Investigation of Low-Frequency Phenomena within Flow Pattern in Standard Mixing Vessel Induced by Pitched Blade Impeller

An experimental study on the flow pattern dynamics in a standard mixing vessel with radial baffles filled water and induced by pitched blade impeller pumping downward is presented. Investigation mainly focused detection analysis of quasi-periodical or periodical low-frequency phenomenon connected time- length-scales considerably exceeding Blade Passage Frequency (hereinafter BPF) common turbulent eddies. This phenomenon, which expressed as large-scale mean-flow variations, generally known Macro-Instability MI). It could break-down just below liquid surface, it crashes to surface causes its Macro-Swelling MS). Our investigation was based classical two-dimensional (2D) Particle Image Velocimetry PIV) measurement within 3 selected vertical planes subsequent velocity field. The dominant frequencies evaluated points overall macro-flow behavior be shown. Identification substructures appeared performed using Oscillation Pattern Decomposition OPD) method. Observation patterns confirmed presence structures detected at identical pilot plant setup previous investigations MIs i.e., primary circulation loop strong discharge jet located lower segment ascending wall current baffle, very often. A further important contribution presented work both vicinity middle sector far from showing significant difference. Low-frequency (or quasi-periodical) investigated macro-structures qualitatively results quantified evaluation, noted below. frequency brings insight into supposed interconnections between adjacent structures. Detected different main plane near inclined reveal influence baffle local flow, especially upper part vessel. Quite appears tangentially front behind where wake revealed, indicating tangential flow. new findings represent better understanding physical phenomena process.