| Vortex flowmeter is a kind of oscillator flowmeter developed from the end of 1960s. Under definite flow condition, some kinetic energy of the fluid transfers to flow oscillation and the oscillator frequency is proportional to the flow velocity. This novel velocity-type flowmeter has its advantages of high stabilization, low pressure loss and wide measurement range, which is widely used in chemical industry, petroleum, metallurgy, light industry, food industry and other flow industry. At low flow rate, the signal amplitude of the vortex flowmeter is very slim and many kinds of noises will add on it in application. So it is still a hot spot on how to widen the measurement range with high accuracy. It is meaningful to research the vortex character under different fluid conditions and create a new method to pick up the vortex signal in wide flow range.The main researches of this thesis are listed below:1. The thesis firstly introduces the principle of vortex flowmeter and its state of development. A series of theory related to the flowmeter is then cited, including the foundation of hydromechanics and the method of CFD simulation. The disadvantage of traditional methods based on time domain and frequency domain are also discussed. All the introduction and analysis above provide instructions to the following chapters, which also clarify the main research of this thesis: how to tracking the vortex signal at low flow rate to enhance the measure ratio.2. It is presented how to simulate the phenomenon of Karman Vortex Street when fluid passes the meter by CFD software. With the parameters measured on the product of generator and detector separating sensor, the relationship of the lift force on different parts of the sensor is clearly presented. The CFD simulation results validate the character of vortex output signal on the detector.3. Vortex flowmeter momentum relation, amplitude consistency relation and frequency-amplitude restriction are discussed in the thesis. Then the creative signal processing method based on momentum flow is put forward. According to the relationship of signal amplitude and its frequency, the module of non-linear filter is designed, which will ensure to exactly capture the real vortex pulsation even in low flow velocity with all kinds of noises. 4. The thesis then puts forward the two-channel signal processing method to realize the signal measurement over the whole flow range. With the flow volume increasing, the output of the amplifier will be saturated and momentum flow relation is no longer met. So it is necessary to combine one channel of traditional vortex signal processing method in high flow velocity with the other of momentum-flow signal processing method in low flow velocity to ensure the measurement accuracy in the whole range. Meanwhile the criterion of the channel shift is created in the thesis according to the signal character.5. The solution of the signal processing method is presented in the thesis. The hardware and software functions are introduced of the wide range flowmeter. The prototype is able to at last realize the flow measurement with the measure ratio of 1:40.6. Online Verification tests are done both in lab and in calibration field with this prototype of wide range flowmeter. The test results on meter error, repeatability and linearity are discussed in this thesis. Further, the system uncertainty is also taken into consideration to analyze the meter's capability.
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