Effect of periodic aerodynamic pulsation on flow over a confined butterfly valve

An experimental investigation of the flowfield characteristics of a butterfly valve under periodic flow has been made. The results concern a valve at large angles corresponding to high area contraction ratios (K > 0.3). In steady flow, the results show that the flowfield within the valve is conditioned by the internal jet formed in the trailing edge fluid area. For very high area contraction ratios (K> 0.65), the equivalent diameter of that fluid area is the preponderant length scale of the how. In periodic how, an increase in the length scale of flow instabilities is observed. The reorganization length of the flow is, thus, shorter, producing a marked reduction in valve head-loss. This phenomen is maximum when the excitation frequency is close to the nominal instabilities frequency (found in steady flow).