An analysis of the effect of gravity on interacting DWO/PDO instability modes.

摘要

This thesis presents an analysis of the possible interaction of pressure-drop oscillations (PDO) and density-wave oscillations (DWO) for a typical NASA-type phase change system on earth and aboard the International Space Station (I.S.S.). Linear exact analytical models based on the Homogeneous Equilibrium Model (HEM), a phasic slip (i.e., drift-flux) model, and a compressible volume (e.g., an accumulator) dynamics model. Next, transient nonlinear lumped parameter models were developed for use in the analysis of the time-domain dynamics of phase change systems. These nodal models, both linear and nonlinear, were developed with varying degrees of complexity, including: HEM, drift-flux, and subcooled boiling physics. Various numbers of nodes were studied to access nodal convergence. A dynamic accumulator model was also connected to the heated channel, which was modeled by nodal models ranging from a two-node HEM to an eight-node subcooled boiling, drift-flux model. The numerical evaluations of these models, both linear and nonlinear, were performed in either Engineering Equation Solver, (i.e., EES) or Matlab. The nonlinear transient integrations were performed either by the default EES scheme (especially for cases in which the flow at the outlet of the heated channel became single-phase) or a fourth-order Runge-Kutta method for the Matlab integration scheme. Interesting nonlinear interactions were shown between the heated channel and the accumulator, and these types of interactions are much richer than has been previously discussed in the literature.