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

Abstract

An experimental study on the flow pattern dynamics in a standard mixing vessel with radial baffles filled with water and induced by a pitched blade impeller pumping downward is presented. Investigation is mainly focused on detection and analysis of quasi-periodical or periodical low-frequency phenomenon connected with time-and length-scales considerably exceeding the blade passage frequency (hereinafter BPF) and common turbulent eddies. This phenomenon, which is expressed as large-scale mean-flow variations, is generally known as flow macro-instability (hereinafter MI). It could break-down just below the liquid surface, or it crashes to the liquid surface and causes its macro-swelling (hereinafter MS). Our investigation was based on classical two-dimensional (2D) particle image velocimetry (hereinafter PIV) measurement within 3 selected vertical planes in the vessel and subsequent