Oscillating residuals (convergence problem?)
 

Hi guys!
I'm new to the CFD-online forum and I've started working with ANSYS Fluent software 2 months ago.

I'm trying to simulate a sneeze/coughing from the mouth of a person (diameter = 5cm, velocity = 10 m/s or variable according to a sine function (UDF)) in an office (5m*3m*3m) with an open window with constant air flow (2 m/s) entering in the office and an open door on the opposite side of the office.
I'm using the Discrete Phase Model (Interaction with continuous phase, Unsteady particle tracking and physical models: two-way turbulence coupling, stochastic collision, coalescence and breakup) in order to simulate the presence of droplets in the air emitted from the mouth (water liquid and water vapor) with rosin-rammler-logarithmic diameter distribution and .
I applied the k-epsilon model (Realizable, Standard wall functions).

My big problem is that I don't know how obtain convergence because i've sinusoidal residuals (like in the picture) and where I'm wrong: maybe I've to refine mesh?

Thank for your help!:)