Study On Some Key Techniques Of Open Channel Flow Measurement

In this paper, the limitation and shortage of the open channel flow measurement are pointed out based on the review of the flow measurement methods and velocity distribution in open channel. The law of the velocity distribution in regular open channel is studied by combining measurement results with numerical simulation, and empirical equations of velocity distribution in regular open channel are presented for the flow measurement by 'velocity-water level method'.In order to study the velocity distribution in open channel, a 3-D turbulent numerical model is established firstly. Reynolds-averaging N-S equations are closed by renormalization group, RNG, k-ε model. The fields of pressure and velocity are solved by SIMPLE arithmetic. Considering the influence of the air on the velocity of flow, Volume Of Fluids (VOF) method is used to track the free surface. The donor-accepter method is used to solve the governing equations of fluid volume function. Finally, the comparison between the computed values and the measured values is made, and it is shown from the comparison results that the numerical simulation has got good results and that the model presented in the paper is reasonable. So simulations by use of the model can be used for analyzing some law of open channel flow.Being convinced of the reliability of the model presented above, the simulation of flow in narrow and deep open channel combined by different bed slope, different roughness and different section form are performed. Analyzing the computed results, the primary factor of affecting the velocity distribution on vertical and transect direction in open channel is obtained, and some velocity distribution empiricalrelationships between relative velocity u/V and relative depth y/H are established.Logarithmic function is used to describe the velocity distribution on vertical direction in the lower part and parabolic function is used to describe the velocity distribution onvertical direction in the upper region, as well as function is used todescribe the velocity distribution on transect direction. Moreover, the study of the coefficient is practiced, and the relationship between coefficient and correlative factor is obtained. Finally, the measured results are given to demonstrate the efficiency of the presented formula and the high precision.Finally, the presented empirical formula are applied to the 'velocity-water level method' flow measurement with the computed results in good coincidence with the measured results. So the 'velocity-water level method' flow measurement on the basis of the empirical formula describing velocity distribution in this paper has the precision required in water project.