Variable density flows are basically those in which density variations cannot be neglected and hence the density is treated as a variable. This formidable change in density may be caused by either of three variables of the ideal gas equation (when dealing with gases) namely pressure, temperature and molar-mass. When pressure causes considerable change in density, the flow is no longer incompressible and they are dealt separately under compressible flows. But when density variation is caused by the other two aforementioned variables then the flow is still incompressible but the density will vary. Presence of varying density in governing equations poses a formidable challenge for numerical simulation as there is a very strong coupling between momentum and scalar transport equations. This work involves the development of three-dimensional Navier-Stokes solver to compute variable density incompressible flows on hybrid unstructured grids. The density variation due to temperature and species concentration has been considered. © Springer India 2017.