Study On Effect Mechanism And Compensation Methods Of Temperature Gradient In Cryogenic Balance

Cryogenic balance is a force sensor in wind tunnel test,which directly determines the accuracy of the test.Under the condition of cryogenic wind tunnel operation,the airflow temperature is not only very low,but also the range of variation is very large,which will lead to the temperature gradient on the balance and affect the accuracy of the balance measurement.The influence of temperature gradient on the axial force element of the balance is the greatest and the most difficult to correct,and the existing compensation method of temperature gradient is not ideal.Thus this paper refers to the relevant data of the foreign cryogenic wind tunnel tests,and adopts the analogy analysis and simulation method to study the software compensation method of the balance axial force measurement component temperature gradient.The main research contents are as follows:(1)The influence of temperature gradient on the measurement of axial force element of balance is studied.According to the balance structure form and measurement principle,the mathematical model expression of output strain of axial force element is established,and the influence of temperature gradient on measurement is analyzed theoretically.(2)The simulation of the effect of temperature gradient on the strain output of the balance axial force measuring element is carried out.The analysis of the effect of the temperature gradient of the balance on the thermal strain of the axial force element is simulated in ANSYS software.Then,a simplified wind tunnel balance model is established,and the flow of the fluid-thermal-solid coupling simulation of the balance is introduced.(3)Optimization of temperature sensors' layout strategy,by which the identification of key temperature measuring points on balance is realized: According to the temperature data obtained from simulation and the output error under different temperature gradients,the key temperature measurement points of balance temperature sensor are identified by using the improved temperature variable grouping optimization method and the fuzzy C-means clustering method based on subtraction clustering optimization,and the optimal temperature variable combination for modeling is selected to determine the layout strategy of temperature sensors.The results finally reduce the number of temperature sensors from 24 to 4,which optimized the layout strategy and reduced the complexity of the model under the premise of ensuring accuracy.(4)The method of temperature gradient error compensation for balance axial force element based on different algorithms is studied: Based on optimized temperature variable data and temperature gradient error output data,using BPNN,DFNN and DBN,the temperature gradient error compensation model of cryogenic balance is established and assessed.Then the compensation method is verified and results show that the model compensation effect based on the subtraction clustering optimization FCM algorithm combined with the deep confidence network is optimal,and the error variation range can be reduced from ±22.33 ?VV/ to ±2.06 ?VV/,and the proposed method has good generalization ability.