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978-3-8439-4213-3, Reihe Luftfahrt
Design and Analysis of an Ultra-Compact Turbocharger Rotor Supported by Aerodynamic Bearings
121 Seiten, Dissertation Universität Stuttgart (2019), Softcover, A5
This dissertation ﬁrstly presents a new principle of turbocharger design suitable for aerodynamic bearings and secondly a novel quaternion form of Euler equation which is used to study rotor’s motion.
The ﬁrst part presents traditional design of automotive turbocharger with plain or ball bearings situated between impeller and turbine. It discusses turbocharger’s operation condition for typical passenger car such as the maximal thermal load on turbine for gasoline and diesel engine, maximal rotational speed, which is limited by material strength in impeller and which limits whole power of a turbocharger. The next section shows some existing turbocharger designs that utilize aerodynamic bearings. It is clariﬁed, that all of them have the traditional layout with axial and radial bearings between the impeller and turbine. This design inevitably causes that the rotor is either ﬂexible or its maximal rotational speed is not limited by material strength of the impeller as it is usual in the automotive industry. Then it shows a various kinds of aerodynamic bearings and their advantages and limiting factors are discussed. It is especially highlighted that aerodynamic bearings have small speciﬁc load capacity and small damping which makes transition over the resonant frequency diﬃcult if not impossible. These turbocharger operating conditions and limits of aerodynamic bearings leads to a new design of turbocharger rotor with aerodynamic bearings which is intentionally made rigid so as to avoid the problem of crossing the resonant frequency during its operation. The rigidness of the shaft was attained by placing the bearings at its ends instead of its middle section as in traditional designs. On top of that, it was designed a stator with eﬀective heat barrier between the compressor and turbine housings.
The second part of this dissertation concerns rotordynamics. Novel form of differential equation describing a rigid body motion (including possible interactions with other bodies or external forces) is used to model the rotor. The chapter 4 and appendix introduce quaternions to mechanical engineering community on the example of Euler equation. No previous knowledge of quaternions is assumed, though good familiarity with complex numbers (which may be regarded as a special case of quaternions) is an advantage.