Notes by Eric: Professor Littman was not here today. In his absence, we were joined by a guest: Professor Luigi Martinelli
- Broad overview of the role of fluid mechanics, and more generally whatever happens when you try to move against air or water
- Whenever you are doing mundane tasks, you are dealing with fluid flows. Either they are opposing your motion or helping you.
o Two regimes—organized (laminar) and chaotic (turbulent)
- Chaotic flow will offer more resistance to the motorcycle
- Cost of turbulent flow vs. closing the wake is a tradeoff constantly considered.
- Distance between back of ride and wake seeks to be minimized.
- Some helmets are designed to minimize the gap between the rider and the air flow
- Often propulsion requires a working fluid
o The flow rate—the amount of fluid that can go in or out—is determined by the shape of the valve.
o The sizing of the fin is determined by the property of the flow of the engine head; therefore, the extent of the fin design of an air cool engine
- Sometimes the two combine
o In a sail boat, the systems are integrated—balance, steering, and other properties of the sail
o Other, seemingly more complex systems, such as a rocket, are actually simpler.
- Two vs. four stroke. Two-stroke—as you draw in fresh mixture, you exhaust from the previous combustion; the two-stroke exhaust may let out unburned fuel. If you solve the environmental problem, you would have a lighter engine because you do not need a valve. In a four-stroke engine, one stroke pulls in and compresses fuel then ignites it (power stroke), then the next stroke pushes out the exhaust.
o The Tiger Cub has two valves to have a desirable mass flow rate. The cam controls how quickly the valves open and close
- Engine cooling—require heat exchange between the engine and the outside air
- Overview of aerodynamic forces on ground vehicles
CARBURATION
- Venturi effect: for an incompressible flow, a reduction of area causes an increase in local flow velocity and a consequent decrease in pressure.
o Always have high velocity, low pressure
- The carburetor then fulfills 3 primary functions:
o Control engine power by adjusting the air intake flow
o Meter the fuel flow in the air flow aspirated maintaining the ratio air/fuel to optimal values throughout the engine operating range
o Homogenize the mixture of air and fuel to enable the subsequent combustion
- It is possible to obtain optimal thickness, spacing of the fins by mathematical computations
- There are two approaches to improving design: evolutionary and computational
External aerodynamics
- Even with seemingly benign topics, it is hard to optimize,
- Hybrid between electric bike and moped is most efficient
- The speed at which the oil moves around is quite low; our motorcycle has a dry sump reduces the complexity of the system; if we had a
- Land speed records