Numerical investigation of turbulence characteristics and upstream disturbance of flow through standard and multi-hole orifice flowmeters

In this research, the flow through the standard and improved multi-hole orifices of Shaaban, Singh and Huang is simulated numerically. The main objective is to study the turbulence characteristics of the downstream flow of the orifices, the discharge coefficient as the efficiency criterion of the orifices and the effect of disturbance of the upstream flow, due to putting an out of plane double elbow, on orifice performance and downstream flow characteristics. The three-dimensional steady, incompressible turbulent flow with a Reynolds number of 9200 is considered. The conservation equations are solved using finite volume method on hybrid meshes. The turbulence model employed in this research is the standard kappa-epsilon model. The simulation results indicate the gradual development of the turbulent kinetic energy and turbulent energy dissipation rate from the orifice plate to fully developed turbulent flow in the downstream of the standard orifice. However, for the multi-hole orifices, these characteristics are reduced at a higher rate with increasing the distance from orifice, and thus, unlike the standard orifice, it is possible to achieve a fully developed turbulent flow in a shorter downstream distance. In addition, all types of the improved orifices have the higher discharge coefficient with respect to the standard ones. Among them, Singh's model has the highest discharge coefficient. The numerical results indicate that for the ineffectiveness of the flow rate measurement from the upstream disturbance of the orifice, the straight pipe length between the source of disturbance and the orifice for the standard type should be at least 60 t greater than the pipe diameter. While this length is about 25 times greater than the diameter of the pipe for the multi-hole orifices. These three important advantages of the shorter length of the developing turbulent region, the higher discharge coefficient and the lower sensitivity to the upstream disturbances for the improved orifices compared to the standard type show an increase in the accuracy and efficiency of these new kinds of orifices while using them as the flowmeters.