Research On Error Correction And Test System Of Shadows Effect In Ultrasonic Wind Measurement

Wind speed and direction are key parameters for meteorological observations.It plays an extremely important role in weather prediction,marine aviation,industrial and agricultural production,as well as transportation.According to different working principles,the instruments currently used for wind speed and direction measurement can be roughly divided into Mechanical wind measuring instrument,ultrasonic wind instruments,and Laser Doppler Anemometer.They all have extensive and flexible applications.However,the existing studies at home and abroad show that the shadow effect has a significant influence on the wind speed and direction measured by the ultrasonic aerogenometer.In order to eliminate the measurement error caused by the shadow effect under different wind speed,wind direction and temperature conditions,this paper takes the ultrasonic wind measurement instrument as the research object and combines the ultrasonic time difference method to measure the wind principle to propose a computational fluid dynamics(CFD)simulation and back propagation(BP)neural network data processing shadow effect error compensation method,the main work is as follows:Firstly,based on the principle of measuring the wind speed by ultrasonic time difference method,this paper analyzes the source of the ultrasonic wind shadow effect and proposes a specific error correction method.Then,an ultrasonic wind measurement hardware system based on FPGA and STM32 is designed and implemented.The system adopts the master-slave control structure,with STM32 as the master and FPGA as the mode.The system mainly includes the minimum system and peripheral circuit of FPGA and STM32,the ultrasonic wave transmitting and receiving circuit,data communication circuit,as well as bluetooth circuit module and so on.The internal functional modules of FPGA is designed by using the Verilog language programming,based on which,the ultrasonic signal transmission and receiving,finite state machine control as well as data acquisition and transmission,also the data communication with the STM32 are realized.Through the STM32 programming to control the peripheral devices,and to achieve data computing and Bluetooth wireless transmission.Secondly,this paper simulates and analyzes the wind field of ultrasonic anemometer with CFD simulation software Fluent.As a result,the sample data of wind speed,wind direction and temperature,which are affected by the shadow effect,are obtained.And,these samples are applied to reduce the relative error from the BP neural network algorithm for the performance of the application in the ultrasonic wind instrument was systematically studied and analyzed.Finally,in order to verify the accuracy of the shadow effect's error compensation method proposed in this paper,the developed ultrasonic anemometer system was placed in a wind tunnel for experiment.The experimental measurements with different wind speeds were conducted,and the tested resrults were compared and analyzed.The experimental results show that the accuracy of the wind speed and direction measurement of the ultrasonic wind instrument developed in this paper is significantly improved by the correction of the shadow effect based on the prediction model of CFD simulation and BP neural network fusion.The overall relative error is generally within±7%,which basically meets the measurement needs of higher precision ultrasonic wind measurement.In a word,the research results have certain reference value for the development of high precision ultrasonic wind instrument.