Aerodynamic drag is a force acting opposite to the relative motion of any object. It can exist between two layers of a solid surface. Unlike other resistive sets, such as dry friction, which are almost independent of speed, the resistance forces obey this value. Despite the fact that the ultimate cause of action is viscous friction, turbulence does not depend on it. The resistance force is proportional to the velocity of the laminar flow.
The concept
Aerodynamic drag is a force that acts on any moving solid in the direction of the flowing fluid. In terms of the near field approximation, resistance is the result of forces due to the distribution of pressure over the surface of the object, symbolized by D. Due to skin friction, which is the result of viscosity, is denoted by De. Alternatively, the resistance force calculated from the point of view of the flow field arises as a result of three natural phenomena: shock waves, a vortex layer, and viscosity. All this can be found in the aerodynamic drag table.
Overview
The distribution of pressure acting on the surface of the body affects large forces. They, in turn, can be summarized. The components of this value that act downstream make up the power of resistance, Drp, due to the pressure distribution that affects the body. The nature of these forces combines the effects of a shock wave, the generation of a vortex system, and the mechanisms of the wake.
The viscosity of a fluid has a significant effect on resistance. In the absence of this component, the pressure forces acting to slow down the vehicle are neutralized by the power that is located in the stern and pushes the vehicle forward. This is called pressure recovery, with the result that the aerodynamic drag is zero. That is, the work that the body performs on the air flow is reversible and restored, since there are no friction effects to convert the energy of the flow to heat.
Pressure recovery is effective even in the case of viscous movement. This value, however, leads to power. It is the dominant drag component in the case of vehicles with split flow areas in which pressure recovery is considered rather ineffective.
The friction force, which is the tangential power on the surface of the aircraft, depends on the configuration of the boundary layer and viscosity. The aerodynamic drag, Df, is calculated as the projection of the bog sets downstream, estimated over the surface of the body.
The sum of friction and pressure resistance is called viscous resistance. From a thermodynamic perspective, bog effects are irreversible phenomena and, therefore, they create entropy. The calculated viscous resistance Dv uses changes in this value to accurately predict the response force.
It is also necessary to give the formula for the density of air for gas: P * V = m / M * R * T.
When the aircraft produces lift, another rebuff component occurs. Induced Resistance, Di. It occurs due to changes in the pressure distribution of the vortex system, which accompanies the production of the elevator. An alternative lift perspective is achieved by considering changes in airflow momentum. The wing intercepts the air and makes it move down. This leads to the fact that the wing is affected by the equal and opposite drag force, which is the lifting power.
Changing the pulse of the air flow downward leads to a decrease in the return value. That it is the result of the force acting forward on the applied wing. An equal but opposite mass acts on the back, which is the induced resistance. It tends to be the most important component for aircraft during take-off or landing. Another drag object, wave drag (Dw), arises from shock waves at transonic and supersonic speeds of flight mechanics. These shafts cause changes in the boundary layer and pressure distribution over the surface of the body.
History
The idea that a moving body passing through air (density formula) or another liquid meets resistance has been known since Aristotle. An article by Louis Charles Breguet, written in 1922, began efforts to reduce resistance through optimization. The author continued to translate his ideas into reality, creating several record aircraft in 1920 and 1930. Ludwig Prandtl's theory of the boundary layer in 1920 provided an incentive to minimize friction.
Another important call for ordering was made by Sir Melville Jones, who introduced theoretical concepts to convincingly demonstrate the importance of ordering in aircraft design. In 1929, his work Streamlined Airplane, presented to the Royal Aviation Society, was fruitful. He proposed the ideal aircraft, which would have minimal resistance, which would lead to the concept of a “clean” monoplane and retractable undercarriage.
One of the aspects of the work of Jones, which shocked designers most of all at that time, was his graph of the dependence of horse power on speed for a real and ideal plane. If you look at the data point for an airplane and extrapolate it horizontally to an ideal curve, you can see the gain in speed for the same power. When Jones finished his presentation, one of the audience called the results of the level of importance that the Carnot cycle in thermodynamics.
Elevator-induced resistance
The resistance caused by the lift arises as a result of creating a slope on a three-dimensional body, such as a wing or an aircraft fuselage. Induced braking consists mainly of two components:
- Drag and drop due to the creation of trailing vortices.
- The presence of additional viscous resistance, which is not when the rise is zero.
The back vortices in the flow field, present as a result of the lifting of the body, are due to turbulent mixing of air from above and below the object, which flows in several different directions as a result of the creation of the lifting force.
With other parameters that remain the same as the rise created by the body, the resistance caused by the slope also increases. This means that with an increase in the angle of attack of the wing, the lift coefficient increases, as does the rebuff. At the beginning of stalling, the inclined aerodynamic force decreases sharply, as does the drag caused by the lift. But this value increases due to the formation of a turbulent unconnected flow after the body.
Spurious Drag and Drop
This is the resistance caused by the movement of a solid object through a liquid. Parasitic drag consists of several components, including movement under viscous pressure and due to surface roughness (friction sheathing). In addition, the presence of several bodies in relative proximity can cause so-called interference resistance, which is sometimes described as a component of this term.
In aviation, the induced rebuff tends to be more powerful at lower speeds, because a large angle of attack is required to maintain lift. However, with increasing speed, it can be reduced, as well as the induced resistance. The parasitic resistance, however, becomes larger because the fluid flows faster around the protruding objects, increasing friction.
At higher speeds (transonic), the impedance goes to a new level. Each of these forms of repulse varies in proportion to the others depending on the speed. Thus, the general resistance curve shows a minimum with some air swiftness - the aircraft will have optimal efficiency or approach it. Pilots will use this speed to maximize endurance (minimum fuel consumption) or glide range in the event of engine failure.
Aviation Power Curve
The interaction of parasitic and induced resistance depending on air speed can be represented as a characteristic line. In aviation, this is often called a power curve. It is important for pilots, because it shows that below a certain airspeed and to maintain it, more thrust is counterintuitively required while decreasing speed, and not less. The consequences of being behind the scenes in flight are important and are taught as part of pilot training. At subsonic air speeds, where the U-shape of this curve is significant, the impedance has not yet become a factor. That is why it does not appear on the curve.
Braking in a transonic and supersonic flow
Compression tug-of-war is a drag that is created when the body moves in a compressible fluid and at speeds close to the speed of sound in water. In aerodynamics, wave drag consists of many components, depending on the mode of motion.
In transonic flight aerodynamics, the wave drag is the result of the formation of shock rolls in the liquid, which are formed when local regions of supersonic flow are created. In practice, such a movement occurs on bodies moving much lower than the swiftness of the signal, since the local air velocity increases. However, the full supersonic flow above the vehicle will not develop until the value goes much further. Airplanes flying at transonic speed often experience a wave state during normal flight. In transonic flight, such a rebuff is usually called transonic compressibility resistance. It increases significantly with increasing flight speed, dominating other forms at these speeds.
In supersonic flight, the wave resistance is the result of shock rolls present in the liquid and attached to the body, formed on its front and rear edges. In supersonic flows or in housings with sufficiently large angles of rotation, loose shock or bent waves will instead form. In addition, local regions of the transonic flow can occur at lower supersonic speeds. Sometimes they lead to the development of additional shock rolls present on the surfaces of other lifting bodies, similar to those found in transonic flows. In powerful modes, the wave resistance flows are usually divided into two components:
- Supersonic lift depending on the value.
- Volume, which also depends on the concept.
A closed-shape solution for the minimum wave impedance of a fixed-length rotation body was found by Sears and Haack and is known as the Sears-Haack Distribution. Similarly, for a fixed volume, the form for minimum wave impedance is Von Karman Ogive.
The Buzeman biplane, in principle, is generally not subject to such an action when operating at design speed, but it is also not capable of generating lift.
Products
A wind tunnel is a tool used in research to study the effects of air moving past solid objects. This design consists of a tubular passage with a test object mounted in the middle. Air moves past an object using a powerful fan system or other means. The test facility, often referred to as the pipe model, is equipped with appropriate sensors for measuring air forces, pressure distribution, or other aerodynamic characteristics. It is also necessary in order to notice and correct a problem in the system in time.
What are the aircraft
Let's turn to the story first. The earliest wind tunnels were invented at the end of the 19th century, in the early days of aviation research. It was then that many tried to develop successful aircraft heavier than air. The wind tunnel was conceived as a means of reversing the usual paradigm. Instead of standing still and moving an object through it, the same effect would be obtained if the object stood motionless and the air moved at a speed higher. In this way, a stationary observer can study the flying product in action and measure the practical aerodynamics imposed on it.
The development of pipes accompanied the development of the aircraft. Large aerodynamic products were built during World War II. Tests in such a tube were considered strategically important during the development of supersonic aircraft and rockets during the Cold War. Today, aircraft can be anything. And almost all the most important developments have already been introduced into everyday life.
Later, wind tunnel research was taken for granted. The influence of the wind on artificial structures or objects needed to be studied when the buildings became tall enough to present large surfaces to the wind, and the forces arising had to resist the internal elements of the building. The definition of such sets was required before building codes could determine the required strength of structures. And such tests continue to be used for large or unusual buildings so far.
Even later, checks were applied to the aerodynamic drag of cars. But this was not in order to determine the forces as such, but to establish ways to reduce the power needed to move the car along the road with a given speed. In these studies, the interaction between the road and the vehicle plays a significant role. It must be taken into account when interpreting test results.
In a real situation, the carriageway moves relative to the vehicle, but the air is stationary relative to the track. But in a wind tunnel, air moves relative to the road. While the latter is stationary relative to the vehicle. Some test wind tunnels include moving belts under the test vehicle. This is in order to get closer to the actual state. Similar devices are used in the wind tunnel of aircraft take-off and landing configurations.
Equipment
Samples of sports equipment have also been distributed for many years. These included clubs and golf balls, Olympic bobsledding and bicyclists, as well as racing car helmets. The aerodynamics of the latter are especially important in vehicles with an open cab (Indycar, Formula One). Excessive lifting force on the helmet can cause a significant load on the driver’s neck, and the separation of the flow on the back side can cause a turbulent seal and, as a result, poor vision at high speeds.
Advances in computational fluid dynamics (CFD) modeling on high-speed digital computers have reduced the need for wind tunnel tests. However, CFD results are still not completely reliable; this tool is used to check CFD forecasts.