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熟知的，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研究。除了本研究團隊在2003年、2008年曾經針對大雨對二維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。而三維翼胴合一飛機(Blended-Wing-Body,　BWB)則因其高效率與節能，將是下一代飛機的主流。本研究首先回顧前人所做的因大雨效應而使得飛機性能減低的相關研究，並使用數值方法做進一步的探討，並參考文獻，模擬出相似性能之三維翼胴合一飛機（BWB)外型，大雨的模擬則是採用現有的商用軟體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。本研究首先進行飛機性能的驗證工作，並成功模擬出三維三維翼胴合一飛機在大雨下的性能衰減，其衰減程度會隨著降雨量的增加而加大，而失速的情形也有提前發生的現象，研究結果之升力係數減少、阻力係數增加的程度和Bezos 實驗結果相比較而有類似趨勢。本研究所得到的量化資料將能對航空公司運作上有所幫助，長遠來說，不管是未來飛機設計，或飛行安全考量都更有助益。

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 decades there are neither experimental nor numerical researches about heavy rain except our research team conducted at 2003 and 2008. This paper first reviews some research findings in creating a geometrical model of Blended-Wing-Body configuration and its aerodynamic performance degradation due to heavy rain effects. Secondly, a commercial CFD package FLUENT and preprocessing tool Gambit is used as our main analytical tools, and the simulation of heavy 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 Blended-Wing-Body aerodynamic efficiency at cruise condition and the degradation effect under the heavy rain at low speed. The BWB aerodynamic degradation rate increases with the rain rate as expected. When comparing with experimental data, our numerical results show that the lift coefficients decrease, drag coefficients increase. 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 aircraft design and improve aviation safety for future Blended-Wing-Body transport aircraft.

Contents	V
List of Tables	VI
List of Figures	VII
Nomenclature	X
Chapter 1 Introduction	1
Chapter 2 Research Background	8
2.1 Literature Review	8
2.2 Aerodynamics of the Blended-Wing-Body Concept	14
2.3 Characteristics of Rain on Airfoil	15
2.4 Physics and Influences of an Airfoil in Rain	18
Chapter 3 Numerical Modeling	23
3.1 Geometry Model Construction	23
3.2 Grid Generation	30
3.3 Turbulence Modeling	27
3.4 Flow Solver	31
3.5 Multi-Phase Flow Approach	36
3.6 Verification	44
Chapter 4 Results and Discussion	50
4.1 Blended-Wing-Body Geometry Model Construction	50
4.2 The Influence of Heavy Rain Condition	56
Chapter 5 Conclusions	73
References	75
Appendix	i

List of Tables
Table 3-1 ONERA M6 wing geometry	45
Table 4-1 Aerodynamic performance of Blended-Wing-Body	56
Table 4-2 several distance upstream from two-dimensional airfoil leading-edge	57
Table 4-3 The change of lift, drag, and moment coefficient numerical results (Reynolds number=3E+6)	60
Table 4-4 The change of lift and drag coefficient numerical results (Reynolds number=6E+7)	63
Table 4-5 The comparing with lift and drag degradation (Reynolds number=6E+7 LWC=25 g/m3)	64
Table 4-6 The comparing with lift and drag degradation (Reynolds number=6E+7 LWC=39 g/m3)	66

















List of Figures
Fig 1-1 Airbus product line and BWB profile [1]	2
Fig 2-1 Aircraft design evolution [9].	8
Fig 2-2 Early blended configuration concept [9].	9
Fig 2-3 Surface area of BWB concept [9]	15
Fig 2-4 Sketch of water behavior on top of wing surface [4]	18
Fig 2-5 Characteristics of four surface water flow regions: 1. droplet-impact region; 2. film-convection region; 3. rivulet-formation region; and 4. droplet-convection region [21].	18
Fig 2-6 Streamline patterns at stalled angle of attack for two different surface conditions (a) Stall at clean wing configuration, (b) Stall at contaminated (rain) surface [4].	21
Fig 3-1 Blended-Wing-Body geometry model	24
Fig 3-2 Far mesh of the Blended-Wing-Body	26
Fig 3-3 Near mesh of the Blended-Wing-Body	26
Fig 3-4 The solution loops of the pressure-based solver [26]	34
Fig 3-5 Physics of splashing, momentum, heat, and mass transfer for the wall-film [26]	41
Fig 3-6 Heat, mass, and momentum transfer between discrete and continuous phase [26]	42
Fig 3-7 Pressure coefficients on the wing surface at section (y/b)=0.20	46
Fig 3-8 Pressure coefficients on the wing surface at section (y/b)=0.44	46
Fig 3-9 Pressure coefficients on the wing surface at section (y/b)=0.65	47
Fig 3-10 Pressure coefficients on the wing surface at section (y/b)=0.80	47
Fig 3-11 Pressure coefficients on the wing surface at section (y/b)=0.90	48
Fig 3-12 Pressure coefficients on the wing surface at section (y/b)=0.95	48
Fig 3-13 Pressure coefficients on the wing surface at section (y/b)=0.99	49
Fig 4-1  The airfoil section profile at y=0.0, 1.0, 3.0, 6.0 m	50
Fig 4-2  The airfoil section profile at y=10.0, 13.0 m	51
Fig 4-3  The airfoil section profile y=17.5, 23.5, 38.75 m	52
Fig 4-4  Twist angle distribution	53
Fig 4-5 Blended-Wing-Body with no twist and no winglet	54
Fig 4-6 Blended-Wing-Body with no winglet	54
Fig 4-7 Blended-Wing-Body	55
Fig 4-8 Lift coefficients for numerical and experimental results [7]	56
Fig 4-9 Drag coefficients for numerical and experimental results [7]	57
Fig 4-10 Lift coefficients for 2 numerical results comparing to experiment data	59
Fig 4-11 Drag coefficients for 2 numerical results comparing to experiment data	59
Fig 4-12 Wall Yplus on the section profile (y/b=0.20) at angle of attack of 2 degree	60
Fig 4-13 Lift coefficients for 3 numerical results comparing	62
Fig 4-14 Drag coefficients for 3 numerical results comparing	63
Fig 4-15 The comparing with lift drag degradation with 64210 Numerical and Bezos’ (Reynolds number=6E+7 LWC=39g/m3)	67
Fig 4-16 The comparing with lift drag degradation with 64210 Numerical and Bezos’ (Reynolds number=6E+7 LWC=39g/m3)	68
Fig 4-17 The comparing with lift drag degradation with 64210 Numerical and Bezos’ (Reynolds number=6E+7 LWC=39g/m3)	68
Fig 4-18 The comparing with drag degradation with 64210 Numerical and Bezos’ (Reynolds number=6E+7 LWC=39 g/m3)	69
Fig 4-19 Numerical results of the Lift-to-Drag change	70
Fig 4-20 Two numerical results at Reynolds number of the Lift Coefficient Decrease Ratio	70
Fig 4-21 Two numerical results at Reynolds number of the Drag Coefficient Increase Ratio	71
Fig 4-22 Pressure coefficients on the wing surface at section (y/b)=0.20	72
Fig 4-23 View of aircraft under the mantle of heavy rain	72

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