Assessment of Steady and Unsteady Model Predictions for a Subsonic Centrifugal Compressor Stage

2012 ◽  
Author(s):  
Y. Bousquet ◽  
X. Carbonneau ◽  
I. Trebinjac
Keyword(s):  
Centrifugal Compressor ◽  
Industrial Development ◽  
Pressure Ratio ◽  
Stability Limit ◽  
Compressor Stage ◽  
Common Procedure ◽  
Centrifugal Compressor Stage ◽  
Steady Simulation ◽  
The Stability ◽  
High Level

The most common procedure to obtain the performance of a centrifugal compressor in an industrial development process is based on the use of a steady RANS model with the mixing-plane approach. However some phenomena such as the flow interaction between the impeller and the diffuser can be the source of unsteady effects which can affect the steady model prediction. This paper investigates the ability of a steady simulation to predict the overall performance and the flow structures in a subsonic centrifugal compressor stage by comparison with time-dependent results. Simulations are performed considering three operating points: peak efficiency, close to the stability limit and close to the blockage. The results show that the steady model is accurate enough to predict the stage static-to-total pressure ratio. However, in location where high level of fluctuation is expected, the steady model shows some weakness to predict the time-averaged quantities of the flow structure.

scholarly journals Comparative Study on Steady and Unsteady Flow in a Centrifugal Compressor Stage

2019 ◽  
Vol 2019 ◽  
pp. 1-12
Author(s):  
Changhee Kim ◽  
Changmin Son
Keyword(s):  
Unsteady Flow ◽  
Centrifugal Compressor ◽  
Industrial Development ◽  
Navier Stokes ◽  
Compressor Stage ◽  
Common Procedure ◽  
Vaned Diffuser ◽  
Centrifugal Compressor Stage ◽  
Rans Simulation ◽  
And Performance

Steady Reynolds-averaged Navier-Stokes (RANS) simulation with the mixing-plane approach is the most common procedure to obtain the performance of a centrifugal compressor in an industrial development process. However, the accurate prediction of complicated flow fields in centrifugal compressors is the most significant challenge. Some phenomena such as the impeller-diffuser flow interaction generates the unsteadiness which can affect the steady assumption. The goal of this study is to investigate the differences between the RANS and URANS simulation results in a centrifugal compressor stage. Simulations are performed at three operating points: near surge (NS), design point (DP), and near choke (NC). The results show that the RANS simulation can predict the overall performance with reasonable accuracy. However, the differences between the RANS and URANS simulation are quite significant especially in the region that the flows are highly unsteady or nearly separated. The RANS simulation is still not very accurate to predict the time-dependent quantities of the flow structure. It shows that the URANS calculations are necessary to predict the detailed flow structures and performance. The phenomena and mechanisms of the complex and highly unsteady flow in the centrifugal compressor with a vaned diffuser are presented and analyzed in detail.

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.

Improving the Accuracy of Tests for Centrifugal Compressor Stage Performance Prediction

2006 ◽  
Author(s):  
Daniele Fiaschi ◽  
Giampaolo Manfrida ◽  
Libero Tapinassi
Keyword(s):  
Special Reference ◽  
Centrifugal Compressor ◽  
Pressure Ratio ◽  
Transfer Model ◽  
Compressor Stage ◽  
Stage Design ◽  
Centrifugal Compressor Stage ◽  
Expected Performance ◽  
Total Temperature ◽  
Gas Market

A design of experiment approach was used to solve problems on the new centrifugal compressor stage development test beds at the Nuovo Pignone – GE Oil&Gas premises in Florence, Italy. The company is able to provide centrifugal compressor equipment tailored to the user’s requests, with special reference to the oil & gas market. In order to provide this service, an archive of designs is available which can be adapted to different requirements: CFD is widely used to improve the turbomachinery performance, and on each new stage design extensive fluid dynamics test campaigns are routinely run, in order to confirm the expected performance. Recently inadequacy of the accuracy of the measurements became evident: the cause was traced back to thermal effects which introduced a large uncertainty in the test results, with special reference to machines having large operating Mach number, and low pressure ratio. The present work included: a) The development of a heat transfer model capable of predicting the observed trend of the experimental data. b) The improvement of the accuracy of total temperature measurements, needed to confirm the results of the model. The positive results allow the company to guarantee with increased confidence the expected performance levels.

Study on Aerodynamic Redesign of a High Pressure Ratio Centrifugal Compressor

2010 ◽  
Author(s):  
Chaolei Zhang ◽  
Qinghua Deng ◽  
Zhenping Feng
Keyword(s):  
Centrifugal Compressor ◽  
Cfd Simulation ◽  
Pressure Ratio ◽  
Aerodynamic Performance ◽  
Compressor Stage ◽  
Operation Condition ◽  
Vaned Diffuser ◽  
Centrifugal Compressor Stage ◽  
Optimum Configuration ◽  
Operation Conditions

This paper describes the aerodynamic redesign and optimization of a typical single stage centrifugal compressor, in which the total pressure ratio was improved from the original 4.0 to final 5.0 with the restrictions of keeping the impeller tip diameter, the design rotational speed and the design mass flow rate unchanged. Firstly the backsweep angle and the outlet blade height of the impeller were adjusted and the vaned diffuser was redesigned. Then a sensitivity analysis of the aerodynamic performance correlated to the primary redesign centrifugal compressor stage with respect to the chosen redesign variables was conducted, according to the parameterized results of the impeller and the vaned diffuser. Secondly the impeller and the vaned diffuser were optimized respectively under the stage environment at the design operation condition to improve the stage isentropic efficiency by using a global optimization method which coupled Evolutionary Algorithm (EA) and Artificial Neural Network (ANN), provided by the commercial software NUMECA DESIGN-3D. Subsequently the detailed performance maps of the centrifugal compressor stage corresponding to the primary redesign configuration and the optimum configuration were presented by Computational Fluid Dynamics (CFD) simulation. Finally the flow fields correlated to the centrifugal compressor configurations before and after optimization at the design operation condition were also compared and analyzed in detail. As a result the design target was achieved after the primary redesign, as a 2.7% gain in stage efficiency and a 3.6% increase in stage pressure ratio were obtained when compared with the primary redesign configuration after optimization. Moreover, the aerodynamic performance of the optimum configuration at the off-design operation conditions was also improved.

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.

Effect of Unsteadiness on the Performance of a Transonic Centrifugal Compressor Stage

2009 ◽  
Vol 131 (4) ◽  
Author(s):  
Isabelle Trébinjac ◽  
Pascale Kulisa ◽  
Nicolas Bulot ◽  
Nicolas Rochuon
Keyword(s):  
Shock Wave ◽  
Mass Flow ◽  
Centrifugal Compressor ◽  
Pressure Ratio ◽  
Wake Flow ◽  
Experimental Investigations ◽  
Compressor Stage ◽  
Vaned Diffuser ◽  
Centrifugal Compressor Stage ◽  
Transonic Centrifugal Compressor

Numerical and experimental investigations were conducted in a transonic centrifugal compressor stage composed of a backswept splittered unshrouded impeller and a vaned diffuser. The characteristic curves of the compressor stage resulting from the unsteady simulations and the experiments show a good agreement over the whole operating range. On the contrary, the total pressure ratio resulting from the steady simulations is clearly overestimated. A detailed analysis of the flow field at design operating point led to identify the physical mechanisms involved in the blade row interaction that underlie the observed shift in performance. Attention was focused on the deformation in shape of the vane bow shock wave due its interaction with the jet and wake flow structure emerging from the impeller. An analytical model is proposed to quantify the time-averaged effects of the associated entropy increase. The model is based on the calculation of the losses across a shock wave at various inlet Mach numbers corresponding to the moving of the jet and wake flow in front of the shock wave. The model was applied to the compressor stage performance calculated with the steady simulations. The resulting curve of the overall pressure ratio as a function of the mass flow is clearly shifted toward the unsteady results. The model, in particular, enhances the prediction of the choked mass flow.

Investigation of Unsteady Impeller-Diffuser Interaction in a Transonic Centrifugal Compressor Stage

2010 ◽  
Author(s):  
Yangwei Liu ◽  
Baojie Liu ◽  
Lipeng Lu
Keyword(s):  
Centrifugal Compressor ◽  
Flow Direction ◽  
Equation System ◽  
Compressor Stage ◽  
Spatial Correlations ◽  
Tip Leakage Flow ◽  
Vaned Diffuser ◽  
Centrifugal Compressor Stage ◽  
Transonic Centrifugal Compressor ◽  
Steady Simulation

In this paper, unsteady impeller-diffuser interaction in a transonic centrifugal compressor stage, which is composed of an impeller with splitter blade and a vaned diffuser, was studied numerically. The unsteady interaction has a significant impact on the time-averaged flow, which are presented by the so-called deterministic correlations in the average-passage equation system (APES) proposed by Adamczyk. Both steady and unsteady simulations were carried out at the design and off-design conditions. Results from the steady and unsteady simulations were compared to highlight the importance of the unsteady interactions and to help assess the shortcomings of simple mixing-plane methods. The comparisons indicate that the unsteady interactions should be considered in the simulations since the differences between the time averaged unsteady results and steady simulation results are significant especially at off-design conditions. Then the interactions between impeller and diffuser were studied in detail to advance the understanding of the flow physics involved. The results show that the impeller/diffuser interaction can affect a range of 30% impeller chord from impeller trailing edge on impeller performance, while whole chord length on diffuser performance. The potential effects of the diffuser cause an unsteady pressure disturbance at the impeller exit, leading to the unsteadiness of impeller load, tip leakage flow and losses. While the unsteadiness of impeller exit flow cause period varieties of inlet flow conditions for the diffuser and have large impacts on diffuser performance. Based on the unsteady results, deterministic correlations in the APES framework were computed and analyzed in order to reveal some shortcomings of present deterministic correlations models and to make some contributions to the modeling development. The distribution characteristics of deterministic correlations were studied. The study indicates that the deterministic correlations in the impeller and diffuser have the similar magnitudes, and that the correlations in the passages have large gradients in circumferential direction and decrease rapidly in flow direction especially in the vaneless space. The deterministic correlations at the impeller/diffuser interface were compared with their spatial correlations using the framework of the deterministic decomposition. The comparisons show that the spatial correlations have some discrepancies with the total deterministic correlations at the impeller/diffuser interface.

Experimental and Numerical Investigation of Vaned Hub and Shroud Wall Contoured Diffusers Designed to Improve Flexibility and Efficiency of an Open Impeller Centrifugal Compressor Stage

2021 ◽  
Author(s):  
Daniel Hermann ◽  
Manfred Wirsum ◽  
Douglas Robinson ◽  
Philipp Jenny
Keyword(s):  
Centrifugal Compressor ◽  
State Of The Art ◽  
Pressure Ratio ◽  
Design Stage ◽  
Total Efficiency ◽  
Compressor Stage ◽  
Local Flow ◽  
Efficient Operation ◽  
Centrifugal Compressor Stage ◽  
Operating Range

Abstract State-of-the-art centrifugal compressor stages are required to provide both a flexible and a highly efficient operation. To extend the stable operating range and to improve the design-point polytropic total-to-total efficiency of an open impeller centrifugal compressor stage, three vaned contoured diffusers characterized by geometric modifications of the hub and shroud wall in the vaneless space upstream the diffuser vanes and within the diffuser passages were designed. In this paper, a shroud wall, a hub wall and a hub and shroud wall contoured diffuser and a state-of-the-art baseline diffuser are experimentally examined. For the hub-contoured diffuser an operating range extension of 5.3% was measured at design stage Mach number. For the shroud-contoured diffuser an improvement of polytropic total-to-total efficiency by up to 0.3% is observed. The experimental data including normalized total-to-static pressure ratio and 5-hole-probe data is utilized to validate the numerical setup. By means of the CFD simulations the hub- and the shroud-contoured diffuser designs are analyzed and the hub-contoured diffuser’s effect on the local flow at diffuser vane leading edge is investigated. The results illustrate the local effect of the hub-contoured diffuser design on the flow field in the examined centrifugal compressor stage.

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