Research Of Characteristics Of Transition Flow In Pipes

At present, saving energy and reducing pollutants become a national policy, so the measurement of energy becomes a basic technology working. The ultrasonic flowmeter is the main device for the measurement, and its accuracy is important to the energy measurement. But compared with the foreign made products, the technology and the measurement accuracy of homemade ultrasonic flowmeter are not adequate. The main reason is that the study of characteristics of transition flow is lack. Accordingly, it becomes an important task of the study of characteristics of transition flow in pipes to improve the measurement accuracy of ultrasonic flowmeter.The relationship of profile-linear average velocity is the main factor to influence the measurement accuracy of ultrasonic flowmeter, and it is defined to coefficient k. The traditional study has advanced the modified method to the relationship for the laminar flow and turbulent flow, but the study is rarely for the transition region. The traditional method is to regard the transition flow as the turbulent flow to obtain the relationship of the profile-linear average velocity, and this simplified method must lead to measurement errors when the water flow in the pipes is a transition flow. There are many conditions that would lead to the transition flows in industry application. So, it has a important theoretical significance and industrial application value to study the relationship of the profile-linear average velocity of transition region flow in pipes.In this paper, the methods of the numerical simulation and experiment with PIV are used to study the characteristics of the flow with Re=2000 to 20000 in pipes, and the relationship of the profile-linear average velocity of pipes is obtained. Based on the studies of pipes, the characteristics of two different structure ultrasonic flowmeters are also studied. The following researches have been done in this paper.The standard k-εmodel is used to calculate the flow field with Re=5400 in pipes. Compared with the experimental results of Westerwell, there is much error of the profile velocity used the model. Thus the LES model is used to simulate the flow field with the same Re number, and it is indicated that the flow field calculated by the LES model is matched with the experimental results. The flow fields with Re=5400,6000,7000,8000,9000,10000 in pipes are calculated by the LES model, and the relationships of profile-linear average velocity of transition flow are obtained via the results of LES model. The numerical simulation results show that there is 4.38% measurement error of the traditional method which regard the transition flow as the turbulent flow to obtain the relationship of the profile-linear average velocity.The laboratory table of PIV is established and hydraulic calculation shows that the flux of laboratory table is satisfied the experimental demands. The measurement errors of the PIV system is analyzed and the errors are reduced by the certain methods. The flow field with Re=2000 to 20000 in pipes are measured by the PIV system, the analysis of flow field shows that the range of PIV measurement full covered the transition region. The relationships of profile-linear average velocity with different incidence angle are studied, and the results shows that the incidence with 30°is better. The curve of relationship with Re number is provided, and it can be divided to four parts, and the fitted formulas of every part are also provided. The transmit paths with horizontal incidence are also studied. The relationships of profile-linear average velocity of 11 paths with horizontal incidence are measured, and the results show that three paths near the center of pipes are reasonable, and the curve of k with horizontal incidence is provided.In order to analyze the relationship of profile-linear average velocity with different basal meter, the circuit board of measuring flux of ultrasonic flowmeter is developed in this paper. The TDC-GP2 chip is used to measure the flux signal, and MSP430F417 chip producted by the TI corporation is used to control TDC-GP2 and calculate the flux.The ultrasonic flowmeter of U type reflected with bracket reflection device is studied by the method of experiment via the circuit board of TDC-GP2 and the laboratory table of flux measurement. The measurement flux is 0.045-0.909 m3/h, Re=1000-20000, and the relationship of average velocity is obtained. It is shown that the changing of k is approximately match to the pipes. Because of the influence of reflection device, the flow advanced developed to the transition region, and the region of 0.091—0.246m3/h is the most unstable region. The method of modified coefficient k of U type reflected is obtained via the relationship. The results of high temperature conditions show that this reflection device is influenced by the temperature, and the main reason is that the bracket is inflenced by the temperature to distortion, which lead to unstable measurement error.The ultrasonic flowmeter of U type reflected with stainless steel reflection device is studied. The method of modified coefficient k obtained by the bracket reflection device is adopted to modify the flux, and the measurement errors of experiment are small and stable, and it reaches the two level meter standard. The results of experiment show that the ultrasonic flowmeter with stainless steel reflection device is not influenced by the temperature.In this paper, the relationship of profile-linear average velocity of transition region is studied by the method of numerical simulation, and the law of coefficient k is provided; The PIV system is used to study the profile-linear average velocity relationship, and the empirical formulas are obtained; The ultrasonic flowmeters of DN20 with different reflection device are studied, and the law of relationship of profile-linear average velocity of transition region is obtained, and it can supply the theory of designing ultrasonic flowmeter.