1P1 Fluid Mechanics

Question 1

Define a fluid.

Answer 1

A fluid cannot sustain shear stress when at rest.

Question 2

Key facts about pressure.

Answer 2

Pressure acts noramlly to surfaces
Pressure acts uniformally in all directions

Question 3

Pressure in a manometer.

Answer 3

pm = rho x g x h + patm

Question 4

How does a mercury barometer work?

Answer 4

Weight of mercury in the column = atmospheric pressure

Question 5

How do you calculate total force on a submergd plate?

Answer 5

Integrating the forces along it with respect to area.

Question 6

How do you find the centre of pressure?

Answer 6

Integrating the moments to find the average moment arm needed to balance the force.

Question 7

Quick way to find horizontal force on a submerged plate.

Answer 7

Find the force on a submerged vertical plate wiht the same projected area.

Question 8

Quick way to find vertical force on a submerged plate.

Answer 8

Find the total weight of the water above the plate.

Question 9

Define the streamline.

Answer 9

A line which are in line with the velocity vectors at each point in flow.

Question 10

Define a stagnation point in a flow.

Answer 10

Where the flow velocity is zero.

Question 11

What is flow seperation?

Answer 11

When flow perpetrates from the surface when they cannot follow its curvature.

Question 12

Define unsteady flow.

Answer 12

The trajectory of a particle will change with time.

Question 13

Define the no slip condition.

Answer 13

The fluid at the surface of a body will have 0 velocity.

Question 14

Define the boundary layer.

Answer 14

The layer of fluid around a body where the velocity varies.

Question 15

Define inviscid flow.

Answer 15

Flow where the effects of friction are ignored.

Question 16

What causes flow seperation.

Answer 16

Viscosity.

Question 17

What is true for a control volume in steady flow?

Answer 17

A region of fluid where the net mass flow in and out of the volume is zero.
mdot in = mdot out

Question 18

How do you calculate mass flow with a non uniform velocity distribution?

Answer 18

mdot = integral(rho x v x dA)

Question 19

How do you calculate mass flow with velocity which is not perpendicular to the area?

Answer 19

mdot = rho x A x vn (normal component of velocity)

Question 20

Integral form of momentum flow rate.

Answer 20

integral(rho x vel in direction
xv . dA)

Question 21

Where do you derive Bernoulli’s eq from?

Answer 21

Apply newton 2 to a fluid element in the streamwise direction.
F = -(dp/ds) dV
F = ma = mv(dv/ds)
Then equate and integrate.

Question 22

What assumptions must you make to apply Bernoulli’s eq?

Answer 22

That the flow is incompressible
That it is used along a streamline (sometimes can be used throughout a flow)

Question 23

Where does the normal point in fluid dynamics?

Answer 23

Away from the centre of curvature.

Question 24

How do you derive the eq for pressure gradients with streamline curvature?

Answer 24

Apply N2 vertically using a pressure differentia.
Then use eq for centripetal force of mv^2/r

Question 25

What is the Coanda Effect.

Answer 25

A jet of fluid will attach itself to a body due to its curvature