# How can I calculate the Relative Reynolds Number in DPM?

Now I am working with a DPM case that are influenced by the magnetic field. I want to track the movements of particle in the flow field. I add the electromagnetic force by using the DPM_BODY_FORCE macro. Now the problem is that the particle movements are not so regular. Now I want to know how the Relative Reynolds Number is calculated during the calculation to analyze the phenomenon. I have read the formula given in the Theory Guide, but I dont know how the relative velocity between the particle and the flow field is calculated. Is the fluent uses the velocity in the current step or in the last step? And is there three Reynolds number in three direction or just one Reynolds number?

Thanks

Xin

## Answers

2,326Hello,

Here is the definition of Relative Reynolds Number (Fluent Theory Guide).

Since this definition is featuring as source terms in the equations, these are computed based on the velocities from the previous time-step. Please see the Pressure-Based Segregated & Coupled Solver algorithms for additional details.

Thanks.

Karthik