aerodynamic simulations with acusolve
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Innovation Intelligence®
Aerodynamic Simulations with AcuSolve
Dr. Marc Ratzel
April 2013
Copyright © 2012 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved.
Agenda
1. Motivation
• Applications of aerodynamics
2. AcuSolve for external aerodynamics
• Quick overview of AcuSolve
3. Aerodynamic examples
• Automotive aerodynamics
• Fluid-Structure-Interaction for a 100m wind turbine
4. Summary
Copyright © 2012 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved.
1. Motivation
• Aerospace
• No ground effects
• A380 900 km/h (Mach 0.75)
• Interest: lift/drag ratio, stall point, capacity,…
• Automotive
• Proximity to the ground
• My car 150 km/h (Mach 0.13)
• Interest: drag, lift, noise,…
• Buildings
• Several objects in close proximity
• Avg. wind speed 20 km/h (Mach 0.02)
• Interest: pressure loads, max. speed,…
Copyright © 2012 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved.
Characteristics of external flows
• Numerical model
• Large models (+50Mio volume elements)
• Complex geometry (e.g. engine, underbody)
• Very fine mesh near walls (Boundary layer, BL)
• Physics
• Different scales time/length scales
(e.g. sounds travels much faster than airflow,
high/low frequency, small/large eddies)
• Turbulence
• Transient phenomena (e.g. airborne noise CAA, wake)
• Fluid-Structure-Interaction
(e.g. structural vibration of hood noise, eigenmodes)
• Discontinuities (e.g. shock wave aerospace)
• Moving boundaries (e.g. train, wheels of a car)
Boundary layer mesh
Turbulent wake, wind turbine
Shock wave
Copyright © 2012 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved.
2. AcuSolve (CFD solver)
• General
• General purpose, 3-dimensional, unstructured solver
• Based on Finite Element method (GLS)
• Originated at Stanford University (T. Hughes et al.)
• Integration with other HyperWorks tools (HyperMesh, HyperView, RADIOSS,..)
• Numerics
• 2nd order accuracy in time and space for all flow variables
• Designed from day one for large scale problems
• Advanced turbulence models (SST, k-w, SA, DES, DDES, …)
• Comprehensive physics (fan/radiator component, sliding mesh, radiation,…)
• Robust fast volume mesher included (e.g. 90Mio car, engine, underbody, 80min)
• Very low requirement for element quality (e.g. tetras in boundary layer, skew>0.999)
Excellent fit for external aerodynamics
Copyright © 2012 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved.
AcuSolve (Fluid-Structure-Interaction, FSI)
• Rigid body dynamics
• 6 DOF rigid body solver
• No structural displacement
• Practical FSI (P-FSI)
• No run-time coupling
• Structural displacement computed in AcuSolve based on eigenmodes
• Limited to linear structural displacement
• Directly coupled FSI (DC-FSI)
• Codes communicate during run-time
• Loads/displacement exchange
• Non-linear structural behaviour
• Supported for RADIOSS, Abaqus, MD-Nastran
Copyright © 2012 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved.
3.1 Automotive aerodynamics
• Drag force
• Accounts for 75% of the car’s resistance (100km/h)
• Computation:
• Drag reduction by minimizing CD shape optimization
• Drag coefficients CD
drag side
lift
Car shape Frontal area
Modern car: ~ 0.29 Eiffel Tower: 1.8 – 2.0 Man (upright): 1.0 – 1.3
Copyright © 2012 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved.
Asmo model (Daimler & Volvo)
Amed body (S.R. Ahmed)
C_p, underbody C_p, rear C_p, roof
Drag coeff.: 0.162 (exp) / 0.164 (AcuSolve)
Drag coeff.: 0.23 (exp) / 0.23 (AcuSolve)
Classical external aero benchmarks
AcuSolve
Exp. (Volvo, Daimler)
Copyright © 2012 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved.
Fluid-Structure-interaction for rear wing
• P-FSI analysis
• Generic model of an automotive rear wing
• Soft plastic material, thickness of 2mm
• 20 & 100 eigenmodes computed with OptiStruct
fixed
monitor point
Displacement of monitor point
(20 & 100 eigenmodes) Down force for rigid and elastic
4%
Copyright © 2012 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved.
Fluid-Structure-interaction for rear wing
• P-FSI analysis
• Generic model of an automotive rear wing
• Soft plastic material, thickness of 2mm
• 20 & 100 eigenmodes computed with OptiStruct
fixed
monitor point
Structural deformation (vel. contour) Structural deformation (vel. contour)
Copyright © 2012 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved.
Altair’s Virtual Wind Tunnel (VWT)
• External automotive CFD analysis
• Advanced physics (rot. wheels, radiator, FSI,…)
• Efficient case setup
Copyright © 2012 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved.
Altair’s Virtual Wind Tunnel (VWT)
• External automotive CFD analysis
• Advanced physics (rot. wheels, radiator, FSI,…)
• Efficient case setup
• AcuSolve as CFD solver
• Automatic post-processing
Copyright © 2012 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved.
3.2 Wind turbine (Fluid-Structure-Interaction analysis)
• Facts
• Cooperation with Sandia National Laboratories, CA, USA
Blade length 100m
Weight 1.1t
Max. chord 7.6m
Material Fiberglass, Resin, Foam,…
Max. operation speed 7.44 RPM (tip speed 80m/s)
Power output ~ 13MW
human scale 1.8m
Copyright © 2012 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved.
Numerical models
• Structural model
• OptiStruct used as solver (eigenmode analysis)
• Composite model
• 100 eigenmodels
• CFD model
• Steady state, Multiple-Reference-Frame (MRF)
• Spalart-Allmaras RANS turbulence model
• ~ 50Mio elements
inflow periodic
outflow farfield
blade
Not true to scale
Eigenmode
CFD mesh
Copyright © 2012 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved.
Results (varying inflow speed & rotor RPM)
• Surface streamlines
• Power / Thrust
4.0 m/s Wind Speed 17.0 m/s Wind Speed
Larger separation bubble
Discrepancy with FAST results Some discrepancy
(due to separation bubble)
Remark: FAST and WT_Perf are commonly used tools in the wind turbine domain, containing simplifications for the CFD part
Copyright © 2012 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved.
4. Summary
• Challenges for external aero
• Large complex models (+50Mio cells)
• Advanced physics (e.g. diff. scales, turbulence)
• Transient (e.g. FSI, noise)
• AcuSolve
• Accurate, scalable, robust CFD solver
• Fluid-Structure-Interaction (FSI) capabilities
• Altair’s Virtual Wind Tunnel for external automotive aero
• Aerodynamic examples
• Automotive: Classical benchmarks (ASMO, Ahmed)
& FSI rear wing
• Wind turbine: FSI of turbine blade
• Both cases very good match with exp. data
Parking turbine blade
Virtual Wind Tunnel