Transcript Document

Rotor Blade Erosion Phenomenology
Mr. Robert Lee
Military Systems Technologies, LLC.
and
Dr. William F. Adler
University of California at Santa Barbara
International Helicopter Safety Symposium
Montreal, Canada
September, 2005
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Motivation
•
Basic rotor blade erosion due to particulate impact is not well
understood. Consequently, the current approach to develop blade
erosion protection material via laboratory testing is often costly and
performs poorly in the field.
•
A robust Modeling and Simulation tool is sought to augment the
laboratory testing which will improve the developmental time and cost,
and ultimately, provide a better protection solution.
•
A predictive tool will increase the life cycle of rotor blades thereby
reducing replacement costs and increase operational readiness of
current assets in the theater of operation.
•
Better understanding of blade rotor erosion will increase the safety of
the rotorcraft.
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Phenomenon
Potential damage to
window and other
components
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Mechanisms/Processes
• Rotor Induced Flowfield Environment
– Aerodynamic Load
– Trimmed and Articulated Rotor
• Particulate Trajectory
– define impact conditions
– Non-spherical particles
• Particulate/Blade Impact Interaction
– FEA Analysis
• Surface/Substrate Damage
initiation -> crack growth -> material removal
• Prediction of Surface Erosion
– Requires both Modeling and Testing
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Rotorcraft Aerodynamics
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Rotorcraft Aerodynamics
• Industrial Standard (Potential Theory)
– Blade Element Analysis (Prandtl Lifting Line)
– Wake Analysis (Vortex-Lattice)
• Aeromechanics
– Blade Dynamics (pitch,flap,yaw)
– Trimmed Rotor
• Modern Approach
– CFD using Navier-Stokes methodology
• Structured-Grid Solver
• Overset Grid Solver (OVERFLOW)
• Unstructured-Grid Solver (FUN3D, Cobalt, CRUNCH)
– Multi-Field Approach for Fluid-Structure Interaction
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Potential Theory
• Blade Element Analysis
• Vortex Wake Tracking
Biot-Savart Law
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Vortex-Lattice Method
• Based on the solution of incompressible, inviscid
flow equations
• Good accuracy can be obtained with coarse grid
• Difficult to predict detailed tip vortex roll-up
• Does not account for thickness, viscous,
separation, or compressibility effects
• Computational time can be short
• Uses either “prescribed wake” (based on
experimental data) or “free wake” (wake structure
solved for directly at each time step)
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HELIWAKE Model
• Free Wake Analysis Model
• An earlier assessment of the HELIWAKE model
formulated by Dr. Crimi from Cornell University
showed good agreements with experimental data
• Rotor tip vortices are tracked in time and the
vortex induced velocity field is calculated via
Biot-Savart Law
• This model was rewritten under the Phase I effort
• Model was coupled to the Lagrangian particle
solver
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HELIWAKE Solution
Cornell Aeronautical Lab Experiment Case
7% of R below rotor plane
20% of R below rotor plane
Comparison between predicted and measured downwash velocity
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Georgia Tech Single Rotor Case
Experimental Set-up
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Velocity comparison
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HELIWAKE Hover Solution
Periodic Solution
Downwash
Velocity Contour
Tip Vortex
Structure from
Rotor Blades
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Wake Solution
Hover Mode
Forward Flight Mode
Hover Solution using HELIWAKE Module
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Modern CFD Methods
Structured Grid
Unstructured Grid
• Simplifications must be made (e.g. rigid blades)
• Requires high grid resolution
high computational cost
• Transient simulation is still too costly
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CFD Solution
elsA
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OVERFLOW
FUN3D
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Numerical Dissipation
• Conventional modern CFD schemes preserves fluxes but
does not preserve vorticity
• Vorticity preserving scheme requires conservation of
vorticity transport equation.
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V  t      U     U    U   dV  0
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Morton, K.W., and Roe, P.L., “Vorticity-Preserving LaxWendroff Schemes for the System Wave Equation”, J. of Sci.
Comp., Vol. 23, No. 1, pp. 170-192, January 2001.
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Vortex Preserving Solution
Standard Roe/TVD Flux Split Scheme
Vorticity Preserving Scheme
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Mechanisms/Processes
• Rotor Induced Flowfield
– Aerodynamic Load
– Trimmed Rotor
• Particulate Trajectory
– define impact conditions
• Particulate/Blade Impact Interaction
– FEA Analysis
• Surface/Substrate Damage
initiation -> crack growth -> material removal
• Prediction of Surface Erosion
– Requires both Modeling and Testing
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Trajectory Calculation
• Lagrangian Particle Tracking
– Weber number correlation for Liquids
– Empirical Drag Law
simpler models but fast running
• Eulerian Particulate Solver
– Dilute particulate cloud density is assumed
– Particulate volumetric effect and particle-particle interaction is
ignored
Resulting equation is similar to NS equations
• DSMC Method (Stochastic)
– Particle-Particle Interaction
– Particle-Surface Interaction
Beyond the scope of current effort
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Lagrangian Solver
Two Bladed Hover Case
0.1 m m Particle in Hover
1.00E+01
0.00E+00
UP
-1.00E+01
Velocity
VP
WP
-2.00E+01
UG
VG
-3.00E+01
WG
-4.00E+01
3360
2940
2520
2100
1680
1260
840
420
0
-5.00E+01
PSI (Degrees)
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Eulerian Particles
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Assume dilute Gas/Particle mixture
Low volumetric loading but occupy significant mass
Particle-Particle interaction is neglected
Assume spherical particle shape with no break-up or
agglomeration
• Particle size distribution is represented in discrete bins
• Gas/Particle interaction is obtained from viscous drag
and heat transfer
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Eulerian Formulation
Gas-Particle
Interaction Terms
Particle Equation in
conservation form
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Solid Rocket Motor
Gas Density
Multi-Phase Nozzle Flowfield Simulation
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Particle Environment
• Empirically characterize far-field boundary profile
– Sieve Analysis to determine the size profile
– Shape characterization
• Make equivalent spherical particle profile
– Size
– Shape
• Convect the particles to the Rotor plane
– Eulerian
– Lagrangian
• Populate cells with representative angular particles
• Use FEA analysis to simulate particle impacts
– LSDYNA
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Mechanisms/Processes
• Rotor Induced Flowfield
– Aerodynamic Load
– Trimmed Rotor
• Particulate Trajectory
– define impact conditions
• Particulate/Blade Impact Interaction
– FEA Analysis
• Surface/Substrate Damage
initiation -> crack growth -> material removal
• Prediction of Surface Erosion
– Requires both Modeling and Testing
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FEA/Solid Mechanics Model
• LSDYNA (Lawrence Livermore Lab)
–
–
–
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Surface Deformation
Impact Model
Large material database
Generalized Motion
• CTH Code (Sandia Lab)
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–
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Impact Physics
Multi Material
Large Deformation
Eulerian Framework
Adaptive Mesh Refinement
• Commercial Code
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LSDYNA Model Example
Sphere Model, Target Mesh, Size
Stochastic impact sites after 10 and 200 events
Sphere/Surface Interaction for 10,100,200 impacts
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Sphere Impacting Plate Cases
LSDYNA Code
CTH Code
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Mechanisms/Processes
• Rotor Induced Flowfield
– Aerodynamic Load
– Trimmed Rotor
• Particulate Trajectory
– define impact conditions
• Particulate/Blade Impact Interaction
– FEA Analysis
• Surface/Substrate Damage
initiation -> crack growth -> material removal
• Prediction of Surface Erosion
– Requires both Modeling and Testing
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Structural Complexity
• Rotor blades incorporate thin walled design concepts
• Blades have a complex internal structure to withstand load and service conditions
• Honeycomb structures are used in blades and plates
Crack Growth
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Crack Growth Analysis
Load Spectrum
Load Cycle
Stress Range
Update Crack
Length
Crack Growth
dA For ΔK
dN
Stress Intensity
Factor ΔK
Empirical Data
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Empirical Data
Polyurethane
3M 8663 Tape
Single Impact Tests
Testing
Material Response
Characterization
Observation and
Analysis
Mechanics of Failure
and Degradation
Physical and
Computational Models
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Optical and SEM
Microphotograph
Strain Gages
Thermocouple
Rotor Erosion
Tool Kit
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Summary of Phase I Effort
• A vortex tracking module was written
• A Lagrangian particle tracking module was written
• Survey of literature was conducted with regard to
CFD application of helicopter flowfields
• LS-DYNA model was evaluated
• Examined particle characterization issues
– Angular particles
– Shape and Size
• Examined Particle/Surface Interaction Models
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Phase I Efforts (continued)
• Initiated empirical work
– Silica particles (sieving, shape factor, mechanical and
physical property)
– 3M 8663 protective tape
• Particle Impact Experiment Test Matrix
• Formulate Erosion Tool Architecture
– Identify necessary component modules
– Identify FD-CADRE approach as backbone of tool
architecture
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Computational Architecture
Process Manager
User
Erosion Tool Kit
Aerodynamic
Particle
Damage
Crack Growth
Material Removal
Data
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FEA
Empirical Model
Communication
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Future Work
Aerodynamic Module
Potential Solver (HELIWAKE, PMARC, CHARM/CAMRAD II ?)
CFD Models (Cobalt, OVERFLOW, FUN3D ? )
Particulate Module
Lagrangian
Eulerian
FEA Module
LS-DYNA
Experimental Matrix ( polyurethane )
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Spherical Particles
Far Field Property
mapping
• Lagrangian or Eulerian Particle Solver
Near Rotor Plane
Inverse mapping
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Shape Characterization Methods
• Geometrical
– Equivalent Volume
– Equivalent Mass
– Complex Fourier Descriptor Method
• Measurement
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Microscopy
Image Analysis
Sieve Analysis
Static Light Scattering
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Angular Particle Impact on Polyurethane
• Graded Silica Particle Definition
– Evaluate shape factors
– Mechanical and Physical Properties
• Particle Impact Experiments
– Experimental Set-Up and Diagnostics
– Test Matrix
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Characterization of Particle Impact Damage
• Particle Dynamics
• Analytical Description of observed interactions
• Observation of Damage Modes
– Optical Microscopy
– Scanning Electron Microscopy (SEM)
• Identify onset of failure and damage progression
• Identify conditions for material removal
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Computational Model Development
• Angular Particles
– Concentration
– Size Distribution
– Impact Locations
• Formulate Multiple particle Impacts
• Develop criteria for initial damage
• Develop criteria for damage growth for random
multiple particle impacts
• Develop criteria for material removal
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Rotor Blade Erosion Tool
Aerodynamic
Damage
Crack Growth
Material Removal
Particle
FEA
Empirical Model
Balanced Modeling and Empirical Work is planned
Acknowledgement
The support of Army Research, Development and Engineering
Command (RDEC) is gratefully acknowledged.
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