DON27TZ02-NV007 TITLE: Multi-Modal Luminescent Paint Systems for Underwater Surface Diagnostics

COMPONENT TECHNOLOGY PRIORITY AREA(S): Advanced Materials

PROJECTED CMMC LEVEL REQUIREMENT: Level 2 (Self)

OBJECTIVE: Develop an integrated, multi-modal luminescent paint system optimized for simultaneous, non-intrusive, large-scale, high-resolution global measurement of wall pressure, shear stress, and temperature fluctuations on complex, curved geometries in underwater environments.

DESCRIPTION: Quantifying coupled boundary layer interactions along hydrodynamic surfaces require non-intrusive, full-field imaging of surface pressure, temperature, and skin friction (shear stress). While optical diagnostics have revolutionized aerodynamic testing, adapting luminescent paints to hydrodynamic testing in water introduces fundamental physical and application constraints that current state-of-the-art systems cannot overcome:

• Pressure-Sensitive Paint (PSP): Conventional PSP relies on oxygen-quenching physics. When submerged, oxygen diffusion into the polymer binder is severely inhibited by the liquid boundary layer and low oxygen solubility, rendering standard PSPs insensitive or plagued by extremely slow response times. Furthermore, severe temperature cross-sensitivity corrupts the pressure signal.
• Temperature-Sensitive Paint (TSP): Accurate dynamic temperature measurements are crippled by the standard utilization of Taylor’s frozen-flow hypothesis, which inaccurately assumes turbulent structures remain unchanged as they advect. In water, non-equilibrium flow, high thermal mass and rapid localized diffusion cause this hypothesis to break down, failing to capture true high-frequency temperature fluctuations.
• Mechano-Luminescent Paint (MLP): MLPs offer a direct optical pathway to map shear stress via mechanical deformation. However, current MLP formulations are in their technological infancy, suffering from poor dynamic range, low luminous efficiency, and signal degradation from material fatigue and hydrostatic pressure cross-talk.

In addition to the above challenges, current formulations are difficult to apply uniformly over large areas. Existing techniques fail to maintain a consistent, repeatable coating thickness on complex, curved, or non-flat surfaces. This inconsistency skews calibration and compromises measurement reliability across large-field hydrodynamic models. Innovative material architectures, such as utilizing distinct, multi-color mechano-luminescent particles or multi-core/shell dye structures, may enable simultaneous, uncoupled optical separation of pressure, shear, and temperature in all flow environments, i.e. gas, liquid, and multiphase flows.

This STTR topic seeks an integrated material, application, and optical processing suite. The system must decouple cross-sensitivities and deliver simultaneous, high dynamic range, full-field quantitative maps of the wall pressure, shear, and temperature fluctuations.

PHASE I: Develop a concept for advanced formulations for water-compatible PSP, TSP, and MLP systems capable of measuring pressure fluctuations from 10 Pa to 100 kPa, shear stress from 0.1 to 100 Pa, and temperature variations from 0.05 to 20°C, as well as providing uniform spatial sampling capable of resolving unsteadiness up to 50 kHz without relying on Taylor’s hypothesis. Evaluate the conceptual system’s ability to decouple cross-sensitivities in simultaneous mapping of wall pressure, shear stress, and temperature through analytic modeling and laboratory testing. Identify potential application methodologies (e.g., specialized spray or deposition techniques) that ensure uniform, repeatable adhesion to curved, non-flat structures. Perform an initial cost estimate and identify technical risks to be addressed in Phase II.

PHASE II: Demonstrate a fully functional, multi-modal prototype paint system on a large-scale (greater than a square meter), curved hydrodynamic model in a test facility. Evaluate the dynamic range, resolution, and frequency response of the system. Validate analytic models of the cross-sensitivities developed in Phase I. Demonstrate a highly repeatable application process achieving less than 5% thickness variation across complex curves, ensuring consistent calibration. Evaluate paint degradation, peeling, or leaching under flow velocities up to 15 m/s over continuous 8-hour test windows. Conduct a detailed cost and manufacturing analysis. Prepare a Phase III commercialization/transition plan.

PHASE III DUAL USE APPLICATIONS: Develop an improved formulation and manufacturing plans using the knowledge gained during Phases I and II in order to support transition of the technology for Navy use and use in hydrodynamics, aerospace, automotive, energy system, and electronics packaging applications.

REFERENCES:

1. Gregory, James W.; Sakaue, Hirotaka; Liu, Tianshu and Sullivan, John P. "Fast Pressure-Sensitive Paint for Flow and Acoustic Diagnostics." Annual Review Fluid Mechanics 2014, 46, pp. 303-330. https://doi.org/10.1146/annurev-fluid-010313-141304
2. Running, C.L. and Juliano, T.J. "Global measurements of hypersonic shock-wave/boundary-layer interactions with pressure-sensitive paint." Exp Fluids 62, 91, 2021. https://doi.org/10.1007/s00348-021-03194-8
3. Miozzi, M. et al. "Skin-friction from temperature and velocity data around a wall-mounted cube." Exp Fluids 65, 156, 2024. https://doi.org/10.1007/s00348-024-03881-2

KEYWORDS: Naval Hydrodynamics; Hydro-Acoustics; Advanced Diagnostics; Pressure Sensitive Paint

TPOC 1: Julie Young
yinlu.young.civ@us.navy.mil

TPOC 2: Mark Spector
mark.spector.civ@us.navy.mil