Low Speed True/False

Question 1

In considering the incompressible flow of fluid through a tube, the average velocity is always less than or equal to the maximum velocity.

Answer 1

True

Question 2

A fluid is a substance that deforms continuously under the influence of a normal stress.

Answer 2

False, A fluid is a substance that deforms continuously under the influence of SHEAR stress.

Question 3

A “stagnation streamline” and a “separation streamline” mean the same thing.

Answer 3

False

Question 4

A streamtube cannot be defined in a viscous fluid.

Answer 4

False, A streamtube is a control volume bounded by streamlines

Question 5

Laminar flow is always steady.

Answer 5

False

Question 6

The maximum lift coefficient for a simple airfoil is about 10.

Answer 6

False

Question 7

If a flow velocity is given as V = axy i + bz j, the flow is two dimensional and steady.

Answer 7

False, there are there dimensions (x,y,z) in the equation

Question 8

A streamline is the same as a streakline in steady flow.

Answer 8

True

Question 9

P/roh + (V^2)/2 + gz = constant along a streamline if flow is incompressible, inviscid and steady.

Answer 9

True

Question 10

The no-slip boundary condition is the appropriate boundary condition for viscous flow.

Answer 10

True

Question 11

P = rhoRT for simple liquids such as water

Answer 11

False

Question 12

Pgage = Pabs - Patm

Answer 12

True

Question 13

The buoyant force acting on a body fully submerged in water is equal to the weight of the water displaced. This is true whether the body is made of Styrofoam or steel.

Answer 13

True

Question 14

The Principle of Dimensional Homogeneity states that all additive terms in a single equation must have the same dimensions is the equation is to have physical meaning.

Answer 14

True

Question 15

The dimensions of abs viscosity, mu, can be written as a force/(area*time).

Answer 15

False, mu is equal to force*time/area

Question 16

If I want to study the drag on a Cessna 172, I can build a 1/10th scale model and simply test it in an atmospheric pressure/temperature wind (air) tunnel at 10 times flight speed. Since I will thus match Reynolds numbers between flight and model, T will be assured that the drag coefficients will also match.

Answer 16

False

Question 17

The exponential scale height of Earth’s lower atmosphere is about 9km (“about” here means within 20%).

Answer 17

True

Question 18

The area integral of the pressure obtained from the hydrostatics equation P - Pnaut = rhogH around a closed body fully submerged in a single component liquid produces no net force.

Answer 18

False

Question 19

While the absolute viscosity of a gas increases with an increase in temperature, that of a liquid decreases with an increase in temperature.

Answer 19

True

Question 20

Flow induced chemical changes should only be expected in airflow over a vehicle if the flow is hypersonic. Similarly, for practical purposes, the flow is virtually incompressible if the Mach number if 0.1.

Answer 20

True

Question 21

We can expect boundary layer transition on a smooth flat plate in a zero pressure gradient flow at Re of about 500,000.

Answer 21

True

Question 22

The lift curve for an airfoil (Lift coef vs. alpha) is linear for small angles of attack.

Answer 22

True

Question 23

At a modest angle of attack of several degrees, the lift coefficient and the drag coefficient on a simple thin airfoil are both of similar size of order one.

Answer 23

False

Question 24

In a steady flow a streamline, pathline, and streakline through a given point all follow the same path. In an unsteady flow, these three lines may also follow the same path. (think about 1-D flow, for example).

Answer 24

True

Question 25

The area integral term in the continuity equation represents the net rate of mass flux through a control surface.

Answer 25

True

Question 26

V = ay i + by^2 j represents a one dimensional steady flow.

Answer 26

True

Question 27

All of the additive terms in the integral form of the momentum equation have the same dimensions, a force.

Answer 27

True

Question 28

A Newtonian fluid will continue to deform under the influence of normal stress.

Answer 28

False, A Newtonian fluid will continue to deform under the influence of SHEAR stess

Question 29

P = rho*R*T applies to gasses away from their critical point.

Answer 29

True

Question 30

The drag coefficient, Cd, represents a ratio of forces - the drag force divided by a force which would be created by the dynamic pressure times a suitable normalizing area.

Answer 30

True

Question 31

If dimensional analysis yields the result that there is only one appropriate Pi group, that group must be equal to zero.

Answer 31

False, that Pi group must be equal to a constant.

Question 32

We derived an expression for hydrostatics in class. If we had instead assumed that the fluid was undergoing a uniform acceleration, a, (e.g., think of doing an experiment in a railroad car undergoing acceleration a), then the equation would have been -delP + rho*(g-a) = 0.

Answer 32

True

Question 33

g*R/T is the atmospheric scale height. Here, g is the gravitational acceleration, R the gas constant and T the abs temperature.

Answer 33

False, atmospheric scale height is R*T/g

Question 34

A ship was floating, and then a leak developed and the ship sank. The ship displaced the same weight of water whether is was floating or sunk.

Answer 34

False

Question 35

The viscosity of a gas increases with increasing temperature.

Answer 35

True

Question 36

Consider a Couette flow experiment. On a plot of shear stress vs. strain rate, the slope of the line is the absolute viscosity. (Strain rate is along the x-axis). Moreover, for a Newtonian fluid, that slope is a constant everywhere along the line.

Answer 36

True

Question 37

If we consider a simple laminar boundary layer developing on a thin flat plate in a uniform flow, the shear stress in the fluid is greatest at the plate surface and approaches zero at the boundary layer edge. Also, at the same height above the plate but still within the boundary layer, the shear stress will decrease with increasing distance from the plate leading edge.

Answer 37

True

Question 38

The speed of a capillary wave should be proportional to the square root of the liquid surface tension.

Answer 38

True

Question 39

Reynolds number represents the ratio of gravitational to viscous forces in a flow.

Answer 39

False, the Reynolds number is the ratio of inertial forces to viscous forces.

Question 40

Dynamic similarity should apply to the flow about two objects if they are goemetrically similar and if all of the Pi-groups (like Reynolds number, Mach number,...) are the same.

Answer 40

True

Question 41

A wing stalls when the flow on the lower surface separates and becomes turbulent.

Answer 41

False, Stall occurs when the flow on the UPPER surface separates and becomes turbulent.

Question 42

If I am swimming at the bottom of a small pool (like a hot tub) and a huge person enters the tub and floats while no water is lost from the tub, the pressure I feel will rise.

Answer 42

True

Question 43

If I am again swimming at the bottom of a small pool (like a hot tub) and a huge person enters the tub but sinks while no water is lost from the tub, the pressure I feel will not rise.

Answer 43

False, the water's weight is still in the tub. The added weight of the fat swimmer will increase the pressure.

Question 44

A boundary layer is the thin layer of fluid near a body moving through the flow in which shear stresses are important.

Answer 44

True

Question 45

The boundary condition for a real fluid beside a real solid is the there is both no-through-flow and no-slip of the fluid with respect to the solid.

Answer 45

True

Question 46

An ordinary airplane would commonly cruise at a lift to drag ratio of about one.

Answer 46

False, lift would have to be significantly higher than drag.

Question 47

The viscosity of a gas decreases as its temperature increases. Similarly, the thermal conductivity which represents heat diffused across a temperature gradient by the thermal motion of molecules also decreases with an increase in temperature.

Answer 47

False, viscosity of a gas increases as its temperature increases.

Question 48

The center of pressure is the location where the resultant force of a distributed load acts on a body.

Answer 48

False

Question 49

V = ay i = bx^2 j represents a one dimensional steady flow.

Answer 49

False, there are more than one coordinate axis.

Question 50

The absolute pressure of a gas must always be positive while the gauge pressure may be positive or negative.

Answer 50

True

Question 51

A liquid is not compressible under any circumstances.

Answer 51

False, the Tate equations shows how it is possible for liquids to be compressible under extremely heavy loads.

Question 52

The Principal of Dimensional Homogeneity says that all additive terms in an expression representing physical reality must be dimensionless.

Answer 52

False, not dimensionless but have the same dimensions

Question 53

In an isothermal liquid as in an isothermal gas the hydrostatic pressure varies exponentially with distance above of below a fixed height.

Answer 53

False

Question 54

We should expect a laminar boundary layer over a flat plate to transition to turbulence at an Re of about 500,000.

Answer 54

True

Question 55

Since both an airfoil and a circular cylinder in a flow have a smooth and round leading edge, they both have about the same drag coefficient, something around one.

Answer 55

False, the streamlining at the end of an airfoil greatly reduces drag.

Question 56

The ratio of the lift coefficient to the drag coefficient of an airfoil placed at a few degrees angle of attack could reasonably be 1000.

Answer 56

False

Question 57

A streamline and a streakline, both passing through the same point in space, are the same line even in an unsteady flow.

Answer 57

True

Question 58

V = atx i + aty j represents a two dimensional unsteady flow.

Answer 58

True

Question 59

If we consider water emanating horizontally from a converging nozzle must be greater than atmospheric pressure.

Answer 59

Ture

Question 60

Since we derived Bernoulli's equation in class using a differential sized control volume whose periphery was made up of streamlines, we can use the resulting equation for either viscous of inviscid flow problems.

Answer 60

False

Question 61

The dimension(s) of a momentum flux is a Force.

Answer 61

True

Question 62

It is thought that the drag, F, on a block submerged in a flow depends on the block's length, width and depth as well as on the free steam velocity, freesteam density and the freestream viscosity. This physical relationship can be expected to be able to be represented with two dimensionless Pi-groups.

Answer 62

False

Question 63

The buoyancy force exerted be the atmosphere on an empty one liter soda bottle (with its cap on) is about one newton.

Answer 63

False

Question 64

Shock waves can't occur if the flow well upstream of an ordinary airfoil is subsonic. Also, in a hypersonic flow over some vehical one should expect there to be shock waves and the oxygen and nitrogen in the air may become hot enough to dissociate into their constituent atoms.

Answer 64

False, new chemical reactions will occur at hypersonic flight.