Influence of the inclined leading edge diffuser vanes on the aerodynamic performance of a transonic centrifugal compressor

The demands to apply transonic centrifugal compressor have increased in the advanced gas turbine engines. Various techniques are used to increase the aerodynamic performance of the centrifugal compressor. The effects of the inclined leading edges in diffuser vanes of a transonic centrifugal compressor on the flow-field unsteadiness and noise generation are investigated by solving the compressible, three-dimensional, transient Navier–Stokes equations. Diffuser vanes with various inclination angles of the leading edge from shroud-to-hub and hub-to-shroud are numerically modeled. The results show that the hub-to-shroud inclined leading edge improves the compressor performance (2.6%), and the proper inclination angle is effective to increase the stall margin (3.88%). In addition, in this study, the transient pressure variations and radiated noise prediction at the design operating point of the compressor are emphasized. The influences of the inclined leading edges on the pressure waves were captured in time/space domain with different convective velocities. The pressure fluctuation spectra are calculated to investigate the tonal blade passing frequency (BPF) noise, and it is shown that the applied inclination angles in the diffuser blades are effective, not only to improve the aerodynamic performance and stall margin, but also to reduce the BPF noise (7.6 dB sound pressure level reduction). Moreover, it is found that the diffuser vanes with inclination angles could suppress the separation regions and eddy structures inside the passages of the diffuser, which results in reduction of the overall sound pressure level and the broadband noise radiated from the compressor.

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Effects of Upstream Bend on Aerodynamic Performance of a Transonic Centrifugal Compressor

Volume 2B: Turbomachinery ◽

10.1115/gt2019-90794 ◽

2019 ◽

Author(s):

Kazutoyo Yamada ◽

Masato Furukawa ◽

Hiromitsu Arai ◽

Sasuga Ito

Keyword(s):

Flow Rate ◽

Centrifugal Compressor ◽

Leading Edge ◽

Aerodynamic Performance ◽

Circumferential Velocity ◽

Low Flow ◽

Inlet Pipe ◽

Reversed Flow ◽

Transonic Centrifugal Compressor ◽

Bent Pipe

Abstract This paper describes the influence of a bent inlet pipe installed immediately upstream of a transonic centrifugal compressor on the aerodynamic performance and the stability. In order to clarify the influence of the bent inlet pipe, the internal flow fields in the inlet pipe, the impeller, and the diffuser of the compressor have been numerically investigated by a DES (Detached Eddy Simulation). For the purpose of comparison, the simulation was also conducted for the case of uniform axial inflow using a straight pipe. In order to make clear the influence of non-uniform flow with a bent pipe as far as possible, a 90-degree bent pipe was installed immediately upstream of the compressor, that is 0.86 times the inlet inner diameter. In the case of installing the bent pipe on the upstream of the compressor, the pressure ratio decreased on the high flow rate side in the compressor performance characteristic, whereas it increased at the low flow rate side. At the low flow rate operating point, there is a reversed flow occurring in the compressor impeller on the shroud side near the blade leading-edge. Installation of the bent pipe promotes mixing between the reversed flow and the main flow at the inlet of the compressor thanks to occurrence of a secondary flow. Since the reversed flow comes out from inside of the impeller, it has a high circumferential velocity. Therefore, the mixing of the reversed flow makes the compressor inlet flow a pre-swirl flow, and thereby the incidence decreases. As a result, leading-edge separation on the blade tip side of the impeller is suppressed, and the flow field inside the impeller is improved. In the diffuser section, when the bent pipe is installed, the circumferential velocity of the impeller exit flow increases on the hub side, whereas the radial velocity decreases. As a result, the diffuser performance is deteriorated and the diffuser stall tends to occur.

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Influences of Tip Leakage Flows Discharged From Main and Splitter Blades on Flow Field in Transonic Centrifugal Compressor Stage

Volume 2B: Turbomachinery ◽

10.1115/gt2018-75345 ◽

2018 ◽

Cited By ~ 1

Author(s):

Masanao Kaneko ◽

Hoshio Tsujita

Keyword(s):

Flow Field ◽

Centrifugal Compressor ◽

Leading Edge ◽

Tip Clearance ◽

Blade Loading ◽

Tip Leakage Vortex ◽

Tip Leakage ◽

Leakage Flows ◽

Transonic Centrifugal Compressor ◽

Tip Leakage Flows

A transonic centrifugal compressor impeller is generally composed of the main and the splitter blades which are different in chord length. As a result, the tip leakage flows from the main and the splitter blades interact with each other and then complicate the flow field in the compressor. In this study, in order to clarify the individual influences of these leakage flows on the flow field in the transonic centrifugal compressor stage at near-choke to near-stall condition, the flows in the compressor at four conditions prescribed by the presence and the absence of the tip clearances were analyzed numerically. The computed results clarified the following noticeable phenomena. The tip clearance of the main blade induces the tip leakage vortex from the leading edge of the main blade. This vortex decreases the blade loading of the main blade to the negative value by the increase of the flow acceleration along the suction surface of the splitter blade, and consequently induces the tip leakage vortex caused by the negative blade loading of the main blade at any operating points. These phenomena decline the impeller efficiency. On the other hand, the tip clearance of the splitter blade decreases the afore mentioned acceleration by the formation of the tip leakage vortex from the leading edge of the splitter blade and the decrease of the incidence angle for the splitter blade caused by the suction of the flow into the tip clearance. These phenomena reduce the loss generated by the negative blade loading of the main blade and consequently reduce the decline of the impeller efficiency. Moreover, the tip clearances enlarge the flow separation around the diffuser inlet and then decline the diffuser performance independently of the operating points.

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Suppression of Secondary Flows in a Transonic Centrifugal Compressor Impeller Using an Inverse Design Method Based on Meridional Viscous Flow Analysis

Volume 3A: Fluid Applications and Systems ◽

10.1115/ajkfluids2019-5319 ◽

2019 ◽

Author(s):

Sasuga Ito ◽

Shin Okada ◽

Yuki Kawakami ◽

Kaito Manabe ◽

Masato Furukawa ◽

...

Keyword(s):

Viscous Flow ◽

Secondary Flow ◽

Centrifugal Compressor ◽

Pressure Ratio ◽

Aerodynamic Performance ◽

Secondary Flows ◽

Low Energy ◽

Design Concept ◽

Transonic Centrifugal Compressor ◽

Compressor Impeller

Abstract Secondary flows in transonic centrifugal compressor impellers affect their aerodynamic performance. In open-type impellers, low energy fluids can accumulate on the suction surfaces near the trailing edge tip side since the secondary flows and tip leakage flows interfere each other and complex flow phenomena can be generated around the impellers. Therefore, designers must consider the effect of secondary flows to avoid the aerodynamic performance degradation while designing compressor impellers. In this paper, a novel design concept about suppression of secondary flows in centrifugal compressor impellers to improve their aerodynamic performance. A transonic centrifugal compressor impeller was redesigned with the present design concept by a two-dimensional inverse method based on a meridional viscous flow calculation in this study. A design concept was introduced in above calculation process. As the design concept, by bending vortex filaments with controlling peak positions of the blade loading distributions, induced velocity due to bound vortices at the blades was generated in radial opposite direction of the secondary flows on the suction surface. Due to investigate the effect of the design concept in this paper, three-dimensional Reynolds Averaged Navier-Stokes simulations were carried out, and the vortex cores were visualized by a critical point theory and colored by non-dimensional helicity. In the conventional transonic centrifugal compressor impeller, the secondary flow vortices were confirmed and one of the vortices was broken down. In the redesigned impeller, the breakdown of the secondary flow vortices was not observed and the accumulation of the low energy fluids was suppressed compared with the conventional impeller. The total pressure ratio and adiabatic efficiency of the redesign impeller were higher than that of the conventional impeller, and the secondary flows were successfully suppressed in this research.

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Influences of the Flow Cut and Axial Lift of the Impeller on the Aerodynamic Performance of a Transonic Centrifugal Compressor

Energies ◽

10.3390/en12234503 ◽

2019 ◽

Vol 12 (23) ◽

pp. 4503

Author(s):

Kun Park ◽

In Jung ◽

Sung You ◽

Seung Lee ◽

Ali Zamiri ◽

...

Keyword(s):

Flow Rate ◽

Centrifugal Compressor ◽

Total Pressure ◽

Relative Velocity ◽

Axial Direction ◽

Aerodynamic Performance ◽

Design Flow ◽

Design Point ◽

Transonic Centrifugal Compressor ◽

Design Flow Rate

In this study, the influences of the flow cut and axial lift of the impeller on the aerodynamic performance of a transonic centrifugal compressor were analyzed. The flow cut is a method to reduce the flow rate by decreasing the impeller passage height. The axial lift is a method of increasing the impeller passage height in the axial direction, which increases the impeller exit width (B2) and increases the total pressure. A NASA CC3 transonic centrifugal compressor with a backswept angle was used as a base compressor. After applying the flow cut, the total pressure at the target flow rate was lower than the total pressure at the design point due to the increase in the relative velocity at the impeller exit. After applying the axial lift, the total pressure at the design flow rate was increased, which was caused by the reduction in the relative velocity as the passage area at the impeller exit was increased. By applying the flow cut and axial lift methods, it was shown that the variation in relative velocity at the impeller exit has a significant effect on the variation in total pressure. In addition, it was found that the relative velocity at the impeller exit of the target flow rate is maintained similar to the base impeller when the flow cut and the axial lift are combined. Therefore, by combining the flow cut and the axial lift, three transonic centrifugal impellers with flow fractions of 0.7, 0.8, and 0.9 compared to the design flow rate were newly designed.

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Unsteady Effects of Blade Row Interaction on Flow Field and Aerodynamic Performance of a Transonic Centrifugal Compressor Impeller

10.1115/gt2021-59462 ◽

2021 ◽

Author(s):

Kazutoyo Yamada ◽

Kosuke Kubo ◽

Kenichiro Iwakiri ◽

Yoshihiro Ishikawa ◽

Hirotaka Higashimori

Keyword(s):

Steady State ◽

Flow Field ◽

Centrifugal Compressor ◽

Aerodynamic Performance ◽

Vaned Diffuser ◽

Tip Leakage ◽

Transonic Centrifugal Compressor ◽

Compressor Performance ◽

Unsteady Effects ◽

Rans Analysis

Abstract This paper discusses the unsteady effects associated with the impeller/diffuser interaction on the internal flow field and aerodynamic performance of a centrifugal compressor. In centrifugal compressors with a vaned diffuser, the flow field is inherently unsteady due to the influence of interaction between the impeller and the diffuser, and the unsteadiness of the flow field can often have a great influence on the aerodynamic performance of the compressor. Especially in high-load compressors, it is considered that large unsteady effects are produced on the compressor performance with a strong flow unsteadiness. The unsteady effect on aerodynamic performance of the compressor has not been fully revealed yet, and sometimes the steady-state RANS simulation finds it difficult to predict the compressor performance. In this study, numerical simulations have been conducted for a transonic centrifugal compressor with a vaned diffuser. The unsteady effects were clarified by comparing the numerical results between a single-passage steady-state RANS analysis and a full-annulus unsteady RANS analysis. The comparison of simulation results showed the difference in entropy generation in the impeller. The impingement of diffuser shock wave with the impeller pressure surface brought about a cyclic increase in the blade loading near the impeller trailing edge. Accordingly, with increasing tip leakage flow rate, a second tip leakage vortex was newly generated in the aft part of the impeller, which resulted in additional unsteady loss generation inside the impeller.

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Unsteady and Three-Dimensional Flow Phenomena in a Transonic Centrifugal Compressor Impeller at Rotating Stall

Volume 7: Turbomachinery, Parts A and B ◽

10.1115/gt2009-59516 ◽

2009 ◽

Cited By ~ 3

Author(s):

Kenichiro Iwakiri ◽

Masato Furukawa ◽

Seiichi Ibaraki ◽

Isao Tomita

Keyword(s):

Centrifugal Compressor ◽

Wavelet Transforms ◽

Three Dimensional ◽

Axial Compressor ◽

Internal Flow ◽

Leading Edge ◽

Rotating Stall ◽

Detached Eddy Simulation ◽

Transonic Centrifugal Compressor ◽

Compressor Impeller

This paper presents a combined experimental and numerical analysis of rotating stall in a transonic centrifugal compressor impeller for automotive turbochargers. Stall characteristics of the compressor were examined by two high-response pressure transducers mounted on the casing wall near the impeller inlet. The pressure traces were analyzed by wavelet transforms to estimate the disturbance waves quantitatively. Three-dimensional unsteady internal flow fields were simulated numerically by Detached Eddy Simulation (DES) coupled LES-RANS approach. The analysis results show good agreements on both compressor performance characteristics and the unsteady flow features at the rotating stall. At stall inception, spiral-type breakdown of the full-blade tip leakage vortex was found out at some passages and the brokendown regions propagated against the impeller rotation. This phenomenon changed with throttling, and tornado-type separation vortex caused by the full-blade leading edge separation dominated the flow field at developed stall condition. It is similar to the flow model of short-length scale rotating stall established in an axial compressor rotor.

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Investigation on steady and unsteady performance of a SCO2 centrifugal compressor with splitters

Thermal Science ◽

10.2298/tsci17s1185g ◽

2017 ◽

Vol 21 (suppl. 1) ◽

pp. 185-192 ◽

Cited By ~ 1

Author(s):

Ding Guo ◽

Dongbo Shi ◽

Di Zhang

Keyword(s):

Carbon Dioxide ◽

Centrifugal Compressor ◽

Rotor Blade ◽

Critical Phenomenon ◽

Leading Edge ◽

Aerodynamic Performance ◽

Unsteady State ◽

Ansys Cfx ◽

Sst Turbulence Model ◽

Unsteady Performance

Supercritical carbon dioxide (SCO2 ) is widely concerned with its excellent physical properties. Its high density helps to achieve a compact mechanical structure, especially in all kinds of turbomachinery. In this paper, a SCO2 centrifugal compressor with splitter blades is displayed and numerically investigated. A thorough numerical analysis of the steady and unsteady performance of this SCO2 centrifugal compressor is performed in ANSYS-CFX with SST turbulence model. Streamlines, pressure and temperature under steady- and unsteady-state are compared and analyzed. Moreover, the trans-critical phenomenon at the leading edge of the rotor blade and the aerodynamic performance are covered. The results in this paper provide the foundation for the design and numerical investigation of SCO2 centrifugal compressors.

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Aerodynamic Optimization of a Transonic Centrifugal Compressor by Using Arbitrary Blade Surfaces

Journal of Turbomachinery ◽

10.1115/1.4038908 ◽

2018 ◽

Vol 140 (5) ◽

Cited By ~ 9

Author(s):

Alexander Hehn ◽

Moritz Mosdzien ◽

Daniel Grates ◽

Peter Jeschke

Keyword(s):

Centrifugal Compressor ◽

Three Dimensional ◽

Leading Edge ◽

Suction Side ◽

Ruled Surfaces ◽

Flank Milling ◽

Specific Work ◽

Vaneless Diffuser ◽

Aerodynamic Optimization ◽

Transonic Centrifugal Compressor

A transonic centrifugal compressor was aerodynamically optimized by means of a numerical optimization process. The objectives were to increase the isentropic efficiency and to reduce the acoustic signature by decreasing the amplitude of pre-shock pressure waves at the inlet of the compressor. The optimization was performed at three operating points on the 100% speed line in order to maintain choke mass flow and surge margin. At the design point, the specific work input was kept equal. The baseline impeller was designed by using ruled surfaces due to requirements for flank milling. To investigate the benefits of arbitrary blade surfaces, the restrictions of ruled surfaces were abolished and fully three-dimensional (3D) blade profiles allowed. In total, therefore, 45 parameters were varied during the optimization. The combined geometric and aerodynamic analysis reveals that a forward swept leading edge (LE) and a concave suction side at the tip of the LE are effective design features for reducing the shock strength. Beyond that, the blade shape of the optimized compressor creates a favorable impeller outlet flow, which is the main reason why the performance of the vaneless diffuser improves. In total, a gain of 1.4% points in isentropic total-to-static efficiency, evaluated by computational fluid dynamics (CFD) at the exit plane of the vaneless diffuser, is achieved.

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Numerical Investigation of the Inclined Leading Edge Diffuser Vane Effects on the Flow Unsteadiness and Noise Characteristics in a Transonic Centrifugal Compressor

Volume 2C: Turbomachinery ◽

10.1115/gt2017-65117 ◽

2017 ◽

Cited By ~ 2

Author(s):

Ali Zamiri ◽

Byung Ju Lee ◽

Jin Taek Chung

Keyword(s):

Centrifugal Compressor ◽

Pressure Ratio ◽

Pressure Fluctuations ◽

Leading Edge ◽

Pressure Recovery ◽

Vaned Diffuser ◽

Transonic Centrifugal Compressor ◽

Transient Simulations ◽

Leading Edges ◽

Compressor Efficiency

The three-dimensional, compressible, unsteady Navier-Stokes equations are solved to investigate the influence of the inclined leading edge diffuser vanes on the flow field and radiated noise from a transonic centrifugal compressor with high compression ratio. The computational domain is consisted of an inlet duct and a rotating impeller with splitter blades followed by a two-dimensional wedge vaned diffuser. The numerical method was validated by comparing the steady computational results with those of experiments in terms of pressure ratio and compressor efficiency at different operating points for the original diffuser. The transient simulations were verified by comparison of the velocity distribution with PIV data in normal flow condition before the onset of surge. In the case of steady simulations, seven types of diffuser vane with various inclination angles of leading edge were numerically modeled to investigate the effects of inclined leading edge on the diffuser pressure recovery and total pressure loss characteristics. The vaned diffuser with inclined leading edge reduces the interaction between the impeller discharge flow and diffuser leading edge which leads to improve the pressure recovery characteristics within the diffuser passage. Detailed flow analysis inside the diffuser passage showed the pressure ratio and compressor efficiency have been improved by the inclined leading edges. The maximum diffuser pressure recovery coefficient, 0.7185, and compressor efficiency, 84.80%, were observed in the case of 30 degree inclination angle from hub-to-shroud. In the case of transient simulations, five different inclined leading edge diffuser vanes were numerically conducted. The present study focuses on the unsteady pressure fluctuations and noise prediction within the impeller and diffuser passages at the compressor design point. The influences of inclination angle of diffuser vane leading edges on the pressure waves with different convective velocities, generated by the impeller-diffuser interaction and pseudo-periodic unsteady separation bubbles, were captured in the time/space domain along the diffuser blade surfaces. Since it is important to understand that the far-field acoustics are dominated by the internal pressure fluctuations inside the passages, the near-field pressure fluctuation spectra captured at the impeller-diffuser interface are evaluated to analyze the tonal BPF noise as the main noise source in the centrifugal compressors. It is shown that the inclined leading edges are very useful not only for improvement of the pressure recovery characteristics within the diffuser but also for the reduction of the interaction tonal BPF noise (around 7.6 dB SPL reduction). Furthermore, it was found that by using the inclined leading edge, the vortical structures and separations within the diffuser passages were reduced which may cause the attenuation of the broadband noise components and the overall sound pressure level.

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