Study On Inner Flow-field Characteristics And Shunt-hedging And Multi-stage Expansion Combined Automatic Sand Sampler

Study on soil erosion must rely on advanced research tools and methods, so that we can obtain a large and accurate wind data. The sand sampler can collect erodibility particles carried by wind in the soil erosion process. It is a key equipment in the observation of sand flow structure and sand movement research, which play an important role in studying physical mechanism of sand movement, revealing the occurrence and development of soil erosion and evolution and effectively controlling soil erosion.With the widely application of automation technology, developing a new type of automatic sand sampler which has high measure precision and high sand collection efficiency, increasing the continuity, science and reliability of observation data, satisfying the complex changeable wind erosion observation requirements becomes a major task in relevant studies. This paper introduces and analyzes the automatic sand sampler that exist problems in the shock at the weighing sensor because of the strong wind oscillation, which affect the accuracy of the test data, high efficiency separation of sand in sand collection instrument. Proposed a diversion gas hedging method and multilevel expansion combination in order to reduce the airflow velocity in sand sampler. Combining the theories, simulation with experiments and base on the design of the initial sand separator with the principle of shunt hedging decreasing velocity, study on the shunt-hedging and multi-stage expansion combined automatic sand sampler with its flow field characteristics. Build the physical model of sand separator. Analysis of the relationship between the characteristics of airflow decreasing velocity, gas-solid separation and flow field characteristics. explore the main reason of affecting sand collecting efficiency. Reveal the deceleration mechanism of shunt-hedging and multi-stage expansion combined. Designed the shunt-hedging and multi-stage expansion combined automatic sand sampler of single channel data acquisition and testing the performances of sand collection, which provides theory and technology for the development of sand sampler with multi-channel data acquisition and higher sampler efficiency. The major study conclusions are as follows:(1) By using shunt-hedging principle of aiflow, design the key component of sand sampler-an initial sand separator. Test shows, deceleration amplitude is 86.42% of desilting mouth airflow,can slow desilting mouth airflow disturbance on the weighing sensor set under the sandbox; deceleration amplitude is 86.42% of exhaust pipe airflow,can collect soil particles which size is larger than 0.032mm; equal dynamic of inlet is 92.03%, basically satisfy equal dynamic requirement; average collection efficiency is 89.6% when wind speed is 9-18m/s.(2) According to decreasing velocity theory of expanding pipeline, propose a decreasing velocity method of shunt-hedging and multi-stage expansion combined, design a modified sand separator. Test shows, deceleration amplitude is 93.45% of desilting mouth airflow, deceleration amplitude is 89.98% of exhaust pipe airflow,can collect soil particles that their size is larger than 0.024mm; equal dynamic of inlet is 94.74%; average sand collection efficiency is 91.25%.(3) A large number of pulsating flow distributes in the turbulent kinetic energy field, pulsating flow extracts more easily dissipated energy from the time-average flow, is the main component of airflow energy loss. Mass energy loss and greatly reducing velocity of airflow attribute to formation of the turbulent kinetic energy field in the modified sand separator.(4) When wind speed, soil particle size distribution, acquisition time, etc. are constant, to modified sand separator with high gas-solid separation efficiency, to further improve collection efficiency, the key is to improve sampling efficiency of the inlet.(5) Shunt-hedging and multi-stage expansion combined automatic sand sampler has an anti-strong wind interference performance.can real time, continuous and long distance wireless acquire data, starting wind speed of free rotation is 4.23m/s, average sand collection efficiency is 90.42%,power supply ability of data automatic collection and wireless transmission system is up to 31 hours or more, signal transmission distance is 208.51m in the a barrier-free environment, can satisfy the demand of automatic measurement of soil erosion.