TURBULENT-FLOW FIELD IN TANGENTIALLY INJECTED SWIRL FLOWS IN TUBES

The turbulent flow field in a tube has been experimentally studied when fluid is injected tangentially. The experiments were conducted by injecting air through injectors placed on the periphery of an 88.9 mm inside diameter and 1.5 m-long acrylic tube. Four injectors of 15.88-mm inside diameter and six injectors of 22.23-mm inside diameter were used in the two sets of experiments. Tangential to total momentum flux rate ratio of 7.84 and 2.67 respectively were obtained in the two sets of experiments. Using a single rotated straight hot wire and a single rotated slanted hot wire anemometer, profiles for mean velocities in the axial and tangential directions, as well as the Reynolds stresses were obtained. Axial velocity profile shows existence of a flow reversal region in the central portion of the tube and an increased axial velocity near the wall. Tangential velocity profiles have a local maximum, the location of which moves radially inwards with distance. Turbulence intensities are increased by swirl motion significantly due to the destabilizing distribution of angular momentum in the free vortex zone and the large shear stress near the boundary of the reversed flow. Reynolds stress data show an anisotropy in eddy viscosity. Turbulence energy and maximum axial velocity have been correlated with local swirl intensity.