For either a closed-circuit or open-circuit low-speed wind tunnel, how does the speed of the airflow entering the settling chamber compare to the speed of the airflow in the test section?
The correct answer and explanation is:
Correct Answer:
The speed of the airflow entering the settling chamber is lower than the speed of the airflow in the test section.
Explanation:
In both open-circuit and closed-circuit low-speed wind tunnels, the airflow follows a specific path to ensure smooth, uniform flow in the test section. One key part of this path is the settling chamber, which comes before the contraction cone and the test section.
The settling chamber is a wide area that slows down the air entering the test section. This reduction in speed helps reduce turbulence and makes the flow more uniform. The air may also pass through screens and honeycombs in the settling chamber to straighten and calm the flow.
After the settling chamber, the air passes through a contraction cone. This section has a decreasing cross-sectional area. According to the principle of conservation of mass, in an incompressible fluid (like air at low speeds), a decrease in cross-sectional area must be matched by an increase in velocity to maintain constant mass flow rate. As a result, the speed of the airflow increases as it moves from the wide settling chamber into the narrower test section.
So, the test section has a much higher airflow speed than the settling chamber. This design allows engineers to test models under controlled high-speed flow while maintaining a calm, low-speed environment upstream to minimize disturbances.
To summarize, in both open-circuit and closed-circuit low-speed wind tunnels, the airflow enters the settling chamber at a low speed, becomes more uniform and less turbulent, then accelerates through the contraction cone, and reaches high speed in the test section where experiments are conducted. This arrangement ensures accurate and reliable aerodynamic testing.