CFD Research Overview

Dr. Chris Roy

Associate Professor

Aerospace & Ocean Engineering

Virginia Tech

2

Outline

• My background

• Research interests

• Research projects

• Shape optimization for tractor trailer drag reduction

• CFD of gas flow through microfibrous materials

• Potential research projects for Fall 2008

• Undergraduate teaching plans

• Graduate teaching plans

3

My Background

• BSE Mechanical Engineering, Duke Univ. 1992

• MS Aerospace Engineering, Texas A&M 1994

• PhD Aerospace Eng., North Carolina State Univ. 1998

• 1998-2003: Aerosciences Department, Sandia

National Labs (NM)

• 2003-2007: Assistant Professor, Aerospace

Engineering Department, Auburn University

• 2007-present: Associate Professor, Aerospace and

Ocean Engineering, Virginia Tech

4

Research Interests

• Computational Fluid Dynamics (CFD)

• Turbulence modeling

• Turbulence simulations

• Bluff-body aerodynamics (e.g., trucks)

• Microscale gas flows

• Hypersonic flows

• Verification (mathematical correctness) and Validation

(physical correctness) of computer simulations, or V&V

• Estimation of grid-related numerical errors

• Grid adaptation

• Validation of turbulence models

5

Truck Aerodynamics: Motivation

There are more than 2 million tractor-trailers on U.S. roads

• In 2003 each tractor-trailer averaged 62,900 miles traveled†

• On average they got 5.2 miles/gallon, resulting in a total

consumption of 26 billion gallons of diesel fuel†

• With diesel at $2.33/gallon, this corresponds to ~$60 billion

Aerodynamic drag increases with the square of the speed

†US DOE Transportation Energy Data Book: Edition 23, 2003,

http://www-cta.ornl.gov/data/

• 20% drag reduction gives ~10%

reduction in fuel consumption

• Savings of 2.6 billion gallons of

fuel/year, or ~$6 billion/year

6

Truck Aerodynamics

DES: Large-Scale Turbulent

Wake Structures Resolved

(fundamental physics:

expensive)

RANS: All Turbulent

Structures Modeled

(appropriate for design)

Two approaches to turbulence:

Wake Z-Vorticity in Vertical Streamwise Plane

8

Optimization of Aerodynamic Drag

Currently developing a multi-university effort to optimize

base drag reduction devices for heavy trucks

• Advances in computing infrastructure now allow CFD to be used

within the design optimization process

• VT AOE is responsible for developing high-efficiency CFD

predictions (Roy) and conducting wind tunnel experiments

(Devenport)

• Auburn University is responsible for the Genetic Algorithm (GA)-

based optimization procedure and full-scale vehicle testing

• Currently gathering industry support and developing a 4 year,

$2.5M proposal to DOE

9

Drag Reduction via Base Flaps

Prior experiments on boattail flaps reduced drag by 18%;

however, these devices were not optimized to minimize drag

Tractor-Trailer with Base Flaps Wind-Averaged Drag Coefficient

10

Preliminary Study: 2D Base Flaps

11

Preliminary Study: 2D Base Flaps

12

H2 Reformation for PEM Fuel Cells

Proton Exchange Membrane (PEM) fuel cells are popular for transportation applications

• Protons (H+ ions) are exchanged across the electrically-insulated membrane

• Electrons are forced to travel through the electric circuit, generating electric current

• Clean technology since gaseous hydrogen and air are combined to produce water & heat

• Anode catalyst is irreversibly poisoned by ppb levels of sulfur and ppm levels of CO

• The pollutants can arise when jet fuel (JP-8), diesel, or hydrocarbons are reformed to H2

(courtesy Wikipedia)

13

Microfibrous MaterialsInterdisciplinary work with Auburn

University's Chemical Engineering Dept.

(funded by US Army TACOM)

• New structure of matter developed by

embedding catalytic particles (~100 microns) in

a matrix of microfibers (~10 microns)

• Microfibrous materials have demonstrated

remarkable properties, increasing reactivity by

nearly a factor of five

• Our goal: use CFD to identify the fundamental

mechanisms behind increased reactivity and to

help design new microfibrous materials

SEM of a Typical

Microfibrous Material

Applications include chemical processing (desulphurization of fuel

cells, ozone removal, etc.) and filtration (gas mask CO filters, etc.)

14

Geometric Modeling

Microfibrous materials are

difficult to characterize

• Initial work employs geometric

simplifications, thus allowing us to

make use of symmetry

• Particles modeled as smooth

spheres

• Fibers modeled as straight cylinders

with axes aligned in the y and z

directions (normal to the flow)

• Fluent commercial CFD code

employed in this work

Face Velocity [m/s]

Lo

gR

ed

uctio

n

0.02 0.04 0.06 0.08 0.1

10

20

30

40 Packed Bed - Simulation

Packed Bed - Experimental

Glass Fiber - Simulation

Glass Fiber - Experimental

15

Pressure Drop & Reactivity Predictions

H2S removal shows good agreement

with experiments for packed beds

and microfibrous materials

Face Velocity [m/s]

Pre

ssu

reG

rad

ien

t-

P/L

[mm

H2O

/mm

]

0.4 0.8 1.2

101

102

CFD = 0.41

Experiment = 0.41

CFD = 0.47

Experiment = 0.47

0.2

Pressure drop predictions within

15% of experiments

16

Potential Fall 2008 Research Projects

• Aerodynamic Drag Optimization for Tractor-Trailers, US

Department of Energy (DOE)

• CFD Analysis of Flow through Microfibrous Materials, US

Army Tank and Automotive Command (TACOM)

• Estimation of Grid Errors and Mesh Adaptation for CFD, NASA

Marshall Space Flight Center (Huntsville, AL)

• Verification and Validation for Power Electronics Systems,

Boeing (collaborative w/ CPES at VT)

• Verification, Validation, and Uncertainty Quantification for

Hypersonic Flows, NASA Johnson Space Center (Houston, TX)

17

Undergraduate Teaching

• Core aero/hydro courses

• Introduction to CFD (senior elective)

• Integrate CFD into core undergraduate courses

• Involve undergraduates in research

• One-on-one mentoring

• Mentoring by graduate students

18

Graduate Teaching

• New course next Spring: Verification and

Validation in Computational Simulation• Co-instructed by Dr. William Oberkampf (retiring from

Sandia Labs)

• Writing a graduate textbook by the same name

• Advanced CFD course next year

• Course on turbulence modeling (future?)

• Plan to hire 1-2 postdoctoral fellows and 5-6

doctoral students over the next 2 years

Web Site:http://www.aoe.vt.edu/~cjroy/

Questions?