senior presentation old format

8/14/2019 Senior Presentation Old Format

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By Kos Barsukov


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The Task

The Problem:

When designing motorcyclesaerodynamic efficiency is often sacrificedfor style and comfort

Because the shapes are so inefficient,minute changes can substantiallydecrease drag and increase top speed.

Goals:

Examine the design features of a sportmotorcycle and quantify their affect onthe drag coefficient of a motorcycle.

Design features which produce less dragwithout decreasing function


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The PlanExamine the aerodynamic characteristics of motorcycles

using simple 2D CFD models

Examine the aerodynamic characteristics of a 1/9 scalemotorcycle 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 featurescontribute to drag.

Design an optimal set of fairings, construct scale models

using rapid prototyping and test them on the 1/9th

scalemodel to determine effect on drag.


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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 :

Where F is the drag force, A is the frontal area, p isthe 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 bymeasuring 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 finiteelement analysis

2

2

VA

FCd

=


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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 beingpushed away

The pressure differential between the front and rear causespressure drag


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Due to the fairing and lower riding position the faired bike caused aflow that separated later, thus causing a lower Cd

Air flowing over the top of the rider was sped up in order torecombine with the rest of the flow at the back of the wake.

Cd=.375 Cd=.243


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Without the rider the unfaired bikes Cd decreased by 2.9% to.365

The faired bikes Cd increased by 38.2% to .336, signifying thaton faired bikes the rider plays an important aerodynamic role.

The edge of the windscreen caused flow separation to happenmuch earlier


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Dragforce(N)

Cd

774000 0.610 0.243

885000 0.612 0.244

774000 0.610Re

166000 0.444 0.177

Drag decreased ifmodifications to the front of

the model caused the flow toseparate later

Changes to the back of themotorcycle had no effect ondrag when they were in theturbulent region

2D analysis is limited becauseit does not allow modeling ofair going around the sides ofmotorcycles

Cannot test effects of

mufflers, mirrors, turn signals,side fairings


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Varying Cd

Frontal are of full size motorcycle calculated to be .55 m2

Drag force calculated by Fd=1/2Cd**V2 *A

Variation in Cd happened in a test where the motorcycle wheelswere on the plate, and one where the motorcycle was 1 centimeterabove the plate.

Cd was high for a motorcycle because the rider was not placed infull tucking position

Hz V

Drag

Force

(N)Velocity in

(mph)

Cd Re

V for a full

size

motorcyle

(mph)

(m/s)

15 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


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Power calculations for a full size

motorcycle of this shape

Cd= 0.865

V (mph) V (m/s)

Drag Force

(N)

PowerRequired

(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


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3D CFD model

Models air flow around all sides of the motorcycle Allows to more accurately determine pressure points

More accurately models ground effect


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Surface Pressure Plot

High pressurepoints on wheel,radiator, and forktubes cause drag

Fairings can beadded to the modelto reduce drag.

At 25 m/s, dragforce was 0.46 N,

Cd=0.36


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