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Fluid Mechanics > Fluid Dynamics > Flashcards

Fluid Dynamics Flashcards

1
Q

What is hydraulics?

A

The study of the practical laws of fluid flow and resistance in pipes and open channels.

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2
Q

What is the continuity equation?

A

The mass flow rate and volumetric flow rate are constant in a frictionless pipe for an incompressible fluid.

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3
Q

What is the Bernoulli equation?

A

States that the total energy of a fluid flowing without friction losses in a pipe is constant.

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4
Q

What kind of flow is needed for the Bernoulli equation to be valid?

A

incompressible frictionless flow.

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5
Q

What is the total energy or Bernoulli equation equal to?

A

It is equal to the sum of its pressure, kinetic, and potential energies.

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6
Q

What is the Reynolds number?

A

Is a dimensionless number interpreted as the ratio of inertial forces to viscous forces of the fluid.

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7
Q

What is laminar flow?

A

If all of the fluid particles move in paths parallel to the overall flow direction.

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8
Q

What is turbulent flow?

A

Three dimensional movement of the fluid particles superimposed on the overall direction of motion.

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9
Q

What is the critical zone or transition flow?

A

When the flow is said to be between laminar and turbulent.

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10
Q

What limits does the critical zone create?

A

This zone or region sets the upper and lower critical limits. Which are the Reynolds number before turbulent flow and the Reynolds number before laminar flow.

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11
Q

What are non Newtonian fluids?

A

Fluids that have viscosities that change with shear rate.

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12
Q

What are pseudo plastics?

A

Non Newtonian fluids that exhibit a decrease in viscosity the faster they are agitated.

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13
Q

What are dilatant fluids?

A

Non Newtonian fluids that exhibit an increase in viscosity the faster they are agitated.

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14
Q

What is the power law?

A

Is the equation to calculate the Reynolds number for non Newtonian fluids.

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15
Q

What is the bulk velocity?

A

It is the average velocity.

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16
Q

How is shear stress and flow related?

A

The shear stress created by the flow varies with location.

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17
Q

How is the pressure effected when analyzing reservoirs or large tanks for steady incompressible flow?

A

The gauge pressure is commonly used so that the reservoirs surface pressure can be zero.

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18
Q

How is the velocity effected when analyzing reservoirs or large tanks for steady incompressible flow?

A

The surface fluid level of the reservoir ot tank changes slowly when drawing from it making the velocity of the fluid surface zero.

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19
Q

What head loss due to friction do?

A

It causes a pressure drop for a pipe of constant cross sectional area and elevation.

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20
Q

What is the Darcy Weisbach equation?

A

A method for calculating the frictional energy loss for fluids.

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21
Q

What kind of flow can the Darcy Weisbach equation be used for?

A

It can be used for laminar and turbulent flow.

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22
Q

What factors effect the Darcy Weisbach friction factor?

A

The fluid flow and the relative roughness of the pipe surface.

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23
Q

How does flow effect the Darcy Weisbach friction factor?

A

The friction factor is not constant and decreases as the Reynolds number increases.

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24
Q

What happens to the Darcy Weisbach friction factor when full turbulent flow is reached?

A

When full turbulent flow is reached the friction factor is no longer effected by flow.

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25
Q

What is the Moody chart?

A

Its a chart used to obtain the friction factor.

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26
Q

What is the Hagen Poiseuille equation?

A

Its the equation used to calculate the flow rate when there is a pressure drop and the flow is through a pipe and laminar.

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27
Q

What is the hydraulic radius?

A

Its defined as the area in flow divided by the wetted perimeter.

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28
Q

What is the area in flow defined by?

A

Its the cross sectional area of the fluid flowing.

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29
Q

What is the wetted perimeter defined by?

A

Its the length of the line representing the interface between the fluid and the pipe or channel. It does not include the free surface length.

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30
Q

What is the free surface?

A

The interface between the fluid and atmosphere.

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31
Q

What is the characteristic dimension?

A

The physical length of an object that the process is dependent on.

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32
Q

What is the hydraulic diameter equal to?

A

Its equal to 4 times the hydraulic radius.

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33
Q

How to calculate the frictional energy loss by a fluid in a non circular duct?

A

The frictional energy loss is calculated from the darcy equation by using the hydraulic diameter in place of the normal diameter.

34
Q

What are considered minor losses?

A

Frictional losses resulting from fittings in the line, changes in direction, and changes in flow area.

35
Q

What is the method of loss coefficients?

A

The method for calculating the minor losses in the energy conservation equation. This is usually ignored.

36
Q

What is the loss coefficient?

A

A coefficient associated with a specific fitting or pipe exit and entrance in tanks.

37
Q

What is a pipe loop?

A

A set of two pipes placed in parallel, both originating and terminating at the same junction.

38
Q

What is the head loss in each branch or pipe in a pipe loop?

A

The flow divides in such a manner to make the head loss in each branch the same.

39
Q

What is the head loss between the two junctions in a pipe loop?

A

The head loss between the two junctions is the same as the head loss in each branch.

40
Q

What is the total flow rate equal to in a pipe loop?

A

It is the sum of the flow rates in the two branches.

41
Q

What is an open channel?

A

An open channel is a fluid passageway that allows part of the fluid to be exposed to the atmosphere.

42
Q

When is the Manning’s equation used?

A

Is used to find the flow velocity of any open channel.

43
Q

What is Hazen Williams equation used for?

A

It is used to calculate the flow velocity in pipes and to find the head loss in circular pipes.

44
Q

What is specific energy equal to and what is it associated with??

A

It is associated with open channel flow and it is equal to the total head with respect to the channel bottom.

45
Q

What are the contributors to specific energy?

A

Kinetic and pressure energy.

46
Q

Why doesn’t potential energy contribute to specific energy?

A

Because the channel bottom is the reference elevation for potential energy.

47
Q

What is uniform flow?

A

Flow with constant width and depth.

48
Q

How does uniform flow effect specific energy?

A

Total head decreases due to frictional effects (elevation increases), but specific energy is constant.

49
Q

How does non uniform flow effect specific energy?

A

Total head also decreases, but specific energy may increase or decrease.

50
Q

What is critical depth?

A

The depth of flow that will minimize the energy of flow in a channel.

51
Q

What is the critical depth dependent on?

A

Its dependent on the shape of the channel.

52
Q

What is the critical depth independent of?

A

It is independent of the channel slope.

53
Q

What is the unit discharge?

A

It’s the ratio of the flow rate to the channel width.

54
Q

What is the Froude number used for?

A

It is used to determine whether the flow is subcritical or supercritical.

55
Q

What does a Froude number of less than one tell us?

A

The flow is subcritical.

56
Q

If flow is subcritical. What does that tell us about the depth and velocity?

A

The depth of flow is greater than the critical depth and the flow velocity is less than the critical velocity.

57
Q

What does a Froude number of greater than one tell us?

A

The flow is super critical.

58
Q

If flow is supercritical. What does that tell us about the depth and velocity?

A

The depth of flow is less than the critical depth and the flow velocity is greater than the critical velocity.

59
Q

What happens when the Froude number is equal to one?

A

The flow is critical.

60
Q

What is momentum equal to?

A

A vector quantity defined as the product of the object’s mass and velocity.

61
Q

What is impulse equal to?

A

It is the product of the force’s magnitude and the length of time the force is applied.

62
Q

What is the impulse momentum principle?

A

States that the impulse applied to a body is equal to the change in that bodies momentum.

63
Q

What is the result from applying the impulse momentum principle to a control volume?

A

The resultant of all external forces acting on the control volume is equal to the difference of momentum of the fluid entering and leaving the control volume.

64
Q

When is fluid momentum conserved in the impulse momentum principle?

A

When the forces of gravity, gage pressure, friction, and turning forces from walls and vanes are absent.

65
Q

What is assumed if the friction between a fixed blade and fluid is ignored?

A

The absolute velocity at the beginning will be equal to the absolute velocity at the end.

66
Q

What is an impulse turbine?

A

A series of blades mounted around a wheel.

67
Q

How is the powered transferred from a fluid jet to the blades of a impulse turbine calculated ?

A

It is calculated from the x component of force on the blades.

68
Q

What is done with the y force component on a impulse turbine blade?

A

It is ignored, as the turbine is stationary.

69
Q

What is the velocity for an impulse turbine?

A

It’s the tangential blade velocity.

70
Q

What is the runaway speed?

A

The maximum theoretical tangential blade velocity which is the velocity of the jet.

71
Q

When can the runaway speed occur?

A

It can only occur when the turbine is unloaded.

72
Q

What is the power from an impulse turbine dependent on?

A

The velocity of the blade and the deflection angle.

73
Q

At what velocity does the maximum power occur from an impulse turbine?

A

The maximum power will be found to occur when the blade is traveling at half of the jet velocity.

74
Q

At what deflection angle does the maximum power occur from an impulse turbine?

A

The maximum power will be found to occur when the deflection angle of the blade is 180.

75
Q

What is drag?

A

The frictional force that acts parallel but opposite to the direction of motion.

76
Q

What is the drag coefficient dependent on?

A

It depends primarily on the Reynolds number and the shape of the object.

77
Q

What is the chord length of an airfoil?

A

The front to back dimension of the airfoil.

78
Q

What is the aspect ratio of the airfoil?

A

Its the ratio of the wing length to chord length.

79
Q

What is lift?

A

Lift is the force that is exerted on an object as the object passes through a fluid.

80
Q

What does the coefficient of lift measure?

A

It measures the effectiveness of the airfoil.

Fluid Mechanics (6 decks)

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