Applications and Recent Developments of the Open-Source Computational Fluid Dynamics High-Fidelity Spectral/Hp Element Framework Nektar++ for Turbomachinery Configurations

Abstract Reynolds-Averaged-Navier-Stokes (RANS) modelling has had a significant amount of success within the industrial setting. In fact, such techniques are used on a daily basis to compute the flow field around a broad spectrum of geometries in very different conditions. To this end, many codes have now reached a good level of maturity in terms of capabilities and robustness. However, there is a growing need for more efficient designs and higher performance. Therefore, aspects that are either challenging or impossible to capture by means of standard second-order steady discretisations are starting to become of interest. The computational hardware improvements seen over the decades and the persistent development of high-order numerical techniques, are allowing Implicit Large Eddy Simulation (iLES) if not Direct Numerical Simulation (DNS). These would allow accurate capturing of unsteady flow phenomena that can be critical to properly understand aspects such as flow separation, reattachment and transition to turbulence in components relevant to the turbomachinery community. The advantage that high-order solvers, such as Nektar++, have over their standard second-order discretisation counterpart, relates to their ability to reach higher fidelity solutions with a saving in terms of number of degrees of freedom and therefore computational cost. In this paper, a detailed introduction to the characteristics and features of the open-source high-order Nektar++ Computational Fluid Dynamics (CFD) framework will be given. An initial discussion of the numerics will be provided, therefore explaining the main features of this solver, followed by a set of different capabilities that are of interest to the turbomachinery community, such as meshing, incompressible and compressible solvers and post-processing. Examples of successful deployment of these features to jet engine components will then be presented. To start, preliminary design components, such as flat plates with different loadings will be discussed. In these cases, the effects of adverse and favourable pressure gradients representative of those seen on modern engine intakes and fan blades, respectively, on boundary layers will be studied. Following, a description on low and high pressure turbine components will be provided with a discussion relating to the relevant experimental comparison. Finally, future developments and improvements to the code will be detailed, such as new schemes and interfaces to hardware enhancements, i.e. Graphical Processing Units.