Simulating the dispersion of rotor-wash entrained dustJ.D. McAlpineAtms 790 seminarApril 2, 2007Collaborators:Dr. D. KoracinDr. J. GilliesDr. D. Boyle

IntroductionForecasting Desert Terrain Projectsponsored: Army Research Office project coordinator: Dr. Eric McDonaldOur 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

Developing a modeling method: outlineWhy 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

Why is dust entrainment a concern?Regulation:PM emission inventoriesClean air act: U.S. base operationsRegional Haze Rule

Operation:Training simulationVisibilityEquipment damage

Unknowns: flow field and dust source Rotor jet distribution and impingement

Turbulent burst

3. Surface jet

Vortex shedding

Re-entrainment of dust

Modeling Scheme Elements

Proposed Modeling SchemeComputational Fluid Dynamics (FLUENT)Virtual Blade Model (VBM): DRI Lagrangian Particle ModelDust source termCFD & VBMDRI LPM Atmospheric simulation scheme CAD Model

Post-processor:FiltererShear stress Dust source term

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)initializationiterationsolution

Virtual Blade Modelvs.Full blade modelingVBM: momentum source only time-averaged flow field needed effects of flow on individual blades irrelevant VBM: sophisticated technique- heli. specific

Virtual Blade Model: Blade PhysicsForce= lift(L) drag(D):Blade Element Theory:Lift & drag coefficients (CL and CD): f(angle)U: function of blade orientation

Virtual Blade Model: in actionModel accounts for: trimming, twist, chord var., flapping, coningSource evolves with solution: numerically stableExample: static pressure of validation case:UntrimmedTrimmed

Atmospheric simulation1st case: steady state neutral atmosphere

Desert Measurement Project Comparisons:- steady state profiles - unsteady real-time

Final Product: - Coupled mesoscale-LES boundary layer model

Atmospheric simulation: 1st case- Neutral atmosphere, k-epsilon turbulence model

1st: validate: - TKE profile - epsilon profile - wind profile

2nd: rotor simulationBlackhawk heli.

3rd: LPM inputAdapt CFD results-Ensure same atmos.conditions INPUTS:

-surface roughness-wind profile:

-TKE profile and source term:

-epsilon profile:

Results: in progress1st case:Light winds-Blackhawk dimensions

Current work:-Simplified BlackhawkGeometry-Proper rotor variables -Validation of pressureDistributionTKE, wind dist. validation

Dust Source TermPhysics of particle entrainment:

Shear Stress:

Aerodynamic Lift: -determined from shear stress, velocity -overcome sliding friction 1st -overcome gravity next

Dust Source TermLifting potential of a shearing flow at the surface:

Factors: vegetation, surface consistency, supply, saltation

Dust Source TermHelicopter case: more sophisticated methodneeded? Why?Highly turbulent: varying friction velocitySignificant local pressure gradientsSignificant vertical velocitiesRapid saltation, source depletion

Lagrangian Particle ModelStochastic termDrift termGaussian Random AccelerationMany Particles: Statistical Dispersion Modeling

Lagrangian Particle Model

Review of modeling scheme1.CFD & VBM2.Atmospheric simulation scheme Post-processor:FiltererShear stress 4. LPM3. Dust Source TermComparison 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

Desert Rotor Entrainment StudyIn planning: Summer 2007 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

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

PM concentrations

Shear StressesHelicopter Flight over Irwin sensors

Modeling validation

Model ValidationSignificant variations? - source decay handling?- instrument error?- simulation errors?- atmospheric setup- shear stress calculation - landing/take-off cycleMore sophisticated model runs- non steady state vs. steady state solution?

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

Future workReassessment of the LPM turbulence schemesImprovement of the LPM algorithmValidation of improved modelCoupled WRF-LES microscale model for atmospheric inputOther sources: artillery, fixed-wing, tracked vehicles, wheeled vehicles

Questions?Thank you to:

Army Research Office

Sierra Pacific