An anemometer is an instrument used to measure air velocity. The wind speed measured by the anemometer is displayed in units such as meters per second or knots. Its working principle is based on the pressure difference generated when air flows through the sensor. This pressure difference is usually detected by technologies such as thermistors, wind pressure sensors, or ultrasonic sensors. Among them, thermistor anemometers determine wind speed by measuring the cooling effect of air flowing through the sensor, while wind pressure sensors calculate wind speed by measuring the pressure change when air flows through the sensor.
Classification of Anemometers
Wind speed is a vector. Therefore, there are many anemometers that can measure both wind speed (i.e. size) and wind direction (i.e. direction). Wind speed measurement is a vital part of meteorology, environmental science, and engineering. With the advancement of science and technology, wind speed measurement equipment is constantly being updated. Therefore, there are many types of anemometers according to their working principles and uses. The most commonly used ones can be divided into cup anemometers, propeller (windmill) anemometers, hot wire anemometers, and ultrasonic anemometers. Whether in terms of technical principles, performance characteristics, and application fields, they all have different advantages. You can choose more full-featured anemometers in the SISCO Online Shop.
Cup Anemometer
The cup anemometer is the most commonly used anemometer in meteorological stations. It consists of three parabolic cone empty cups fixed on a bracket at 120° to each other, and the concave surfaces of the empty cups are all in one direction. The entire sensing part is installed on a vertical rotating shaft. Under the action of wind force, the cups rotate around the shaft at a speed proportional to the wind speed.
Hot Wire Anemometer
The basic principle of the hot wire anemometer is to place a thin metal wire in a fluid, pass an electric current to heat the metal wire and make its temperature higher than the temperature of the fluid. Therefore, the metal wire anemometer is called a "hot wire". When the fluid flows through the metal wire in a vertical direction, it will take away part of the heat of the metal wire, causing the temperature of the metal wire to drop. According to the forced convection heat exchange theory, it can be derived that there is a relationship between the heat Q dissipated by the hot wire and the velocity v of the fluid.
Spiral Anemometer
The spiral anemometer uses a propeller. When the wind blows through the propeller, the power of the wind causes the propeller to rotate. The rotation speed of the propeller is proportional to the wind speed. By measuring the speed of the propeller's rotation, the wind speed can be calculated. This anemometer usually contains a gearbox that converts the high-speed rotation of the propeller into a lower-speed rotation that can be counted.
Ultrasonic Anemometer
The ultrasonic anemometer mainly relies on the propagation characteristics of ultrasonic signals in the air to measure wind speed and direction. The instrument usually consists of multiple ultrasonic sensors that transmit and receive ultrasonic pulses. When the wind blows, the propagation speed of the ultrasonic wave changes under the influence of the wind. By measuring the propagation time of ultrasonic pulses on the same path, the wind speed can be calculated.
Advantages and Disadvantages of Anemometers
Advantages of Anemometers
High measurement accuracy: Anemometers are usually compact in design, have less interference with airflow, and can make measurements without significantly changing the airflow state. Different types of anemometers can provide more accurate instantaneous and average values of wind speed within their respective applicable ranges. It has good repeatability under the same conditions and can continuously monitor instantaneous wind direction and wind speed.
Wide range of applications: it can be used not only for gases but also for liquids, and can be used in subsonic, transonic, and supersonic flows of gases. In addition to measuring average velocity, it can also measure pulsation values and turbulence amounts; in addition to measuring motion in one direction, it can also measure velocity components in multiple directions simultaneously. It can be used in many fields, including meteorology, aviation, navigation, agriculture, environmental protection, etc., and can meet the needs of wind speed measurement in different scenarios.
Simple structure and long service life: Some anemometers (such as hot wire anemometers) have the advantages of simple structure and are easy to carry (such as handheld cup anemometers). And they can maintain a long service life under normal use conditions.
Fast response speed: Anemometers such as hot-wire anemometers have a fast response speed and can measure rapidly changing wind speeds. They are suitable for scenarios such as atmospheric flow measurement.
Disadvantages of Anemometers
Some interference with the flow field: The hot wire anemometer has a large measurement error at higher wind speeds, and there are zero drift and stability problems. The cup anemometer is large in size and has some interference with the flow field.
Greatly affected by environmental factors (some types): Ultrasonic wind direction and anemometers are easily affected by temperature, humidity, and wind pressure, and temperature compensation is required to correct the wind direction and wind speed values. In addition, dust can easily block the ultrasonic signal hole and cause damage, and icing can also affect the normal use of the instrument.
High starting wind speed (some types): The starting wind speed of the propeller-type wind direction and anemometer is relatively high, at 0.9m/s - 1m/s, and cannot be used in light wind areas.
Main Uses of Anemometers
- Measure the speed and direction of the average flow: widely used in meteorological stations and environmental protection, it is an important instrument for daily weather forecasts, climate research, and environmental monitoring.
- Measure the pulsating speed and spectrum of the incoming flow. This function is very important for studying the characteristics of atmospheric turbulence and can help scientists better understand the behavior and impact of wind.
- Measure the Reynolds stress in turbulence and the velocity correlation and time correlation between two points, which is of great significance for engineering applications and scientific research, especially in the field of aerospace.
- Measure the wall shear stress, usually using a hot film probe placed flush with the wall, the principle is similar to the hot wire velocity measurement. This has important applications in fluid mechanics research and industrial applications.
- Measure the fluid temperature: by measuring the change curve of the probe resistance with the fluid temperature in advance, the temperature can be determined based on the measured probe resistance. This is very useful in situations where both temperature and speed need to be monitored simultaneously.
