scholarly journals Experimental and Numerical Analysis of a Compressor Stage under Flow Distortion

2021 ◽  
Vol 6 (4) ◽  
pp. 43
Author(s):  
Alberto Baretter ◽  
Benjamin Godard ◽  
Pierric Joseph ◽  
Olivier Roussette ◽  
Francesco Romanò ◽  
...  
Keyword(s):  
Boundary Condition ◽  
Flow Behavior ◽  
Pressure Ratio ◽  
Pressure Sensors ◽  
Rotating Stall ◽  
Dynamic Mode Decomposition ◽  
Dynamic Mode ◽  
Compressor Stage ◽  
Flow Distortion ◽  
Inlet Boundary Condition

On many occasions, fan or compressor stages have to face azimuthal flow distortion at inlet, which affects their performance and stability. These flow distortions can be caused by external events or by some particular geometrical features. The aim of this work is to propose a joined numerical and experimental analysis of the flow behavior in a single axial compressor stage under flow distortion. The distortions are generated by different grids that are placed upstream to the rotor. Experimentally, the flow analysis is based on the measurements obtained by a series of unsteady pressure sensors flush-mounted at the casing of the machine rotor. URANS computations are conducted using the elsA software. The flow distortion is simulated by a drop of stagnation pressure ratio at the inlet boundary condition. The study is focusing first on the ability of a pressure drop, imposed as an inlet boundary condition in CFD, to reproduce accurately the effect of a flow distortion. The analysis is conducted using singular value decomposition (SVD) and dynamic mode decomposition (DMD). A special attention is then paid, on the experimental level, to the arising of rotating stall, from the onset of the instability up to completely developed stall cells.

Characteristics of Stable Rotating Stall Cells in an Axial Compressor

2017 ◽  
Author(s):  
Adam R. Hickman ◽  
Scott C. Morris
Keyword(s):  
Flow Field ◽  
High Speed ◽  
Pressure Ratio ◽  
Pressure Sensors ◽  
Axial Compressor ◽  
Field Measurements ◽  
Rotating Stall ◽  
Flow Coefficient ◽  
Stable Operation ◽  
Double Phase

Flow field measurements of a high-speed axial compressor are presented during pre-stall and post-stall conditions. The paper provides an analysis of measurements from a circumferential array of unsteady shroud static pressure sensors during stall cell development. At low-speed, the stall cell approached a stable size in approximately two rotor revolutions. At higher speeds, the stall cell developed within a short amount of time after stall inception, but then fluctuated in circumferential extent as the compressor transiently approached a stable post-stall operating point. The size of the stall cell was found to be related to the annulus average flow coefficient. A discussion of Phase-Locked Average (PLA) statistics on flow field measurements during stable operation is also included. In conditions where rotating stall is present, flow field measurements can be Double Phase-Locked Averaged (DPLA) using a once-per-revolution (1/Rev) pulse and the period of the stall cell. The DPLA method provides greater detail and understanding into the structure of the stall cell. DPLA data indicated that a stalled compressor annulus can be considered to contained three main regions: over-pressurized passages, stalled passages, and recovering passages. Within the over-pressured region, rotor passages exhibited increased blade loading and pressure ratio compared to pre-stall values.

Understanding Effects of Wet Compression on Separated Flow Behavior in an Axial Compressor Stage Using CFD Analysis

2011 ◽  
Vol 133 (3) ◽  
Author(s):  
Lanxin Sun ◽  
Qun Zheng ◽  
Yijin Li ◽  
Rakesh Bhargava
Keyword(s):  
Flow Field ◽  
Flow Behavior ◽  
Pressure Ratio ◽  
Water Flow Rate ◽  
Separated Flow ◽  
Operating Conditions ◽  
Compressor Stage ◽  
Compressor Cascade ◽  
Suction Surface ◽  
Wet Compression

The effects of wet compression on the flow field within a compressor stage, particularly in the presence of the separated flow region, are not fully understood. Numerical simulations of 3D compressible separated flows within a wet compression compressor stage are carried out using a computational fluid dynamics (CFD) program. Numerical computations of flow fields in a compressor cascade with wet compression assume that a separated region exist in the corner of the rotor blade suction surface and hub surface in the case of dry compression. Under different operating conditions and with wet compression, this study presents the changes in the extent of separated region on the flow channel surfaces, compression efficiency, pressure ratio and specific compression work, etc. Also, effects of factors such as droplet size, droplet temperature, and injected water flow rate on the compressor stage performance and flow field within compressor stage passage have been investigated. The results show that wet compression could weaken and eliminate the flow separation and then the efficiency and pressure ratio maintain a high level.

Spike and Modal Stall Inception in an Advanced Turbocharger Centrifugal Compressor

2009 ◽  
Vol 131 (3) ◽  
Author(s):  
Z. S. Spakovszky ◽  
C. H. Roduner
Keyword(s):  
Centrifugal Compressor ◽  
High Speed ◽  
Pressure Ratio ◽  
Pressure Sensors ◽  
Rotating Stall ◽  
Vaned Diffuser ◽  
Stall Inception ◽  
Compression System ◽  
The Impact ◽  
Highly Loaded

In turbocharger applications, bleed air near the impeller exit is often used for secondary flow systems to seal bearing compartments and to balance the thrust load on the bearings. There is experimental evidence that the performance and operability of highly-loaded centrifugal compressor designs can be sensitive to the amount of bleed air. To investigate the underlying mechanisms and to assess the impact of bleed air on the compressor dynamic behavior, a research program was carried out on a preproduction, 5.0 pressure ratio, high-speed centrifugal compressor stage of advanced design. The investigations showed that bleed air can significantly reduce the stable flow range. Compressor rig experiments, using an array of unsteady pressure sensors and a bleed valve to simulate a typical turbocharger environment, suggest that the path into compression system instability is altered by the bleed flow. Without the bleed flow, the prestall behavior is dominated by short-wavelength disturbances, or so called “spikes,” in the vaneless space between the impeller and the vaned diffuser. Introducing bleed flow at the impeller exit reduces endwall blockage in the vaneless space and destabilizes the highly-loaded vaned diffuser. The impact is a 50% reduction in stable operating range. The altered diffuser characteristic reduces the compression system damping responsible for long-wavelength modal prestall behavior. A four-lobed backward traveling rotating stall wave is experimentally measured in agreement with calculations obtained from a previously developed dynamic compressor model. In addition, a self-contained endwall blockage control strategy was employed, successfully recovering 75% of the loss in surge-margin due to the bleed flow and yielding a one point increase in adiabatic compressor efficiency.

Compressor Rotating Stall in Uniform and Nonuniform Flow

1980 ◽  
Vol 102 (4) ◽  
pp. 762-769 ◽  
Author(s):  
B. F. J. Cossar ◽  
W. C. Moffatt ◽  
R. E. Peacock
Keyword(s):  
Structural Damage ◽  
Static Pressure ◽  
Pressure Ratio ◽  
Flow Characteristics ◽  
Rotating Stall ◽  
Maximum Pressure ◽  
Flow Distortion ◽  
Inlet Flow ◽  
Pressure Profiles ◽  
Compressor Performance

Rotating stall in axial compressors consists of regions or cells of retarded flow moving around the annulus relative to the blades. Planar symmetry is destroyed, resulting in stalled blades in part of the annulus and unstalled blades in the remainder. The stall cell moves in the direction opposite to the rotor, relative to the blades, but since the relative speed of propagation is usually less than the rotor speed, the cell is seen to move in the same direction as the rotor from an absolute reference frame. The presence of the stall cells results in a deterioration of compressor performance since the maximum pressure ratio is not achieved in regions of retarded flow. Furthermore, since this self-induced distortion is periodic, the forced frequencies generated may coincide with the natural harmonics of the blading, tending to cause structural damage. This paper describes a series of experiments in which a single-stage, lightly loaded compressor operated under stall-free conditions and with rotating stall, both with uniform inlet flow and with distortions generated by an upstream screen of uniform porosity. Not only was the overall compressor performance determined in the traditional manner, but the distribution of static pressure over the rotor suction and pressure surfaces was measured with high response instrumentation. The rotor pressure profiles measured in both undistorted and distorted flow are presented for operation before and after the onset of rotating stall and the latter are compared with the steady flow results. It is observed that two distinctly different types of rotating stall exist depending upon whether or not an inlet flow distortion is present. These cells differ not only in macroscopic properties—rotational speed, circumferential extent, mass-averaged flow conditions, etc.—but also in detailed flow characteristics as evidenced by the rotor blade static pressure distributions. It is further observed that not all inlet distortion geometries lead to the development of rotating stall.

Experimental and numerical investigations on the acoustic characteristics and unsteady behaviors of a centrifugal compressor for fuel cell vehicles

2020 ◽  
pp. 095440622094744
Author(s):  
Siyue Chen ◽  
Shuguang Zuo ◽  
Kaijun Wei
Keyword(s):  
Fuel Cell ◽  
Centrifugal Compressor ◽  
High Speed ◽  
Full Range ◽  
Rotating Stall ◽  
Dynamic Mode Decomposition ◽  
Fuel Cell Vehicle ◽  
Dynamic Mode ◽  
Acoustic Characteristics ◽  
Surge Line

Compared to other air compressors, high-speed centrifugal compressors are considered a more suitable choice for a mid-to-high-power fuel cell system due to its high-pressure ratio. As the centrifugal compressor is the most intensive noise source in the fuel cell vehicle, its acoustic characteristics become a major concern in the passenger comfort experience. Unlike the turbocharger compressor, the centrifugal compressor in a fuel cell vehicle tends to operate at near-surge conditions, which leads to flow instabilities and increases the noise level. In this paper, the acoustic characteristics of a centrifugal compressor for a fuel cell vehicle were measured on a compressor test rig covering the full range of the compressor map. The experimental results show that the lowest sound pressure level at the compressor inlet occurs in the design operating area, while the highest level occurs near the mild-surge line. Experimental work was complemented by numerical simulations. Time-averaged flow fields were compared between the near-choke and mild-surge conditions and the detached eddy simulations (DES) were performed at mild-surge conditions. Sparsity-promoting dynamic mode decomposition (SPDMD) was employed as a post-processing method to extract the flow structures associated with corresponding noise features. It was observed that the rotating stall of the impeller inducer is the main cause of the narrow-band whoosh noise near the mild-surge line. The location, number, and speed of the stall cells were identified by SPDMD in rotational and stationary frames.

Spike and Modal Stall Inception in an Advanced Turbocharger Centrifugal Compressor

2007 ◽  
Author(s):  
Z. S. Spakovszky ◽  
C. H. Roduner
Keyword(s):  
Centrifugal Compressor ◽  
High Speed ◽  
Pressure Ratio ◽  
Pressure Sensors ◽  
Rotating Stall ◽  
Vaned Diffuser ◽  
Stall Inception ◽  
Compression System ◽  
The Impact ◽  
Highly Loaded

In turbocharger applications bleed air near the impeller exit is often used for secondary flow systems to seal bearing compartments and to balance the thrust load on the bearings. There is experimental evidence that the performance and operability of highly loaded centrifugal compressor designs can be sensitive to the amount of bleed air. To investigate the underlying mechanisms and to assess the impact of bleed air on the compressor dynamic behavior, a research program was carried out on a pre-production, 5.0 pressure ratio, high-speed centrifugal compressor stage of advanced design. The investigations showed that bleed air can significantly reduce the stable flow range. Compressor rig experiments, using an array of unsteady pressure sensors and a bleed valve to simulate a typical turbocharger environment, suggest that the path into compression system instability is altered by the bleed flow. Without bleed flow, the pre-stall behavior is dominated by short wavelength disturbances, or so called ‘spikes’, in the vaneless space between the impeller and the vaned diffuser. Introducing bleed flow at impeller exit reduces endwall blockage in the vaneless space and destabilizes the highly-loaded vaned diffuser. The impact is a 50% reduction in stable operating range. The altered diffuser characteristic reduces the compression system damping responsible for long wavelength, modal pre-stall behavior. A four-lobed backward traveling rotating stall wave is experimentally measured, in agreement with calculations obtained from a previously developed dynamic compressor model. In addition, a self-contained, endwall blockage control strategy was employed, successfully recovering 75% of the loss in surge-margin due to bleed flow and yielding a 1 point increase in adiabiatic compressor efficiency.

Application of Dynamic Mode Decomposition to Study Temporal Flow Behavior in a Saccular Aneurysm

2021 ◽  
Author(s):  
Paulo Yu ◽  
Vibhav Durgesh
Keyword(s):  
Flow Behavior ◽  
Frame Rate ◽  
Dynamic Mode Decomposition ◽  
Mode Shapes ◽  
Dynamic Mode ◽  
Mode Decomposition ◽  
The Impact ◽  
Temporal Flow ◽  
Inflow Conditions ◽  
Low Order

Abstract Aneurysms are abnormal expansion of weakened blood vessels which can cause mortality or long-term disability upon rupture. Several studies have shown that inflow conditions spatially and temporally influence aneurysm flow behavior. The objective of this investigation is to identify impact of inflow conditions on spatio-temporal flow behavior in an aneurysm using Dynamic Mode Decomposition (DMD). For this purpose, low-frame rate velocity field measurements are performed in an idealized aneurysm model using Particle Image Velocimetry (PIV). The inflow conditions are precisely controlled using a ViVitro SuperPump system where non-dimensional fluid parameters such as peak Reynolds number (Rep) and Womersely number (α) are varied from 50-270 and 2-5, respectively. The results show the ability of DMD to identify the spatial flow structures and their frequency content. Furthermore, DMD captured the impact of inflow conditions, and change in mode shapes, amplitudes, frequency, and growth rate information is observed. The DMD low-order flow reconstruction also showed the complex interplay of flow features for each inflow scenario. Furthermore, the low-order reconstruction results provided a mathematical description of the flow behavior in the aneurysm which captured the vortex formation, evolution, and convection in detail. These results indicated that the vortical structure behavior varied with the change in α while its strength and presence of secondary structures is influenced by the change in Rep.

Experimental Measurement of In-Plane Rolling Nonpneumatic Tire Vibrations Using High-Speed Imaging

2019 ◽  
Vol 47 (3) ◽  
pp. 196-210
Author(s):  
Meghashyam Panyam ◽  
Beshah Ayalew ◽  
Timothy Rhyne ◽  
Steve Cron ◽  
John Adcox
Keyword(s):  
High Speed ◽  
Image Correlation ◽  
Dynamic Mode Decomposition ◽  
Dynamic Mode ◽  
High Speed Imaging ◽  
Correlation Algorithm ◽  
Mode Decomposition ◽  
Series Of Experiments ◽  
Plane Deformations ◽  
Dominant Frequencies

ABSTRACT This article presents a novel experimental technique for measuring in-plane deformations and vibration modes of a rotating nonpneumatic tire subjected to obstacle impacts. The tire was mounted on a modified quarter-car test rig, which was built around one of the drums of a 500-horse power chassis dynamometer at Clemson University's International Center for Automotive Research. A series of experiments were conducted using a high-speed camera to capture the event of the rotating tire coming into contact with a cleat attached to the surface of the drum. The resulting video was processed using a two-dimensional digital image correlation algorithm to obtain in-plane radial and tangential deformation fields of the tire. The dynamic mode decomposition algorithm was implemented on the deformation fields to extract the dominant frequencies that were excited in the tire upon contact with the cleat. It was observed that the deformations and the modal frequencies estimated using this method were within a reasonable range of expected values. In general, the results indicate that the method used in this study can be a useful tool in measuring in-plane deformations of rolling tires without the need for additional sensors and wiring.

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