Research On A Flow Measurement Method Based On PVDF

The determination of fluid flow velocity is not only of great significance in the scientific research of fluid properties,but also plays a key role in practical applications such as the measurement of speed of navigating bodies and hydrological monitoring.Currently,the most widely used flow velocity measurement technologies on the market are mainly impeller flow meters and Doppler velocimeters,but both have shortcomings.The impeller flowmeter itself uses a propeller structure,which is complicated to install and affects the flow state of the fluid.After long-term use,it is likely to cause wear of the mechanical structure,which has a great impact on measurement accuracy.The Doppler velocimeter has the disadvantages of large volume,high price,and the measurement results are more easily affected by impurities in water.In addition,the Pitot tube used for aircraft speed measurement will change the fluid motion structure.The hot wire anemometer used for standard flow velocity calibration can only be used in the air.Therefore,there is still much room for improvement in the field of flow velocity measurement.As the fluid flows on the plate structure,turbulent pressure pulsations are created on its surface.If a PVDF film is used to make a piezoelectric sensor,the flow velocity can be measured by detecting pressure pulsations at different flow velocities.Thanks to the high sensitivity of the PVDF piezoelectric film and its simple mechanical structure(the PVDF film can be attached to the wall when in use),this method can avoid the shortcomings of common flow velocity measurement technologies on the market.While measuring with high accuracy,it has less interference with the motion state of the flow field itself.It can be applied to the determination of wind / water tunnel flow velocity,aircraft airspeed estimation,ship speed measurement,and carrier deck wind field measurement.It has high practical value.This paper first conducts theoretical research.The physical properties of PVDF thin films are studied,the piezoelectric characteristics and sensing principles of PVDF are analyzed;the turbulent boundary layer is studied,and the role of turbulent pulsating pressure is analyzed;the phenomenon of noise interference may be mixed into the PVDF sensor measurement process so the signal processing method of removing noise interference is studied.Secondly,the simulation work of turbulent boundary layer is carried out in this paper.The principle of fluid simulation is studied,and the feasibility of turbulent boundary layer simulation is analyzed.The numerical composition method is used to analyze and discuss the relationship between the composition and magnitude of pressure turbulence in the turbulent boundary layer.For the air and underwater environments,the grids were drawn and the steady-state and transient flow fields were simulated;the turbulent pressure fluctuations obtained from the simulation was extracted,and the relationship of the power spectrum and the flow velocity verifies the correctness of the theoretical part.Finally,a flow velocity measurement experiment based on PVDF was performed in this paper.The self-made PVDF piezoelectric sensor was used to measure the electrical output at different flow velocities,and the relationship between the power spectrum of the voltage signal and the flow velocity was summarized.The fitted relational formula was obtained to verify the correctness of the theoretical and simulation parts.An error analysis was performed to verify the feasibility of the flow velocity measurement method.Experimental results show that flow velocity measurement can be achieved by the PVDF-based flow velocity measurement method.