||Aerodynamic Performance Analysis Under the Influence of Heavy Rain by Using Two-Phase Flow Approach
||Department of Aerospace Engineering
Two Phase Flow
||對飛行安全有害的氣象現諸如風切、雷雨、冰或雪這些危險因子是大眾所了解的，而大雨對飛機所造成的氣動力損失則是正在進行中的研究主題且需要長遠的進行研究。除了本研究團隊在2003年曾經針對大雨對機翼性能分析有過分析之外，近10年來不論是在實驗或是在數值計算方面已鮮少有相關的研究。本研究首先對回顧前人所做的因大雨效應而使得飛機性能減低的研究並使用數值方法做進一步的探討，並使用NACA 64-210二維機翼和現有的商用軟體FLUENT，大雨的模擬則是採用FLUENT內的二相流 (Two-Phase Flow)離散相的DPM模組(Discrete Phase Model)來完成並計算空氣動力特性的改變，如升阻力係數和攻角等。本研究首先進行乾淨機翼的驗證工作，並成功模擬出二維機翼在大雨下的性能衰減，其衰減程度會隨著降雨量的增加而越大，而失速的情形也有提前發生的現象，研究發現升力係數減少、阻力係數增加的程度與Bezos 實驗結果相近。本研究所得到的量化資料能夠能對航空公司運作上有所助益，長遠來說，可以使得飛機飛行的更安全。
||The detrimental effects of some meteorological phenomenon such as wind shear, thunderstorm, ice/snow etc, to aviation safety are relatively well known. But aerodynamic influences due to heavy rain are still the on-going research subject, and needs further investigation. But for the past decade there are neither experimental nor numerical researches about heavy rain except our research team conducted at 2003. This paper first review some research finding of heavy rain effects on aerodynamic performance degradation. Secondly, a commercial CFD package FLUENT and preprocessing tool Gambit is used as our main analysis tools, and the simulation of rain is accomplished by using Two-Phase Flow approach’s Discrete Phase Model (DPM) provided by FLUENT. The results shows that this research successfully simulate the aerodynamic efficiency degradation under the heavy rain. The degradation rate increases with the rain rate, and the premature stall phenomenon is also discovered. It is expected that the quantitative information gained in this paper could be useful to the operational airline industry, and greater effort should put in this direction to further improve aviation safety.
List of Tables IV
List of Figures V
Chapter 1 Introduction 1
Chapter 2 Research Background 5
2.1 Literature Review 5
2.2 Characteristics of Rain on Airfoil 7
2.3 Physics and Influences of an Airfoil in Rain 9
Chapter 3 Numerical Modeling 13
3.1 Grid Generation 13
3.2 Turbulence Modeling 15
3.3 Flow Solver 18
3.4 Multi-Phase Flow Approach 22
3.5 Verification 29
Chapter 4 Results and Discussion 32
Chapter 5 Conclusions 50
List of Tables
Table 4-2 Drag coefficients error percentage for 3 numerical results comparing to experimental data 34
Table 4-3 Numerical results of lift coefficients degradation percentage for 2 rain rate cases 39
Table 4-4 Experimental lift coefficients degradation percentage for 2 rain rate cases 39
Table 4-5 Numerical results of drag coefficients increasing percentage for 2 rain rate cases 41
Table 4-6 Experimental drag coefficients increasing percentage for 2 rain rate cases 41
Table 4-7 Numerical results of lift to drag (L/D) value degradation percentage for 2 rain rate cases 43
Table 4-8 Experimental results of lift to drag (L/D) value degradation percentage for 2 rain rate cases 44
List of Figures
Fig 2-1 Sketch of water behavior on top of wing surface  9
Fig 2-2 Characteristics of four surface water flow regions: 1. droplet-impact region; 2. film-convection region; 3. rivulet-formation region; and 4. droplet-convection region . 9
Fig 2-3 Streamline patterns at stalled angle of attack for two different surface conditions (a) Stall at clean wing configuration, (b) Stall at contaminated (rain) surface. 12
Fig 3-1 Far mesh of NACA 64-210 14
Fig 3-2 Near mesh of NACA 64-210 14
Fig 3-3 The solution loops of the pressure-based solver  20
Fig 3-4 Physics of splashing, momentum, heat, and mass transfer for the Wall-Film  26
Fig 3-5 Heat, mass, and momentum transfer between discrete and continuous phase  27
Fig 3-6 Wall Y plus at angle of attack 0 deg 30
Fig 3-7 Lift coefficients comparison between numerical results and theory 31
Fig 3-8 Drag coefficients comparison between numerical results and theory 31
Fig 4-1 Lift coefficients for 3 different numerical results comparing to experimental data 32
Fig 4-2 Drag coefficients for 3 different numerical results comparing to experimental data 34
Fig 4-3 Lift coefficients for no rain condition at AOA 0 deg. 36
Fig 4-4 Drag coefficients for no rain condition at AOA 0 deg. 36
Fig 4-5 Lift coefficients for numerical and experimental results 37
Fig 4-6 Drag coefficients for numerical and experimental results 38
Fig 4-7 Lift degradation rate at LWC=25g/m3for numerical and experimental results 40
Fig 4-8 Lift degradation rate at LWC=39g/m3 for numerical and experimental results 40
Fig 4-9 Drag increasing rate at LWC=25g/m3 for numerical and experimental results 42
Fig 4-10 Drag increasing rate at LWC=39g/m3 for numerical and experimental results 42
Fig 4-11 L/D degradation rate at LWC=25g/m3 for numerical and experimental results 44
Fig 4-12 L/D degradation rate at LWC=39g/m3 for numerical and experimental results 45
Fig 4-13 Global view of rain distribution 46
Fig 4-14 Local view of rain droplets near airfoil 46
Fig 4-15 Local view of instance of rain droplets impacting airfoil 47
Fig 4-16 Lift coefficients convergence process at AOA 2 deg 48
Fig 4-17 Drag coefficients convergence process at AOA 2 deg 48
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