Browsing by Subject "hypersonic"

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    Conjugate Heat Transfer Simulations for Hypersonic Vehicles
    (2020-08) Reinert, John
    The accurate prediction of thermal responses is important for optimizing the design and operability for hypersonic flight vehicles. In order to efficiently simulate this process, a loosely coupled conjugate heat transfer solver was developed. Conjugate heat transfer simulations involve fluid and solid solvers. The fluid solver computes the flow field over the vehicle, and the solid solver calculates the transient heat conduction into the vehicle body. The two solvers are ``loosely'' coupled because both solvers exchange information at the surface of the vehicle, but operate on different time scales. The present work details the derivation of the conjugate heat transfer solver. The simulations were performed with US3D, an implicit finite volume unstructured compressible flow solver, with a newly developed implicit finite element transient heat conduction solver. The finite element solver is verified by comparing with analytical solutions for a bar, cylinder, and sphere. Validation cases for two geometries are shown: a fin-cone and HIFiRE-1. Both cases were shown to match well with the experimental data and flight test data. Additionally, the finite element method is compared to a finite volume method for solving the transient heat conduction equation. The comparison showed the benefits of the finite element method, such as refined temperature distribution and improved grid independence. Finally, the boundary layer transition (BoLT) vehicle is simulated for a segment of the trajectory. Results show the heating of the leading edge through time and the three-dimensional heating of the vehicle. At a specific time in the trajectory, the boundary layer and flow field are investigated. A comparative study is performed for the variable wall temperature and isothermal wall flow fields. The variable wall temperature was found to affect the wall heat flux and flow field structures. These results highlight the importance of performing conjugate heat transfer simulations when comparing to flight tests and experimental data.
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    Hypersonic Simulations and Analysis of Transition to Turbulence on BoLT-2
    (2022-11) Johnston, Zachary
    The study of laminar to turbulent boundary layer transition has been a flow phenomenonof research for many decades. Recently, there has been interest in understanding how transition occurs for hypersonic boundary layers of increasingly complex geometries. Therefore, the Air Force Research Laboratory/Air Force Office of Scientific Research (AFRL/AFOSR) introduced the Boundary Layer Turbulence (BoLT-2) flight experiment to help in the understanding and prediction of boundary layer transition to turbulence at high-speeds by collecting data in flight. The BoLT-2 research geometry allows for the existence of multiple instabilities to coexist and potentially interact thus leading to transition. This allows for the opportunity to assess current stability analysis tools and numerical methods to help improve prediction of thermal loading under flight conditions. In support of this task, the objective of this dissertation is to quantify transition mechanisms contributing to nonlinear breakdown using a forced DNS approach. Modal analysis techniques are applied to simulation datasets to extract pertinent information associated with dominant instabilities contributing to breakdown. This is meant to help in the understanding of the underlying flow physics contributing to breakdown on BoLT-2. Comparisons are made with experiments conducted in the Mach 6 Quiet Tunnel (M6QT) at Texas A & M University and show excellent agreement. Furthermore, flight conditions are investigated to identify instabilities that are potentially present at flight conditions. This is meant to help with the interpretation of flight data once it becomes available to the research community. The numerical methodology of the DNS approach presented in this dissertation is one that can be used to predict transition and help towards the development of multi-dimensional stability analysis methods for transition prediction.