UC Irvine

Due to the dramatic increase in global energy consumption in the past decade, thermodynamic power cycles such as Oraganic Rakine Cycle and Supercritical Carbon Dioxide Cycle have drawn lots of attention recently because of their high efficiency in waste heat recovery. The fluids in these power cycles usually have complex molecular structures. They operate near the saturation vapor line and critical point, where the gas behavior significantly deviates from the ideal gas behavior. Objective of this dissertation is to numerically investigate and understand the peculiar gas behavior in this region.The fundamental derivative of gas dynamics is a measurement of the variation of the speed of sound of a gas with respect to pressure in an isentropic process. The van der Waals model is used to confirm the existence of negative fundamental derivative regions for dense gas. Regions of Γ < 0, 0 < Γ < 1 and 1 < Γ are identified and mapped out in the p- v diagram. Jump relations are investigated in three regions of Γ, i, e.Γ > 1, 0 < Γ < 1 and Γ < 0 respectively. The non-monotone dependence of the speed of sound along a shock adiabat is demonstrated to increase the sound speed across normal shock waves in the region where 1 > Γ > 0. Expansion shock solution is obtained in the region where Γ < 0. Double sonic shock wave are confirmed admissible where fluid can be expanded and accelerated through a discontinuity with Mach number being unity before and after the discontinuity. Unconventional gas behaviors of the isentropic quasi-1D flow have been investigated systematically and in depth for dense gas. Analysis indicates that dense gas behavior in one dimensional nozzle is directly related to the value of Γ. For example, when Γ < 0, the divergent-convergent nozzle is needed to accelerate flow from subsonic to supersonic. A real gas numerical solver using Jameson-Schmidt-Turkel scheme is developed. Simulation result of dense gas over compression ramp and expansion ramp shows agreement with the analytical solution. It confirms the existence of complicated wave field such as expansion shock and expansion shock-fan. Results of unsteady shock tube simulation show that shock tube can produce different wave fields depending on the initial conditions. More results of dense gas over corners and arc surface are presented and discussed in details.