TUFLOW General Discussion: Difference between revisions

The graphs below explains the Herschel-Bulkley approach and it’s flexibility.

 

 

With a Newtonian fluid, the shear stress is linearly proportional to the shear rate.

 

For a non-Newtonian fluid, the shear stress varies non-linearly with shear rate, this is what is represented with the power law model in the graph above.

 

 

We then have Bingham plastics which have a linear shear stress to shear rate relationship but this time an offset which means there needs to be some force for the fluid to move, but then the shear stress varies linearly with shear rate.

 

 

The Heschel-Bulkley model takes aspects from both the Bingham Plastic Model and the Power Law Model resulting in the following.

 

 

It should be seen that where Ƭ0=0, the Herschel-Bulkley equation is the same as the power law model. If n is 1, then the Herschel-Bulkley equation is the same as the Bingham Plastic model. If Ƭ0=0 and n =1, then the Herschel-Bulkley equation is the same as the Newtonian fluid approach. By using the Herschel-Bulkley equation as a Newtonian model, it does allow you to define the viscosity coefficient for the fluid. In your case you’ll need to convert the viscosity from centiStokes to Pa S (if using an N value of 1). You can then define the fluid density using the <font color="blue"><tt>Density of Water</tt></font> command you mention.