Effects of Scalloped Centrifugal Impellers on Aerodynamic and Rotordynamic Performance Using CFD Techniques

2000 ◽  
Author(s):  
J. Jeffrey Moore
Keyword(s):  
Flow Field ◽  
Static Pressure ◽  
Rotating Stall ◽  
Thermodynamic Efficiency ◽  
Moderate Increase ◽  
Primary Flow ◽  
Axial Thrust ◽  
Flow Angle ◽  
Baseline Case ◽  
Shaft Power

Abstract Impeller scallops are intentional cuts in the hub and shroud surfaces at the exit of centrifugal impellers that are intended to prevent high cycle fatigue in these areas. The goal of this analysis is to determine what effect the scallops have on aerodynamic performance, rotordynamic stability, rotating stall criteria, axial thrust, and mechanical shaft power. Furthermore, this study improves the understanding of the interaction with the secondary passage and determines the effect on the flow field entering the diffuser. A 3D viscous CFD model is generated of a single blade passage that couples the primary flow passage with the secondary shroud passage. This approach captures the complex interaction that occurs at the impeller exit due to the presence of the scallops. The predictions show a small penalty in thermodynamic efficiency with the presence of the scallops compared to a baseline case. The results also show a moderate increase in shaft horsepower calculated by integrating static pressure and shear stress acting on the impeller and shroud surfaces. Circumferential swirl in the shroud passage shows only modest increases with the addition of the scallops. Therefore, rotordynamic performance is not significantly affected nor is axial thrust acting on the impeller. The predictions demonstrate the effect the scallops have on the flow field entering the diffuser including variations in flow angle at the impeller exit.

Numerical and Experimental Investigation of Return Channel Vane Aerodynamics With Two-Dimensional and Three-Dimensional Vanes

2016 ◽  
Vol 139 (1) ◽  
Author(s):  
A. Hildebrandt ◽  
F. Schilling
Keyword(s):  
Experimental Investigation ◽  
Flow Field ◽  
Static Pressure ◽  
Three Dimensional ◽  
Pressure Rise ◽  
Field Performance ◽  
Two Dimensional ◽  
Flow Angle ◽  
Overall Performance ◽  
Return Channel

The present paper deals with the numerical and experimental investigation of the effect of return channel (RCH) dimensions of a centrifugal compressor stage on the aerodynamic performance. Three different return channel stages were investigated, two stages comprising three-dimensional (3D) return channel blades and one stage comprising two-dimensional (2D) RCH vanes. The analysis was performed regarding both the investigation of overall performance (stage efficiency, RCH total pressure loss coefficient) and detailed flow-field performance. For detailed experimental flow-field investigation at the stage exit, six circumferentially traversed three-hole probes were positioned downstream the return channel exit in order to get two-dimensional flow-field information. Additionally, static pressure wall measurements were taken at the hub and shroud pressure and suction side (SS) of the 2D and 3D return channel blades. The return channel system overall performance was calculated by measurements of the circumferentially averaged 1D flow field downstream the diffuser exit and downstream the stage exit. Dependent on the type of return channel blade, the numerical and experimental results show a significant effect on the flow field overall and detail performance. In general, satisfactory agreement between computational fluid dynamics (CFD)-prediction and test-rig measurements was achieved regarding overall and flow-field performance. In comparison with the measurements, the CFD-calculated stage performance (efficiency and pressure rise coefficient) of all the 3D-RCH stages was slightly overpredicted. Very good agreement between CFD and measurement results was found for the static pressure distribution on the RCH wall surfaces while small CFD-deviations occur in the measured flow angle at the stage exit, dependent on the turbulence model selected.

Effects of Inlet Flow Field Conditions on the Stall Onset of Centrifugal Compressor Vaned Diffusers

2003 ◽  
Author(s):  
Sabri Deniz
Keyword(s):  
Flow Field ◽  
Axial Flow ◽  
Rotating Stall ◽  
Field Conditions ◽  
Test Facility ◽  
Straight Channel ◽  
Inlet Flow ◽  
Vaned Diffuser ◽  
Flow Angle ◽  
Operating Range

This paper considers the performance and operating range of vaned diffusers for use in high performance centrifugal compressors. An experimental and numerical investigation is performed to determine the effects of inlet flow field conditions on pressure recovery and stall onset of different type vaned diffusers, such as discrete-passage and straight-channel diffusers. Diffuser inlet flow conditions examined include Mach number, flow angle, blockage, and axial flow non-uniformity. The investigation was carried out in a specially built test facility, designed to provide a controlled inlet flow field to the test diffusers. Unsteady pressure measurements showed the operating range of a compressor stage was limited by the onset of rotating stall, triggered by the loss of stability in the vaned diffuser, independent of the impeller operating point. For both diffusers investigated, loss of flow stability in the diffuser occurred at a critical value of the momentum-averaged flow angle into the diffuser. To provide additional information on diffuser flow development and to complement previous experimental work performed on straight-channel type diffuser, a computational investigation has been undertaken and important results are presented.

Numerical and Experimental Investigation of Return Channel Vane Aerodynamics With 2D and 3D Vanes

2016 ◽  
Author(s):  
A. Hildebrandt ◽  
F. Schilling
Keyword(s):  
Experimental Investigation ◽  
Flow Field ◽  
Static Pressure ◽  
Pressure Rise ◽  
Field Performance ◽  
Two Dimensional ◽  
Flow Angle ◽  
Overall Performance ◽  
Return Channel ◽  
2D And 3D

The present paper deals with the numerical and experimental investigation of the effect of return channel dimensions of a centrifugal compressor stage on the aerodynamic performance. Three different return channel stages were investigated, two stages comprising 3D (three-dimensional) return channel blades and one stage comprising (2D) two-dimensional RCH (Return Channel) vanes. The analysis was performed regarding both the investigation of overall performance (stage efficiency, RCH total pressure loss coefficient) and detailed flow field performance. For detailed experimental flow field investigation at the stage exit, six circumferentially traversed three-hole probes were positioned downstream the return channel exit in order to get two-dimensional flow field information. Additionally, static pressure wall measurements were taken at the hub and shroud pressure and suction side of the 2D and 3D return channel blades. The return channel system overall performance was calculated by measurements of the circumferentially averaged 1D flow field downstream the diffuser exit and downstream the stage exit. Dependent on the type of return channel blade, the numerical and experimental results show a significant effect on the flow field overall and detail performance. In general, satisfactory agreement between CFD-prediction and test-rig measurements was achieved regarding overall and flow field performance. In comparison with the measurements, the CFD calculated stage performance (efficiency and pressure rise coefficient) of all 3D-RCH stages was slightly over-predicted. Very good agreement between CFD and measurement results was found for the static pressure distribution on the RCH wall surfaces while small CFD-deviations occur in the measured flow angle at the stage exit, dependent on the turbulence model selected.

Effects of Inlet Flow Field Conditions on the Performance of Centrifugal Compressor Diffusers: Part 2 — Straight-Channel Diffuser

1998 ◽  
Author(s):  
Sabri Deniz ◽  
Edward M. Greitzer ◽  
Nicholas A. Cumpsty
Keyword(s):  
Mach Number ◽  
Flow Field ◽  
Centrifugal Compressor ◽  
Axial Flow ◽  
Rotating Stall ◽  
Pressure Recovery ◽  
Straight Channel ◽  
Inlet Flow ◽  
Flow Angle ◽  
Operating Range

This is Part 2 of an examination of influence of inlet flow conditions on the performance and operating range of centrifugal compressor vaned diffusers. The paper describes tests of straight-channel type diffuser, sometimes called a wedge-vane diffuser, and compares the results with those from the discrete-passage diffusers described in Part 1. Effects of diffuser inlet Mach number, flow angle, blockage, and axial flow non-uniformity on diffuser pressure recovery and operating range are addressed. The straight-channel diffuser investigated has 30 vanes and was designed for the same aerodynamic duty as the discrete-passage diffuser described in Part 1. The ranges of the overall pressure recovery coefficients were 0.65–0.78 for the straight-channel diffuser and 0.60–0.70 for the discrete-passage diffuser; the pressure recovery of the straight-channel diffuser was roughly 10% higher than that of the discrete-passage diffuser. Both types of the diffusers showed similar behavior regarding the dependence on diffuser inlet flow angle and the insensitivity of the performance to inlet flow field axial distortion and Mach number. The operating range of the straight-channel diffuser, as for the discrete-passage diffusers was limited by the onset of rotating stall at a fixed momentum-averaged flow angle into the diffuser, which was for the straight-channel diffuser, αcrit = 70° ±0.5°. The background, nomenclature and description of the facility and method are all given in Part 1.

scholarly journals The Model V84.3 Shot Tests: Compressor Flow Field Measurements and Evaluation

1994 ◽  
Author(s):  
M. Janssen ◽  
R. Mönig ◽  
J. Seume ◽  
H. Hönen ◽  
R. Lösch-Schloms ◽  
...  
Keyword(s):  
Flow Field ◽  
Total Pressure ◽  
Static Pressure ◽  
Pressure Rise ◽  
Full Scale ◽  
Test Facility ◽  
Design Calculation ◽  
Flow Measurements ◽  
Flow Angle ◽  
Probe Measurements

Detailed experimental investigations were carried out at the Siemens test-facility in Berlin to validate and develop further the compressor design of the Model V84.3 gas turbine and to generate a comprehensive data base for the verification of the flow calculation programs. The test facility enables Siemens to confirm the design with regard to performance and reliability in the full scale machine under full load and off-design condition. Various measuring techniques well established in the laboratory were applied to the full scale compressor to examine the flow field. Along with rather conventional 5-hole probes for measuring the flow field in the core region, miniaturized 3-hole probes were developed at the Turbomachinery Laboratory of the Technical University of Aachen, tested and finally used for the measurements of endwall boundary layer profiles and their development throughout the compressor. In addition to the probe measurements, wall static-pressure measurements, as well as probed vane measurements, were carried out. The paper briefly describes the test facility, the compressor under investigation, and the instrumentation for the flow measurements. A comparison of the 3-hole and 5-hole probe measurements is presented. The experimental results are compared with calculated results taken from a two-dimensional off-design calculation program with standard loss models. By means of the measured static-pressure rise at the casing wall and the total pressure distributions downstream of the rotor rows, a modification of the loss modeling was performed. The calculated flow field is compared to the results of the 3-hole and 5-hole probe measurements in terms of radial distributions for flow angle. Mach number and total pressure.

Experimental Study of Pinch in Vaneless Diffuser of Centrifugal Compressor

2009 ◽  
Author(s):  
Teemu Turunen-Saaresti ◽  
Aki-Pekka Gro¨nman ◽  
Ahti Jaatinen
Keyword(s):  
Experimental Study ◽  
Flow Field ◽  
Centrifugal Compressor ◽  
Static Pressure ◽  
Pressure Ratio ◽  
Compressor Stage ◽  
Vaneless Diffuser ◽  
Moderate Amount ◽  
Flow Angle ◽  
Isentropic Efficiency

A centrifugal compressor is often equipped with a vaneless diffuser because the operation range of a vaneless diffuser is wider than the operation range of vaned diffuser, and the geometry of the vaneless diffuser is simple and inexpensive. The flow field after the centrifugal compressor rotor is highly complicated and the velocity is high. A moderate amount of this velocity should be recovered to the static pressure. It is important to study the flow field in the vaneless diffuser in order to achieve guidelines for design and an optimal performance. In this article, the experimental study of the pinch in the vaneless diffuser is conducted. Five different diffuser heights were used, b/b2 = 1, b/b2 = 0.903, b/b2 = 0.854, b/b2 = 0.806 and b/b2 = 0.903 (shroud). In three of the cases, the pinch was made to both walls of the diffuser, hub and shroud, and in one case, the pinch was made to the shroud wall. The total and the static pressure, the total temperature and the flow angle were measured at the diffuser inlet and outlet by using a cobra-probe, kiel-probes and flush-mounted pressure taps. In addition, the static pressure in the diffuser was measured at three different radius ratios. The overall performance, the mass flow, the pressure ratio and the isentropic efficiency of the compressor stage were also monitored. Detailed flow field measurements were carried out at the design rotational speed and at the three different mass flows (close to the surge, design and close to the choke). The isentropic efficiency and the pressure ratio of the compressor stage was increased with the pinched diffuser. The efficiency of the rotor and the diffuser was increased, whereas the efficiency of the volute/exit cone was decreased. The pinch made to the shroud wall was the most effective. The pinch made the flow angle more radial and increased the velocity at the shroud where the secondary flow (passage wake) from the rotor is present.

The Effects of Reynolds Number on the Stall and Pre-Stall Behaviour of Compact Axial Compressors

2020 ◽  
Author(s):  
Jack Hutchings ◽  
Cesare Hall
Keyword(s):  
Reynolds Number ◽  
Flow Field ◽  
Static Pressure ◽  
Three Dimensional ◽  
Pressure Rise ◽  
Critical Value ◽  
Rotating Stall ◽  
Secondary Flows ◽  
Transitional Flow ◽  
Number Range

Abstract Compact axial compression systems are of interest to the domestic appliance industry. The associated low Reynolds number leads to high losses compared to large-scale compressors due to a transitional flow field with large regions of separation. This paper investigates how Reynolds number variations affect the three-dimensional and unsteady flow field in a compact compressor both pre-stall and in stall. An experimental study has been conducted using a scaled-up singlestage axial compressor across a Reynolds number range of 104 to 105. Steady and unsteady casing static pressure measurements, along with rotor upstream and downstream unsteady velocity measurements, have been used to observe the rotor flow field. As the Reynolds number is reduced below a critical value, 60,000 in the case of the compressor studied, the pressure rise coefficient of the compressor decreases. The exact value of the critical Reynolds number is expected to vary with the compressor geometry. This fall off in performance corresponds to an increase in the compressor rotor secondary flows. Prior to stall, a broadband hump at around 50% of the blade passing frequency is present in the near-field casing static pressure spectra. At Reynolds numbers below the critical value, multiple equally spaced peaks also appear around the peak of the broadband hump. The spacing of these peaks has been found to be exactly equal to the measured stall cell speed once rotating stall is established. When operating in stall, the stall cell is found to increase in size and slow down as Reynolds number decreases. The measured spectra and observed flow structures show that disturbances exist prior to stall at frequencies consistent with the frequencies within stall. The size and shape of the stall cells that form are related to the extent of the three-dimensional flow field present prior to stall. Below a critical value, all of these flow features are highly sensitive to Reynolds number.

Effects of Inlet Flow Field Conditions on the Performance of Centrifugal Compressor Diffusers: Part 2—Straight-Channel Diffuser

1998 ◽  
Vol 122 (1) ◽  
pp. 11-21 ◽  
Author(s):  
S. Deniz ◽  
E. M. Greitzer ◽  
N. A. Cumpsty
Keyword(s):  
Mach Number ◽  
Flow Field ◽  
Centrifugal Compressor ◽  
Rotating Stall ◽  
Pressure Recovery ◽  
Maximum Pressure ◽  
Straight Channel ◽  
Inlet Flow ◽  
Flow Angle ◽  
Operating Range

This is Part 2 of an examination of the influence of inlet flow conditions on the performance and operating range of centrifugal compressor vaned diffusers. The paper describes tests of a straight-channel type diffuser, sometimes called a wedge-vane diffuser, and compares the results with those from the discrete-passage diffusers described in Part 1. Effects of diffuser inlet Mach number, flow angle, blockage, and axial flow nonuniformity on diffuser pressure recovery and operating range are addressed. The straight-channel diffuser investigated has 30 vanes and was designed for the same aerodynamic duty as the discrete-passage diffuser described in Part 1. The ranges of the overall pressure recovery coefficients were 0.50–0.78 for the straight-channel diffuser and 0.50–0.70 for the discrete-passage diffuser, except when the diffuser was choked. In other words, the maximum pressure recovery of the straight-channel diffuser was found to be roughly 10 percent higher than that of the discrete-passage diffuser investigated. The two types of diffuser showed similar behavior regarding the dependence of pressure recovery on diffuser inlet flow angle and the insensitivity of the performance to inlet flow field axial distortion and Mach number. The operating range of the straight-channel diffuser, as for the discrete-passage diffusers, was limited by the onset of rotating stall at a fixed momentum-averaged flow angle into the diffuser, which was for the straight-channel diffuser, αcrit=70±0.5 deg. The background, nomenclature, and description of the facility and method are all given in Part 1. [S0889-504X(00)00201-4]

Flow Field Structures of the Impeller Backside Cavity and Its Influences on the Centrifugal Compressor

2009 ◽  
Author(s):  
Zhigang Sun ◽  
Chunqing Tan ◽  
Dongyang Zhang
Keyword(s):  
Flow Field ◽  
Centrifugal Compressor ◽  
Pressure Ratio ◽  
Flow Patterns ◽  
Operating Conditions ◽  
Leakage Flow ◽  
Coupled Flow ◽  
Axial Thrust ◽  
Aerodynamic Performances ◽  
Shaft Power

The impeller backside cavity is one of the unique features of the centrifugal compressors, it can affect the aerodynamic performances of a centrifugal compressor in many ways. This paper presents the researches on the coupled flow fields between a centrifugal compressor main flow passage and its impeller backside cavity. The flow field structures and features of the impeller backside cavity are presented for different leakage flow patterns, and its influences on the flow field details, axial thrust, shaft power, pressure ratio and efficiency of the centrifugal compressor have been studied. Some general conclusions are drawn for different centrifugal compressor operating conditions and impeller backside cavity leakage flow patterns.

Influence of Low-Solidity Cascade Diffuser on Spike Stall Inception in a Centrifugal Compressor

2012 ◽  
Author(s):  
Satoshi Joukou ◽  
Yasushi Shinkawa ◽  
Toshio Kanno ◽  
Hideo Nishida ◽  
Takahiro Nishioka ◽  
...  
Keyword(s):  
Flow Separation ◽  
Static Pressure ◽  
Rotating Stall ◽  
Short Length ◽  
Radius Ratio ◽  
Length Scale ◽  
Small Disturbance ◽  
Flow Angle ◽  
Stall Inception ◽  
Wing Section

Stall inception patterns for three low-solidity cascade diffusers were experimentally investigated to extend the operating range of centrifugal compressor. Pressure fluctuations on the wall and flow distributions at the diffuser inlet were measured, and static pressure-rises across the diffuser vane were also measured to clarify the mechanism of rotating stall inception. In the case of the original diffuser (LSD_O), which had the radius ratio between the impeller outlet and the diffuser vane inlet of 1.10 and a flat plate wing section, a short length-scale stall cell known as a spike first appeared in the positive slope of the diffuser static pressure-raise (after the flat slope was maintained), and then a surge occurred as flow-rate decreased. The propagation speed of short length-scale stall cell was about 13% of the impeller rotation speed. The measured flow distribution at the inlet of the LSD_O suggested that the flow separation occurred in the vaneless space and this separation influenced the rotating stall. In the case of the LSD_A, which had the radius ratio of 1.10 and the NACA 63 wing section, a short length-scale stall cell that was smaller than that of LSD_O was appeared in the positive slope of the diffuser static pressure-raise (without the flat slope). A surge also occurred as further flow-rate decreased. The propagation speed of short length-scale stall cell was about 13% just prior to surge point. In contrast, in the case of LSD_B, which had the radius ratio of 1.05 and the NACA 63 wing section, a small disturbance appeared without spike just prior to surge point and rotating stall did not occur. The small disturbance did not propagate in the circumferential direction. Moreover, the flow separation did not occur in the semi-vaneless space. At the stall inception point of LSD_O and LSD_A, the averaged absolute flow angle at the diffuser inlet agreed with the onset flow angel of rotating stall in vaneless diffuser predicted by Senoo. Therefore, it was considered that the flow separation also occurred in the vaneless space and this separation influenced the rotating stall in the case of LSD_A. Moreover, it was considered that the difference of two stall cell patterns between LSD_O and LSD_A depended on the static pressure-rise characteristic of diffuser determined by the design specifications in case of that the rotating stall occurred in the vaneless space. In contrast, at the point of the small disturbance appeared of LSD_B, the averaged absolute flow angle at the diffuser inlet is smaller than that predicted by Senoo. Therefore, in case of small the radius ratio, the reverse flow in vaneless diffuser is suppressed, and the rotating stall is also suppressed.

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