Orion是當今最先進的太空船之一，其將會在近期執行深度太空任務，例如火星任務及小行星登陸。此外，Orion太空船是鈍體的一種，因此，高度的壓力阻力及空氣動力加溫現象會在重返大氣層時體驗到。
被震波所激起的壓力阻力及氣動力加熱是極音速飛行的主要挑戰，並且為了更好的熱分佈，鈍體乃是在極音速流域中的主要構型，但其會在物體表面上引致大量的阻力。因此，氣尖與氣盤均可被有效地運用來當作減阻之方法。此外，極音速物體的減阻及熱傳之意涵在未來的太空科學與科技發展之中扮演一個很重要的角色。
在此份論文中，我們將研究伴隨不一樣間隙寬度的氣盤之氣尖裝置在減阻上的效應。因此，我們透過ANSYS Fluent來執行一連串的計算流體力學(CFD)數值模擬工作以研究及解釋極音速流體流經鈍體的相關行為現象。此外，氣尖鈍體的阻力係數及其相關減阻效率將可以透過克里金法的最佳化演算法來得到。
對於我們所研究的構型之中，我們可以發現有氣尖裝置的鈍體之阻力遠低於其在無氣尖時。減阻效率將被迴流區域的大小規模所主導，其會隨著氣尖長度及氣盤間隙大小的增加而增加，故減阻性能將相依於物體的設計參數，例如主物體構形、氣尖長度、頂端形狀與減阻方法。本論文之結果可以成為未來極音速鈍體及太空探測載具之設計基石。

Orion MPCV (Multi-Purpose Crew Vehicle) is one of the state-of-the-art manned space vehicles nowadays which will engage in the deep space missions in the near future such as the journey to Mars and the asteroid landing. Besides, Orion spacecraft is a kind of blunt body, thus the phenomena concerning the high levels of pressure drag and aerodynamic heating are experienced during the atmospheric re-entry process. 
Pressure drag and aeroheating stirred by the shock wave is the main challenge of hypersonic flight, and the blunt body is always the principle configuration at hypersonic flow regime for heat distribution, but it would induce tremendous drag to the body. Therefore, both aerospikes and aerodisks can be efficiently utilised as the approach for drag reduction purpose. Furthermore, the implication of drag and heat transfer reduction for the hypersonic bodies plays a crucial part in the future development of space science and technology. 
In this thesis, we would research the effect of different geometric shapes of aerospikes with different disk gap widths on drag reduction. Accordingly, we implemented a series of Computational Fluid Dynamics (CFD) numerical simulation work via ANSYS Fluent CFD code to investigate and interpret the behaviour in relation to hypersonic flow over aerospiked blunt bodies. Moreover, the drag coefficient and the drag reduction efficiency of spiked blunt bodies would be worked on and acquired via Kriging-based optimisation method.
For the models we studied, we found that the drag on the spiked blunt bodies is much lower than the spike off one. The drag reduction efficiency especially would be predominated by the scale of recirculation zone, which increases as both the spike length and the gap size of aerodisk increase. Hence, the performance of drag diminution will depend on the design parameters of bodies such as main body configurations, aerospike length, tip geometric shapes and drag reduction schemes. The results from this research could be the cornerstone for the design of future hypersonic blunt bodies and space exploration vehicles.

Contents
Acknowledgement	i
摘要	ii
Abstract	iii
List of Figures	vi
List of Tables	xi
Nomenclature	xii
Chapter 1	Introduction	1
1.1	Hypersonic Flow	1
1.1.1	Physical Effects of Hypersonic Flow	1
1.1.2	Hypersonic Bodies	8
1.2	Drag Reduction	12
1.2.1	Aerospike-Based Drag Reduction	12
1.2.2	Counterflow-Based Drag Reduction	16
1.2.3	Energy-Deposition-Based Drag Reduction	17
1.3	Research Goals	18
Chapter 2	Governing Equations  and Numerical Modelling	22
2.1	Geometric Configurations	22
2.1.1	Validation Models	22
2.1.2	Investigation Models	24
2.2	Mesh Generation	27
2.3	Governing Equations	32
2.4	Numerical Modelling	33
2.4.1	Computational Fluid Dynamics Code	33
2.4.2	Boundary Conditions	34
2.5	Optimisation	36
Chapter 3	Results and Discussion	39
3.1	Validation Cases	39
3.1.1	Aerospike Off	39
3.1.2	Aerospike On	45
3.2	Blunt Body Without Aerospike	53
3.3	Blunt Bodies with Aerospikes	60
3.3.1	Different Aerospike Lengths	60
3.3.2	Different Gap Widths	70
3.4	Optimisation Case	77
Chapter 4	Conclusions	80
Chapter 5	Future Work	82
Bibliography	84

List of Figures
Figure 1.1 Physical effects of flow over hypersonic airplane.	2
Figure 1.2 Hypersonic shock wave and layer.	3
Figure 1.3 The entropy layer.	4
Figure 1.4 The viscous interaction of hypersonic flow on a flat plate: (a) no viscous interaction, and (b) viscous interaction.	6
Figure 1.5 Shock layer induced by high temperature.	7
Figure 1.6 Flow regimes and equations regarding the Knudsen number.	8
Figure 1.7 The flow patterns of different Mach numbers.	10
Figure 1.8 The flow pattern around the hypersonic body with aerospike, and the three types of aerodisks.	14
Figure 1.9 The flow fields around the hypersonic body with different counterflows.	17
Figure 1.10 The flow field around the hypersonic body caused by the energy deposition.	18
Figure 1.11 The comparison between Orion and Apollo.	20
Figure 2.1 The geometric configuration of validation cases.	22
Figure 2.2 The geometric configuration of spike off validation case in global view.	23
Figure 2.3 The geometric configurations of spike on validation case in global view.	24
Figure 2.4 The prototype model of spiked blunt body.	25
Figure 2.5 The design detail of aerodisk.	25
Figure 2.6 The geometric configuration of blunt body without spike in global view.	26
Figure 2.7 The geometric configurations of spiked blunt body in global view.	26
Figure 2.8 The mesh quality distribution of spike off validation case.	28
Figure 2.9 The skewness distribution of spike off validation case.	28
Figure 2.10 The mesh quality distribution of spike on validation case.	29
Figure 2.11 The skewness distribution of spike on validation case.	29
Figure 2.12 The mesh of spike off validation case in global view.	30
Figure 2.13 The mesh of spike off validation case in local view.	30
Figure 2.14 The mesh of spike on validation case in global view.	31
Figure 2.15 The mesh of spike on validation case in local view.	31
Figure 2.16 The boundary conditions of CFD computation work.	36
Figure 2.17 Correlations with Θ.	38
Figure 2.18 Correlations with P.	38
Figure 3.1 The convergence history of drag coefficient: aerospike off validation case.	40
Figure 3.2 The surface pressure distribution of aerospike off case.	41
Figure 3.3 The pressure contours of aerospike off case.	42
Figure 3.4 The pressure contours of aerospike off case in local view.	42
Figure 3.5 The surface temperature distribution of aerospike off case.	43
Figure 3.6 The temperature contours of aerospike off case.	43
Figure 3.7 The wall Y plus of aerospike off case.	44
Figure 3.8 The Mach number contours of aerospike off case.	45
Figure 3.9 The residuals of aerospike on case.	46
Figure 3.10 The convergence history of drag coefficient: aerospike on validation case.	46
Figure 3.11 The surface pressure distribution of aerospike on case.	48
Figure 3.12 The pressure contours of aerospike on case.	49
Figure 3.13 The pressure contours near the hemispherical main body of aerospike on case in local view.	49
Figure 3.14 The surface temperature distribution of aerospike on case.	50
Figure 3.15 The temperature contours of aerospike on case.	51
Figure 3.16 The wall Y plus of aerospike on case.	51
Figure 3.17 The Mach number contours of aerospike on case.	52
Figure 3.18 The flow patterns around the hypersonic blunt bodies with and without spikes.	53
Figure 3.19 The residuals of plain blunt body.	54
Figure 3.20 The pressure distribution along the plain blunt body arc-length normalised by the pressure of freestream.	55
Figure 3.21 The pressure contours in the vicinity of the plain blunt body nose.	56
Figure 3.22 The pressure contours in the vicinity of the blunt body nose.	58
Figure 3.23 The Mach number contours in the vicinity of the blunt body nose.	58
Figure 3.24 The pressure distribution along the spike-off blunt body arc-length normalised by the pressure of freestream.	59
Figure 3.25 The drag coefficients of different spiked blunt body configurations when spike length at constant: (a) total drag coefficient, (b) pressure drag coefficient and (c) viscous drag coefficient. The drag coefficients of the hypersonic spiked blunt bodies are subject to the length of aerospike and the size of gap.	64
Figure 3.26 The drag reduction efficiency as indicated by the percentage of total drag reduction when aerospike length at constant.	65
Figure 3.27 The streamlines around different spiked blunt bodies when S1/L2=0: (a) L1/D=1.5, (b) 2.0, (c) 2.5, (d) 3.0, and (e) 3.5, and (f) 4.0.	66
Figure 3.28 The pressure contours around different spiked blunt bodies when S1/L2=0: (a) L1/D=1.5, (b) 2.0, (c) 2.5, (d) 3.0, (e) 3.5, and (f) 4.0.	66
Figure 3.29 The pressure distribution along the main body arc-length normalised by the pressure of freestream: (a) S1/L2=0, (b) 0.2, (c) 0.4, and (d) 0.6. The compression and expansion waves are located ahead and behind the peak pressure values of every pressure distribution curves, respectively.	67
Figure 3.30 The streamlines around different spiked blunt bodies when L1/D=4.0: (a) S1/L2=0, (b) 0.2, (c) 0.4, and (d) 0.6.	69
Figure 3.31 The pressure contours around different spiked blunt bodies when L1/D=4.0: (a) S1/L2=0, (b) 0.2, (c) 0.4, and (d) 0.6.	69
Figure 3.32 The drag coefficients of different spiked blunt body configurations when gap width at constant: (a) total drag coefficient, (b) pressure drag coefficient and (c) viscous drag coefficient. The drag coefficients of the hypersonic spiked blunt bodies are subject to the length of aerospike.	72
Figure 3.33 The drag reduction efficiency as indicated by the percentage of total drag reduction when gap width at constant.	73
Figure 3.34 The streamlines around different spiked blunt bodies when L1/D=1.5: (a) S1/L2=0, (b) 0.2, (c) 0.4, and (d) 0.6.	74
Figure 3.35 The pressure contours around different spiked blunt bodies when L1/D=1.5: (a) S1/L2=0, (b) 0.2, (c) 0.4, and (d) 0.6.	74
Figure 3.36 The streamlines around different spiked blunt bodies when S1/L2=0.6: (a) L1/D=1.5, (b) 2.0, (c) 2.5, (d) 3.0, (e) 3.5, and (f) 4.0.	76
Figure 3.37 The pressure contours around different spiked blunt bodies when S1/L2=0.6: (a) L1/D=1.5, (b) 2.0, (c) 2.5, (d) 3.0, (e) 3.5, and (f) 4.0.	76
Figure 3.38 The prediction of total drag coefficient via Kriging method.	78
Figure 3.39 The pressure distribution of spiked blunt bodies with L1/D=4 and 5.	78
Figure 3.40 The streamlines around the blunt body with an aerospike L1/D=5.0 and S1/L2=0.6.	79
Figure 3.41 The pressure contours around the blunt body with an aerospike L1/D=5.0 and S1/L2=0.6.	79
Figure 5.1 NASA’s Orion spacecraft with ESA’s European Service Module.	83
Figure 5.2 The vertical structure of Saturnian atmosphere.	83

List of Tables
Table 1.1 The flow regimes of different Mach numbers.	9
Table 1.2 Four categories of hypersonic vehicles.	11
Table 1.3 Literature review	14
Table 2.1 The geometric dimensions of validation cases.	23
Table 2.2 The geometric dimensions of investigation cases.	25
Table 2.3 The mesh detail of validation cases.	27
Table 3.1 The values of pressure and viscous forces and related coefficients.	57

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