AN INVESTIGATION OF COMPRESSIBLE FLOW THROUGH BUTTERFLY VALVES

An experimental investigation was conducted to study the compressible flow through butterfly valves. Two- and three-dimensional models were used during the course of this investigation. Two-dimensional scale butterfly valve models have been used to identify the characteristics of the compressible flowfield and the corresponding performance characteristics of the models. One of the two-dimensional models, a flat plate model, is a streamwise midplane cross-section of the three-dimensional model which is a geometrically similar scale model of a commercially available butterfly valve. The second two-dimensional model is a biconvex circular arc profile, a simple profile formed by the intersection of two identical circular arcs. The circular arc profile was chosen for its simple shape and because it is a common airfoil profile that has been extensively investigated in a transonic free stream flow. The two-dimensional models were included to facilitate flow visualization techniques and simplify instrumentation. The overall operating characteristics of these valves have been determined, and in the case of the flat plate valve disk, have been compared to the characteristics of the three-dimensional prototype. These models were operated over a wide range of valve disk angles and pressure conditions. This investigation included an extensive effort to identify the particular flowfield phenomena associated with butterfly valves. These experiments included Schlieren visualization of the flowfield, surface flow visualization on the valve surfaces, and detailed static pressure measurements on all of the disk and test section surfaces. These experiments were undertaken with the understanding that the two-dimensional experiments would not identically reproduce the flowfield of the three-dimensional prototype, but that they could identify the general fluid dynamic mechanisms related to the operating characteristics of butterfly valves. Several important characteristics are identified which contribute to both the operation and stability of butterfly valves.