N132-102 TITLE: Modeling of interior nozzle flows for transient effects, realistic high performance nozzle physics and coupling to Large Eddy Simulation modeling of the jet plumes

TECHNOLOGY AREAS: Air Platform

ACQUISITION PROGRAM: JSF-Prop

OBJECTIVE: Design and develop new methods of modeling the interior of high performance turbine engine exhaust nozzle aerodynamics to include unsteady effects to a greater accuracy than is currently available. Of emphasis are effects due to throttle transients and due to the presence of walls particularly those in multiple exhaust streams.

DESCRIPTION: Technologies are needed for advancing the state-of-the-art in the Modeling & Simulation (M&S) of the interior flows in high performance turbine engine exhaust nozzles, including those for advanced engine architectures with multiple exhaust streams. The primary intent is to improve the (thrust) performance of those nozzle designs, as well as durability from the improved understanding of the structural loads on the nozzle components from throttle transients and multiple flow streams. A secondary intent is to employ the developed M&S tool to explore nozzles of low jet noise emissions.

It is recognized that significant advancements have been made, to date, in the LES modeling of hot, supersonic exhaust nozzles plumes for aerodynamics and acoustics. But such modeling has not been effectively extended to the nozzle interiors because of the inability of the LES methodology to handle wall effects. The remedies have included the coupling of Reynolds Averaged Navier Stokes (RANS) schemes to LES for wall/nozzle interior modeling, Detached Eddy Simulation (DES), or schemes that model the wall shear stress term directly.

But it is generally recognized these are more-or-less ad-hoc attempts and that need to be revisited for a more thorough examination of the mathematics involved. The general outlining mathematical problem is the coupling of non-linear operators. The derived iterative numerical scheme should efficiently converge the coupled operators in the overall solution domain that includes the nozzle walls, core and plume. It is also required that the developed scheme is efficiently parallelizable, e.g., in a domain decomposition fashion, to take full advantage of available state-of-the-art parallel supercomputers.

The developed methodology should seamlessly couple with fully transient analyses of nozzle plumes with the technique of Large Eddy Simulation (LES). It should be scalable to take advantage of state-of-the-art High Performance Computing (HPC) hardware and software and efficient with respect to clock turnaround times for a complete interior/exterior nozzle simulation. The new tool will be transitioned to NAVAIR Propulsion & Power as well as to Engine OEMs, if they choose to purchase/lease it.

PHASE I: Develop and demonstrate a simulation of one government-furnished nozzle geometry and boundary conditions and compare to existing experimental data. The simulation should include the interior of the nozzle and the LES of the exterior jet plume. Propose a methodology for the Phase II that incorporates transient effects, wall effects modeling, more realistic boundary conditions and full coupling to interior/exterior to the nozzle LES coupling.

PHASE II: Implement the proposed methodology and validate for high performance nozzle simulations that incorporates transient effects, wall effects modeling, more realistic boundary conditions and full coupling to interior/exterior to the nozzle LES plume.

Validate the developed scheme for a series of nozzle designs provided by the government.

Transition the beta version of the developed software to NAVAIR Propulsion & Power.

PHASE III: Transition the alpha version of the developed tool, appropriate platforms for design/implementation in "second generation" nozzles hardware for current/future aircraft programs.

PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: Both military and commercial gas turbine engine nozzle design applications for increased durability and performance including identification of jet noise reduction concepts.

REFERENCES:
1. Schlueter, J.U., Wu, X., Kim, S., Alonso, J.J., & Pitsch, H. (2003). Integrated RANS-LES Computations of Turbomachinery Components: Generic Compressor/Diffuser. Center for Turbulence Research, 357-368.

2. Georgiadis, N.J., Alexander, J.D., & Reshotko, E. (2001). Hybrid Reynolds-Averaged Navier-Stokes/Large-Eddy Simulations of Supersonic Turbulent Mixing. AIAA Journal, 41(2) 218-229.

3. Gatski, T.B., Rumsey, C.L., & Manceau, R. (2007). Current Trends in Modeling Research for Turbulent Aerodynamic Flows. Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, 365(1859) 2389-2418.

4. Kawai, S., & Larsson, J. (2012). Wall-Modeling in Large Eddy Simulation. Physics of Fluids, 24(1). doi:10.1063/1.3678331

5. Piomelli, U., & Balaras, E. (2002). Wall-layer models for large-eddy simulations. Annual Review of Fluid Mechanics, 34 349-374.

6. Spalart, P.R. (2009). Detached-eddy simulation. Annual Review of Fluid Mechanics, 41 181-202.

KEYWORDS: High Performance Variable Cycle Engines Exhausts; Transient Nozzle Effects Modeling; Rans/Les Coupling; LES wall modeling; Computational Fluid Dynamics of Interior Flows; Aeroacoustics of Nozzle flows.

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