Properties of fluids
Properties of fluids
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| Fluid Properties |
Before going into complex aerodynamics it is mandatory to know about basic fluid property. Let's take a look at fluid property one by one.
Pressure:
Pressure is simply force applied on the body per unit area.
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| Fluid property - Pressure |
P= F/A
where A tends to zero
where A tends to zero
The unit of Pressure is N/m^2.
It is a point property and the pressure acting on a fluid varies from point to point.
It is a point property and the pressure acting on a fluid varies from point to point.
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| Fluid property - Pressure |
Density:
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| Fluid property- Density |
In very simple terms, consider density as a property of fluid to measure how thick fluid is. Density is given by mass of an element in space
to the volume of space occupied by it . So over here density is the ratio of the mass of the fluid
element being considered, ‘m’ to the
volume of fluid over which the mass is
being considered, ‘v’.
Density = m/v
The unit of Density is kg/m^3. The density of air at sea level is about 1.2 kg/m3
The unit of Density is kg/m^3. The density of air at sea level is about 1.2 kg/m3
Volume:
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| Fluid property - Volume |
Lets talk about volume now. You have definitely come across this term many
times before in your life. To define volume, let us consider a jar of water having
a volume of 20 liters. This means that the water jar can maximum contain 20
liters of water. This signifies that volume is the measurement of the amount of
a fluid that is being contained in a system. Volume is 3D quantity. If you multiply area of any shape by its thickness you get volume. If jar is in rectangular shape, it can be calculated as the
product of length, breadth and height(thickness) of fluid. In other way volume is
taken as the ratio between the mass (m) of the fluid being considered, to the
density(ρ) of the fluid being considered.
V = m/ρ
The unit for Volume is m^3
Temperature:
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| Fluid property - Temperature |
In the field of aerodynamics, temperature is considered only for high speed flight. Because in high speed flight, production of heat due to friction is considerable. We will talk in depth about this in our forthcoming posts. Now coming back to temperature in relation to subsonic flow. Let us begin with a simple example, what happens to a young kid when you give him a little too much chocolate to have? He will get hyper and find a way to expend all his energy until he gets tired, yes? (Just wanted to tell about excitation) Similarly, when the molecules of a fluid are excited by an external stimulus, they start to move rapidly, colliding with one and other. Due to this rapid collision, heat is generated and the temperature of the flow increases.
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| Fluid property - Temperature |
High energy means high temperature!
Velocity:
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| Fluid property - Velocity |
Consider a fluid flowing with some velocity ‘u’. Now what do we mean when we say ‘flowing with some velocity’? It basically means that the fluid is being displaced from one point to another or the rate of change of displacement. When we talk about the velocity of a solid, say a ball, we can safely say that the entire ball is being displaced with the same velocity. But in the case of fluids, it is not the same, velocity is a point property and it varies from point to point. This is mainly due to the physical property of a fluid i.e. Viscosity.
Viscosity is simply resisting force to the motion of the fluid. It is analogous to friction force in solid.
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