| High-altitude latex balloon,as a kind of near space vehicle,has the function of exploring near space and carrying experimental platforms.With the continuous exploration of near space,its application scenarios are becoming more and more extensive,playing an important role in weather detection,emergency rescue and high-altitude reconnaissance missions.Traditional single-layer latex balloons explode after a certain level of expansion in the air to end the detection work,how to make the high-altitude balloon to maintain a long time flat drift is a key concern in this field.Therefore,this topic takes the long-time flat drifting device of high-altitude latex balloon as the research object,combines its space environment characteristics,uses the simulation method to optimize the design of high-altitude latex balloon exhausting and ballast releasing device,and carries out the cryogenic experiment of ballast releasing device to verify the simulation reliability.The main research contents and results of this paper are as follows:(1)The high-altitude balloon exhausting device was designed,and the exhaust valve structure was optimized.Using the high-altitude atmospheric model and the atmospheric experimental data in the Huaihua area of Hunan Province,the balloon exhaust gas flow state was calculated to determine the turbulent flow.On this basis,the simulation results of the exhaust flow characteristics of the ball valve and the butterfly valve at high altitude were compared using the computational fluid dynamics method,i.e.,the exhaust valve response speed and adjustment range.The results show that the butterfly valve has 18.9% faster response speed and 11.25% wider adjustment range than the ball valve,which identifies the butterfly valve as the exhaust valve of the high-altitude latex balloon.In order to reduce the airflow fluctuation near the exhaust valve,the steady-state performance of the exhaust valve airflow under three shaft diameter ratios(0.1,0.2 and 0.3)of the butterfly valve was simulated and calculated.The velocity fluctuation of the butterfly valve is smaller and the flow is more stable when the shaft diameter ratio Z=0.2.The maximum exhaust velocity of the butterfly valve was determined to be0.201g/s at 150 Pa differential pressure and 100% opening.(2)Optimized the design of the storage disk of the high-altitude latex balloon ballast releasing mechanism.According to the low-temperature working environment of high-altitude latex balloon,a simulated experimental environment for the measurement of contact parameters of loaded particles was built,and the contact parameters between nylon spherical particles and polycarbonate at-40℃ were measured for the simulation design calculation of high-altitude balloon ballast releasing mechanism.Discrete element method simulation was used to study the leakage releasing rate of the storage disk for three kinds of storage tanks,namely,triangular,rectangular and semi-circular,for the structural optimization of the storage tray.In the same releasing time of35 s,the calculation results show that the releasing leakage rate of the triangular storage tank is the lowest among the three storage tanks.In the case of 6.28 rad/s,the highest releasing speed of the triangle-shaped storage tank is3.58 g/s,and its leakage rate is 20% and 44.3% lower than that of the semicircular and rectangular storage tanks respectively,which is more suitable to be selected as the storage tank of the high-altitude latex balloon ballast releasing device.(3)The optimally designed ballast releasing mechanism was fabricated,and ground ballast releasing and missed throwing rate experiments simulating the high-altitude low-temperature environment were conducted.The mechanical parts of the ballast releasing structure were prepared by a combination of 3D printing and laser machining.The experimental temperature was controlled in the range of-25～20℃ and the rotation speed of the storage tray was 1.57rad/s.The results showed that the corresponding ballast releasing volume was 677.04～964.6g and the leakage rate was within5.8% in the temperature difference range of 20.1～29.4℃.This experimental result verifies the validity of the discrete element simulation calculation,the validity of the optimized designed ballast releasing mechanism and the reliability of the operation.(4)Based on the optimized design of the exhaust valve and the ballast releasing mechanism,a computational model of the long-time flat drift trajectory of the high-altitude latex balloon exhaust and ballast releasing was established.Using the summer atmospheric data of Huaihua,Hunan,China,as the atmospheric environment model,the trajectories of the high-altitude balloon exhausting and ballast releasing cases were calculated.The results show that,compared with the traditional high-altitude latex balloon without exhaust and ballast releasing mechanism,the long-time flat drift control device developed in this study can effectively keep the trajectory of high-altitude latex balloon in the range of 23～25km,and the flat drift time can reach 78.7h(3.3 days),and three exhausts and three ballast released were performed respectively during the whole flat drift process,with a total of285.42 g of gas exhausted,accounting for 22.3% of the balloon ground inflation,throwing out ballast nylon granules 2380 g,throwing out particles accounted for 95.2% of the total weight of ballast particles.Among them,the first exhaust volume was 5.14% larger than the last two exhaust volumes,24.11%,and the first releasing was 8.33% larger than the last two releasing. |
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