Can High-Fidelity Jet Flow Simulations Transform the Aerospace Industry

Simulating high-speed jet flows is both a technical challenge and an exciting frontier in fluid dynamics. As aerospace technology evolves, particularly in supersonic and hypersonic travel, gaining insights into the complex behaviors of fluid motion at these extreme velocities has become increasingly important. At speeds beyond Mach 1, the nature of aerodynamic forces undergoes significant transformation, giving rise to shock waves. These shockwaves lead to specific flow patterns that can markedly influence the performance, stability, and maneuverability of aircraft.

As flight speeds reach Mach 3 and beyond, particularly in scramjet engines, the temperature variations caused by friction and compression can exceed 1,500 degrees Celsius. This extreme thermal environment can lead to material fatigue and failure if not properly accounted for in designs. With computational fluid dynamics (CFD) tools like the Fidelity LES Solver (formerly Cascade CharLES), researchers can now explore the physics of high-speed flight with a level of precision that was once unattainable.

But what does it take to simulate these extreme conditions accurately? How can we address the myriad challenges that these simulations present? This blog will explain the challenges in simulating high speed jet flows, showcasing the Fidelity LES Solver's capabilities, and highlighting its potential through a case study.

Challenges of Simulating High-Speed Jet Flows

Simulating high-speed jet flows presents several significant challenges stemming from the complex interactions between temperature, pressure, and turbulence. At high Reynolds numbers, the turbulence becomes unpredictable, necessitating powerful algorithms and high-performance computing to achieve accurate results.

One of the primary challenges is capturing compressibility effects. At high speeds, variations in density and interactions with shock waves can drastically change flow behavior, making precise modeling crucial. Additionally, the intricate flow structures within high-speed jets call for effective turbulence modeling; finding the right balance between accuracy and computational efficiency remains a significant hurdle.

Other important aspects are heat transfer and numerical stability. Steep temperature gradients require carefully defined boundary conditions to prevent reflection artifacts in simulations. While high-resolution schemes are essential for capturing these gradients, they often lead to increased computational costs.

Predicting noise is critical in terms of sound. Accurate modeling of jet noise involves integrating flow simulations with aeroacoustics models to effectively capture sound propagation in various environments. Furthermore, including fuel jets adds a layer of complexity that demands robust models for mixing, as the behavior of the fuel affects overall jet performance.

Furthermore, the challenge of validation against experimental data cannot be overlooked. Limited experimental benchmarks often mean simulations must work with incomplete data and differing assumptions, complicating the verification process.

Together, these challenges emphasize the need for advanced computational tools and dependable access to high-performance computing infrastructure to enhance the accuracy and efficiency of high-speed jet flow simulations.

Solution: Fidelity LES Solver

Fidelity LES Solver is a high-fidelity computational fluid dynamics (CFD) analysis tool tailored for hypersonic and supersonic flow simulations. This innovative tool expands large eddy simulations (LES) into critical aerospace applications, addressing the unique challenges faced in extreme flow regimes. It combines advanced numerical methods, high-quality mesh generation, and exceptional scalability for large eddy simulations (LES) in extreme aerospace environments.

Key highlights of Fidelity LES Solver include:

• Polyhedral Mesh Generation: This tool utilizes advanced clipped Voronoi diagrams to achieve robust and efficient meshing even for intricate geometries, ensuring precise and scalable simulations.
• Scalability: Designed to perform seamlessly on both CPU and GPU high-performance computing systems, Fidelity LES excels in delivering high-resolution results efficiently.
• Predictive High-Fidelity Simulations: With state-of-the-art algorithms, it offers unparalleled precision in capturing the intricate physics of high-speed jet flows, from shock wave interactions to acoustic wave propagation.

Case Study: Exploring Nonlinear Acoustic Waveforms

Cumulative nonlinear acoustic waveform distortions from high-speed jets (J.Fluid Mech., 2014)

To demonstrate the capabilities of the Fidelity LES Solver, a case study was conducted to simulate high-speed jet flows and analyze their acoustic properties. The study's main objective was to analyze the propagation of nonlinear acoustic waveforms from a jet nozzle with an exit Mach number of 3 and validate these results against experimental data.

Setup

• A Fidelity LES Ideal Gas solver modeled compressible flow.
• A timestep of 1E-7 seconds ensured temporal resolution.
• The simulation achieved 0.1 seconds of physical time over 60 hours on the Cadence Millennium Platform using one GPU node with 8 GPUs.
• Noise was recorded with microphones located at x/Dj = 20, with frequency cut-offs at ~54kHz. Signal clarity benefited from Hanning windowing with 50% overlap.

Background mesh of 100mm with mesh refinement at the nozzle at 0.4mm (first cell height)

Results and Insights

The simulation results aligned exceptionally well with experimental data, highlighting the solver's predictive accuracy. While some discrepancies in the spectral resolution were observed—attributable to differences in data smoothing methods—the simulation captured key trends and validated the experimental findings. Variations in low-frequency noise (St < 0.03) were linked to tunnel reflections affecting experimental sound propagation.

Comparison of far-field noise results from Fidelity LES and Experiment

Flow Mach Number from Fidelity LES

Moving Forward

High-speed jet flow simulations remain a critical nexus of theoretical research and practical aerospace innovation. By addressing the inherent complexities of these flows with tools like the Fidelity LES Solver, researchers are paving the way for quieter, more efficient flight systems and groundbreaking advancements in hypersonic travel.

Reference

Baars, W. J., Tinney, C. E., Wochner, M. S., & Hamilton, M. F. (2014). On cumulative nonlinear acoustic waveform distortions from high-speed jets. Journal of Fluid Mechanics, 749, 331–366. doi:10.1017/jfm.2014.228

Curious to see how simulating high-speed flows using Fidelity LES Solver can push your project to new heights? Request a demo today!