Stress Tensor Measurements within the Vaneless Diffuser of a Centrifugal Compressor

1989 ◽  
Vol 203 (1) ◽  
pp. 51-59 ◽  
Author(s):  
T M A Maksoud ◽  
M W Johnson
Keyword(s):  
Centrifugal Compressor ◽  
Sampling Technique ◽  
Phase Lock Loop ◽  
Tangential Component ◽  
Secondary Flows ◽  
Axial Component ◽  
Reynolds Stresses ◽  
Vaneless Diffuser ◽  
Cross Sectional ◽  
Impeller Outlet

Distributions of normal and shear (Reynolds) stresses inside the vaneless diffuser of a low-speed centrifugal compressor are presented. The measurements were made using a triple hot-wire system and a phase lock loop sampling technique. Results were obtained on cross-sectional planes at eight radial stations between the impeller outlet and the diffuser exit at three different flowrates. The turbulence was highly anisotropic and became more so as the flowrate was increased. The tangential component of turbulent intensity was found to be significantly smaller than either the radial or axial component. The blade wake observed at the diffuser inlet decays very rapidly due to the strong tangential Reynolds stresses generated by the opposed secondary flows on either side of the wake. The passage wake decays very much more slowly and is still identifiable at the diffuser discharge.

Measurements of Reynolds stresses in centrifugal compressor vaned diffusers

2008 ◽  
Vol 222 (8) ◽  
pp. 1487-1503 ◽  
Author(s):  
A Pinarbasi ◽  
K M Guleren ◽  
A Ozturk
Keyword(s):  
Centrifugal Compressor ◽  
Three Dimensional ◽  
Leading Edge ◽  
Sampling Technique ◽  
Phase Lock Loop ◽  
Reynolds Stresses ◽  
Design Strategies ◽  
Vaned Diffuser ◽  
Phase Lock ◽  
Flow Mechanisms

A phase lock loop sampling technique has been developed in order to perform detailed measurements for the flow field downstream of a turbomachinery rotor. Measurements have been carried out in the vaned diffuser of a low-speed centrifugal compressor using a triple hot wire anemometer. The phase lock loop technique employed in this work has provided a comprehensive representation of the complex three-dimensional unsteady flow in these diffusers. The diffuser vanes were found to have a significant influence on the flow in the vaneless space. The mixing out of the blade wakes is enhanced and accordingly the Reynolds stress levels drop rapidly between the impeller exit and the vane leading edge. The results provide an insight into the flow mechanisms responsible for the losses and hence can be used to develop better design strategies in the future. The flow also exhibits high levels of anisotropy, especially at the mid-vane positions. This suggests that basic Reynolds-averaged Navier—Stokes (RANS) models, including standard one- or two-equation models, might not be sufficient to accurately model the flow in centrifugal compressor diffusers.

Investigation on Effect of Curvilinear Element Blades on Centrifugal Impeller Performance

2017 ◽  
Author(s):  
Kiyotaka Hiradate ◽  
Hiromi Kobayashi ◽  
Takahiro Nishioka
Keyword(s):  
Centrifugal Compressor ◽  
Performance Test ◽  
Design Guidelines ◽  
Secondary Flows ◽  
Flow Coefficient ◽  
Numerical Calculations ◽  
Centrifugal Impeller ◽  
Compressor Stage ◽  
Vaneless Diffuser ◽  
Compressor Impeller

This study experimentally and numerically investigates the effect of application of curvilinear element blades to fully-shrouded centrifugal compressor impeller on the performance of centrifugal compressor stage. Design suction flow coefficient of compressor stage investigated in this study is 0.125. The design guidelines for the curvilinear element blades which had been previously developed was applied to line element blades of a reference conventional impeller and a new centrifugal compressor impeller with curvilinear element blades was designed. Numerical calculations and performance tests of two centrifugal compressor stages with the conventional impeller and the new one were conducted to investigate the effectiveness of application of the curvilinear element blades and compare the inner flowfield in details. Despite 0.5% deterioration of the impeller efficiency, it was confirmed from the performance test results that the compressor stage with the new impeller achieved 1.7% higher stage efficiency at the design point than that with the conventional one. Moreover, it was confirmed that the compressor stage with the new impeller achieved almost the same off-design performance as that of the conventional stage. From results of the numerical calculations and the experiments, it is considered that this efficiency improvement of the new stage was achieved by suppression of the secondary flows in the impeller due to application of negative tangential lean. The suppression of the secondary flows in the impeller achieved uniformalized flow distribution at the impeller outlet and increased the static pressure recovery coefficient in the vaneless diffuser. As a result, it is thought that the total pressure loss was reduced downstream of the vaneless diffuser outlet in the new stage.

Off-Design Flow Measurements in a Centrifugal Compressor Vaneless Diffuser

1995 ◽  
Vol 117 (4) ◽  
pp. 602-608 ◽  
Author(s):  
A. Pinarbasi ◽  
M. W. Johnson
Keyword(s):  
Flow Rate ◽  
Centrifugal Compressor ◽  
Secondary Flows ◽  
Design Flow ◽  
Vaneless Diffuser ◽  
Flow Measurements ◽  
Vaned Diffuser ◽  
Flow Angle ◽  
Flow Rates ◽  
Study Results

Detailed measurements have been taken of the three-dimensional velocity field within the vaneless diffuser of a backswept low speed centrifugal compressor using hot-wire anemometry. A 16 percent below and an 11 percent above design flow rate were used in the present study. Results at both flow rates show how the blade wake mixes out more rapidly than the passage wake. Strong secondary flows inherited from the impeller at the higher flow rate delay the mixing out of the circumferential velocity variations, but at both flow rates these circumferential variations are negligible at the last measurement station. The measured tangential/radial flow angle is used to recommend optimum values for the vaneless space and vane angle for design of a vaned diffuser.

Detailed Flow Measurements in a Centrifugal Compressor Vaneless Diffuser

1994 ◽  
Vol 116 (3) ◽  
pp. 453-460 ◽  
Author(s):  
A. Pinarbasi ◽  
M. W. Johnson
Keyword(s):  
Centrifugal Compressor ◽  
Turbulent Mixing ◽  
Phase Lock Loop ◽  
Wake Flow ◽  
Hot Wire ◽  
Velocity Measurements ◽  
Vaneless Diffuser ◽  
Flow Measurements ◽  
Loop Technique ◽  
Made In

Hot-wire anemometer measurements have been made in the vaneless diffuser of a 1-m-dia low-speed backswept centrifugal compressor using a phase lock loop technique. Radial, tangential, and axial velocity measurements have been made on eight measurement planes through the diffuser. The flow field at the diffuser entry clearly shows the impeller jet-wake flow pattern and the blade wakes. The passage wake is located on the shroud side of the diffuser and mixes out slowly as the flow moves through the diffuser. The blade wakes, on the other hand, distort and mix out rapidly in the diffuser. Contours of turbulent kinetic energy are also presented on each of the measurement stations, from which the regions of turbulent mixing can be deduced.

Detailed Flow Measurements in a Centrifugal Compressor Vaneless Diffuser

1993 ◽  
Author(s):  
Ali Pinarbasi ◽  
Mark W. Johnson
Keyword(s):  
Centrifugal Compressor ◽  
Turbulent Mixing ◽  
Phase Lock Loop ◽  
Wake Flow ◽  
Hot Wire ◽  
Velocity Measurements ◽  
Vaneless Diffuser ◽  
Flow Measurements ◽  
Loop Technique ◽  
Made In

Hot wire anemometer measurements have been made in the vaneless diffuser of a 1 metre diameter low speed backswept centrifugal compressor using a phase lock loop technique. Radial, tangential and axial velocity measurements have been made on eight measurement planes through the diffuser. The flow field at the diffuser entry clearly shows the impeller jet-wake flow pattern and the blade wakes. The passage wake is located on the shroud side of the diffuser and mixes out slowly as the flow moves through the diffuser. The blade wakes, on the other hand, distort and mix out rapidly in the diffuser. Contours of turbulent kinetic energy are also presented on each of the measurement stations, from which the regions of turbulent mixing can be deduced.

scholarly journals A Study of Reynolds Stresses and Loss Generation at the Inlet to a Centrifugal Vaneless Diffuser

1995 ◽  
Author(s):  
Ali Pinarbasi ◽  
Mark W. Johnson
Keyword(s):  
Boundary Layer ◽  
Significant Contribution ◽  
Shear Layers ◽  
Secondary Flows ◽  
Reynolds Stresses ◽  
Vaneless Diffuser ◽  
Flow Measurements ◽  
Passage Vortex ◽  
The Mean ◽  
Turbulence Production

Detailed flow measurements at the inlet to a centrifugal compressor vaneless diffuser are presented. The mean velocities and six component stress tensor are used to determine the turbulence production terms which lead to total pressure loss. Four regions in the flow are identified as potential sources of loss — the blade wake, the shear layers between passage wake and jet, the thickened hub boundary layer and the interaction region between the secondary flow within the blade wake and the passage vortex. The blade wakes generate most turbulence, with smaller contributions from the hub boundary layer and secondary flows, but no significant contribution is apparent from the passage wake shear layers.

scholarly journals Experimental Flow Field Investigation in a Centrifugal Compressor Vaned Diffuser

1995 ◽  
Author(s):  
Ali Pinarbasi ◽  
Mark W. Johnson
Keyword(s):  
Kinetic Energy ◽  
Flow Field ◽  
Centrifugal Compressor ◽  
Field Investigation ◽  
Vaneless Diffuser ◽  
Mean Velocity ◽  
Cross Sectional ◽  
Impeller Blade ◽  
Vaned Diffuser ◽  
Flow Angle

The purpose of this study was to improve the understanding of the flow physics in a centrifugal compressor vaned diffuser. A low speed compressor with a 19 bladed backswept impeller and diffuser with 16 wedge vanes was used. The measurements were made at three inter-vane positions and are presented as mean velocity, turbulent kinetic energy and flow angle distributions on eight diffuser cross sectional planes. The impeller blade wakes mix out rapidly within the vaneless space and more rapidly than in an equivalent vaneless diffuser. Although the flow is highly non uniform in velocity at the impeller exit, there is no evidence in the results of any separation from the diffuser vanes. The results do however suggest that the use of twisted vanes within the diffuser would be beneficial in reducing losses.

Radial Forces in a Centrifugal Compressor Equipped With Vaned Diffusers

2009 ◽  
Author(s):  
Ahti Jaatinen ◽  
Jari L. H. Backman ◽  
Teemu Turunen-Saaresti
Keyword(s):  
Centrifugal Compressor ◽  
Radial Force ◽  
Magnetic Bearing ◽  
Design Flow ◽  
Vaneless Diffuser ◽  
Rotating Shaft ◽  
Vaned Diffuser ◽  
Pressure Distributions ◽  
Impeller Outlet ◽  
Radial Forces

A non-uniform pressure distribution in a volute of a centrifugal compressor causes a radial force on the impeller and the rotating shaft. The diffuser preceding the volute determines how the flow field entering to the volute, and affects the radial forces that are caused by the volute towards the impeller. The radial forces were measured for three different vaned diffuser geometries and one vaneless diffuser with a pinch. The force measurements were made for each assembly with the same compressor using active magnetic bearings. The impeller forces were found to be the smallest near the design flow and higher at choke and at stall for all configurations. The radial forces on the impeller were higher with the vaneless diffuser than with the vaned diffuser. The force distributions with the vaned diffusers were uniform and clearly different from those of the vaneless diffuser. In addition, the radial forces were estimated using static pressure distributions measured at the impeller outlet. The radial force determined from the pressure measurements verified the measured forces obtained in the magnetic bearing measurements.

Numerical Investigation of the Effect of Different Back Sweep Angle and Exducer Width on the Impeller Outlet Flow Pattern of a Centrifugal Compressor With Vaneless Diffuser

2006 ◽  
Author(s):  
A. Hildebrandt ◽  
M. Genrup
Keyword(s):  
Flow Pattern ◽  
Numerical Investigation ◽  
Centrifugal Compressor ◽  
Angle Distribution ◽  
Vaneless Diffuser ◽  
Deviation Angle ◽  
Flow Angle ◽  
Impeller Outlet ◽  
Flow Deviation ◽  
Outlet Flow

This paper presents a numerical investigation of the effect of different back sweep angles and exducer widths on the steady-state impeller outlet flow pattern of a centrifugal compressor with a vaneless diffuser. The investigations have been performed with commercial CFD and in-house programmed 1-D codes. CFD calculations aim to investigate how flow pattern from the impeller is quantitatively influenced by compressor geometry parameters; thereby, the location of wake and its magnitude (flow angle and relative velocity magnitude) are analyzed. Results show that the increased back sweep impeller provides a more uniform flow pattern in terms of velocity and flow deviation angle distribution, and offers better potential for the diffusion process inside a vaneless (or vaned) diffuser. Secondary flux fraction and flow deviation angle from CFD simulation are implemented into the 1-D two-zone program to improve 1-D prediction results.

Experimental Study of Rotating Stall in Vaneless Diffuser of a Centrifugal Compressor

2013 ◽  
Author(s):  
S. Ohuchida ◽  
T. Kawakubo ◽  
H. Tamaki
Keyword(s):  
Flow Structure ◽  
Centrifugal Compressor ◽  
Phase Locking ◽  
Rotating Stall ◽  
Propagation Mechanism ◽  
Vaneless Diffuser ◽  
Cross Sectional ◽  
Present Measurement ◽  
Separation Pattern ◽  
Sectional Measurement

In this study, with a focus on the rotating stall phenomenon in the vaneless diffuser of a centrifugal compressor, 2D-PIV is conducted to better understand the flow structure. Although many studies have reported concerning this problem, most data is obtained through experiments under lower speed conditions, using a simplified model or equipment. Unlike such studies, a ship board turbocharger compressor with a higher impeller rotation speed is selected as an application for the present measurement. In the measurement, an ensemble-averaged phase locking technique is also selected to compensate for the lack of time resolution of the PIV system. Since rotating stall in vaneless diffuser results in a huge amplitude of pressure fluctuation, the trigger signal for the ensemble-averaged measurement was constructed from diffuser wall pressure. The equipment layout for PIV is set to a cross sectional measurement of constant span height in the diffuser passage. PIV is conducted through a sight glass mounted on the diffuser shroud wall, the field of view of which is limited by its size. To obtain the whole flow structure of the diffuser passage, the measurement is repeated for different cyclic phases of the phenomenon. Five different span heights ranging from diffuser hub to shroud were selected as velocity measurement planes. The result obtained at the mid span indicates a typical pattern of the flow field containing containing low and high-velocity regions mutually in a circumferential direction. Considering other results obtained at different span heights, the whole flow structure is visualized and utilizing this data, both a wall separation pattern and a stall propagation mechanism are considered.

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