Physical and Numerical Physical and Numerical Visualizations of Unsteady Visualizations of Unsteady

Separated Flows Separated FlowsSeparated Flows Separated Flows

Fathi FinaishFathi Finaish

Department of Mechanical and Aerospace Engineering Department of Mechanical and Aerospace Engineering Missouri University of Science and TechnologyMissouri University of Science and Technology

Great Midwestern Regional Space Grant Consortia Meeting

Cleveland, Ohio

September 24-25, 2009

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The Hubble Space Telescope snapped this image of a dying starthat looks like a delicate butterfly

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NASA releases new Hubble photosNASA releases new Hubble photos

This image released by NASA on Wednesday (9/9/09) was taken by the refurbished Hubble Space Telescope. It shows stars bursting to life in the chaotic Carina Nebula.

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Hubble Space Telescope Servicing Mission:The Soft Capture MechanismThe Soft Capture Mechanism

• Instrument replacement

• Battery replacement

• Gyro replacement

• Installing the Soft Capture

Mechanism (SCM).

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Jacopo Frigerio is a Senior Staff Engineer and Project Manager with Lockheed Martin Space Systems Company’s (LMSSC) Engineering Resources & Development organization. Jacopo has 14 years of engineering, design, project management and leadership experience at Lockheed Martin Space Systems Company (SSC), including 8 years in propulsion engineering and 7 years as a project manager leading teams in developing test, prototype and flight hardware. He is also a graduate of the Advanced Technical Leadership Program at SSC. Most recently he has been on a 1 year assignment in the Engineering Resources and Development organization, working to improve Workforce Development and Knowledge Management.

Jacopo Frigerio Lockheed Martin Space Systems

Hubble Servicing Mission Program – Chief Engineer developing the Soft Capture Mechanism

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Unsteady Separated FlowsUnsteady Separated Flows

Separated flows are encountered in many Separated flows are encountered in many engineering applicationsengineering applications

–– Low and high angle of attack aircraft maneuversLow and high angle of attack aircraft maneuvers–– Turbo machineryTurbo machinery–– Flutter/Transonic flowsFlutter/Transonic flows–– Aircraft stallAircraft stall–– Rocket launchesRocket launches–– ………….. ..

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An exampleAn example

Separated flows are encountered in many Separated flows are encountered in many practical applicationspractical applications

–– Low and Low and high angle of attack aircraft maneuvershigh angle of attack aircraft maneuvers–– Turbo machineryTurbo machinery–– FlutterFlutter–– Aircraft stallAircraft stall–– Rocket launchesRocket launches–– ………….. ..

unsteady turbulent flow past a high-lift airfoil

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Steady Attached vs. Steady Attached vs. Unsteady Unsteady SeparatedSeparated FlowsFlows

Attached Flows: Traditional AerodynamicsAttached Flows: Traditional Aerodynamics–– Keep flow attachedKeep flow attached–– Maximize performance (Lift to Drag Ratio)Maximize performance (Lift to Drag Ratio)–– Control boundary layer flow developmentsControl boundary layer flow developments

Separated Flows: New DirectionsSeparated Flows: New Directions–– Force flow separationForce flow separation–– Encourage subsequent vortex formationEncourage subsequent vortex formation–– Control Vortex development and make use of itControl Vortex development and make use of it–– Enhance performance (maneuverability/agility, flow mixing)Enhance performance (maneuverability/agility, flow mixing)

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CharacteristicsCharacteristics

–– UnsteadyUnsteady–– ThreeThree--DimensionalDimensional–– ViscousViscous–– Turbulent Turbulent –– ……..

Extensive requirement of computational Extensive requirement of computational resourcesresources

Complicated flows physicsphysics

Large parameter space

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LimitsLimits

Complex flow physics associated with these flows Complex flow physics associated with these flows coupled with extensive requirement of computational coupled with extensive requirement of computational resources are limiting even ambitious studies to spot resources are limiting even ambitious studies to spot investigations. investigations.

The lack of validation sources prevented calibrations The lack of validation sources prevented calibrations and economic use of computational resources. and economic use of computational resources.

Thus, despite the availability of modern CFD tools, Thus, despite the availability of modern CFD tools, using them in computing separated flows remains to using them in computing separated flows remains to be difficult and expensive. be difficult and expensive.

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A few ExamplesA few Examples

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High Lift High Lift SystemsSystems

Today CFD is used to design complex high lift Today CFD is used to design complex high lift systems; however, the prediction of systems; however, the prediction of CLCLmaxmax by by direct computation is still difficult.direct computation is still difficult.

Confluent boundary layers and flow separation Confluent boundary layers and flow separation are at the center of the difficulties that computer are at the center of the difficulties that computer code developers and designers of highcode developers and designers of high--lift airfoils lift airfoils must deal with.must deal with.

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The tripleThe triple--slotted slotted flap system flap system used on the 737used on the 737

Schematic of Geometry Configuration CFD Simulation

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CFD SimulationCFD Simulation

JSF Vertical TakeoffJSF Vertical Takeoff

For multiple jets, an upward flow is created.

Multiple jets Flow Interactions near Ground

Unsteady Separated Flows: An Unsteady Separated Flows: An ExampleExample

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Development of an Accelerating Flow Development of an Accelerating Flow Over A High Angle of Attack AirfoilOver A High Angle of Attack Airfoil

L.E

T.E

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Development of an Accelerating flow Development of an Accelerating flow over a high angle of attack aircraft wing over a high angle of attack aircraft wing

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TwoTwo--Dimensional & Corresponding ThreeDimensional & Corresponding Three--dimensional Flow development downstream of an dimensional Flow development downstream of an accelerated wing model at high angle of attackaccelerated wing model at high angle of attack

L.E Vortex Development

T.E Vortex Sheet Development

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Development of a Development of a vortex sheet vortex sheet downstream of an downstream of an accelerated wing at 20 accelerated wing at 20 degrees angle of attackdegrees angle of attack

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Turbulence Turbulence

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Turbulence Turbulence

Initial Initial StagesStages

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Evolution of Turbulent SpotEvolution of Turbulent Spot

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Evolution of Turbulent SpotEvolution of Turbulent Spot

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Evolution of Turbulent SpotEvolution of Turbulent Spot

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Applications and Limit of Applications and Limit of Modern CFD Codes in Modern CFD Codes in Predicting Separated Flow Predicting Separated Flow Developments: A Few ExamplesDevelopments: A Few Examples

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A Computational Study of the Flow Fields Around Supersonic Airfoils at Low Mach Numbers

Case Study

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AcknowledgementsAcknowledgements

The support for this projects was provided byThe support for this projects was provided by

NASANASACalmar ResearchCalmar ResearchUMRUMR

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MotivationMotivation

This work is motivated This work is motivated by the recent efforts on by the recent efforts on the development of the development of Supersonic Business JetsSupersonic Business Jets

Lack of available data on Lack of available data on the development of the development of separation bubbles over separation bubbles over supersonic airfoils at low supersonic airfoils at low Mach numbersMach numbers

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Research GoalsResearch Goals

Develop computational procedure to analyze the Develop computational procedure to analyze the development of separated bubbles over supersonic development of separated bubbles over supersonic airfoils.airfoils.

Examine the influence of the bubbles on the Examine the influence of the bubbles on the aerodynamic performance of several airfoils at low aerodynamic performance of several airfoils at low Mach numbers. Mach numbers.

Conduct computational parametric study and Conduct computational parametric study and compare produced results with the limited available compare produced results with the limited available experimental measurementsexperimental measurements

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Laminar Separation Bubble (LSB)Laminar Separation Bubble (LSB)

Physics of FormationPhysics of Formation–– Geometry InducedGeometry Induced–– Adverse Pressure GradientAdverse Pressure Gradient–– Reversal of flow in boundary layerReversal of flow in boundary layer

Effect on Aerodynamic PerformanceEffect on Aerodynamic Performance–– Increase in drag Increase in drag –– Onset of StallOnset of Stall–– Promotion of Unsteady FlowPromotion of Unsteady Flow

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Schematic of Separation BubbleSchematic of Separation Bubble

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Grid Generators EmployedGrid Generators Employed

Surface Grid Generation Surface Grid Generation Aerodynamic Grid and Paneling System (AGPS)Aerodynamic Grid and Paneling System (AGPS)

Volume Grid Generation Volume Grid Generation (Chimera Grid Tools)(Chimera Grid Tools)

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Typical Grids Typical Grids Generated around Generated around the Double Wedge the Double Wedge

AirfoilAirfoil

Sharp Leading EdgeSharp Leading Edge4.23% Thick4.23% ThickMax Thickness at MidMax Thickness at Mid--ChordChord

Even Density- 325,440 Total Pts

Top Front- 229,400 Total Pts

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325,440 Total Grid Points

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Flow Visualizations as Depicted by Flow Visualizations as Depicted by The Flow StreamlinesThe Flow Streamlines

αα = 3.8= 3.8oo, Re = 5.8 X 10 , Re = 5.8 X 10 66, M = 0.17, M = 0.17

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Visualizations of Velocity Profiles Visualizations of Velocity Profiles And Pressure DistributionAnd Pressure Distribution

αα = 3.8= 3.8oo, Re = 5.8 X 10 , Re = 5.8 X 10 66, M = 0.17, M = 0.17

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Sample of Surface Pressure DistributionSample of Surface Pressure Distribution

αα = 2= 2oo ,Re = 5.8 X 10,Re = 5.8 X 1066, M = 0.17, M = 0.17

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αα = 3= 3oo , Re = 5.8 X 10, Re = 5.8 X 1066, M = 0.17, M = 0.17

Sample of Surface Pressure DistributionSample of Surface Pressure Distribution

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Comparison of Bubble over Comparison of Bubble over Different Airfoil ConfigurationsDifferent Airfoil Configurations

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CFD simulation of separation bubble development and subsequent massive separation over a supersonic airfoil at low Mach number.

Re = 5.8x106, M = 0.17

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ConclusionsConclusions

Attached regions are well predicted (Good Attached regions are well predicted (Good agreement outside of LSB region)agreement outside of LSB region)

Pressure plateau is not as prominent as Pressure plateau is not as prominent as experimental data suggests experimental data suggests

Fully Turbulence model implemented over Fully Turbulence model implemented over entire domain correlated best with entire domain correlated best with experimental resultsexperimental results

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Current Research EffortsCurrent Research Efforts

Collection of reliable experimental dataCollection of reliable experimental data

33--D ModelingD Modeling

Bubble Modification TechniquesBubble Modification Techniques

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A Computational Study of A Computational Study of ThreeThree--Dimensional Flow Dimensional Flow Fields in A Mixing ChamberFields in A Mixing Chamber

Case Study

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AcknowledgmentAcknowledgment

This project was funded by in part byThis project was funded by in part by

Ruskin Research LaboratoryRuskin Research Laboratory

ASHRAE TRPASHRAE TRP--1045 1045 ““Verifying Mixed Air Verifying Mixed Air Damper Temperature and Air Mixing Damper Temperature and Air Mixing CharacteristicsCharacteristics””

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MotivationMotivation

The purpose of the study was to determine The purpose of the study was to determine whether mixed air dampers perform theirwhether mixed air dampers perform theirintended functions of the mixing of twointended functions of the mixing of twostreams of air with dissimilar temperaturesstreams of air with dissimilar temperaturesand COand CO2 2 concentrationconcentration..

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Schematic of the Flow Problem: A Typical Flow Through Air Handling Unit

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BackgroundBackground

Thermal stratification of the mixed outside and return air streams results in regions of hot and cold air on the conditioning coils.

If the outside air is < 32°F, more serious conditioning coil freezeup and/or tube rupture could occur.

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Research GoalsResearch Goals

Develop a CFD model that is useful for studying thermal mixing and flow development.

Use the CFD model to analyze the relationship between thermal mixing and input parameters of damper blade angles and flow velocity ratio.

Identify the flow developments in the mixing chamber that have primary influence on the thermal mixing.

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Test FacilityTest Facility

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Test FacilityTest Facility

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Temperature Sensors at the Mixed Air StationTemperature Sensors at the Mixed Air Station

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Comparison with Experimental Measurements

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Temperature distribution for best mixing: Configuration 1Temperature distribution for best mixing: Configuration 1

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[Best Case]

Confiuration 1 Test No: 7Percent Outside Air: 15 Blade Size of Damper: 6"Outside Air Temperature: 37.0 F Return Air Temperature: 76.9 FThermal Mixing Effectiveness- Range: 0.89 Statistical: 0.95

PLOT OF TEMPERATURE DISTRIBUTION

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Temperature distribution for least mixing in Configuration 1Temperature distribution for least mixing in Configuration 1

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[Worst Case]

Confiuration 1 Test No: 6Percent Outside Air: 30 Blade Size of Damper: 4"Outside Air Temperature: 35.2 F Return Air Temperature: 74.3 FThermal Mixing Effectiveness- Range: 0.62 Statistical: 0.79

PLOT OF TEMPERATURE DISTRIBUTION

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View of Typical Grid 26 Blocks, 174,160 Grid Points

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CrossCross--section of Mixing Chambersection of Mixing Chamber

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An example shows dimensionless Flow Speed of outside airflow in the mixing chamber.

VOA=1,500 fpm, OA damper angle = 0°

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ThreeThree--dimensional flow computation in a mixing Chamber. dimensional flow computation in a mixing Chamber. Dimensionless flow speed distributionDimensionless flow speed distribution

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Visualization of vortex development in the mixing chamber. VRA=1,500 fpm

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Flow visualization of outdoor and return airflows in the mixing chamber.

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Samples of Temperature Distribution in the mixing chamber

VOA=VRA=1,500 fpm : fRA=fOA=0°

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Comparison of Temperature Distributions VOA=VRA=1,500 fpm

0° 30° 45° 60°

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ConclusionsConclusions

The temperature distribution in the Mixing chamber is determined Primarily by the Velocity Ratio.

Temperature Mixing Effectiveness Increases with Downstream Distance

The Mixing Effectiveness Generally Increases with Increasing Velocity Ratio and with Increasing Damper Angle

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Final Concluding RemarksFinal Concluding Remarks

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Final ConclusionsFinal Conclusions

The two examples presented demonstrate the application of The two examples presented demonstrate the application of modern CFD tools in simulating external and internal flow modern CFD tools in simulating external and internal flow configurations dominated by separated flows. configurations dominated by separated flows.

While the simulation results correlated well with While the simulation results correlated well with corresponding experimental measurements, flow computations corresponding experimental measurements, flow computations in the separated bubble (example 1) and the upstream flow in the separated bubble (example 1) and the upstream flow region deviated considerably from experimental region deviated considerably from experimental measurements. measurements.

The second example reveals the complex flow interactions The second example reveals the complex flow interactions between the two airflow streams as dominated by flow between the two airflow streams as dominated by flow separation and subsequent vortex developments downstream in separation and subsequent vortex developments downstream in the mixing chamber. There still need for further experimental the mixing chamber. There still need for further experimental measurements, in order to assess the simulation results.measurements, in order to assess the simulation results.

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Final ConclusionsFinal Conclusions

Obtaining reliable experimental measurement Obtaining reliable experimental measurement and visualizations of separated flows would be and visualizations of separated flows would be useful resource for assessing, calibrating, and useful resource for assessing, calibrating, and economizing the use of modern CFD tools. economizing the use of modern CFD tools.

Experimental data needs to be collected with Experimental data needs to be collected with careful attention paid toward the free stream careful attention paid toward the free stream and wall conditions, as these are required for and wall conditions, as these are required for successful validations of parallel successful validations of parallel computational efforts. computational efforts.

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OutlookOutlookExploring possibilities of utilizing separated flows in many Exploring possibilities of utilizing separated flows in many engineering application may lead to new fruitful opportunities engineering application may lead to new fruitful opportunities in the future. in the future.

For instance, new flow control technologies and techniques to For instance, new flow control technologies and techniques to control massive flow separation may open up new control massive flow separation may open up new opportunities in making effective use of separated flows in a opportunities in making effective use of separated flows in a wide range of engineering applications. wide range of engineering applications.

However, understanding of these flows still limited. However, understanding of these flows still limited.

Experimental and computational studies that been conducted Experimental and computational studies that been conducted on unsteady separated flows revealed complex flow physics on unsteady separated flows revealed complex flow physics associated with these flows and the challenge to document their associated with these flows and the challenge to document their time dependent nature. time dependent nature.

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