Secondary Flows in the Return System of a Centrifugal Compressor Stage

2020 ◽  
Vol 142 (9) ◽  
Author(s):  
T. Rossbach ◽  
J. Bisping ◽  
D. R. Grates ◽  
P. Jeschke ◽  
A. Hildebrandt ◽  
...  
Keyword(s):  
Centrifugal Compressor ◽  
Measurement Data ◽  
Leading Edge ◽  
Numerical Data ◽  
Secondary Flows ◽  
Flow Coefficient ◽  
High Mass ◽  
Pressure Losses ◽  
Return Channel ◽  
Analytical Approaches

Abstract This paper presents an analysis of the flow in the return system of a centrifugal compressor with a flow coefficient of 0.15. Based on the detailed experimental and numerical data, the areas of high losses and potentials for improving the return system geometry are revealed. Special emphasis is placed on the interaction of the flow in the return system components, including the U-bend, the vaned return channel, and the final L-bend. Strong flow redistribution occurs due to the sharp curvature of the U-bend, forming a blockage area at the hub near the vane leading edge. This causes a strong passage vortex, which is further intensified by the pressure gradient induced by the L-bend. Additionally, the flow near the shroud accelerates due to the large blockage area near the hub at the exit of the U-bend, resulting in high friction losses. To identify the main causes of loss, a method was evolved. It was validated and supplied by pneumatic measurement data. On this basis, analytical approaches were taken to quantify the total pressure losses due to friction, secondary flows, incidence, and trailing edge flow. As a result, approximately 60% of the return system losses arise due to friction. Another 30–40% are caused by secondary flows. It can be concluded that the results of the investigation contribute to the understanding of the secondary flow structures inside a centrifugal compressor return system of high mass flowrates. By combining the knowledge acquired in respect to the sources of highest losses with the experimental data, a well-founded basis for future optimization is achieved and the validation of numerical approaches is possible.

Secondary Flows in the Return System of a Centrifugal Compressor Stage

2019 ◽  
Author(s):  
T. Rossbach ◽  
J. Bisping ◽  
D. R. Grates ◽  
P. Jeschke ◽  
A. Hildebrandt ◽  
...  
Keyword(s):  
Centrifugal Compressor ◽  
Measurement Data ◽  
Leading Edge ◽  
Numerical Data ◽  
Secondary Flows ◽  
Flow Coefficient ◽  
High Mass ◽  
Pressure Losses ◽  
Return Channel ◽  
Analytical Approaches

Abstract This Paper presents an analysis of the flow in the return system of a centrifugal compressor with a flow coefficient of 0.15. Based on detailed experimental and numerical data, the areas of high losses and potentials for improving the return system geometry are revealed. Special emphasis is placed on the interaction of the flow in the return system components, including the U-bend, the vaned return channel and the final L-bend. Strong flow redistribution occurs due to the sharp curvature of the U-bend, forming a blockage area at the hub near the vane leading edge. This causes a strong passage vortex, which is further intensified by the pressure gradient induced by the L-bend. Additionally, the flow near the shroud accelerates due to the large blockage area near the hub at the exit of the U-bend, resulting in high friction losses. To identify the main causes of loss, a method was evolved. It was validated and supplied by pneumatic measurement data. On this basis analytical approaches were taken to quantify the total pressure losses due to friction, secondary flows, incidence and trailing edge flow. As a result, approximately 60 % of the return system losses arise due to friction. Another 30–40% are caused by secondary flows. It can be concluded that the results of the investigation contribute to the understanding of the secondary flow structures inside a centrifugal compressor return system of high mass flow rates. By combining the knowledge acquired in respect to the sources of highest losses with the experimental data, a well-founded basis for future optimization and the validation of numerical approaches is possible.

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.

scholarly journals Numerical Simulation of 3D Viscous Flow in a Linear Compressor Cascade With Tip Clearance

1994 ◽  
Author(s):  
Shun Kang ◽  
Charles Hirsch
Keyword(s):  
Viscous Flow ◽  
Flow Structure ◽  
Leading Edge ◽  
Secondary Flows ◽  
Tip Clearance ◽  
Flow Coefficient ◽  
Compressor Cascade ◽  
Tip Leakage Flow ◽  
Linear Compressor ◽  
Linear Compressor Cascade

A Navier-Stokes solver is applied to investigate the 3D viscous flow in a low speed linear compressor cascade with tip clearance at design and off-design conditions with two different meshes. The algebraic turbulence model of Baldwin-Lomax is used for closure. Relative motion between the blades and wall is simulated for one flow coefficient. Comparisons with experimental data, including flow structure, static and total pressures, velocity profiles, secondary flows and vorticity, are presented for the stationary wall case. It is shown that the code predicts well the flow structure observed in experiments and shows the details of the tip leakage flow and the leading edge horseshoe vortex.

Steady and Transient Computations of Interaction Effects in a Centrifugal Compressor With Different Types of Diffusers

2010 ◽  
Author(s):  
S. Anish ◽  
N. Sitaram
Keyword(s):  
Centrifugal Compressor ◽  
Static Pressure ◽  
Leading Edge ◽  
Design Flow ◽  
Flow Coefficient ◽  
Pressure Recovery ◽  
Maximum Efficiency ◽  
Vaned Diffuser ◽  
Lower Flow ◽  
Transient Simulations

A computational study has been conducted to analyze the performance of a centrifugal compressor under various levels of impeller-diffuser interactions. The study has been conducted using a low solidity vaned diffuser (LSVD), a conventional vaned diffuser (VD) and a vaneless diffuser (VLD). The study is carried out using Reynolds-Averaged Navier-Stokes simulations. A commercial software ANSYS CFX is used for this purpose. The intensity of interaction is varied by keeping the diffuser vane leading edge at three different radial locations. Frozen rotor and transient simulations are carried out at four different flow coefficients. At design flow coefficient maximum efficiency occurs when the leading edge is at R3 (ratio of radius of the diffuser leading edge to the impeller tip radius) = 1.10. At lower flow coefficient higher stage efficiency occurs when the diffuser vanes are kept at R3 = 1.15 and at higher flow coefficient R3 = 1.05 gives better efficiency. It is observed that at lower flow coefficients positive incidence causes separation of flow at the suction side of the diffuser vane. When the flow rate is above design point there is a negative incidence at the leading edge of the diffuser vane which causes separation of flow from the pressure side of the diffuser vane. Compressor stage performance as well as performance of individual components is calculated at different time steps. Large variations in the stage performances at off-design flow coefficients are observed. The static pressure recovery coefficient (Cp) value is found to be varying with the relative position of impeller and diffuser. It is observed that maximum Cp value occurred at time step where Ψloss value is lowest. From the transient simulations it has been found that the strength and location of impeller exit wake affect the diffuser vane loading which in turn influences the diffuser static pressure recovery.

Inverse Design and Optimization of a Return Channel for a Multistage Centrifugal Compressor

2004 ◽  
Vol 126 (5) ◽  
pp. 799-806 ◽  
Author(s):  
A´rpa´d Veress ◽  
Rene´ Van den Braembussche
Keyword(s):  
Design Method ◽  
Design Procedure ◽  
Leading Edge ◽  
Secondary Flows ◽  
Inverse Design ◽  
Navier Stokes ◽  
Design And Optimization ◽  
The Cross ◽  
Return Channel ◽  
The Impact

The design and optimization of a multistage radial compressor vaneless diffuser, cross-over and return channel is presented. An analytical design procedure for 3D blades with prescribed load distribution is first described and illustrated by the design of a 3D return channel vane with leading edge upstream of the cross-over. The analysis by means of a 3D Navier–Stokes solver shows a substantial improvement of the return channel performance in comparison with a classical 2D channel. Most of the flow separation inside and downstream of the cross-over could be avoided in this new design. The geometry is further improved by means of a 3D inverse design method to smooth the Mach number distribution along the vanes at hub and shroud. The Navier–Stokes analysis shows a rather modest impact on performance but the calculated velocity distribution indicates a more uniform flow and hence a larger operating range can be expected. The impact of vane lean on secondary flows is investigated and further performance improvements have been obtained with negative lean.

Effect of Reduced Inlet Space on a Medium Flow Coefficient Centrifugal Compressor Stage

2000 ◽  
Author(s):  
William Hohlweg ◽  
Naresh Amineni
Keyword(s):  
Centrifugal Compressor ◽  
Flow Coefficient ◽  
Radius Of Curvature ◽  
Compressor Stage ◽  
Stage Design ◽  
Centrifugal Compressor Stage ◽  
Medium Flow ◽  
Multistage Compressor ◽  
Return Channel ◽  
Reduced Space

Abstract Test versus CFD predictions are presented for a medium flow coefficient, centrifugal compressor stage with 10% shorter axial stage space. Short axial length is achieved by reducing the shroud radius of curvature of the upstream return channel inlet. Situations often occur in multistage compressor applications where either rotor dynamics on new equipment or existing casing length on revamped units necessitate shorter stage space. The effect of the reduced space on various stage performance parameters is discussed referenced to the original, full length, stage design. CFD analysis for both configurations is also presented to compare with the test results and help explain the aerodynamic source of the increased losses. The complete stage is modeled on the program CFX-TASCflow beginning with a radial inlet and continuing through the impeller, diffuser and return channel.

Characterization and Impact of Secondary Flows in a Discrete Passage Centrifugal Compressor Diffuser

2018 ◽  
Author(s):  
David W. Erickson ◽  
Choon S. Tan ◽  
Michael Macrorie
Keyword(s):  
Boundary Layer ◽  
Aspect Ratio ◽  
Centrifugal Compressor ◽  
Incidence Angle ◽  
Pressure Rise ◽  
Leading Edge ◽  
Layer Growth ◽  
Secondary Flows ◽  
The Impact ◽  
Boundary Layer Growth

Truncating the exit of a discrete passage centrifugal compressor diffuser is observed to enhance a research compressor’s stall line. By interrogating the experimental data along with a set of well-designed Reynolds-Averaged Navier Stokes computations, this improvement is traced to reduced impact of secondary flows on the truncated diffuser’s boundary layer growth. The secondary flow system is characterized by counter-rotating streamwise vortex pairs that persist throughout the diffuser passage. The vortices are traced to two sources: background vortices resulting from impeller exit flow non-uniformity, and incidence vortices resulting from flow separation off the leading edge cusps unique to a discrete passage diffuser. The incidence vortices detrimentally impact the diffuser pressure rise capability by accumulating high loss flow along the diffuser wall near the plane of symmetry between the vortices. This contributes to a large passage separation in the baseline diffuser. Using reduced order flow modeling, the impact of the vortices on the boundary layer growth is shown to scale inversely with diffuser aspect ratio, and thus the separation extent is reduced for the higher aspect ratio truncated diffuser. Because the diffuser incidence angle influences the strength and location of the vortices, this mechanism can affect the slope of the compressor’s pressure rise characteristic and impact its stall line. Stall onset for the baseline diffuser configuration is initiated by the transition of the vortex location and corresponding passage separation between diffuser pressure and suction sides with increased cusp incidence. Conversely, because the extent of the passage separation in the truncated diffuser is diminished, the switch in separation from pressure to suction side does not immediately initiate instability.

Characterization and Impact of Secondary Flows in a Discrete Passage Centrifugal Compressor Diffuser

2019 ◽  
Vol 141 (7) ◽  
Author(s):  
David W. Erickson ◽  
Choon S. Tan ◽  
Michael Macrorie
Keyword(s):  
Boundary Layer ◽  
Centrifugal Compressor ◽  
Incidence Angle ◽  
Pressure Rise ◽  
Leading Edge ◽  
Streamwise Vortex ◽  
Layer Growth ◽  
Secondary Flows ◽  
The Impact ◽  
Boundary Layer Growth

Truncating the exit of a discrete passage centrifugal compressor diffuser is observed to enhance a research compressor's stall line. By interrogating the experimental data along with a set of well-designed Reynolds-Averaged Navier–Stokes computations, this improvement is traced to the reduced impact of secondary flows on the truncated diffuser's boundary layer growth. The secondary flow system is characterized by counter-rotating streamwise vortex pairs that persist throughout the diffuser passage. The vortices originate from two sources: flow nonuniformity at the impeller exit and separation off the leading edge cusps unique to a discrete passage diffuser. The latter detrimentally impacts the diffuser pressure rise capability by accumulating high loss flow along the diffuser wall near the plane of symmetry between the vortices. This contributes to a large passage separation in the baseline diffuser. Using reduced-order modeling, the impact of the vortices on the boundary layer growth is shown to scale inversely with the diffuser aspect ratio, and thus, the separation extent is reduced for the truncated diffuser. Because the diffuser incidence angle influences the strength and location of the vortices, this mechanism can affect the slope of the compressor's pressure rise characteristic and impact its stall line. Stall onset for the baseline diffuser configuration is initiated when the vortex location and the corresponding passage separation transition from pressure to suction side with increased cusp incidence. Conversely, because the extent of the passage separation in the truncated diffuser is diminished, the switch in separation side does not immediately initiate instability.

Clearance Effects on the Onset of Instability in a Centrifugal Compressor

2006 ◽  
Author(s):  
Matthias Schleer ◽  
Seung Jin Song ◽  
Reza S. Abhari
Keyword(s):  
Pressure Distribution ◽  
Mass Flow ◽  
Flow Rate ◽  
Centrifugal Compressor ◽  
Leading Edge ◽  
Operating Conditions ◽  
High Mass ◽  
Time Resolved ◽  
Flow Rates ◽  
Blade Loading

This report intends to shed an insight into the effect of large relative tip clearances on the onset of instability in a highly loaded centrifugal compressor. Time-resolved pressure measurements have been performed along the casing of a scaled-up model of a small compressor for two clearances at a wide range of operating conditions. Based on these time-resolved measurements the pressure distribution along the meridional length and the blade loading distribution are calculated for each operating condition. In addition, the phase locked pressure fluctuation and its deviation are computed. The results show the behavior of each sub-component of the compressor at different flow conditions and explain the role of the relative tip clearance on the onset of instability. For high mass flow rates the steady pressure distribution along the casing reveals that the inducer acts as an accelerating nozzle. Pressure is only built up in the radial part due to the centrifugal forces and in the subsequent diffuser due to area change. For off-design conditions incidence effects are seen in the blade loading distribution at the leading edge while the inducer is unloaded. A region of high pressure deviation originates at the leading edge of the main blade and convects downstream. This feature is interpreted as the trajectory of the leakage vortex. The trajectory of these vortices is strongly affected by the mass flow coefficient. If the mass flow rate is sufficiently small the trajectory of the leakage vortex becomes perpendicular to the axis of rotation, the leakage vortex interacts with the adjacent blade, and inlet tip recirculation is triggered. If the flow rate is further reduced, the leakage vortex vanishes and rotating stall is initiated in the diffuser. For larger clearances, stronger vortices are formed, stall is triggered at higher flow rates and the overall compressor performance deteriorates.

Effects of Return Channel With Splitter Vanes on Performance of Multistage Centrifugal Compressor

2015 ◽  
Author(s):  
Manabu Yagi ◽  
Takahiro Nishioka ◽  
Hiromi Kobayashi ◽  
Hideo Nishida ◽  
Satoru Yamamoto
Keyword(s):  
Centrifugal Compressor ◽  
High Flow ◽  
Operating Conditions ◽  
Design Flow ◽  
Flow Coefficient ◽  
Optimum Location ◽  
Trailing Edge ◽  
Overall Efficiency ◽  
Return Channel ◽  
Multistage Centrifugal Compressor

The effects of a return channel with splitter vanes on the performance of a multistage centrifugal compressor were investigated. As a preliminary study, the optimum location of the splitter vanes was numerically examined with the aim of achieving high overall efficiency. The results indicated that the optimum location was the 30% of the normalized pitchwise distance from the suction side of the main vane, with the leading-edge located at a radius ratio to the main vane trailing-edge of 1.77. To investigate the effects of the return channel with and without the optimum splitter vanes on the overall performance, performance tests were carried out using a one-and-half-stage test rig. Three pre-swirl vanes, whose vane angles from the tangential direction at the trailing-edge were 20, 30 and 40° were used to simulate three operating conditions with low, design and high flow coefficients, respectively. The design flow coefficient of the downstream impeller was 0.073 and the peripheral Mach number was 0.87. The test results showed that the return channel with the optimum splitter vanes achieved 11.8% higher overall efficiency at the high flow coefficient with respect to the case without the splitter vanes while maintaining the same efficiency at both low and design flow coefficients. The return channel with the optimum splitter vanes was concluded to be effective for improving the efficiency of a multistage centrifugal compressor.

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