The propagation of turbulence produced by a stenosis

Abstract

Model experiments to determine the downstream extent of turbulence produced by single flow pulses through a stenosis are reported. The reasons for changes in the shape of the velocity waveform with distance from the stenosis were also studied by simultaneous flow visualization and point velocity measurements. It was shown that turbulence propagated with the fluid particles that had passed through the stenosis during the pulse. Therefore the extent of turbulence beyond the stenosis ( z t ) could be determined by a flow visualisation technique. The jet produced by the constriction results in some fluid particles being propagated much further downstream than would occur in an unobstructed tube flow. The data show that for very small stroke volumes the flow behaves like a free jet and z t depends only upon stenosis diameter ( d) and stroke volume ( V) and is independent of the downstream tube diameter ( D). For larger V, z t depends upon all three variables and can be expressed by the relationship z t D = f( d D ) + 1.65( V D 3 ≥ 1.5 .