Industrial Centrifugal Compressor Research Articles

Experimental and Numerical Analysis of Different Unsteady Modes in a Centrifugal Compressor With Variable Vaned Diffuser

The flow instability always varies within different compressors; however, even in one compressor, there may be still multiple various unsteady modes. To study the triggering mechanism for these unsteady modes, a detailed experimental research on an industrial centrifugal compressor with variable vaned diffuser is performed from design point to surge. The multiposition dynamic pressure measurement is conducted during the whole valve-adjusting process. The characteristics of pressure fields under some specific operating conditions are focused on, especially the prestall, stall and surge conditions. According to the collected data, the features of different unsteady modes can be obtained, such as the surge pattern and the propagation direction of stall cells. In addition, when the diffuser vane setting angle (DVA) is adjusted, the core factors to trigger total instability will change. To better complement the experimental analysis, a multipassage numerical simulation is carried out. Based on the agreement of performance curves obtained by the two methods, the flow field characteristics in the prestall state shown in the simulation results are indeed a good complement to the dynamic experimental analysis. Meanwhile, with the help of dynamic mode decomposition (DMD) method, a few low-frequency unsteady structures are extracted from the transient numerical result over a long time, which correlate with the experimental result. Through detailed analysis, an insight into the different unsteady modes in a centrifugal compressor with variable vaned diffuser is obtained.

Numerical Investigation on Labyrinth Seal Leakage Flow and Its Effects on Aerodynamic Performance for a Multistage Centrifugal Compressor

Labyrinth seals are widely used in industrial centrifugal compressors to reduce leakage. However, no work has been conducted to numerically investigate the detailed seal leakage flow and its effects in an environment of multistage centrifugal compressor. To clarify the flow mechanism of leakage flow and the interaction mechanism between leakage and mainstream flow in multistage centrifugal compressors, the flow of the last two stages from a four-stage centrifugal compressor is studied using computational fluid dynamics (CFD) model with and without considerations of labyrinth seal leakage paths, i.e., two shroud seals, one interstage seal, and one balance piston seal. The results show that the leakage flow in shroud and hub cavities can be described as a Batchelor-type flow. The Ekman number of the cavity Batchelor flow is small and corresponds to thin boundary layers while the Rossby number is at unity order implying the importance of rotating effects. The leakage flow through the shroud, interstage, and balance piston labyrinth seals is decreased by the combined effects of throttling and diffusion flow, and has distinctive flow structures associated with the type of labyrinth seal. The influence of leakage flow on the mainstream flow can be described by suction or injection mode. The suction mode is beneficial to the improvement of mainstream flow quality while the injection mode is harmful. This work is of scientific significance to enrich the knowledge of internal fluid mechanics and of potential application value to control and design the leakage flow in real configurations of multistage centrifugal compressors.

Industrial Centrifugal Compressors Design Validation, using Rapid Method Evolutionary Algorithms to Predict Map Characteristics Evaluation.

Industrial Centrifugal Compressors Design Validation, using Rapid Method Evolutionary Algorithms to Predict Map Characteristics Evaluation. - written by J. C. Statharas, N. W. Vlachakis published on 2019/01/11 download full article with reference data and citations

Large-Scale Flow Measurements and Analysis for Radial Inlets of Industrial Centrifugal Compressors Based on Multi-hole Probe System

Multi-hole probe (MHP), as a classical measuring instrument, continues to play an important role in the pressure and velocity measurements for industrial applications by virtue of its robust and reliable performance as well as the simple structure and low cost. But the flow directionality limitations and the low efficiency of traditional operations become obstacles to the large-scale measurements of MHPs. In this paper, an improved operating method is adopted for conventional MHPs to extend their measuring range of incidence angles, and a corresponding auto-measuring system has been developed to realize automatic calibration and measurement of MHPs for industrial large-scale flow measurements. Measurement uncertainties of the system have been experimentally analyzed, verifying a good accuracy: errors of 0.36° in pitch angle, 0.40° in yaw angle and 0.83% in velocity magnitude (95% CI). Furthermore, this auto-measuring system has been applied in the large-scale measurements on different radial inlets for industrial centrifugal compressors, which provide valuable flow information that was not previously available for industrial productions and assist with the improvement study. Analysis and applications in this paper prove that the developed system not only reduces the flow directionality limitations of conventional MHPs, but also significantly improves the experimental efficiency and the control-precision of the probe, achieves a good repeatability and ensures the reliability of the experimental data, which satisfies the requirements of large-scale measurements in industrial applications. Meanwhile, the portability of the system makes it more convenient and flexible to be applied in various industrial productions.

Numerical and Experimental Fluid–Structure Interaction-Study to Determine Mechanical Stresses Induced by Rotating Stall in Unshrouded Centrifugal Compressor Impellers

Unshrouded industrial centrifugal compressor impellers operate at high rotational speeds and volume flow rates. Under such conditions, the main impeller blade excitation is dominated by high frequency interaction with stationary parts, i.e., vaned diffusers or inlet guide vanes (IGVs). However, at severe part load operating conditions, sub-synchronous rotating flow phenomena (rotating stall) can occur and cause resonant blade vibration with significant dynamic (von-Mises) stress in the impeller blades. To ensure high aerodynamic performance and mechanical integrity, part load conditions must be taken into account in the aeromechanical design process via computational fluid dynamics (CFD) and finite element method (FEM) analyzes anchored by experimental verification. The experimental description and quantification of unsteady interaction between rotating stall cells and an unshrouded centrifugal compression stage in two different full scale compression units by Jenny and Bidaut (“Experimental Determination of Mechanical Stress Induced by Rotating Stall in Unshrouded Impellers of Centrifugal Compressors”, ASME J. Turbomach. 2016; 139(3):031011-031011-10) were reproduced in a scaled model test facility to enhance the understanding of the fluid–structure interaction (FSI) mechanisms and to improve design guide lines. Measurements with strain gauges and time-resolved pressure transducers on the stationary and rotating parts at different positions identified similar rotating stall patterns and induced stress levels. Rotating stall cell induced resonant blade vibration was discovered for severe off-design operating conditions and the measured induced dynamic von-Mises stress peaked at 15% of the mechanical endurance limit of the impeller material. Unsteady full annulus CFD simulations predicted the same rotating stall pressure fluctuations as the measurements. The unsteady Reynold's Averaged Navier-Stokes simulations were then used in FEM FSI analyses to predict the stress induced by rotating stall and assess the aerodynamic damping of the corresponding impeller vibration mode shape. Excellent agreement with the measurements was obtained for the stall cell pressure amplitudes at various locations. The relative difference between measured and mean predicted stress from fluid–structure interaction was 17% when resonant blade vibration occurred. The computed aerodynamic damping was 27% higher compared to the measurement.

Development of a Criterion for a Robust Identification of Diffuser Rotating Stall Onset in Industrial Centrifugal Compressors

Recent studies showed that a prompt detection of the stall inception, connected with a specific model to predict its associated aerodynamic force, could provide room for an extension of the left margin of the operating curve of high-pressure centrifugal compressors. In industrial machines working in the field, however, robust procedures to detect and identify the phenomenon are still missing, i.e., the operating curve is almost ever cut preliminarily by the manufacturer by a proper safety margin; moreover, no agreement is found in the literature about a well-defined threshold to define the onset of the stall. In particular, in some cases, the intensity of the arising subsynchronous frequency is compared to the revolution frequency, while in many other ones it is compared to the blade passage frequency. A large experience in experimental stall analyses collected by the authors revealed that in some cases unexpected spikes could make this direct comparison not reliable for a robust automatic detection. To this end, a new criterion was developed based on an integral analysis of the area subtended to the entire subsynchronous spectrum of the dynamic pressure signal of probes positioned just outside the impeller exit. A dimensionless parameter was then defined to account for the spectrum area increase in proximity to stall inception. This new parameter enabled the definition of a reference threshold to highlight the arising of stall conditions, whose validity and increased robustness was here verified based on a set of experimental analyses of different types of full-stage test cases of industrial centrifugal compressors at the test rig.

Investigation on Axial Displacement Fault Mechanism Based on Dynamic Characteristic Coefficients Identification of Tilting-Pad Thrust Bearing

To prevent the thrust bearing damage faults, the thrust bearing pad temperature and the static axial displacement variation are usually monitored and cared about, but axial vibration caused by axial dynamic excitation can also result in the severe rubbing. An electric oil pump system with overflow valve is designed on a similar industrial centrifugal compressor test-rig to apply the axial low-frequency excitation from 3 to 7 Hz, and the axial and radial vibration response amplitudes are analyzed. Then, the stiffness and damping coefficients of tilting-pad thrust bearing (TPTB) are identified by instrumental variable filter (IVF) algorithm to reveal the mechanism of TPTB dynamic characteristics affecting axial vibration. Finally, a fault case about surge and the rubbing of thrust bearing is studied. Compared with axial vibration, radial vibration does not directly correlate to axial excitation, and the axial frequency spectrum is an effective method to diagnose axial displacement faults; the static axial load, the dynamic excitation amplitude and the excitation frequency all exert influence on thrust bearing dynamic characteristics and axial vibration response. The research results can guide the design of thrust bearings and help to diagnose the axial displacement faults, while the test device and method can be used to measure the static and dynamic characteristics of thrust bearings.

Canonical variable analysis and long short-term memory for fault diagnosis and performance estimation of a centrifugal compressor

Centrifugal compressors are widely used for gas lift, re-injection and transport in the oil and gas industry. Critical compressors that compress flammable gases and operate at high speeds are prioritized on maintenance lists to minimize safety risks and operational downtime hazards. Identifying incipient faults and predicting fault evolution for centrifugal compressors could improve plant safety and efficiency and reduce maintenance and operation costs. This study proposes a dynamic process monitoring method based on canonical variable analysis (CVA) and long short-term memory (LSTM). CVA was used to perform fault detection and identification based on the abnormalities in the canonical state and the residual space. In addition, CVA combined with LSTM was used to estimate the behavior of a system after the occurrence of a fault using data captured from the early stages of deterioration. The approach was evaluated using process data obtained from an operational industrial centrifugal compressor. The results show that the proposed method can effectively detect process abnormalities and perform multi-step-ahead prediction of the system’s behavior after the appearance of a fault.

JET ENGINE INLET DISTORTION SCREEN AND DESCRIPTOR EVALUATION

Total pressure distortion is one of the three basic flow distortions (total pressure, total temperature and swirl distortion) that might appear at the inlet of a gas turbine engine (GTE) during operation. Different numerical parameters are used for assessing the total pressure distortion intensity and extent. These summary descriptors are based on the distribution of total pressure in the aerodynamic interface plane. There are two descriptors largely spread around the world, however, three or four others are still in use and can be found in current references. The staff at the University of Defence decided to compare the most common descriptors using basic flow distortion patterns in order to select the most appropriate descriptor for future department research. The most common descriptors were identified based on their prevalence in widely accessible publications. The construction and use of these descriptors are reviewed in the paper. Subsequently, they are applied to radial, angular, and combined distortion patterns of different intensities and with varied mass flow rates. The tests were performed on a specially designed test bench using an electrically driven standalone industrial centrifugal compressor, sucking air through the inlet of a TJ100 small turbojet engine. Distortion screens were placed into the inlet channel to create the desired total pressure distortions. Of the three basic distortions, only the total pressure distortion descriptors were evaluated. However, both total and static pressures were collected using a multi probe rotational measurement system.

Influences of flow loss and inlet distortions from radial inlets on the performances of centrifugal compressor stages

Radial inlets are typical upstream components of multistage centrifugal compressors. Unlike axial inlets, radial inlets generate additional flow loss and introduce flow distortions at impeller inlets. Such distortions negatively affect the aerodynamic performance of compressor stages. In this study, industrial centrifugal compressor stages with different radial inlets are investigated via numerical simulations. Two reference models were built, simulated, and compared with each original compressor stage to analyze the respective and coupling influences of flow loss and inlet distortions caused by radial inlets on the performances of the compressor stage and downstream components. Flow loss and inlet distortions are validated as the main factors through which radial inlets negatively affect compressor performance. Results indicate that flow loss inside radial inlets decreases the performance of the whole compressor stage but exerts minimal effect on downstream components. By contrast, inlet distortions induced by radial inlets negatively influence the performance of the whole compressor stage and exert significant effects on downstream components. Therefore, when optimizing radial inlets, the reduction of inlet distortions might be more effective than the reduction of flow loss. This research provides references and suggestions for the design and improvement of radial inlets.

A new method for reliable performance prediction of multi-stage industrial centrifugal compressors based on stage stacking technique: Part I – existing models evaluation

The growing acceptability of the natural gas as an energy source yields to place a higher research concentration on improving the centrifugal compressor design and performance prediction techniques. This is the first part of a two-part study that aims to introduce a new integrated method for reliable performance prediction of multi-stage industrial centrifugal compressor based on stage stacking technique. In this part, two most common existing models are adapted to be valid for industrial centrifugal compressors and the predicted characteristics are evaluated against measured data. Based on the conducted evaluation, a new model will be derived in the second part which incorporates the advantages of both approaches with more accurate prediction. Lüdtke method predicts the compressor design efficiency based on the correction of the derived experimental set of data. This approach has been applied for a single stage centrifugal compressor at a single speed and flow values. Recently, Casey–Robinson method uses a new set of algebraic equations to obtain the compressor curve with less dependency on the geometrical features. This model has been tested with a single stage turbocharger compressor where the performance curve can be derived without considering the mechanical stages. This approximation will introduce a more significant impact when this method is used for large industrial compressors. Therefore, these models will be improved to be suitable for multi-industrial centrifugal compressors and their prediction capability to estimate the performance map will be examined in this paper.

A new method for reliable performance prediction of multi-stage industrial centrifugal compressors based on stage stacking technique: Part II–New integrated model verification

This is the second part of a conducted study to develop a new integrated model for reliable performance prediction of multi-stage industrial centrifugal compressors. The conducted evaluation in part 1 revealed a high deviation between the predicted surge flows using Casey–Robinson approach and measured values especially at low rotational speeds. Besides, a significant difference between the estimated and the experimental characteristics was observed at choke and surge conditions and this deviation is growing as the Mach number increases. One of the main disadvantages of this model is the dependency on the peak and design efficiencies and associated flow coefficients at both normal and low Mach number operations which are obviously not available at early preliminary stage. In contrast, Lüdtke method fails to detect the instable flow regions and with lower degree of accuracy in the predicted efficiencies. However, the predicted design efficiency was found very close to the experimental value. Therefore, this paper introduces a new approach to estimate the performance map of multistage industrial centrifugal compressors based on stage staking principle and by incorporating the advantages of both methods. The new model has been tested at both low and high flow coefficients applications and for vaned and vaneless diffusers. Comparing with the existing models, the developed method was proven to generate more accurate estimation for performance characteristics of multistage centrifugal compressors with less dependency on the geometrical features. One of the unique advantages of the new method is the fact that it does not require a prior knowledge of the peak and design efficiencies and associated flow coefficients.

Sample of CFD optimization of a centrifugal compressor stage

Industrial centrifugal compressor stage is a complicated object for gas dynamic design when the goal is to achieve maximum efficiency. The Authors analyzed results of CFD performance modeling (NUMECA Fine Turbo calculations). Performance prediction in a whole was modest or poor in all known cases. Maximum efficiency prediction was quite satisfactory to the contrary. Flow structure in stator elements was in a good agreement with known data.The intermediate type stage “3D impeller + vaneless diffuser+ return channel” was designed with principles well proven for stages with 2D impellers. CFD calculations of vaneless diffuser candidates demonstrated flow separation in VLD with constant width. The candidate with symmetrically tampered inlet part b3 / b2 = 0,73 appeared to be the best. Flow separation takes place in the crossover with standard configuration. The alternative variant was developed and numerically tested. The obtained experience was formulated as corrected design recommendations.Several candidates of the impeller were compared by maximum efficiency of the stage. The variant with gas dynamic standard principles of blade cascade design appeared to be the best. Quasi - 3D non-viscid calculations were applied to optimize blade velocity diagrams - non-incidence inlet, control of the diffusion factor and of average blade load. “Geometric” principle of blade formation with linear change of blade angles along its length appeared to be less effective.Candidates’ with different geometry parameters were designed by 6th math model version and compared. The candidate with optimal parameters - number of blades, inlet diameter and leading edge meridian position - is 1% more effective than the stage of the initial design.

Experimental and numerical studies on the influence of inlet guide vanes of centrifugal compressor on the flow field characteristics of inlet chamber

Inlet chambers (IC) are the typical upstream component of centrifugal compressors, and inlet guide vanes in the IC have a great impact on its internal flow and aerodynamic loss, which will significantly influence the performance of the downstream compressor stages. In this paper, an experimental study was carried out on the flow characteristics inside a radial IC of an industrial centrifugal compressor, including five testing sections and 968 measuring points for two schemes with and without guide vanes. Detailed distributions of flow parameters on each section were obtained as well as the overall performance of the radial IC, and the causes of the flow loss inside the IC and the non-uniformity of flow parameters at the outlet section were investigated. Besides, numerical simulations were performed to further analyze the flow characteristics inside the radial IC. The experimental and numerical results indicate that, in the scheme without guide vanes, sudden expansions in the spiral channel and flow separations in the annular convergence channel are the major sources of flow loss and distortions generated in the radial IC; while in the scheme with guide vanes, the flow impacts, separations and wakes caused by the inappropriate design of guide vanes are the main reasons for the flow loss of the IC itself and the uneven flow distributions at the IC outlet.

Numerical Studies of Twisted Vaned Diffuser on the Performance of a Centrifugal Compressor Stage

This paper examines the effect of twist in diffuser vane from hub to shroud on the performance of an industrial centrifugal compressor stage. The chosen diffuser has an aerofoil section with varying blade chord from hub to shroud due to blade twist or in other words, the solidity of the diffuser blade is varied from hub to shroud. The twisting is given to the diffuser blade by rotating the diffuser blade opposite to the direction of rotation of the impeller keeping its leading edge as origin resulting in different stagger angles from hub to shroud. The analysis was conducted at an impeller tip Mach number of 0.35. The overall stage performance is evaluated in terms of head coefficient, stage efficiency and power coefficient of the stage and static pressure recovery coefficient of diffuser vanes for different diffuser vane twist angles with varying flow coefficients. The observed optimum twist for the best performance is 9° for the chosen impeller diffuser configuration. impeller diffusion. Therefore, it is necessary to develop methods which reduce the energy losses associated with diffusion and also increase the stable operating ranges of diffusion systems. The diffuser has to convert as much of the kinetic energy as possible into pressure energy. With radial compressors, about half of the energy imparted to the fluid in the rotor resides in the outflow velocity. Various diffuser types are employed, depending on the application and the design. A basic distinction is made between vaneless and vaned diffusers. Subsequently Low Solidity Vaned Diffusers (LSVD) have come into existence to overcome the deficiencies of vaneless and vaned diffusers.

A New Approach to Designing the S-Shaped Annular Duct for Industrial Centrifugal Compressor

The authors propose an analytical method for designing the inlet annular duct for an industrial centrifugal compressor using high-order Bezier curves. Using the design of experiments (DOE) theory, the three-level full factorial design was developed for determination of influence of the dimensionless geometric parameters on the output criteria. Numerical research was carried out for determination of pressure loss coefficients and velocity swirl angles using the software system ANSYS CFX. Optimal values of the slope for a wide range of geometric parameters, allowing minimizing losses in the duct, have been found. The study has used modern computational fluid dynamics techniques to develop a generalized technique for future development of efficient variable inlet guide vane systems. Recommendations for design of the s-shaped annular duct for industrial centrifugal compressor have been given.

Experimental investigation of the casing treatment effects on steady and transient characteristics in an industrial centrifugal compressor

In this paper, a method of holed casing treatment is put forward and applied to an industrial centrifugal compressor. A series of experimental investigations are conducted to study the effects of casing treatment on steady and transient performance of the compressor. Dynamic pressure is monitored under stable operating point and surge occurrence condition at following positions: two ends of the treated holes, 37%-chord impeller tip position and the vaneless diffuser. By use of the casing treatment, the surge margin of the compressor is increased by about 10%Qdesign with negligible decrease in efficiency. Pulsating pressure change is taken as an indicator for evaluating the flow direction in the hole. Near surge point, when the static pressure of the bleeding port is larger than the turning point, a sudden increase in pulsating pressure indicates that the bleeding flow occurs. Near choke side, when the static pressure of the turning point is larger than the bleeding port, a severe change in pulsating pressure indicates that the bypass flow occurs. Signal analysis of the dynamic pressure at surge occurrence shows that the compressor stalls with a modal inception rather than a spike wave no matter casing treatment is applied or not. The travelling speed of the stall cell found in the compressor with casing treatment is faster than that with solid casing. The occurrence of modal precursor wave is delayed with casing treatment.

Empirical Design Considerations for Industrial Centrifugal Compressors

Computational Fluid Dynamics (CFD) has been extensively used in centrifugal compressor design. CFD provides further optimisation opportunities for the compressor design rather than designing the centrifugal compressor. The experience-based design process still plays an important role for new compressor developments. The wide variety of design subjects represents a very complex design world for centrifugal compressor designers. Therefore, some basic information for centrifugal design is still very important. The impeller is the key part of the centrifugal stage. Designing a highly efficiency impeller with a wide operation range can ensure overall stage design success. This paper provides some empirical information for designing industrial centrifugal compressors with a focus on the impeller. A ported shroud compressor basic design guideline is also discussed for improving the compressor range.

The effects of radial inlet with splitters on the performance of variable inlet guide vanes in a centrifugal compressor stage

Variable inlet guide vanes (VIGVs) can regulate pressure ratio and mass flow at constant rotational speed in centrifugal compressors as a result of inducing a controlled prewhirl in front of impellers. Radial inlets and VIGVs are typical upstream components in front of the first-stage impellers in many industrial centrifugal compressors. However, previous investigations on VIGVs in centrifugal compressors were mostly conducted under the condition of axial inlets, and this study aims to focus on the effects of radial inlet on the VIGVs performance of a centrifugal compressor stage. The axial inlet stage model is compared with the radial inlet stage model with splitters using numerical flow simulation. The flow from the radial inlet was non-uniform in both circumferential and radial directions; thus, the VIGVs, the impeller, the vaneless diffuser, and the return vane channel are modelled with fully 360° passages. The three-dimensional (3D) flow field is numerically simulated at VIGVs setting angles ranging from - 20° to 60°. The overall stage performance parameters are obtained by integrating the field quantities. Though the splitters are equipped in the radial inlet, the overall stage polytropic efficiency decreases by an average of 4 per cent and total pressure ratio decreases by an average of 3.3per cent in comparison with the axial stage model. This can be attributed to the effect of both flow non-uniformity induced by radial inlet and flow loss in the radial inlet at different VIGV setting angles. The flow loss in the radial inlet with splitters is the main reason of the stage performance decrease compared with the flow non-uniformity. The simulation results show that the performance of VIGVs is degraded by its inlet flow distortions resulting from a radial inlet. The results in this study can be applied to centrifugal compressor design and optimization.

Rotordynamic Force Prediction of Centrifugal Compressor Impellers Using Computational Fluid Dynamics

The energy industry depends on centrifugal compressors to produce, process, reinject, and transport many different gases. Centrifugal compressors use one or more impellers to impart momentum to the flowing gas and, thereby, produce an increase in pressure through diffusion. As the operating pressure in a compressor increases, the fluid-rotor interaction at the seals and impellers become more important. Also, the new generation of megascale liquefied natural gas compressors is dependent on accurate assessment of these forces. The aerodynamic forces and cross-coupled stiffness from the impellers cannot be accurately predicted with traditional methods and must be estimated with semiempirical formulations. The result of these inaccuracies is a potential for compressor designs that can experience unexpected, dangerous, and damaging instabilities and subsynchronous vibrations. The current investigation is intended to advance the state of the art to achieve an improved, physics-based method of predicted aerodynamic destabilizing cross-coupling forces on centrifugal compressor impellers using computational fluid dynamics (CFD). CFD was employed in this study to predict the impeller-fluid interaction forces, which gives rise to the aerodynamic cross coupling. The procedure utilized in this study was developed by Moore and Palazzolo (2002, “Rotordynamic Force Prediction of Centrifugal Impeller Shroud Passages Using Computational Fluid Dynamic Techniques With Combined Primary Secondary Flow Model,” ASME J. Eng. Gas Turbines Power, 123, pp. 910–918), which applied the method to liquid pump impellers. Their results showed good correlation to test data. Unfortunately, no such data exist for centrifugal compressors. Therefore, in order to validate the present model, comparisons will be made to predict the instability of an industrial centrifugal compressor. A parametric CFD study is then presented leading to a new analytical expression for predicting the cross-coupled stiffness for centrifugal impellers.