Fluid Dynamics

Question 1

Fluid

Answer 1

• Flows under the action of forces, while deforming ‘continuously’ for as long as force is applied.(lacks ability to offer resistance to a deforming force)
• force acting on solid produces a change in shape (small strain) only remains as long as force is applied

Question 2

Shear stress

Answer 2

t=u*(du/du)

t=sheer stress
u=viscosity
du=rate of strain (speed)
du=perpendicular distance from fixed surface

Question 3

Viscosity

Answer 3

Measure of a liquids resistance to flow

High viscosity>thick fluid (like honey)>low flow rate

Question 4

Viscosity in gases and liquids

Answer 4

• in gas if temp increase the collision frequency increases hence increasing viscosity
• in liquid when temp increases the separation between molecules increases hence viscosity decreases. (High pressure also affects it unlike gases)

Question 5

Kinematic viscosity

Answer 5

•kinematic viscosity defined as ratio u/p (absolute viscosity/fluid density)

Question 6

surface tension

Answer 6

The property of a liquid that lets insects walk on water defined as the force per unit length surface tension (N/m unit)

Question 7

Capillarity

Answer 7

If a open tube at both ends is lowered vertically into a liquid the level of liquid will rise along the tube

Concave meniscus water

Co’vex does like it self so opposite direction

Question 8

Pressure

Answer 8

Hydraulic lift- pressure kept constant and area changed so less force needed to push car up.

When pushing down 1/1=p constant=10000/10000

Question 9

Vapour pressure

Answer 9

•vapour pressure (space is confined equilibrium will be reached then molecules produce this vapour pressure)

Question 10

Cavitation

Answer 10

cavitation low pressure to higher pressure forms bubbles to access this regions

Question 11

Bulk modulus

Answer 11

For liquids K tends to suffer a small change because they are incompressible meaning no change of volume unlike gases

K=-V(dP/dV) = p(dP/dp)

Question 12

Bernoulli’s equation

Answer 12

Sum of the pressure, kinetic and potential energy is always constant for an ideal incompressible and non viscous fluid having stream line steady flow (stream line not changing with time)

No heat loss or added to system
No energy lost to friction
No energy lost in fluid

Question 13

Continuity equation

Answer 13

Mass flow conserved-

p1 A1 v1 =p2 A2 v2

Volume continuity if fluid is incompressible:

A1 v1 = A2 v2

Question 14

Verna contracta

Answer 14

If the exit around the hole is not curved and is sharp then the diameter of the jet (stream line exiting) will be less than of the hole. Which means not constant pressure thus no uniform velocity

Cc(contraction coefficient)=area of stream/area of hole

Question 15

Stream line

Answer 15

The tangent of the velocity vectors of each particles path in a steady flow