The flow around solid bodies involves small density changes due to the compressibility of the air even with small Mach number. Since these small density fluctuations cannot be predicted by the incompressible method, the use of the weak compressibility method is proposed. The flow around a cylinder was simulated using the weak compressibility method and the incompressible method. The results obtained by the weak compressibility and the incompressible methods were compared. It was confirmed that the weak compressible method is capable to simulate the flow with low Mach number and take in account the density changes. The use of the weak compressibility method in this case, clarified the relation between the density fluctuation due to complex phenomena such as turbulence transition or separation.
