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Air Flow Modeling Studies in Air Flow Modeling Studies in Support of InstrumentationSupport of Instrumentation

Dave Rogers 24-March-2008Dave Rogers 24-March-2008

Outline:Outline:CFD activities in EOLCFD activities in EOLmodeling proceduresmodeling proceduressimulations:simulations:

• pressure rake pressure rake • trailing conetrailing cone• laser velocimeterlaser velocimeter• particle bounce - FSSP particle bounce - FSSP • ice nuclei chamberice nuclei chamber

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EOL air flow studies groupEOL air flow studies group• Cindy Twohy & Dave RogersCindy Twohy & Dave Rogers• http://www.eol.ucar.edu/raf/Airflow/http://www.eol.ucar.edu/raf/Airflow/

applications:applications:• instrument design instrument design • airborne probe placement & alignmentairborne probe placement & alignment• flow & thermodynamics inside of flow & thermodynamics inside of

instrumentsinstruments• particle trajectoriesparticle trajectories• improving measurements & their improving measurements & their

interpretationinterpretation• identify problems, suggest fixesidentify problems, suggest fixes

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softwaresoftware1. FLUENT/Gambit1. FLUENT/Gambit

• Gambit = geometry & computational meshGambit = geometry & computational mesh• FLUENT = flow solverFLUENT = flow solver• http://www.fluent.com/http://www.fluent.com/• 4 licenses4 licenses

2. STAR-CD family of programs2. STAR-CD family of programs• Star-CD, pro-am, Star-CCM+, etc.Star-CD, pro-am, Star-CCM+, etc.• http://www.cd-adapco.com/http://www.cd-adapco.com/• 10 licenses10 licenses

Linux & MS-WindowsLinux & MS-Windows• annual license feesannual license fees

Tutorial downloads, webinars, training (fee-based)Tutorial downloads, webinars, training (fee-based)Both 1 + 2 are user-friendly with graphic user interfaces & menusBoth 1 + 2 are user-friendly with graphic user interfaces & menus

• Steep learning curveSteep learning curve• Frequent use is necessary for proficiencyFrequent use is necessary for proficiency

+ Plug-in + Plug-in For CADFor CAD

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What kind of problems What kind of problems can be addressed? can be addressed?

Laminar or turbulentLaminar or turbulentCompressible Compressible Heat transfer Heat transfer Multi-phase Multi-phase (evaporating particles, bubbles, melting, (evaporating particles, bubbles, melting,

freezing, boiling, ..)freezing, boiling, ..)Chemical reactionsChemical reactionsSteady-state or non-steady Steady-state or non-steady (moving grid)(moving grid)AcousticsAcoustics + more …+ more … + user-defined functions+ user-defined functions

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flow simulation stepsflow simulation steps

1.1. build geometrybuild geometry• from basic shapes or import CAD filefrom basic shapes or import CAD file

2.2. create computational meshcreate computational mesh• edges, surfaces, volumesedges, surfaces, volumes• check for quality (size, skewness, ..)check for quality (size, skewness, ..)• export to flow solverexport to flow solver

3. set boundary conditions (P, T, RH, velocity, ..)3. set boundary conditions (P, T, RH, velocity, ..)4. run numerical solver 4. run numerical solver 5. display results & derived quantities5. display results & derived quantities

• velocity, pressure, temperature, drag force, ..velocity, pressure, temperature, drag force, ..• particle trajectories, animationsparticle trajectories, animations

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Example 1: BL depth on HIAPERExample 1: BL depth on HIAPER

Scientific need: sample air outside of the flow Scientific need: sample air outside of the flow boundary layer to avoid possible boundary layer to avoid possible contaminationcontaminationAdvice from Gulfstream: BL = 1% of distance Advice from Gulfstream: BL = 1% of distance from nosefrom nose

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Gulfstream laminar flow modelGulfstream laminar flow model

1:100

1:100

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build geometry & meshbuild geometry & mesh

geometry from CAD file import + lots geometry from CAD file import + lots of cleanupof cleanup

insert into wind tunnel box ~3 m long:insert into wind tunnel box ~3 m long:7xLong, 3xTall, 8xWide7xLong, 3xTall, 8xWide

540,000 cells540,000 cells

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dynamic pressuredynamic pressuresea level, 123 m/ssea level, 123 m/s

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pressures in vertical plane pressures in vertical plane upstream of pitot tipsupstream of pitot tips

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Progressive Science Project - 2005Progressive Science Project - 2005

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resultsresults

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resultsresults

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Example 2: Example 2: trailing conetrailing cone10” dia x 12” tall10” dia x 12” tall

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flow model – domain cylinder wind flow model – domain cylinder wind tunnel 30” dia x 75” longtunnel 30” dia x 75” long

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trailing conetrailing conedomain ~220,000 cells. domain ~220,000 cells. sea level 204 m/s sea level 204 m/s drag force 245 lb. drag force 245 lb.

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Example 3:Example 3: laser velocimeter for HIAPERlaser velocimeter for HIAPER

(artist’s concept)(artist’s concept)wing podswing pods

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laser velocimeter for HIAPERlaser velocimeter for HIAPERdomain ~4 x 2 x 2 mdomain ~4 x 2 x 2 m33 500,000 cells 500,000 cells

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40,000 ft40,000 ft 227 m/s227 m/sattack 0°attack 0° laminarlaminar

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cell velocities along horizontal & cell velocities along horizontal & vertical sections centered on one podvertical sections centered on one pod

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Example 4: Example 4: particle bounce - FSSPparticle bounce - FSSP

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animationanimation

(change to FLUENT display)(change to FLUENT display)

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Example 5: Example 5: ice nuclei chamberice nuclei chamber

Description of Chamber• annular space ~1 cm between concentric cylinders• inner walls covered with ice ~ 0.1 mm thick• flow laminar, downward• sample air (1 LPM) slit injection• sheath air (9 LPM) through series of holes

Cylinder radii 4 cm & 5 cm. Length 90 cm (airborne); 150 cm (lab). Bottom of outer wall dry or ice-covered.

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Computational Mesh 5° wedge, 233,000 nodes

Full length of model ~1 cm x 90 cm

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Parcel Thermodynamic Histories

Earlier 1-D approximation begins with vapor & temperature walls.

FLUENT has dry cold wall & plastic warm wall on first 11 cm then ice coatings begin. These are accurate boundary conditions and indicate slightly different evolution in first 20 cm.

Both studies show response to boundary condition change (dry outer wall) at 62 cm.

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Velocity ProfilesFLUENT simulations show flow adjustment occurs through entrance region. At location 42 cm from sample inlet, the FLUENT profile agrees with analytical steady-state solution.

For this case, max velocity ~10 cm/s and contains the sample air lamina.

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Particle TrajectoriesOutlet cone - no wall loss for dia < 10 µmTotal residence times ~ 11 sec

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Recirculation & Reverse Flow

Stagnation regionStagnation region(small velocities)(small velocities)

Col

d w

all

Recirculation of sheath airRecirculation of sheath air

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Other studies: Other studies: air sample inletsair sample inlets