Design And Fabrication Of High Temperature MEMS Surface Fence For Wall Shear Stress Measurement

Knowledge of accurate wall shear stress is very important for understanding boundarly-layer flow and skin-friction.Nowadays,a variety of MEMS shear stress sensors have been proposed.However,the vast majority of those sensors can not be used in high temperature environment due to materials and/or measuring principles.It is of great scientific value and engineering significance to study the high-temperature MEMS surface fence.In the design and fabrication process,the structure optimization and the orthogonal experimental design are used to determine the sensing element structure of the sensor.The properties of the heavily-doped polysilicon material are investigated,and the parameters of the ion implantation process for the 100 nm Ultra-shallow junction are determined.Through the study of the overall manufacturing technology of the MEMS surface fence,in conjuction with the special packaging design,the high-temperature shear stress sensor are fabricated.In calibration and testing,the high-temperature characteristic testing system is presented,and the upper limite operating temperature of the sensor is determined to be 400?.The wall shear stress sensors are calibrated against a Preston tube at wind tunnel.A dynamic calibration technique based on Stokes layer excitation is presented to estimate the frequency response function(FRF)of the MEMS surface fence.Compared with the previous researches in the relevant field(the high-temperature bulky friction balance),a tenfold promotion in response frequency is achieved.A MEMS dual-fences gauge is developed to measure simultaneously the magnitude and direction of wall shear stress in wind tunnel under two-dimensional turbulent boundary layer.The packaged sensor is used to examine the development of the transient flow of the scramjet ignition process,and the results show that the sensor is able to detect the transient flow conditions of the scramjet ignition process including shock impact,flow correction,steady state,and hydrogen off.The significant contribution or innovation of this study consists in the following.(1)Fabrication of the high-temperature MEMS surface fence.Investigation of high temperature resistance including heat-resistant mechanism and process,in conjunction with high temperature packaging design,enable the sensor to be used in environment up to 400 ?.(2)The wall shear stress measurement technology for high-enthalpy scramjet flow.The theoretical method of wall shear stress evaluation which is based on the Van-Driest method is proposed,and the method of shear stress evaluation is proved by the example data of the literature.Finally,the MEMS surface fence is applied in the scramjet flow tests,and for the first time,the wall shear stress measurement of transient combustion flow field has been realized.(3)Directional MEMS dual-fences gauges technology.To investigate the influence of separation distance of dual-fences on the flow field disturbance,the modeling and flow simulation optimization is carried out using Gambit and Fluent,and the FE-analysis results are verified by comparing the output curve of the single fence and the dual-fences.Directional sensitivity of dual-fences is calibrated in a wind tunnel and the results show that MEMS dual-fences are suitable for detecting not only the forward and reverse flow,but also the direction of wall shear stress.