Accurate Airframe Noise Predictions Using Large Eddy Simulations

Airframe noise generated by the undercarriage (landing gear, cavities) and high-lift devices is by far the most dominant source of noise during approach conditions and has been known to cause adverse health effects in communities residing near airports. There is a desperate need for computational tools that can rapidly and accurately predict this noise in order to integrate acoustic analysis in the design design process and to meet the regulatory goals around noise reduction. The current industry standard appears to be a single Lattice Boltzmann hybrid RANS/LES solver; the work proposed in this Phase-I research is intended to remedy this by mitigating several known limitations in the current state-of-the-art. Volcano ScaLES, an immersed boundary wall-modeled Large Eddy Simulation (WMLES) will be utilized to demonstrate accurate broadband noise predictions on a variety of test cases such as the PDCC-NLG landing gear model, the 30p30n multi-element airfoil and a the 10% scaled high-lift common research model in landing configuration. We intend to demonstrate that these cases can be completed with overnight turnaround (<16 hours of walltime) using single server/node resources with up to 8 general purpose computing GPUs (such as the Nvidia L40S). Furthermore, highly automated and rapid mesh generation capable of representing un-simplified complex geometries will be utilized along with entirely in-situ post-processing for farfield acoustics propagation and flow visualization. Beyond the 3 demonstration problems, additional code enhancements targeting the Ffowcs Williams-Hawkings (FHW) formulation to address the method's well-known drawbacks (such as need for quadrupole corrections) will be also be considered in Phase-I. If successfully achieved, the goals outlined in the work would represent a major advancement computational predictions of airframe noise, and we anticipate significant interest from both airframe developers and government agencies. Enabling "design-to-noise" of individual components is critically needed to achieve regulatory airframe-noise reduction goals on new airframe designs which are likely to feature shorter landing gears and higher lift generation at lower approach speeds. Volcano ScaLES, a compressible Navier-Stokes Wall-Modeled Large Eddy Simulation solver is ideally suited to tackle this challenge. Some key advantages of ScaLES over the existing state-of-the-art a) representation of a wide range of spatio-temporal scales without any turbulence-related model tuning, b) the ability to represent highly complex geometries with a high degree of detail without the need for simplification, and c) efficiently utilize in-expensive general-purpose Graphical Processing Units (GPUs) to allow for high-resolution simulations of >1 Billion point grids with overnight turnaround times with single-node resources. In-situ acoustic propagation and flow visualization further minimize user-tuning and inputs allowing for wider adoption of complex tools such as FWH solvers in routine engineering design and analysis .

Accurate and user-friendly Computational Fluid Dynamics (CFD)/ Computational Aeroacoustics (CAA) tools for airframe noise predictions will be enabled with the incorporation of the proposed CAA technology into our low-cost wall-modeled large eddy simulation (WMLES) solver - Volcano ScaLES. It will support NASA’s Advanced Air Transport Technology (AATT) and Commercial Supersonic Technology (CST) projects as the newly developed tools can be used to improve the understanding of noise footprint during aircraft landing and takeoff. It will also help noise source identification and the analysis of the noise generation mechanism of conventional and advanced aircraft designs such as Truss-Braced Wing that have more integration between airframe and propulsive noise. In contrast to many other scale-resolving solvers that require the use of large high-performance computing clusters with many high-end CPUs and scientific GPU cards (e.g., A100, H100, etc), our solver enables the WMLES to be run on just a workstation, or a single-node server with only a few low-cost consumer GPU cards, such as NVIDIA RTX 4090 or L40S, where the simulations have similar turnaround times as those with legacy CFD methods such as RANS and URANS. As a result, our technology will also support NASA’s Transformational Tools and Technologies (TTT) Project as the ScaLES will largely reduce the cost and turnaround time of high-fidelity airframe noise predictions, and this will enable the consideration of the noise reduction in the earlier stages of conventional and novel aircraft designs. A primary objective of Volcano Platforms Inc. is to accelerate the transition from the use of legacy Computational Fluid Dynamics methods (such as RANS and URANS) to higher-fidelity scale-resolving methods. As an early-stage startup initiated in March 2023, we have made significant progress towards this target. Volcano ScaLES wall-modeled large eddy simulations of highly complex flows involving massive flow separation is not only substantially more accurate than legacy methods (such as steady state RANS) but also costs roughly the same as these legacy methods on the current state-of-the-art commercial software. As of today, a single Lattice-Boltzmann Method (LBM) software remains the prevailing industry standard in this community, and the substantial technical and commercial advantages offered by Volcano ScaLES are likely to make it highly competitive in the market. As an example, the Navier-Stokes formulation in ScaLES removes the ambiguity associated with lattice-dependent Mach number validity seen in all commercial LBM solvers.  We anticipate high-performance computing to make up a substantially larger portion of the CFD software market (which is already growing at roughly 10% according to a TechNavio market report) in 5 years from now in large part due to emergence of GPUs. Volcano Platforms Inc. is perfectly positioned to capitalize on this growth due to our targeted focus on LES. With the use of WMLES, higher fidelity airframe noise predictions can be obtained for conventional or more advanced airframes such as aircrafts with truss-braced wing involving more coupling of propulsion system with airframe aerodynamics. We will continue to pursue collaborations with industrial players such as the Boeing Company, Gulfstream Aerospace Corporation, Lockheed-Martin, etc. many of whom have already shown interest in Volcano ScaLES.

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