I'm looking for a way to generalize and simlify polygon to remove "internal spikes" as ilustrated below. The violet in input and green expected poligon.
There's a few tools available for simplifying polygons:
Processing Toolbox > QGIS geoalgorithms > Vector geometry tools
Processing Toolbox > GRASS GIS 7 commands > Vector (v.*)
Plugins > Manage and Install Plugins