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The point of minimum static pressure on a positively cambered aerofoil flying at a low subsonic speeds at a positive angle of attack is…
  • A
    on the upper surface, where the speed is highest.
  • B
    on the upper surface, where the speed is lowest.
  • C
    on the lower surface, where the dynamic pressure is lowest.
  • D
    on the lower surface, where the dynamic pressure is highest.

Refer to figure.
Bernoulli’s theorem when applied to the airflow past an aerofoil at less than Mach 0.4 shows that the total pressure is equal to the sum of the dynamic pressure (the pressure caused by the movement of the air) and the static pressure (the pressure of the air not associated with its movement) and can be expressed as the following equation:

Total Pressure (pt) = Dynamic Pressure (q) + Static Pressure (ps)

The total pressure is constant along a streamline flow. Therefore, if dynamic pressure increases then static pressure decreases and vice versa.

The flow over the top of the section accelerates rapidly around the nose and over the leading portion of the surface - inducing a substantial decrease in static pressure in those areas.

The pressure reduces continuously from the stagnation value through the free stream value to a position on the top surface where a peak negative value is reached. From there onwards the flow continuously slows down again and the pressure increases back to the free stream value in the region of the trailing edge.

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