# PowerFLOW Results:



# Presentation in Ann Arbor May 26, 2011 Kevin Horrigan Doug Hatfield2

# Agenda  Feedback from EPA  Review Results Delivered on 5/18/11 – Project goals – Description of geometry process – Results – Conclusions 

#  Comparison of Results to Other Test Methods – Key considerations: Wind Tunnel and Coastdown – Highlights from other recent Exa studies 

#  Proposed Future Work3

# Agenda  Review Results Delivered on 5/18/11 – Project goals – Description of geometry process – Results 

## – Conclusions 

#  Comparison of Results to Other Test Methods – Key considerations: Wind Tunnel and Coastdown 

## – Highlights from other recent Exa studies 

#  Proposed Future Work – Recommended action plan4 

# Project Goals  Evaluate Use of CFD to Predict Drag 

#  Test Variations to Proposed CFD Requirements  Compare Results to Other Test Methods – Coastdown Testing 

## – Wind Tunnel Testing 

#  Provide Input for Final GHG Ruling5 

# Overview of Simulations

Finest Resolution [mm] Environmental

Condition Floor Status Tires Condition Grille

Position Yaw Angles

Tested 6 Wind Tunnel Static Floor Fixed Open 0,1,3,6,9 6 Open Road Moving Ground Rotating Open 0,1,3,6,9 6 Open Road Moving Ground Rotating Closed 0,1,3,6,9 3 Wind Tunnel Static Floor Fixed Open 0 3 Open Road Moving Ground Rotating Open 0 3 Open Road Moving Ground Rotating Closed 0 1.5 Wind Tunnel Static Floor Fixed Open 0,1,3,6,9 1.5 Open Road Moving Ground Rotating Open 0,1,3,6,9 1.5 Open Road Moving Ground Rotating Closed 0,1,3,6,9 A finest resolution of 1.5 mm was tested instead of 1 mm to allow more straightforward comparison to other resolution schemes (i.e. adding another resolution level at 1⁄2 the voxel size in the near wall region).6

# Setup Conditions

 Wind Tunnel Conditions Setup to Match NRC – Based on previous work on class 8 tractor in NRC tunnel Wind Tunnel Open Road Velocity 22.46 m/s 26.82 m/s Ambient Pressure* 101325 Pa 101325 Pa Ambient Temperature 30.95 ° C 20 ° C Ambient Density 1.161 kg/m3 1.204 kg/m3 Kinematic Viscosity 1.49e- 5 m2/s 1.49e- 5 m2/s Characteristic Length 2.591 m 2.591 m Reynolds Number 3.91e6 4.66e6 60 mph * Measured at outlet of computational domain7 

# International ProStar Model 2009 International ProStar Premium 6x4 Sleeper Cab w/ High Roof Fairing, and Aero Treatment (1660- HD-01) Engine Family = 9CEXH0912XAK VIN = 2HSCUAPR6AC168660 Engine = Cummins ISX 450 ST Rating = 450 hp Cab Wt. = 20,260 lbs Frontal Area = 96.91 ft 2 Tires = 11R22.5 Front = G395 LHS Rear = G362 Wheel Size=22.5x8.25 Axle Ratio = 3.55 Odometer = 55,471 Frontal Area with Box and Tandem Trailer = 103.37 sqft, with Flat Bed = 96.91 sqft Procurement of Above 2/17/2010 Weekly Rental of Above Check- In & Test Prep. of Above8 

# EPA Scanning Process9 

# EPA Scanning Process10 

# Geometry Provided to Exa11 

# Geometry Provided to Exa12 

# PowerFLOW Model Time to prepare model and incorporate more detailed underhood geometry: 3 man days13 

# PowerFLOW Model – Closed Grille Grille and bumper openings were sealed for the “Closed Grille” Simulations14 

# NRC Wind Tunnel Setup  NRC 9.1 X 9.1 m Tunnel – closed- wall atmospheric pressure tunnel Boundary Layer Control System Turntable Moving Belt15 

# NRC Wind Tunnel Setup 28’ Trailer Fully Detailed Tunnel CrossSection and Mounting Scheme 

### 9.1m16 

# NRC Wind Tunnel Setup Detailed Turntable and Mounting Platforms17 

# Resolution Setup Standard Exa Practice Refinement 1 Refinement 2 Finest voxel size 6 mm 3 mm 1.5 mm Total Voxels 60.0 x 10 6 63.8 x 10 6 65.8 x 10 6 Total Surfels 11.7 x 10 6 12.1 x 10 6 12.6 x 10 6 Physical Time / Timestep 28.8 μs 14.4 μs 7.2 μs Finer resolution was added to front end regions with high curvature18 

# Lattice - Boltzmann vs. Navier Stokes  Resolution Requirements Differ for LBM  PowerFLOW Uses Advanced Boundary Layer Model – Includes effects for longitudinal pressure gradient – Skin friction is directly controlled – Not necessary to calculate velocity gradient near wall  Requires many cells for N - S finite volume methods 18 V in V

out Bounce Back Reflection V in V out Specular Reflection Vtin Vn in Vtout

Vnout Slip Condition (frictionless) Normal component inverted Tangential component unchanged Momentum balance  normal force only No Slip Condition Normal component inverted Tangential component inverted Momentum balance  normal & tangential force1920 

# Transient Animation Velocity Magnitude @ 6deg yaw21 

# Simulation Results  Comparison of Resolution Tests  Open Grille vs. Closed Grille 

#  Impact of Updating Engine Geometry22 

# Results Summary

 Average ΔCd of 0.004 between 6mm and 1.5 mm resolution23 

# Wind Averaged CD Results

 Resolution Has Very Small Impact on Wind Avg. Cd – Open road setup: < 1% change – Wind tunnel setup: < 1% change * The wind averaged drag coefficient is calculated using SAE J1252, and assumes a wind speed of 7 mph and a truck speed of 55 mph. The results are normalized to the drag coefficient for the open road, moving ground, rotating tire, open grille case with f inest resolution of 6 mm.24 

# Resolution Study: Closed Grille Runs

* Note: Drag coefficients are normalized to open road environment with open grille at 0 degrees yaw using 6 mm finest resolution.25 

# Resolution Study: Open Grille Runs

* Note: Drag coefficients are normalized to open road environment with open grille at 0 degrees yaw using 6 mm finest resolution.26 

# Resolution Study: WT Runs

* Note: Drag coefficients are normalized to open road environment with open grille at 0 degrees yaw using 6 mm finest resolution.27 

# Analysis of Resolution Differences

6 mm Setup 1.5 mm Setup Isosurface of constant total pressure28 

# Analysis of Resolution Differences 6 mm Setup 1.5 mm Setup29 

# Summary  Small Results Influence of Increased Resolution – Average deviation of ~1% across all yaw angles 

#  Large Computational Cost Increase – Cost increases for 1.5 mm runs: > 2x factor 

#  Recommend Standard Exa Best Practice (6 mm)30 

# Simulation Results  Comparison of Resolution Tests  Open Grille vs. Closed Grille 

#  Impact of Updating Engine Geometry  Comparison to Other Test Methods31

# Drag Development – Open vs Closed

• Similar Overall Drag • However, significant differences in drag distribution across truck32 

# Open Grille vs. Closed Grille Static Pressure Open Closed Different pressure distribution between open and closed grille models33 

# Open Grille vs. Closed Grille Centerline Velocity Magnitude

Open Closed Grille flow redistributed around underhood region34 

# Case Study: Design change with Open / Closed Grille  Exa Performed Additional Study  Goal of Evaluating Drag Delta from Design Change – Open grille vs. closed grille

Baseline No Side Fairing35 

# Case Study: Design change with Open / Closed Grille

 Closed Grille Predicts the Incorrect Delta Drag Environmental Condition Floor Status Tire Condition Grille

Position Finest

Cell Size Char. Area [m2] Δ (No Fairing - Fairing) [%] Open Road Moving Ground Rotating Open 6.0 9.8 +0.6% Open Road Moving Ground Rotating Closed 6.0 9.8 +2.3%36 

# Case Study: Design change with Open / Closed Grille Baseline Design Update37 

# Case Study: Design change with Open / Closed Grille Baseline Design Update38 

# Summary: Open Grille vs. Closed Grille  Significant Differences in Pressure Distribution – Closed grille causes increase in flow around hood – Leads to different drag contributions of downstream parts 

#  Open Grille Necessary for Assessing Designs – Correct “delta drag” can only be predicted with open grille – Demonstrated by removal of side fairing study39 

# Simulation Results  Comparison of Resolution Tests  Open Grille vs. Closed Grille 

#  Impact of Updating Engine Geometry  Comparison to Other Test Methods40 

# Drag Summary – Engine Comparison Environmental Condition Floor Status Tire Condition Grille

Position Yaw Char.

Area [m2] Δ

(Engine 2 – Engine 1) [%] Open Road Moving Ground Rotating Open 0 9.8 +1.3% Open Road Moving Ground Rotating Open 1 9.8 +0.9% Open Road Moving Ground Rotating Open 3 9.8 +2.0% Open Road Moving Ground Rotating Open 6 9.8 +0.6% Open Road Moving Ground Rotating Open 9 9.8 - 0.2%41

# Drag Development Engine Swap – 0deg

Engine 1 Engine 242 

# Engine Swap Centerline Velocity Magnitude

Engine 1 Engine 243 

# Engine Swap Underbody Surface Pressure

Engine 1 Engine 244 

# Summary: Engine Update  Measurable Drag Difference  Altered mass flow split – Different component drag contributions 

#  Recommend Using Correct Engine Bay Parts45 

#  Review Results Delivered on 5/18/11 – Project goals – Description of geometry process – Results 

## – Conclusions 

#  Comparison of Results to Other Test Methods – Key considerations: Wind Tunnel and Coastdown 

## – Highlights from other recent Exa studies 

#  Proposed Future Work – Recommended action plan 

# Agenda46 

# Open Road vs. Wind Tunnel Drag

+42% +53%47 

# Open Road versus WT: Static Pressure

Open Road Wind Tunnel

Lower pressure due to wind tunnel blockage from walls Static floor and presence of wheel mounts alters pressure distribution in underbody48 

# Drag Development Open Road vs. Wind Tunnel49 

# Open Road versus WT: Static Pressure

Open Road Wind Tunnel50 

# Open Road vs. WT: Velocity Magnitude Wind Tunnel Walls Open Road Wind Tunnel51

# Isosurface of Total Pressure Coeff.52 

#  ProStar Results Consistent with Volvo Study – SAE Paper: 2010-01 -2040 

# Comparison to Other Studies
2010-01 -2040 Wind Tunnel Simulation53 NRC Wind Tunnel (28’ Trailer @ 0° Yaw) Lower pressure due to wind tunnel blockage from walls Static floor and presence of wheel mounts alters pressure distribution in underbody 

# Wind Tunnel Effects vs. Open Road

Open Road (28’ Trailer @ 0° Yaw)54 

# Volvo Study: SAE 2010 - 01 - 2040  Wind - avg. Drag Predicted within 1% of Experiment Wind Tunnel Note: PowerFLOW simulations of NRC tunnel environment, including walls and mounting fixtures, were compared to NRC drag force measurements before corrections are made for blockage. This allows an A - to -B comparison to assess simulation accuracy.55 

# Comparison to Open Road Setup Wind Tunnel Results are Corrected Down by 25% Simulation of

open road environment shows a decrease of 37% 53’ trailer simulation

in open road environment shows different yaw performance56 

# Wind Tunnel Study: KW T2000 Simulation of Wind Tunnel Simulation of Open Road Published Study (SAE COMVEC 2007)57 

# Summary: Open Road vs. Wind Tunnel  Large Difference Between Open Road and WT – Consistent with existing studies  Paper with Volvo: SAE 2010 - 01 - 2040  Kenworth study at University of Washington Tunnel 

#  Many Contributors – High blockage environment  Further exaggerated at yaw 

## – Different trailer – Measurement system influencing flow – Others58 

#  Comparison of Resolution Tests  Open Grille vs. Closed Grille 

#  Impact of Updating Engine Geometry  Comparison to Other Test Methods – Wind Tunnel 

## – Coastdown Testing 

# Simulation Results59 

# Comparison to Coastdown Testing  Conducted Study in Early May  Simulations with OEM To Investigate: – Impact of uncontrolled test conditions  Wind conditions  Tractor/trailer vertical movement 

## – Other factors affecting comparison to CFD  Variable Reynolds # during coastdown  Impact of truck mounted anemometer60 

# Wind Conditions During Coastdown  Assume Typical Low Wind Conditions – Wind direction perpendicular to truck – Average speed of 4 mph – Oscillating between 2 and 6 mph at 2 Hz61

# Impact on Yaw Angle Relative Air Velocity Wind Velocity Truck Velocity62 

# Sample Raw Anemometer Data SW Runs NE Runs63 

# Simulation Results

* Simulation CD results are normalized to a value of 0.65 at a truck speed of 60 mph64 

# Summary: Coastdown Comparisons  Wind Conditions Can Have Significant Impact – Even relatively low wind speeds result in high yaw – Can increase aerodynamic drag by up to 46% 

#  Variability Makes Comparison to CFD Difficult – Ideally, CFD should match measured conditions  On - board anemometer measurements from single run 

## – Exa recommends coastdown testing with low wind speeds 

#  Other Important Coastdown Considerations – Exa is performing additional studies  Influence of anemometer  Road roughness  Sensitivity of tractor trailer vertical movement 

## – Suggest follow- up meeting to review results65 

#  Review Results Delivered on 5/18/11 – Project goals – Description of geometry process – Results 

## – Conclusions 

#  Comparison of Results to Other Test Methods – Key considerations: Wind Tunnel and Coastdown 

## – Highlights from other recent Exa studies 

#  Proposed Future Work – Recommended action plan 

# Agenda66 

# Proposed Future Work  Additional Invesigations of Coastdown Effects – Wind conditions and variable truck speed – Anemometer influence – Sensitivity of tractor- trailer movement 

#  Additional Simulations on the ProStar – Fill in additional points on original matrix 

## – To be discussed with EPA