چكيده به لاتين
The present study is a numerical model for prediction of turbine flowmeter performance, using the equation of motion based on torque balance theory. In this model, numerical simulations were carried out for a 2 inch diameter G65 and PN/ANSI 150 gas turbine flowmeter which was made by Vemmtec Company, in steady state, using Multiple Reference Frame (MRF) model and Standard k-ε turbulence model using Fluent software. In order to model torque balance equation and calculate angular velocity of rotor, a UDF (User Defined Function) code was created and was added to the software. In order to evaluate the model's accuracy, simulation results were compared with experimental data which was obtained from manufacturer of the meter. The difference between the simulation results and experimental data was 0.16%, approximately, which indicates the accuracy of the proposed model in simulating of turbine gas flowmeter performance. The results obtained from the simulation indicate that the velocity distribution asymmetry was more than 0.4 Qmax at the downstream of the meter, and because this phenomenon had no negative effect on flow measurement, the suitable length for the flow development for the downstream of meter was done using simulation at least 10 times the diameter of the pipe was proposed. Then, using the proposed model, the effect of operating pressure in three pressures (1, 4 and 10 bar on gas) on turbine meter performance were studied. The simulation results showed that the rotor angular velocity measurement error was 5% for 4 bar and 6% for 10 bar. In addition, according to the results of the distribution of flow parameters (velocity, turbulent kinetic energy and the turbulent dissipation rate) in a rotor, it was concluded that the increase in pressure does not affect the distribution of flow parameters, which reduces the quantitative parameters of these parameters. As a result, it can be seen that the effect of the pressure on increasing the driving force is considered. To compensate for the turbine flow measurement error, the mechanical frictional force is proportional to the increase of the driving force caused by the increase in pressure to the meter, which is done by adding various gears in the type and number of tooth is placed in the index of the meter. Therefore, using the proposed model, the capital cost of design and optimization of turbine flowmeters can be reduced.
