Are you looking for the latest mechanical engineering seminar topics? If yes, then you come to the right place. In this article, we will give you a complete guide about seminar topics for mechanical engineering. Aerodynamics is one of the essential seminar topics for mechanical engineering.
Table of Contents
SEMINAR TOPICS FOR MECHANICAL ENGINEERING: Aerodynamics
AERODYNAMICS, a branch of continuum mechanics in which the laws of motion of air and other gases are studied. As well as the characteristics of bodies moving in the air. The aerodynamic characteristics of bodies include lift and drag forces and their distribution over the surface.
As well as heat fluxes to the surface of the body caused by its movement in the air. In atmospheric aerodynamics, the diffusion of solid particles (for example, smoke, smog, dust) in the atmosphere and aerodynamic forces acting on buildings and other structures are studied.
Below we consider the problems associated with the movement of aircraft. However, the same principles can be applied to describe other phenomena studied in general hydro aeromechanics( see… HYDROAEROMECHANICS).
It outlines the physical laws governing air movement and the concepts needed to understand the mechanisms of lift and drag at various flight speeds, including shock wave flows. Due to the very high altitudes (over 60 km), some changes in the flow pattern around the body occur due to the very low air density.
CHARACTERISTICS OF AIR AND OTHER FLUIDS
Aerodynamics considers the properties of air, such as density, pressure, temperature, and molecular composition. Air consists of several chemical elements, mainly nitrogen (78%) and oxygen (21%).
There are also small impurities of argon, carbon dioxide, hydrogen, and other gases. The number of molecules per unit volume of air is enormous. For example, at a temperature of 15 ° C at sea level, 1 m 3 contains 2.7 × 10 25 molecules.
SEMINAR TOPICS FOR MECHANICAL ENGINEERING: AIR NAVIGATION
Pressure is the force per unit area. Air molecules are in constant motion; they hit and bounce off the air-bounding surface. The sum of all impulses imparted by molecules falling on a unit surface area per unit time is equal to the pressure. The temperature of air (or some other gas) is a measure of the average kinetic energy of molecules (equal to half the product of mass by the square of velocity) per unit mass.
An important physical characteristic of a gas that depends only on temperature is the speed of sound. The speed of sound an (m / s) in the air can be calculated, knowing the absolute temperature T (K), using the formula. Communication between the pressure p, a density of r, and the absolute temperature T is given by p = r RT, where R – gas constant equal to 287.14 m 2 / s 2 × K for air. Boyle’s law follows from this formula, according to which at constant temperature p / r = const, i.e., the change in density is directly proportional to the change in pressure.
Changes in air pressure and density with height are consistent with these laws. Pressure and a density decrease, compared with their values at sea level, by 2 times at an altitude of 6 km, 5 times at an altitude of 12 km, and 100 times at an altitude of 30 km.
SEMINAR TOPICS FOR MECHANICAL ENGINEERING: MECHANICS
In the lower atmosphere, the air temperature also decreases with increasing altitude. For example, the standard temperature at sea level is 288 K. It decreases to 256 K at an altitude of 5 km and 217 K at an altitude of 12 km. An essential characteristic of a moving medium is its viscosity.
Viscosity manifests itself through the property of adhesion of the fluid to the surface. While the non-viscous medium freely slides along the streamlined surface. To illustrate the effect of viscosity. This generates a force that slows down the flow (drag force) and considers two large parallel plates, A and B (Fig. 1), one of which moves relative to the other. A dense medium adheres to each of the plates.
Random motions of molecules create the effect of “mixing,” tending to equalize the average flow rates, the velocity of which on plate B is equal to V, and on plate A- zero. Thus, the length of the arrows is proportional to the velocity at a given point of the flow and the height between the plates.
The amount of force required to maintain the motion of plate B at a speed of 1 m / s (or hold in place a stationary plate A ), provided that the distance between the plates is 1 m. The area of each of them is 1 m 2, which is called the viscosity coefficient m … For air at a temperature of 0 ° C and a pressure of 1 atm m = 1.73 H 10 –5 H H s / m 2. Experiments show that the coefficient of viscosity of air changes with temperature in proportion to T 0.76.
SEMINAR TOPICS FOR MECHANICAL ENGINEERING: FUNDAMENTAL LAWS
Aerodynamics is described by the fundamental physical laws of continuum mechanics. They express the property of conservation of mass, energy, and momentum for each elementary volume of a moving medium. The force acting on a body in an airstream depends only on the relative speed of the body and air and does not depend on whether the body moves in the air at rest or the air moves relative to a stationary body.
Let us apply the conservation laws, not to individual molecules. But to some moving elementary volume of the medium containing a large number of molecules. This simplified approach seems inevitable if we remember that molecules and moving with the flow perform random movements.
And the laws describing these movements must take into account collisions between different molecules in which their directions of movement, velocities, etc., change. Let us consider, for example, an elementary volume in the form of a cube with a side of 0.01 mm. The volume of which is 10 –6 mm 3.
This small volume still contains 2.7 x 10 10molecules, and each of them moves randomly. However, because the volume contains many molecules, it will move at an average velocity along the flow streamlines shown in Fig.
According to another condition, this elementary volume should be so small. Thus, we consider the elementary volume of the medium. Which is large enough to contain a large number of molecules and small enough compared to the “characteristic scale” of the flow. At very high altitudes, where the air density is low. The concept of a particle of a medium loses its meaning. And one has to consider the movements of individual molecules.
As applied to the particles of the flowing medium under consideration, the law of conservation of mass means. The mass flow of air passing between streamlines A and B in Fig. 2 is the same, wherever it is measured. Therefore, line A 1 B 1 is the same as the airflow through line A 2 B 2.
The law of conservation of momentum is an expression of Newton’s second law applied to particles of the current medium. It can be written in the following form:
Strength = Change in momentum per second.
THE PARAMETERS OF THE FLOW AND THE MOVING BODY.
The force acting on a moving body can be expressed using a specific dimensionless parameter. Which also has the dimension of force. According to Newton’s second law, the force F is equal to the product of mass and acceleration and has the dimension ml / t 2. The quantity having the dimension of force is the product of the density r.
The square of the velocity of the body in medium v 2, and the area S… The required dimensionless parameter. The factor 1/2 is introduced for convenience since the same factor is in the Bernoulli equation above. Force as a vector quantity is characterized by its components having different directions. Accordingly, three force coefficients are distinguished: the lift force coefficient (typical to the incoming flow velocity).
The drags force coefficient (directed along with the incoming flow velocity). And the lateral force coefficient (orthogonal to the previous two).
The force coefficient itself depends on other dimensionless parameters. One of them is the Reynolds number Re, introduced by the English engineer Osborne Reynolds (1842-1912). Which has the dimension m/lt.
INCOMPRESSIBLE FLOWS: LIFTING FORCE
When the wing flows around, a flow moving with a Mach number much less than unity (i.e., the flow velocity is much less than the speed of sound). Then the pressure distributions over its upper and lower surfaces have the form shown in Fig. 3. The streamlines gave in the same place characterize the trajectories of elementary particles of the flowing medium. The velocities of which are related to pressure by the Bernoulli equation. The occurrence of areas of low and high pressure means. That the flow velocity on the upper surface is more significant than on the lower one.
Since the pressure on the lower surface is correspondingly more significant, an upward force, or lift, acts on the wing. At a constant value of the Reynolds number. The lift Y is proportional to the air density r, the square of the flight speed v2, the wing area S. And the angle of attack between the wing chord and the direction of motion. This dependence is written as,
Y = 1 / 2 r v 2 Ska ,
where k is the coefficient of proportionality
Dividing both sides of this ratio at 1 / 2 r v 2 S, we obtain the dimensionless lift coefficient expression. Thus, c Y is proportional to the angle of attack.
On the upper surface, the pressure decreases due to an increase in the flow velocity. And on the lower surface, it increases, pushing the wing upward. The coefficient of proportionality k takes different values for wings of different shape in plan (Fig. 4), and its value also depends on the aspect ratio of the wing l, determined by the relation l = b 2 / S. That is, the ratio of a square of the wingspan b 2 to the surface area S. According to the theory developed by the German scientist Ludwig Prandtl (1875-1953),
At angles of attack less than 12 °, the actual value of k is approximately 10% less than the value determined by this formula. The influence of the aspect ratio on the value of the coefficient k and, therefore, on the wing lift is called the tip effect. In fig. 5 is a rear view of the wing. Due to the pressure difference, air flows from the lower surface to the upper one near the end of the wing. This circular air movement persists behind the wing, and it generates the tip vortices shown in Fig.
SEMINAR TOPICS FOR MECHANICAL ENGINEERING: INFLUENCE OF VISCOSITY
Above, the viscosity coefficient was determined, and it was noted. The velocity changes from the velocity of motion of the body surface to the velocity of free flow at the outer boundary of the boundary layer. At present. The study of the boundary layer is based on the results of Prandtl and Theodor von Karman (1881-1963).
But gradually swirls (becomes turbulent) downstream. One of the critical problems of aerodynamics is to determine the position of the transition point from laminar to turbulent flow. The turbulent boundary layer is much thicker than the laminar one. And their thicknesses depend on the Reynolds number Re. Defined as the product of r v / m by the distance from the leading edge x.
Thus, the distance x = 1 m from the leading edge at v = 10 m / s, r = 1.23 kg / m 3 , m = 1.73 × 10 -5 kg / m W with thickness of the laminar boundary layer is 0, 62 × 10 –2 m. And the thickness of the turbulent boundary layer is 2.5 × 10 –2 m. Thus, the turbulent boundary layer is four times thicker than the laminar one; nevertheless, these thicknesses are relatively small in both cases.
SEMINAR TOPICS FOR MECHANICAL ENGINEERING: COMPRESSIBLE FLOWS
Suppose the speed of movement of a body (or air relative to a stationary body) becomes comparable to the speed of sound. Then the air density in the flow changes. Consider first a thin body with a pointed toe. Such as a needle or razor blade at zero angles of attack. The pressure disturbances created by the nose of such a body are minor.
And these disturbances propagate in all directions from the nose at the speed of sound equal to 340 m / s at a standard temperature of 288 K (15 ° C). Next, consider two flight modes and two wave diagrams illustrating the propagation of pressure disturbances (waves). Diagram fig. 10, a corresponds to subsonic flight (with M <1), and Fig. 10, b – supersonic flight (with M> 1).
A body moving with speed v travels distance AB in time t, so that AB = vt… During the same time, the wave travels the distance and moves forward relative to the body in subsonic flight. During the supersonic flight, the wave lags behind the body. And its front, tangent to the circles of the propagation of disturbances. Forms an angle b with the direction of motion of the body. Which is the smaller, the larger the Mach number.