Advanced contacting seals, such as leaf seals or brush seals, can offer reduced leakage during engine operation when compared to conventional labyrinth seals. The flexible elements of these seals provide better compliance with the rotor during flight maneuvers. The functionality and performance retention attributes of an engine-scale prototype leaf seal have been investigated on a seal test facility at Rolls-Royce that achieves engine-representative pressures and speeds and allows dynamic control of the seal position relative to the rotor, both concentric and eccentric. In this paper, the experimental setup and the test method are described in detail, including the quantification of the measurement uncertainty developed to ASME standard PTC 19.1. Experimental data are presented that show the variations in leakage and torque over typical variations of the test parameters. Insight is gained into the interactions between the operating pressure and speed and the concentric and eccentric movements imposed on the seal.
Secondary air system seals in aero engines sit at the intersection between all the major aspects of the physics of the system. Their behavior is affected by the air system, the thermal physics, the effect of flight loads and is highly dependent on the engine component movements, the operating conditions, and the supporting hardware. Due to the number of functional and physical interfaces in the engine, seal design is therefore a highly coupled multi-physics problem and requires multiple iterations during the design process to converge to a solution that meets system requirements and optimizes engine specific fuel consumption. At different stages of the design process, simulation models with different levels of fidelity can be built. Due to the long runtimes of high-fidelity coupled multi-disciplinary models and to the iterative nature of the process, seal design in industry presents significant computational cost challenges, in particular in the phases of the design that require multiple simulation runs. Multi-fidelity computational techniques for surrogate modelling and optimization such as Kriging and co-Kriging have been demonstrated on a number of industrial applications and have the potential to significantly reduce the number of function evaluations for computationally expensive optimization problems, improve the accuracy of the predictions of surrogate models and allow the development of improved simulation strategies for a specific product design. This paper demonstrates the use of multi-fidelity simulation techniques on aero engine secondary air system seal design and shows how these techniques can be used in the context of system, sub-system and component design. This is achieved by combining results from a simple two-dimensional Finite Element Analysis with those from a coupled secondary air system-thermomechanical model. Depending on the stage of the design process and on the specific design decisions being made, the use of computational power in simulation often comes down to a trade-off between reduced overall computational time and improved result accuracy. Multi-fidelity simulation frameworks provide the environment to drive holistic choices on the simulation strategy, reducing the cost of the design and offering agility in the industrial response to market changes or new technologies. Moreover, this methodology establishes an infrastructure for updating the virtual product at each step of the product lifecycle, allowing experimental or service data to feed the system-level simulation models to produce a digital twin.
Current turbomachinery design and analysis is a time consuming process, involving multiple teams and multi-disciplinary physics to be considered during the design stages. The geometry definition is a key enabler requiring better, clean and flexible designs at desired level of fidelity for all analyses. In order to achieve this, a fully parametric approach has been developed using a feature library (user defined features – UDFs) in a CAD package together with multiple tools to prepare the geometry for analysis. The paper will describe the approach towards feature library creation for a whole aero engine application, the relevant steps to prepare the geometry for analysis, and the limitations. The feature library has been used to enable a new aero engine conceptual design from the whole engine aerodynamic gas path definition all the way to the structural design, providing the additional flexibility to perform trade-off studies through design of experiments (DOE). Results will be shown on variation of critical design parameters such as casing thicknesses, flange positions, and number of struts. The selected example will clearly demonstrate the time-saving and better-quality product achieved compared to the traditional process, and the ability of the engineer to explore the design space better with inter-linked analysis tools through a master geometry definition.
Secondary air system seals are crucial in aero engine design as they have a direct impact on specific fuel consumption. Their behavior is affected by several aspects of the physics of the system: the air system, the engine thermal physics, the effect of flight loads and several other effects. As a consequence, their design is a complex and iterative process, which is highly dependent on the location of the seal in the engine, on the system requirements and on the system behavior. This paper describes a methodology for multi-disciplinary assessment of secondary air system seals within an engine environment and supports standard seal design, trade-off studies on novel concepts and system-level optimization. Defining the seal design intent for a specific engine location in the form of objectives, it is possible to embed process automation into traditionally manual multi-disciplinary design processes. This allows transforming modelling and simulation tools, which typically provide predictions for a specific seal design over reference cycles, into design and optimization tools, which can provide the optimum seal design for a specific set of requirements. This approach provides predictive models of both seal performance and performance degradation and is capable of taking into account all sources of variation, for instance manufacturing variations or engine operating conditions, delivering a robust design, specific to the engine location. The methodology enables a holistic approach to system and sub-system design and provides a deeper understanding of the impact of the seal onto system and of the system onto the seal, allowing optimization of the overall solution and informing the business case for introduction of different sealing strategies. Examples of the application of this methodology are provided for both labyrinth seals and leaf seals.
Advanced contacting seals, such as leaf seals or brush seals, can offer reduced leakage during engine operation when compared to conventional labyrinth seals. The flexible elements of these seals provide better compliance with the rotor during flight manoeuvres. The functionality and performance retention attributes of an engine-scale prototype leaf seal have been investigated on a seal test facility at Rolls-Royce that achieves engine-representative pressures and speeds and allows dynamic control of the seal position relative to the rotor, both concentric and eccentric. In this paper the experimental setup and the test method are described in detail, including the quantification of the measurement uncertainty developed to ASME standard PTC 19.1. Experimental data are presented that show the variations in leakage and torque over typical variations of the test parameters. Insight is gained into the interactions between the operating pressure and speed and the concentric and eccentric movements imposed on the seal.
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