Torque validation of mixing impeller in herschel bulkley fluid
 

Hello guys, iam new to cfd fluent and ive been working on project were ive to select the right motor size for an agitation system. the impeller are just two flate plate paddles and the dimensions are: 200mm dia, 40mm width, 5mm thickness
The tank dimensions are: 300mm*300mm.
Iam using MRF method to simulate the impeller rotation. I refined the mesh at the impeller region to a good values with 129550 elements and 0.25 avg. skewness. The fluid iam simulating is food waste slurry which is shear thinning fluid with herschel bulkley behavior. I’d run the simulation with different rpm 20, 40, 60, 80, 100, 200, 300, 400,…, 900. The torque of impeller is required and i used the equations for calculating the power and reynolds number from the following paper:

https://doi.org/10.1002/cjce.21616

The power number for pseudoplastic fluids is acuired using the graph against reynold number as shown in the figure below
Attachment 91661

I made a manual graph of The calculated torque error vs reynold number which is shown below:

The error seems to be large when the reynold number is at the begging of the transition region which is between 10 and 10000.

How do i get accurate results? Is there a module to accurately capture the fluid behavior in the transitional region? Is this a software limitations so the error can be accepted? If so how should i describe this limitation and say that the error is acceptable for a presentation?