Shubham Kumar, Seamus Garvey, Hervé Morvan
2016 unpublished
With the aero-engine manufacturers aiming for Operating Power Ratios (OPRs) higher than 50:1 and improved engine efficiency, the capabilities of the present sealing systems are bound to be severely tested. Air riding seals have emerged as potential candidates to deal effectively with the high pressure discharge air from the compressor. The simplest types of air-riding seals are those with an axial gap. Radial gap seals can provide another level of advantage in terms of their applicability and
more » ... e total axial travel that needs to be accommodated. This paper provides an overview on a preliminary design effort in modelling and designing a radial gap air riding seal having a continuous ring structure. It investigates a key issue regarding these seals: developing a positive radial stiffness in the air-film to drive the sealing ring to accommodate for any radial shaft movement while maintaining a minimum clearance from the shaft to avoid any contact (in effect, having sort of a bearing-like action). The paper discusses the results from 1D and 2D analyses of the flow through a small sector of the seal, and demonstrates a methodology to calculate the stiffness and damping coefficients of the fluid-film. This is followed by steady state and transient CFD simulations to further analyse the characteristics of this fluid film and understand the time-constants associated with perturbations of the film. INTRODUCTION The aviation industry has been one of the most prolific sectors of development over the last 10-15 years. Passenger traffic as measured by revenue passenger kilometers (RPK) is expected to rise by 4.9% each year for the next two decades, thus leading to a need of around 38,050 aircrafts [1]. The rise in aircraft demand would also imply a significant rise in aero-engine demand to power these aircrafts. The Rolls-Royce Market Outlook [2] predicts a requirement of 55,000 engines over the next decade, generating around 1,600 million pounds of installed thrust. Most of the aero-engine manufacturers are in pursuit of technologies that show promise of high performance to cost benefit ratios. To obtain the low Specific Fuel Consumption (SFC) desired for the next-gen engines, more progress must be made in increasing core efficiencies. Advanced engine seals show promise of reducing engine losses and maintaining these performance benefits over the service interval of the engine. Studies performed by [3], and supported by [4], estimated that making the same performance improvements by improving seal technology would cost 4 to 5 times less than that brought about by improving the present compressors or turbines by other means. Air riding seals rely on a thin film of air to separate the seal faces and they show promise of reducing wear and leakage to its practical limit. These seals can be designed to operate at the high pressures and temperatures anticipated for next-generation gas turbine engines. There are two classes of film riding seals being developed for gas turbines: hydrostatic and hydrodynamic seals. Hydrostatic face seals port high pressure fluid to the sealing face to induce opening force and to maintain controlled face separation. Hydrodynamic or self-acting