Control of an axisymmetric jet using a passive ring

Abstract

This study examines the development of an axisymmetric jet, which is disturbed by placing a thin wire ring axisymmetrically in the mixing layer close to the nozzle exit (0.1⩽ x/ D⩽0.5). Mixing layer development up to x/ D=5 is examined in detail using X-hotwire measurements, whereas far field development up to x/ D=30 is examined using single hotwire measurements on the jet axis. The introduction of the ring in the mixing layer results in a significant reduction in both the mixing layer growth rate and jet spread rate. The turbulence level in the mixing layer is substantially reduced for both axial and radial fluctuations (≈20% and 15% respectively). In addition to these reductions, the normalised distributions of mean velocity, axial and radial velocity fluctuations as well as the skewness and flatness factor of these fluctuations in the mixing layer all exhibit improved similarity. Variations of the jet Reynolds number (and thus the wire Reynolds number of the ring) and the axial location of the ring yield nearly identical changes to the characteristics of jet mixing layer. Increasing jet Reynolds number reduces the effect of the ring in the region 5< x/ D<30.