脊状结构对翼型流动及噪声特性的影响研究

发布时间：2019-02-11 12:43

【摘要】：脊状表面减阻作为仿生减阻的重要技术之一,以其低能耗和减阻效果明显而著称,是一种高效、实用的边界层减阻技术。目前,该技术在航海、交通工具、航空航天、流体机械、油气输运、体育、医疗等领域得到了较为广泛应用。本文通过数值模拟的方法,以三维槽道为研究对象,研究在不同速度下脊状结构顶角β对流动阻力的影响。该部分从脊状结构对局部压力的影响入手,逐步分析脊状结构对近壁面速度分布、速度梯度分布、壁面剪切应力分布、摩擦阻力系数等基本流动参数影响,得到不同工况下的减阻效果。为了对减阻效果进行更好的解释,研究了脊状结构对法向速度脉动、流向涡的影响,从涡结构的角度对减阻机理进行探索分析。结果表明:沟槽内形成的漩涡结构可以有效的减小脊状结构布置区域速度梯度和壁面剪切应力,最终减小摩擦阻力。脊状结构顶角β=90°,25m/s的速度下取得的最大减阻率为9.71%。在脊状结构布置的区域,流向涡的涡头上扬的角度变大,致使由流向涡引起的“上扬”和“下扫”事件减弱,有效的减小了摩擦阻力。此外,脊状结构布置区域流向涡的失稳破碎明显;流经脊状结构段后,流向涡的空间密度分布显著减小,这个可能是因为脊状结构影响了y+在20?60范围内自维持过程中流向涡的再生,同样达到了减小壁面的摩擦阻力的效果。在得到脊状结构减阻机理后,本文研究了脊状结构布置位置和压力梯度对NACA0018翼型流动及噪声特性的影响。主要分析了脊状结构对翼型边界层速度分布、尾迹速度分布、表面压力系数、升阻比的影响,并且通过熵产分析的方法研究了脊状结构对能量耗散的控制作用,最后对监视点处噪声信号的时域和频率进行分析,研究了脊状结构对NACA0018翼型噪声特性的影响。结果表明:α=6°攻角下,riblet-H脊状结构翼型可以有效的减小边界层的分离区域,减小尾迹速度亏损,此外还可以提高翼型的升力系数,减少翼型阻力系数,24m/s的工况下升阻比相对光滑翼型而言提高了53.418%。在噪声方面,riblet-H翼型模型有效的减少了0-3000Hz频率范围内的噪声。通过对漩涡结构及熵产的分析发现,在α=6°攻角下riblet-H翼型可以有效的控制漩涡结构的生成和高熵产结构的能量耗散。
[Abstract]:As one of the important bionic drag reduction techniques, ridged surface drag reduction is known for its low energy consumption and obvious drag reduction effect. It is an efficient and practical boundary layer drag reduction technology. At present, the technology has been widely used in navigation, transportation, aerospace, fluid machinery, oil and gas transportation, sports, medical treatment and other fields. In this paper, the effect of the top angle 尾 of the ridge structure on the flow resistance at different velocities is studied by means of numerical simulation. Starting with the influence of ridge structure on local pressure, the influence of ridge structure on velocity distribution, velocity gradient distribution, wall shear stress distribution, friction resistance coefficient and other basic flow parameters are analyzed step by step. The drag reduction effect under different working conditions is obtained. In order to better explain the drag reduction effect, the effect of ridged structure on normal velocity pulsation and flow vortex is studied, and the mechanism of drag reduction is analyzed from the point of view of vortex structure. The results show that the vortex structure formed in the groove can effectively reduce the velocity gradient and wall shear stress in the arrangement area of the ridge structure, and finally reduce the friction resistance. The maximum drag reduction rate obtained at the velocity of 25m/s is 9.71 for the ridge structure with a parietal angle 尾 = 90 掳. In the region with ridged structure, the angle of vortex head rising becomes larger, which weakens the "upward" and "downward sweep" events caused by the flow vortex, and effectively reduces the friction resistance. In addition, the instability and breakage of vortex flow direction in the arrangement area of ridged structure is obvious. The spatial density distribution of the flow vortex decreases significantly after flowing through the ridge structure, which may be due to the fact that the ridge structure affects the regeneration of the flow vortex in the self-sustaining process of y in the range of 20 ~ 60, and also achieves the effect of reducing the friction resistance of the wall. After obtaining the drag reduction mechanism of the ridged structure, the effects of the position of the ridged structure and the pressure gradient on the flow and noise characteristics of the NACA0018 airfoil are studied in this paper. The effects of ridge structure on velocity distribution of boundary layer, wake velocity distribution, surface pressure coefficient and lift-drag ratio of airfoil are analyzed. The control effect of ridged structure on energy dissipation is studied by entropy production analysis. Finally, the time domain and frequency of the noise signal at the surveillance point are analyzed, and the influence of the ridge structure on the noise characteristics of the NACA0018 airfoil is studied. The results show that when 伪 = 6 掳angle of attack, riblet-H ridge structure airfoil can effectively reduce the separation area of boundary layer and the wake velocity loss, in addition, it can also increase the lift coefficient of airfoil and reduce the drag coefficient of airfoil. The rise-to-drag ratio of 24m/s is increased by 53.418 in comparison with the smooth airfoil. In the aspect of noise, riblet-H airfoil model can effectively reduce the noise in the range of 0-3000Hz frequency. Through the analysis of vortex structure and entropy production, it is found that riblet-H airfoil can effectively control the formation of swirl structure and the energy dissipation of high entropy production structure at the angle of attack of 伪 = 6 掳.
【学位授予单位】：华北电力大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：TB53

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