Influence of the Swirling Flow in the Side Cavities of a High-Pressure Centrifugal Compressor on the Characteristics of Excited Acoustic Modes

2012 ◽  
Author(s):  
N. Petry ◽  
S. König ◽  
F.-K. Benra
Keyword(s):  
High Pressure ◽  
Flow Field ◽  
Centrifugal Compressor ◽  
Swirling Flow ◽  
Frame Of Reference ◽  
Circumferential Velocity ◽  
Experimental Investigations ◽  
Element Analysis ◽  
Acoustic Modes ◽  
At Resonance

Previous experimental investigations revealed the existence of acoustic modes in the side cavities of a high-pressure centrifugal compressor. These modes were excited by pressure patterns which resulted from rotor/stator-interactions (often referred to as Tyler/Sofrin-modes). The acoustic modes were significantly influenced by the prevailing flow in the side cavities. The flow field in such rotor/stator-cavities is characterized by a high circumferential velocity component. The circumferential velocity of the flow and the phase velocity of the acoustic eigenmode superimpose each other, so that the frequencies of the acoustic eigenmodes with respect to the stator frame of reference follow from the sum of both velocities. In the previous study the circumferential velocity was estimated based on existing literature and the phase velocities of the acoustic modes were calculated via an acoustic modal analysis. Based on these results the rotational speeds of the compressor, where acoustic modes were excited in resonance, were determined. The present paper is based on these results and focuses on the influence of the swirling flow and the coupling of the excited acoustic modes between the two side cavities. Such a coupling has been predicted in previous numerical studies but no experimental evidence was available at that time. In this study the circumferential velocities of the flow are determined by measuring the actual radial pressure distribution in the side cavities and assuming radial equilibrium. The determined values are directly used for the prediction of the rotational speeds at resonance. The values for the rotational speeds at resonance predicted that way are compared to the resonance speeds found in the experiments. Further on, simultaneously measured pressure fluctuations in the shroud and hub side cavities with respect to the rotor frame of reference give evidence about the coupling of the acoustic modes between the two side cavities in case of resonance. If the experimentally determined swirling flow velocity is accounted for in the prediction of acoustic resonances, the calculated rotational speeds of resonance are in good agreement with the experimental findings in most cases. Neglecting the flow in the cavities, however, leads to large deviations between calculated and experimentally determined rotational speeds. Varying the operating point of the compressor results in changes of the circumferential velocities in the side cavities and, therefore, in changes of the rotational speeds of resonance. Contrary to the acoustic modes calculated via a Finite Element Analysis by the authors of this paper in previous studies the excited acoustic modes in the experiments are mostly not coupled between the two side cavities, but are localized to one of both cavities. This finding is assumed to be caused by the flow field in the compressor.

Influence of the Swirling Flow in the Side Cavities of a High-Pressure Centrifugal Compressor on the Characteristics of Excited Acoustic Modes

2013 ◽  
Vol 135 (3) ◽  
Author(s):  
N. Petry ◽  
S. König ◽  
F.-K. Benra
Keyword(s):  
High Pressure ◽  
Flow Field ◽  
Centrifugal Compressor ◽  
Swirling Flow ◽  
Frame Of Reference ◽  
Circumferential Velocity ◽  
Experimental Investigations ◽  
Element Analysis ◽  
Acoustic Modes ◽  
At Resonance

Previous experimental investigations revealed the existence of acoustic modes in the side cavities of a high-pressure centrifugal compressor. These modes were excited by pressure patterns which resulted from rotor/stator-interactions (often referred to as Tyler/Sofrin-modes). The acoustic modes were significantly influenced by the prevailing flow in the side cavities. The flow field in such rotor/stator-cavities is characterized by a high circumferential velocity component. The circumferential velocity of the flow and the phase velocity of the acoustic eigenmode superimpose each other, so that the frequencies of the acoustic eigenmodes with respect to the stator frame of reference follow from the sum of both velocities. In the previous study the circumferential velocity was estimated based on existing literature and the phase velocities of the acoustic modes were calculated via an acoustic modal analysis. Based on these results the rotational speeds of the compressor, where acoustic modes were excited in resonance, were determined. The present paper is based on these results and focuses on the influence of the swirling flow and the coupling of the excited acoustic modes between the two side cavities. Such a coupling has been predicted in previous numerical studies but no experimental evidence was available at that time. In this study the circumferential velocities of the flow are determined by measuring the actual radial pressure distribution in the side cavities and assuming radial equilibrium. The determined values are directly used for the prediction of the rotational speeds at resonance. The values for the rotational speeds at resonance predicted that way are compared to the resonance speeds found in the experiments. Further on, simultaneously measured pressure fluctuations in the shroud and hub side cavities with respect to the rotor frame of reference give evidence about the coupling of the acoustic modes between the two side cavities in case of resonance. If the experimentally determined swirling flow velocity is accounted for in the prediction of acoustic resonances, the calculated rotational speeds of resonance are in good agreement with the experimental findings in most cases. Neglecting the flow in the cavities, however, leads to large deviations between calculated and experimentally determined rotational speeds. Varying the operating point of the compressor results in changes of the circumferential velocities in the side cavities and, therefore, in changes of the rotational speeds of resonance. Contrary to the acoustic modes calculated via a finite element analysis by the authors of this paper in previous studies the excited acoustic modes in the experiments are mostly not coupled between the two side cavities, but are localized to one of both cavities. This finding is assumed to be caused by the flow field in the compressor.

Boundary-layer velocity profiles in a swirling convergent flow field

1972 ◽  
Vol 52 (2) ◽  
pp. 357-367 ◽  
Author(s):  
T. M. Houlihan ◽  
D. J. Hornstra
Keyword(s):  
Boundary Layer ◽  
Flow Field ◽  
Swirling Flow ◽  
Theoretical Calculations ◽  
Experimental Investigations ◽  
Conical Nozzle ◽  
Flow Conditions ◽  
Boundary Layer Flows ◽  
Layer Velocity ◽  
Convergent Flow

Velocity distributions within the boundary layer of a swirling flow of incompressible fluid in a convergent conical nozzle have been investigated. Theoretical calculations with boundary conditions more appropriate to physically existent situations discounted the existence of 'super-velocities’ within the boundary layer. Parallel experimental investigations demonstrated an interdependence of core and boundary-layer flows which precluded the maintenance of the flow conditions required by the analysis.

Computational and experimental investigations in a cyclone dust separator

1997 ◽  
Vol 211 (4) ◽  
pp. 247-257 ◽  
Author(s):  
S M Fraser ◽  
A M Abdel-Razek ◽  
M Z Abdullah
Keyword(s):  
Flow Field ◽  
Richardson Number ◽  
Swirling Flow ◽  
Laser Doppler Anemometry ◽  
Experimental Studies ◽  
Three Dimensional ◽  
Experimental Results ◽  
Experimental Investigations ◽  
Cyclone Chamber ◽  
Dust Separator

Three-dimensional turbulent flow in a model cyclone has been simulated using PHOENICS code and experimental studies carried out using a laser Doppler anemometry (LDA) system. The experimental results were used to validate the computed velocity distributions based on the standard and a modified k-∊ model. The standard k-∊ model was found to be unsatisfactory for the prediction of the flow field inside the cyclone chamber. By considering the strong swirling flow and the streamlined curvature, a k-∊ model, modified to take account of the Richardson number, provided better velocity distributions and better agreement with the experimental results.

Parker-Type Acoustic Resonances in the Return Guide Vane Cascade of a Centrifugal Compressor: Theoretical Modeling and Experimental Verification

2010 ◽  
Author(s):  
Sven Ko¨nig ◽  
Nico Petry
Keyword(s):  
High Pressure ◽  
Centrifugal Compressor ◽  
Vortex Shedding ◽  
Guide Vane ◽  
Experimental Results ◽  
Mode Shapes ◽  
Centrifugal Compressors ◽  
Acoustic Modes ◽  
Trailing Edges ◽  
Acoustic Resonances

The potential of acoustic resonances within vane arrays of turbomachinery has been known since the fundamental investigations of Parker back in the sixties and seventies. In his basic studies on flat plate arrays (and later on for an axial compressor) he could show that vortex shedding from the respective trailing edges may excite acoustic resonances that are localized to the vaned flow region. In principle, such phenomena are conceivable for any kind of turbomachinery; however, no such investigations are publicly available for the centrifugal type. The current investigation is one part of an extended research program to gain a better understanding of excitation and noise generating mechanism in centrifugal compressors, and focuses on Parker-type acoustic resonances within the return guide vane cascade of a high-pressure centrifugal compressor. A simplified model to calculate the respective acoustic eigenfrequencies is presented, and the results are compared with finite element analyses. Furthermore, the calculated mode shapes and frequencies are compared with experimental results. It is shown that for high-pressure centrifugal compressors, according to the nomenclature of Parker, acoustic modes of the α, β, γ, and δ type exist over a wide operating range within the return guide vane cascade. For engine representative Reynolds numbers, the experimental results indicate that the vortex shedding frequencies from the vane trailing edges cannot be characterized by a definite Strouhal number; the excitation of the Parker-type acoustic modes is mostly broadband due to the flow turbulence. No lock-in phenomenon between vortex shedding and acoustic modes takes place, and the amplitudes of the acoustic resonances are too small to cause machines failures or excessive noise levels.

Wake–Wake Interaction and Its Potential for Clocking in a Transonic High-Pressure Turbine

2001 ◽  
Vol 124 (1) ◽  
pp. 69-76 ◽  
Author(s):  
Frank Hummel
Keyword(s):  
High Pressure ◽  
Flow Field ◽  
Flow Direction ◽  
Numerical Procedure ◽  
Flow Simulation ◽  
Suction Side ◽  
Frame Of Reference ◽  
High Pressure Turbine ◽  
Trailing Edge ◽  
Time Resolved

Two-dimensional unsteady Navier–Stokes calculations of a transonic single-stage high-pressure turbine were carried out with emphasis on the flow field behind the rotor. Detailed validation of the numerical procedure with experimental data showed excellent agreement in both time-averaged and time-resolved flow quantities. The numerical timestep as well as the grid resolution allowed the prediction of the Ka´rma´n vortex streets of both stator and rotor. Therefore, the influence of the vorticity shed from the stator on the vortex street of the rotor is detectable. It was found that certain vortices in the rotor wake are enhanced while others are diminished by passing stator wake segments. A schematic of this process is presented. In the relative frame of reference, the rotor is operating in a transonic flow field with shocks at the suction side trailing edge. These shocks interact with both rotor and stator wakes. It was found that a shock modulation occurs in time and space due to the stator wake passing. In the absolute frame of reference behind the rotor, a 50-percent variation in shock strength is observed according to the circumferential or clocking position. Furthermore, a substantial weakening of the rotor suction side trailing edge shock in flow direction is detected in an unsteady flow simulation when compared to a steady-state calculation, which is caused by convection of upstream stator wake segments. The physics of the aforementioned unsteady phenomena as well as their influence on design are discussed.

The Experimental Investigations of Centripetal Air Bleed With Tubed Vortex Reducer for Secondary Air System in Gas Turbine

2014 ◽  
Author(s):  
Xiao Chen ◽  
Ye Feng ◽  
Lijun Wu
Keyword(s):  
High Pressure ◽  
Flow Field ◽  
Gas Turbine ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Pressure Loss ◽  
Experimental Investigations ◽  
Pressure Losses ◽  
Nozzle Guide

In a modern gas turbine, the air bled through High Pressure Compressor (HPC) rotor drums from the main flow is transported radially inwards and then transferred to cool the High Pressure Turbine (HPT). The centripetal air flow creates a strong vortex, which results in huge pressure losses. This not only restricts the mass flow rate, but also reduces the cooling air pressure for down-stream hot components. Adding vortex reducer tubes to the centripetal air bleed can reduce the pressure loss and ensure the pressure and mass flow rate of the supply air. Design optimization of the tubed vortex reducer is essential in minimizing the pressure losses. This paper describes experimental investigations of different configurations of tubed vortex reducers at different rotational speeds and mass flow rates. Particular attention is paid to the shape of the drum hole, the length of the tubed vortex reducers at the same installation location, and the angles of the nozzle guide vane outlets. The core section of test rig is comprised of two steel disks, one drum rotor and stationary cases with nozzle guide vanes. It operates at representative engine parameters, such as the turbulent flow parameter, λT(0.2–1.8) and the Rossby number Ro(0.05–0.08). Three conclusions can be drawn based on the experimental results. 1) The shape of the drum hole is a key factor of the bleed system pressure loss. An oval hole configuration has less flow resistance and results in lower pressure losses compared with a circular hole design. 2) The tests prove that tubed vortex reducers are instrumental in minimizing centripetal air flow. These components effectively restrain the free vortex development and decrease the pressure losses in the cavity. 3) Basically, the flow field consists of a free vortex and a forced vortex. The length of the tube influences the flow field and the pressure losses at the inlet and outlet of the tubed vortex reducer. However, the tube length is less important when compared with the shape of drum hole.

Finite Element Analysis of Pipe Bends under External Loads

2017 ◽  
pp. 209-238
Author(s):  
Sumesh S. ◽  
A. R. Veerappan ◽  
S. Shanmugam
Keyword(s):  
Finite Element Analysis ◽  
Plastic Deformation ◽  
Finite Element ◽  
High Pressure ◽  
Experimental Investigations ◽  
Toxic Substances ◽  
Element Analysis ◽  
Piping Systems ◽  
Critical Components ◽  
External Loads

Pipelines are being used to convey different sorts of fluids from hazardous and toxic substances to high pressure steam. Piping systems are subjected to various external loads leading to major failures with gross plastic deformation. Pipe bends are incorporated into piping systems not only to change the direction of flow but also to provide flexibility, hence they are considered to be critical components and its safe design under various loads becomes important. Earlier studies of pipe bends utilized analytical methods to determine the plastic loads. The evolution of FEM and the advancements in computational capabilities have enabled analysts to generate large number of data which is expensive and time consuming with experimental investigations. In this chapter, the major studies on pipe bends by various researchers are explored. Different studies on pipe bends namely stress analysis and the influence of geometric shape imperfections are also presented.

Parker-Type Acoustic Resonances in the Return Guide Vane Cascade of a Centrifugal Compressor – Theoretical Modeling and Experimental Verification

2012 ◽  
Vol 134 (6) ◽  
Author(s):  
Sven König ◽  
Nico Petry
Keyword(s):  
High Pressure ◽  
Centrifugal Compressor ◽  
Vortex Shedding ◽  
Guide Vane ◽  
Experimental Results ◽  
Simplified Model ◽  
Centrifugal Compressors ◽  
Acoustic Modes ◽  
Trailing Edges ◽  
Acoustic Resonances

The potential of acoustic resonances within vane arrays of turbomachinery has been known since the fundamental investigations of Parker back in the sixties and seventies. In his basic studies on flat plate arrays (and later on for an axial compressor) he could show that vortex shedding from the respective trailing edges may excite acoustic resonances that are localized to the vaned flow region. In principle, such phenomena are conceivable for any kind of turbomachinery; however, no such investigations are publicly available for the centrifugal type. The current investigation is one part of an extended research program to gain a better understanding of excitation and noise generating mechanism in centrifugal compressors, and focuses on Parker-type acoustic resonances within the return guide vane cascade of a high-pressure centrifugal compressor. A simplified model to calculate the respective acoustic eigenfrequencies is presented, and the results are compared with finite element analyses. Furthermore, the calculated mode shapes and frequencies are compared with experimental results. It is shown that for high-pressure centrifugal compressors, according to the nomenclature of Parker, acoustic modes of the α, β, γ, and δ type exist over a wide operating range within the return guide vane cascade. For engine representative Reynolds numbers, the experimental results indicate that the vortex shedding frequencies from the vane trailing edges cannot be characterized by a definite Strouhal number; the excitation of the Parker-type acoustic modes is mostly broadband due to the flow turbulence. No lock-in phenomenon between vortex shedding and acoustic modes takes place, and the amplitudes of the acoustic resonances are too small to cause machines failures or excessive noise levels. The simplified model presented in the current paper has been successfully validated for the return guide vane cascade of a centrifugal compressor but can also be applied for arbitrary blade and vane arrays, given that the chord-to-pitch ratio is sufficiently high. With this model, frequency components in measured pressure signals, that were left unexplained in the past, can be easily inspected for possible Parker-type resonances.

Effects of Disk Geometry on Strength of a Centrifugal Compressor Impeller for a High Pressure Ratio Turbocharger

2012 ◽  
Author(s):  
Xinqian Zheng ◽  
Lei Jin ◽  
Yangjun Zhang ◽  
Huihua Qian ◽  
Fenghu Liu
Keyword(s):  
High Pressure ◽  
Centrifugal Compressor ◽  
Internal Combustion Engines ◽  
Maximum Stress ◽  
Pressure Ratio ◽  
Equivalent Stress ◽  
Geometric Parameters ◽  
Element Analysis ◽  
High Pressure Ratio ◽  
Compressor Impeller

High pressure ratio turbocharger technology is widely used to lower fuel consumption, reduce emissions and improve power density of internal combustion engines. The centrifugal compressor is the key component of turbochargers. The reliability of compressor impeller becomes critical with increasing pressure ratio. For extending its maximum rotational speed limits, it is important to improve the impeller’s disk geometry to decease stress. In order to investigate the effects of disk geometric parameters on the strength of a centrifugal compressor impeller, a 3-D finite element analysis (FEA) with various disk geometric parameters was performed in this paper. Subsequently, the impeller’s disk geometry was improved to decrease the maximum stress. The results show that the maximum von Mises equivalent stress in the core of the disk of the improved impeller could be decreased by 19%. Further, the maximum stress of another improved impeller without shaft bore decreases by 50%. That means, the improved impeller can bear higher pressure ratios or use cheaper material with lower ultimate tensile strength.

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