Title Page
Contents
Abstract 11
Nomenclature 15
Chapter 1. Introduction 26
1.1. Background 26
1.2. Literature Review 31
1.3. Motivation 53
1.4. Objective 54
1.5. Outline of this Study 56
Chapter 2. Numerical Analysis 58
2.1. Governing Equation 58
2.2. Turbulence Model 62
2.2.1. RANS 64
2.2.2. LES 72
2.2.3. DNS 77
2.3. Finite Volume Method 78
2.3.1. Discretization of Finite Volume Equation 81
2.3.2. Pressure-Velocity Coupling Algorithm 91
2.4. Linear Solver 101
2.4.1. Direct solver 103
2.4.2. Iteration solver 104
2.5. Open Source Field Operation and Manipulation 110
2.6. Closure 114
Chapter 3. Study on circular cylinder flow 115
3.1. Problem Description 115
3.1.1. Study strategy 116
3.2. Verification 121
3.2.1. Mesh independence and Dimensional sensitivity study 122
3.2.2. Turbulence Model Selection 128
3.3. Validation 132
3.3.1. Data analysis 132
3.4. Closure 135
Chapter 4. Vortex Suppression Effect of Rotating Ratio 137
4.1. Problem description 137
4.2. Result and discussion 139
4.2.1. Wake Flow Structures 139
4.2.2. Vortex visualization 147
4.2.3. Data analysis 151
4.2.4. Trend and prediction 158
4.3. Closure 160
Chapter 5. Vortex Suppression Effect of Helical Strake Parameter 162
5.1. Outline 162
5.2. Effect of Attaching Strake 167
5.3. Effect of Strake Number 173
5.3.1. Problem description 173
5.3.2. Result discussion 173
5.4. Effect of Strake Pitch 181
5.4.1. Problem description 181
5.4.2. Result discussion 182
5.5. Effect of Strake Height 189
5.5.1. Problem description 189
5.5.2. Result discussion 190
5.6. Effect of Strake Thickness 197
5.6.1. Problem description 197
5.6.2. Result discussion 198
5.7. Closure 205
Conclusions 207
Appendices 209
Abstract in Korean 213
References 217
Table 3.1. Simulation setting imformation. 117
Table 3.2. Case classification for mesh independence for verification. 122
Table 3.3. Previous scholars' experiments are summarised for validation. 134
Table 4.1. General parameters of rotating cylinder cases. 139
Table 5.1. Case classification for mesh independence. 163
Table 5.2. Literature review summary. 164
Table 5.3. Strake cases mesh independence. 167
Figure 1.1. Turbulence flow shown in Leonardo's series of deluge drawings. 27
Figure 1.2. Wake of cylindrical structrue with different Reynolds numbers. 28
Figure 1.3. Several examples structural design of marine and offshore engineerin. 48
Figure 2.1. Scheme of turbulence energy cascade. 63
Figure 2.2. The shceme of the mean velocity field. 64
Figure 2.3. Practice case of RANS and LES comparison. 72
Figure 2.4. Scheme of control volume. 79
Figure 2.5. The scheme of central difference. 83
Figure 2.6. The scheme of up wind. 84
Figure 2.7. The scheme of calculating (∇φ)f in duffusion term.[이미지참조] 86
Figure 2.8. Flowchart of SIMPLE algorithm. 93
Figure 2.9. Flowchart of PISO algorithm. 96
Figure 2.10. Flowchart of PIMPLE algorithm. 99
Figure 2.11. The advantage of using AMG. 109
Figure 2.12. Matrix with structured mesh. 109
Figure 2.13. Matrix with unstructured mesh. 110
Figure 2.14. Matrix with renumber mesh mesh. 110
Figure 2.15. OpenFOAM mainly three release version. 111
Figure 2.16. OpenFOAM workflow. 112
Figure 2.17. OpenFOAM working case folder structrue. 113
Figure 3.1. Wake velocity along streamline distribution in previous scholar's study. 118
Figure 3.2. Streamline velocity at difference location from previous scholar results. 119
Figure 3.3. The drag and lift coefficient results concluded by previous scholar. 119
Figure 3.4. relevant results summary by Zdravkovich. 120
Figure 3.5. The scheme of domain setting and mesh generation. 122
Figure 3.6. Stream wise velocity distribution with 2D cases. 123
Figure 3.7. Stream wise velocity distribution with 3D cases. 124
Figure 3.8. Clip view of Velocity distribution in the X-Z plane. 125
Figure 3.9. Vottex visualization comparison. 125
Figure 3.10. Drag and lift coefficient distribution with time. 127
Figure 3.11. Stream line distribution with 3D cases. 127
Figure 3.12. Streamline distribution with different turbulence models. 128
Figure 3.13. The scheme of section plane selection. 129
Figure 3.14. Streamline velocity distribution with different turbulence model. 130
Figure 3.15. Velocity distribution in the vertical direction at different distances from the cylinder in RANS. 131
Figure 3.16. Velocity distribution in the vertical direction at different distances from the cylinder in LES. 131
Figure 3.17. Drag and lift coefficient result by WALE LES model. 133
Figure 3.18. FFT analysis based on lift coefficient of WALE. 133
Figure 3.19. Stream velocity distribution for validation process. 134
Figure 3.20. Velocity contour and streamline distribution. 135
Figure 4.1. The application of rotating cylinder for wind turbien. 138
Figure 4.2. Computation domain and mesh generation. 139
Figure 4.3. Wake flow structure comparison (a)Current Study velocity distribution in X-Y plane at t*=705, (b) Seyed-Aghazadeh et al.[62] experiment results. 140
Figure 4.4. Snapshots of instantaneous streamwise velocity (t*=150 ~ 154) (α=0 ~ π). 141
Figure 4.5. Pressure distribution on streamline and LIC. (a)Pressure Distribution at X-Y plane and visualized by line integral convolution (LIC) Technical (b)... 143
Figure 4.6. The scheme of the velocity distribution location. 144
Figure 4.7. Stream wise velocity distribution with different rotating ratio. 145
Figure 4.8. Velocity distribution in the vertical direction at distances 1.06. 146
Figure 4.9. Velocity distribution in the vertical direction at distances 1.54. 146
Figure 4.10. Velocity distribution in the vertical direction at distances 2.02 147
Figure 4.11. Wake Flow Vortex Visualization for X-Y plane with iso-surface of Q-criterion (Q=0.1), the rotating ratio from up to down equal to 0 ~ π. 149
Figure 4.12. Wake Flow Vortex Visualization for X-Z plane with iso-surface of Q-criterion (Q=0.1), the rotating ratio from up to down equal to 0 ~ π. 150
Figure 4.13. The monitoring of drag and lift coefficients throughout the simulation process. 151
Figure 4.14. Recording of all cases in drag coefficient. 152
Figure 4.15. Recording of all cases in lift coefficient. 153
Figure 4.16. FFT analysis result with α=0. 154
Figure 4.17. FFT analysis result with α=π/4. 154
Figure 4.18. FFT analysis result with α=1. 155
Figure 4.19. FFT analysis result with α=π/2. 155
Figure 4.20. FFT analysis result with α=2. 156
Figure 4.21. FFT analysis result with α=2.5. 156
Figure 4.22. FFT analysis result with α=3. 157
Figure 4.23. FFT analysis result with α=π. 157
Figure 4.24. Lift coefficient trend with changing rotating ratio. 158
Figure 4.25. Drag coefficient trend with changing rotating ratio. 159
Figure 4.26. Strouhal number trend with changing rotating ratio 160
Figure 5.1. The schematic of Computational domain. 166
Figure 5.2. Mesh generation around the cylindrical structure. 166
Figure 5.3. Instantaneous velocity distribution of bare and strake attached cylinder. 167
Figure 5.4. Visualization of vortex(Q=0.01). (a) Front view, (b) Plan view (c) Side view. 169
Figure 5.5. Mean Pressure and velocity distribution. 170
Figure 5.6. Drag and lift coefficients of cylindrical structure. (a)Drag coefficient (b) Lift coefficient. 171
Figure 5.7. Spectra of lift coefficient Cl for the cylinder with and without helical strake.[이미지참조] 172
Figure 5.8. Model of strake start. 173
Figure 5.9. Vortex visualization of front view (Q=0.01). 174
Figure 5.10. Vortex visualization of side view (Q=0.01). 175
Figure 5.11. Result of drag coefficient with different strake start. 176
Figure 5.12. Result of lift coefficient with different strake start. 177
Figure 5.13. Spectrum result with bare cylinder. 178
Figure 5.14. Spectrum result with 2-start strake. 179
Figure 5.15. Spectrum result with 3-start strake. 179
Figure 5.16. Spectrum result with 4-start strake. 180
Figure 5.17. Scheme of shrake pitch cases. 181
Figure 5.18. Scheme of shrake pitch definition. 182
Figure 5.19. Vortex visualization of front view (Q=0.01). 183
Figure 5.20. Vortex visualization of side view (Q=0.01). 183
Figure 5.21. Drag coefficients with different strake pitch. 184
Figure 5.22. Lift coefficients with different strake pitch. 185
Figure 5.23. Spectra of lift coefficient Cl for the cylinder with strake pitch 05D.[이미지참조] 186
Figure 5.24. Spectra of lift coefficient Cl for the cylinder with strake pitch 10D.[이미지참조] 187
Figure 5.25. Spectra of lift coefficient Cl for the cylinder with strake pitch 15D.[이미지참조] 187
Figure 5.26. Spectra of lift coefficient Cl for the cylinder with strake pitch 20D.[이미지참조] 188
Figure 5.27. Scheme of shrake height cases. 189
Figure 5.28. Scheme of shrake height definition. 190
Figure 5.29. Vortex visualization of front view (Q=0.01). 191
Figure 5.30. Vortex visualization of side view (Q=0.01). 191
Figure 5.31. Drag coefficients with different strake height. 192
Figure 5.32. Lift coefficients with different strake height. 193
Figure 5.33. Spectra of lift coefficient Cl for the cylinder with SH06.[이미지참조] 194
Figure 5.34. Spectra of lift coefficient Cl for the cylinder with SH09.[이미지참조] 195
Figure 5.35. Spectra of lift coefficient Cl for the cylinder with SH12.[이미지참조] 195
Figure 5.36. Spectra of lift coefficient Cl for the cylinder with SH15.[이미지참조] 196
Figure 5.37. Scheme of shrake thick cases. 197
Figure 5.38. Scheme of shrake thick definition. 198
Figure 5.39. Vortex visualization of front view (Q=0.01). 199
Figure 5.40. Vortex visualization of side view (Q=0.01). 199
Figure 5.41. Drag coefficients with different strake thick. 200
Figure 5.42. Lift coefficients with different strake thick. 201
Figure 5.43. Spectra of lift coefficient Cl for the cylinder with ST01.[이미지참조] 202
Figure 5.44. Spectra of lift coefficient Cl for the cylinder with ST02.[이미지참조] 203
Figure 5.45. Spectra of lift coefficient Cl for the cylinder with ST03.[이미지참조] 203
Figure 5.46. Spectra of lift coefficient Cl for the cylinder with ST04.[이미지참조] 204