Improved Vehicle Fuel Economy Through Optimization Aaron Godfrey - PowerPoint PPT Presentation

Improved Vehicle Fuel Economy Through Optimization Aaron Godfrey – CD-adapco Michael Elmore – CD-adapco

The Challenge of Tradeoffs Building an optimized car has difficult tradeoffs: – Seal the front end to lower drag – Open the front end to increase cooling Car must give the lowest drag while keeping the engine cool Drag is analyzed at high speed on flat ground The engine is at maximum load moving uphill

Coupled Analyses We encounter the largest drag at high speed We encounter the largest heat load uphill A particular low drag design must be capable of rejecting a large amount of heat in a scenario when drag is not important! Uphill 𝑬 𝑰𝑺 High-speed We must determine the car’s HR needs based upon how it’s driving to determine if a design is feasible Consider these scenarios from the perspective of power usage This description will allow us to calculate the HR for a scenario!

Power Budget The engine provides power to move the car: 𝑭𝒐𝒇𝒔𝒉𝒛 𝒋𝒐 𝒈𝒗𝒇𝒎 𝝑 = 𝒘(𝑬𝒔𝒃𝒉 + 𝑺𝒑𝒎𝒎𝒋𝒐𝒉 𝑺𝒇𝒕𝒋𝒕𝒖𝒃𝒐𝒅𝒇 + 𝑮𝒑𝒔𝒅𝒇 𝒆𝒗𝒇 𝒖𝒑 𝑯𝒔𝒃𝒘𝒋𝒖𝒛) 𝒖𝒋𝒏𝒇 But due to inefficiency, it must also be cooled: 𝑭𝒐𝒇𝒔𝒉𝒛 𝒋𝒐 𝒈𝒗𝒇𝒎 𝟐 − 𝝑 = 𝑺𝒇𝒓𝒗𝒋𝒔𝒇𝒆 𝑰𝒇𝒃𝒖 𝑺𝒇𝒌𝒇𝒅𝒖𝒋𝒑𝒐 𝒖𝒋𝒏𝒇 So our budget for power must balance: 𝑰𝑺 = 𝟐 − 𝝑 𝒘(𝑬 + 𝑺 𝒔 + 𝑮 𝒉 ) 𝝑 How do we calculate the components of the RHS?

Equations for Each Component 𝑰𝑺 = 𝟐 − 𝝑 𝒘(𝑬 + 𝑺 𝒔 + 𝑮 𝒉 ) 𝝑 𝑬 = 𝟐 𝟑 𝝇𝒘 𝟑 𝑫 𝒆 𝑩 We try to minimize this component 𝑺 𝒔 = 𝑫 𝒔𝒔 𝒏𝒉 ∗ 𝐝𝐩𝐭(𝛊) C rr is the rolling resistance coefficient 𝑮 𝒉 = 𝒏𝒉 ∗ 𝐭𝐣𝐨(𝛊) θ is the incline (hill) angle for R r and F g Now we have a series of equations that describes our car in any scenario For a given C d , we can determine the required HR!

Solution Technique 1. Determine C d 2. Calculate the required HR 3. Impose the required HR on the radiator 4. Modify the radiator inlet temperature until this HR is achieved This procedure is carried out for both (high speed and uphill) cases for each design If the output of 4 is too high (boiling coolant), the design is considered infeasible Goal: Minimize drag while maintaining a feasible coolant temperature

Optimization Variables: Grill Grill can be modified in many ways – Change the vane angle – Change the horizontal baffle length – Change the vertical baffle length

Optimization Variables: Lower Bumper Lower bumper can be modified in many ways: – Change the open area width – Change the open area height

Another Variable - Fan One way to increase HR is to use a fan We do not want this fan to be too loud As a secondary objective, we will minimize the fan RPM and maximize its radius Optimate allows us to say these variables are not as important

Grid Generation Surface wrapper used to close geometry Trimmer with prism cells volume mesh – 5.2M cells

Physics Dual-stream heat exchanger utilized to calculate radiator inlet temperature A single-stream heat exchanger (a condenser) is in front of the radiator Radiator, condenser treated as porous media Steady, 3D, RANS • Ideal gas • Realizable k- ε Turbulence • Two-layer wall treatment • 50/50 Glycol coolant •

Drag ag case se For each design: Tow case se For all designs: Crea eate e and d conver nverge ge Setup up Optim imate ate base selin line Evaluat aluate e Desig sign SHERPA PA STAR-CC CCM+ + determ ermines ines desig sign n build ilds s CAD and d perform rforman ance ce mesh sh Crea eate e New w Desig sign

Best Designs

Design Comparisons Baseline Optimized

Design Comparison Baseline Optimized

Design Comparison Baseline Optimized

Design Comparison Baseline Optimized

Design Comparison Baseline Optimized

Design Comparison Baseline Optimized

By the Numbers With 60 designs run, Optimate has shown large improvement Drag reduced by 12.7% Baseline Parameterize in 3D-CAD, Mesh (5.2M cells) case 8.5 Converge baseline run Hours Man Time: 4 hours Machine Time: 4.5 hours Optimization Set up Optimate and submit for 70 design iterations 4 simultaneous jobs x 32 cores each = 128 cores 40 Man Time: 10 minutes Hours Machine Time: 157.5 hours/ 4 runs = ~40 hours