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A note on versions:The version presented here may differ from the published version or from the version of record. If you wish to cite this item you are advised to consult the publisher's version. Please see the repository url above for details on accessing the published version and note that access may require a subscription. Abstract. In this article we consider the a posteriori error estimation and adaptive mesh refinement of discontinuous Galerkin finite element approximations of the bifurcation problem associated with the steady incompressible Navier-Stokes equations. Particular attention is given to the reliable error estimation of the critical Reynolds number at which a steady pitchfork or Hopf bifurcation occurs when the underlying physical system possesses reflectional or Z 2 symmetry. Here, computable a posteriori error bounds are derived based on employing the generalization of the standard DualWeighted-Residual approach, originally developed for the estimation of target functionals of the solution, to bifurcation problems. Numerical experiments highlighting the practical performance of the proposed a posteriori error indicator on adaptively refined computational meshes are presented.Key words. Incompressible flows, bifurcation problems, a posteriori error estimation, adaptivity, discontinuous Galerkin methods, Z 2 symmetry 1. Introduction. Due to the highly nonlinear governing equations and complex geometries involved, understanding fluid flow remains one of the fundamental engineering challenges today. Often it is impossible to obtain analytical solutions to problems and numerical methods must instead be exploited. Broadly speaking, there are two numerical approaches to understanding the Navier-Stokes equations: the first involves direct 'simulation' of the time dependent problem, while the second, less commonly used approach focuses on applying nonlinear analysis to compute paths of steady solutions using numerical continuation methods and to determine their stability based on eigenvalue information. In this article we focus on the latter technique, specifically where we seek to understand how the solution structure changes as one parameter of interest is varied; in the case of the incompressible Navier-Stokes equations this parameter is typically the Reynolds number. We are particularly interested in the location of critical parameters at which a bifurcation first occurs; a review of techniques for bifurcation detection can be found in Cliffe et al. [16], for example.Over the past few decades, ...