Experimental Eulerian and Lagrangian investigations in simple turbulent flows

This thesis consists of three parts. The first part consists of a study of high-Reynolds number, homogeneous, isotropic turbulence in wind tunnels which has been strained via an axi-symmetric contraction. The effect of strain on the turbulence is studied by detailed hot-wire measurements. The results are compared with Rapid Distortion Theory (RDT). The return to isotropy of the strained turbulence is studied and compared with Rotta's linear theory. The effect of strain on intermittancy as well as the structure of turbulence is also studied. In the second part the experimental measurements of inertial particle Lagrangian accelerations are described. These are the first measurements of inertial particle accelerations in a well documented high-Reynolds number wind-tunnel flow. Using a high-speed camera which moves with the mean speed of the flow, inertial particle trajectories are obtained. The trajectories are analyzed to obtain the particle accelerations. The acceleration probability distribution functions (PDFs) are compared with those of recent computer simulations. The last part consists of an analysis of inertial particle motion in turbulent flows. A new model called the Vortex model is proposed and used to study the inertial particles in turbulent-like flows. Using this model, several mechanisms through which attenuation of inertial particle accelerations may occur in real turbulent flows are studied. We also compare the results of the Vortex model with those of the DNS simulations of Bec et al. [\textit{J. Fluid Mech} \textbf{550} (2006)]. The range of applicability and shortcomings of stochastic acceleration models for inertial particle modeling are also discussed. The results of this work have a wide range of applicability. The complex spectral dynamics associated with relatively simple straining flow and subsequent relaxation which is found in many engineering and natural flows is explored in detail. These results can be used to build better models for strained flows. Inertial particle accelerations are suspected to play major roles in determining rain drop formations, particle agglomeration in industrial flows, pollutant transport and other related phenomena. The modeling and experimental results will aid in developing more accurate models of inertial particle dynamics