scholarly journals The Effect of Variable Geometry on the Operating Range and Surge Margin of a Centrifugal Compressor

1976 ◽  
Author(s):  
A. Whitfield ◽  
F. J. Wallace ◽  
R. C. Atkey
Keyword(s):  
Centrifugal Compressor ◽  
Peak Pressure ◽  
Pressure Ratio ◽  
Variable Geometry ◽  
Vaneless Diffuser ◽  
Flow Rates ◽  
Lower Flow ◽  
Operating Range ◽  
Surge Margin ◽  
Isentropic Efficiency

Two variable geometry techniques have been applied to a small turbocharger compressor, with the objective of trying to move the peak pressure ratio operating point to lower flow rates, thereby yielding a broad flow range map. Variable prewhirl guide vanes and variable vaneless diffuser passage height have been studied separately. The results obtained with both techniques are compared and the relative merits and demerits with respect to improved flow range and isentropic efficiency penalties are considered.

Design and Experimental Study on the Surge Performance Improvement by the Effects of Bleed Slot Casing of a Centrifugal Compressor

2014 ◽  
Author(s):  
Hong Won Kim ◽  
Jae Hoon Chung ◽  
Hyo Seong Lee ◽  
Min Ouk Choi
Keyword(s):  
Centrifugal Compressor ◽  
Stokes Equations ◽  
Pressure Ratio ◽  
Three Dimensional ◽  
Navier Stokes ◽  
Design Parameters ◽  
Navier Stokes Equations ◽  
Operating Range ◽  
Surge Margin ◽  
Commercial Code

The primary design goal of a compressor is focused on improving efficiency. Secondary objective is to widen the compressor’s operating range. This paper presents a numerical and experimental investigation of the influence of the bleed slot to enlarge operating range for the 1.2MW class centrifugal compressor installed in a turbocharger. The main design parameters of the bleed slot casing are upstream slot position, inlet pipe slope, downstream slot position and width. The DOE (design of experiment) method was carried out to optimize the casing design. Numerical analyses were done by the commercial code ANSYS-CFX based on the three dimensional Reynolds-averaged Navier-Stokes equations. From the analysis, as the downstream slot position and width are smaller and upstream position is located away from impeller inlet, efficiency and pressure ratio are increased. Experimental works were done with and without the bleed slot casing. The simulation results were in good agreement with the test data. In case without the bleed slot casing, the surge margin value came out to be only 11.8% but with the optimized bleed slot design, the surge margin reached 23%. Therefore, the surge margin increase of 11.2% was achieved.

scholarly journals The Performance of a Centrifugal Compressor With High Inlet Prewhirl

1997 ◽  
Author(s):  
A. Whitfield ◽  
A. H. Abdullah
Keyword(s):  
Centrifugal Compressor ◽  
Pressure Ratio ◽  
Low Flow ◽  
Variable Geometry ◽  
Pressure Pulsations ◽  
Operating Range ◽  
Swirl Generator ◽  
Geometry Design ◽  
Wide Range ◽  
Inlet Swirl

The performance requirements of centrifugal compressors usually include a broad operating range between surge and choke. This becomes increasingly difficult to achieve as increased pressure ratio is demanded. In order to suppress the tendency to surge and extend the operating range at low flow rates inlet swirl is often considered through the application of inlet guide vanes. To generate high inlet swirl angles efficiently an inlet volute has been applied as the swirl generator, and a variable geometry design developed in order to provide zero swirl. The variable geometry approach can be applied to progressively increase the swirl or to switch rapidly from zero swirl to maximum swirl. The variable geometry volute and the swirl conditions generated are described. The performance of a small centrifugal compressor is presented for a wide range of inlet swirl angles. In addition to the basic performance characteristics of the compressor the onset of flow reversals at impeller inlet are presented, together with the development of pressure pulsations, in the inlet and discharge ducts, through to full surge. The flow rate at which surge occurred was shown, by the shift of the peak pressure condition and by the measurement of the pressure pulsations, to be reduced by over 40%.

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 Performance of a Centrifugal Compressor With High Inlet Prewhirl

1998 ◽  
Vol 120 (3) ◽  
pp. 487-493 ◽  
Author(s):  
A. Whitfield ◽  
A. H. Abdullah
Keyword(s):  
Centrifugal Compressor ◽  
Pressure Ratio ◽  
Low Flow ◽  
Variable Geometry ◽  
Pressure Pulsations ◽  
Operating Range ◽  
Swirl Generator ◽  
Geometry Design ◽  
Wide Range ◽  
Inlet Swirl

The performance requirements of centrifugal compressors usually include a broad operating range between surge and choke. This becomes increasingly difficult to achieve as increased pressure ratio is demanded. In order to suppress the tendency to surge and extend the operating range at low flow rates, inlet swirl is often considered through the application of inlet guide vanes. To generate high inlet swirl angles efficiently, an inlet volute has been applied as the swirl generator, and a variable geometry design developed in order to provide zero swirl. The variable geometry approach can be applied to increase the swirl progressively or to switch rapidly from zero swirl to maximum swirl. The variable geometry volute and the swirl conditions generated are described. The performance of a small centrifugal compressor is presented for a wide range of inlet swirl angles. In addition to the basic performance characteristics of the compressor, the onsets of flow reversals at impeller inlet are presented, together with the development of pressure pulsations, in the inlet and discharge ducts, through to full surge. The flow rate at which surge occurred was shown, by the shift of the peak pressure condition and by the measurement of the pressure pulsations, to be reduced by over 40 percent.

Investigation of Vaned Diffusers as a Variable Geometry Device for Application to Turbocharger Compressors

1992 ◽  
Vol 206 (3) ◽  
pp. 209-220 ◽  
Author(s):  
P M Jiang ◽  
A Whitfield
Keyword(s):  
Pressure Ratio ◽  
Leading Edge ◽  
Variable Geometry ◽  
Vaneless Diffuser ◽  
Double Row ◽  
Guide Vanes ◽  
Operating Range ◽  
Consequent Reduction ◽  
Inlet Angle ◽  
Vane Angle

The potential of guide vanes as a variable geometry device, placed in the conventional vaneless diffuser, to extend the operating range of a turbocharger compressor is investigated. Vaned diffusers are not normally employed in turbocharger applications as the consequent reduction in operating range is more damaging than the beneficial improvement in peak efficiency and pressure ratio. The variable geometry concept considered here is primarily one in which the guide vanes are introduced at the near surge flow conditions. The leading edge vane angle is set to accept the highly tangential flow at the near surge conditions, and the vane is then used to guide the fluid towards the radial direction in order to reduce the long flow path through the diffuser. Four types of vane arrangements are considered: (a) 12 and 6 full length vanes, with inlet vane angles of 75° and 80°; (b) 6 short inlet vanes to give a high aspect ratio; (c) 12 and 6 short vanes located in the outer half of the vaneless diffuser passage; and (d) double-row vane rings. It is shown that short vanes deployed at the diffuser outlet not only improve the efficiency and pressure ratio but also extend the high flow operating range. Further, the introduction of short inlet vanes with an inlet angle of 80° improves the peak pressure ratio and efficiency, and extends the near surge operating range.

Numerical Study on the Range Enhancement of a Centrifugal Compressor With a Ring Groove System

2011 ◽  
Author(s):  
ChiYong Park ◽  
YoungSeok Choi ◽  
KyoungYong Lee ◽  
JoonYong Yoon
Keyword(s):  
Centrifugal Compressor ◽  
High Performance ◽  
High Efficiency ◽  
Numerical Study ◽  
Pressure Ratio ◽  
Low Flow ◽  
Ring Groove ◽  
Guide Vanes ◽  
Operating Range ◽  
Surge Margin

This paper presents a numerical study of casing treatments on a centrifugal compressor in order to improve stability and the surge margin. High efficiency, a high pressure ratio, and a wide operating range are required for a high-performance centrifugal compressor. A ring groove casing treatment is effective for flow range enhancement in centrifugal compressors. In the present study, compressor performance was analyzed according to the ring groove location and the results were compared with the case without a ring groove. The effect of guide vanes in the ring groove was also investigated. Four more variants of grooves were modeled and simulated using computational fluid dynamics (CFD) in order to optimize the groove location. The numerical analysis was carried out using a commercial code ANSYS-CFX program. The simulation results showed that the ring groove increased the operating range of the compressor. The ring groove with guide vanes improved both the compressor’s performance at low flow rates and improved the compressor’s surge margin.

scholarly journals Characterization of the Performance of a Turbocharger Centrifugal Compressor by Component Loss Contributions

Energies ◽  
2019 ◽  
Vol 12 (14) ◽  
pp. 2711 ◽  
Author(s):  
Nima Khoshkalam ◽  
Mohammad Mojaddam ◽  
Keith R. Pullen
Keyword(s):  
Numerical Model ◽  
Centrifugal Compressor ◽  
Pressure Ratio ◽  
Blade Angle ◽  
Loss Mechanism ◽  
Impeller Blade ◽  
Operating Range ◽  
Surge Margin ◽  
Wide Range ◽  
Loss Mechanisms

The performance of an automotive turbocharger centrifugal compressor has been studied by developing a comprehensive one-dimensional (1D) code as verified through experimental results and a three-dimensional (3D) model. For 1D analysis, the fluid stream in compressor is modeled using governing gas dynamics equations and the loss mechanisms have been investigated and added to the numerical model. The objective is to develop and offer a 1D model, which considers all loss mechanisms, slip, blockage and also predicts the surge margin and choke conditions. The model captures all features from inlet duct through to volute discharge. Performance characteristics are obtained using preliminary geometry and the blade characteristics. A 3D numerical model was also created and a viscous solver used for investigating the compressor characteristics. The numerical model results show good agreement with experimental data through compressor pressure ratio and efficiency. The effect of the main compressor dimensions on compressor performance has been investigated for wide operating range and the portions of each loss mechanism in the impeller. Higher pressure ratio is achievable by increasing impeller blade height at outlet, impeller blade angle on inlet, diffuser outlet diameter and by decreasing impeller shroud diameter at inlet and blade angle at outlet. These changes may cause unfavorable consequences such as a lower surge margin or shorter operating range, which should be compromised with favorable changes. At lower rotational speeds, impeller skin friction mainly impacts the performance and at higher rotational speeds, impeller diffusion, blade loading and recirculation losses are more important. The results allow the share of each loss mechanism to be quantified for different mass flow rates and rotational speed, shedding new light on which losses are most important for which conditions. For a turbocharger, which must operate over a wide range of conditions, these results bring new insight to engineers seeking to optimize the compressor design as part of an internal combustion engine system.

Effect of Circumferential Static Pressure Non-Uniformity Caused by a Volute on Flow in High Pressure Ratio Centrifugal Compressor With Vaneless and Vaned Diffuser

2013 ◽  
Author(s):  
Hideaki Tamaki ◽  
Masaru Unno ◽  
Xinqian Zheng ◽  
Yangjun Zhang
Keyword(s):  
Centrifugal Compressor ◽  
Gas Turbines ◽  
Static Pressure ◽  
Incidence Angle ◽  
Low Flow ◽  
Vaneless Diffuser ◽  
Vaned Diffuser ◽  
Flow Rates ◽  
Operating Range ◽  
Surge Line

Centrifugal compressors are deemed to have a wide operating range. Recirculation devices, which comprise a bleed slot, an upstream slot and an annular cavity connecting them, are often used particularly compressors for turbochargers. They remove low energy fluid at the inducer and improve the incidence angle of the impeller leading edge, i.e. the blade loading of the inducer, at low flow rates due to the recirculation flow supplied to the compressor inlet. The impeller of a centrifugal compressor is often housed in a volute. Since the geometry of the volute is not axisymmetric, the impeller might be surrounded by an asymmetric flow field, hence there is the potential to enlarge the compressor operating range and improve efficiency using a recirculation device with an asymmetrically-distributed bleed slot, referred to here as a non-axisymmetric recirculation device. The authors [1] applied non-axisymmetric recirculation devices to a compressor with a vaneless diffuser. The results showed the effectiveness of a non-axisymmetric recirculation device with a bleed slot partially channeled in the circumferential direction. They also showed that the surge line of the compressor characteristics, which is the line connecting the operational points of the smallest flow rates on all peripheral Mach numbers, was significantly affected by the change in the circumferential position of the bleed slot relative to the volute tongue. The tested compressor was originally designed to feature a vaned diffuser [2]. Enhancing the compressor operating range is the key for marine use turbochargers, integrally geared compressors, multistage compressors and gas turbines as well as automotive turbochargers. These compressors normally use vaned diffusers. In this study the authors tried to apply non-axisymmetric recirculation devices developed in their previous study [1] to compressors with a vaned diffuser. Moreover different circumferential positions of the bleed slot relative to the volute tongue were tested as well as the vanelss diffuser case. The change in the surge line of the compressor characteristics was much smaller compared to the compressor with the vaneless diffuser. The circumferential static pressure distributions in the compressors in combination with vaneless and vaned diffusers were measured to determine the above reason as well as conducting unsteady calculations with a simplified outlet boundary condition. These measurements and calculations showed that the impeller with the vaned diffuser was surrounded by a less distorted static pressure field than that with the vaneless diffuser. These results implied that the vaned diffuser depresses the spread of the circumferential static pressure non-uniformity effect caused by a volute to the impeller.

Experimental Study of a Novel Centrifugal Compressor with Two Successive and Independent Rotors

2021 ◽  
Author(s):  
Van-Thang Nguyen ◽  
Cheikh Brahim Abed ◽  
Amélie Danlos ◽  
Florent Ravelet ◽  
Richard Paridaens ◽  
...  
Keyword(s):  
Experimental Study ◽  
Centrifugal Compressor ◽  
Design Method ◽  
Pressure Ratio ◽  
Second Step ◽  
Operating Parameters ◽  
Rotor Speed ◽  
Flow Rates ◽  
Surge Margin ◽  
Wide Range

Abstract The present study deals with a low pressure-ratio centrifugal compressor consisting of two counter-rotating rotors called a Counter-Rotating Centrifugal Compressor (CRCC). The design method based on the loss model was presented to determine the geometric parameters of the two counter-rotating rotors. According to this method, the rotor of a selected Single Rotor Centrifugal Compressor (SRCC) has been redesigned into two counter-rotating rotors (upstream and downstream rotors) by choosing the value of meridional Length Ratio (LR). The meridional view, the volute shape, and the operating parameters of SRCC are preserved during the design process. In the first step, the counter-rotating mode at a constant rotor speed of 11k rpm has been carried out. The overall characteristics of CRCC are compared to those of SRCC. In the second step, the map-characteristic of CRCC is established for seven speed ratios. The results show that CRCC increases up to 4,6% for the pressure ratio and 3.5% for the efficiency compared to SRCC at the same tip-speed. In addition, CRCC can operate at a lower tip-speed by about 2k rpm to produce the same characteristics as SRCC, with better efficiency over a wide range of flow rates. However, the surge margin of the CRCC is shifted to higher flow rates. This disadvantage of the CRCC was solved by choosing the adequate pair of the rotational speeds of the two rotors that will be presented in other publication.

The Effect of Vaneless Diffuser Geometry on the Surge Margin of Turbocharger Compressors

1989 ◽  
Vol 203 (2) ◽  
pp. 91-98 ◽  
Author(s):  
A Whitfield ◽  
A J Sutton
Keyword(s):  
Pressure Ratio ◽  
Engine Management System ◽  
Test Facility ◽  
Full Potential ◽  
Variable Geometry ◽  
Vaneless Diffuser ◽  
Unstable Flow ◽  
Surge Margin ◽  
Road Haulage ◽  
Engine Testing

A study into the effect of two methods of changing the geometry of a vaneless diffuser on the performance of the compressor of a road haulage diesel engine turbocharger is described. The development of compressor variable geometry will enable the full potential of variable geometry turbines to be realized. This will give a more flexible power unit which will provide, for example, better low-speed torque and hence a smaller gearbox, and shorter journey times or larger payloads than are currently the practice. The disadvantages are added complexity and cost in the relatively simple turbocharger, and the need for an engine management system. The latter is currently being implemented on many vehicles to meet tight emissions regulations in Europe and elsewhere, and is thus not a drawback limited to variable geometry turbocharging. A compressor test facility, including appropriate instrumentation and a computer-based data-acquisition system, was constructed with the specific aim of investigating the unstable flow regime prior to and including surge. Alternative fixed vaneless diffuser geometries were designed to simulate a variable geometry diffuser which could be achieved through a flexing diffuser wall and a sliding throttle ring. Both the converging wall and throttle ring arrangement moved the peak pressure ratio to lower flowrates, and at the near surge flowrates (where the device would be introduced, when operating in a variable geometry mode) improvements in both pressure ratio and efficiency are shown. While the converging wall concept exhibited slightly better aerodynamic performance than the throttle ring, it has implementation difficulties with respect to material integrity under continuous flexing when developed to a fully variable geometry device. The simplicity of the sliding throttle ring makes it a more viable proposition. Prototype variable geometry (VG) devices have been constructed with a view to further rig and engine testing.

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