Summary
This study presents the development of a numerical model, using the Volume of Fluid Computational Fluid Dynamics method, to characterise the flow behaviour of Newtonian and non-Newtonian formulations in the NasaDoseTM device; Bespak’s proprietary unit dose nasal spray device. The two formulations studied were water and a 50% w/v aqueous polyethylene glycol 4000 (PEG) solution. From the simulations, it was observed that both formulations formed an air-core at the centre of the nozzle geometry, which is crucial for atomisation in swirl nozzles, however, the time taken for this air-core to start forming differed between the two formulations, ~0.007 s for water and ~0.014 s for PEG. As expected, at the nozzle, velocity of water (~70 m/s) was higher than PEG (~50 m/s). For both formulations, the strain rates were highest in the atomisation nozzle and at the liquid-air interface, due to the high velocity and vorticity observed in these regions. The velocity at needle entry was approximately 7 m/s for both formulations, as a result of setting the inlet velocity of 0.131 m/s for both simulations. Consequently, a greater pressure gradient was generated due to the higher resistance to flow of PEG, under an inlet velocity of 0.131 m/s. Future work will involve simulation of a variable inlet velocity reflecting realistic clinical use.