FAST and AeroDyn Enhancements - Sandia...
Transcript of FAST and AeroDyn Enhancements - Sandia...
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FAST and AeroDyn Enhancements
Sandia Blade Workshop
Khanh Nguyen
May 30-June 1, 2012
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Outline
• FAST Structural Modelo Motivationo Current FAST modelo Structural model enhancement
• AeroDyno AeroDyn Overhaul o BEMT numerical solutionso Generalized dynamic wake modelo Dynamic stall model
• Conclusions
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CAE ToolsFAST-AeroDyn-HydroDyn Coupling
CAE: Computer-Aided Engineering
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Motivation
Trends in blade design:o Future blades tend to be longer and more flexibleo Blade torsion important in aeroelastic responseso Aeroelastic coupling designs to reduce loads
– Material coupling (anisotropic beam)– Geometric coupling (sweep, pre-bend)
o Advanced controls with blade mounted actuatorso Aeroelastic stability could be a design driver
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Current FAST
FAST is an aero-hydro-servo-elastic code for HAWT Key features
o FAST formulation based on multi-body dynamics with elastic elements represented by structural modes
o Controls implementation with subroutines, DLLs, or Simulink®
o Coupled to AeroDyn for aeroelastic and HydroDyn for hydro-elastic simulations
o Land-based or sea-based with monopiles or floating platforms
Current blade structural modelo Modal representation of straight blade with isotropic materialso No axial or torsion deflections, coupled flap and edge modes
– Include radial shortening, centrifugal, Coriolis, gyroscopic effects o Modes imported from external source, such as BModeso No blade-pitch actuator dynamics
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Structural Model Enhancement
• Geometric Exact Beam (Hodges 2006)o Timoshenko beamo Nonlinear, curved, anisotropic beam modelo Developed with VABS (Variational Asymptotic Beam Section
Analysis), a cross-sectional analysis• GEBT (Geometric Exact Beam Theory)
o Open-source software developed by Prof. Yu based on Hodges’ geometric exact beam theory
o Mixed formulation based on Hamilton’s extended principleo Implemented with linear finite elements
• GEBT is planned for FAST structural enhancemento FEMo Modal representation for efficient computation
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AeroDyn - Overhaul
• Overhaul plan based ono AeroDyn Overhaul Meeting 2008o Code reviews
– Leishman– Peters
• v13.00.01a-bjj, released February 2012o Improved interfaces with FAST and TurbSimo Added ability to read-in HAWC wind format (Mann turbulence)o Several minor changes and bug fixeso Initiate code modularization
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BEMTNumerical Solutions
• Blade element momentum theory provides quasi-static solutions to axial and tangential inductions a, a’
• Current BEMT solutions, based on fixed-point iteration, not robust
• Use relaxation improves convergenceai+1 = f*ai + (1-f)*F(ai)a’i+1 = g*a’i + (1-g)*G(a’i)where f, g are relaxation factors ∈ [0,1)
o Number of iterations can be high • Using Brent’s method reduces
computing time and eliminates convergence problems
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Tip Speed Ratio
Bla
de P
itch,
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Non-convergent cases (f, g=0)
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Blade Station Index
No.
of I
tera
tion
Fixed PointBrent
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Generalized Dynamic Wake
• GDW models inflow dynamics based on acceleration potential of actuator disk (Peters & He)
• AeroDyn review by Prof. Peters:o Possible to include tangential induction directlyo Identify source of low speed instability, associated with
transition through vortex ring stateo Include yaw rate effects with skew wake
Burton et al. (2001)
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Dynamic Stall
• Dynamic stall is characterized by stall delays and large lift and moment overshoots over static values
• AeroDyn includes a modified version of Leishman modelo Main difference is the modeling of static airfoil behaviorso Need to validate modified version with original model
• Leishman dynamic stall model (below) implemented based on Gupta & Leishman Wind Energy 2006 paper
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CL
OSU DataModel
α = 20 + 5sinωt, k=0.07, Re=106
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Angle of Attach, deg
CM
OSU DataModel
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AeroDynCurrent & Planned Work
• BEMTo Update numerical solution with a robust root finding method
• Dynamic Stallo Validate AeroDyn implementation with original modelo Revise algorithms per recommendation of Leishman
• GDWo Revise algorithm per Peters’ recommendationo Include tangential inductiono Resolve problems with low speed instabilityo Include yaw rate effects
• Wakeso Include vortex wake methods (prescribed and free wakes)o Add a Dynamic Wake Meandering model (with UMass & DTU Wind)
• General:o Improve modularization:
– Create separate modules for wind inflow, airfoil aerodynamics, and inductiono Interface AeroDyn with the ECN AWSM free-wake vortex codeo Interface AeroDyn with the DTU Wind HAWC2 aero module
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Conclusions
• FASTo Progress under way to implement new blade
structural model for FAST
• AeroDyno Improved interfaces with FAST and TurbSimo Modularize codeo Improve BEMT numerical solutions o Verify dynamic stall modelo Identify enhancements to GDW
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OverhaulReasons for Overhaul
• Trouble developing, maintaining, and using AeroDyn• Common request from users• Desire to have improved:
o Functionalityo Usabilityo Code readability
• Eliminate problems• Make it easier to include additional aerodynamic theories• Develop a standardized & streamlined interface to structural
dynamic analysis programs• Important because proper aerodynamic modeling is critical for
accurate performance, loads, & stability analyses
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OverhaulRecent Work (Wind Inflow Module in v13.00.00)
• All wind-inflow routines & variables are contained in a separate module with clear interface
• Can read TurbSim’s binary full-field “.bts” & tower “.twr” files• Full-field wind files are relative to the ground, not the turbine
hub-height• Can be used outside of AeroDyn, e.g. the module has been
made into a MATLAB mex function (allows easy access to the wind file data)
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Extra
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uctio
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BrentFixed Point
• Compare numerical solutions of a, a’ using Brent’s method and fixed-point iteration