Impinging supersonic jets can generate intense sound through a resonance phenomena, with tones approaching 15 dB beyond the already-loud baseline noise levels. The source of impinging jet noise, including that created by jet blast deflectors, is broadly the interaction between jet and deflecting plane, which can in certain cases close a resonant feedback loop. Accurate prediction of the noise is necessary for understanding the as-yet unknown detailed source mechanism(s), as well as enabling development of mitigation procedures. We seek to apply our validated LES prediction tool in Phase I to two well-documented cases of under-expanded jets impinging on a ground plane: one case resonates while the other does not. Our objective is to use our existing adjoint-based optimization methodology to highlight flow regions most sensitive to design changes or control strategies to reduce radiated noise. As shown in our previous, validated noise reduction efforts for turbulent jets, the adjoint provides a direct investigation into those areas of the flow, such as at the nozzle exit or ground plane, where a noise reduction strategy can be designed. GE Global Research has confirmed their strong interest in this R&D effort, and has agreed to provide critical guidance and review throughout Phase I.
Benefit: Phase I will define the feasibility regimes of our current state-of-the-art compressible flow solver in a demonstration simulation directly relevant to predicting the aeroacoustic behavior of high-speed impinging jets. Enabling high-fidelity simulations in complex geometries is a key innovation in CFD techniques in general. For Phase II, proof of predictive feasibility is the key enabling technology for our goal of accurate large-eddy simulation of noise generation. Extension of RocfloCM, and successful completion of Phase II will provide a demonstrated capability for design predictions of high-speed impinging jet acoustics for which there is currently no existing capability with sufficient fidelity. Jet impingement on surrounding structure is a major contributor to overall aircraft noise and is a key issue faced by both engine and airframe manufacturers, but its cause cannot be easily measured experimentally. Successful demonstration of such a unique predictive capability will lead directly to Phase III commercialization prospects. For Phase II, the RocfloCM tool will be extended (based on the insights from Phase I) and embedded within a commercially-oriented design tool for predictive modeling. The anticipated Phase II result is that we will have fully demonstratedon realistic hardware geometries and flow conditionsa new methodology that permits high-fidelity predictive simulations of jet impingement on surrounding systems. The Phase II demonstration will significantly extend the state of the art in terms of computational efficiency and predictive accuracy against Navy-supplied (and potentially other publically available) data. It is fully expected that this new methodology will be an enabling technology for the high-fidelity prediction of turbulent flows in complex jet and nozzle applications. This program will provide pathways to two salable products: software and engineering services. Software: A new simulation technology will be available for prediction of jet aeroacoustics in high-speed impinging applications, a key issue in the design of all modern civilian and military aircraft ground systems. We expect that a special-purpose user interface will be developed to facilitate the use of this high-performance predictive tool in design settings. Engineering services: Analytical and consulting services will be available based on the new simulation capability at the end of Phase II. We envision identifying acoustic mechanisms and predicting noise levels of novel designs for government prime contractors and members of the aircraft industry.
Keywords: jet blast deflector, jet blast deflector, Jet noise, noise abatement., adjoint-based optimization, impinging jets, shock capturing, LES
