This paper reports the progress made in a parametric design and rapid meshing system (PADRAM) developed under two recent UK national sponsored research programs. PADRAM is designed to parametrically change the blade geometry and rapidly generate body-conformal high-quality viscous meshes. This allows speeding up the CFD loop by making the meshing process fully automatic on the basis of pre-designed templates. The geometry parameterisation is done within the mesh generator, making its integration within the optimisation loop straightforward. The paper presents examples that demonstrate how incorporating real geometry features into PADRAM is fundamental to achieve numerical models closer to reality. This is key factor in trusting the CFD solution and making use of it to further improve current designs. It also shows that feature-based structured mesh is good for cases that need to be repeatable across sites and teams, where consistency of the mesh is crucial and quick answers required to cope with tight project deadlines. The incorporation of additional complex geometrical features limits the applicability of the template structured approach and can be sometimes at the expense of mesh quality. In this regard, novel unstructured meshing technologies have been developed and implemented into PADRAM in order to deal with non standard and complex configurations. Two of these methods are presented in this paper (i.e., Zipper Layer and Delaunay Cavity). The paper shows how these can be used to paste together various multi-block structured meshes, hence providing the most suitable meshing topology to be used for each component separately. This makes the PADRAM code a unique meshing tool, able to combine the advantages of the template-topology approach to the flexibility of fully unstructured meshes. A number of supportive examples is reported in the paper.

The present paper deals with the redesign of cyclic variation of a set of fan outlet guide vanes by means of high-fidelity full-annulus CFD. The necessity for the aerodynamic redesign originated from a change to the original project requirement, when the customer requested an increase in specific thrust above the original engine specification. The main objectives of this paper are: 1) make use of 3D CFD simulations to accurately model the flow field and identify high-loss regions; 2) elaborate an effective optimisation strategy using engineering judgement in order to define realistic objectives, constraints and design variables; 3) emphasise the importance of parametric geometry modelling and meshing for automatic design optimisation of complex turbomachinery configurations; 4) illustrate that the combination of advanced optimisation algorithms and aerodynamic expertise can lead to successful optimisations of complex turbomachinery components within practical time and costs constrains. The current design optimisation exercise was carried out using an in-house set of software tools to mesh, resolve, analyse and optimise turbomachinery components by means of Reynolds-averaged Navier-Stokes simulations. The original configuration was analysed using the 3D CFD model and thereafter assessed against experimental data and flow visualisations. The main objective of this phase was to acquire a deep insight of the aerodynamics and the loss mechanisms. This was important to appropriately limit the design scope and to drive the optimisation in the desirable direction with a limited number of design variables. A mesh sensitivity study was performed in order to minimise computational costs. Partially converged CFD solutions with restart and response surface models were used to speed up the optimisation loop. Finally, the single-point optimised circumferential stagger pattern was manually adjusted to increase the robustness of the design at other flight operating conditions. Overall, the optimisation resulted in a major loss reduction and increased operating range. Most important, it provided the project with an alternative and improved design within the time schedule requested and demonstrated that CFD tools can be used effectively not only for the analysis but also to provide new design solutions as a matter of routine even for very complex geometry configurations.

This paper presents the application of an in-house automatic design system to the aerodynamic optimisation of one HP turbine stage. The main objectives of this study are: point out the importance of parametric geometry modelling and meshing for automatic design optimisation; move a step forward towards the exploitation of novel numerical tools to improve modern turbine performance with high-fidelity geometry configurations. In the present work, the system has been applied to the non-axisymmetric hub endwall optimisation of a research Rolls-Royce design HPT stage. The following main issues have been taken into account: high-fidelity CFD by means of multirow 3D simulations; parametric modelling and rapid meshing of real geometry features; modelling of film cooling flows. It is demonstrated that the integration of parametric models of secondary geometrical features within the mesh generator is a key issue in order to develop an effective and fully automated design procedure. It is shown that some of the benefits achieved optimising a simplified model of the stage are lost when applying the high-fidelity geometry configuration. A significant reduction of secondary flows and a corresponding increase of stage efficiency are achieved when taking into account the main real geometry features directly into the optimisation, even if at the cost of higher computational requirements.

Numerical investigation of the compressible flow in the Turbine Center Frame (TCF) duct was carried out using a Reynolds-averaged Navier-Stokes (RANS) method, and a Hybrid RANS/Large Eddy Simulation (HLES) method, i.e. Stress-Blended Eddy Simulation (SBES). The reference Reynolds number based on the TCF inlet condition is 530,000, and the inlet Mach number is 0.41. It is found that the boundary layer flow behavior is very sensitive to the incoming turbulence characteristics, so the upstream grid used to generate turbulence in the experiment is also included in the computational domain. Results have been validated carefully against experimental data, in terms of static pressure distribution on hub and casing walls, total pressure and Mach number profiles on the TCF measurement planes, as well as over-all pressure loss coefficient. Further, various fundamental mechanisms dictating the intricate flow phenomena, including concave and convex curvature effects, interactions between inlet turbulent structures and boundary layer, and turbulent kinetic energy budget, have been studied systematically. The current study is to evaluate the performance of HLES method for TCF flows and develop a further understanding of unsteady flow physics in the TCF duct. The results obtained in this work provide physical insight into the mechanisms relevant to the turbine intercase or TCF duct flows subjected to complex inlet disturbances.

The objective of this work is to analyze the end wall leakage interaction in shrouded high pressure turbines to provide useful indications about the flow pattern and its impact on performances. The prediction of flow through the seal and the understanding of the leakage jet interaction with the main flow in turbine end wall regions is nowadays possible using 3D CFD approaches. Modern solvers allow the coupling of the labyrinth and the main vane flows accounting for most of the geometric and aerodynamic features characterizing this phenomenon. Two similar shroud configurations are here analysed for two high pressure turbine configurations. Each configuration refers to a different blade technology commonly used by ANSALDO ENERGIA. The computational algorithm is based on a numerical solver developed and applied for the simulation of compressible Navier-Stokes equations in a multi rows unsteady environment. In order to reproduce the basic physic of the leakages, the problem has been investigated modelling the unsteady 1 1/2 stage interaction together with the complete geometry of the labyrinth seals. The CFD results are commented addressing the potential source of losses to help the development of solutions for reducing the leakage losses.