Mechanical Properties of Fluids Test - 3

The flow velocity u of a fluid is a vector field u=u(x,t)

which gives the velocity of an element of fluid at a position x and time t.

The flow of a fluid is said to be steady if u does not vary with time. That is if δu/δt = 0.

laminar flow (or streamline flow) occurs when a fluid flows in parallel layers, with no disruption between the layers. At low velocities, the fluid tends to flow without lateral mixing, and adjacent layers slide past one another like playing cards.

When any liquid is flowing more than the velocity of it's critical velocity then flow becomes turbulent.

The Magnus effect is an observable phenomenon that is commonly associated with a spinning object that drags air faster around one side, creating a difference in pressure that moves it in the direction of the lower-pressure side.

The Magnus effect often occurs when a spinning sphere (or cylinder) curves away from its principal flight path.

This phenomenon is important in the study of the physics of many ball sports. It is also an important factor in the study of the effects of spinning on guided missiles—and has some engineering uses, for instance in the design of rotor ships and Flettner aeroplanes.

This is the application of Bernoulli's Theorem.

If air speeds up the pressure is lowered.Thus,a wing generates lift because the air goes faster over the top creating a region of low pressure,and thus lift.

The degree to which a fluid resists flow under an applied force, expressed as the ratio of the shearing stress to the velocity gradient. The coefficient of viscosity of liquids decreases as temperature increases because the bonds between molecules are weakened.

The force of viscosity on a small sphere moving through a viscous fluid is given by:
F_d = 6πηRv

Where:

• F_d is the frictional force – known as Stokes' drag – acting on the interface between the fluid and the particle
• η is the dynamic viscosity 
• R is the radius of the spherical object
• v is the flow velocity relative to the object.

In SI units, F_d is given in Newtons, η in Pa·s, R in meters, and v in m/s.