Development of control valve design tools utilizing computational fluid dynamics

A study using computational fluid dynamics (CFD) as a control valve design tool is undertaken. The study includes valves with linear characteristics and valves with equal percentage characteristics. In addition, the valve relative capacity factors range from 2.5 to 13. The three dimensional geometry of a control valve is modeled in two dimensions using the K-ε turbulence model in an incompressible flow field. The converged pressure field is used to calculate the valve Cv. These results are then compared to experimentally determined values and the manufacturer's published values. Other verification techniques include pressure and flow visualization. A three dimensional model is also attempted for comparison to the two dimensional model. Several conclusions are drawn from this study. One conclusion is that axisymmetric numerical models qualitatively predict the general shape of the characteristic curve and quantitatively predict the valve Cv in regions where the plug has not retracted past the plane of the seat. The accuracy of the two dimensional model depends on grid resolution and grid quality. Three dimensional models are both excessively complex and expensive in terms of time and resources, and therefore, are impractical as a design tool in situations where the geometry changes shape over its operating range. In addition, analytical studies have identified behavior at locations which may be identified with simplified fluid dynamics. The final conclusion is that loss mechanisms are identified that verify axisymmetric flow as the primary flow phenomenon.