Numerical Simulation And Experimental Research On Detecting Vortex Frequency Of Vortex Flowmeter Based On Differential Pressure Principle

The flow measurement accounts for a large share of many process measurements in the industry, such as thermal engineering, chemical engineering and metallurgy. It is one of the greatest difficulties in process measurement technology. The dissertation is focusing on the detection of vortex frequency, which is the key technical problem of vortex flowmeter, a sort of promising and rapidly developing flowmeter.In order to solve some key problems of vortex flowmeter and to detect vortex frequency more accurately with stronger anti-disturbance, a new method for vortex frequency detection has been put forward by the author. By this method, the vortex frequency of vortex flowmeter is obtained by detecting frequency of differential pressure near duct wall downstream bluff body.Based on this idea, the combinative technique of theoretical analysis, numerical simulation and experimental verification is adopted. In the dissertation, detecting vortex frequency of vortex flowmeter based on differential principle is the main research object, Computational Fluid Dynamics(CFD) software FLUENT is used as auxiliary tool, and at last the method is realized by experiments. The main contribution and results are as follows:1) By reading home and foreign relevant literature extensively, the development process, measurement principle, configuration, merits and drawbacks of vortex flowmeter were summarized; its present status and progress tendency were generalized.2) The commonly used vortex frequency detection methods were commented. To overcome shortcomings of existing methods, a newmethod has been put forward. By this method, the vortex frequency of vortex flowmeter is obtained by detecting frequency of differential pressure near duct wall downstream bluff body. Its feasibility was theoretically analyzed and some proposals were brought forward to solve its technical difficulties.3) According to the characteristics of vortex yielding and shedding, a numerical simulation model for flow field in vortex flowmeter was established. Flow in vortex flowmeter was simulated with FLUENT, and static pressure on some given points near duct wall was monitored, analyzed and compared.4) On the basis of numerical simulation results, experiments were separately carried out using two different types of fluid, air and water. The results show that vortex frequency can be properly detected by duct-wall differential pressure method, and the errors are all less than the permissible error of the vortex flowmeter. Some efforts were also made to compare the performances of static pressure at different sampling positions, and it reveals that the better result is achieved by the sampling position near the against-flow face of bluff body.