Flows transporting particles are ubiquitous in natural processes (pyroclastic flow, formation of rain droplets in clouds) and industrial systems (combustion of fuel droplets in engine, industrial mixer, pollutants transport). In most practical situations, the carrier flow is turbulent. Due to the random and multi-scale nature of the turbulence structures and the various characteristics of the particles, the interactions between the flow and the particles are complex. In this thesis, we focus on highly seeded particle laden flows, when the couplings between the particles dynamics and the carrier flow are very strong. We investigate this situation in a turbulent von Kármán swirling flow, driven with a single disk rotating along a vertical axis and focus on addressing the following questions: how is the particle suspension affected by the turbulence and the mean flow, and how do particles modify the turbulence ?In a first stage, using optical diagnoses, we investigated weakly seeded flows with the aim to characterize the spatial distribution of re-suspended inertial particles on one hand and to explore the competition between suspension and sedimentation phenomena on the other hand. Then we studied the modification of turbulence intensity when increasing the volume fraction of particles from 0% to 20%. In highly seeded situations, the suspension becomes opaque and classical optical diagnostics cannot be used anymore. We have therefore developed and implemented indirect "multi-scale" measurements: (i) a global measurement of the mechanical power injected by the engine required to maintain the flow mean velocity (ii) a measurement of local pressure fluctuations to investigate the typical scales at which the flow is impacted by the particles. Through these measurements, we have demonstrated both, an effect of the effective density of the mixture on large scale and a significant redistribution of the fluctuations across scales, with non-trivial dependencies on particle diameter. These point towards a leading role of two important mechanisms related to a modified effective rheology of the turbulent suspension on one hand and to an inertial reinjection of energy at the scale of particles wake on the other hand. Finally, in order to confirm these trends, a first attempt to directly measure velocity fluctuations in highly seeded suspension by Laser Doppler Velocimetry (LDV) have been made using an optical index matched solution adapted between the fluid and the particles. This opens promising perspectives for future studies.