Impeller–Vaned Diffuser Interaction in a Centrifugal Compressor at the Best Efficiency Point

2011 ◽  
Author(s):  
P. Gaetani ◽  
G. Persico ◽  
A. Mora ◽  
V. Dossena ◽  
C. Osnaghi
Keyword(s):  
Centrifugal Compressor ◽  
High Performance ◽  
Fluid Dynamic ◽  
Fast Response ◽  
Cfd Simulations ◽  
Vaned Diffuser ◽  
Power Exchange ◽  
Complex Fluid ◽  
Point Data ◽  
Aero Engines

Centrifugal compressors find a huge number of applications in industry and in aero-engines; the detailed comprehension of the complex fluid-dynamic mechanisms occurring in these machines is crucial to improve their efficiency and their operating range. The paper presents a study on the impeller–vaned diffuser interaction in a high-performance compressor stage, in the frame of a wide experimental campaign devoted to the comprehension of unsteady flows in centrifugal compressor stages. The paper focuses on the best efficiency operating point. Data were collected in the impeller–vaned diffuser gap by applying a fast response probe. The impeller runs at 12500 RPM and the peripheral Mach number is 0.77. At first, data are reduced to highlight the main flow structures released by the impeller. CFD simulations — first verified against experimental data — were also performed to get detailed information of the flow field inside the impeller. The core of the paper is the discussion of the impeller–diffuser interaction. Results evidence the effect of the diffuser on the impeller in terms of static pressure and flow velocity. Moreover, the interaction process makes the average flow rate discharged by an impeller channel and the power exchange to be unsteady.

scholarly journals On the Development and Application of the FRAP® (Fast-Response Aerodynamic Probe) System in Turbomachines: Part 2 — Flow, Surge and Stall in a Centrifugal Compressor

1999 ◽  
Author(s):  
Christian Roduner ◽  
Peter Kupferschmied ◽  
Pascal Köppel ◽  
George Gyarmathy
Keyword(s):  
Centrifugal Compressor ◽  
Low Frequency ◽  
Fast Response ◽  
Rotating Stall ◽  
Period Length ◽  
Absolute Pressure ◽  
Time Behavior ◽  
Ensemble Averaging ◽  
Vaned Diffuser ◽  
Averaging Methods

The present paper, Part 2 of a trilogy, is primarily focussed on demonstrating the capabilities of a FRAP® system configuration based on the simplest type of fast-response probe. A single cylindrical probe equipped with a single pressure sensor is used to measure absolute pressure and both velocity components in an essentially two-dimensional flow field. The probe is used in the pseudo-3-sensor mode (see Part 1). It is demonstrated that such a 1-sensor probe is able to measure high-frequency rotor-governed systematic fluctuations (like blade-to-blade phenomena) alone or in combination with flow-governed low-frequency fluctuations as rotating stall (RS) and mild surge (MS). However 3-sensor probes would be needed to measure stochastic (turbulence-related) or other aperiodic velocity transients. The data shown refer to the impeller exit and the vaned diffuser of a single-stage high-subsonic centrifugal compressor. Wall-to-wall probe traverses were performed at the impeller exit and different positions along the vaned diffuser for different running conditions. The centrifugal compressor was operated under stable as well as under unstable (pulsating or stalled) running conditions. The turbomachinery oriented interpretation of these unsteady flow data is a second focus of the paper. A refined analysis of the time-resolved data will be done in Part 3 where different spatial/temporal averaging methods are compared. Two different averaging methods were used for the data evaluation. Impeller based ensemble averaging for blade-to-blade systematic fluctuations (with constant period length at a constant shaft speed) and flow-based class averaging for the relatively slow MS and RS with slightly variable period length. Due to the ability of fast-response probes to simultaneously measure velocity components as well as total and static pressure, interesting insights can be obtained into impeller and diffuser channel flow structures as well as into the time behavior of large-domain phenomena as RS and MS.

scholarly journals The Flow and Rotation Characteristics of a Centrifugal Compressor During Surge

1994 ◽  
Author(s):  
D. Jin ◽  
H. Hasemann ◽  
U. Haupt ◽  
M. Rautenberg
Keyword(s):  
Centrifugal Compressor ◽  
Pressure Difference ◽  
Pressure Fluctuations ◽  
Pressure Oscillation ◽  
Suction Side ◽  
Fast Response ◽  
Rotor Speed ◽  
Vaned Diffuser ◽  
Rotating Speed ◽  
Rotation Direction

Unsteady flow and the rotor rotational behavior during surge in a single stage centrifugal compressor have been investigated to study the physical mechanism of this special operating period. The experiments were performed for the compressor with vaneless and vaned diffuser at different rotational speed. The centrifugal compressor was driven by a 1350 kw dc-motor with Leonard-control. Unsteady pressure was measured with fast response dynamic transducers while rotor speed was simultaneously measured with a capacitive impulser. At the beginning and the end of the surge, the pressure signals measured in the meridional direction from the impeller inlet to the diffuser exit show obvious pressure oscillation. During the whole surge period, the pressure signal at the impeller exit shows periodic fluctuations with very large amplitudes at a high frequency. The further pressure analyses indicate that these pressure fluctuations is produced by the pressure difference across blade pitch. The pressure side and the suction side of the blade are inversed compared with that in the normal compressor operating condition. This reverse pressure difference produces an additional torque on the impeller blades in the impeller rotation direction. The rotating speed of the compressor rotor during surge was also studied. It is shown that during the surge the rotor speed increases slowly until the surge stops. Since the compressor-motor system is controlled by the Leonard-set, the increase in rotor speed indicates the torque reduction of the compressor.

Impeller-Vaned Diffuser Interaction in a Centrifugal Compressor at Off Design Conditions

2012 ◽  
Vol 134 (6) ◽  
Author(s):  
P. Gaetani ◽  
G. Persico ◽  
A. Mora ◽  
V. Dossena ◽  
C. Osnaghi
Keyword(s):  
Flow Rate ◽  
Strong Dependence ◽  
Maximum Flow ◽  
Fast Response ◽  
Huge Number ◽  
Vaned Diffuser ◽  
Experimental Campaign ◽  
Flow Features ◽  
Aero Engines ◽  
Operating Points

As centrifugal compressors find a huge number of applications in industry and in aero-engines, the detailed analysis and comprehension of the impeller-vaned diffuser interaction is of interest to improve the efficiency and the operating range. This paper presents the results of a wide experimental campaign devoted to the understanding of the impeller-diffuser interaction; in particular, the paper focuses on the features occurring when the compressor works in off design conditions. Data were taken at three operating points (near surge, best efficiency, and maximum flow rate point) in the impeller-vaned diffuser gap by a fast response probe; the single stage compressor runs at 12,500 RPM giving a peripheral Mach number of 0.77. At first, data are reduced to evidence the main impeller flow features, which are compared at different flow rates. Furthermore time mean diffuser effects on the impeller are commented and finally the impeller-diffuser interaction is discussed. Results evidence the effect of the diffuser on the impeller, mainly in terms of static pressure and flow velocity, which have a strong dependence on the flow rate.

NASA Low-Speed Centrifugal Compressor for Three-Dimensional Viscous Code Assessment and Fundamental Flow Physics Research

1992 ◽  
Vol 114 (2) ◽  
pp. 295-303 ◽  
Author(s):  
M. D. Hathaway ◽  
J. R. Wood ◽  
C. A. Wasserbauer
Keyword(s):  
Centrifugal Compressor ◽  
Computational Fluid Dynamic ◽  
High Performance ◽  
Fluid Dynamic ◽  
Three Dimensional ◽  
Field Measurements ◽  
Experimental Investigations ◽  
Nasa Lewis Research ◽  
Low Speed ◽  
Flow Physics

A low-speed centrifugal compressor facility recently built by the NASA Lewis Research Center is described. The purpose of this facility is to obtain detailed flow field measurements for computational fluid dynamic code assessment and flow physics modeling in support of Army and NASA efforts to advance small gas turbine engine technology. The facility is heavily instrumented with pressure and temperature probes, in both the stationary and rotating frames of reference, and has provisions for flow visualization and laser velocimetry. The facility will accommodate rotational speeds to 2400 rpm and is rated at pressures to 1.25 atm. The initial compressor stage being tested is geometrically and dynamically representative of modern high-performance centrifugal compressor stages with the exception of Mach number levels. Preliminary experimental investigations of inlet and exit flow uniformity and measurement repeatability are presented. These results demonstrate the high quality of the data that may be expected from this facility. The significance of synergism between computational fluid dynamic analyses and experimentation throughout the development of the low-speed centrifugal compressor facility is demonstrated.

Experimental and Numerical Investigation of the Unsteady Flow Field in a Vaned Diffuser of a High-Speed Centrifugal Compressor

2015 ◽  
Vol 137 (7) ◽  
Author(s):  
Klemens Vogel ◽  
Reza S. Abhari ◽  
Armin Zemp
Keyword(s):  
Centrifugal Compressor ◽  
High Speed ◽  
Pressure Fluctuations ◽  
Leading Edge ◽  
Fast Response ◽  
Operating Conditions ◽  
Wake Flow ◽  
Vaned Diffuser ◽  
Wide Range ◽  
The Impact

Vaned diffusers in centrifugal compressor stages are used to achieve higher stage pressure ratios, higher stage efficiencies, and more compact designs. The interaction of the stationary diffuser with the impeller can lead to resonant vibration with potentially devastating effects. This paper presents unsteady diffuser vane surface pressure measurements using in-house developed, flush mounted, fast response piezoresistive pressure transducers. The unsteady pressures were recorded for nine operating conditions, covering a wide range of the compressor map. Experimental work was complemented by 3D unsteady computational fluid dynamics (CFD) simulations using ansys cfx V12.1 to detail the unsteady diffuser aerodynamics. Pressure fluctuations of up to 34.4% of the inlet pressure were found. High pressure variations are present all along the vane and are not restricted to the leading edge region. Frequency analysis of the measured vane surface pressures show that reduced impeller loading, and the corresponding reduction of tip leakage fluid changes the characteristics of the fluctuations from a main blade count to a total blade count. The unsteady pressure fluctuations in the diffuser originate from three distinct locations. The impact of the jet-wake flow leaving the impeller results in high variation close to the leading edge. It was observed that CFD results overpredicted the amplitude of the pressure fluctuation on average by 62%.

scholarly journals Unsteady Flow Characteristics in a Centrifugal Compressor With Vaned Diffuser

1987 ◽  
Author(s):  
A. N. Abdel-Hamid ◽  
U. Haupt ◽  
M. Rautenberg
Keyword(s):  
Centrifugal Compressor ◽  
High Performance ◽  
Dynamic Pressure ◽  
Flow Characteristics ◽  
Rotating Stall ◽  
Operating Conditions ◽  
Impeller Speed ◽  
Vaned Diffuser ◽  
Wide Range ◽  
Flow Oscillations

Self-excited flow oscillations in a high performance centrifugal compressor with vaned diffuser have been experimentally investigated over a wide range of operating conditions. The space and time characteristics of the flow oscillations in the compressor from inlet to outlet were measured using fast response dynamic pressure transducers on the shroud wall and blade mounted straingages. Multi-channel signal analysis techniques in the frequency domain clearly identified the onset of the oscillations and its type. Rotating stall was found to exist in certain regimes of the compressor map but did not necessarily preceed the occurrence of the surge phenomena. At compressor speeds below 13600 rpm the rotating non-uniform flow when it occurred was composed of three lobes and rotated at approximately 5–6 % of the impeller speed. Above 13600 rpm the rotating pattern changed to two lobes and rotated at approximately 16–20 % of the impeller speed. The direction of rotation of both patterns was opposite to that of the impeller. Analysis of the performance characteristics of the compressor components prior to and during flow oscillations indicates that the relative magnitude of the flow fluctuations in the semi-vaneless space downstream of the impeller are the largest which points towards the close relationship between the conditions leading to the onset of the oscillations and the flow details in this region of the compressor. Additional confirmation of this relationship is obtained from comparison between the results obtained in this study and those obtained when the same compressor was operated with a vaneless diffuser.

Experimental and Numerical Investigation of the Unsteady Flow Field in a Vaned Diffuser of a High-Speed Centrifugal Compressor

2014 ◽  
Author(s):  
Klemens Vogel ◽  
Reza S. Abhari ◽  
Armin Zemp
Keyword(s):  
Centrifugal Compressor ◽  
High Speed ◽  
Pressure Fluctuations ◽  
Leading Edge ◽  
Fast Response ◽  
Operating Conditions ◽  
Wake Flow ◽  
Vaned Diffuser ◽  
Wide Range ◽  
The Impact

Vaned diffusers in centrifugal compressor stages are used to achieve higher stage pressure ratios, higher stage efficiencies and more compact designs. The interaction of the stationary diffuser with the impeller can lead to resonant vibration with potentially devastating effects. This paper presents unsteady diffuser vane surface pressure measurements using in-house developed, flush mounted, fast response piezo-resistive pressure transducers. The unsteady pressures were recorded for 9 operating conditions, covering a wide range of the compressor map. Experimental work was complemented by 3D unsteady CFD simulations using ANSYS CFX V12.1 to detail the unsteady diffuser aerodynamics. Pressure fluctuations of up to 34.4% of the inlet pressure were found. High pressure variations are present all along the vane and are not restricted to the leading edge region. Frequency analysis of the measured vane surface pressures show that reduced impeller loading and the corresponding reduction of tip leakage fluid changes the characteristics of the fluctuations from a main blade count to a total blade count. The unsteady pressure fluctuations in the diffuser originate from three distinct locations. The impact of the jet wake flow leaving the impeller results in high variation close to the leading edge. It was observed that CFD results overpredicted the amplitude of the pressure fluctuation on average by 62%.

On the Development and Application of the Fast-Response Aerodynamic Probe System in Turbomachines—Part 2: Flow, Surge, and Stall in a Centrifugal Compressor

1999 ◽  
Vol 122 (3) ◽  
pp. 517-526 ◽  
Author(s):  
Christian Roduner ◽  
Peter Kupferschmied ◽  
Pascal Ko¨ppel ◽  
Georg Gyarmathy
Keyword(s):  
Centrifugal Compressor ◽  
Fast Response ◽  
Rotating Stall ◽  
Period Length ◽  
Absolute Pressure ◽  
Time Behavior ◽  
Ensemble Averaging ◽  
Vaned Diffuser ◽  
Averaging Methods ◽  
Probe System

The present paper, Part 2 of a trilogy, is primarily focussed on demonstrating the capabilities of a fast-response aerodynamic probe system configuration based on the simplest type of fast-response probe. A single cylindrical probe equipped with a single pressure sensor is used to measure absolute pressure and both velocity components in an essentially two-dimensional flow field. The probe is used in the pseudo-three-sensor mode (see Part 1). It is demonstrated that such a one-sensor probe is able to measure high-frequency rotor-governed systematic fluctuations (like blade-to-blade phenomena) alone or in combination with flow-governed low-frequency fluctuations as rotating stall (RS) and mild surge (MS). However, three-sensor probes would be needed to measure stochastic (turbulence-related) or other aperiodic velocity transients. The data shown refer to the impeller exit and the vaned diffuser of a single-stage high-subsonic centrifugal compressor. Wall-to-wall probe traverses were performed at the impeller exit and different positions along the vaned diffuser for different running conditions. The centrifugal compressor was operated under stable as well as unstable (pulsating or stalled) running conditions. The turbomachinery-oriented interpretation of these unsteady flow data is a second focus of the paper. A refined analysis of the time-resolved data will be performed in Part 3, where different spatial/temporal averaging methods are compared. Two different averaging methods were used for the data evaluation: impeller-based ensemble-averaging for blade-to-blade systematic fluctuations (with constant period length at a constant shaft speed), and flow-based class averaging for the relatively slow MS and RS with slightly variable period length. Due to the ability of fast-response probes to simultaneously measure velocity components and total and static pressure, interesting insights can be obtained into impeller and diffuser channel flow structures as well as into the time behavior of such large-domain phenomena as RS and MS. [S0889-504X(00)01103-X]

The Performance Evaluation With Diffuser Geometry Variations of the Centrifugal Compressor in a Marine Engine (70MW) Turbocharger

2008 ◽  
Vol 131 (1) ◽  
Author(s):  
Hong-Won Kim ◽  
Jong-II Park ◽  
Seung-Hyup Ryu ◽  
Seong-Wook Choi ◽  
Sang-Hak Ghal
Keyword(s):  
Centrifugal Compressor ◽  
High Efficiency ◽  
Fluid Dynamic ◽  
Pressure Ratio ◽  
Prediction Method ◽  
Pressure Recovery ◽  
Vaned Diffuser ◽  
High Pressure Ratio ◽  
Work Input ◽  
Cfd Analyses

An examination of the condition of the flow leaving the impeller exit kinetic energy often accounts for 30–50% of the shaft work input to the compressor stage; for energy efficiency, it is important to recover as much of this as possible. This is the function of the diffuser, which follows the impeller. Effective pressure recovery downstream of an impeller is very important in order to realize a centrifugal compressor with a high efficiency and a high pressure ratio, and an appropriate selection of a diffuser for a specific impeller is a critical step in order to develop the compressor accordingly. The purpose of this study is to investigate the sensitivity of how compressor performances change as the vaned diffuser geometry is varied. Three kinds of vaned diffusers were studied and compared with its results. The first vaned diffuser type is based on a modified NACA airfoil, the second is a channel diffuser, and the third is a conformal transformation of NACA 65-(4A10)06 airfoil. A mean-line prediction method was applied to investigate the performance and stability for three kinds of diffusers. Computational fluid dynamic (CFD) analyses and a detailed interior flow pattern study have been done. In this study, the off-design behavior of three different types of diffusers, given by the mean-line prediction, was investigated using CFD results and the NACA 65 diffuser geometry, which satisfies a wider operating range and has a higher pressure recovery than the others, was selected. The numerical results were compared with experimental data for validation and showed good agreement.

Computational and Experimental Study of Hot Streak Transport Within the First Stage of a Gas Turbine

2019 ◽  
Author(s):  
Paolo Gaetani ◽  
Giacomo Persico ◽  
Lorenzo Pinelli ◽  
Michele Marconcini ◽  
Roberto Pacciani
Keyword(s):  
Gas Turbine ◽  
High Speed ◽  
Fluid Dynamic ◽  
Spatial Coherence ◽  
Inlet Temperature ◽  
Turbine Stage ◽  
Complex Flow ◽  
Cfd Simulations ◽  
Azimuthal Position ◽  
Aero Engines

Abstract The paper discusses the migration, the interaction with the blades, and the attenuation of hot streaks generated by combustor burners, during their propagation within the first turbine stage of aero-engines. Experiments and Computational Fluid Dynamic (CFD) simulations were carried out in the framework of the European Project RECORD and on its follow-up. Measurements considering burner-representative temperature perturbations injected upstream of an un-cooled high-pressure gas turbine stage were performed in the high-speed closed-loop test-rig of the Politecnico di Milano (Italy). The hot streaks were injected in streamwise direction at the stage inlet in four different circumferential positions with respect to the stator blade. They feature a 20% over-temperature with respect to the main flow. Detailed temperature measurements as well as unsteady aerodynamic measurements upstream and downstream of the blade rows were performed. Time-accurate CFD simulations of the flow upstream and within the turbine stage were performed with the TRAF code, developed by the University of Florence. Measurements show a relevant attenuation of hot streaks throughout their transport within the stator and the rotor blade rows, highly depending on the injection azimuthal position. The perturbations were observed to lose their spatial coherence, especially in the transport within the rotor, and to undergo severe spanwise migration. Simulations exhibit a good agreement with the experiments on the measurement planes and allow tracking the complex flow phenomena occurring within the blade rows. Finally the aerodynamic and thermal implications of the inlet temperature perturbations are properly highlighted and discussed.

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