Rotor-to-stator rub is a very common topic in rotor dynamics and several models
have been proposed in the literature. Anyhow these models are often able to explain
only the experimental dynamical behaviour of simple test rigs, which are
deliberately reproducing a Jeffcott rotor. On the contrary case, histories related to
real machines are seldom presented and analysed. The aim of this paper is to
present an actual case history of a large turbogenerator unit that was subjected to
partial arc rubs. The experimental results are shown and discussed along with the
model-based diagnostic strategy employed to identify the fault severity and the
location of the shaft cross-sections where the heaviest rubs occurred. Comparisons
between experimental data and simulated vibrations caused by the identified fault
are shown to validate the proposed methodology.

Paolo  Pennacchi

Andrea  Vania

Analysis of Rotor-to-Stator Rub in a Large Steam Turbogenerator

The present work involves experimental investigation of the effects of aspect ratio, channel orientation angle, rib pitch-to-height ratio (P/e), and number of ribbed walls on friction factor in orthogonally rotating channel with detached ribs. The ribs are separated from the base wall to provide a small region of flow between the base wall and the ribs. Experiments have been conducted at Reynolds number ranging from 10000&#8211;17000 with rotation numbers varying from 0&#8211;0.38. Pitch-to-rib height ratios (P/e) of 5 and 10 at constant rib height-to-hydraulic diameter ratio (e/D) of 0.1 and a clearance ratio (C/e) of 0.38 are considered. The rib angle of attack with respect to mainstream flow is <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msup><mml:mrow><mml:mn>90</mml:mn></mml:mrow><mml:mo>&#x2218;</mml:mo></mml:msup></mml:mrow></mml:math>. The channel orientation at which the ribbed wall becomes trailing surface (pressure side on which the Coriolis force acts) is considered as the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msup><mml:mn>0</mml:mn><mml:mo>&#x2218;</mml:mo></mml:msup></mml:mrow></mml:math> orientation angle. For one-wall ribbed case, channel is oriented from <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msup><mml:mn>0</mml:mn><mml:mo>&#x2218;</mml:mo></mml:msup></mml:mrow></mml:math> to <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msup><mml:mrow><mml:mn>180</mml:mn></mml:mrow><mml:mo>&#x2218;</mml:mo></mml:msup></mml:mrow></mml:math> about its axis in steps of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msup><mml:mrow><mml:mn>30</mml:mn></mml:mrow><mml:mo>&#x2218;</mml:mo></mml:msup></mml:mrow></mml:math> to change the orientation angle. For two-wall ribbed case, the orientation angle is changed from <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msup><mml:mn>0</mml:mn><mml:mo>&#x2218;</mml:mo></mml:msup></mml:mrow></mml:math> to <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msup><mml:mrow><mml:mn>90</mml:mn></mml:mrow><mml:mo>&#x2218;</mml:mo></mml:msup></mml:mrow></mml:math> in steps of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msup><mml:mrow><mml:mn>30</mml:mn></mml:mrow><mml:mo>&#x2218;</mml:mo></mml:msup></mml:mrow></mml:math>. Friction factors for the detached ribbed channels are compared with the corresponding attached ribbed channel. It is found that in one-wall detached ribbed channel, increase in the friction factor ratio with the orientation angle is lower for rectangular channel compared to that of square channel for both the pitch-to-rib height ratios of 5 and 10 at a given Reynolds number and rotation number. Friction factor ratios of two-wall detached ribbed rectangular channel are comparable with corresponding two-wall detached ribbed square channel both under stationary and rotating conditions.

K.  Arun

S. V. Prabhu

Effect of Aspect Ratio, Channel Orientation, Rib Pitch-to-Height Ratio,  and Number of Ribbed  Walls on Pressure Drop Characteristics in a Rotating Channel with Detached Ribs

The results of a complete study of mistuning identification on an industrial blisk are presented. The identification method used here is based on a model-updating technique of a reduced order. This reduced-order model is built using component mode synthesis, and mistuning is introduced as perturbations of the cantilevered-blade modes. The measured modal data are extracted from global measurements of the blisk's forced response. As we use a single point excitation, this measurement procedure allows the acquisition of all the modes of a given family with a quite simple experimental set-up. A selection of the best identified modal data is finally performed. During the mistuning identification procedure, these measured data are regularized using an eigenvector assignment technique which reduces the influence of eventual measurement errors. An inverse problem, based on the perturbed (mistuned) modal equation, is defined with measured modes as input and mistuning parameters as unknown. Then, the reduced-order model is updated with the identified mistuning, we first perform a correlation on modal responses (using eigenfrequency deviation criteria and MACs). Finally, correlation results on forced responses are presented and discussed.

D.  Laxalde

F.  Thouverez

J.-J.  Sinou

J.-P.  Lombard

S.  Baumhauer

Mistuning Identification and Model Updating of an Industrial Blisk

Numerical simulations on impeller-diffuser interactions in radial 
            diffuser pumps are conducted to investigate the unsteady flow, and more 
            attention is paid to pressure fluctuations on the blade and vane surfaces. 
            Calculations are performed at different operating points, different blade number 
            configurations, and different radial gaps between the impeller and diffuser to 
            examine their effects on the unsteady flow. Computational results show that 
            a jet-wake flow structure is observed at the impeller outlet. The biggest pressure 
            fluctuation on the blade is found to occur at the impeller trailing edge, on 
            the pressure side near the impeller trailing edge, and at the diffuser vane leading 
            edge, independent of the flow rate, radial gap, and blade number configuration. All 
            of the flow rate, blade number configuration, and radial gap influence significantly 
            the pressure fluctuation and associated unsteady effects in the diffuser pumps.

Jianjun Feng

Friedrich-Karl Benra

Hans Josef Dohmen

Numerical Investigation on Pressure Fluctuations for Different Configurations of Vaned Diffuser Pumps

This work aims at studying the influence of adding splitter blades on the performance of a hydraulic centrifugal pump. The studied machine is an ENSIVAL-MORET MP 250.200.400 pump (diameter <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mo>=</mml:mo></mml:math> 408 mm, 5 blades, specific speed <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mo>=</mml:mo></mml:math> 32), whose impeller is designed with and without splitter blades. Velocity and pressure fields are computed using unsteady Reynolds-averaged Navier-Stokes (URANS) approach at different flow rates. The sliding mesh method is used to model the rotor zone motion in order to simulate the impeller-volute casing interaction. The flow morphology analysis shows that, when adding splitter blades to the impeller, the impeller periphery velocities and pressures become more homogeneous. An evaluation of the static pressure values all around the impeller is performed and their integration leads to the radial thrust. Global and local experimental validations are carried out at the rotating speed of 
900 rpm, for both the original and the splitter blade impellers. The head is evaluated at various flow rates: 50<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>&#x0025;</mml:mi></mml:math>, 80<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>&#x0025;</mml:mi></mml:math>, 100<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>&#x0025;</mml:mi></mml:math>, and 120<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>&#x0025;</mml:mi></mml:math> of the flow rate at the best efficiency point (BEP). The pressure fluctuations are measured at four locations at the BEP using dynamic pressure sensors. The experimental results match the numerical predictions, so that the effect of adding splitter blades on the pump is acknowledged. Adding splitters has a positive effect on the pressure fluctuations which decrease at the canal duct.

G.  Kergourlay

M.  Younsi

F.  Bakir

R.  Rey

Influence of Splitter Blades on the Flow Field of a Centrifugal Pump:
Test-Analysis Comparison

A simulation strategy is developed for the computation of the time-accurate flow through low pressure turbines with periodically impinging wakes generated by moving cylinder rods. For the simulations, different time steps and turbulent inflow conditions and their impact on the laminar separation on the suction side are considered. A realizable cubic low-Reynolds number <mml:math id="E1" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>k-</mml:mi><mml:mi>ɛ</mml:mi></mml:math> turbulence model and a linear V2F model are utilized to capture transitional effects, in particular the laminar separation bubble at the suction side. For comparison with experimental data, published in a companion paper, pressure distribution and boundary layer profiles of the mean and fluctuation RMS velocity are considered. While the periodically disturbed flow is predicted with a reasonable accuracy by each model, for the undisturbed flow, an additional realizability condition based on a turbulent time scale bound is incorporated into the cubic model in order to capture the reattachment of the flow.

Romuald Skoda

Rudolf Schilling

Meinhard T. Schobeiri

Numerical Simulation of the Transitional and Unsteady Flow  through a Low Pressure Turbine

About this journal

International Journal of Rotating Machinery publishes original research articles as well as review articles on all types of rotating machinery employing gas, vapor, particle, liquid, and their mixtures (including slurry) as the working substances.

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International Journal of Rotating Machinery - Table of contents 2007

International Journal of Rotating Machinery | Hindawi

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International Journal of Rotating Machinery publishes original research articles as well as review articles on all types of rotating machinery employing gas, vapor, particle, liquid, and their mixtures (including slurry) as the working substances.

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International Journal of Rotating Machinery

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International Journal of Rotating Machinery