Research

Laminar-to-Turbulent Transition in High-Speed Flows

The transition from laminar to turbulent flow is a critical phenomenon with profound effects on drag and heat transfer in high-speed flight vehicles. And accurately predicting laminar-to-turbulent transition remains a significant challenge in the design of such vehicles. The onset of turbulence can often be traced back to the amplification of small-scale disturbances, including acoustic, entropic, and vortical fluctuations within the boundary layer.

This research explores the underlying mechanics of transition using direct numerical simulations (DNS) and stability theory. We investigate the influence of a broad spectrum of perturbations on boundary layer stability, with a focus on understanding how specific acoustic, entropic, or vortical modes initiate and drive the transition process. The insights gained helped refine predictive models and guide the design of more efficient vehicles.

Turbulent Shear Flows

Shear layers, fomed at the interface between two fluid streams of differing velocities or between a freestream and a solid surface, are fundamental to the study of turbulent flows. These layers play a critical role in a wide range of engineering and environmental applications, including the wakes of aircraft and submarines, flow over moving structures, atmospheric jet steams, and the dynamics within combustion chambers of propulsion systems. Understanding their behavior is essential or advancing fluid dynamics and optimizing designs in these fields.

This research focuses on investigating the complex physics of turbulent shear flows with the following objectives:

• High-Fidelity Numerical Simulations: Conducting simulations of compressible reacting and non-reacting shear layers to capture intricate flow dynamics
• Mixing Mechanisms: Exploring the fundamental processes governing the mixing of mass, momentum, and energy in turbulent regions to improve predictive capabilities
• Turbulent/Non-Turbulent Interface (TNTI): Analyzing the mechanics of TNTI to understand how turbulence spreads and interacts with quiescent regions of the flow

By leveraging advanced computational tools and high-performance computing, this project aims to deepen our understanding of turblent shear flows and provide insights that can inform the development of more efficient and reilable engineering systems, from aircraft design to propulsion technologies and environmental applications.

Combustion Modeling in High Mach Number Turbulent Flows

Combustion is a complex, highly nonlinear process involving a multitude of chemical reactions and species interactions. At high speeds, these complexities are further amplified as mixing layers, shocks, expansion fans, flames, and turbulence interact in intricate and unpredicatable ways. Developing efficient and accurate models for turbulent combustion is crucial for advancing next-generation propulsion systems and power generation technologies. These advancements promise to extend vehicle range, improve energy efficiency, reduce environmental impact, and enhance safety. However, the inherently interdisciplinary nature of combustion makes it one of the most challenging areas to model and predict.

This research initiative focuses on the dynamics of chemically reactive turbulent shear layers under high-Mach number conditions, with the following objectives:

• Model Development: Creating a robust computational framework to simulate chemically reactive flows, incorporating key factors such as finite-ray chemistry and real-gas effects
• Scientific Discovery: Gaining deeper insights into the underlying physics of combustion in turbulent high-speed flows to address critical knowledge gaps
• Predictive Tools: Leveraging high-fidelity numerical simulations and experimental data to inform and enhance lower-fidelity models using advanced data assimilation and maching learning techniques

By addressing these objectives, this research seeks to advance the understanding of turbulent combustion at high speeds and deliver computational tools that can support the development of cleaner, safer, and more efficient propulsion and power systems.

Strategies for Flow Control and Reducing Heat Transfer & Drag in High-Speed Flows

The laminar-to-turbulent transition in the boundary layers of high-speed vehicles remains a critical challenge. Once turbulence develops, it significantly enhances the transport of mass, momentum, and energy, offering advantages like improved mixing and delayed stall. However, these same effects can have detrimental consequences when the design goals prioritize minimizing drag and heat transfer. A pivotal factor influencing transition location and mechanism in the spectral composition of instability waves in the pre-transitional region. The inherent uncertainty of environmental conditions further complicates achieving robust and reliable flow designs for high-speed vehicles.

To address this challenge, our research adopts optimization approaches to develop robust strategies for delaying the transition to turbulence. This project investigates the effects of physical and thermal surface roughness on laminar-to-turbulent transition in high-Mach-number boundary layers. By analyzing these influences, we optimize roughness parameters to maximize the delay of turbulence onset.