Experimental and numerical characterization of turbulence in fluid flow

Abstract

This dissertation presents experimental measurements on a round free turbulent jet and numerical simulations on a flow past a surface mounted cylinder. The experimental measurements map the Reynolds stresses in a vertical round free jet. A 12 mm diameter nozzle with exit velocity of 8 m/s with corresponding Reynolds number of 6000 were used to determine the differences in mean velocity profiles, turbulence intensity profiles, and velocity spectra in the flow of a vertical round free jet at room conditions. Constant Temperature Anemometry (CTA) with 1D probe was used to measure the mean and fluctuating velocity components to obtain the Reynolds stress correlations. The results show that different mechanisms may have control in various types jet flows or in different regions of a jet flow. In free jet flows, the downstream region is dominated by turbulence structure whereas coherent eddy-structure can have a strong influence on the near field; particularly for low-Reynolds number jet flows. The present study is an attempt to review the current information on vertical round free turbulent jet flows. The influence of origin of the jet (initial conditions) and the boundary conditions on the jet flow structure is considered. The result depicts that the exit conditions of the jet play a very important role in the development of the jet in the near field but the far field flow remains independent of the exit conditions of the jet. The numerical solution is preform by using large eddy simulations (LES) for the flow around a surface mounted cylinder. Cylinder of height-to-diameter ratios of 2.5 with a thin boundary layer of the approach flow have been analyzed and compared to the available literature using StarCCM+. The detailed study presented confirms largely the flow behavior of the fluid flow comprehensively when the fluid interacts with a bluff (solid) body (cylinder). It also provides further insight and quantitative information on the mean flow, the turbulent fluctuations and the unsteady flow features. The mean-flow behavior is analyzed with the aid of streamlines and contour plots of mean-velocity and fluctuation components. The vortex shedding flow pattern past the cylinder is further analyzed for determining the Reynolds stresses. Alternating shedding is found to occur over the cylinder. The shedding is observed mainly near the ground where it is also mostly alternating but intermittently also symmetrical. The aim of the work is to characterize turbulence in a fluid flow in terms of Reynolds stresses.