Abstract
The design of the support system (shaft, bearings, and mechanical coupling devices) of the rotor plays a key role in the development of efficient micro-gas turbines (micro-GTs) for distributed power generation. Foil air bearings are the most widespread technical solution well suited to design a reliable support system, although they cannot withstand a large number of start-stop cycles of the units. In order to overcome such limitation, we have recently proposed an innovative support system that takes advantage of spline couplings and two bearing types (e.g., air and rolling-element bearings). The devised support system employs splines as both convenient coupling systems and actuators for the load partition between the two bearing types. In the present work, the helical spline coupling is studied by means of structural FEM analyses including contact simulation in order to design the support system. Numerical results confirm previous findings in that the load transfer through the spline coupling is mainly a function of the helix angle. In addition, friction factor and structural stiffness cannot be neglected in the accurate design of the spline coupling. Such design parameters are now included in the proposed design procedure, which formerly assumed frictionless contact and rigid bodies.
Highlights
IntroductionDue to the high speeds of rotation (in the order of 105 rpm) and operating temperatures (up to 1000∘C), bearings are among the most stressed mechanical components in microgas turbine (micro-GT) systems, and lubrication as well as a support system plays a key role in the operation of the machine.The adoption of a single type of bearing is typical of bearing arrangements that are usually employed in commercial micro-GT units
Due to the high speeds of rotation and operating temperatures, bearings are among the most stressed mechanical components in microgas turbine systems, and lubrication as well as a support system plays a key role in the operation of the machine.The adoption of a single type of bearing is typical of bearing arrangements that are usually employed in commercial micro-GT units
In order to overcome such limitation, we have recently proposed an innovative support system that takes advantage of spline couplings and two bearing types
Summary
Due to the high speeds of rotation (in the order of 105 rpm) and operating temperatures (up to 1000∘C), bearings are among the most stressed mechanical components in microgas turbine (micro-GT) systems, and lubrication as well as a support system plays a key role in the operation of the machine.The adoption of a single type of bearing is typical of bearing arrangements that are usually employed in commercial micro-GT units. Conventional bearings (rolling-element type) are still used in micro-GT systems for reasons of size and cost; for example, since 1999, Capstone have offered a version of their Model 330 microturbine with a ball-bearing-based compressor and continued to offer the ball bearing compressor as an economical option for medium-pressure applications. In the design of a novel support system for the shaft, it is reasonable to consider magnetic bearings as a convenient alternative Their advantages over conventional bearings are as follows: oil-free operation, extreme temperature as well as active control for active magnetic bearings (AMBs) [1], ease of miniaturization [2], and independence of external energy input for passive magnetic bearings (PMBs) [3]. The advantage of the resistance to high temperatures makes AMBs the preferred choice for the application at hand
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