## Auslegung zentraler Entlastungseinrichtungen zur Axialschubkompensation und rotordynamische Beurteilung an einer mehrstufigen Hochdruck-Gliederpumpe

### Study of the balancing device for compensating the axial thrust and rotordynamic analyses of a multistage ring-section-pump

• This study should contribute to the research of the use of the balancing device as a product lubricated radial bearing. Removing the seal to the outside would result in a shorter pump shaft and therefore optimizes the rotordynamic behaviour of ring section type pumps. Therefore the vibrational behaviour of a multistage ring-section-pump is examinated, different profiles at the central balancing piston were compared. Based on these tests a balancing device with injection is realized, which takes over the function of a hybrid bearing, so the characteristics can be optimized and the influence of a long throttling gap on the rotordynamic can be shown. As a hybrid bearing the single piston as central balancing device is choosen, therefore it is possible to realize a simple supply of the injection and the resulting axial thrust can be measured with a cardanic ring. In order to design the piston for the balancing, the axial hydraulic thrust needs to be known. As a part of this study a software for the calculation design of centrifugal pumps was developed at the Institute for Flow and Positive Displacement Pumps. With that program the pressure distribution on the shroud of the impeller, the pressure drop, the circumferential velocity of the fluid as well as the hydraulic thrust can be calculated. To verify the calculation models the impeller side chamber of the last stage is equipped with miniature pressure sensors and a displacement sensor in the experimental part of this study. The bearing forces and the operating point is measured with a cardanic ring, were strain gages are applied and therefore measure the axial thrust. Also the dynamic signals of the pressure sensors and the cardanic ring are used to describe variations regarding the vibrational behaviour and the correlation of pressure between the impeller side chamber and the long throttling gap of the balancing. After that the influence of the injection for the balancing device was tested. As a results of this study it was shown, that the injection increases the loss coefficient between point of injection and the impeller side chamber. The injection reduces the circumferential velocity of the absolute flow, the rotation factor towards part load decreases. Therefore the balancing force can be controlled by the injection. In the frequency spectra the frequency of the impeller vanes is dominant, whose amplitude is dampened with decreasing radius of the impeller. Towards part load this frequency exceeds the first harmonic frequency and dominates the frequency spectrum. The impeller side chamber is dominated by the hydraulic interaction of impeller and diffuser. From a relative flow of q<0.5, a broad band increase of the subsynchrous frequencies can be detected. They are based on recirculation at the exit of the impeller (recirculation swirl). The configuration without injection obviously promotes the frequencies, which are generated by the interaction of impeller and diffuser behind the balancing device. This is favored by double gap clearances, which result in an increased sensibility of the excitation towards the rotor. If there is an injection in the central balancing device, the vibration behaviour of the pump can be improved. It is also remarkable that in regards of the rotordynamic the best configuration (MR2) can be beaten by a worse one (MR3+MR4) in combination with injection. Obviously the cross stiffness is clearly reduced (compare swirl brakes) which results in stabilizing the rotor (FT). The best solution regarding rotordynamic is the configuration with injection at the centre of the gap (MR4b).

Author: Christian Trautmann urn:nbn:de:hbz:386-kluedo-18139 D.-H. Hellmann Doctoral Thesis German 2005 2005 Technische Universität Kaiserslautern Technische Universität Kaiserslautern 2004/11/12 2005/02/10 Axialschub ; Drosselspalt ; Hybridlager ; Kreiselpumpe ; Rotordynamik Fachbereich Maschinenbau und Verfahrenstechnik 6 Technik, Medizin, angewandte Wissenschaften / 62 Ingenieurwissenschaften / 620 Ingenieurwissenschaften und zugeordnete Tätigkeiten Standard gemäß KLUEDO-Leitlinien vor dem 27.05.2011

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