This communication focusses on the approximation problems that may arise when compressible flow solvers are applied in contexts close to the incompressible limit. The asymptotic behavior of the Roe flux difference splitting scheme is analysed together with its modification by the Turkel preconditionner when Mach number tends to zero. It is shown that Turkel preconditioning restores a correct asymptotic behavior of the pressure field while the original Roe scheme support pressure fluctuations an order of magnitude larger than the correct value. Iterative efficiency is also considered for the so-called tridiagonal or Defect Correction preconditioning. Robustness issues are then discussed by comparing Roe and HLLE splittings. Applications to unsteady flows are presented.
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