Final answer:
The pitot tube measures the total pressure of the flow in a wind tunnel, allowing for the calculation of fluid speed using Bernoulli's principle by differentiating between static and dynamic pressures.
Step-by-step explanation:
The purpose of a pitot tube when inserted into the test-section flow of a wind tunnel is to measure the total pressure of the flow. It utilizes Bernoulli's principle to determine fluid speed by measuring the pressure difference. According to Bernoulli's principle, the total pressure is a sum of static and dynamically induced pressures. In essence, a pitot tube has two components: one that measures the static pressure and another, which faces the flow and measures the stagnation pressure, allowing the determination of the dynamic pressure.
When a pitot tube is placed in a fluid flow, the fluid strikes the pitot tube and is brought to a stop, creating what is known as a stagnation point. The pressure measured at this stagnation point is the total pressure of the incoming flow. The pitot tube can then derive the velocity of the flow using Bernoulli's equation, which relates the measured static, dynamic, and total pressures. Determining velocity involves subtracting static pressure from total pressure, yielding dynamic pressure, which is proportional to the square of the velocity.