To begin, we will discuss Lift and Drag. This refers to how much force is exerted upon an object or material. The higher the velocity of the object, the higher the lift. In the same vein, the lower the velocity, the lower the drag. If you have a car and you accelerate, the air flowing past you exerts less force upon the car than if you don’t accelerate at all.
Next we will discuss Momentum. This refers to the rate of change of any particular fluid. For example, if a rubber ball is rolling down a hill, its momentum will continue to increase as it rolls over the bumps in the ground. This can be expressed as a force that continues to apply until the fluid reaches its final state of no momentum. Kinematics experts divide momentum into two categories: kinetic and potential.
Now we will discuss air flows and their effect on kinematics. When the airflow past a body encounters a body of fluid with zero lift, it will begin to create a downward force. This downward force can cause the fluid to resist upward movement and cause it to compress.
How is this related to kinematics? If a given body of fluid moves through the course of its journey at a constant velocity, it will not experience a change in momentum. The same thing will happen if the angle of attack changes. Therefore, changes in velocity will not alter the fluid’s path. In a way, these disturbances are called zero-slip kinematics.
Now let us look at a much more complicated situation involving fluid and air. If the fluid is pumped at high pressure from a jet nozzle, the jet will create a very large amount of pressure underneath the nozzle. This may cause the fluid to push against the tank of the jet nozzle or even cause the surrounding air to be pressurized. The sudden rise in pressure can be damaging to the pump’s efficiency, so it is critical that an engineer design these pumps with special features to counteract such effects.
These special features will include a re-profile tip, which forces the fluid to flow into a smaller hole or nozzle. In the case of a rising air stream, the stream will slow down as it ascends. However, as it descends, the stream moves closer to the pore wall where it becomes stagnant. As it reaches the bottom of the pore, the pressure of the air and the water drops below atmospheric. This will cause the fluid to be drawn into a lower volume and pressurized. A re-profile tip on the tip of the pump will allow this to happen without changing the direction of the stream.
Kinematics is an important concept in fluid dynamics, but not so much in aerodynamics. Fluid kinematics only indirectly affects aerodynamics; it just uses the concept to describe how the movement of the fluid takes place. The main thing to remember is that kinematics is a dynamic equilibrium state. It is not concerned with the transition between zero lift and high pressure as it is in mechanics. For more information on fluids and kinematics, please see the references below.
