Session: 17-01-01: Research Posters

Paper Number: 150903

150903 - Analysis of Real Fluid Thermodynamic Nonlinearities on Turbulent Mixing in Supercritical Fluids 

Supercritical fluids, characterized by their unique thermodynamic properties and significant deviations from ideal gas behavior, pose considerable challenges and opportunities for various engineering applications. Understanding the nonlinearities in these properties and their impact on fluid dynamics is essential for the design and optimization of energy systems, propulsion devices, and other advanced technologies. This research investigates the influence of thermodynamic nonlinearities on fluid dynamics using a supercritical mixing layer as a model system. By analyzing the behavior of supercritical fluids, particularly supercritical carbon dioxide (CO₂), under specific conditions, this study aims to elucidate the mechanisms by which these nonlinearities modulate key fluid dynamic processes.

The motivation for this research stems from the need to understand how supercritical fluid behavior differs from that of an ideal gas. Supercritical fluids exhibit highly nonlinear variations in their equation of state, thermodynamic quantities, and transport properties. These variations can significantly affect quantities such as enthalpy, isothermal compressibility, speed of sound, and Prandtl number, etc., leading to amplification of the local pressure and temperature perturbations in the system. This study provides a comprehensive understanding of these nonlinear effects and their implications for confined flows, such as those in combustors, where enhanced pressure oscillations can couple with the acoustic modes of the geometry, potentially leading to operational instabilities.

The methodology employed in this research involves a combination of theoretical analysis, computational simulations, and data visualization. Initially, Maxwell's relations are utilized to express properties like the speed of sound and isothermal compressibility as functions of partial derivatives of density with respect to pressure and temperature. These partial derivatives have well-defined physical meanings that highlight the role of thermodynamic nonlinearities at supercritical conditions. The study then proceeds by recasting the conservation equations in terms of pressure, velocity, and temperature to demonstrate how these quantities affect respective fluid dynamic operators. The Jacobian inversion technique is applied to maintain the integrity of the operators in the governing equations, illustrating the modulation of fluid dynamic operators by thermodynamic metrics.

A vital aspect of this research is the examination of a supercritical mixing layer designed to perturb these nonlinearities deliberately. Computational techniques, including Direct Numerical Simulations (DNS) and Wall-Resolved Large Eddy Simulations (LES), are employed to simulate the mixing layer and generate contour plots of pressure, temperature, density, etc. These visualizations provide a qualitative understanding of the property variations within the layer. Line plots are extracted to analyze the spatial variations of key parameters across the mixing layer to quantify the degree to which they modulate quantities such as pressure and temperature.

Results demonstrate that at certain supercritical conditions, property variations can significantly amplify pressure oscillations and temperature fluctuations. This amplification has critical implications for confined flows, where enhanced pressure oscillations can couple with the acoustic modes of the geometry, leading to potential operational instabilities. The study underscores the importance of understanding these mechanisms to predict and control the effects of thermodynamic nonlinearities in practical applications.

In conclusion, this research advances the understanding of thermodynamic nonlinearities in supercritical fluids and their impact on fluid dynamics. By comparing supercritical and ideal gas conditions, the study highlights the significant modulation of key fluid dynamic processes by nonlinear thermophysical properties. The insights gained from this research contribute to developing strategies for mitigating adverse effects in engineering systems, ensuring more stable and efficient operation. Future work will focus on refining the analytical models and extending the computational analysis to more complex geometries and flow conditions, ultimately paving the way for improved predictions in complex fluid dynamics scenarios involving supercritical fluids.

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 and serves as a graduate research assistant in the Center for High Pressure Combustion (CHPC) in Microgravity at PVAMU. Under the mentorship of Dr. Ziaul Huque (PVAMU) and Dr. Joseph Oefelein (Georgia Institute of Technology), S M Al Mamun Or Roshid's research focuses on the critical area of liquid fuel combustion at high pressure. Their work contributes to advancing the understanding of combustion processes under extreme conditions, with significant implications for both academic research and practical applications.

Authors:

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