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QUESTION - 3: List and explain the different types of sensors and measurement devices commonly used in wind tunnel tests .How would you choose an appropriate sensor for measuring the pressure distribution over an airfoil?
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In wind tunnel tests, various sensors and measurement devices are used to capture different aerodynamic parameters. Here is a list of common types of sensors and measurement devices along with their explanations:1. **Pressure Sensors:** - **Pitot Tubes:** Measure the total (stagnation) pressure of the airflow. They are often used to determine airspeed. - **Static Pressure Ports:** Measure the static pressure on the surface of a model or in the flow field. - **Pressure Transducers:** Convert pressure into an electrical signal for precise measurements. They can be used to measure both static and dynamic pressures.2. **Force and Moment Balances:** - These devices measure the aerodynamic forces (lift, drag) and moments (pitching, rolling, yawing) acting on a model. They can be internal or external balances depending on their placement relative to the test model.3. **Flow Visualization Techniques:** - **Smoke Wands/Tufts:** Used to visualize airflow patterns around the model. - **Oil Flow Visualization:** A thin layer of oil applied to the model surface shows flow direction and separation points. - **Particle Image Velocimetry (PIV):** Uses laser-illuminated particles to measure velocity fields in the flow.4. **Velocity Measurement Devices:** - **Hot-Wire Anemometers:** Measure flow velocity by detecting changes in heat loss from a heated wire. - **Laser Doppler Anemometry (LDA):** Uses laser beams to measure the velocity of particles in the flow.5. **Temperature Sensors:** - **Thermocouples:** Measure temperature changes in the airflow or on the model surface. - **Infrared Cameras:** Detect temperature distribution over the model surface.6. **Strain Gauges:** - Measure deformation or strain on the model structure due to aerodynamic loads.### Choosing an Appropriate Sensor for Measuring Pressure Distribution Over an Airfoil:When selecting a sensor for measuring pressure distribution over an airfoil, consider the following factors:1. **Accuracy and Sensitivity:** Choose sensors that provide high accuracy and sensitivity to detect small pressure variations across the airfoil surface.2. **Spatial Resolution:** Ensure the sensor array has sufficient spatial resolution to capture detailed pressure distribution, especially in areas with steep gradients like leading and trailing edges.3. **Frequency Response:** Consider the frequency response of the sensors if dynamic pressure measurements are required, such as during unsteady flow conditions.4. **Environmental Conditions:** Select sensors that can withstand the environmental conditions of the wind tunnel, including temperature, humidity, and potential contamination.5. **Data Acquisition Compatibility:** Ensure the sensors are compatible with the data acquisition system used in the wind tunnel for seamless integration and data processing.6. **Cost and Availability:** Balance the cost of the sensors with the budget constraints while ensuring they meet the necessary technical requirements.For pressure distribution over an airfoil, pressure transducers or pressure-sensitive paint (PSP) are commonly used due to their ability to provide detailed and accurate pressure maps.