The work is devoted to experimental study of one-phase and two-phase swirling flow in a horizontal vortex chamber with a tangential swirler. Special attention is paid to an emergence of unsteady vortex structures. Formation of a precessing vortex core (PVC) in the nozzle has been detected in the case of one-phase flow. Linear dependence of the PVC precession frequency and quadratic dependence of the full pressure drop in the vortex chamber on the fluid flow rate were confirmed experimentally. In the case of two-phase flow a high-speed visualization allowed to reveal the presence of the secondary vortex structures in cylindrical region behind the zone of sudden expansion. Adding a gas phase into the flow leads to a sharp decline of the precession frequency and full pressure drop decrease in the vortex chamber. The frequency smoothly decreases with further increase of gas content and pressure drop changes insignificantly: slightly increases or decreases depending on the water flow rate. At the same time there is a coherent change of the flow’s integral characteristics at changing the flow rates of liquid and gas.