Particle Separation Efficiency in Canonical Vortex Tube Separator Arrays.pptx

This study focuses on the development of a custom-designed Particle Separation Rig wind tunnel at the Virginia Tech’s Advanced Propulsion and Power Lab (𝐴𝑃𝑃𝐿) to enable a detailed
investigation into the particle separation efficiency of Vortex Tube Separator (𝑉𝑇 𝑆) arrays,
producing a comprehensive dataset that serves as a benchmark for computational modeling
and system optimization. The experiments analyzed the performance of Soda Lime Glass
Spheres (𝑆𝐿𝐺𝑆) and MIL-E-5007C (𝐶𝑆𝑃𝐸𝐶) particles, encompassing a wide range of sizes and
compositions, including those meeting current military specifications. By examining unfiltered
and filtered particle sizing and correlating the results with other parameters, the study offers
a first view into the dynamics of particle separation efficiency in 𝑉𝑇 𝑆 arrays. The findings
demonstrate that separation efficiency is significantly influenced by particle characteristics such
as size, density, shape, and ambient environmental factors. 𝑆𝐿𝐺𝑆 particles, characterized by
their spherical shape and hygroscopic composition, exhibited considerable variability, with 3–6
𝜇𝑚 𝑆𝐿𝐺𝑆 achieving a mean separation efficiency of only 41.4±5.3% (95% confidence), while the
65–75 𝜇𝑚 𝑆𝐿𝐺𝑆 exhibited higher but inconsistent separation efficiencies. Largely influenced by
fluctuating humidity conditions, they averaged between 20%-60% on low humidity days and
between 80%-90% on high humidity days. Conversely, 𝐶𝑆𝑃𝐸𝐶 particles, with their irregular
shapes and non-hygroscopic nature, achieved consistent performance across all conditions.
They achieved a mean separation efficiency of 88.7±1.5% (95% confidence). Stokes number
(𝑆𝑡) analysis revealed its critical role in particle separation, with higher 𝑆𝑡 particles benefiting
from greater inertia, leading to more effective separation, while lower 𝑆𝑡 particles tended to
follow fluid streamlines, making them harder to isolate. Our findings show that hygroscopic
effects are as important as 𝑆𝑡. The study also compares experimental results with theoretical
predictions using the single-tube separator model, identifying discrepancies in mean separation
efficiency values arising from particle shape assumptions, environmental sensitivity, and system
limitations.

1. Jubel Kurian, Pranay V. Patel, K. Todd Lowe, and Wing F. Ng Advanced Propulsion and Power Lab, Virginia Tech AIAA SciTech Forum, 6 th -10 th January 2025 Copyright © by Virginia Polytechnic Institute and State University Published by the American Institute of Aeronautics and Astronautics, Inc., with permission. Particle Separation Efficiency in Canonical Vortex Tube Separator Arrays

2. 2 Introduction & Motivation CH-47 rotorcraft operating in brown-out conditions in a very dusty environment 1 Sand ingestion in engines up to 2-4 lbs /min 2 Causes significant compressor erosion 3 Leads to engine failure , high maintenance and shortened lifespans 4 Solution : Engine Air Particle Separators (EAPS) Vortex Tube Separators (VTS)

3. 3 Singular Vortex Tube Separator CH-47 rotorcraft operating in brown-out conditions in a very dusty environment 1

4. 4 How Does a VTS Work? Helical Vanes Separation Region FLOW Dirty Air Clean Air VTSs filter particles by employing Centrifugal Forces in a vortical airstream. Inlet Large Particle Small Particle Filtered Unfiltered

5. 5 VTS Test Article and Scaling The test array has 7 VTS tubes and was scaled up by 2.5x (a) (b) (c) Upstream and downstream sections with 7 VTS tubes . Assembled with part 'C' sliding into 'B’. Fully assembled VTS array in scavenge casing.

6.     6 Background and Theory Particle Separation Efficiency ( )   Non-Dimensional Parameters of Interest = Airflow rate through VTS = Separation region length = Critical radius of separation H = Helical vane pitch length   Where,   Ratio of inertial to viscous forces within the flow.     Ratio of particle inertia to fluid drag, determining particle-following ability in a flow.   (1) = 52,000 for the inlet of each separator  

7. 7 Experimental Setup – VTS Particle Separation Rig Scavenge Flow Rate: (7% of Inlet flow rate) 3*9 = 27 SCFM Sand Feed Rate: ~ 0.18 g/s Core Flow : ~ 10.0 m/s inlet flow velocity

8. 8 Particle Feeding System Nozzle exit placement w.r.t VTS inlet.

9. 9 Particle Used for Testing Soda Lime Glass Spheres (SLGS) MIL-E-5007C (CSPEC) Shape: Spherical, Uniform shape Size Range: 3-6 μ m and 63-75 μ m Composition: Silica, Na 2 CO 3 , CaCO 3 Density: 2.50 g/cm 3 Shape: Irregular, Non-uniform shape Size Range: 1-1000 μ m Composition: Silica, Trace Metal Oxides Density: 2.65 g/cm 3

10. 10 Results – Boundary Condition Validation The PSR's velocity profiles matched HSWT data closely, with minor deviations, confirming reliability for VTS sand ingestion testing.

11. 11 Results – Particle Separation Efficiency SLGS Particles CSPEC Particles Varying separation efficiencies due to hygroscopic behavior, with smaller particles (3-6 μm ) averaging 41.4±5.3% efficiency and larger particles (65-75 μm ) ranging from 20% to 91%, with a positive correlation to increasing humidity. Consistent and stable separation efficiencies between 85% and 95% (mean: 88.7±1.5%), unaffected by humidity variations due to their non-hygroscopic nature.

12. 12 Results – Stokes Number Analysis Stokes Number Impact: Low St particles showing low separation efficiency while larger particles with higher Stokes numbers achieved higher efficiency. Theoretical vs. Experimental: Experimental results match theoretical predictions for small SLGS particles (could be coincidental!) but diverge for larger SLGS and CSPEC particles. Equation 1 does not take array effects into account.

13. 13 Conclusion Boundary conditions validation demonstrate strong reliability of the experimental methodology. Evident role of Stokes’ number in separation efficiency. SLGS particles are hygroscopic in nature, leading to variable separation efficiency, while CSPEC particles provided consistent results due to their non-hygroscopic nature. VTS arrays validated in separating particles across a range of particle types and sizes and has highlighted the significant influence of particle properties and environmental factors on performance. This lays the foundation for future experimental studies on VTS, along with benchmarking separation efficiency data for particles meeting current military specifications. Future work include: New VTS design configurations, new particle types, r efine theoretical models to better account for irregular particle shapes and array configurations, and perform numerical simulations to validate against the experimental data.

14. 14 References https://australianaviation.com.au/2022/01/in-praise-of-the-chinook/ Pall, D., “Vortex Air Cleaner Assembly having Uniform Particle Removal Efficiency throughout the Array of Air Cleaners”, US Patent 3520114, 1968 Potts, J., “Why an Engine Air Particle Separator (EAPS)?”, Gas Turbine and Aeroengine Congress and Exposition, 1990, Brussels, Belgium Van der Walt, J. P., Nurick , A., “Erosion of Dust-Filtered Helicopter Turbine Engines Part 1”, Journal of Aircraft, Vol. 32, 1995, pp. 106-111 Collins, A. S., “Development of a Novel Probe for Engine Ingestion Sampling in Parallel With Initial Developments of a High-speed Particle-laden Jet,” Ph.D. thesis, Virginia Tech, 2021. Acharya, A. S., “Aerodynamic Interactions in Vortex Tube Separator Arrays,” Doctoral dissertation, Virginia Tech, 2023.