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Question 5 (10+10=20 Points): For an incompressible subsonic flow, the freestream airspeed is 20m/s Above a flat plate the flow speed decreases to 15m/s and below the flat plate increases to 25m/s The free-stream pressure is 101 kPa and rho =1.225kg/m^3 (a) Calculate the pressures on the top of the plate and on the bottom of the plate separately. (b) Calculate the lift created on the flat plate if the plate surface area is 0.5m^2
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Profesyonel · 6 yıl öğretmeni
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(a) To calculate the pressures on the top of the plate and on the bottom of the plate, we can use Bernoulli's equation, which states that the total pressure in a streamline is constant. The total pressure is the sum of the static pressure and the dynamic pressure.The dynamic pressure is given by the equation:
where
is the dynamic pressure,
is the density of the fluid, and
is the velocity of the fluid.For the top of the plate, the velocity is
, so the dynamic pressure is:
The total pressure on the top of the plate is the sum of the free-stream pressure and the dynamic pressure:
For the bottom of the plate, the velocity is
, so the dynamic pressure is:
The total pressure on the bottom of the plate is the sum of the free-stream pressure and the dynamic pressure:
(b) To calculate the lift created on the flat plate, we can use the lift equation:
where
is the lift force,
is the pressure on the bottom of the plate,
is the pressure on the top of the plate, and
is the surface area of the plate.Substituting the values we have:
Therefore, the lift created on the flat plate is
.