Study On Fluid-structure Interaction And Mixing Performance Of Novel Perturbed Impeller In Pseudoplastic Fluid

Fluid mixing in the stirred tank mainly consist of three forms:macroscopic migration,local diffusion and molecular diffusion.Changing the blade structure optimize macroscopic migration form of fluid,which can improve macroscopic flow field structure and promote efficient fluid mixing.This method is frequently used by designers.As to N-6PBT impeller,it is based on the structure of 6PBT impeller,and the flexible piece is added to the tip of the blade.The structure enhances the local diffusion of fluid mixing through the vibration of the free end of flexible pieces without changing macroscopic migration form of fluid.Thus,fluid mixing is promoted in the stirred tank.Using ANSYS Workbench software,the dynamic characteristics and mixing performance for N-6PBT impeller were deeply studied through the bidirectional fluid-structure interaction?FSI?method.The main conclusions in this paper are summarized as follows:?1?The flow field numerical model of N-6PBT impeller was established by Fluent.The model was verified by the agitator power consumption experiment and the results showed the reliability of the numerical simulation method.The correctness that this paper had used power-law model were proved through rheological experiment and non-linear fitting.And the parameters of xanthan gum solution were obtained.?2?Compared with 6PBT impeller,the turbulent kinetic energy dissipation rate of the local flow field was obviously increased and the local diffusion behavior of the fluid was enhanced,which is beneficial to fluid mixing in the stirred tank.Fluid was subjected to greater force when N-6PBT impeller stirred the fluid.Furthermore,the stirring powers that the two impellers had was almost the same.Under different rotational speeds and rheological conditions,the dynamic characteristics of N-6PBT impeller were studied.With the increase of rotational speed,the local diffusion behavior of the fluid was enhanced,and the whole fluid velocity increased in the stirred tank.With increasing mass fraction of fluid,the rheological index decreased.The turbulent kinetic energy dissipation rate and fluid diffusion of the local flow field were weakened.And power consumption increased.In addition,N-6PBT impeller met the strength check criteria under various conditions.?3?Static modal analysis and prestressed modal analysis at 250 r·min^-1,350 r·min^-1,450 r·min^-1 and 550 r·min^-1 were carried out for N-6PBT impeller.The first eight natural frequencies and modes were obtained.The natural frequencies of each order varied slightly.For the vibration modes,the vibration of the blade was not obvious,and the vibration mainly occurs on the flexible piece.1-3 steps were bending modes,4-6 steps were torsional modes and 7-8 steps were compound modes that were wave-like.The results showed that the centrifugal force and fluid-structure coupling force had small influence on the modal parameters of N-6PBT impeller,and there was no obvious prestressing effect.?4?Compared with 6PBT impeller,the mixing performance of N-6PBT impeller was studied at the above four rotational speeds.It was found that the mixing efficiency of6PBT impeller was the highest when the rotation speed was 350 r·min^-1,and the mixing efficiency of N-6PBT impeller was the highest when the rotation speed was 450 r·min^-1.This is because that the phenomenon of the columnar reflux near the stirring shaft became obvious with the increase of the stirring speed,which was not conductive to fluid mixing.However,the mixing efficiency of N-6PBT impeller was higher than that of 6PBT impeller under different rotational speeds,indicating that N-6PBT impeller was more favorable to the efficient mixing of pseudoplastic fluid than 6PBT impeller.