Experimental Study of a Bulb Turbine Model During Start-Up and at Speed-No-Load Conditions, Based on the Measurement of Unsteady Pressure

2020 ◽  
Vol 142 (8) ◽  
Author(s):  
Maxime Coulaud ◽  
Jean Lemay ◽  
Claire Deschenes
Keyword(s):  
Pressure Fluctuations ◽  
Pressure Sensors ◽  
Suction Side ◽  
Rotating Stall ◽  
Operating Conditions ◽  
Time Frequency ◽  
Runner Blade ◽  
Start Up ◽  
Morlet Wavelet Transform ◽  
Bulb Turbine

Abstract Experimental analysis of a bulb turbine during the start-up sequence and in speed-no-load (SNL) operating conditions was performed in a closed-loop circuit. This study focuses on pressure fluctuations across the machine. The turbine was equipped with 26 pressure sensors on one runner blade and 16 in the stationary reference frame. Strain measurements were also performed on two other runner blades. The first section of this analysis focuses on SNL operating conditions using standard Fourier data processing. The results show that three rotating flow phenomena are only present close to the runner. One of them corresponds to the interblade vortex at f/fr=4.00, whereas the two others, which have subsynchronous runner frequencies, are consistent with a possible rotating stall. These phenomena, which exist predominantly on the suction side, have a strong influence on runner blade strain. The second section of the study concentrates on a time-frequency analysis using the Morlet wavelet transform. It reveals that the two subsynchronous flow structures appear at the end of the start-up and exhibit bistable behavior. As well, each of these phenomena acts differently on the blade. These phenomena also interact with the interblade vortex.

Prediction of Rotating Stall During Startup for Axial Compressors

2019 ◽  
Author(s):  
Ryosuke Mito ◽  
Satoshi Yamashita
Keyword(s):  
Pressure Fluctuations ◽  
Measurement Data ◽  
Rotating Stall ◽  
Operating Conditions ◽  
Axial Compressors ◽  
Start Up ◽  
Stable Operating ◽  
Stator Vane ◽  
Starting Conditions ◽  
Variable Stator

Abstract In a compressor used for power generation, a rotating stall due to an operating point mismatch between the front and rear stages occurs at front stages in low-speed condition during startup. IGV, VSV opening schedule and bleed flow rates are determined in order to obtain stable operating conditions, with the occurrence of pressure fluctuations or blade excitation force derived from the rotating stall. The setting of the number of stages for variable stator vane, the vane opening and the bleed flow rate are largely based on the rig test and experience of the actual machine, however we focused on the capability study for direct simulation with unsteady CFD for the rotating stall. If this can be predicted in advance, it makes it possible to reduce the number of stages of the variable stator vanes, the capacity of the thyristor, and to make the bleed chambers and piping compact, leading to cost reductions. The method of rotating stall prediction during startup condition, and the comparison between predicted and actual measurements on how this number changes with different starting conditions and different machines, are shown in this paper. CFD shows the different stall cell position, the number of stall cells and the pressure fluctuation level in each condition, and these results were consistent with the measurement data. Furthermore, we have found that these phenomena can be controlled by variable stator vane angle during start up.

scholarly journals Strong Azimuthal Combustion Instabilities in a Spray Annular Chamber With Intermittent Partial Blow-Off

2017 ◽  
Vol 140 (3) ◽  
Author(s):  
Kevin Prieur ◽  
Daniel Durox ◽  
Thierry Schuller ◽  
Sébastien Candel
Keyword(s):  
Light Intensity ◽  
High Speed ◽  
Transverse Velocity ◽  
Pressure Fluctuations ◽  
Pressure Sensors ◽  
Nodal Line ◽  
Operating Conditions ◽  
Acoustic Energy ◽  
Transverse Motion ◽  
Azimuthal Mode

This article reports experiments carried out in the MICCA-spray combustor developed at EM2C laboratory. This system comprises 16 swirl spray injectors. Liquid n-heptane is injected by simplex atomizers. The combustion chamber is formed by two cylindrical quartz tubes allowing full optical access to the flame region and it is equipped with 12 pressure sensors recording signals in the plenum and chamber. A high-speed camera provides images of the flames and photomultipliers record the light intensity from different flames. For certain operating conditions, the system exhibits well defined instabilities coupled by the first azimuthal mode of the chamber at a frequency of 750 Hz. These instabilities occur in the form of bursts. Examination of the pressure and the light intensity signals gives access to the acoustic energy source term. Analysis of the phase fluctuations between the two signals is carried out using cross-spectral analysis. At limit cycle, large pressure fluctuations of 5000 Pa are reached, and these levels persist over a finite period of time. Analysis of the signals using the spin ratio indicates that the standing mode is predominant. Flame dynamics at the pressure antinodal line reveals a strong longitudinal pulsation with heat release rate oscillations in phase and increasing linearly with the acoustic pressure for every oscillation levels. At the pressure nodal line, the flames are subjected to large transverse velocity fluctuations leading to a transverse motion of the flames and partial blow-off. Scenarios and modeling elements are developed to interpret these features.

The Cavitation-Induced Pressure Fluctuations in a Mixed-Flow Pump under Impeller Inflow Distortion

Machines ◽  
2021 ◽  
Vol 9 (12) ◽  
pp. 326
Author(s):  
Huiyan Zhang ◽  
Fan Meng ◽  
Yunhao Zheng ◽  
Yanjun Li
Keyword(s):  
Frequency Domain ◽  
Pressure Fluctuation ◽  
Dynamic Pressure ◽  
Pressure Fluctuations ◽  
Pressure Sensors ◽  
Mixed Flow ◽  
Guide Vanes ◽  
Time Frequency ◽  
Critical Cavitation ◽  
Flow Pump

To reduce cavitation-induced pressure fluctuations in a mixed-flow pump under impeller inflow distortion, the dynamic pressure signal at different monitoring points of a mixed-flow pump with a dustpan-shaped inlet conduit under normal and critical cavitation conditions was collected using high-precision digital pressure sensors. Firstly, the nonuniformity of the impeller inflow caused by inlet conduit shape was characterized by the time–frequency-domain spectra and statistical characteristics of pressure fluctuation at four monitoring points (P4–P7) circumferentially distributed at the outlet of the inlet conduit. Then, the cavity distribution on the blade surface was captured by a stroboscope. Lastly, the characteristics of cavitation-induced pressure fluctuation were obtained by analyzing the time–frequency-domain spectra and statistical characteristic values of dynamic pressure signals at the impeller inlet (P1), guide vanes inlet (P2), and guide vanes outlet (P3). The results show that the flow distribution of impeller inflow is asymmetric. The pav values at P4 and P6 were the smallest and largest, respectively. Compared with normal conditions, the impeller inlet pressure is lower under critical cavitation conditions, which leads to low pav, pp-p and a main frequency amplitude at P1. In addition, the cavity covered the whole suction side under H = 13.6 m and 15.5 m, which led the pp-p and dominant frequency amplitude of pressure fluctuation at P2 and P3 under critical cavitation to be higher than that under normal conditions.

Incipient Surge Detection in Large Volume Energy Systems Based On Wigner-Ville Distribution Evaluated On Vibration Signals

2021 ◽  
Author(s):  
Carlo Alberto Niccolini Marmont Du Haut Champ ◽  
Paolo Silvestri ◽  
Mario L. Ferrari ◽  
Aristide Fausto Massardo
Keyword(s):  
Research Field ◽  
Rotating Stall ◽  
Operating Conditions ◽  
Rolling Bearings ◽  
Time Frequency ◽  
Rotating Machine ◽  
Large Size ◽  
Critical Issues ◽  
Volume Energy ◽  
Transient Operations

Abstract Compressor response investigation in nearly unstable operating conditions, like rotating stall and incipient surge, is a challenging topic nowadays in the turbomachinery research field. Indeed, turbines connected with large-size volumes are affected by critical issues related to surge prevention, particularly during transient operations. Advanced signal-processing operations conducted on vibrational responses provide an insight into possible diagnostic and predictive solutions which can be derived from accelerometer measurements. Indeed, vibrational investigation is largely employed in rotating-machine diagnostics together with time-frequency analysis such as smoothed pseudo-Wigner Ville (SPWVD) time-frequency distribution (TFD) considered in this paper. It is characterized by excellent time and frequency resolutions and thus it is effectively employed in numerous applications in the condition monitoring of machinery. The aim and the innovation of this work regards SPWVD utilization to study turbomachinery behavior in detail in order to identify incipient surge conditions in the centrifugal compressor starting from operational vibrational responses measured at significant plant locations. To this aim, an experimental campaign has been conducted on a T100 microturbine connected with different volume sizes to collect significant data to be analyzed. The results show that SPWVD is able to successfully identify system evolution towards an unstable condition, by recognizing different levels and features of the particular kind of instability that is going to take place within the plant. Instability phenomena regarding rolling bearings have also been identified and their interaction with surge onset has been investigated for diagnostic purposes.

Experimental Investigation of a 10 MW Prototype Axial Turbine Runner: Vortex Rope Formation and Mitigation

2020 ◽  
Vol 142 (10) ◽  
Author(s):  
Arash Soltani Dehkharqani ◽  
Fredrik Engström ◽  
Jan-Olov Aidanpää ◽  
Michel J. Cervantes
Keyword(s):  
Experimental Investigation ◽  
Pressure Fluctuations ◽  
Suction Side ◽  
Clear Understanding ◽  
Pressure Side ◽  
Vortex Rope ◽  
Load Variations ◽  
Pressure Transducers ◽  
Load Variation ◽  
Runner Blade

Abstract The transient load fluctuations on the runner blades of prototype hydraulic turbines during load variations are one of the main causes of fatigue and eventual structural failure. A clear understanding of the dynamic loads on the runner blades is required to detect the source of the fluctuations. In this paper, an experimental investigation of vortex rope formation and mitigation in a prototype Kaplan turbine, namely, Porjus U9, is carried out. Synchronized unsteady pressure and strain measurements were performed on a runner blade during steady-state and load variation under off-cam condition. The normalized pressure fluctuation during load variations remained approximately within ±0.2Pref for all the pressure transducers installed on the blade pressure side and is even slightly lower during the transient cycle. Higher pressure fluctuations were found on the blade suction side, approximately four times higher than that of on the pressure side. The synchronous and asynchronous components of the vortex rope were clearly observed at the low discharge operating point and transient cycles. The spectral analysis of the pressure signals showed that the synchronous component appears before the asynchronous component during the load reduction, and it lasts longer during the load increase. These frequencies slightly change during the load variation. In addition, the results proved that the strain fluctuation component on the runner blade arises from the synchronous component of the vortex rope at low discharge while the asynchronous component influence is negligible.

scholarly journals CFD Investigation of a High Head Francis Turbine at Speed No-Load Using Advanced URANS Models

2018 ◽  
Vol 8 (12) ◽  
pp. 2505 ◽  
Author(s):  
Jean Decaix ◽  
Vlad Hasmatuchi ◽  
Maximilian Titzschkau ◽  
Cécile Münch-Alligné
Keyword(s):  
Power Plants ◽  
Turbulence Modeling ◽  
Suction Side ◽  
Hydraulic Turbine ◽  
Operating Conditions ◽  
Francis Turbine ◽  
Hydroelectric Power ◽  
Electrical Grid ◽  
Runner Blade ◽  
Pumped Storage

Due to the integration of new renewable energies, the electrical grid undergoes instabilities. Hydroelectric power plants are key players for grid control thanks to pumped storage power plants. However, this objective requires extending the operating range of the machines and increasing the number of start-up, stand-by, and shut-down procedures, which reduces the lifespan of the machines. CFD based on standard URANS turbulence modeling is currently able to predict accurately the performances of the hydraulic turbines for operating points close to the Best Efficiency Point (BEP). However, far from the BEP, the standard URANS approach is less efficient to capture the dynamics of 3D flows. The current study focuses on a hydraulic turbine, which has been investigated at the BEP and at the Speed-No-Load (SNL) operating conditions. Several “advanced” URANS models such as the Scale-Adaptive Simulation (SAS) SST k - ω and the BSL- EARSM have been considered and compared with the SST k - ω model. The main conclusion of this study is that, at the SNL operating condition, the prediction of the topology and the dynamics of the flow on the suction side of the runner blade channels close to the trailing edge are influenced by the turbulence model.

Distinctions Between Two Types of Self Excited Gas Oscillations in Vaneless Radial Diffusers

1979 ◽  
Author(s):  
A. N. Abdelhamid ◽  
J. Bertrand
Keyword(s):  
Static Pressure ◽  
Pressure Fluctuations ◽  
Rotating Stall ◽  
Operating Conditions ◽  
Flow Coefficient ◽  
Width Ratio ◽  
Flow Conditions ◽  
Oscillating Flows ◽  
Frequency Domains ◽  
Order Of Magnitude

Experiments were conducted to determine the characteristics of oscillating flows in a centrifugal compression system with vaneless diffusers. The system was operated without a diffuser and with eight different diffuser configurations to determine the effects of diffuser diameter and width ratios on the unsteady behavior of the system. Mean and fluctuating velocity and static pressure measurements were carried out in the time and frequency domains. The system without a diffuser was found to be stable at all operating conditions. The installation of any of the eight diffusers resulted in the generation of self-excited oscillations at some operating conditions. It was found that the critical flow coefficient at which onset of oscillations was observed increased as the diffuser width ratio was decreased and as the diameter ratio was increased. Comparison between the characteristics of the oscillations observed in the present study and those observed by other investigators indicate that rotating stall in two geometrically similar diffusers can be an order of magnitude different in the non-dimensional rotational speed and level of unsteady pressure fluctuations. These differences point towards the possibility of existence of more than one set of flow conditions which could lead to the occurrence of the unsteady phenomena.

Rotating Instability in an Annular Cascade: Detailed Analysis of the Instationary Flow Phenomena

2013 ◽  
Vol 136 (6) ◽  
Author(s):  
Benjamin Pardowitz ◽  
Ulf Tapken ◽  
Robert Sorge ◽  
Paul Uwe Thamsen ◽  
Lars Enghardt
Keyword(s):  
Unsteady Flow ◽  
High Speed ◽  
Pressure Sensors ◽  
Rotating Stall ◽  
Operating Conditions ◽  
Tip Vortex ◽  
Pressure Waves ◽  
Flow Profile ◽  
Rotating Instability ◽  
Annular Cascade

Rotating instability (RI) occurs at off-design conditions in compressors, predominantly in configurations with large tip or hub clearance ratios of s* ≥3%. RI is the source of the blade tip vortex noise and a potential indicator for critical operating conditions like rotating stall and surge. The objective of this paper is to give more physical insight into the RI phenomenon using the analysis results of combined near-field measurements with high-speed particle image velocimetry (PIV) and unsteady pressure sensors. The investigation was pursued on an annular cascade with hub clearance. Both the unsteady flow field next to the leading edge as well as the associated rotating pressure waves were captured. A special analysis method illustrates the characteristic pressure wave amplitude distribution, denoted as “modal events” of the RI. Moreover, the slightly adapted method reveals the unsteady flow structures corresponding to the RI. Correlations between the flow profile, the dominant vortex structures, and the rotating pressure waves were found. Results provide evidence to a new hypothesis, implying that shear layer instabilities constitute the basic mechanism of the RI.

Time-Frequency Analysis of Pressure Fluctuations on a Hydrofoil Undergoing a Transient Pitching Motion Using Hilbert-Huang and Teager-Huang Transforms

2007 ◽  
Author(s):  
S. Benramdane ◽  
J. C. Cexus ◽  
A. O. Boudraa ◽  
J.-A. Astolfi
Keyword(s):  
Frequency Analysis ◽  
Pressure Coefficient ◽  
Pressure Fluctuations ◽  
Low Frequency ◽  
Suction Side ◽  
Intrinsic Mode Functions ◽  
Pitching Motion ◽  
Time Frequency Analysis ◽  
Time Frequency ◽  
The Hilbert Transform

In this paper, time-frequency analysis of wall pressure signals of a hydrofoil’s suction side undergoing a forced transient pitching motion with incoming flow is conducted. A novel method recently introduced by Huang et al., the Empirical Mode Decomposition (EMD), is first used to decompose resulting non-stationary signals into frequency sub-band components called Intrinsic Mode Functions (IMFs). EMD-filtered pressure coefficient signals are then reconstructed from few selected IMFs from low frequency modes and time-frequency analysis performed on high frequency modes. For this latter purpose, two analysis methods are used. The first one consists in demodulating IMFs into their Instantaneous Amplitude (IA) and Instantaneous Frequency (IF) using the Hilbert transform and the second one is based on the Teager energy tracking operator (TEO). The transition occurrence is analyzed using IA and IF of extracted IMFs from chordwise pressure transducer’s signals. This transition occurrence is then described in time-frequency domain.

Aerothermal Impact of Stator-Rim Purge Flow and Rotor-Platform Film Cooling on a Transonic Turbine Stage

2008 ◽  
Author(s):  
M. Pau ◽  
G. Paniagua ◽  
D. Delhaye ◽  
A. de la Loma ◽  
P. Ginibre
Keyword(s):  
Heat Transfer ◽  
Film Cooling ◽  
Pressure Fluctuations ◽  
Pressure Sensors ◽  
Suction Side ◽  
Turbine Stage ◽  
Purge Flow ◽  
Rotor Disk ◽  
Transonic Turbine ◽  
The Impact

This paper describes the effects on the mainstream flow of two types of cooling techniques in a transonic turbine stage: purge gas ejected out of the cavity between the stator rim and the rotor disk, as well as film cooling gas discharged from the rotor-platform. The tests were carried out in a full annular stage fed by a compression tube, at M2is = 1.1, Re = 1.1×106, and at temperature ratios reproducing engine conditions. The stator outlet was instrumented to allow the aerothermal characterization of the purge flow. The rotor blade was heavily instrumented with fast-response pressure sensors and double-layer thin film gauges. The tests are coupled with numerical calculations performed using the ONERA’s code elsA. The stator-rotor interaction is seen to be significantly affected by the stator-rim seal, both in terms of heat transfer and pressure fluctuations. The flow exchange between the rotor disk cavity and the mainstream passage is mainly governed by the vane shock patterns. The purge flow leads to the appearance of a large coherent vortex structure on the suction side of the blade which enhances the overall heat transfer coefficient due to the blockage effect created. Secondly, the impact of the platform cooling is observed to be restricted to the platform, with negligible effects on the blade suction side. The platform cooling results in a clear attenuation of pressure pulsations at some specific locations. Finally the turbine performance was analyzed, comparing measured and CFD results. A detailed loss breakdown analysis has been done using correlations, in order to isolate the different loss component contributions. The presented results should help designers improve the protection of the rotor platform and minimize the amount of coolant used.

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