Senior Presentation Old Format

By Kos Barsukov

The Task  The Problem:  When designing motorcycles

aerodynamic efficiency is often sacrificed for style and comfort  Because the shapes are so inefficient, minute changes can substantially decrease drag and increase top speed.  Goals:

Examine the design features of a sport motorcycle and quantify their affect on the drag coefficient of a motorcycle.  Design features which produce less drag without decreasing function

The Plan  Examine the aerodynamic characteristics of motorcycles

using simple 2D CFD models  Examine the aerodynamic characteristics of a 1/9 scale motorcycle model in the wind tunnel by using drag measurements and particle image velocimetry.  Design a detailed 3D CFD model based on the 1/9 the scale model and use CFD to quantify how different features contribute to drag.  Design an optimal set of fairings, construct scale models using rapid prototyping and test them on the 1/9th scale model to determine effect on drag.

Results  2D CFD models were created based on 1/9th scale models of a

Ducati Monster and Yamaha YZR M1. Drag coefficient was determined by the formula :

2F Cd = AρV 2

Where F is the drag force, A is the frontal area, p is the air density, and V is the velocity

Drag force can be calculated in two ways-by measuring the pressure acting on the frontal area, and by measuring the change in velocity of air as it reflects from the surface.  Because of complicated surfaces involved in motorcycles, this calculation was performed in Cosmos Flow Works, using finite element analysis

• Models of a faired and unfaired motorcycle were tested • The ambient conditions were set at 293.2 K, 101.325kpa. • Wind speed was set at 44 m/s, approximately 100 mph • Both models showed high pressures in front where air was being

pushed away • The pressure differential between the front and rear causes pressure drag

 Due to the fairing and lower riding position the faired bike caused a

flow that separated later, thus causing a lower Cd  Air flowing over the top of the rider was sped up in order to recombine with the rest of the flow at the back of the wake. Cd=.375

Cd=.243

 Without the rider the unfaired bike’s Cd decreased by 2.9% to

.365  The faired bike’s Cd increased by 38.2% to .336, signifying that on faired bikes the rider plays an important aerodynamic role.  The edge of the windscreen caused flow separation to happen much earlier

Drag force (N)

Cd

 Drag decreased if

774000

0.610

0.243

885000

0.612

0.244

774000

0.610 Re

166000

0.444

0.177

modifications to the front of the model caused the flow to separate later  Changes to the back of the motorcycle had no effect on drag when they were in the turbulent region  2D analysis is limited because it does not allow modeling of air going around the sides of motorcycles  Cannot test effects of mufflers, mirrors, turn signals, side fairings

Wind Tunnel Testing  Tested at 15, 25, 35, 45, 55 Hz  Molded rider for accurate

measurements  T=23 degrees Celsius  Frontal area = 67.77 cm2 , calculated from a frontal picture traced in Solid Works  Bike mounted close to the bottom plate to simulate movement over a road

Varying Cd  Frontal are of full size motorcycle calculated to be .55 m2  Drag force calculated by Fd=1/2Cd*ρ*V2 *A  Variation in Cd happened in a test where the motorcycle wheels

were on the plate, and one where the motorcycle was 1 centimeter above the plate.  Cd was high for a motorcycle because the rider was not placed in full tucking position

Hz

V (m/s)

15

Drag Force (N)

Velocity in (mph)

Cd

Re

V for a full size motorcyle (mph)

9.556

0.414215 21.377

1.110897 138808.3

2.375

25 18.689

1.296999 41.806

0.909514 271459.4

4.645

35 27.373

2.703125 61.232

0.883611 397596.1

6.804

45 35.966

4.5212 80.455

0.856059 522413.8

8.939

55 44.279

6.736618 99.053

0.841518 643174.6 11.006

Power calculations for a full size motorcycle of this shape Cd=

V (mph)

0.865

V (m/s)

Power Drag Force Required (N) (kw)

Power (hp)

30

13.4112

51.55504

0.691415

0.927203

55

24.5872

173.2822

4.260525

5.713457

75

33.528

322.219

10.80336

14.48754

85

37.9984

413.8724

15.72649

21.08957

100

44.704

572.8338

25.60796

34.34084

110

49.1744

693.1289

34.0842

45.70765

120

53.6448

824.8806

44.25056

59.34096

130

58.1152

968.0891

56.26069

75.44682

150

67.056

1288.876

86.42687

115.9003

185

82.7024

1960.524

162.14

217.4333

200

89.408

2291.335

204.8637

274.7267

3D CFD model  Models air flow around all sides of the motorcycle  Allows to more accurately determine pressure points  More accurately models ground effect

Surface Pressure Plot  High pressure

points on wheel, radiator, and fork tubes cause drag  Fairings can be added to the model to reduce drag.  At 25 m/s, drag force was 0.46 N, Cd=0.36

Future Plans  Make 3d models of fairings, exhaust, wind screen, blinkers and

rider and test how they affect Cd  Design optimized features to minimized drag  Create these features using rapid prototyping and test them on the

scale model in the wind tunnel.  Design a full fairing system that minimizes drag without sacrificing

function or style.