Fluid Me

ABSTRACT
This report aims to measure the pressure variation and different contributing components of the drag force on a circular cylinder. The devices used in this experiment were a fan, closed-channel venturi-shape pipe, a Pitot tube, circular cylinder with holes of different angles, U-tube manometers and a barometer.

INTRODUCTION
When a fluid is passing through an object, it produces a total force on the object. This force is a combined force of lift and drag forces (Anderson 2007). External flows past objects have been studied extensively because of their many practical applications. For example, airfoils are made into streamline shapes in order to increase the lifts, and at the same time, reducing the aerodynamic drags exerted on the wings. On the other hand, flow past a blunt body, such as a circular cylinder, usually experiences boundary layer separation and very strong flow oscillations in the wake region behind the body (Anderson 2007). In certain Reynolds number range, a periodic flow motion will develop in the wake. In this experiment we will study the pressure variation and different contributing components of the forces on the circular cylinder (Anderson 2007).

METHODOLOGY
In this experiment, circular cylinder with 27 holes was placed behind the Pitot tube. 18 holes were adjusted to 5°, 10°, 15° and so on until 90°, and the next 9 holes were adjusted to 100°, 110° and so on until 180°. All these holes were connected to U-tube manometers which can read the pressure difference between all the holes. Pitot tube was also used to measure the static pressure and the stagnation pressure or usually called the total pressure. Pitot tube was placed in front of the circular cylinder and against flow of fluid which is air in this case.
Another device to be used was barometer which is to measure the atmospheric pressure of the room. A fan was placed in front of Pitot tube with Venturi pipe between them to maximise the velocity of the flow. The large fan was switched on and a strong flow of wind would be going pass through the Venturi-shape pipe and passing through the Pitot tube and circular cylinder. The total pressure and static pressure could be then known by reading Pitot tube. The pressure difference in each of angles in the circular cylinder could be known by looking at the inclined U-tube manometers. All the results were recorded in the Results section below.
PITOT TUBE
Anderson (2007) explains that a Pitot tube is the most common device for measuring flight velocities of airplanes. A Pitot tube is now inserted into the flow with an open end facing directly into the flow. That is the plane of the opening of the tube is perpendicular to the flow. The other end of the Pitot tube is connected to a pressure gauge (Anderson 2007). For the first few milliseconds after the Pitot tube is inserted into the flow, the gas will rush into the open end and will fill the tube. However, as he tube is closed at the end, there is no place for the gas to go and hence after a brief period of adjustment the gas inside the tube will stagnate that the gas velocity inside the tube will go to zero (Anderson 2007). Hence the open face of the Pitot tube is a stagnation point where V= 0. In turn from Bernoulli’s equation, we know that pressure increases as the velocity decreases. Hence, the pressure at the stagnation point is called the stagnation pressure or the total pressure (Anderson 2007).

DISCUSSION
RELEVANCE TO OTHER SUBJECTS
The study and understanding of this experiment and this topic is really important to everyday’s life. It is relevant to almost applications in our life. Nearly everything is designed based on the key principles of this experiment which are lift, drag, laminar and turbulent motion. All cars, planes, trains, trucks, all automobiles and basically all forms of transportation cannot be designed properly without understanding the key principle of this experiment (Dunbar 2010). NASA has more wind tunnels than any other group. One of the main ways, NASA uses wind tunnels is to learn more about airplanes and how things move through the air (Dunbar 2010). Wind tunnels help NASA test ideas for ways to make aircraft better and safer.
Dunbar (2010) adds that NASA also works with others that need to use wind tunnels. That way, companies that are building new airplanes can test how the planes will fly. NASA also uses wind tunnels to test spacecraft and rockets (Dunbar 2010). Wind tunnels are important in making the new Ares rockets and Orion spacecraft. Ares and Orion are new vehicles that will take astronauts into space. NASA engineers test ideas for the design of Ares in wind tunnels. They needed to see how well Ares would fly. They needed to know what would happen to different designs when the spacecraft came back through the atmosphere (Dunbar 2010)..

DISCUSSION ON POSSIBLE APPLICATIONS
Almost everyday’s simple applications are related to this topic. This is because we are surrounded by fluids. Our air is one of the common examples. We are surrounded by air so we have air pressure acting on us. From the times we are walking or running, we are experiencing this aerodynamics situation.
One of the possible applications that we could probably think of is when civil engineers are designing buildings or bridges. Surely, these buildings or bridges will be experiencing some force or pressure exerted by the wind. So the civil engineers have to find designs that are suitable to withstand this force so the buildings will not collapse. Although the level of complexity will not be as high as aerodynamics in airplanes, it is still applicable in civil engineering area. It will be all about laminar and turbulent motion of the wind and the shear stress acting on the building by the wind.
When athletes are swimming or playing soccer, the body of the swimmer and the ball will experience force and pressure due to the fluid around the body and the ball. This is because the body and the ball is immersed in fluids which are water and air in this case. Although the level of complexity is not as complex as aerodynamics in airplanes, it is still important to understand the aerodynamics of moving things.

REFERENCE
Anderson, J.D. 2007, ‘Fundamentals of Aerodynamics, Fourth Edition’ , The McGraw- Hill Companies, Inc, New York
Dunbar, B. 2010, ‘What are wind tunnels’, viewed 26 October 2011, <http://www.nasa.gov/audience/forstudents/k-4/stories/what-are-wind-tunnels-k4.html>