Report on Shop Class Last Tuesday:
- Electrical team: Continued to work with plugs.
- Forks: Cleaned and sandblasted joints.
- Wheels: Continued to clean spokes. Sandblasted parts of the frame.
- Clutch &Transmission: Continued to study assembly of clutch and how the parts will come together again.
- Top end: Cleaned parts using the parts cleaner.
- Bottom End: Continued to clean the engine casing.
- Fasteners: Checked the gaskets and recut some of them.
- Frame: Continued to clean engine covers, buffing and polishing using Scotch Bright pad.
Professor Littman introduces Professor Martinelli who begins with a talk of his work and how he has ended up here.
– Professor Martinelli completed his undergraduate studies in aeronautical engineering at the Politecnico di Milano.
– Earned his Ph.D. at Princeton in 1987.
– He remained at Princeton as a Research Staff member to continue the development of computational fluid dynamics methods in collaboration with his former Ph.D. adviser Antony Jameson (at a time in which the MAE department was one of the worldwide leading centers in the field.)
– He joined the faculty in 1994, and has been teaching courses in Aerodynamics, Applied and Computational Mathematics, and Design.
– Professor Martinelli’s research is primarily motivated by the desire of improving the aerodynamics efficiency of airplanes, cars, ships, and energy conversion devices, and is concerned with a variety of fundamental problems at the intersection of aerodynamics, computational science and engineering design.
– When he first came to Princeton, the biggest problem he faced was with his mathematics and computation methods. Because of this he spent the next 10 years working diligently on his applied math skills.
– Another problem was that the computational technology was not at a high enough level yet to avoid physical testing which would enable the process of design to become a lot cheaper. This meant he devoted a lot of time to developing computational methods.
– The world took leaps in this area with us nowadays we are able to run computations in a fraction of the time and for a fraction of the price – a $4million computer in 1990 vs our laptops today.
– Professor Martinelli demonstrated the effects of better fluid mechanics as he told us of how his work with some students allowed him to help Switzerland – a landlocked country – to win the Americas Cup in 2003.
– Working with racing cars is much harder than working with planes. With a plane you know and can predict the environment, you know the speed and what is surrounding it. Whereas with a car the flow becomes time dependent, there are lots of vortices which bounce around and are energetic with interacts with the flow field.
– Other things he has worked with – Building wind turbines, helicopter rotors, planes of all speeds (subsonic to 5x speed of sound).
– Professor Martinelli showed us a slide of a bike and rider in a wind tunnel. It showed how they trace the air flow over bodies and how flow becomes turbulent. Initially it is all laminar flow (smooth) to start with to turbulent flow (rough). He talked about how they try and make the air particles follow the back of the rider because it gives the minimum drag.
– How fluid mechanics relates to motorcycles internally and how it is important in the engine. It’s key in the mixing of the air and gasoline in the piston, and how the flow pattern is effected by the intake, shape and curve of the piston.
– Venturi Effect – for an incompressible flow a reduction of area causes an increase in local flow velocity and a consequent decrease in pressure. This effect is what causes the downforces on a race car. Mechanics try and shape the bottom of the car so that it creates suction so the vehicle sticks down.
– Fins on the engine – their only purpose is to cool the engine more efficiently.
Questions and Answers:
- What is fluid mechanics?
– – The study of the motion and dynamics of any continual media – liquid/ gas and the interaction of the particles.
- How do commercial and military planes differ in their aerodynamics?
– Not so much the use of the plane but rather the mission of the plane.
– Difference between fighter and civil. – ratio between area and wing span. Efficiency needs high aspect ratio, gliders up to 20 whereas fighters have small ratio (roughly 3)
– Lift comes from the spin. Idea of baseball.
– Can maneuver in high angle of attack.
– Keep span very low in the military jet.
– Sweep wing angle, angle dependent on speed of flight, Mach 2 = 30 degrees.
- What technological advances are you eager for in aerodynamics?
– Looking forward to reducing and removing drag. Trying to fly supersonic (faster) with the same cost of flight. The problems with this at the moment are the strength of the shockwaves (creating environmental problems) which are created by drag. Strength of wave = weight of aircraft. However, you would need a noticeable difference in weight to make difference the strength of the shockwaves– 150,000lb at 1.6 Mach is what we can get away with at the moment. By increasing the speed of flights it would reduce the cost of flying as the main cost at the moment is leasing planes from banks, so you either have to move more people to make more money. This can be achieved by bigger planes or more flights. At the moment more flights through faster flight times is the most achievable option.
- How does fluid mechanics vary from air to water? / are there general principles that apply to boats, motorcycles, planes and rockets?
– Water is incompressible and gas at low speeds is also incompressible, but in a gas at high speeds when you go faster it can be compressible and you have to worry about the thermodynamics. Water if you go fast has another problem, it can make bubbles, and cavitation’s.
– US military working on super capitating torpedo which makes an air bubble around them.
– Reynolds number = inertial forces/ viscous forces. Keep the number the same in water and gas then everything behaves the same. – On mars there is a low Reynolds number and high mac number which is very bad for flying.