Research On Calibration Method Of Spherical Multi-Hole Probe In Middle Atmosphere Three-Dimensional Flow Field

As an important part of the earth’s atmosphere,the middle atmosphere not only affects the spacecraft flying in it,but also the dynamics of the middle atmosphere plays an important role in the transportation of the upper and lower atmospheres and global circulation.Therefore,it is essential to monitor three-dimensional flow fields of the middle atmosphere,but there is still a lack of in-situ measurements for three-dimensional flow fields of the middle atmosphere.The Multi-hole probe measurement system,as a detection instrument with simple structure and strong environmental adaptability among the three-dimensional flow field measurement instruments,is the first choice for in-situ measurement of the three-dimensional flow field in the middle atmosphere.In order to improve the calibration efficiency of the Multi-hole probe,the calibration method of the spherical Multi-hole probe was studied to achieve the purpose of shortening the calibration process of the Multi-hole probe.Firstly,a comparative analysis of various probes of different shapes was carried out,and by comparing their advantages and disadvantages,the hemispherical 7-hole probe was finally selected as the research object.By studying the distribution of the pressure coefficient on the surface of the spherical probe,the probe heads with different opening methods,opening positions and opening sizes were simulated by numerical simulation.The extreme difference and significance test of the pressure in the hole were analyzed to determine the optimal hemispherical 7-hole probe head structure is presented.Secondly,the pressure-velocity parameterized equation based on the flow around the sphere is derived.Based on Bernoulli’s principle,the pressure distribution on the sphere when the fluid flows around the sphere,and the pressure-velocity parametric equation directly related to the 7 hole pressure and the incoming velocity is established.The ANSYS Fluent was used to simulate the situation of the probe in the middle atmosphere for numerical calibration,and the parameter equation coefficients were determined.After completing the numerical calibration,select a point at different speeds and use a parametric equation to inverse the flow field.The results show that the error is in line with the expectation,indicating the feasibility of the inversion of the flow field by the pressure velocity parametric equation.Thirdly,the experiment is carried out in a low-speed straight open wind tunnel.A set of calibration stand for wind tunnel testing was designed to adjust the probe to any angle relative to the incoming flow,and the pressure was measured with a MEMS micro-pressure sensor.The hemispherical 7-hole probe was calibrated at four different speeds,and a calibration data set was established to calibrate the probe.The calibration results are compared with the numerical simulation results,and the two results are in good agreement.Finally,an experiment of flow around a cylinder was carried out in the wind tunnel.The periodic vortex is generated by the flow around the cylinder,and the generated periodic vortex is measured.By analyzing the frequency spectrum of the pressure measured by the seven-hole probe,the period and size of the measured vortex are obtained,which verifies the feasibility of the hemispherical seven-hole probe for measuring vortices,and at the same time proves that the calibration experiment system can measure vortices in the experimental environment.