Aerodynamic actions

Question 1

47) How must be the pressure gradients in order to have reduced wake?
a) Positive;
b) Negative;
c) Null.

Answer 1

b) Negative;

Question 2

48) Of how much is it possible to increase the Cx
of an articulated truck with increasing βa ?
a) Little (0.01 – 0.1);
b) Sensibly (0.9 – 1.4);
c) Much (1.5 – 2.0)

Answer 2

b) Sensibly (0.9 – 1.4);

Question 3

49) The Cx
of an industrial vehicle grows with increasing the sideslip angle:
a) In a very limited way (few %);
b) In a limited way (10 %);
c) In a noticeable way (20 – 30 %

Answer 3

c) In a noticeable way (20 – 30 %)

Question 4

50) The Cx
for a vehicle is included between:
a) 0.2 and 0.4;
b) 0.3 and 0.5;
c) 0.4 and 0.6.

Answer 4

b) 0.3 and 0.5

Question 5

51) The detachment of the current is facilitated:
a) For positive gradients of pressure;
b) For negative gradients of pressure;
c) At the presence of the turbulent limit state.

Answer 5

a) For positive gradients of pressure;

Question 6

52) The fuse with rectilinear axis:
a) Is the best shape from the point of view of the aerodynamic resistance;
b) Is the best shape from the point of view of the aerodynamic resistance, but only at great
distances from the ground;
c) Is the best shape from the point of view of the aerodynamic resistance, but only at Reynolds
numbers greater than those characteristic for the automotive application

Answer 6

b) Is the best shape from the point of view of the aerodynamic resistance, but only at great
distances from the ground

Question 7

53) In automotive field, the aerodynamic coefficients have:
a) Limited dependence on the Reynolds number;
b) Strong dependence on the Reynolds number, also if in general it is not considered;
c) Strong dependence on the Reynolds number and it must be taken into account at the
aerodynamic studies.

Answer 7

a) Limited dependence on the Reynolds number;

Question 8

54) In normal conditions, the vehicles travel:
a) In turbulent motion;
b) In laminar motion;
c) Depends on the air conditions

Answer 8

a) In turbulent motion;

Question 9

55) In an articulated truck, the motion field presents:
a) Only one arresting point;
b) Two arresting points;
c) Two arresting points if there is passage of the air current between truck and trailer.

Answer 9

c) Two arresting points if there is passage of the air current between truck and trailer.

Question 10

56) In a body with low aerodynamic fineness, usually is convenient to make the limit state turbulent because:
a) It reduces the induced resistance;
b) It delays the detachment of the current;
c) It reduces the friction resistance.

Answer 10

b) It delays the detachment of the current;

Question 11

57) The adoption of a spoiler allows to reduce:
a) The lift and the induced resistance;
b) The lift and the friction resistance;
c) The lift and the shape resistance.

Answer 11

a) The lift and the induced resistance;

Question 12

58) The aileron with negative lift:
a) Increases the induced resistance;
b) Increases the shape resistance without increasing the induced resistance;
c) Increases the shape resistance with the increase of the induced resistance.

Answer 12

c) Increases the shape resistance with the increase of the induced resistance.

Question 13

59) The efficiency of the wind tunnels (ratio between the installed power and the jet power): a) Is lower than 1 (open circuit);
b) Is always greater than 1 (closed circuit or recirculation);
c) Can be greater than 1.

Answer 13

c) Can be greater than 1.

Question 14

60) The presence of a wake of reduced dimensions accompanied by big vortexes as is noticed in case of some “fast back” vehicles:
a) Leads to low values of the aerodynamic resistance;
b) Leads to a strong aerodynamic resistance, but anyways lower than those that would characterize a wake of big dimensions;
c) Leads to a strong aerodynamic resistance, greater that those that would characterize a wake of big dimensions.

Answer 14

c) Leads to a strong aerodynamic resistance, greater that those that would characterize a wake of big dimensions.

Question 15

61) The pressure in wake is:
a) High (given that v is low, Bernoulli’s equation);
b) Low (given that the …. Dissipates the current);
c) Low because of the presence of vortexes.

Answer 15

b) Low (given that the …. Dissipates the current);

Question 16

62) The aerodynamic resistance, at constant speed, is as more important as:
a) The greater is the vehicle’s class;
b) The lesser is the vehicle’s class;
c) As heavier is the vehicle’s weight.

Answer 16

b) The lesser is the vehicle’s class;

Question 17

63) The modern wind tunnels are, at the greater part of the cases:
a) At closed circuit and closed test chamber;
b) At open circuit and open test chamber;
c) At open circuit and closed test chamber.

Answer 17

b) At open circuit and open test chamber;

Question 18

64) The boundary layer is the zone at immediate contact with the body at which: a) The viscous effects are preponderant;
b) The flow is turbulent;
c) Reynolds number is low.

Answer 18

a) The viscous effects are preponderant;

Question 19

65) In order to render minimum the induced resistance, occurs:
a) To delay the detachment of the current;
b) To reduce the pitching aerodynamic torque;
c) To reduce the lift.

Answer 19

c) To reduce the lift.

Question 20

66) In order to reduce the Cx of an industrial vehicle representable with a parallelepiped:
a) It’s enough to round off the edges;
b) It’s enough to round off a lot the edges;
c) It’s necessary to profile the front part.

Answer 20

a) It’s enough to round off the edges;

Question 21

67) In order to delay the current detachment:
a) The positive gradients of pressure must be reduced;
b) The negative gradients of pressure must be reduced;
c) The boundary layer must be made laminar.

Answer 21

a) The positive gradients of pressure must be reduced;

Question 22

68) How much does it influence the Reynolds number over the friction resistance?
a) Much, if the body has a good aerodynamic fineness;
b) Little;
c) Doesn’t influence.

Answer 22

a) Much, if the body has a good aerodynamic fineness;

Question 23

69) The reduction of the points of detachment of the air stream:
a) Reduction of the negative gradients of pressure;
b) Reduction of the positive gradients of pressure;
c) It needs to render the boundary layer laminar.

Answer 23

b) Reduction of the positive gradients of pressure;

Question 24

70) An aileron with negative lift in a competition vehicle:
a) Generates a notable induced resistance;
b) Reduces the shape resistance;
c) Doesn’t produce induced resistance because the negative lift…

Answer 24

a) Generates a notable induced resistance;

Question 25

71) A wing that generates lift produces also induced resistance. In order to reduce it, one must: a) Reduce the elongation (ratio between length and chord);
b) Act over the profile characteristics;
c) Build screens over the extremities.

Answer 25

c) Build screens over the extremities.