N23A-T003   TITLE: DIGITAL ENGINEERING - Improved Physics Modeling for Sand Particulate Tracking and Deposition in Gas Turbine Engines

OUSD (R&E) CRITICAL TECHNOLOGY AREA(S): General Warfighting Requirements (GWR)

OBJECTIVE: Improve time-varying modeling and simulation capabilities to couple representative reactive sand particulates with modern propulsion systems, including inlet and turbomachinery.

DESCRIPTION: Naval aircraft powered by gas turbine engines experience safety, performance, and reliability concerns when operating in degraded visual environments with significant concentrations of reactive dust and sand. Sand particulates�including sand, salt, dust, and volcanic ash that aren't filtered or separated by an existing inlet or engine mounted filtration system�are ingested into the gas turbine engine.

Improved modeling and simulation tools will help better characterize the sand particulate impact on turbomachinery within aircraft propulsion systems. Current systems can have safety impacts when operating in sand and dust related to sand deposition within the turbine leading to engine surge and potential loss of aircraft. Engine reliability is heavily impacted by sand ingestion, which can lead to faster engine deterioration with significant life cycle cost. Improved understanding of the impacts and design changes using modeling tools would have a positive impact on capability, performance, and cost.

Ingested particles can degrade compressor performance via surface erosion, deform leading and trailing edges of blade airfoils, and open rotor tip-clearances [Ref 4]. Sand particulates that make it through to the combustor are elevated to high temperatures and can deposit on turbine airfoil surfaces�shrinking throat clearances�or deposit on turbine shroud and degrade turbine tip clearances. Sand particulates can also enter cooling passages and create deposits that block cooling flows resulting in exceedance of airfoil material temperature limits. This can affect both military and commercial aircraft and rotorcraft. Sand ingestion and deposition can be further impacted by relevant sand properties (geology, chemical composition, size distribution, shape, concentration) [Ref 3].

Airflow restrictions can occur rapidly on wing, and result in sand related operability impacts that can cause safety issues with undesired engine surge and stall events. Additionally, performance loss from significant turbine airfoil damage typically cannot be recovered entirely via engine wash or other maintenance procedures. This can lead to more frequent engine replacements and an overall reliability concern for the propulsion system. Complex propulsion systems of interest include inlets, inertial separators, hot and cold rotating turbomachinery with and without secondary cooling air flow, as well as the coupling of multiple of these components.

Current state-of-the-art modeling and simulation tools typically couple steady-state Reynold's averaged navier stokes (RANS) computational fluid dynamics (CFD) solvers to a discrete particle tracking tool. This method has several disadvantages, including inaccurate inclusion or modeling of turbulent particle dispersion, limited particle-to-particle collisions and interaction, simplified particle shapes that affect drag estimates and wall-impacts/rebounds, one-way coupled particles that don't affect gas aerodynamics, and deposition predictions that use frozen geometry shapes and wall properties that can't change in time as the deposit size increases. Unsteady Large Eddy Simulation (LES) typically include more rich physics-based models that incorporate more of the above RANS deficiencies; however, they can also be computationally expensive and too long to impact design iterations or active acquisition programs. Additionally, the vast amount of data available from a resolved simulation with millions of particulates is frequently difficult to post-process and analyze efficiently. Efficient algorithms and post-processing methodologies to cumulatively understand time-accurate statistical measures of the ingested sand particulates are required.

Modeling and simulation tools need to be improved to be able to accurately predict time-varying particle trajectories, wall-impacts, surface erosion, and surface deposition within inlet systems and engine turbomachinery [Ref 5]. Improvements to accuracy and confidence of modeling methodologies, as well as significant improvements to computational cost and efficiency to be able to impact a typical design cycle, are desired. The proposed approach's accuracy and applicability to relevant, complex propulsion systems should be demonstrated via comparisons against available (published), acquired experimental data, or government-provided test data.

A focus on robust, parallel, highly efficient software improvements that can be utilized for complex geometries (such as inertial separators and rotating turbomachinery with secondary and cooling flows) with relevant sand particle constituents, size distributions, and cloud concentrations [Ref 1], is required.

Although not required, it is highly recommended that the proposer work in coordination with the original equipment manufacturer (OEM) to ensure proper design and to facilitate transition of the final technology.

PHASE I: Demonstrate understanding of relevant sand properties, including those of reactive sand and dust (geology, chemical composition, size distribution, shape, concentration). Demonstrate and validate the use of a commercially available CFD solver that has been coupled to incorporate sand particulates. Validate selected aerodynamic software on relevant turbomachinery geometry. Define the approach to be used in Phase II for improved physics modeling and robust, efficient solver development that can be applied to complex propulsion systems. Provide risk mitigation information. The Phase I effort will include prototype plans to be developed under Phase II.

PHASE II: Develop and demonstrate the prototype improved sand and dust modeling capability. Show efficient integration of reactive capability with existing, commercially available CFD software. Evaluate and report on the tool improvements impact on accuracy against available (published), acquired experimental data, or government-provided test data. Provide clear documentation of the theory, applied models and methods, assumptions, limitations, and instructions for use of the coupled aerodynamic and sand predictive tool. Demonstrate computational efficiency and robustness on DoD High Performance Computing assets.

PHASE III DUAL USE APPLICATIONS: Transition developed tool and capability to government for implementation on fleet aircraft. Modify tools based on feedback from use within a DoD acquisition program. Support the application of advanced, mature, robust tools on aircraft engine and inlet analysis and redesign.

Commercial aircraft engines experience sand and dust deterioration over long-time exposures. This can also impact performance and reliability of commercial engines. Improved modeling and simulation for better understanding and design methodologies will also impact aircraft engines for rotary- and fixed-wing commercial aircraft.

REFERENCES:

1.       Cowherd, C. (2007). MRI project no. 110565: Sandblaster 2 support of see-through technologies for particulate brownout. Midwest Research Institute. https://apps.dtic.mil/sti/pdfs/ADA504965.pdf

2.       Guha, A. (2008). Transport and deposition of particles in turbulent and laminar flow. Annu. Rev. Fluid Mech., 40, 311-341. https://doi.org/10.1146/annurev.fluid.40.111406.102220

3.       Walock, M. J., Barnett, B. D., Ghoshal, A., Murugan, M., Swab, J. J., Pepi, M. S., Hopkins, P. D., Gazonas, G., Rowe, C., & Kerner, K. (2017). Micro-scale sand particles within the hot section of a gas turbine engine. Mechanical Properties and Performance of Engineering Ceramics and Composites XI, 606, 159. https://doi.org/10.1002/9781119320104.ch14

4.       Hamed, A., Tabakoff, W. C. and Wenglarz, R. V. "Erosion and deposition in turbomachinery. Journal of propulsion and power, 22(2), 350-360. https://doi.org/10.2514/1.18462

5.       Jain, N., Le Moine, A., Chaussonnet, G., Flatau, A., Bravo, L., Ghoshal, A., Walock, M. J., Murugan, M., & Khare, P. (2021). A critical review of physical models in high temperature multiphase fluid dynamics: turbulent transport and particle-wall interactions. Applied Mechanics Reviews. https://doi.org/10.1115/1.4051503

6.       DoD High Performance Computing Modernization Program (DoD HPCMP). https://centers.hpc.mil/systems/hardware.html

 

KEYWORDS: Gas Turbine Engines; Degraded Visual Environments; Sand and Dust Ingestion; Computational-Fluid Dynamics; High Performance Computing; Sand Deposition

---