표제지
요약
목차
1. 서론 13
1.1. 연구 배경 13
1.2. 선행 연구 14
1.3. 연구 목적 및 내용 16
2. 수치해석 17
2.1. 수치해석 기법 17
2.1.1. 지배방정식 17
2.1.2. 캐비테이션 모델 20
2.1.3. Vorticity confinement model 20
2.1.4. Grid dependency test 21
3. Cloud Cavitation 23
3.1. 경계조건 및 격자 계 23
3.2. Wetted flow 25
3.3. Cavitating flow 27
3.3.1. Lift Coefficient 27
3.3.2. Shedding frequency 29
3.3.3. Cavitation features 32
3.3.4. Pressure coefficient 34
3.3.5. Shedding frequency &Pressure coefficient 37
3.3.6. SPL (Sound Pressure Level) 39
3.3.7. SPL according to Cavitation number 45
4. Tip Vortex Cavitation (TVC) 50
4.1. 경계조건 및 격자 계 50
4.2. Cavitation features 52
4.3. TVC 유동 분석 54
4.4. SPL (Sound Pressure Level) 60
4.4.1. SPL according to Cavitation number 62
5. Submarine Propeller (DARPA Suboff) 66
5.1. POW & Resistance test 70
5.2. Self-propulsion test 72
5.3. Cavitation test 73
결론 84
참고문헌 88
Table 1. Time-averaged lift coefficient at wetted flow according to the number of grids and turbulence models (RANS, DES, LES) 25
Table 2. Time-averaged lift coefficient at wetted flow according to the time steps and turbulence models (RANS, DES, LES) 26
Table 3. GCI of lift coefficient according to turbulence models and time steps 26
Table 4. Time-averaged lift coefficient at cavitating flow according to the time steps and turbulence models (RANS, DES, LES) 28
Table 5. Shedding frequency and Strouhal number according to the time steps and turbulence models (RANS, DES, LES) 29
Table 6. Shedding frequency according to turbulence model and other numerical study 29
Table 7. Location of probe to monitor pressure at top wall 39
Table 8. The results of SPL of wall pressure 40
Table 9. SPL₁ and SPL of wall pressure using LES model according to turbulence models 43
Table 10. SPL₁ and SPL of wall pressure using LES model according to time steps 43
Table 11. Comparison difference of SPL1 and SPL according to cavitating flow and wetted flow 44
Table 12. SPL1, SPL, and cavitation volume according to cavitation number 47
Table 13. Experiment and simulation conditions for simulation verification 52
Table 14. Simulation conditions according to cavitation number 62
Table 15. Main Specifications of DARPA Suboff 66
Table 16. Main Specifications of INSEAN E1619 68
Table 17. Comparison of total resistance with simulation results and results of model experiments conducted by Liu and Huang 71
Table 18. Comparison of self-propulsion simulation results 72
Table 19. Cavitation test condition and results 74
Figure 1. Domain of cavitation tunnel(a) and Geometry of Delft Twist11 Hydrofoil(b) 24
Figure 2. Lift coefficient according to the number of grids 26
Figure 3. Lift coefficient according to turbulence model at a narrow time interval 28
Figure 4. Power spectral density of lift coefficient(PSD of CL) according to turbulence model (a) and time step (b) 31
Figure 5. Comparison RANS(left), DES(middle) and LES(right); iso-surfaces show the volume fraction α=0.5 and Q-criterion 33
Figure 6. Mean Cp curve of cavitating flow at y/S=0.3 (a), 0.4 (b), 0.5 (c) according to turbulence models 35
Figure 7. Mean volume of fraction (VOF) at y/S= 0.5 according turbulence models (a) RANS, (b) DES, (c) LES. 36
Figure 8. Lift coefficient of LES model according to time series (a), Cp curve in order of time series (b) 38
Figure 9. Cavitation features and pressure coefficient at y/S=0.5 according to time series of Figure 8 (a). 38
Figure 10. Geometry of Delft Twist11 hydrofoil and location of probes 1 to 6 39
Figure 11. SPL of wall pressure with distance from LE/c according to turbulence models. 41
Figure 12. SPL of wall pressure using LES model according to time steps (a) and turbulence model (b) 42
Figure 13. Comparison LES, DES, and RANS models; SPL of wall pressure according to cavitating flow and wetted flow 44
Figure 14. Condition of simulation according to cavitation number (a), and SPL-frequency graph of wall pressure according to cavitation number 46
Figure 15. Cavitation volume/time graph according to cavitation number (a), Cp curve according to cavitation number (b). 48
Figure 16. Cavitation features according to cavitation number. From (a) to (f), the cavitation number is 4.17-1.07 (experiment condition) 49
Figure 17. NACA16-020 shape and specification (a) and simulation domain (b) 51
Figure 18. Comparison of cavitation features according to simulation conditions, (a), (b), (c) are the experimental results, (d), (e), (f) are the RSM... 53
Figure 19. Cp distribution and Vw /V0 in spanwise direction at X/C=0.5 according to LES and RSM models[이미지참조] 55
Figure 20. Lambda 2 criterion, Vorticity and Z-velocity at σ=2.97 according to turbulence model 56
Figure 21. Lambda 2 criterion, Vorticity and Z-velocity at σ=2.44 according to turbulence model 57
Figure 22. Lambda 2 criterion, Vorticity and Z-velocity at σ=2.29 according to turbulence model 58
Figure 23. Comparison of shear stress & streamline by turbulence model according to σ=2.97, 2.44, 2.29 59
Figure 24. SPL results according to the cavitation number. Experimental results of 홍지우, 안병권 [5] (a), RSM model (b), LES model (c) 61
Figure 25. Comparison of cavitation features according to cavitation numbers 63
Figure 26. Time-pressure graph(a) and frequency-SPL graph(b) according to cavitation number 64
Figure 27. Time-pressure graph (a), time-volume fraction of air graph (b) and frequency-SPL graph (c) at σ=4.0 65
Figure 28. Main Specifications of DARPA Suboff 67
Figure 29. DARPA Suboff used for resistance and self-propulsion simulation 67
Figure 30. INSEAN E1619 used for POW and self-propulsion simulation 67
Figure 31. Computational domain and boundary conditions 68
Figure 32. The grid system used in the simulation: POW test (a), Resistance test (b), Self-propulsion test (c) 69
Figure 33. Simulation result and model experiment POW curve performed by INSEAN 70
Figure 34. Comparison of total resistance with simulation results and results of model experiments conducted by Liu and Huang 71
Figure 35. The grid system used in the cavitation simulation 74
Figure 36. Cavitation observation: EXP[8] (a), CFD[8] (b), RANS (c), LES (d) 75
Figure 37. Pressure and velocity distribution at stern and Y-plane: RANS (a), LES (b) 76
Figure 38. Q=5000 iso-surfaces for different turbulence model and TKE (Turbulent Kinetic Energy): RANS (a), LES (b) 77
Figure 39. Pressure distribution at suction side of propeller: RANS (a), LES (b) 79
Figure 40. Pressure distribution at pressure side of propeller: RANS (a), LES (b) 80
Figure 41. Position of probe x, probe y, probe z from the propeller hub 81
Figure 42. Frequency-pressure graph at probes by turbulence model 81
Figure 43. Blade Pressure Frequency at probe x, y, z according to turbulence models 82
Figure 44. SPL results according to the turbulence model 83