Aerodynamic actions Flashcards
47) How must be the pressure gradients in order to have reduced wake?
a) Positive;
b) Negative;
c) Null.
b) Negative;
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)
b) Sensibly (0.9 – 1.4);
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 %
c) In a noticeable way (20 – 30 %)
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.
b) 0.3 and 0.5
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.
a) For positive gradients of pressure;
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
b) Is the best shape from the point of view of the aerodynamic resistance, but only at great
distances from the ground
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.
a) Limited dependence on the Reynolds number;
54) In normal conditions, the vehicles travel:
a) In turbulent motion;
b) In laminar motion;
c) Depends on the air conditions
a) In turbulent motion;
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.
c) Two arresting points if there is passage of the air current between truck and trailer.
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.
b) It delays the detachment of the current;
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.
a) The lift and the induced resistance;
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.
c) Increases the shape resistance with the increase of the induced resistance.
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.
c) Can be greater than 1.
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.
c) Leads to a strong aerodynamic resistance, greater that those that would characterize a wake of big dimensions.
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.
b) Low (given that the …. Dissipates the current);
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.
b) The lesser is the vehicle’s class;
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.
b) At open circuit and open test chamber;
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.
a) The viscous effects are preponderant;
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.
c) To reduce the lift.
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.
a) It’s enough to round off the edges;
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.
a) The positive gradients of pressure must be reduced;
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.
a) Much, if the body has a good aerodynamic fineness;
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.
b) Reduction of the positive gradients of pressure;
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…
a) Generates a notable induced resistance;
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.
c) Build screens over the extremities.
