An OpenFOAM implementation of Ice Accretion for Rotorcraft

An OpenFOAM implementation of Ice Accretion for Rotorcraft Michael P. Kinzel, Ralph W. Noack, Christian M. Sarofeen, David A. Boger, and Scott T. Miller Penn State University, Applied Research Laboratory

Support from: NASA under NASA Cooperative Agreement NNX08AW92A with Richard E. Kreeger as contract monitor 1

Challenges in Rotorcraft Icing •

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Multi-phase/physics: – Air Flow (baseline1) – Droplet flow (Eulerian approach2) – Runback (model film and freezing water2) – Heat conduction and convection (modeled2) Disparate scales – Time: Rotor: ~0.2s/rev ; Accretion time: ~tens of minutes Complex Geometry: – Rotor motion & blade dynamics – Time dependent complex ice shapes • Need to accommodate ice

Approaches

Using baseline and inhouse solvers (See references for additional information) Time-Advancing Acceleration approaches (Zonal) Overset meshes, Immersed Boundary methods

Figure borrowed from: Jose Palacios

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Overview: How it all fits together

Blade Motion: Trim, blade dynamics, … CFD Code: Flow solution Accommodate Iced Geometry

Droplet Solver: droplet deposition(b) Surface Solver

Ice Shape 3

Overview

Blade Motion: Trim, blade dynamics, …

Accommodating mesh using Overset libraries (SUGGAR3, DirRTib4, and foamedOver5)

CFD Code: Flow solution Accommodate Iced Geometry

Droplet Solver: droplet deposition(b) Surface Solver

Ice Shape

Clean-Blade Motion for Trimmed Helicopter Using Blade-Element-Momentum Theory Code6: •Collective: q0 •Longitudinal Cyclic: q1s •Lateral Cyclic: q1c •Flapping blade dynamics: b(y) •Vehicle Attitude 4

Flow Solver

Blade Motion: Trim, blade dynamics, … CFD Code: Flow solution Accommodate Iced Geometry

Droplet Solver: droplet deposition(b) Surface Solver

Ice Shape 5

Flow Solver Module (FSM) • Unstructured-Mesh, Flow solution Solver • OpenFOAM • •

Inherit baseline solvers: Incompressible flow, compressible flow, potential flow (~hour calcs, massive problems, on personal CPU). Developing in-house solvers (compressible/incompressible)

M=0.001

Scales to fuselage, M=0.2

M=0.9 Rotor Blade, M=0.2

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Droplet Solver Module (DSM)

Blade Motion: Trim, blade dynamics, … CFD Code: Flow solution Accommodate Iced Geometry

Droplet Solver: droplet deposition(b)

Drag-Term Coupling (same mesh)

Surface Solver

Ice Shape 7

Droplet Solver Module (DSM) •

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3D, time dependent, unstructured, Eulerian droplet Solver • Droplet momentum driven by pressure gradient, gravity, and drag • Dual-time with scalar dissipation2 -> larger Dt, Courant Num. ~1000! Providing reasonable deposition rates (b in the icing community) • Evaluating helicopter-relevant problems7 Compares favorably with experiment2and LEWICE7

Droplet Mass Cons.: Deposition Rate: Droplet Momentum Cons.:

LEWICE(a=0) OpenFOAM(a=0) OpenFOAM(a=5) LEWICE(a=5)

Extending to 3D geometries

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Ice Accretion Module (IAM)

Blade Motion: Trim, blade dynamics, … CFD Code: Flow solution Accommodate Iced Geometry

Droplet Solver: droplet deposition(b)

p, tw b

Volume-to-surface interpolation (second surface mesh)

Surface Solver Ice Accretion Module Ice Shape 9

Ice Accretion Module (IAM) • • •

Droplet solver: local deposition rates Flow Solver: Wall Shear/Pressure mDrops 2 Surface-Film Solver : – Mass/Momentum/Energy on Film – 1-cell thick, finite volume solver (clumsy but works) A – Models: • Numerous mass, momentum, energy sources • Air/Film Convection2 • Conduction through ice/skin2 mFilm,in

y/c

mFilm,out

mIce

3D Simulated Ice Shapes from the IAM x/c

y/c x/c

Ice Deformation Module (IDM)

Blade Motion: Trim, blade dynamics, … CFD Code: Flow solution Accommodate Iced Geometry

Droplet Solver: droplet deposition(b) Surface Solver

Ice Shape 11

Ice Deformation Module (IDM) Immersed Boundary Method • Complex ice surfaces develop

Figure borrowed from: Jose Palacios Penn State University

– Initially deform mesh – Mesh quality issues • Too much deformation degrades unstructured mesh

– How do we “capture” these complexities

• Approach to capture boundary shape:

IBM: Acting on air flow

IBM: Interacts with droplets

– Immersed Boundary Method • Sarofeen (future M.S. Thesis)

– Using a piso-based solver with droplets 12

Zonal Approach

Blade Motion: Trim, blade dynamics, …

Multi-Region Solver •Accelerate time marching •Active/frozen regions

CFD Code: Flow solution Accommodate Iced Geometry

Droplet Solver: droplet deposition(b) Surface Solver

Ice Shape 13

Zonal Approach: First Attempt Pitching Airfoil: •Buffered overset “fringe” data3,4,5 •Assume: Azimuthal periodicity •Flow Solver/Single Processor •Zone 1: Run Every time step •Zone 2: Frozen every even oscillation •OpenFOAM-frame simplifies this •pointer lists & referencing •Easy to vary •Eqn. sets, mesh, etc. •Extending to all solvers •Surface-film solver

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Final Thoughts •

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OpenFOAM: Provides an excellent environment for such multiphysics projects – Easy to incorporate the numerous: models/equation sets/algorithms, etc. – Sharable platform: Expect to pass code onto NASA • Manageable code! Not without challenges: – Compressible solvers still need work – Data transfer (volume to surfaces) still clumsy – Automation/streamlining difficult – Mesh deformation

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References 1. 2. 3. 4. 5. 6. 7.

OpenCFD, “OpenFOAM Documentation,” April 2010, http://www.opencfd.com. Kinzel, M. P., Sarofeen, C. M., Noack, R. W., Morris, P. J., and Kreeger, R. E., “A Finite- Volume Approach to Modeling Ice Accretion,” AIAA-2010-4230, June 2010. Ralph W. Noack, "SUGGAR: A General Capability for Moving Body Overset Grid Assembly," AIAA Paper 20055117, 17th AIAA Computational Fluid Dynamics Conference, Toronto, Ontario, Canada, June 6-9 2005. Ralph W. Noack, "DiRTlib: A Library to Add an Overset Capability to Your Flow Solver," AIAA Paper 2005-5116, 17th AIAA Computational Fluid Dynamics Conference, Toronto, Ontario, Canada, 6-9 June 2005. Boger, D.A., Noack, R. W., and Paterson, E. G., “Dynamic overset Grid implementation in OpenFOAM,” 5th OpenFOAM Workshop, Gothenburg, Sweden, 21-24 June 2010. Kinzel, M. P., “Miniature Trailing-Edge Effectors for Rotorcraft Applications,” M.S. Thesis, Department of Aerospace Engineering, The Pennsylvania State University, University Park, PA, Aug. 2004. Sarofeen, C. M., Kinzel, M. P., Noack, R. W., Morris, P. J., and Kreeger, R. E., “A Numerical Investigation of Droplet/Particle Impingement on Dynamic Airfoils and Rotor Blades,” AIAA-2010-4229, June 2010.

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