  Purpose: Computational Fluid Dynamics (CFD) simulations are performed to
investigate the impact of adding a grid to a two-inlet dry powder inhaler
(DPI). The purpose of the paper is to show the importance of the correct choice
of closure model and modeling approach, as well as to perform validation
against particle dispersion data obtained from in-vitro studies and flow
velocity data obtained from particle image velocimetry (PIV) experiments.
Methods: CFD simulations are performed using the Ansys Fluent 2020R1 software
package. Two RANS turbulence models (realisable $k - \epsilon$ and $k - \omega$
SST) and the Stress Blended Eddy Simulation (SBES) models are considered.
Lagrangian particle tracking for both carrier and fine particles is also
performed. Results: Excellent comparison with the PIV data is found for the
SBES approach and the particle tracking data are consistent with the dispersion
results, given the simplicity of the assumptions made. Conclusions: This work
shows the importance of selecting the correct turbulence modelling approach and
boundary conditions to obtain good agreement with PIV data for the flow-field
exiting the device. With this validated, the model can be used with much higher
confidence to explore the fluid and particle dynamics within the device.
