本文關鍵詞：展弦比對薄片翻滾下落運動的影響　出處：《清華大學》2016年博士論文　論文類型：學位論文

  更多相關文章： 薄片翻滾運動 翼尖渦 展弦比 下落參數(shù)

【摘要】：本文通過實驗測量與理論分析兩種方法,研究了展弦比從2到10的自由下落薄片的翻滾運動,得到了展弦比對翻滾運動規(guī)律的影響。在實驗研究中,我們設計并構造了薄片下落發(fā)射裝置,可以以固定角度發(fā)射薄片。發(fā)射位置足夠高,以便薄片下落能飄移足夠距離,方便實驗記錄穩(wěn)定翻滾下落狀態(tài)。采用高速攝像機記錄薄片翻滾下落的運動軌跡,并構造了實驗結果處理方法,以此得到瞬時以及時間平均后的運動學和氣動參數(shù),包括下飄角、轉速、下落速度、升力和阻力系數(shù)以及他們的波動譜。作為實驗研究重要結果之一,我們發(fā)現(xiàn),在某些范圍的展弦比下,存在一個伴隨著周期倍增的雙周期旋轉現(xiàn)象,對此現(xiàn)象,我們利用傅里葉分析明確了其頻率的倍增。三維薄片即使在固定大攻角狀態(tài),流場也異常復雜。對于翻滾下落,除了旋轉導致的復雜流場,瞬時大攻角狀態(tài)下,也存在旋渦脫落以及非定常流動。因此,通過理論分析研究此類問題以獲得展弦比對翻滾運動規(guī)律的影響,是具有較高復雜度的問題。在本文中,我們通過將考慮了翻滾的二維情況下的氣動力與力矩估算公式,加入流向渦與轉動環(huán)量的影響帶來的修正,得到了三維情況下的升阻力以及力矩估算公式。其中涉及到的一些比例系數(shù)與展弦比無關,因此由展弦比足夠大的實驗結果標定。利用這些氣動參數(shù)估算,我們構造了薄片下落的運動學模型。在翻滾下落處于平衡狀態(tài)時,這樣得到的運動學模型就可以給出下飄角、下落速度和旋轉頻率。通過與實驗結果進行比較,我們驗證了理論模型的有效性。以此理論模型,我們研究了各種參數(shù)尤其展弦比對下落規(guī)律的影響。實驗和理論模型分析均表明:下飄角和下落速度垂直分量是展弦比的遞減函數(shù),轉速和下落速度水平分量是展弦比的遞增函數(shù)。原因是隨著展弦比的減小,由翼尖渦和轉動環(huán)量導致的誘導阻力加大,造成升阻比的減小,因此下飄角增大,而平動誘導阻力導致的耗散力矩,會使轉速減小。
[Abstract]:By means of experimental measurement and theoretical analysis, the rolling motion of a freely falling sheet with a aspect ratio of 2 to 10 is studied, and the effect of the aspect ratio on the rolling motion is obtained. We have designed and constructed a wafer falling launcher that can fire the wafer at a fixed angle. The emission position is high enough so that the falling flake can drift far enough. It is convenient for the experiment to record the stable tumbling state. The high-speed video camera is used to record the motion track of the thin slice rolling and falling, and the processing method of the experimental results is constructed. The kinematics and aerodynamic parameters, including the angle of falling, rotation speed, falling velocity, lift and drag coefficient and their wave spectrum, are obtained from the instantaneous and time-averaged kinematics and aerodynamic parameters, which are one of the important results of the experimental study. We find that under some range of aspect ratio, there exists a double period rotation phenomenon with double periods. We use Fourier analysis to determine the multiplication of its frequency. The flow field is extremely complex even in the fixed large angle of attack state. For tumbling and falling, except for the complex flow field caused by rotation, the instantaneous large angle of attack state. There are also vortex shedding and unsteady flow. Therefore, it is a high complexity problem to study this kind of problems through theoretical analysis to obtain the effect of aspect ratio on the rolling motion. By taking into account the two dimensional aerodynamic force and torque estimation formula of rolling, we add the effect of flow vortex and rotation ring to the correction. The formulas for estimating the lift resistance and torque in three dimensional cases are obtained. Some of the proportional coefficients involved are independent of the aspect ratio, so the experimental results with a large aspect ratio are used to estimate the aerodynamic parameters. The kinematics model of thin sheet falling is constructed. When the roll is in equilibrium, the kinematics model can give the angle of falling, the velocity of falling and the frequency of rotation. The results are compared with the experimental results. We verify the validity of the theoretical model. The effects of various parameters, especially the aspect ratio, on the falling law are studied. The experimental and theoretical model analysis show that the vertical component of the falling velocity and the falling angle are the decreasing functions of the aspect ratio. The horizontal component of rotational speed and falling velocity is an increasing function of the aspect ratio, because with the decrease of the aspect ratio, the induced resistance caused by the vorticity of the wingtip and the amount of the rotation ring increases, resulting in the decrease of the ratio of lift to drag, so the falling angle increases. And the dissipative torque caused by the translational induced resistance will decrease the rotational speed.
【學位授予單位】：清華大學
【學位級別】：博士
【學位授予年份】：2016
【分類號】：O353.4

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