Stereo‐PIV experiments and large eddy simulations of flow fields in stirred tanks with Rushton and curved‐Blade turbines

Abstract

The flow characteristics in pilot-scale stirred tanks with Rushton and curved-blade turbines were investigated by using stereoscopic particle image velocimetry (SPIV) experiments and large eddy simulation (LES) methods. The velocity and turbulent kinetic energy (TKE) in the impeller discharge regions were carefully resolved with a high resolution SPIV system, and the detailed phase-resolved velocity and TKE profiles were used to validate the LES results. The effects of Reynolds number and blade shape on the flow characteristics were discussed. The LES results of velocity, TKE, and the evolution of trailing vortices were compared with the SPIV experimental data, and good agreement was obtained at various phase angles. The effects of subgrid scale model and hybrid grid with different mesh resolutions on the LES results were investigated. LES is a computationally affordable method for the accurate predictions of the complex flow fields in pilot-scale stirred tanks is presented.

Transitional flow in a Rushton turbine stirred tank

“…Camera B was placed such that it satisfied the Scheimpflug condition, which requires the measurement, image, and lens principal planes to intersect at a common point. 6 The optical axis of the front lens of Camera B was at an angle of 50 o with the measurement plane; the optical axis of the lens of Camera A was at 90 o . Therefore the offset half-angle between the two axes of both cameras was at 20° in this work.…”

“…Time-averaged velocity fields of stirred tank flow at high Reynolds numbers show Reynolds-independent behavior: average velocities and velocity fluctuation levels (quantified by root-mean-square values of the fluctuations) are to a good approximation independent of the Reynolds number when scaled with an appropriate macroscopic velocity scale (usually this is taken as the impeller tip speed v tip ND π = ). 3,6 One objective of our research is to investigate below what Reynolds number the average flow characteristics cease to be Reynolds independent.…”

“…This is a de-facto standard stirred tank configuration that has been the subject of many experimental as well as computational research studies. [6][7][8][9] Over the years, the experimental work has moved towards non-intrusive flow measurements that are able to probe local liquid velocities. In that respect, research on stirred tank flows has benefitted much from the availability of PIV instruments.…”

“…This Stereoscopic PIV (SPIV) approach thus allows for estimating the turbulent kinetic energy (TKE) and the way it is distributed in a plane. Only few studies have used SPIV in turbulent mixing tanks: it has been employed to investigate the flow induced by a Rushton turbine 6,12 and by a sawtooth impeller. 13 It has -as of yet -not been used for transitional flow in mixing tanks.…”

Dynamic delayed detached eddy simulation of a multi‐inlet vortex reactor

“…Large eddy simulation (LES) is usually able to produce satisfactory results for the mean velocity and turbulent structure for turbulent swirling flow. [11][12][13] Cheng et al and Bensaid et al have used LES to simulate the flow in the microscale MIVR. 14,15 However, LES becomes very expensive when simulating the wall-bounded flow in the MIVR as the Reynolds number increases greatly in the scaled-up reactor.…”