Turbulent Shear Flow Experiments: Design of Natural Convection Rig and LDA Measurement in Swirling Jets

Licentiatavhandling, 2006

This work consist of two sections. In the first part, a facility has been installed and modified from an existing rig in order to measure velocity and temperature field of axisymmetric turbulent natural convection boundary layers. With using laser doppler anemometry and cold wire resistance thermometry. A vertical aluminum pipe, heated by circulating water, creates a boundary layer around its outer surface which at the upper region of its 4.5m height becomes turbulent with a high Grashof number (Gr > 10E11). A vertical tunnel confines the flow from ambient, and air enters uniformly into the tunnel from below by using a set of vanes after it passes through three rows of screen and an axisymmetric contraction to decrease the turbulence intensity of air. The air is collected at the top section of rig and carried to the tranquillity chamber. In the second part, incompressible swirling jets at different swirl numbers have been studied using the same experimental method as the first part. This experiment supplied the empirical data for a similarity study on the far-field of free jets with and without initial tangential velocity. The effects of different swirl numbers have been studied on the growth rate and velocity distribution of jet. The result shows the same self-similar solution for swirling and non-swirling axisymmetric jet. The tangential momentum displaces the virtual origin as soon as the swirl number exceeds S > 0.2.