Development of an operational predictive tool
for visibility degradation and brownout caused
by rotorcraft dust entrainment
J.D. McAlpine*, Darko Koracin: DAS-DRI, Reno, NV
Steven Bacon, Sophie Baker, Eric McDonald:
DEES-DRI, Reno, NV
jdmac@dri.edu, DRI 2215 Raggio Pkwy, Reno, NV 89503
Introduction
• Brownout problem
• Modeling Categories:
- Pilot-in-loop & Simulation
- Air Quality Purposes
- Risk Assessment & Planning
• Development of an efficient predictive tool:
1) Wake u*
2) Landform Soil
Database
3) Dust Entrain.
Model
4) Visibility Risk 5) Downwind
Tool
Dispersion
Tool
Experimental data
• U.S. Army Yuma Proving
Grounds (May 2007):
rotorcraft dust
entrainment study
-Dust emissions
-Visibility impacts
-Helicopter wake structure
• Variation: speed, height
• 70 flight passes, UH-1
Desert Pavement Emission Rate Data
Shear stress predictor
New
Empirical
Method
CFD
Shear stress predictor
Experimental wake structure data
Empirical
Impinging
Jet equations
Wake velocity estimates
Soils database, dust entrainment model
j 4
FV (di )   j M j
j 0
DRI Integrated
Terrain Landform
And Soils Database
2000 m
 f (e
Dp i 1
i
c ,i
) FH ( Dp i ) pi ( Dp i )
4 Soil Categories
- Dust flux physics
Saltation flux
- Threshold friction vel.:
-Soil moisture
Distribution of
Particle size
Performance of entrainment model
Brownout risk
Example: Full Brown-out, Rating: 10
Example: Full Brown-out, Rating: 8
Brownout risk
Example: Significant Visibility Impacts,
Rating 6 (vortex beneath heli)
Example: Significant Visibility Impacts,
Rating 7 (vortex in front of heli)
Brownout risk
Example: Moderate Visibility Impacts, Rating
5
Example: Moderate Visibility Impacts, Rating
4
Brownout risk
Example: Minor Visibility Impact, Rating
2
Brownout risk
Brownout risk assessment mapping
Scenario 1:
- Slow speed / landing
- Recirculation Pattern
- Light winds, neutral
Brownout risk assessment mapping
Scenario 2:
- Moderate speed
- Light head wind (left)
- Moderate side wind (right)
Brownout risk assessment mapping
Scenario 3:
Scenario 4:
- Faster, vortex beneath heli.
- Moderate side wind
- Very fast, wing-vortex shaped wake
- Moderate side wind
Probabilistic
Emission and
Brownout
Potential:
• non-linear
• ensemble approach
• many variables:
Environment:
- wind speed
- wind direction
- stability/ turb.
- roughness
- soil type/dist.
- gravel cover
- crust cover
Aircraft:
- rotor height
- rotor thrust
- rotor angle
- turb. flux
- ground speed
- wake structure
fluctuation
Tool in-development visual example
Conclusions
• Efficient brownout/ dust-entrainment tool in development for the purposes of:
- risk assessment
- air quality / visibility impacts
- local-scale planning
• Empirical helicopter wake model:
- prediction of shear stress field
- shown to adequately produce
• State-of-the-art dust entrainment model
- emission rates compare well to experimental data
- adequately predicts brownout/ vis. Impact potential
- ensemble method produces a probability distribution
of risk
• Applications presented:
- brownout risk mapping
- dispersion tool for operation planning
Acknowledgements:
• This material is based upon work supported by the U.S. Army
Research Laboratory and the U.S. Army Research Office under
contract number DAAD 19-03-1-0159. This work is part of the DRI
Integrated Desert Terrain Forecasting for Military Operations
Project.
• We would also like to acknowledge the contributions from the
Strategic Environmental Research and Development Program
(SERDP), Sustainable Infrastructure Project SI-1399, of logistical
support in the field to J.D. McAlpine and the dust concentration data
used in our analysis.
• The team would also like to express their gratitude to the Natural
Environments Test Office, Yuma Proving Ground, Yuma AZ for
financial and logistical support of the helicopter flights.