Simulating the dispersion of rotor-wash entrained dust

1. Simulating the dispersion of rotor-wash entrained dust J.D. McAlpine Atms 790 seminar April 2, 2007 Collaborators: Dr. D. Koracin Dr. J. Gillies Dr. D. Boyle

2. Introduction • Forecasting Desert Terrain Project sponsored:Army Research Office project coordinator: Dr. Eric McDonald • Our Aspect: - Exploring the flow field around a helicopter in ground effect - What aspects of the flow field contribute the most to dust emission? - Developing a method to simulate dust entrainment due to the helicopter flow field - Coupled modeling of various scales mesoscale  microscale

3. Developing a modeling method: outline • Why is helicopter dust emission a significant concern? • Modeling plan outline: - Computational Fluid Dynamics (CFD)- rotor wake simulation - Dust entrainment simulation - Particle modeling simulation • Upcoming Desert Terrain Rotorcraft Experiment - Measurement of helicopter flow features and dust dispersion

4. Why is dust entrainment a concern? Regulation: • PM emission inventories • Clean air act: U.S. base operations • Regional Haze Rule Operation: • Training simulation • Visibility • Equipment damage

5. Unknowns: flow field and dust source • Rotor jet • distribution and • impingement • Turbulent burst • 3. Surface jet • Vortex shedding • Re-entrainment • of dust

6. Modeling Scheme Elements

7. Proposed Modeling Scheme • Computational Fluid Dynamics (FLUENT) • Virtual Blade Model (VBM): • DRI Lagrangian Particle Model • Dust source term Post-processor: Filterer Shear stress CAD Model CFD & VBM DRI LPM Atmospheric simulation scheme Dust source term

8. Fluent CFD simulations: • Equations of motion solved over a discretized domain: • Continuity equation • Conservations of momentum • Energy equation • Equation of state • Turbulence parameterization scheme (K-eps, LES…) initialization iteration solution

9. Virtual Blade Model vs. Full blade modeling VBM: momentum source • only time-averaged flow field needed • effects of flow on individual blades irrelevant • VBM: sophisticated technique- heli. specific

10. Virtual Blade Model: Blade Physics Blade Element Theory: Force= lift(L) – drag(D): • Lift & drag coefficients (CL and CD): f(angle) • U: function of blade orientation

11. Virtual Blade Model: in action • Model accounts for: trimming, twist, chord var., flapping, coning • Source evolves with solution: numerically stable • Example: static pressure of validation case: Untrimmed Trimmed

12. Atmospheric simulation • 1st case: steady state neutral atmosphere • Desert Measurement Project Comparisons: -steady state profiles - unsteady real-time • Final Product: - Coupled mesoscale-LES boundary layer model

13. Atmospheric simulation: 1st case - Neutral atmosphere, k-epsilon turbulence model • 1st: validate: • - TKE profile • - epsilon profile • - wind profile • 2nd: rotor simulation • Blackhawk heli. • 3rd: LPM input • Adapt CFD results • -Ensure same atmos. • conditions INPUTS: -surface roughness -wind profile: -TKE profile and source term: -epsilon profile:

14. Results: in progress • 1st case: • Light winds • -Blackhawk dimensions • Current work: • -Simplified Blackhawk • Geometry • -Proper rotor variables • -Validation of pressure • Distribution • TKE, wind dist. validation

15. Dust Source Term • Physics of particle entrainment: Shear Stress: Aerodynamic Lift: -determined from shear stress, velocity -overcome sliding friction 1st -overcome gravity next

16. Dust Source Term • “Lifting potential” of a shearing flow at the surface: • Factors: vegetation, surface consistency, supply, saltation

17. Dust Source Term Helicopter case: more sophisticated method needed? Why? • Highly turbulent: varying friction velocity • Significant local pressure gradients • Significant vertical velocities • Rapid saltation, source depletion

18. Lagrangian Particle Model Many Particles: Statistical Dispersion Modeling Drift term Stochastic term Gaussian Random Acceleration

19. Lagrangian Particle Model

20. Review of modeling scheme Post-processor: Filterer Shear stress 1.CFD & VBM 4. LPM 3. Dust Source Term 2.Atmospheric simulation scheme Comparison to Measurement Study: #1: Correct Helicopter config. #1: Correct surface variables #2: Correct profiles #2: Real time simulation? #3: Shear stresses vs. mass #4: Downwind dispersion conc compared to measurements

21. Desert Rotor Entrainment Study • Military Helicopter in ground • effect over desert terrain • Optical Remote Sensing- • PM concentrations: • -LIDAR • -FTIR • Irwin sensors • -Shear Stress • Sonic Anemometer • -Heli. flow and TKE • Standard meteorological • measurements for background In planning: Summer 2007

22. PM concentrations: • Optical Remote Sensing method: • FTIRs • (OP-LTs) • MPL

23. PM concentrations

24. Shear Stresses Helicopter Flight over Irwin sensors

25. Modeling validation

26. Model Validation • Significant variations? - source decay handling? - instrument error? - simulation errors? - atmospheric setup - shear stress calculation - landing/take-off cycle • More sophisticated model runs - non steady state vs. steady state solution?

27. Conclusion: Scientific Value of this Project: - Better understanding of perturbation dynamics through experimental observations and modeling - Better understanding of the perturbation dynamics relationship to dust entrainment - Computer Modeling: Simulation of the dust source and dispersion - Coupling of models of various scales: Mesoscale  CFD  LPM

28. Future work • Reassessment of the LPM turbulence schemes • Improvement of the LPM algorithm • Validation of improved model • Coupled WRF-LES microscale model for atmospheric input • Other sources: artillery, fixed-wing, tracked vehicles, wheeled vehicles

29. Questions? • Thank you to: • Army Research Office • Sierra Pacific