Liquid ring compressors (LRC) are used for a wide range of compression and vacuum applications, including corrosive or flammable gases for which other compression technologies may not be feasible. The presence of a surrounding liquid ring may offer the possibility of polytropic compression due to incremental heat loss to the liquid. This aspect may play a critical role in compression (and expansion) processes of heat engine cycles toward approaching the targeted Carnot efficiencies. To date, published research addressing the physical phenomena behind LRC is highly limited. Experimentally studying these machines will result in a demonstration of aggregate performance. In order to improve our understanding of LRC with and without freely rotating casings and to be able to analyze the complex inner workings, a numerical approach using computational fluid dynamics (CFD) tools, supported by available experimental data for validation purposes, has been established. Physical parameters such as water–air interface, temperature, pressure, entropy production, vorticity, and shear strain rate are presented for a baseline geometry taken from the open literature. Finally, temperature-entropy paths and isothermal and isentropic efficiencies are presented. The significant performance gain from the freely rotating casing is highlighted. Detailed results present insights into work addition processes of such machines.