Numerical Simulation of Aerodynamic Instabilities in a Multistage High-Speed High-Pressure Compressor on Its Test-Rig—Part I: Rotating Stall

2014 ◽  
Vol 136 (10) ◽  
Author(s):  
Flore Crevel ◽  
Nicolas Gourdain ◽  
Stéphane Moreau
Keyword(s):  
High Pressure ◽  
Numerical Simulations ◽  
Rotational Speed ◽  
High Speed ◽  
Low Frequency ◽  
Flow Patterns ◽  
Rotating Stall ◽  
Implicit Time ◽  
Test Rig ◽  
The Third

Aerodynamic instabilities such as stall and surge may lead to mechanical failures. They can be avoided by better understanding and accurate prediction of the associated flow phenomena. Numerical simulations of rotating stall do not often match well the experiments as the number of cells and/or their rotational speed are not correctly predicted. The volumes surrounding the compressor have known effects on rotating stall flow patterns; therefore, an increased need for more realistic simulations has emerged. In that context, this paper addresses a comparison of numerical stall simulation in a compressor alone with a numerical stall simulation including the additional compressor rig. This study investigates the influence of the upstream and downstream volumes of the compressor rig on the rotating stall flow patterns and the consequences on surge inception in a high-pressure, high-speed research compressor. The numerical simulations were conducted using an implicit, time-accurate, 3D compressible Reynolds-averaged Navier–Stokes (URANS) solver. First, rotating stall is simulated in both configurations, and then the outlet nozzles are further closed to bring the compressors to surge. The numerical results show that when the compressor rig is accounted for, fewer cells develop in the third stage and their rotational speed is slightly higher. The major difference linked to the presence of the rig lays in the existence of a 1D low frequency oscillation of the static pressure, which affects the entire flow and modifies surge inception. The analysis of the results leads to a calculation of the thermo-acoustic modes in the whole configuration, which shows that this low frequency corresponds to the third thermo-acoustic mode of the complete test-rig.

Numerical Simulation of Aerodynamic Instabilities in a Multistage High-Speed High-Pressure Compressor on Its Test Rig—Part II: Deep Surge

2014 ◽  
Vol 136 (10) ◽  
Author(s):  
Flore Crevel ◽  
Nicolas Gourdain ◽  
Xavier Ottavy
Keyword(s):  
Numerical Simulation ◽  
High Pressure ◽  
High Speed ◽  
Aircraft Engine ◽  
Recovery Phase ◽  
Implicit Time ◽  
Test Rig ◽  
Reversed Flow ◽  
Mechanical Integrity ◽  
Flow Phase

Aerodynamic instabilities such as stall and surge may occur in compressors, possibly leading to mechanical failures so their avoidance is crucial. A better understanding of those phenomena and an accurate prediction are necessary to improve both the performance and the safety. A surge event in a compressor threatens the mechanical integrity of the aircraft engine, and this remains true for a research compressor on a test rig. As a result, few experimental data on surge are available. Moreover, there are technological, restrictive constraints that exist on test rigs and limit severely the type of data obtainable experimentally. This partially explains why numerical simulation has become a usual, complementary and convenient tool to collect data in a compressor, as it does not disturb the flow nor does it encounter technological limits. Despite the inherent difficulties, an entire surge cycle has been simulated in a high-speed, high-pressure, multistage research compressor, using an implicit, time-accurate, 3D compressible unsteady Reynolds-averaged Navier–Stokes solver. First, the paper presents the main features of the surge cycle obtained, along with those from the experimental cycle, for a validation purpose. Four phases compose the surge cycle: surge inception, the reversed-flow phase, the recovery phase, and the repressurization of the compressor flow. All of them are described, and focus is put on surge inception and the reversed-flow phase, as they induce greater risk for the mechanical integrity of the machine.

Experimental and Analytical Leakage Characterization of Annular Gas Seals: Honeycomb, Labyrinth and Pocket Damper Seals

2011 ◽  
Author(s):  
Nuo Sheng ◽  
Eric J. Ruggiero ◽  
Ravindra Devi ◽  
Jianping Guo ◽  
Massimiliano Cirri
Keyword(s):  
New York ◽  
High Pressure ◽  
High Speed ◽  
System Level ◽  
Operating Pressure ◽  
Test Rig ◽  
Flow Mechanisms ◽  
Successful Design ◽  
Gas Seals ◽  
Analytical Tools

Modern day turbomachinery requires the use of annular gas seals to provide flow restriction from high pressure to low pressure regions within the machine. These flow restrictions are critical design points in the overall performance of the machine and directly impact the system-level efficiency. Consequently, understanding the leakage performance of a given seal element as a function of operating pressure, rotor speed, and rotor offset is critical to the successful design of the turbomachine. In the present work, three annular gas seals are experimentally tested on a leakage test rig at GE Global Research (Niskayuna, New York). The test rig is capable of high-speed, high-pressure flow testing and has a radial degree of freedom that enables non-concentric leakage characterization. The leakage performances of a labyrinth, honeycomb and pocket damper seals are compared over a range of inlet pressures and pressure ratios. Analytical tools, including a CFD model and a Bulk Flow Code, are developed to provide leakage prediction and to establish understanding of underlying flow mechanisms. Predictions of the seal leakage are found to be in good agreement with experimental data.

Numerical and Experimental Study of Multiphase Transient Core-Annular Flow Patterns in a Spouted Bed

2020 ◽  
Vol 142 (9) ◽  
Author(s):  
Ling Zhou ◽  
Chen Han ◽  
Ling Bai ◽  
Weidong Shi ◽  
Ramesh Agarwal
Keyword(s):  
Numerical Simulations ◽  
Flow Pattern ◽  
High Speed ◽  
Annular Flow ◽  
Fluid Phase ◽  
Flow Patterns ◽  
Spouted Bed ◽  
High Speed Imaging ◽  
Spouted Beds ◽  
Number Of Particles

Abstract Dense solid–gas bubbling systems with combined fluid-particle motion are among one of the most extensively used fluidization forms used in the chemical industry. Therefore, it is important to have a good understanding of the hydrodynamic behavior of bubbles. In this paper, both the experiment and numerical simulations are used to investigate the flow patterns in a spouted bed. For numerical simulations, the bidirectional coupling simulations using computational fluid dynamics (CFD) with discrete element method (DEM) are conducted. The results show that the simulations can accurately predict the bubbles morphology compared with the experimental results. When the number of particles is 30,000, only a single core-annular flow pattern appears. When the number of particles is increased to 36,500, the single bubble in the spouted bed transitions into two and a double core-annular flow pattern emerges. As the number of particles is increased to 43,000, a complex multicore-annular flow pattern appears. These flow patterns are also observed in the experiments using high-speed imaging camera. This paper analyzes and explains the causes of these flow phenomena from the dynamic characteristics of particle phase and fluid phase. These results have great significance in providing guidance for optimization of dense phase bubbling spouted beds.

Design of a High-Speed Rotating Test Rig for Adaptive Seal Systems

2015 ◽  
Author(s):  
Laura S. Beermann ◽  
Corina Höfler ◽  
Hans-Jörg Bauer
Keyword(s):  
High Pressure ◽  
Flow Field ◽  
High Speed ◽  
Operating Conditions ◽  
Turbine Engines ◽  
Parameter Study ◽  
Test Rig ◽  
Swirl Chamber ◽  
Mass Flows ◽  
Gap Width

Gas turbine engines are subject to increased performance and improved efficiency, which leads to rising core temperatures with additional cooling needs. Reducing the parasitic leakage in the secondary flow system is important to meet the challenging requirements. New seal designs have to be tested and optimized at engine like conditions, like high pressure of up to 9 bar and surface speed of up to 280 m/s as well as an adjusted flow field. Flexible seal designs are an innovative approach to reduce leakage mass flows significantly. Axial and radial movements during transient operating conditions can be compensated easily, thus allowing a smaller gap width and minimizing rub and heat load. This paper describes the design and construction of a new rotating test rig facility. To the knowledge of the authors, this is the only test rig with an adjustable gap width and flow field in a high pressure and speed range. The facility is capable of up to 8 bar differential pressure across the seal and up to 4 bar back pressure. The high revolution engine facilitates a surface speed of up to 280 m/s. A traversable casing allows a quick change of the gap width during operation and simulates radial and axial rotor/stator movements in the engine. The seal movement as well as the resulting gap width are measured during operation to fully understand the seal behavior. An important feature of the new test rig is the continuously adjustable pre-swirl system. It has been designed to cover the different flow conditions in the real engine. Therefore, a RANS parameter study of the pre-swirl chamber has been conducted, which shows the adjustability of different pre-swirl ratios for constant and changing inlet mass flows.

Proposed Forcing Mechanisms and Non-Linear Effects on Subsynchronous Vibrations in High Performance Turbomachinery

1997 ◽  
Author(s):  
M. F. White ◽  
S. H. Chan
Keyword(s):  
High Speed ◽  
High Performance ◽  
Fluid Dynamic ◽  
Low Frequency ◽  
Rotating Stall ◽  
Rotor Blades ◽  
Stable Form ◽  
Flow Distortion ◽  
Non Linear ◽  
Forcing Mechanisms

This paper suggests that the subsynchronous “instability” observed in many high speed, high performance turbomachines while operating in the supercritical speed range may in some cases be a stable form of lightly damped vibrations. They could be excited by low frequency process forces due to unsteady flow conditions. The non-linearity in the mass, stiffness or damping of the system may have provided a coupling or frequency transformation between the excitation forces and the subsynchronous vibrations. Depending on the kind of non-linear characteristics the critical speeds as defined for a linear system may become regions of “instability”. The degree of non-linearity of the bearing-seal-rotor system has an influence on the sensitivity of the machine to subsynchronous vibrations. Some forcing mechanisms are presented, including non-identical rotor blades, inlet flow distortion and rotating stall. The effect on response of mode shape, internal shaft rotatory damping and frequency dependence of bearing damping at subsynchronous frequencies are discussed. It is recommended that the unsteady fluid dynamic forces, together with the effects of non-linear dynamic characteristics be further investigated to provide more experimental evidence for this hypothesis.

scholarly journals Analysis of Rotating Stall in Vaneless Diffusers of Centrifugal Compressors

1980 ◽  
Author(s):  
Amr N. Abdelhamid
Keyword(s):  
Rotational Speed ◽  
High Speed ◽  
Equations Of Motion ◽  
Unsteady Flows ◽  
Rotating Stall ◽  
Radius Ratio ◽  
Centrifugal Compressors ◽  
Coupling Conditions ◽  
Flow Oscillations ◽  
Vaneless Diffusers

Self-excited flow oscillations in radial vaneless diffusers of centrifugal compressors are investigated analytically using the linearized equations of motion for unsteady flows. Solutions of the differential equations are made to satisfy boundary conditions at diffuser inlet and exit which in typical conversion systems represent the coupling between the diffuser and upstream and downstream components. The results indicate that the rotational speed of the stall pattern is dependent on the diffuser radius ratio and the coupling conditions between the impeller and the diffuser. It is shown that the dependence of the onset of the flow oscillations on the diffuser radius ratio is strong if the conditions at diffuser inlet are such that low speed rotating stall patterns are generated in the diffuser. Onset of high speed rotating stall patterns is more affected by the coupling conditions between the impeller and the diffuser than by the diffuser radius ratio.

Rotating Stall Observations in a High Speed Compressor—Part I: Experimental Study

2015 ◽  
Vol 137 (5) ◽  
Author(s):  
J. Dodds ◽  
M. Vahdati
Keyword(s):  
Experimental Study ◽  
High Speed ◽  
Low Frequency ◽  
Axial Flow ◽  
Rotating Stall ◽  
Strain Gages ◽  
Spectral Content ◽  
Pressure Transducers ◽  
Unsteady Rans ◽  
Variable Stator

In this two-part paper, the phenomenon of part span rotating stall is studied. The objective is to improve understanding of the physics by which stable and persistent rotating stall occurs within high speed axial flow compressors. This phenomenon is studied both experimentally (Part I) and through the use of unsteady RANS simulations (Part II). In this paper, the behavior of an eight stage high speed compressor is studied during slow acceleration maneuvres along a fixed working line. Casing mounted pressure transducers and rotor mounted strain gages are used to examine the spectral content of any unsteadiness in the flow and its behavior across the operating range. By deliberate aerodynamic mismatching of the front stages through adjustment of three rows of variable stator vanes (VSVs), stable rotating stall is initiated. The observed behavior falls into two “families” of high and low frequency when tracked on the instrumentation. Further analysis based on the Doppler shift between the static and rotating measurements confirms that these respective phenomena are due to rotating stall of high and low cell count. Acoustic modes resulting from stall/rotor interaction are also identified. Strong correlation of the stall intensity with simple 1D meanline predicted loading parameters suggests that these families of behavior are independently linked to the stalling of different regions within the compressor.

Stall Inception Behavior in a Centrifugal Compressor

1994 ◽  
Author(s):  
J. Chen ◽  
H. Hasemann ◽  
Li Shi ◽  
M. Rautenberg
Keyword(s):  
Centrifugal Compressor ◽  
Reverse Flow ◽  
Low Frequency ◽  
Rotating Stall ◽  
Time Range ◽  
Stall Inception ◽  
Pressure Transducers ◽  
Axial Compressors ◽  
The Third ◽  
Speed Range

In studying the stall inception process, while most results were reported for axial compressors, the present paper investigates the stall inception behavior typified in a centrifugal compressor. The test was conducted with a radially-bladed impeller and in a speed range of 8000–14000 rpm. Extensive pressure transducers were used to study the frequency characteristics of emerging stall waves. As a result, stall precursors were detected, all with clear mode seen from frequency analysis, but very much different by the behavior of their onset, existence and development. The first type, called the stable-amplitude precursor, exists in a time range of about 20–90 impeller revolutions, with unpredictable and different frequencies from the fully developed stall. Such perturbation, once appeared, may grow to the full stall straightly, or may appear for several times intermittently before finally reaching the full stall, thus acting as a pre-precursor in the whole stall inception process. The second type is the progressive-amplitude precursor when the perturbation emerges as long as 270 impeller revolutions prior to and progressively develops into the full amplitude stall with no change of frequency during this process. The third type, which has been detected for the rotating stall with evident reverse flow symptom, is the precursive pressure increase accompanied with the stable- or progressive-amplitude perturbation, before the full stall establishes. The inception process is also examined for surge during the test of the same compressor, in which the existence of rotating stall in front of every surge cycle and the low frequency precursive wave before surge cycles is demonstrated. Finally, the blade passage frequencies for precursor pressure signals are further analysed to address the monitoring strategy during stall inception process.

Computational and Experimental Study of the Unsteady Convection of Entropy Waves Within a High Pressure Turbine Stage

2020 ◽  
Author(s):  
Lorenzo Pinelli ◽  
Michele Marconcini ◽  
Roberto Pacciani ◽  
Paolo Gaetani ◽  
Giacomo Persico
Keyword(s):  
High Pressure ◽  
High Speed ◽  
Low Frequency ◽  
Frequency Content ◽  
Turbine Stage ◽  
High Pressure Turbine ◽  
Cfd Simulations ◽  
Time Resolved ◽  
Azimuthal Position ◽  
Cfd Method

Abstract This paper describes the transport and the interaction of pulsating entropy waves generated by combustor burners within a high pressure turbine stage for aeronautical application. Experiments and Computational Fluid Dynamics (CFD) simulations were carried out in the context of the European Research Project RECORD. Experimental campaigns considering burner-representative temperature fluctuations (in terms of spot shape, fluctuation frequency and total temperature variation percentage) injected upstream of an un-cooled high-pressure gas turbine stage have been performed in the high-speed closed-loop test-rig of the Fluid Machine Laboratory (LFM) of Politecnico di Milano (Italy). The pulsating entropy waves are injected at the stage inlet in streamwise direction at four different azimuthal positions featuring a 7% over-temperature with respect to the main flow with a frequency of 90 Hz. Detailed time-resolved temperature measurements (in the range of 0–200 Hz) upstream and downstream of the stage, as well as in the stator–rotor axial gap were performed. Time-accurate CFD simulations with and without entropy fluctuations imposed at the stage inlet were performed with the TRAF code, developed by the University of Florence. A numerical post-processing procedure, based on the DFT (Discrete Fourier Transform) of the conservative variables has been implemented to extract the low frequency content connected to the entropy fluctuations. Measurements highlighted a significant attenuation of the entropy wave spot throughout their transport within the stator channel and their interaction with the rotor blade rows, highly depending on their injection azimuthal position. Simulations show an overall good agreement with the experiments on the measurement traverses, especially at the stage outlet. By exploiting the combination of experiments and simulations, the aerodynamic and thermal implications of the temperature fluctuation injected upstream of the stage were properly assessed, thus allowing suggest useful information to the designer. The comparison with the experiments confirms the accuracy of the CFD method to solve the periodic, but characterized by a low frequency content event, associated with the entropy wave fluctuation.

Rotating Stall Observations in a High Speed Compressor: Part 1 — Experimental Study

2014 ◽  
Author(s):  
J. Dodds ◽  
M. Vahdati
Keyword(s):  
High Speed ◽  
Low Frequency ◽  
Axial Flow ◽  
Rotating Stall ◽  
Strain Gauges ◽  
Spectral Content ◽  
Pressure Transducers ◽  
Unsteady Rans ◽  
Observed Behaviour ◽  
Variable Stator

In this two part paper the phenomenon of part span rotating stall is studied. The objective is to improve understanding of the physics by which stable and persistent rotating stall occurs within high speed axial flow compressors. This phenomenon is studied both experimentally (part 1) and through the use of unsteady RANS simulations (part 2). In this paper, the behaviour of an 8 stage high speed compressor is studied during slow acceleration manoeuvres along a fixed working line. Casing mounted pressure transducers and rotor mounted strain gauges are used to examine the spectral content of any unsteadiness in the flow and its behaviour across the operating range. By deliberate aerodynamic mismatching of the front stages through adjustment of three rows of variable stator vanes, stable rotating stall is initiated. The observed behaviour falls into two ‘families’ of high and low frequency when tracked on the instrumentation. Further analysis based on the Doppler shift between the static and rotating measurements confirms that these respective phenomena are due to rotating stall of high and low cell count. Acoustic modes resulting from stall/rotor interaction are also identified. Strong correlation of the stall intensity with simple 1D meanline predicted loading parameters suggests that these families of behaviour are independently linked to the stalling of different regions within the compressor.

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