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Domenic Barsotti MSME Embry-Riddle Aeronautical University * - - PowerPoint PPT Presentation
Domenic Barsotti MSME Embry-Riddle Aeronautical University * - - PowerPoint PPT Presentation
Domenic Barsotti MSME Embry-Riddle Aeronautical University * Introduction * Real World Implications * Problem Description * Initial Simulations * Optimizations * Results Analysis * Future Work * Environmental Impact * Current trends to reduce
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*Environmental Impact
*Current trends to reduce independence on oil
* Development of Hybrid vehicles * Development of aerodynamically efficient vehicles
*Drag is the leading negative force above 45 mph
*Current Drag Reduction Systems (DRS)
*Active Aero (rear wings, duct closing) *Smooth under panels
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*Values are for 2013 Chevrolet Malibu
10% Mass Delta 10% Crr Delta 10% CD Delta Energy Consumption [%] 6.47 1.91 3.49
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*In 1984, Ahmed{1} proposed a bluff body to
simulate vehicle drag
*Angle of slant varies from 0º-90º *25º slant angle is most commonly used for typical
automobile simulations
{1} Ahmed, Ramm, Faltin (1984) “Some Salient Features of the Time-Averaged Ground Vehicle Wake” SAE 840300
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*Domain is 1.4m x 1.86m x 8.5m
*Blockage ratio= 4.3%
*Mesh Continua
*Polyhedral Mesher *Prism Layer Mesher *Surface Remesher
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*Base Size = 0.005 m *Mesh Independence *20.5 million cells
0.35 0.355 0.36 0.365 17 22 27 Cd Cell Count (millions)
Mesh Independence
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*Implicit Unsteady *Constant Density *Segregated Flow Solver *SST K-Omega DES Turbulence Model
*Improved Delayed Detached Eddy Simulation
*Turbulence Viscosity Ratio – 200 *Turbulence Intensity – 0.02 *Time Step = 0.001 s *Total Simulation time = 1.5 s
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*Initial Simulation was compared to experiment {2}
*Reynolds Number Sweep from 1.4 to 2.8 million *Inlet Velocity 21 m/s to 42 m/s *Drag averaged from Time = 0.75 s to 1.5 s *Re = 1.4 million was chosen for highest Cd (0.371)
{2} Joseph, Amandolese, Aider (2012) “Drag Reduction on the 25º slant angle Ahmed reference body using pulsed jets” Exp Fluids
0.3 0.31 0.32 0.33 0.34 0.35 0.36 0.37 0.38 1.2 1.7 2.2 2.7 3.2 Cd Re (millions) Experimental {2} CFD
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*Jets implemented at rear end *4 Variables- velocity
*15m/s – 40 m/s
*Drag averaged from 0.75 -1.5
sec
*Objective function = minimize
average Cd
*30 iterations
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*Optimal Value was minimums (all jets 15 m/s) *Optimized Cd = 0.336 (9.4% reduction)
*10 m/s jets showed increase (Cd=0.339)
*Showed critical information
*Max drag reduction with jet velocities equal *Bottom and side jets were too thin to be
effective
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No Jets Optimized Jets (15 m/s)
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*All jets changed to 10 mm thick
*Bottom and side jets were 5mm
*All velocities set equal *1 Variable – velocity 8 m/s – 20 m/s *Objective function- Minimize Averaged Drag *30 iterations
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0.31 0.315 0.32 0.325 0.33 0.335 0.34 0.345 8 10 12 14 16 18 20 Averaged Cd Velocity (m/s)
Optimized Cd = 0.316 (10.28 m/s)
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*Averaged Cd = 0.316 (14.8% reduction) *Jet velocity of 10.28 m/s
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*Design Exploration conducted using Optimate *Angle of bottom jet (0,5,10,15,20, 25º) *Height of top jet (39.2, 27.2, 15.2, 3.2 mm) *Conducted at 15 m/s jet velocity
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* Found to be a non-critical
dimension
* Averaged Cd range (0.331-
0.334) > 1% difference
* Costly computationally
(requires remesh)
* Future optimizations to not
include
* Value of mild significance * 25 degrees – Cd= 0.3255
3% reduction compared to 0 degree
* Other angles were within 1
count of each other
* Less computational (no
remesh required)
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*All jets 10 mm thickness *Bottom jet angle increased to 25º *Top jet left at 39.2 mm distance *1 design variable- velocity *15 iterations *Objective function – minimize averaged Cd
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0.31 0.312 0.314 0.316 0.318 0.32 0.322 0.324 0.326 0.328 9 10 11 12 13 14 15 Cd Jet Velocity (m/s)
Optimized Cd = 0.312 (10.2 m/s)
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*Critical Values found
*Velocity (easily optimized- no remesh) *Angle (easily optimized- no remesh)
*Non-critical values found
*Distance of jets to edge
*Reduced drag by 16%
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No Jets Cd = 0.371 Optimized Jets Cd = 0.312
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No Jets Cd = 0.371 Optimized Jets Cd = 0.312
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*Determine impact of side jets *Investigate suction along top slant *Test jet system experimentally *Implement on full scale production vehicle
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