Investigation Of Non-equilibrium Condensation In High-speed Expansion Flows

Vapor-liquid transition in high-speed expansion flows and their interaction were investigated numerically and experimentally. Phase transition in high speed flows is often accompanied with latent heat release or absorption that greatly affects the flow field. These interactions make the physical model more complex to describe such phenomena. When a strong expansion wave sweeps over a vapor or vapor/carrier gas mixture region, it will cause the ambient temperature decreasing dramatically and the supersaturated state of the vapor phase will be obtained. In this unstable supersaturated state, non-equilibrium condensation occurs after nuclei have been formed spontaneously. The flow properties are then changed due to the release of latent heat in condensation process, such as choking or self-oscillating in nozzle flows, which is caused by the coupled interaction between the phase-transition and the variation of the flow field.In high speed expansion flows, non-equilibrium condensation often includes two stages: nucleation and droplet growth. For the nucleation rate prediction, the classical nucleation theory has been widely used even up to now. But there are much large errors in the theoretical calculation due to the use of macroscopic properties instead of the microscopic ones in the nucleation theory. Thus, the calculated nucleation rate showed large distance to experimental measurement. In this thesis, a modification of the nucleation theory, which can be widely used in the homogeneous nucleation process, was proposed based on the classical nucleation theory.According to the Hill's moment method, governing equations of condensation can be derived from GDE (General Dynamic Equation) of droplet size distribution function. Combining with the conservation equation, such as Euler equation or Navier-Stokes equation, the unsteady flows with vapor condensation can be completely described. According to the nucleation model suggested in this study with numerical method ASCE2D implemented by Luo, the flow fields can be solved numerically. In order to increase the accuracy and efficiency of the solver, the adaptive unstructured quadrilateral mesh was adopted. The mesh is automatically refined in regions with large truncation errors and coarsened in regions with small truncation errors. In the numerical simulation of shock tube flow with vapor condensation, the reliability and accuracy of the present numerical method were validated through the comparison of the numerical pressure distribution with that of experimental measurement. Then, vapor condensation in the shock tube and nozzle flows were studied in detail experimentally and numerically:...