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Bladed disks are often analyzed under the assumption that the whole structure consists of perfectly identical substructures or sections. But real bladed disks exhibit small variations in geometry and material properties among the sectors. These differences, called mistuning, can have a large impact on the dynamic behavior and stability of the system.

A thorough review of reduced order models is performed for the description of the dynamic behavior of mistuned rotors. A flutter analysis for a mistuned cantilevered and shrouded bladed disk is conducted using a higher order approach and compared against the reduced Fundamental Mistuning Model. For both cases, the first mode family is analyzed which is a bending mode for the cantilevered and a mixed bending-torsion mode for the shrouded bladed disk. An alternate mistuning pattern is implemented by proportionally scaling the Young's modulus of the structural finite element model. This allows taking into account the complete mistuning effects since all the perturbations including the eigenmode, frequency and aerodynamics are present in the flutter computations. The cantilevered bladed disk model, representing a structurally weakly coupled system, is created by removing the cyclic symmetry boundary condition at the blade tip of the shrouded bladed disk.

Using the higher order approach, it is shown that the effect of mistuning has less influence on the structurally strongly coupled system compared to the weakly coupled bladed disk. A small mistuning level positively affects the cantilevered bladed disk. Further increase in mistuning stabilizes the system and the aerodynamic work becomes independent of the inter-sector phase angle. On the other hand, alternate mistuning of rotors with a high number of blades does not alter the eigenmodes of the shrouded bladed disk greatly enough, especially the lower nodal diameters. On the contrary, an unfavorable effect of alternate mistuning is observed which is seldom reported in the literature.

While the tuned results agree quite well between the higher order and reduced order approach, there are some noticeable differences for the mistuned bladed disk. Despite some quantitative differences, the Fundamental Mistuning Model correctly predicts the stabilizing trend with increasing mistuning amplitude of the cantilevered bladed disk. However, the reduced approach fails to qualitatively and quantitatively resemble the mistuned results of the higher order approach for the shrouded case.

turbomachinery --- flutter --- mistuning --- structural coupling --- shrouded --- ROM --- Ingénierie, informatique & technologie > Ingénierie aérospatiale

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Pre-swirl systems are important components for the internal cooling of turbomachinery. They allow to reduce the total relative temperature of the rotor disc and blades by feeding the rotor with a fast and tangential air. The gases exiting the combustion chamber can therefore have higher temperature, thus, increasing the overall efficiency of the turbomachinery. 
This thesis aims at investigating a new design of pre-swirl system from a jet engine high pressure turbine (HPT) core made with additive manufacturing (AM). Indeed, additive manufacturing presents many assets for the aeronautic industry as it offers new possibilities in terms of design while reducing the component mass. The study consists in 3D CFD analysis on Fluent for steady take-off operating conditions. The thermal, aerodynamic, integration and additive manufacturing requirements related to pre-swirl systems are detailed. This led to a pre-swirl system with a curved nozzle and a house shape cross section. Different geometry influence studies are conducted to investigate the new design. The influence of surface ratio between the nozzle inlet and throat surfaces and reduced radius R are examined. An air intake device (AID) located at the inlet of the nozzle is also studied. The configurations are compared to the radial pre-swirl system with vane nozzles of a HP turbine core representing the baseline configuration. The flow performances are evaluated in terms of outlet mass flow, discharge coefficient, throat Mach number and nozzle outlet swirl ratio. 
As preliminary results, the impact of the sub-chamber upstream of the pre-swirl system is studied. The transition between this chamber and the pre-swirl system can be assimilated to an elbow duct. This elbow duct introduces turbulences leading to performance losses. The influence studies have shown that a high surface ratio and a low reduced radius offer the best flow performances. Furthermore, the AID device reduces the losses at the nozzle inlet improving the performances. 
The comparison of all the AM nozzle configuration has shown that the configuration with the highest performances is R=0.2 with AID. However, the current AID design introduces mass to the assembly and doesn’t improve significantly the flow performances for low reduced radius configuration. Therefore, the selected optimum configuration is R=0.2 without AID. This configuration has a lower mass from 30% compared to the baseline configuration. However, in terms of flow performances, it shows lower results compared to the baseline configuration, especially for the Mach number and swirl ratio.

pre-swirl system --- aerodynamics --- thermal --- jet engine --- turbomachinery --- CFD --- Ingénierie, informatique & technologie > Ingénierie aérospatiale

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"The GPPS Journal has been developed to serve the international power and propulsion community in the time of change. The Journal with its close link to the GPPS technical conference series has played and continues to play a uniquely important role. I very much appreciate the contributions made and the solid foundation laid by the founding editor (Prof. Howard Hodson), the associate editors and the editorial office team, and believe that with the help of all involved, including the reviewers and authors, the Journal can and will be progressed further, in terms of the quality and speed of the publications and in terms of the impact on academic and industrial communities of the society"--About GPPS, viewed March 9, 2020.

power generation --- turbomachinery --- propulsion systems --- Propulsion systems --- Turbomachines --- Engines --- Engines. --- Propulsion systems. --- Turbomachines. --- Turbines --- Systems, Propulsion --- Engineering systems --- Machinery

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turbomachinery --- thermodynamics --- industrial energy --- propulsion --- fluid mechanics --- heat transfer --- Turbomachines --- Power (Mechanics) --- Turbomachines. --- Turbines --- Energy --- Mechanics --- Mechanical Engineering - General --- Engineering sciences. Technology

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One aeroelastic phenomenon that has to be avoided at all costs in turbomachinery is flutter. Flutter is a self-sustained and self-excited excitation that jeopardizes the structural life in a matter of seconds. This phenomenon is highly dependent on multiple parameters that makes it unable to be predicted a priori. A key factor is the variation of the inter blade phase angle that must be assessed at each operational condition to guarantee the machine integrity. This process generates an enormous amount of computational flutter analysis that is performed manually increasing the engineering time, and it is dependent on the user's expertise. Producing a need for reproducing reliable results without any user interaction resulting in an engineering time reduction. This need was satisfied by the development of a flutter wizard tool, which works within FINEexttrademark/Turbo. The tool is able to set up and analyze a single or multiple rows for one vibrating blade, at one or multiple operational conditions with or without custom user inputs. By making use of the developed flutter wizard tool the engineering time required was strongly reduced, it only took approximately 1.5\% of the time when compared to a manual set up and analysis. The wizard also provides a flexible and user-friendly set up so the client can reproduce complex or particular cases if desired. Seven cases were analyzed with a variety of geometry, operational conditions imposed motion and imposed. Six cases were contrasted against experimental and numerical data, while the seventh just against numerical data from two software. A close match between steady-state experimental and current results was found in all cases, except where non-linear effects were encountered. A total of 153 non-linear harmonic cases were run with the wizard, in which for an operational condition it provided a direct output of the aeroelastic stability of the system by means of the aerodynamic damping coefficient. A proportional aerodynamic damping coefficient curve per reference was used, as it proved to remove the scaling factor and retrieve the proportional aerodynamic work for each case with a better agreement among results. A manual detailed analysis of the harmonic content at specific blade height locations were performed to validate results. Thus, a collection of results is gathered and analyzed in detailed, providing a description and correlation of the steady and unsteady results. Finally, future work is proposed as a benchmark on a last stage steam turbine, as the actual machine and stator/rotor interaction is taken into account.

flutter --- aeroelasticity --- CFD --- aerodynamic damping --- turbomachinery --- standard configuration --- NUMECA --- non-linear harmonics --- IBPA --- Python --- energetic method --- harmonic method --- Ingénierie, informatique & technologie > Ingénierie aérospatiale