## Friday, August 9, 2019

### Aerodynamics and propulsion Research Paper Example | Topics and Well Written Essays - 1250 words

Aerodynamics and propulsion - Research Paper Example Lift is a force generally associated with an object moving inside the fluid, with the direction being either vertical or in some cases, perpendicular to the direction of motion. A classic example of where lift is used is the wings of an aircraft. As the aircraft moves horizontally, the shape of the wings create a pressure gradient beneath its top and bottom surface, hence creating a vertically upwards force (Munson, Young and Okiishi). When an object moves through a fluid, it mostly experiences a force due to the pressure forces acting on the body. If the forces are acting on opposite ends of different magnitudes, they tend to create a net pressure force. For a symmetric object moving in a fluid, with its line of symmetry being parallel to the direction of motion of the fluid, no lift would be generated because the forces would cancel each other. Hence, to create a lift force, a symmetric object must have its line of symmetry at an angle to the direction of motion, or be non-symmetri c. Non-symmetric objects may also move at an angle inside the fluid, and this angel is called the angle of attack (Munson, Young and Okiishi). In the case of an aerofoil which is depicted below, it can be seen that the section of the top surface over which air is flowing is greater than the area of the bottom surface. To ensure that conservation of mass is not violated, the speed of the air at the top is increased so that the total horizontal displacement of the air at the top and bottom are the same (Abhinav). ... The lift coefficient is a key factor for objects that create lift. It depends on shape, the fluid properties and the surface roughness. A general expression for this coefficient is given as: Where Re is the ratio of inertial forces to viscous forces; Fr is the Froude number, the ration between inertia forces and gravitational forces; Ma is the speed of the fluid relative to the speed of sound in that fluid; and is a measure of surface roughness (Munson, Young and Okiishi). In other words, the fluidÃ¢â‚¬â„¢s temperature, density, speed, viscosity, as well as the shape of the object, surface roughness and angle of attack, amongst other things, have a say in the determination of the lift forces. b) Describe how atmospheric parameters (temperature, pressure, density) affect the generation of lift and drag as an aircraft gains altitude? As discussed previously, the fluidÃ¢â‚¬â„¢s temperature, density, speed, viscosity, as well as the shape of the object, surface roughness and angle of att ack, amongst other things, have a say in the determination of the lift forces. Let us now discuss the effects of a few these parameters on the lift force and lift coefficient. Coming back to the case of the aircraft: as the aircraft moves at a higher altitude, where the air is thinner and less dense because of the gravitational effects forcing the mass of air to move downwards, the lift force, which is directly proportional to the density of the fluid, decreases with the decrease in density. Another factor is temperature. At higher elevations, the temperature of the air is lower, which creates an increase in density, the lift force is likely to