| Understanding how kinetic energy is dissipated in turbulent flows has been a great challenge for many years and would have important implications in many areas such as fundamental research, aeronautics or industry. We use Particle Image Velocimetry (PIV) to measure the instantaneous velocity field of a Von Karman flow at many points of a plane at the same time, down to scales of the order of 1mm. This scale is 10 to 100 times larger than the dissipative scale in large Reynolds number (Re) experiments. In order to study how energy is dissipated in such a flow, we first use a Large Eddy Simulation (LES) approximation to model the effects of the subgrid scales (SGS) in terms of the large scale velocity field. This procedure involves a free parameter that is calibrated using angular momentum balance. Then, we use our PIV measurements to estimate the local and global mean injected and dissipated power from their definitions in terms of velocity gradients, for several types of impellers, for various Reynolds numbers and for various flow topologies. These PIV estimates are then compared with direct mean injected power estimates, provided by torque monitoring at the impellers. The agreement between these two estimates depend on the flow topology. In symmetric situations, we capture 30 to 70% of the actual energy dissipation. However, our results become increasingly inaccurate as the shear layer responsible for most of the dissipation is approaching one of the impeller, where it cannot be resolved by our PIV set-up. |