova-ble measuring device,pitot tube and hotwire anemometer,we measured the dynamic pressure and velocity before and after the correction.The measuredδ* coincides with the theoreticalδ*, and the effect of boundary correction is verified experimentally.Based on the measured velocity distribution,it can be inferred that the boundary layer in the contraction of PAWT is laminar, without transition from laminar to turbulent flow.