scholarly journals Flow Studies in a Centrifugal Compressor Stage

2014 ◽  
Author(s):  
R. Rajendran
Keyword(s):  
Centrifugal Compressor ◽  
Flow Behavior ◽  
Compressor Stage ◽  
Impeller Blade ◽  
Vaned Diffuser ◽  
Flow Angle ◽  
Centrifugal Compressor Stage ◽  
Operating Range ◽  
Impeller Outlet ◽  
Outlet Flow

The overall efficiency of a compressor is dependent on the design of both the impeller and the diffuser. The vaned diffuser reduces the operating range compared to the vaneless diffuser. However, by proper setting of the diffuser with reference to the impeller, it is possible to achieve a good stage performance. This paper describes the experimental investigation of the detailed flow behavior inside a centrifugal compressor stage for three different setting angles of the vaned diffuser with reference to the fixed impeller blade outlet angle. It is seen that diffuser setting angles lower than the impeller outlet flow angle gives wide operating range.

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.

Some Studies on Low Solidity Vaned Diffusers of a Centrifugal Compressor Stage

2005 ◽  
Author(s):  
T. Ch. Siva Reddy ◽  
G. V. Ramana Murty ◽  
Prasad Mukkavilli ◽  
D. N. Reddy
Keyword(s):  
Centrifugal Compressor ◽  
Static Pressure ◽  
Pressure Ratio ◽  
Pressure Recovery ◽  
Compressor Stage ◽  
Recovery Coefficient ◽  
Vaned Diffuser ◽  
Flow Angle ◽  
Centrifugal Compressor Stage ◽  
Pressure Recovery Coefficient

Numerical simulation of impeller and low solidity vaned diffuser (LSD) of a centrifugal compressor stage is performed individually using CFX- BladeGen and BladeGenPlus codes. The tip mach number for the chosen study was 0.35. The same configuration was used for experimental investigation for a comparative study. The LSD vane is formed using standard NACA profile with marginal modification at trailing edge. The performance parameters obtained form numerical studies at the exit of impeller and the diffuser have been compared with the corresponding experimental data. These parameters are pressure ratio, polytropic efficiency and flow angle at the impeller exit where as the parameters those have been compared at the exit of diffuser are the static pressure recovery coefficient and the exit flow angle. In addition, the numerical prediction of the blade loading in terms of blade surface pressure distribution on LSD vane has been compared with the corresponding experimental results. Static pressure recovery coefficient and flow angle at diffuser exit is seen to match closely at higher flows. The difference at lower flows could be due to the effect of interaction between impeller and diffuser combinations, as the numerical analysis was done separately for impeller and diffuser and the effect of impeller diffuser interaction was not considered.

scholarly journals Experimental Investigation of Unsteady Flow Phenomena in a Centrifugal Compressor Vaned Diffuser of Variable Geometry

1999 ◽  
Vol 121 (4) ◽  
pp. 763-771 ◽  
Author(s):  
F. Justen ◽  
K. U. Ziegler ◽  
H. E. Gallus
Keyword(s):  
Centrifugal Compressor ◽  
Pressure Fluctuations ◽  
Suction Side ◽  
Front Wall ◽  
Compressor Stage ◽  
Vaned Diffuser ◽  
Centrifugal Compressor Stage ◽  
Impeller Outlet ◽  
Flow Phenomena ◽  
Radial Gap

The behavior of vaned radial diffusers is generally considered to be due to the flow phenomena in the vaneless and the semi-vaned space in the diffuser inlet region. Even considering unsteady aspects, the adjacent diffuser channel is regarded as less important. The flat wedge vaned diffuser of the centrifugal compressor stage investigated allows an independent continuous adjustment of the diffuser vane angle and the radial gap between impeller outlet and diffuser vane inlet, so that information about the importance of these geometric parameters can be obtained. The time-dependent pressure distribution on the diffuser front wall and on the suction and pressure surfaces of the diffuser vanes reveal that in the semi-vaned space mainly the region near the vane suction side is influenced by the unsteady impeller-diffuser interaction. Downstream in the diffuser channel the unsteadiness does not decay. Here, pressure fluctuations are appearing that are distinctly higher than the pressure fluctuations in the vaneless space. An estimation of the influence of the unsteadiness on the operating performance of the centrifugal compressor stage is made by measurements at choke and surge limit for different diffuser geometries.

CFD Analysis of Effect of Diffuser Vane Setting Angle and Shape on the Performance of a Centrifugal Compressor Stage

2015 ◽  
Author(s):  
Venkateswara Rao Pothuri ◽  
Ramana Murty Govindaraju ◽  
Venkata Rao Ganapathiraju ◽  
Naga Vamsi Palati ◽  
Sivaram Badisa
Keyword(s):  
Centrifugal Compressor ◽  
Constant Thickness ◽  
Computational Results ◽  
Compressor Stage ◽  
Performance Parameters ◽  
Vaned Diffuser ◽  
Flow Angle ◽  
Centrifugal Compressor Stage ◽  
Setting Angle ◽  
Blade Shape

This paper describes the computational results on the performance of a centrifugal compressor stage with Vaneless diffuser (VLD) and low solidity vaned diffuser (LSVD) by varying blade shape and its setting angle. The centrifugal compressor stage configuration consists of a 2-D impeller with a diffuser. Analysis was conducted for VLD and four different blade shapes of LSVD namely Un-cambered constant thickness flat plate (FP), Cambered curved arc constant thickness plate (CCAP), Un-cambered aerofoil profile NACA 0010(NACA 0010) and Cambered aerofoil profile NACA 2410 (NACA 2410) at five different setting angles ranging from 16° to 32° in steps of 4° for each blade. The study is conducted at five different flow coefficients, at 0.8, 0.9, 1.0, 1.1 and 1.2 of design mass flow rate representing the design and off design cases for VLD and LSVD. CFD results are validated with experimental results for stages with VLD and LSVD for certain chosen performance parameters such as head coefficient, stage input power and exit flow angle. The computational results indicate that variations in diffuser vane geometry and its setting angle causes changes in all significant performance parameters like the total head coefficient, total-to-static stage efficiency, power coefficient of the stage and static pressure recovery coefficient of the diffuser. Contour plots were generated from CFD results and analyzed for better understanding of effect of diffuser vane shape and its setting angle on the performance of the centrifugal compressor. As a result of this study, it can be concluded that the centrifugal compressor shows improved performance characteristics for chosen blade shape of low solidity vaned diffuser than VLD.

Analysis of Flow Through a Twisted Vaned Diffuser

2014 ◽  
Author(s):  
Venkateswara Rao Pothuri ◽  
Venkata Ramana Murty Govindaraju ◽  
Venkata Rao Ganapathiraju
Keyword(s):  
Mass Flow ◽  
Centrifugal Compressor ◽  
Pressure Rise ◽  
Power Coefficient ◽  
Computational Results ◽  
Compressor Stage ◽  
Performance Parameters ◽  
Vaned Diffuser ◽  
Flow Angle ◽  
Centrifugal Compressor Stage

This paper describes the computational results on the performance of a centrifugal compressor stage with twisted vaned diffuser by varying the speed of the impeller and direction of twist for the diffuser vane. The centrifugal compressor stage configuration consists of a 2-D impeller (no twist is provided for the impeller vanes) with various configurations of diffusers. Diffuser configurations considered are Vaneless Diffuser (VLD), Low Solidity Vaned Diffuser (LSVD) and Twisted Vaned Diffuser (TVD). The analysis was carried at four different rotational speeds with corresponding mass flow rates of the impeller. 9° twist is given to the diffuser vane from hub to shroud by providing rotation at the leading edge, keeping the profile at hub as reference in the direction of rotation of the impeller and opposite to the direction of rotation of the impeller. The off-design cases considered includes operation at 80%, 90%, 110% and 120% of the design mass flow rate. CFD results are validated with experimental results for stages with VLD and LSVD for certain chosen performance parameters such as head coefficient, stage input power and exit flow angle. The computational results indicate that variations in impeller speed will cause changes in all significant performance parameters like the total pressure rise, power coefficient and efficiency of the stage and static pressure recovery coefficient of the diffuser. Contour plots were generated from CFD results and analyzed for better understanding of effect of rotational speed of the impeller on the performance of the centrifugal compressor. As a result of this study, it can be concluded that twisted vaned diffuser improves the performance in comparison to low solidity vaned diffuser for all the chosen impeller rotational speeds. The performance of the compressor stage is superior when diffuser vane twist is provided in the direction opposite to the rotation of impeller.

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

2017 ◽  
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. 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 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 stabilising mechanism of the porous throat diffuser. The non-uniform 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 non-uniformity at various locations through the compressor stage and diffuser sub-component 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.

Unsteady Flow in a Centrifugal Compressor Stage Equipped With a Vaned Diffuser and Cavities

2017 ◽  
Author(s):  
Mohand Younsi ◽  
Christophe Corneloup ◽  
François Moyroud ◽  
Antoine Baldacci
Keyword(s):  
Centrifugal Compressor ◽  
Transient Flow ◽  
Flow Behavior ◽  
Numerical Procedure ◽  
Transformation Method ◽  
Operating Conditions ◽  
Compressor Stage ◽  
Absolute Level ◽  
Impeller Blade ◽  
Centrifugal Compressor Stage

The purpose of this work is to present the Computational Fluid Dynamics (CFD) transient flow simulations of a centrifugal compressor stage with cavities. The cavities are included in the CFD model for several reasons. First the leakage flows and the windage effects are important to predict the absolute level performance of the stage (efficiency). Secondly the cavities also play an important role in the generation of the aerodynamic forcing on the impeller as well as in the prediction of the aerodynamic damping. As the compressor stage contains unequal numbers of blades and vanes, the Time Transformation method, an extension of the time inclining method is used in this work. This method which requires only a few passages per row is employed to reduce computational load and accurately model the full wheel. The numerical procedure is applied at design point firstly and then extended to the off-design operating conditions, permitting to compare and understand the transient flow behavior. The ability of the method to predict the impeller/diffuser interactions and cavity unsteady pressure response is discussed. The respective contributions of the diffuser, impeller blade passages and side cavities in terms of impeller forcing amplitude and frequency content are studied. In addition to this, comparisons between the experiment, the reduced model and the equivalent part wheel periodic solution are made to demonstrate the accuracy and computational efficiency of the considered transformation method.

High Dimensional Matching Optimization of Impeller–Vaned Diffuser Interaction for a Centrifugal Compressor Stage

2020 ◽  
Vol 142 (12) ◽  
Author(s):  
Ruihong Qin ◽  
Yaping Ju ◽  
Lee Galloway ◽  
Stephen Spence ◽  
Chuhua Zhang
Keyword(s):  
Centrifugal Compressor ◽  
High Speed ◽  
Pressure Ratio ◽  
Sequential Optimization ◽  
High Dimensional ◽  
Compressor Stage ◽  
Optimization Strategy ◽  
Impeller Blade ◽  
Vaned Diffuser ◽  
Flow Angle

Abstract The matching and interaction between the impeller and vaned diffuser is the most important aerodynamic-coupling between the components of a high-speed centrifugal compressor. Many research studies have been carried out during the last decade, both experimentally and numerically, on the flow mechanisms underlying impeller–vaned diffuser matching and interaction, with the aim of achieving a high-performance stage. However, the published work lacks any study that optimizes the matching of the impeller–vaned diffuser components in the environment of a full compressor stage due to two unresolved issues, i.e., identifying an effective matching optimization strategy and the high dimensional nature of the problem. To tackle these difficulties, four different optimization strategies (i.e., (1) integrated, (2) single component, (3) parallel, and (4) sequential optimization strategies) have been proposed and validated through a high dimensional matching optimization of the Radiver compressor test case published by the Institute of Jet Propulsion and Turbomachinery at Rheinisch-Westfälische Technische Hochschule (RWTH) Aachen University. Particular attention has been paid to the slope of the diffuser total pressure ratio characteristic near the surge point to further extend the stage surge margin. The results showed that the integrated optimization strategy was the most effective one for achieving good matching of the impeller–vaned diffuser interaction due to its inherently strong coupling optimization. Compared with the baseline compressor, the optimized stage achieved a gain of 1.2% in total-to-total isentropic efficiency at the peak efficiency point as well as a predicted 26.17% increase in stable operating range. For the stage examined in this study, a fore-loaded design of impeller blade as well as an increased vane angle for the diffuser vane was beneficial to the impeller–vaned diffuser matching. The more uniform spanwise distributions of the impeller discharge flow angle and the diffuser vane incidence presented the opportunity for a more optimized matching of the flow field between the 3D impeller and the 2D vaned diffuser. The outcomes of this work are particularly relevant for the advanced design of high-speed centrifugal compressors.

scholarly journals Operating Range Extension of an Open Impeller Centrifugal Compressor Stage Utilising 3D Diffuser End Wall Contouring

2020 ◽  
Vol 5 (1) ◽  
pp. 4
Author(s):  
Daniel Hermann ◽  
Manfred Wirsum ◽  
Douglas Robinson ◽  
Philipp Jenny
Keyword(s):  
Centrifugal Compressor ◽  
Side Wall ◽  
Stability Limit ◽  
Scale Model ◽  
Compressor Stage ◽  
Vaned Diffuser ◽  
Efficient Operation ◽  
Baseline Design ◽  
Centrifugal Compressor Stage ◽  
Operating Range

State-of-the-art centrifugal compressor units utilised in pipeline and in energy storage applications face the challenge of flexible and highly efficient operation. Geometric contouring on the hub side near a vaned diffuser affects the flow in a way which increases operational flexibility by delaying the incipience of instability and thereby increases compressor operating range. In the present paper, a hub-side wall contouring is applied within the vaneless space and the vaned diffuser of an open impeller centrifugal compressor stage. The performance characteristic of the novel hub contouring is evaluated in a scale-model test rig and compared against a baseline design. A stable operating range increase of 8% is achieved for the contoured design at Mu 2 = 1.16. 5-hole probe measurements covering a complete diffuser blade-to-blade passage are performed upstream the diffuser and compared both against CFD simulations and against the measurements of the baseline design for an operating point near the stability limit.

1D and 3D-Design Strategies for Pressure Slope Optimization of High-Flow Transonic Centrifugal Compressor Impellers

2018 ◽  
Author(s):  
A. Hildebrandt ◽  
T. Ceyrowsky
Keyword(s):  
Centrifugal Compressor ◽  
High Flow ◽  
Flow Coefficient ◽  
Design Parameters ◽  
Angle Distribution ◽  
Compressor Stage ◽  
Impeller Blade ◽  
Design Point ◽  
Centrifugal Compressor Stage ◽  
Transonic Centrifugal Compressor

The present paper deals with the numerical and theoretical investigations of the effect of geometrical dimensions and 1D-design parameters on the impeller pressure slope of a transonic centrifugal compressor stage for industrial process application. A database being generated during the multi-objective and multi-point design process of a high flow coefficient impeller, comprising 545 CFD (Computational Fluid Dynamics) designs is investigated in off-design and design conditions by means of RANS (Reynolds Averaged Navier Stokes) simulation of an impeller with vaneless diffuser. For high flow coefficients of 0.16 < phi < 0.18, the CFD-setup has been validated against measurement data regarding stage and impeller performance taken from MAN test rig experimental data for a centrifugal compressor stage of similar flow coefficient. The paper aims at answering the question how classical design parameter, such as the impeller blade angle distribution, impeller suction diameter and camber line length affect the local and total relative diffusion and pressure slope towards impeller stall operation. A second order analysis of the CFD database is performed by cross-correlating the CFD data with results from impeller two-zone 1D modelling and a rapid loading calculation process by Stanitz and Prian. The statistical covariance of first order 1D-analysis parameters such as the mixing loss of the impeller secondary flow, the slip factor, impeller flow incidence is analyzed, thereby showing strong correlation with the design and off-design point efficiency and pressure slope. Finally, guide lines are derived in order to achieve either optimized design point efficiency or maximum negative pressure slope characteristics towards impeller stall operation.

Sign in / Sign up

Export Citation Format

Share Document