Numerical Investigation on Three-dimensional Effects of Over-expanded Rocket Nozzle

학위논문 (석사)-- 서울대학교 대학원 : 기계항공공학부, 2017. 2. 김종암.In the early stage of liquid rocket engine startup with an over-expanded state, internal flow begins to develop in the form of FSS (Free Shock Separation) which the separated plume stays away from the wall. However, depending on the type of the nozzle shape, a drastic and unpredictable transition occurs to the form of RSS (Restricted Shock Separation) that the separated plume is reattached to the wall surface. In this research, viscous unsteady two-dimensional axisymmetric and three-dimensional nozzle internal flow analysis using CFD simulations were conducted with a structured-unstructured mixed grid system. Especially, the numerical three-dimensional effects when a transition from FSS to RSS occurs were analyzed changing Nozzle Pressure Ratio (NPR). As a result, it was identified that the transition occurs more slowly in the three-dimensional flow analysis than the axisymmetric two-dimensional case as the NPR increases. And the nozzle wall surface temperature asymmetry phenomenon was identified, and the cause for it was analyzed. Also, the magnitude of the side load and the moment acting on the neck of the nozzle generated by the asymmetric pressure distribution on a nozzle wall was measured.Chapter 1 Introduction 1 1.1 Liquid Rocket Engine Nozzle Side-load 1 1.2 Side-load Occurrence Mechanism 1 1.2.1 Free Shock Separation (FSS) 3 1.2.2 Restricted Shock Separation (RSS) 3 1.2.3 Asymmetrical flow at the moment of separation pattern transition 3 1.3 Objectives of Thesis 4 Chapter 2 Numerical Method 6 2.1 Governing Equation 6 2.2 Turbulence Modeling 9 2.2.1 The Menters k-ω SST Two-Equation Model 9 2.3 Spatial Discretization Method 13 2.3.1 RoeM Scheme 13 2.3.2 Higher-Order Spatial Accuracy 15 2.4 Time Integration Method 16 2.4.1 3rd Order TVD Runge-Kutta Scheme 16 Chapter 3 Solver Validations 17 3.1 Mach 5 Shock Wave Boundary Layer Interaction 17 3.2 Seiner Nozzle with Mach 2.0, Heated Jet Flow 20 Chapter 4 Preliminary Works Before Analyzing 23 4.1 Combustion Gas Material Property Modeling 23 4.2 Grid Refinement Test for Unsteady Analysis 24 4.3 Comparison with Experiments 26 4.4 2-D Axisymmetric Steady Analysis 27 4.5 Selection of Pressure-time Slope 28 Chapter 5 Results & Discussion 31 5.1 Transition NPR Range Difference between 2-D & 3-D Results 31 5.1.1 2-D Axisymmetric unsteady RANS results 31 5.1.2 3-D Unsteady RANS results 32 5.1.3 Transition NPR range comparison 33 5.2 Asymmetrical Wall Temperature Distribution in 3-D 35 5.3 Side-load by Asymmetrical Pressure Distribution 38 Chapter 6 Conclusions 41 Chapter 7 References 43 국문 초록 45Maste

Flow separation and nozzle side load simulations for TOP nozzle

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