Introduction
Riblets and tripwires are widely explored and documented structures that have a huge potential for use in drag reduction technology. Passive strategies for drag reduction in air and underwater vehicles, such as airplanes and submarines, are increasingly being investigated as they reduce the cost of operation of the vehicle by increasing its speed and efficiency. This essay discusses riblets and tripwires, and their use in drag reduction technology. Their optimal specifications, mechanism of functioning and potential applications for drag reduction over underwater aerofoils have also been dealt with.
Riblets and tripwires
In case of underwater vehicles, fluid mechanical drag (hydrodynamic drag) reduces the speed with which they travel through water. For a specific limit of engine power, the maximum speed that can be attained by the vehicle is drastically reduced due to the formation of eddies very close to the surface of the vehicle. Apart from this, another source of hydrodynamic drag is the development of pressure drag due to laminar flow at the boundary layers. Riblets can be used to reduce the formation of eddies near the surface of the vehicle, while tripwires can be used to reduce the pressure drag and induce turbulence at the boundary layers.
• Riblets: These are minute grooves, longitudinally placed on the surface of a vehicle or airfoil, and are in alignment with the direction of flow. They “have been shown by Walsh and Lindemann [1984] at the National Aeronautics and Space Administration (NASA) and Reidy and Anderson [1988] at the Naval Ocean Systems Center (NOSC) to produce as much as 8 percent turbulent flow drag reduction on flat plates”.1 Studies on “fully submerged axisymmetric bodies”1 conducted ...
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4. Moin P, Kim J. Tackling Turbulence with Supercomputers. Stanford: Center for Turbulence Research. Available from: http://www.stanford.edu/group/ctr/articles/tackle.html
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Ever since I was little I was amazed at the ability for a machine to fly. I have always wanted to explore ideas of flight and be able to actually fly. I think I may have found my childhood fantasy in the world of aeronautical engineering. The object of my paper is to give me more insight on my future career as an aeronautical engineer. This paper was also to give me ideas of the physics of flight and be to apply those physics of flight to compete in a high school competition.
Slingshot diving fin comes with some innovations such as Gear Shift, Mid-foot Flex Joint, and Power Bands, which are specially designed to provide a great experience while diving. Power Bands are equipped with a pure silicone that provides a boost of energy on the power stroke and reduces fatigue. That allows you accumulate energy and reclaim it prior to the upstroke rather than wasting your energy like with some other diving fins.
The development of the Chaos began with a computer and mathematic problems of random data that can calculate and predict patterns that repeat themselves. For example, it picks up the pattern of a person’s heart beat and the pattern of snowflakes hitting the ground. Researchers have found that the patterns may be viewed as “unstable”, “random” and “disorderly” they tend to mimic zig-zags, lightning bolts or electrical currents. This theory has not only been used by physicist, but has also been used by astronomers, mathematicians, biologists, and computer scientists. The Chaos Theory can be applied to predict air turbulence, weather and other underlying parts of nature that is not easily understood (Fiero, p.
2. http://www.chs.k12.nf.ca/socstud/ssgrassroot/OceanRangerLesson.htm. 3. http://en.wikipedia.org/wiki/drill_string. 4.
Personal Watercrafts or "jet skis" are basically Personal Watercraft (PWC) are basically small inboard boats able to travel at high speeds due to large amounts of power and very light weight. Alomst all PWC's are under 600 lbs and most of todays PWC's have at least 90 hp.Not only are PWC's some of the fastest water vehicles they are also some of the most maneuverable water vehicles. This is because PWC's propultion is based on a jet that also is it's turning mechanism. When the driver turns the handlebars the jet (via cables) turns in the direction of the handlebars so the stern is pushed in the opposite direction. This allows the driver to turn at a much tighter angle than traditional boats with keels and rudders.The main drawback to this maneuverability is the fact that if there is no thrust coming from the engine the ability to turn is effictively zero meaning that anytime the driver presses the kill switch (a large red button) they lose all ability to steer. This is extremely dangerous whenever an inexperienced person may drive the PWC back to dock or into shore. PWC's have no brakes and have no ablilty to stop other than turning around. They have an extremely efficient ability to hydroplane (when most of the PWC is above water) and it takes most PWC's a few hundred feet to come to a stop after being at full throttle. This is because 600 lbs + a rider is traveling at a very high speed with only minimal friction to slow them down (since PWC's are made to travel with very little friction).
Introduction to Aerodynamics Aerodynamics is the study of the motion of fluids in the gas state and bodies in motion relative to the fluid/air. In other words, the study of aerodynamics is the study of fluid dynamics specifically relating to air or the gas state of matter. When an object travels through fluid/air there are two types of flow characteristics that happen, laminar and turbulent. Laminar flow is a smooth, steady flow over a smooth surface and it has little disturbance. Intuition would lead to the belief that this type of air flow would be desirable.
For a plane to create lift, its wings must create low pressure on top and high pressure on the bottom. However, at the tips of the wings, the high pressure pushes and the low pressure pulls air onto the top of the wing, reducing lift and creating a current flowing to the top. This current remains even after the wing has left the area, producing really awesome vortices.
Rushin, S. (2014, 07 13). History of the Bikini Bathing Suit. Retrieved from Bikini Atoll: http://www.bikiniatoll.com
As the air flows over the wing producing lift, it grabs onto the wings surface and causes drag. Drag can be measured by the equation D=Cd 1/2 (pV2)S, much like the lift equation. The drag coeficent Cd is found, again, by determining ...
From Fig.1, using the NACA data, the higher the Reynold number the air has, the further they can extend on the linear region. The linear region has a gradient of 2π and the lift coefficient of zero angle of attack is 0.2 which shows that NACA 2415 aerofoil is a positive cambered foil. A high Reynold number suggest a high velocity flow or less viscous fluid which carries a higher momentum. The Reynold number of the air is at least 20 times lower than all NACA data. It therefore has a lower momentum to push the separation point back to the trailing edge when the angle of attack increases. As it has a lower velocity, the pressure of fluid across the aerofoil is higher than the NACA result. The area of boundary layer will then increase due to continuity equation, it is easier for the separation to happen. The
Mechanical Engineering 130.2 (2008): 6 - 7. Academic Search Complete. Web. The Web. The Web.
NOAA, Office of Ocean Exploration and Research. Technical Diving. 24 Feb 2006. Web 12 Jul 2010. http://oceanexplorer.noaa.gov/technology/diving/technical/technical.html
On a more scientific note I am interested in mechanics of fluids. This interest was enforced last year when I had the opportunity to attend a lecture on fluid mechanics at P&G. At the conference I greatly expanded my knowledge regarding the physical aspect of fluids and their properties. In last year's AS course we have met a topic in this field. I will be applying ideas and knowledge gathered from last year for this investigation.
The aerodynamic efficiency is the single most important element in designing a competitive car for professional racing or getting the car model on the front of a Car and Driver or Motortrend. Aerodynamics is the study of the motion of gases on objects and the forces created by this motion. The Bernoulli effect is one of the most important behind car design. The Bernoulli Effect states that the pressure of a fluid, in gaseous or liquid state, varies inversely with speed or velocity and a slower moving fluid will exert more pressure on and object than the same fluid moving slower (Yager). The goal of car designers is to make the air passing under a car move faster than the air passing over the car. This causes the air passing over the car to create more downforce than the air passing under the car creates upforce creating a force additional to the car’s weight pushing the car to the road. Large amounts of downforce are needed to keep light cars grounded at high speed and keep to cars from sliding around turns at high speeds.
In order to prove this theory, I would work to design an experiment where a variety of winglet designs could be installed onto a scale model of a wind turbine. I would then place the wind turbine into a wind tunnel without any winglets to determine a control. While the turbine is in the wind tunnel, I would measure the amount of power produced for a set amount of time at a constant wind speed. Once I had a control group, I would repeat the process in the same manner with a variety of winglet designs, winglet orientations, and wind speeds.