Cavitation inception in fast startup

The start-up of rocket engine turbopumps is generally performed only in a few seconds. It implies that these pumps reach their nominal operating conditions after only a few rotations. During these first rotations of the blades, the flow evolution in the pump is governed by transient phenomena, based mainly on the flow rate and rotation speed evolution. These phenomena progressively become negligible when the steady behaviour is reached. The pump transient behaviour induces significant pressure fluctuations which may result in partial flow vaporization, i.e. cavitation. An existing experimental test rig has been updated in the LML laboratory (Lille, France) for the start-ups of a centrifugal pump. The study focuses on cavitation induced during the pump start-up. Instantaneous measurement of torque, mass flow rate, inlet and outlet unsteady pressures, and pump rotation velocity enable to characterize the pump behaviour during rapid starting periods

Leakage flow simulation in a specific pump model

This paper deals with the influence of leakage flow existing in SHF pump model on the analysis of internal flow behaviour inside the vane diffuser of the pump model performance using both experiments and calculations. PIV measurements have been performed at different hub to shroud planes inside one diffuser channel passage for a given speed of rotation and various flow rates. For each operating condition, the PIV measurements have been trigged with different angular impeller positions. The performances and the static pressure rise of the diffuser were also measured using a three-hole probe. The numerical simulations were carried out with Star CCM+ 8.06 code (RANS frozen and unsteady calculations). Comparisons between numerical and experimental results are presented and discussed for three flow rates. The performances of the diffuser obtained by numerical simulation results are compared to the performances obtained by three-hole probe indications. The comparisons show few influence of fluid leakage on global performances but a real improvement concerning the efficiency of the impeller, the pump and the velocity distributions. These results show that leakage is an important parameter that has to be taken into account in order to make improved comparisons between numerical approaches and experiments in such a specific model set up

Représentativité thermique d'essais tribologiques à échelle réduite

La conception et l'analyse des performances d'un système de freinage nécessite la caractérisation de son comportement tribologique. Pour réaliser cette caractérisation en fonction de paramètres d'arrêt tels que la pression apparente de contact, le temps de freinage ou la vitesse de glissement, les essais sur tribomètre de freinage à échelle réduite sont plus adaptés que les essais à l'échelle 1, à condition de respecter les sollicitations thermiques de surface rencontrées à l'échelle 1. A partir d'une discussion sur les facteurs d'échelle et d'une analyse des flux de chaleur et d'énergie, tout un ensemble de conditions expérimentales peuvent être définies, qui respectent la même réponse théorique en température de surface. Une série d'essais simulant des freinages d'arrêt à partir de 140 km/h a été réalisée. Elle montre la très bonne corrélation entre prédictions et mesures expérimentales

Comparisons RANS and URANS numerical results with experiments in a vaned diffuser of a centrifugal pump

the paper presents the analysis of the performance and the internal flow behaviour in the vaned diffuser of a radial flow pump using PIV (particles image velocimetry) technique, pressure probe traverses and numerical simula\u2011 tions. PIV measurements have been performed at different hub to shroud planes inside one diffuser channel passage for a given rotational speed and various flow rates. For each operating condition, PIV measurements have been made for differ\u2011 ent angular positions of the impeller. Probe traverses have also been performed using a 3 holes pressure probe from hub to shroud diffuser width at different radial locations in between the two diffuser geometrical throats. the numerical simulations were realized with the two commercial codes: i\u2011Star CCM+ 8.02.011 (rAnS (reynolds Averaged navier Stokes) turbu\u2011 lence model, frozen rotor and unsteady calculations), ii\u2011CFX 10.0 (turbulence modelled with DeS model (Detached eddy Simulation) combining rAnS with leS (large eddy Simulation), unsteady calculations). Comparisons between numerical (fully unsteady calculations) and experimental results are presented and discussed for two flow rates. In this respect, the effects of fluid leakage due to the gap between the rotating and fixed part of the pump model are analysed and discussed

Detailed Pressure Measurements During the Transition to Rotating Stall in an Axial Compressor: Influence of the Throttling Process

This paper presents experimental unsteady pressure measurements gathered on a single stage axial compressor during pre-stall and transition to stall operations. The aim of this study is to analyze the transition from a stable operating point to the fully developed rotating stall regime, and more specifically, the effect of the throttling process on the development of the instabilities. To do so, experiments have been repeated leading the compressor to stall operations with various throttling speed. On one hand, this paper analyses the effect of the throttling speed on the dynamic of the instability development from the first detection of spike type precursors to completely developed rotating stall. On the other hand, a stall warning signal based on the correlation of the instantaneous pressure signal with a reference pressure signal is built. The influence of the location of the pressure transducer used for the warning signal is first analyzed. Then an analysis of the effect of the throttling process on the time between the warning signal and the effective stall development is proposed.The present work was supported by the ANR project NUMERICCS (ANR 15 CE06 0009)

Active flow control in an axial compressor for stability improvement : On the effect of flow control on stall inception

In this paper, the effect of an active flow control system on the onset mechanism of rotating stall in an axial compressor is experimentally investigated. A particular emphasis is thus given on the flow patterns present in the tip region right before stall and how they evolve when active flow control is applied. The mechanisms involved during stall formation without control are carefully assessed and compared to the literature. To this purpose, the development of the first instability into rotating stall is discussed by monitoring its speed inside the compressor. This analysis also relies on instantaneous pressure measurements at the casing of the compressor.Agence Nationale de la Recherche (projet NumERICCS)

Comparisons Between Numerical Calculations and Measurements in the Vaned Diffusor of SHF Impeller

The authors wish to thank Region Nord-Pas de Calais and CNRS for their financial support in the frame of the CISIT programThe paper presents analysis of the performance and the internal flow behaviour in the vaned diffusor of a radial flow pump using PIV (Particle Image Velocimetry) and pressure probe traverses. PIV measurements have already been performed at mid height inside one diffusor channel passage for a given speed of rotation and various mass flow rates. These results have been already presented in several previous communications. New experiments have been performed using a 3 holes pressure probe traverses from hub to shroud diffusor width at different radial locations between the two diffusor geometrical throats. Numerical simulations are also realized with the commercial codes Star CCM+ 7.02.011 and CFX. Frozen rotor and fully unsteady calculations of the whole pump have been performed. Comparisons between numerical results, previous experimental PIV results and new probe traverses one’s are presented and discussed for one mass flow rate. In this respect, a first attempt to take into account fluid leakages between the rotating and fixed part of the pump has been checked since it may affect the real flow structure inside the diffuse

Comparison and Sensibility Analysis of Warning Parameters for Rotating Stall Detection in an Axial Compressor

The present paper aims at evaluating the surveillance parameters used for early stall warning in axial compressors, and is based on unsteady pressure measurements at the casing of a single stage axial compressor. Two parameters—Correlation and Root Mean Square (RMS)—are first compared and their relative performances discussed. The influence of sensor locations (in both radial and axial directions) is then considered, and the role of the compressor’s geometrical irregularities in the behavior of the indicators is clearly highlighted. The influence of the throttling process is also carefully analyzed. This aspect of the experiment’s process appears to have a non-negligible impact on the stall warning parameters, despite being poorly documented in the literature. This last part of this research work allow us to get a different vision of the alert parameters compared to what is classically done in the literature, as the level of irregularity that is reflected by the magnitude of the parameters appears to be an image of a given flow rate value, and not a clear indicator of the stall inception.ANR project NUMERICCS (ANR-15-CE06-0009

Pulsed air injection system characterization for stall margin improvement in an axial compressor

This paper presents the design and the characterization of a pulsed air injection system on a single stage axial compressor. The goal of this system is to delay the rotating stall onset and to extend the compressor operating range. The proposed control system consists in 20 injection blocks of 2 injectors, allowing to adjust some of the fluidic and geometrical parameters of the injected perturbations. Velocity, flow rate and momentum can be varied on a large range and the injectors can be rotated by 15° steps or replaced to change the yaw angle and the outlet section.The present work was supported by the ANR project NUMERICCS (ANR-15-CE06-0009), and this project has received funding from the Clean Sky 2 Joint Undertaking under the European Union’s Horizon 2020 research and innovation programme under grant agreement No. 886352

Leakage Flow Influence on SHF pump model performances

This paper deals with the influence of leakage flow existing in SHF pump model on the analysis of internal flow behaviour inside the vane diffuser of the pump model performance using both experiments and calculations. PIV measurements have been performed at different hub to shroud planes inside one diffuser channel passage for a given speed of rotation and various flow rates. For each operating condition, the PIV measurements have been trigged with different angular impeller positions. The performances and the static pressure rise of the diffuser were also measured using a three-hole probe. The numerical simulations were carried out with Star CCM+ 9.06 code (RANS frozen and unsteady calculations). Some results were already presented at the XXth IAHR Symposium for three flowrates for RANS frozen and URANS calculations. In the present paper, comparisons between URANS calculations with and without leakages and experimental results are presented and discussed for these flow rates. The performances of the diffuser obtained by numerical calculations are compared to those obtained by the three-holes probe measurements. The comparisons show the influence of fluid leakages on global performances and a real improvement concerning the efficiency of the diffuser, the pump and the velocity distributions. These results show that leakage is an important parameter that has to be taken into account in order to make improved comparisons between numerical approaches and experiments in such a specific model set up