航空声学引导风洞收缩段边界层修正的数值模拟和实验研究

根据数值分析得到的低速风洞收缩段边界层位移厚度分布通用曲线,针对航空声学引导风洞收缩段,推导得出收缩段边界层位移厚度分布曲线,并对收缩段型面进行修正设计,给出了修正前后的型面坐标偏差,设计加工了试验件,并进行了收缩段修正前后流场的数值模拟和实验验证。数值模拟结果表明:尽管航空声学引导风洞收缩段的边界层很薄,最大位移厚度只相当于试验段水力直径的0.5%左右,但修正效果明显。对于开口和闭口试验段流场,在收缩段型面设计时考虑粘性影响,进行边界层修正,均可显著降低试验段的动压场系数;减小气流偏角,提高试验段流场品质,有利于风洞部段的精细化设计。收缩段型面出口由于逆压梯度的存在,壁面速度过冲,气流均匀性较差,但进入平直段后,动压不均匀度及气流偏角迅速下降,因此收缩段后16.7%长度的平直段对于改善试验段流场品质很关键。在航空声学引导风洞上,采用移测架、皮托管和热线风速仪进行了修正前后收缩段、试验段动压和速度值测量,测量结果也验证了边界层修正的效果,而且实测的边界层位移厚度与理论推导值吻合。根据测量的收缩段内和出口的边界层速度分布,计算边界层位移厚度、动量损失厚度和形状因子,并据此判定,航空声学引导风洞收缩段内的边界层流动保持层流状态,未发生层流到湍流的转捩。

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.