Centrifugal Compressor Stage Research Articles

Комбинированный метод расчета среднерасходной центробежной компрессорной ступени

The paper focuses on the optimal centrifugal compressor stage design and introduces a new approach to it that implies replacing a physical experiment with a numerical one. The efficiency of this approach is due to numerical testing of a large number of different variants of the compressor stage geometry for the same gas-dynamic parameters. Within the approach, for calculating and optimizing the compressor stage parameters, we developed a combined method not having the most empirical components. Relying on this method, we propose methods for calculating the parameters and optimizing the geometry of the compressor stage.

Algorithm and the examples of multiparametric automated computational optimization for turboexpander compressor stage 3D impellers

The study presents an algorithm and results of the multiparametric optimization for high-flow centrifugal compressor stages. We present the use of a CAD parameterized model of the compressor stage in the automated computational optimization procedure by the AMO – Adaptive Multiple-Objective method in the Ansys complex. To predict the compressor stage efficiency in the design mode, a viscous three-dimensional CFD calculation is used. As an objective function of the optimization problem, the stage total to total polytropic efficiency and the total to total polytropic head coefficient constraint are selected. The algorithm was used for the centrifugal compressor stages improvement. As a result, the efficiency was increased by 1.5-2.5%, and the stages energy–efficient operation zone was expanded by 30% - 60%. The results of the study showed that computational optimization can be successfully applied for the projected centrifugal compressor flow part fine-tuning to obtain the highest efficiency.

Verification and Validation of CFD Modeling for Low-Flow-Coefficient Centrifugal Compressor Stages

In this paper, the numerical model of a centrifugal compressor low-flow stage is verified. The gaps and labyrinth seals were simulated in the numerical model. The task was to determine the optimal settings for high-quality modeling of the low-flow stages. The intergrid interface application issues, turbulence and roughness models are considered. The obtained numerical model settings are used to validate seven model stages for the range of the optimal conditional flow coefficient with Φopt = 0.008–0.018 and the conditional Mach number Mu = 0.785–0.804. The simulation results are compared with the experimental data. The high pressure stage-7 (HPS-7) stage with Φopt = 0.010 and Mu = 0.60 at different inlet pressure of 4, 10 and 40 atm is considered separately. Acceptable validation results are obtained with the recommended numerical model settings; the modeling uncertainty for the polytropic pressure coefficient δη*pol < 4% for the efficiency coefficient δη*pol exceeds the limit of 4% only in the two most low-flow stages, U and V.

Numerical Analysis of Flow Characteristics of the Low-Speed Centrifugal Compressor Stage Comprising Wedge Diffuser

Wedge type diffusers are used generally in the highly loaded stages of smaller jet engines as it is compact in size. Low speed centrifugal compressor (LSCC) is selected for this present study as experimental details are available. A centrifugal compressor stage comprising wedge type diffuser is used in this numerical investigation in which studies are carried out at design mass flow rate (30kg/s) and off-design mass flow rates (23.64kg/s and 36.36kg/s) at constant rotational speed of 1920 rpm. Single passage approach is chosen to model the computational domain which is meshed with unstructured grid. Turbulence model chosen is kω-SST. The investigation revealed the jet-wake structure along the pressure side and suction side of the impeller and its subsequently mixing at impeller exit vaneless diffuser region. Diffusion process in the LSCC is observed to be effective as the outlet values of absolute velocity are lesser compared to its inlet values. Highest static pressure rise is observed for design mass flow rate and followed by below and above off-design mass flow rates.

CFD investigation of flow through a centrifugal compressor diffuser with splitter blades

The aerodynamic losses in centrifugal compressors are mainly associated with the separated flow on the suction sides of impeller and diffuser vanes. The overall performance of such compressors can be improved by adding splitter vanes. The present work examines the effect of varying the geometrical location of the splitter vanes in the diffuser on the overall performance of a high-speed centrifugal compressor stage of a small gas turbine. To increase the pressure recovery through the diffuser, two radial sets of vanes are used. The first set of vanes (diffuser-1) is equipped with splitter vanes, placed mid-distance between the main vanes, while the vanes of the second set (diffuser-2) are conventional vanes. Flow through the compressor was simulated using the ANSYS 19 workbench program. Flow characteristics and compressor performance were obtained and analyzed for different circumferential positions of the splitting vanes relative to the main vanes of diffuser-1. The study covered seven positions of the splitter vanes including the original design of the diffuser where the splitter vanes were located at mid-distance between the main vanes. The analysis shows that, at design conditions, selecting the position of the splitter vanes to be nearer to the pressure side of the main vanes improves the stage performance. In the present study, locating the splitters at 33% of the angular distance between the main vanes leads to the best performance, and a significant improvement in the overall stage performance is recorded. The pressure recovery coefficient is raised by about 17%, the pressure ratio is increased by about 1.13%, and the stage efficiency is increased by about 2.01%, compared to the original splitter position. Performance improvement is related to the suppression of the flow separation and the more uniformity of flow. On the contrary, further moving the splitter closer to the main blade, the pressure recovery coefficient is decreased by about 2% than the position of 33% of the angular distance, but still higher than the original position by about 15% and a limited improvement in the compressor performance is noticed. Moving the splitter far out the main blade annihilates the static pressure recovery of the diffuser by about 2:7% compared with the original position. So, for the investigated compressor, the best position of the splitter blade in the circumferential direction, which provides the best stage performance in our parametric analysis, is not necessary to be at the mid-angular distance between the diffuser’s main blades, but it is achieved by moving the splitter to about 33% of the angular distance where the diminished loss from the suppressed flow separation is more prevailing and the instigated friction losses from splitter surfaces are less critical.

Numerical Investigation of Transient Flow Characteristics in a Centrifugal Compressor Stage with Variable Inlet Guide Vanes at Low Mass Flow Rates

This study numerically investigates the beneficial effects of positive pre-swirl on the aerodynamic performance and internal flow field in a centrifugal compressor stage with variable inlet guide vanes (VIGVs) at low mass flow rates. Four positions of VIGV are considered, including 0°, 30°, 45°, and 60° angle. The latter three positions of VIGV induce positive pre-swirl. Numerical results show that as positive pre-swirl increases, the aerodynamic performance curve of the stage moves in the low mass flow rate direction. In the three cases of positive pre-swirl, there was an improvement of approximately 9.95% of stall/surge margin greater than in conditions with no pre-swirl. The regulation of IGV can effectively improve the unstable flow of the compressor stage at low mass flow rates. A low frequency that has a great influence on the internal flow of the compressor stage is found, and the unstable flow caused by low frequency is analyzed by the combination of streamline distribution, spectrum analysis, vector, entropy increase, and modal decomposition method. Meanwhile, the modal decomposition method and flow field reconstruction techniques are used to investigate the coherent flow structures caused by low frequency under different guide vane openings.

Aerodynamic design and multi-dimensional performance optimization of supercritical CO2 centrifugal compressor

This paper dedicates to develop a systematic approach of design and multi-dimensional performance optimization of the Supercritical carbon dioxide (SCO2) compressor. A 5 MW SCO2 simple regenerative cycle used in small scale lead-cooled fast reactor (SLFR) was firstly proposed and simulated to define the operation condition of SCO2 compressor. Under the inlet and outlet condition of 305.15 K/7.56 MPa and 22 MPa, isentropic efficiency and mass flow rate of 80% and 69.88 kg·s−1 respectively was obtained. Secondly, a single stage centrifugal compressor was applied as the SCO2 compressor and one-dimensional (1D) design based on self-developed code was conducted to determine the basic geometry of the compressor, the code was verified with experiments and shows satisfactory accuracy. Additionally, CFD analysis was carried out to validate the results of 1D design and also shows good agreement. Then, three one-dimensional optimizations, two single objective optimizations using Particle Swarm Optimization (PSO) and one multi-objective optimization using Genetic Algorithm (GA), on aerodynamic efficiency of the SCO2 centrifugal compressor were performed based on 1D design code, five crucial parameters with ± 5% variation range were optimized. The 1D optimization results show that the isentropic efficiency received an improvement of about 5 percentage points compared to that of 1D design. Lastly, three-dimensional optimization concentrated on the blade profile of impeller were conducted on a fully automatic optimization platform to further improve the isentropic efficiency of SCO2 centrifugal compressor. Wrap angle and the leading and trailing edge of the main blade were optimized. Two optimal impellers with wrap angle in the range of + 5% and −5% were obtained respectively, the former impeller got the highest pressure ratio, while the latter one gained a higher isentropic efficiency but the lowest pressure ratio over the whole operation range.

Aerodynamic Functional Diagnostics Based on Angular Momentum Transport Lines

AbstractIn analogy with the classical concept of mass-flux-based streamlines, we define angular momentum transport (AMT) lines as an aerodynamic functional diagnostic tool. The AMT lines are the ones whose tangents are given by the average angular momentum flux. The mathematical and physical properties of these AMT lines are exploited to study the generation, removal, and transport of angular momentum in turbomachinery components. We illustrate the concept by visualizing AMT lines in two relatively simple flows, namely, vaneless incompressible diffuser and von Karman flow (a model of centrifugal compressors). Next, we apply the proposed diagnostic tool to flow in a return channel. A return channel is a part of a multistage centrifugal compressor stage. Its principal function is to remove angular momentum. In this work, we apply the diagnostic tool of AMT lines to a Reynolds-averaged Navier Stokes (RANS) simulation and a wall-modeled large eddy simulation (LES) of flow in the return channel. We show that AMT lines give us insights into the AMT process that are otherwise not available with conventional visualization tools.

Effects of geometric and operational uncertainties on aerodynamic performance of centrifugal compressor stage

No real centrifugal compressor can exactly conform to its design geometry and expected operating conditions due to the uncertainties existing in the manufacturing and operational processes. Such uncertainties have been increasingly recognised to be detrimental to compressor performance. However, quite few studies have focused on the combined effects of geometric and operational uncertainties on compressor performance, and the underlying flow mechanism even remains unclear. In this context, we here present an uncertainty analysis of a centrifugal compressor stage, with both geometric and operational uncertainties taken into account. With the combination of CFD simulation and nonintrusive sparse grid based stochastic collocation methods, the combined and individual effects of total inlet temperature, total inlet pressure, outlet mass flow, impeller tip clearance and hub fillet radius on the stage/impeller performance are quantified and analysed. Particular attention is paid to elucidating the compressor performance variations through flow field and energy decomposition analyses. Results show that the considered uncertainties exert more influence on the compressor stage performance rather than on the impeller performance. Amongst the examined uncertainties, the impeller tip clearance contributes the most to the stage performance. The underlying mechanism lies in that the wake of impeller tip clearance produces distorted flow downstream towards the diffuser, which causes complicated vortex structures and less conversion of kinetic energy to pressure rise in the diffuser passage. The present study lays a theoretical foundation for the further uncertainty quantification and robust design of centrifugal compressors against various sources of uncertainties.

Theory and practice of neural networks application to building mathematical model of centrifugal compressor vane diffusers

Optimal design of centrifugal compressor stages needs special computational and experimental methods, both of them could be costly enough. So new advanced design methods which can provide optimal solution faster are needed. Authors developed the set of mathematical models – Universal modeling method - for describing compressor stages characteristics. Its models are being widened and improved. One the most advanced approaches of model building is based on machine learning. A neural network based method for predicting centrifugal compressor vane diffuser characteristics was developed. Input data for network training was obtained from CFD simulations. The resulting model for diffuser loss coefficient shows good approximation quality and can be used for improvement of VD model in Universal modeling method.

Numerical Study of the Improvement in Stability and Performance by Use of a Partial Vaned Diffuser for a Centrifugal Compressor Stage

The influence of different diffuser configurations on the flow stability and aerodynamic performance of a centrifugal compressor stage with a mass flow coefficient of 0.196 is numerically investigated. Research results show that the performance of a traditional full-height vaned diffuser (TVD) deteriorates rapidly, and a shroud-side partial vaned diffuser (SVD) displays better adaptability in off-design conditions. SVD can suppress the development of vortices generating at the diffuser leading-edge. Therefore, it can reduce the flow loss inside the stage and improve the flow stability of the stage at low mass flow rates. The unsteady analysis for TVD and SVD shows that the stall cell propagates at about 35.7% of impeller rotational speed in the semi-vaneless space and diffuser passages. Furthermore, the internal flow in TVD and SVD is studied by employing the proper orthogonal decomposition (POD) and dynamic mode decomposition (DMD) methods. The flow loss and instability mechanism in the stage are consequently revealed more comprehensively.

Metamodel-Driven Data Mining Model to Support Three-Dimensional Design of Centrifugal Compressor Stage

AbstractThe advanced design of a centrifugal compressor with high efficiency and wide operating range is a challenging task due to the complex flow field arising from the three-dimensional geometry, especially for the high-speed, highly loaded centrifugal compressor stage, which typically has a relatively narrow operating range. A great effort has been undertaken recently to solve the time-costly three-dimensional design problem with the assistance of a metamodel. Some effort has been done to gain insight into the design space with the assistance of the data mining method. However, the published works lack any study that systematically performs the data mining between the performance and three-dimensional geometry data due to two unsolved issues, i.e., lack of reliable systematic data mining model and unresolved high-dimensional data problem in the centrifugal compressor community. To tackle these issues, a systematic metamodel-driven data mining (MDDM) model including six general modules (i.e., problem understanding, data understating, metamodeling, data set preparation, knowledge discovery, and deployment) has been proposed and implemented to the knowledge discovery of the well-known Radiver high-speed centrifugal compressor stage. Particular attention has been paid to develop the design principle of operating range extension for the examined high-speed stage. Four specific data mining techniques, i.e., descriptive statistics, self-organization map, k–d tree, and Sobol index, were used for the statistical, correlation, cluster, and sensitivity analysis. The results showed the performance improvement probabilities, the trade-off relationships between efficiency and pressure ratio/operating range, and the characteristic variation of the performance. Specifically, the wide operating range design subspace and the narrow operating range design subspace were split away from the whole design space. In these subspaces, the two most sensitive geometry parameters that controlled the meridional curvature made a large contribution to the stage performance, especially for the meridional curvature at the shroud side near the impeller outlet. The appropriate variation ranges of the two sensitive geometry parameters were recommended, and the flow mechanism behind them was clarified. The statistical results showed that over 90% of the design stages in the recommended variation ranges had a wide operating range. A design case was chosen randomly in the recommended range to verify the performance improvement via computational fluid dynamics (CFD) simulations. The outcomes of this work are particularly relevant for the advanced design of compressors with high efficiency and a wide operating range for flexibility.

Experimental and Numerical Study of an Open Impeller Centrifugal Compressor Stage Utilizing Three-Dimensional (3D) Diffuser End Wall Contouring for Operating Range Extension

Abstract Highly efficient and concurrent flexible operation are heavy demands on today's centrifugal compressor units. Diffuser end wall contouring is a measure to delay the incipience of instability and therefore to extend the compressor's operating range while maintaining efficient performance. In the presented paper, a hub-side wall contouring, applied in the vaneless space upstream the diffuser vane's leading edge and within the diffuser passage of a state-of-the-art centrifugal compressor stage with an open impeller, is examined. Computational fluid dynamics computations are performed for both a baseline diffuser design with parallel channel walls and the hub-side wall contoured diffuser design. Comparisons of characteristic and diffuser stability decisive flow variables are made in perpendicular sections along an extrapolated camber line of the diffuser vane for full span, near shroud and near hub wall. In operating points near the stability limit at two different stage Mach numbers, the stabilizing effect of the hub-side wall contouring on the diffuser flow is clearly shown. In a scale-model test rig, experimental data including pneumatic five-hole probe data for a full diffuser blade-to-blade passage, static wall pressures at various planes as well as total temperatures were measured. The experimental data are utilized for the validation of the presented numerical calculations. The flow stabilizing effect of the hub-wall contouring is clearly visible in the measurements, which showed 8% range extension at highest stage Mach number Mu2 = 1.16 and a range extension of 2% at design stage Mach number Mu2 = 1.

CFD researches of centrifugal compressor stage vane diffusers in interests of math modeling

CFD researches of centrifugal compressor stage vane diffusers in interests of math modeling

Математическая модель безлопаточного диффузора центробежного компрессора на основе CFD-расчетов

The centrifugal compressor design involves the use of approximate engineering techniques based on mathematical modeling. One of such techniques is the universal modeling method, which proves to be practically applicable. Having generalized a series of CFD calculations, we used a mathematical model in the latest version of the compressor model to calculate flow parameters in vaneless diffusers. The diffuser model was identified based on the results of experimental studies of average-flow model stages carried out at SPbPU. The model is also used to calculate Clark low-flow centrifugal compressor stages with narrow diffusers with a relative width in the range of 0.5--2.0 %. For these stages, the developed mathematical model showed insufficient efficiency, since the dimensions of the diffusers go beyond the limits of its applicability. To solve this problem, we calculated a series of vaneless diffusers with a relative width in the range of 0.6--1.2 % in the ANSYS CFX software package. Relying on the results of CFD calculations, we plotted the gas dynamic characteristics of the loss coefficients and changes in the flow angle depending on the flow angle at the inlet to the vaneless diffuser. To process the calculated data, the method of regression analysis was applied, with the help of which a system of algebraic equations was developed that connects geometric, gas-dynamic parameters and similarity criteria. The obtained equations are included in a new mathematical model of the universal modeling method for calculating the flow parameters of vaneless diffusers. Comparison of the calculated gas-dynamic characteristics according to the new model with experimental data showed the average error of modeling the calculated (maximum) efficiency equal to 1.08 %

Effects of Inlet Guide Vanes on the Performance and Stability of an Aeronautical Centrifugal Compressor

Abstract A research centrifugal compressor stage designed and built by Safran Helicopter Engines is tested at three inlet guide vanes (IGV) stagger angles. The compressor stage includes four blade rows: axial inlet guide vanes, a backswept splittered impeller, a splittered vaned radial diffuser (RD), and axial outlet guide vanes (OGVs). The methodology for calculating the performance is detailed, including the consideration of humidity in order to minimize errors related in particular to operating atmospheric conditions. The shift of the surge line toward lower mass flow rate as the IGV stagger angle increases highly depends on the rotation speed. The surge line shift is very small at low rotation speeds, whereas it significantly increases at high rotation speeds. A first-order stability analysis of the impeller and diffuser sub-components shows that the diffuser (resp. impeller) is the first unstable component at low (resp. high) rotation speeds. This situation is unaltered by increasing the IGV stagger angle. At low rotation speeds below a given mass flow rate, rotating instabilities (RI) at the impeller inlet are detected at zero IGV stagger angle. Their occurrence is conditioned by the relative flow angle at the tip of the leading edge of the impeller. As the IGV stagger angle increases, the mass flow decreases to maintain a given inlet flow angle. Therefore, the onset of the rotating instabilities is delayed toward lower mass flow rates. At high rotation speeds, the absolute flow angle at the diffuser inlet near surge decreases as the IGV stagger angle increases. As a result, the flow is highly alternate over two adjacent channels of the radial diffuser beyond the surge line at IGV stagger angle of 0 deg.

The Impact of Various Modeling Decisions on Flow Field Predictions in a Centrifugal Compressor

Abstract Computational tools have become increasingly important in design and research applications in recent years due to increasing computational resources. In most cases, model geometry and flow physics are simplified to reduce the complexity of the computational model. While this was necessary historically, modern computational tools are capable of including realistic features such as fillets, surface roughness, and heat transfer. This work presents extensive and systematic numerical results from a simulation of a centrifugal compressor stage for an aero-engine application. Numerical results are compared to detailed experimental data to investigate the effect of various modeling decisions, including turbulence models, on the predicted aerodynamics developing through the diffuser passage. Roughness and the inclusion of fillets significantly impact the flow development, especially with the shear-stress transport (SST) turbulence model. This approach leads to the conclusion that the BSL-EARSM model is best able to predict the experimentally determined diffuser flow profiles and overall performance trends with the inclusion of the previously mentioned model features. Additionally, misleading conclusions can be reached if modeling decisions are based on merely matching overall performance values. Finally, frozen rotor simulations are used to roughly approximate the impact of unsteadiness on the flow field. The results show a significant impact and also that the inclusion of approximate unsteady effects tends to further improve the predictive capability of the computational models that were considered.

Повышение качества проектирования малорасходных ступеней центробежных компрессоров путем создания базы данных виртуальных рабочих колес по результатам CFD-моделирования

Повышение качества проектирования малорасходных ступеней центробежных компрессоров путем создания базы данных виртуальных рабочих колес по результатам CFD-моделирования

Flow Control of Radial Inlet Chamber and Downstream Effects on a Centrifugal Compressor Stage

Radial inlet chambers are widely used in various multistage centrifugal compressors, although they induce extra flow loss and inlet distortions. In this paper, the detailed flow characteristics inside the radial inlet chamber of an industrial centrifugal compressor have been numerically investigated for flow control and performance improvement. First, the numerical results are validated against the experimental data, and flow conditions inside the inlet chambers with different structures are compared. They indicate that, in the non-guide vane scheme, sudden expansions, tangential flows and flow separations in the spiral and annular convergent channels are the major causes of flow loss and distortions, while using guide vanes could introduce additional flow impacts, separations and wakes. Based on the flow analysis, structure improvements have been carried out on the radial inlet chamber, and an average increase of 4.97% has been achieved in the inlet chamber efficiencies over different operating conditions. However, the results further reveal that the increases in the performance and overall flow uniformity just in the radial inlet chamber do not necessarily mean a performance improvement in the downstream components, and the distribution of the positive tangential velocity at the impeller inlet might be a more essential factor for the efficiency of the whole compressor.

Performance enhancement of a centrifugal compressor stage using profiled end wall (PEW) treatments in the radial vaned diffuser

Profiled End Wall (PEW) is an effective method that has been employed in recent years in the field of axial flow turbines as a means to reduce secondary flows and associated losses leading to improved efficiency. However, the application of end wall contouring to control the flow field in the radial vaned diffuser of a centrifugal compressor is new and no previous research has been found for this topic. The centrifugal compressor is the most extensively produced type of high-speed turbomachine and is therefore very important for power and propulsion applications. In order to reveal the impact of PEW on the performance and working range of centrifugal compressors, this study reports the outcomes of numerical simulations that were conducted for different PEW treatments and benchmarked against experimental data from the exemplar open test case known as ‘Radiver’. The results show the potential for the compressor operating range to be significantly extended by up to 39% in PEW cases with no significant decrease in efficiency or pressure ratio.