@phdthesis{,
    author = {Hößlin, Stefan von},
    title = {Temperature Decline Thermography for Flow and Heat Transfer Visualization in Aerodynamics},
    editor = {},
    booktitle = {},
    series = {},
    journal = {},
    address = {},
    publisher = {},
    edition = {},
    year = {2021},
    isbn = {},
    volume = {},
    number =  {},
    pages = {},
    url = {},
    doi = {},
    keywords = {Thermography; Flow Visualization; Heat Transfer; Temperature Decline; Aerodynamics; Gas turbine; Transition; Boundary Layer},
    abstract = {The visualization of boundary layer flow and heat transfer phenomena in aerodynamics is an essential approach for the physical understanding and further development of aerodynamic systems. However, it can be extremely challenging particularly for moving surfaces and in unsteady flows. Optical methods provide a promising approach as they combine a high spatial resolution with fast data acquisition and potentially do not disturb the boundary layer flow. In this thesis, Temperature Decline Thermography (TDT) is applied to measure quantitative heat transfer distributions and visualize boundary layer states such as laminar, turbulent, transitional, and separated flow on aerodynamic components. Based on a short-time measurement of transient surface temperatures after an energy pulse, the method enables the contactless analysis of short-duration flow effects and boundary layer conditions in stationary, as well as fast-rotating systems. This work provides
a detailed numerical and analytical description of the TDT measurement approach and a comprehensive characterization of the measurement components. The use of TDT is demonstrated in several applications ranging from simple flat-plates and airfoils, to experimentally challenging vanes and blades of a rotating turbine rig. It is shown that in addition to qualitative flow visualizations on stationary components, quantitative heat transfer distributions can be measured after a calibration. Laminar-
turbulent transition detection with TDT is validated with surface hot films on a NACA 0018 airfoil with different angles of attack and at Reynolds numbers up to Re = 2.3 × 10^5. Based on the short duration of a TDT measurement, an estimation for unsteady transition detection is given. In addition to stationary systems, the application of TDT in fast-rotating systems is demonstrated on a rotating turbine blade at Re = 7.6 × 10^5. Despite the limited optical access and low light conditions, the near-wall traces of a laminar-turbulent transition and vortex systems are visualized under realistic rig conditions for the first time ever. The application of TDT in complex flow situations provides deeper understanding of friction losses and heat transfer distributions on aerodynamic components. It enables the support and validation of numerical models for the further development of highly efficient aerodynamic systems.},
    note = {},
    
    school = {Universität der Bundeswehr München},
    
}