Computational Fluid Dynamic Analysis Of Sounding Temperature And Humidity Sensor And Design Of Error Correction Software

Datum of the spatial and temporal distribution of parameters such as atmospheric temperature and humidity in various height levels are the most direct and basic information of studying atmospheric dynamic and thermodynamic processes. They are also the extremely important basis of understanding and forecasting weather changes, which are the essential information for climate diagnostic forecast and climate change projections. Because of the thermal inertia of radiosonde temperature sensor, the measured value of the sensor is not almost equal to the actual temperature value. Furthermore, temperature difference caused by solar radiation has influence on both the humidity sensor elements and circuit of sounding humidity sensor, which is one of the main factors affecting measuring accuracy.For thermal response time constant of radiosonde temperature sensor, traditional research methods are experimental measurements and empirical formula calculation. It is difficult for the experimental measurements to build platform that simulates real high-altitude environment. Furthermore, calculation models used by the empirical formula are oversimplified. Thus, the accuracy of traditional methods needs to be validated. As for solar radiation temperature difference of sounding humidity sensor, the common methods include installing radiation shield and radiation error correction algorithm. In the process of measuring high-altitude atmospheric humidity, traditional radiation shield is not suitable for applying, and as to radiation error correction algorithm, the data sources have not been reported.A computational fluid dynamics (CFD) method is employed to simulate the sounding temperature and humidity sensors, and the numerical simulation result can provide a basis for future amendments to the difference. In the heat transfer model created by FLUENT software, impact factors such as altitude, solar elevation angle, radiosonde rising speed, shape and size of the sensor, sensor material, surface coating reflectivity are considered.According to the practical issues and physical models of sounding temperature and humidity sensors, simplified geometric models are achieved, and then grids are generated for the established geometrical models. Finally, boundary conditions in line with the real environment around the measured points are applied to achieve fluid-solid coupled heat transfer analysis. Simulation results show that altitude and radiosonde rising speed are important factors that influencing thermal response time constant of the sounding temperature sensor. According to the modeling results, Marquardt and Global Optimization method can be employed in fitting formulas. Using these techniques, the thermal response time constant as a function of the several factors may be obtained precisely, quickly and easily. Solar radiation heating error is inversely related to surface coating reflectivity of the sounding humidity sensor. Among three irradiation states, the plain view is the optimal illumination status to reduce solar radiation. In XOZ plane, maximum measurement error caused by temperature coefficient can reach0.3324%RH, which should be corrected. These results can provide the data and algorithm to optimize of the measurement error correction of sounding temperature and humidity sensor, which has a potential to improve the measuring accuracy of high-altitude atmospheric temperature and humidity.