The Influence of a Diffuser Width on the Unsteady Performance of a Centrifugal Compressor Stage

2002 ◽  
Author(s):  
Abraham Engeda
Keyword(s):  
Centrifugal Compressor ◽  
Time Domain ◽  
Rotating Stall ◽  
Compressor Stage ◽  
Relative Speed ◽  
Vaneless Diffuser ◽  
Flow Rates ◽  
Centrifugal Compressor Stage ◽  
Different Types ◽  
Unsteady Performance

An experimental investigation was conducted to determine the effect of the vaneless diffuser width on the unsteady flow performance of a centrifugal compressor stage. Two compressor configurations with different vaneless diffuser width were investigated at four different impeller speeds and compared in the frequency and time domain. Only one diffuser rotating stall but different types of impeller rotating stalls were detected. The experiments show that the diffuser has a strong influence on the flow in the impeller including in areas way upstream. Analysis of the results indicated: • With increasing diffuser width the onset of impeller rotating stall was shifted to lower flow rates. • With increasing diffuser width the frequencies of the rotating stalls decreased. • There is a common tendency in most of the experiments to lower numbers of rotating cells with increasing relative speed. The impeller rotating stalls can be subdivided in a slow pattern with a relative speed to the impeller of 0.21 to 0.29 and a fast pattern with a relative speed of 0.50 to 0.56. This occurrence of two rotating pressure patterns confirms analytical results presented in previous investigations.

Spreadsheet as a Data Acquisition Tool in Turbomachinery

2010 ◽  
Author(s):  
Abraham Engeda
Keyword(s):  
Data Acquisition ◽  
Rotating Stall ◽  
Relative Speed ◽  
Vaneless Diffuser ◽  
Flow Rates ◽  
One Dimensional ◽  
Measurement And Analysis ◽  
Different Types ◽  
Unsteady Characteristics ◽  
The One

This paper shows the power of spreadsheets as a strong tool in engineering teaching and research labs. In applied thermo-fluid education, even the one dimensional design or simple experimental measurement and analysis becomes a very complex exercise unless the procedure is programmed. Due to lengthy calculations and iterations, simple solutions are not possible. Exercises have therefore been limited in the classroom. But recent advances in powerful spreadsheets have opened a simple and fast way of performing design and advanced measurements. In recent times due to the introduction of a variety of mathematical soft wares, students have been relived from unnecessary time consuming chores; and therefore, complex measurements can now be carried out more comprehensively and easily. This paper reports on an experimental investigation to determine the effect of the vaneless diffuser width on the unsteady flow performance of a centrifugal compressor stage, where the whole data processing was carried out using a spreadsheet both for the steady and unsteady characteristics. Two compressor configurations with different vaneless diffuser width were investigated at four different impeller speeds and compared in the frequency and time domain. Only one diffuser rotating stall but different types of impeller rotating stalls were detected. The experiments show that the diffuser has a strong influence on the flow in the impeller including in areas way upstream. Analysis of the results indicated: • With increasing diffuser width the onset of impeller rotating stall was shifted to lower flow rates. • With increasing diffuser width the frequencies of the rotating stalls decreased. • There is a common tendency in most of the experiments to lower numbers of rotating cells with increasing relative speed. The whole data acquisition, processing and presentation are carried out using Excel.

A Distinction Between Different Types of Stall in a Centrifugal Compressor Stage

1986 ◽  
Vol 108 (1) ◽  
pp. 83-92 ◽  
Author(s):  
N. Ka¨mmer ◽  
M. Rautenberg
Keyword(s):  
Energy Transfer ◽  
Centrifugal Compressor ◽  
High Frequency ◽  
Low Frequency ◽  
Rotating Stall ◽  
Compressor Stage ◽  
Vaneless Diffuser ◽  
Pressure Transducers ◽  
Different Types ◽  
Probe Measurements

The flow at the stall line of a centrifugal compressor with vaneless diffuser was investigated at different speeds. A distinction between three kinds of stall phenomena could be made. One type of stall with regurgitation of fluid at the impeller inlet was of a nonperiodic character, whereas two different types of periodic stall appeared at higher speeds. The rotating nature of these two types of stall was verified from a comparison of signals of peripherally spaced pressure transducers. The low-frequency rotating stall exhibited features of diffuser generated stall and a lobe number of three was measured. From a detailed investigation of the high-frequency rotating stall, which included unsteady probe measurements upstream and downstream of the impeller, it can be shown that this type of rotating stall is generated in the impeller by a periodic breakdown of energy transfer from the rotor to the flow. This conclusion is supported by the distribution of shroud static pressures.

An Investigation of the Stability Enhancement of a Centrifugal Compressor Stage Using a Porous Throat Diffuser

2017 ◽  
Vol 140 (1) ◽  
Author(s):  
Lee Galloway ◽  
Stephen Spence ◽  
Sung In Kim ◽  
Daniel Rusch ◽  
Klemens Vogel ◽  
...  
Keyword(s):  
Centrifugal Compressor ◽  
Compressor Stage ◽  
Vaned Diffuser ◽  
Flow Rates ◽  
Stall Inception ◽  
Centrifugal Compressor Stage ◽  
Operating Range ◽  
Stable Operating ◽  
The Stability ◽  
Circumferential Pressure

The stable operating range of a centrifugal compressor stage of an engine turbocharger is limited at low mass flow rates by aerodynamic instabilities which can lead to the onset of rotating stall or surge. There have been many techniques employed to increase the stable operating range of centrifugal compressor stages. The literature demonstrates that there are various possibilities for adding special treatments to the nominal diffuser vane geometry, or including injection or bleed flows to modify the diffuser flow field in order to influence diffuser stability. One such treatment is the porous throat diffuser (PTD). Although the benefits of this technique have been proven in the existing literature, a comprehensive understanding of how this technique operates is not yet available. This paper uses experimental measurements from a high pressure ratio (PR) compressor stage to acquire a sound understanding of the flow features within the vaned diffuser which affect the stability of the overall compression system and investigate the stabilizing mechanism of the porous throat diffuser. The nonuniform circumferential pressure imposed by the asymmetric volute is experimentally and numerically examined to understand if this provides a preferential location for stall inception in the diffuser. The following hypothesis is confirmed: linking of the diffuser throats via the side cavity equalizes the diffuser throat pressure, thus creating a more homogeneous circumferential pressure distribution, which delays stall inception to lower flow rates. The results of the porous throat diffuser configuration are compared to a standard vaned diffuser compressor stage in terms of overall compressor performance parameters, circumferential pressure nonuniformity at various locations through the compressor stage and diffuser subcomponent analysis. The diffuser inlet region was found to be the element most influenced by the porous throat diffuser, and the stability limit is mainly governed by this element.

Flow Studies on a Centrifugal Compressor Stage With Low Solidity Diffuser Vanes

2002 ◽  
Author(s):  
Prasad Mukkavilli ◽  
G. Rama Raju ◽  
A. Dasgupta ◽  
G. V. Ramana Murty ◽  
K. V. Jagadeshwar Chary
Keyword(s):  
Centrifugal Compressor ◽  
Design Flow ◽  
Flow Coefficient ◽  
Compressor Stage ◽  
Vaneless Diffuser ◽  
Centrifugal Compressor Stage ◽  
Setting Angle ◽  
Set Up ◽  
Flow Improvement ◽  
Stagger Angle

Diffusers are found to play a significant role in the performance of centrifugal compressors. Extensive studies have been in progress in various research laboratories for improvement of performance with various types of diffusers. One such effort for study of performance of a centrifugal compressor stage with Low Solidity Diffuser (LSD) vanes is presented in this paper. The study was conducted at a tip mach number of 0.35. An exclusive test rig was set up for carrying out these flow studies. The LSD vane is formed using standard NACA profile with marginal modification at the trailing edge region. The study encompasses the variation of setting angle of the LSD vane and the vane solidity. The effect of solidity and the setting angle on overall stage performance is evaluated in terms of flow coefficient, head coefficient and efficiency normalised with respect to these parameters for the case of vaneless diffuser at design flow. Improvement in performance as well as static pressure recovery was observed with LSD as compared to vaneless diffuser configuration. It is concluded from these studies that there is an optimum solidity and stagger angle for the given stage with LSD vanes for the chosen configuration.

Analytical and Test Experiences Using a Rib Diffuser in a High Flow Centrifugal Compressor Stage

2001 ◽  
Author(s):  
James M. Sorokes ◽  
Jason A. Kopko
Keyword(s):  
Centrifugal Compressor ◽  
Quantitative Agreement ◽  
High Flow ◽  
Flow Coefficient ◽  
Centrifugal Impeller ◽  
Compressor Stage ◽  
Vaneless Diffuser ◽  
Vaned Diffuser ◽  
Centrifugal Compressor Stage ◽  
Qualitative And Quantitative

The paper addresses the use of a rib style (partial height) vaned diffuser to improve the flowfield downstream of a high flow coefficient centrifugal impeller. Empirical and analytical (3-D CFD) results are presented for both the original vaneless diffuser and the replacement rib configuration. Comparisons are made between the CFD results and the data obtained through single stage rig (SSTR) testing. Comments are offered regarding the qualitative and quantitative agreement between the empirical and analytical results.

Experimental and Numerical Investigation of the Flow in a Vaneless Diffuser of a Centrifugal Compressor Stage. Part 1: Experimental Investigation

2005 ◽  
Vol 219 (10) ◽  
pp. 1053-1059 ◽  
Author(s):  
T Sato ◽  
J M Oh ◽  
A Engeda
Keyword(s):  
Experimental Investigation ◽  
Flow Field ◽  
Boundary Layers ◽  
Centrifugal Compressor ◽  
High Flow ◽  
Flow Coefficient ◽  
Compressor Stage ◽  
Vaneless Diffuser ◽  
Centrifugal Compressor Stage ◽  
Very High

The flow in a radial vaneless diffuser downstream of a centrifugal compressor is highly complex, as the flow is turbulent, unsteady, viscous, and three-dimensional. Depending on the initial state of the end-wall boundary layers and the diffuser length, the flow may become fully developed or may separate from one of the walls. Therefore, to improve the diffuser performance, it is important to understand the flow field in the diffuser in detail. As the diffuser width is generally very small for most radial stages and an adverse pressure gradient exists, secondary flows are generated, making the flow fields more complicated. In addition, skewed boundary layers form on the wall surfaces. As flowrate is reduced, the flow field becomes more complicated and leads to rotating stall. This article presents detailed flow measurements in a vaneless diffuser of a centrifugal compressor stage with a very high flow coefficient radial impeller. Usually, centrifugal compressors with radial impellers are designed in the flow coefficient (ϕ) range ϕ = 0.01 - 0.16. Often, the need arises to design higher flow coefficient, ϕ, radial stages. Detailed measurements were carried out in the vaneless diffuser at seven radial positions downstream of a radial impeller designed for a very high flow coefficient of ϕ = 0.2. The experimental investigation was carried at four rotational speeds 13 000, 15 500, 18 000, and 20 500 r/min, but only the result of 20 500 r/min at near-design-point flowrate (5.11 kg/s) is reported in this article.

Multi-Blade Row Interactions in a Low Pressure Ratio Centrifugal Compressor Stage With a Vaned Diffuser

2011 ◽  
Author(s):  
Kishore Ramakrishnan ◽  
Simon K. Richards ◽  
Franc¸ois Moyroud ◽  
Vittorio Michelassi
Keyword(s):  
Centrifugal Compressor ◽  
Oil And Gas ◽  
Pressure Ratio ◽  
Compressor Stage ◽  
Vaneless Diffuser ◽  
Vaned Diffuser ◽  
Centrifugal Compressor Stage ◽  
Acoustic Interaction ◽  
Field Excitation

Previous experimental and CFD investigation of a GE Oil and Gas centrifugal compressor stage with a vaneless diffuser revealed a complex excitation mechanism caused by an aero-acoustic interaction between three blade rows. In stages with vaned diffusers, additional sources of aeromechanical excitation on the impeller can be expected. This unsteady CFD investigation is a follow-up from the previous vaneless diffuser study to identify any additional sources of excitation that arise in the presence of a vaned diffuser in preparation for aeromechanic tests to be conducted later. The study confirms that excitation from impeller-diffuser interaction generated acoustic modes can dominate the potential field excitation from the diffuser vanes. In addition, a significant aero-acoustic excitation to the impeller at a vane pass frequency corresponding to the sum of the vane counts in the two downstream vane rows is observed, and its origination is discussed. The latter excitation is different from that observed in the vaneless diffuser stage where the vane pass frequency observed by the impeller corresponds to the sum of the vane counts in the upstream and downstream vane rows.

Experimental and Numerical Investigation of the Flow in a Vaneless Diffuser of a Centrifugal Compressor Stage. Part 2: Numerical Investigation

2005 ◽  
Vol 219 (10) ◽  
pp. 1061-1068 ◽  
Author(s):  
T Sato ◽  
J M Oh ◽  
A Engeda
Keyword(s):  
Numerical Investigation ◽  
Centrifugal Compressor ◽  
High Flow ◽  
Flow Coefficient ◽  
Compressor Stage ◽  
Vaneless Diffuser ◽  
Flow Measurements ◽  
Centrifugal Compressor Stage ◽  
Improved Performance ◽  
Very High

As user demands grew for improved performance and more reliable equipment and as compressor vendors sought improved analytical and design methodologies, the application of computational fluid dynamics (CFD) in the industrial world became a necessity. Fortunately, large increases in available, economic computing power together with development of improved computational methods now provide the industrial designer with much improved analytic capability. As CFD algorithms and software have continued to be developed and refined, it remains essential that validation studies be conducted in order to ensure that the results are both sufficiently accurate and can be obtained in a robust and predictable manner. Part I of this paper presented detailed flow measurements in a vaneless diffuser of a centrifugal compressor stage with a very high flow coefficient radial impeller, where measurements were carried out in the vaneless diffuser at seven radial positions downstream of the radial impeller designed for a very high flow coefficient of ϕ = 0.2. This paper, Part II, attempts to verify and validate the results numerically.

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