Session: 30-01 Fluid Properties and Dynamics

Paper Number: 152964

Spatial Dynamics of Turbulence and Thermodynamic Nonlinearities in Supercritical CO2 Mixing Layers 

The impact of thermodynamic nonlinearities on flow properties and turbulence are the main focus of this study, which investigates the spatial dynamics of supercritical carbon dioxide (CO₂) turbulent mixing layers. Beyond their critical point, where parameters such as density, pressure, temperature, enthalpy, isothermal compressibility, and thermal expansion show significant gradients and fluctuations, supercritical fluids deviate sharply from ideal gas behavior. These nonlinearities have a major effect on turbulence and cause complex mixing behavior that has important ramifications for propulsion technologies, energy systems, and other applications that operate in supercritical environments. This work attempts to clarify the differences between ideal gases and supercritical CO₂ fluid dynamics, with a focus on turbulent mixing. Supercritical CO₂ fluid dynamics have extremely nonlinear thermodynamic features. This study's conclusions may help engineers create more effective supercritical fluid systems. 

The study explores the effects of regional variations in important thermodynamic variables on fluid dynamics through the use of Large Eddy Simulations (LES). Four places (X = 6 mm, 12 mm, 24 mm, and 36 mm) downstream of a finite splitter plate are the subject of the analysis. We investigate crucial parameter variations along the Y-axis. Maxwell's relations and the Jacobian inversion method are used to quantify the effects of factors such as isothermal compressibility and the bulk thermal expansion coefficient on observables such as temperature and pressure. This provides a comprehensive understanding of the role played by these thermodynamic nonlinearities in turbulent flow evolution. 

The major findings include sudden inflections in the partial derivative of density with respect to pressure, which signify regions of a marked difference in isothermal compressibility. These changes are more pronounced downstream, highlighting the coupling of thermodynamic properties and turbulence. In temperature profiles, it would be evident that the rise of fluctuations and sharp gradients indicates the formation of turbulent structures. This highlights the heat expansion effect on the mixing. Also, there are large pressure and enthalpy fluctuations in regions with significant thermodynamic gradients. Pressure fluctuations, driven by the nonlinear equation of state, increase in amplitude downstream, potentially leading to instabilities in confined environments.

In a qualitative sense the study shows that thermodynamic nonlinearities lead to reactive flow regimes, where turbulence is enhanced. Quantitatively, the outcomes indicate that near the critical point slight perturbations often produce dramatic property changes necessitating advanced modeling methods. These results highlight how thermodynamic nonlinearities are significant to supercritical CO₂ mixing-layer evolution. This information is critical to the development of more accurate and refined models, as well as for optimizing designs in systems operating under supercritical conditions, such as in energy and propulsion applications.

Presenting Author: S M Al Mamun Or Roshid Prairie View A&M University

Presenting Author Biography: S M Al Mamun Or Roshid is a graduate student in the Mechanical Engineering Department at Prairie View A&M University (PVAMU), where he also serves as a Graduate Research Assistant in the Center for High Pressure Combustion (CHPC) in Microgravity. Under the guidance of Dr. Ziaul Huque (PVAMU) and Dr. Joseph Oefelein (Georgia Institute of Technology), his research focuses on the critical areas of liquid fuel combustion at high pressures.

Authors:

S M Al Mamun Or Roshid Prairie View A&M University
Dhruv Purushotham Georgia Institute of Technology
Joseph Oefelein Georgia Institute of Technology
Ziaul Huque Prairie View A&M University