Iván Sidorovich Aerodynamicist
Agenda •Bicycle aerodynamics background information •Cervélo’s design history •A new tool: STAR-CCM+ •P5 aerodynamic development •Conclusions P5 SIMPLY FASTER - 2
Bicycle aerodynamics background information P5 SIMPLY FASTER - 3
The importance of aerodynamics ~ 365 W (100%) ~ 320 W (88%) ~ 20 W (5%) ~ 25 W (7%) P5 SIMPLY FASTER - 4
How do we measure aerodynamic drag? • We do not measure in Cd, CdA or Force (N) • We measure in grams (g) – Good scale for bicycles • Aero drag rule of thumb – 100 grams of drag • = ~ 10 Watts • = ~ 1 second / km Ref: (Martin et. al., “Validation of a Mathematical Model of Road Cycling Power”, 1998) P5 SIMPLY FASTER - 5
Example: P5 to P4 aero improvements P5 P4 P5 SIMPLY FASTER - 6
Example: P5 to P4 aero improvements Results P5 P4 Diff % diff Average Drag ±20° (g) 2056 2122 -66 3.11 EXAMPLE Time savings (s) Distance savings (m) 50 km TT 33 @ 50 kph 458 @ 50 kph P5 SIMPLY FASTER - 7
Cervélo’s design history P5 SIMPLY FASTER - 8
P2 to P3 aero development P2 P3 • 1 st curve seat tube P2 - P3 P3 - P4 • Aero seat stays Dev time (months) 6 • Pen and paper process Drag savings (g) 32 • Experience • Tunnel validation P5 SIMPLY FASTER - 9
P3 to P4 aero development P3 P4 • Integrated rear brake P2 - P3 P3 - P4 • Drop down tube Dev time (months) 6 24 • Integrated water bottle Drag savings (g) 32 32 • Wind tunnel experimentations (5) P5 SIMPLY FASTER - 10
P5 SIMPLY FASTER - 11
Wind tunnel experimentation • System is bike plus rider • Rider was scanned to make a life-size rider model • Dummy on bike is 100% fixed and repeatable • To properly measure the effects of individual design features • Need to make only one change Mule • Test mule P5 SIMPLY FASTER - 12 SLA
Wind tunnel experimentation • P3 to P4 aero development process involved – Several wind tunnel trips (5) – Numerous SLA parts – VERY expensive! • Limited amount of runs – Constraint • Time (25 runs per day) • Money • Schedule availability – Makes you be more conservative! P5 SIMPLY FASTER - 13
A new tool: STAR-CCM+ P5 SIMPLY FASTER - 14
CFD – Validation case • Need to make sure CFD gives correct results – In absolute terms – In relative terms • A simple case of frame only was chosen from wind tunnel experimentations P5 SIMPLY FASTER - 15
CFD – Validation results • For the mesh we use a combination of • Trim for outer domain • Poly for MRF • 35 million elements • Turbulence • ko-SST for steady state • DES for transient 2.2 % off wind tunnel data P5 SIMPLY FASTER - 16
CFD – Validation results with rider 3.3 % off wind tunnel data P5 SIMPLY FASTER - 17
New aerodynamic design cycle • Phase 1 – CFD initial concepts with a parametric model – Wind tunnel experimentation with best CFD concepts • Phase 2 – CFD detailed analysis – Production model wind tunnel experimentation • Competitor benchmarking P5 SIMPLY FASTER - 18
P4 to P5 aero development P4 P5 • 1 st bike to be fully design with CFD P2 - P3 P3 - P4 P4 - P5 Development time (months) 6 24 7 Drag savings (g) 32 32 66 P5 SIMPLY FASTER - 19
P5 SIMPLY FASTER - 20
P5 aerodynamic development P5 SIMPLY FASTER - 21
3 key design areas • Aerobar • Front end • Seat tube P5 SIMPLY FASTER - 22
Aerobar
Phase 1 – initial parametric model P5 SIMPLY FASTER - 24
Phase 1 – best CFD models Model A Model C P5 SIMPLY FASTER - 25
Phase 1 – best CFD models in the tunnel Model A Model B Model C P5 SIMPLY FASTER - 26
Phase 2 – detailed CFD models TT2 TT2 Low Pylon Version Long Base Ext TT2 Vcap TT2 Vcap Long Base Ext P5 SIMPLY FASTER - 27
Phase 2 – final model selection • Cables can add up to 15 grams of drag when exposed • Ultra low friction cable path P5 SIMPLY FASTER - 28
Front end
Phase 1 – initial head tube parametric model • We started the head tube with a parametric conceptual model to test against P4 P4 Baseline Head tube conceptual x-sections P5 SIMPLY FASTER - 30
Phase 1 – initial head tube parametric model @ 6° yaw P4 Baseline Head tube conceptual design P5 SIMPLY FASTER - 31
Phase 1 – best CFD models in the tunnel Smooth Ridge P5 SIMPLY FASTER - 32
Phase 2 – initial brake model • We started the analysis by investigating the aerodynamics of a naked brake Standard Magura Production P5 SIMPLY FASTER - 33
Phase 2 – best CFD models • It was discovered that Magura model was faster than standard Standard Magura P5 SIMPLY FASTER - 34
Phase 2 – brake head tube integration P5 SIMPLY FASTER - 35
Phase 2 – brake head tube final model P4 P5 P5 SIMPLY FASTER - 36
P4 P5 P5 SIMPLY FASTER - 37
P4 P5 P5 SIMPLY FASTER - 38
Seat tube
Phase 1 – initial parametric model P5 SIMPLY FASTER - 40
Phase 1 – best CFD models Baseline (P4) Straight Full gusset Small Gusset P5 SIMPLY FASTER - 41
Phase 1 – best CFD models in the tunnel Baseline (P4) Straight Full gusset P5 SIMPLY FASTER - 42
Phase 2 – final model selection P5 SIMPLY FASTER - 43
Phase 2 – final wind tunnel experimentation P5 P4 P5 SIMPLY FASTER - 44
RESULTS P4 - P5 Drag savings (g) 66 % savings 3 Time savings (s/km) 0.66 50 km TT 33 180 km Iron Man 119 P5 SIMPLY FASTER - 45
Final results
Competitor benchmarking: 7 total P5 SIMPLY FASTER - 47
P5: Lowest drag of any triathlon bike ever P5 SIMPLY FASTER - 48
P5: Lowest drag of any triathlon bike ever Savings Best Worst Drag (g) 60 110 Power (W) 6 11 Time (s/km) 0.6 1.1 P5 SIMPLY FASTER - 49
Conclusions P5 SIMPLY FASTER - 50
Conclusions • The P5 is the fastest triathlon and time trial bike ever • CCM+ has dramatically speed up the development time to market • The new aerodynamics design cycle has allowed us to be more innovative, yielding better and more exiting bicycles P5 SIMPLY FASTER - 51
Questions?
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