CFD MODELLING OF A CHOKE VALVE UNDER CRITICAL WORKING CONDITIONS

Choke valves are widely used in the oil&gas industry to control the fluid flowing in the system. Some of these valves rely on a "cage and sleeve" functioning, in which an outer, sliding sleeve controls the flow rate by overlapping the holes of an inner, fixed cage. The regulation characteristic of choke valves is typically quantified by the opening curve, which is the plot of the flow coefficient versus the valve opening. Experimental tests performed on a ???cage and sleeve??? choke valve revealed that the orientation of the holes of the cage affects significantly the flow coefficient. This work focuses on the worst situation encountered, in which an anomalous decreasing trend in the opening curve for large valve openings is accompanied by strong vibrations of the device. CFD simulations were run to provide a physical interpretation of this unexpected result. Due to the complexity of the flow field structure at the origin of this behavior particular attention was paid in properly defining the CFD model; the turbulence model and the differencing scheme for the convective fluxes were found to be the most significant parameters. The CFD runs allowed attributing the anomalous trend of the opening curve to the peculiar interactions of the jets within the cage. At last, a modification of the trim design is suggested for avoiding the malfunctioning of the valve and the abnormal vibrations.