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Green Power 5- Development & Management of Resources and Energy Security

February 3-4, 2006, New-Delhi

Presented by:Aditya ChaudharyFluent India, Pune

What is Computational Fluid Dynamics (CFD) ?

CFD is the science of predicting fluid flow, heat transfer, masstransfer, chemical reactions, and related phenomena

by

solving the mathematical equations which govern these processes

using

computational methods

CAD -> Mesh -> Solution

CFD: A Numerical Method

• CFD Solves the Navier Stokes Equations

Getting at the Solution: Interface

• Problem set up or “Pre-Processing”� integration with design group� easy to use interface� parametric studies

• Solver computes the flow field� speed, accuracy, reliability, ease of use� features “models”

• Viewing Results “Post-Processing”� numbers, graphs, figures, animations

The CFD Process• Create or import your geometry using CAD-style tools

• Discretize the geometry: mesh generation

• Define flow conditions, fluid properties, physics

• Submit the calculation (solution of the conservation equations for mass, momentum, energy, chemical species)

• Review results (graphically, numerically)

What Can be Modeled?

• Boilers• Heat Exchangers• Expansion Turbines• Dryers• Separators• Filters• Ducting• Centrifugal Compressors

• Performance• Bearing loads• Clearance effects• Visualization• Erosion• Fouling/plugging• Heat transfer• Noise

ResultsDevices

Setting Expectations

• Values for� Performance� Heat Transfer� Forces� Erosion

• Trends• Parametric studies• Visualization • Investment that pays off

• Replacement for good engineering judgement

• Complete replacement for testing• Something for nothing

� Accurate results require� Detailed models� Knowledge of your

problem� Knowledge of

limitations

What Not To ExpectWhat To Expect

CFD: The Advantages

• Complements physical modelling.

• Provides comprehensive data not easily obtainable from experimental tests.

• Is more cost-effective than physical modelling.

• Reduces the product-to-market time scale.

• Answers the “what if…?” question.

• Highlights the cause not just the effect.

Benefits of CFD

Minimize System Cost

Improve Performance

Understand Problems

Reduce Design Time & Expense

What is unique about CFD• CFD is highly non-linear compared to areas such as FEA (stress analysis)• Physics that is dealt with is fairly complex• Mathematical models are well developed in only 70% of physical phenomenal.

The subject is highly mathematical and numeric oriented• At present, CFD is very laborious• Developing students and teaching them such that they are successful is fairly

challenging• The practical orientation coupled with simplified teaching method generally

bring much better results.

Fluent Inc.Fluent Inc.Fluent Inc.Fluent Inc.(Corporate Overview)(Corporate Overview)(Corporate Overview)(Corporate Overview)

Fluent Asia-Pacific Co.

ATES

SFIAavid-TaiwanFluent

India

LEAP Australia

Fluent Europe - Sheffield, EnglandFluent FranceFluent GermanyFluent ItalyFluent Sweden+ network of11 distributors

Fluent Inc. - Lebanon, NH- Chicago, IL- Ann Arbor, MI- Santa Clara, CA

Fluent Organization • Headquartered in Lebanon, NH, USA• Over two decades of experience in CFD• Focused solely on CFD• World leader in commercial CFD Software and Services

• 4th largest CAE Company globally

14 offices in 9 countries, 35 nationalities, over 600 employees

Fluent India

• Wholly-owned subsidiary of Fluent Inc. USA• Started in 1994 in Pune, with 5 engineers• The largest commercial CFD Organization in

India� Staff of over 120 people � Largest office of Fluent outside USA

• Activities� CFD Software Development� Applications Consulting� Industrial CFD Support� Sales and Marketing� CFD Product Quality Assurance� CFD Documentation

Examples & Case StudiesExamples & Case StudiesExamples & Case StudiesExamples & Case Studies

Retrofit Analysis of Alstom’s VU-40 Stoker Fired Boiler

Courtesy: Alstom Inc.

Retrofit of Retrofit of Retrofit of Retrofit of AlstomAlstomAlstomAlstom’’’’ssss VUVUVUVU----40 Stoker fired Boiler40 Stoker fired Boiler40 Stoker fired Boiler40 Stoker fired Boiler

Project Objectives

• Reduce the Unburned Carbon Levels• Reduce NOx & CO Emissions• Increase Efficiency/Capacity• Measure Pre and Post Conditions• Minimize unit outage duration

Assessment: Pre-Retrofit

• Operation� Limited Capacity � High Unburned Fines� Opacity during start-up� Erosion of ID fan & ductwork� Needed cinder reinjection� Difficulty burning wet bark

• Combustion System� Ineffective air system� Leakage around stoker

Fines Carry-over

Baseline Air Sources

CFD Analysis of the Baseline Result

• Analysis clearly showed malfunctioning of the air distribution system

• Overfire ports have limited impact on the turbulence in the furnace

• Plume rise on the rear of the furnace helps elutriation of unburnt C particles

Retrofit: New Air Distribution System (HMZ™)

CFD Analysis of Retrofit Case

• Analysis shows good turbulence inside the furnace which facilitates good mixing of air with fuel

• The new air distribution system provides good penetration depth to air inside the furnace

Other Results: Predicted CO

Predicted O2

Furnace Temperature

Performance Improvement

Simulation Helps Improving the Efficiency of a Heat Exchanger

Courtesy: Cal Gavin Ltd. UK

Problem description…

• The problem was of a standard shell and tube type heat exchanger.

• The heat exchanger provided far less thermal duty than necessary for application.

• CFD analysis showed that there was huge momentum pressure loss of expanding into the header. Hence majority of the fluid remained concentrated in a few tubes at the center of the bundle.

• The velocity in the center of the bundle was more than double that at the periphery

• Cal Galvin Engineers modified the model by inserting wire matrix into the tubes.

• This increased the resistance across each tube thereby even out the flow distribution in the bundle which is clearly evident from the figure.

• The wire matrix also create swirl inside the tubes which lead to flater velocity profiles thereby increasing heat transfer

• The results after placing wire matrix were so dramatic that the efficiency of the heat exchanger increased nine nine nine nine folds!!!folds!!!folds!!!folds!!!

Swirling Pulverized Coal FlameCourtesy: International Flame Research Foundation, Netherlands

• IFRF industrial scale furnace• Built on simulation by Peters and Weber (1997),

Mathematical Modeling of a 2.4 MW Swirling, Pulverized Coal Flame, Combustion Science and Technology

Exhaust

7 Cooling loops

Measurement locations: z = 0.25m, 0.85m

Combustion air: swirl no. = 0.923, flow rate = 2684kg/h

Coal flow rate = 263 kg/h, with transport air flow rate = 421 kg/h

1/4 Geometry

Grid• 3D, one quarter geometry model due to periodicity• Unstructured hexahedral mesh

� 70k cells before adaption� 260k cells after region adaption near inlet� Maximum equi-angle skew of 0.53

Gas Phase Combustion Modeling • Eddy Dissipation model

� Two step reactionVOL + 2.46O2 2.17CO + 0.633CO2 + 2.118H2O + 0.071N2

CO + 0.5O2 CO2

� Model constants A = 0.6, B = 1020 (standard A = 4, B=0.5)� Adjusted specific heat’s (SI units)

Species c0 c1 c2 c3 c4 c5 c6N2 1.027e3 2.162e-2 1.486e-4 -4.484e-8CH4 2.005e3 -6.814e-1 7.086e-3 -4.714e-6 8.513e-10CO 1.047e3 -1.568e-1 5.399e-4 -3.011e-7 5.050e-11H2 1.415e4 1.737e-1 6.900e-4CO2 5.354e2 1.279 -5.468e-4 -2.382e-7 1.892e-10 H2O 1.938e3 -1.181 3.644e-3 -2.863e-6 7.596e-10O2 8.763e2 1.228e-1 5.583e-4 -1.202e-6 1.147e-9 -5.124e-13 8.566e-17

� ⋅=i

iip TcTc )(

Gas Phase Combustion Modeling

Mean temperature (K)

Gas Phase Combustion Modeling

Mean CO ppm, dry

Discrete Phase Modeling

• Tracks of 1µm particles, colored by particle temperature (K)

NOx Modeling• Thermal and fuel NOx• Post-processed: assumed shape b pdf

Mean NO ppm, dry

Results Temperature Field• Mean temperature (K)

Results Species Field• Mean CO2 (volume %, dry)

Results NOx Field• Mean NO (ppm, dry)

CFD Today

• CFD is not a substitute for good engineering judgement• CFD is not a push-button science

� It is fairly involved and requires substantial efforts to achieve results• Successful CFD usage requires either expertise or support from experts

� More involved than purchasing a commercial code� Requires continued training, and assistance from experts (in-house and

external)• “Doability” function of expertise

� Flow, heat transfer, simple geometries� Complex geometries, complex physics� Cutting-edge physics and numerics

CFD and Testing

• CFD cannot replace physical testing• CFD complements and can help guide physical testing• CFD is reliant on several inputs that are a resulting of actual plant or

experimental measurements (Boundary conditions, material properties, etc.)

Thanks you!Thanks you!Thanks you!Thanks you!Contact:

Aditya ChaudharyBusiness Development Executive

adc@fluent.co.inCell: +91-98233-14089