| Summary: | Shock tube experiments are a key method of reproducing the flow conditions encountered by hypersonic flight vehicles and are the primary source of known thermochemical reaction rates. However, because of the complex nature of hypersonic flows, and also due to the many subtle complexities of the shock facilities themselves, full characterization of the flows they produce is elusive. This work develops a numerical method for the simulation of shock tube experiments using a novel technique of shock tracking to improve the resolution and decrease the computational cost of such simulations. An axisymmetric, Navier-Stokes shock tube simulation code entitled FROSST keeps the shock and contact discontinuity each stationary in their own zone of refinement that slides along a coarse background mesh of the entire facility. Using this solver, the role of shock history in the formation of nonuniformities in shock tube test gases is investigated in the context of ideal gas simulations. Shock speed variations from -29% to +33% are found to influence temperatures in the test slug by as much as 55% in an Argon test gas with a tube-end 2100 m/s. These results give rise to the observation that nearly all nonuniformities in the test gas originate with variations in shock speed along the tube. Based upon this observation, a novel method is devised to use experimentally measured shock speed to predict test flow properties for each experiment. This method tracks the influence of waves associated with shock speed variation upon isentropic slices of shock-processed gas. By tracking a number of such slices, the entire test slug is reconstructed to a high degree of accuracy. The analytical methodology, entitled LASTA, is extensively validated against simulated ideal Argon data and also experiments performed in the Oxford T6 Stalker shock facility with both Argon and thermochemically reacting air. LASTA is found to capture the shot-to-shot nonuniformities to within 1% within minutes on a single core. Real-world application of LASTA is already leading to improved understanding of radiative emissions from shock tube experiments.
|
|---|