Laser diagnostics of the instability onset in the confined vortex flows

This paper focus is the application of optical methods of pulsating vortex flow diagnostics on the example of swirling flow instability in a cylinder with rotating lid and aspect ratio h = 3.3, 3.4. To obtain a complete picture of auto-generated pulsations development, long-term LDV measurements of the tangential velocity component were carried out with a continuous method of the Reynolds number variation from 2000 to 3500 over 8 hours (30,000 seconds). In the view of the smallness of the Reynolds number increase rate ΔRe / Δt = 0.05 s−1, this process can be considered as quasi-equilibrium. A comparison with the widely used discrete method of the Reynolds number variation is made, given range of the Reynolds numbers was studied with a step ΔRe = 50 for 20 minutes per point. It was found that at the same h, Re different vortex structures are formed depending on the Reynolds number variation method. In the case of discrete the Reynolds number variation, the development of pulsations may require up to 2000 rotating lid revolutions or 500 seconds, it should be considered conducting the experiments.