Compressor Simulation Research Articles

Performance Analysis of a Water-Injected Twin-Screw Compressor in a High-Temperature R718 Heat Pump

Abstract High-temperature heat pumps with twin-screw compressors and water (R718) as the working fluid show promising potential for providing industrial heat and process steam at temperature levels of up to 200 °C. This paper presents a simulation approach for a two-layered simulation structure of a water-based high-temperature heat pump system including a twin-screw compressor with water-injection. The heat pump process with two-phase steam compression is investigated with respect to various aspects. In addition to controlling the compressor outlet temperature, the evaporation of the injected liquid leads to an increase in the displaced mass flow rate on the sink side of the heat pump. This effect is analyzed in detail for various system operating points using a thermodynamic simulation framework for the R718-based heat pump cycle and a comprehensive compressor model. The main target of the presented paper is the analysis of system performance and the detailed investigation of the interdependencies. Performance of the twin-screw compressor is determined by means of two-phase chamber model simulations. In the chamber model method thermodynamic properties of both injected liquid and steam are calculated based on the conservation equations of mass and energy for the compression process. Adequate sub-models for internal leakage and heat and mass transfer between vapor and liquid phase are applied. Integral results of the compressor simulations are embedded in the heat pump system simulation using a characteristic map. In conclusion, this paper contributes to the understanding of advanced compression technologies in the field of high-temperature heat pumps, offering a detailed examination of a water-injected steam compressor’s applicability and efficiency in a practical system setting.

Thermodynamic simulation of a water-injected twin-screw steam compressor

Abstract Decarbonisation of industrial heating and process steam generation is crucial for the mitigation of advancing climate change. High-temperature heat pumps can meet these demands while effectively integrating with renewable energy sources, outperforming traditional heating and boiling systems, especially when operating with natural refrigerants. Since compressor efficiency is critical for the effectiveness of heat pump systems, particular care is required in compressor design and specification. Detailed thermodynamic simulations of the compressor system are indispensable in this process. The compression of fluids with a negative saturation vapour curve leads to challenging temperature increases during compression, with substantial superheating of the working fluid. In this context, a promising approach is the injection of liquid working fluid into the compressing chambers for internal cooling. This introduces new complexity to compressor simulations for heat-pump applications. In this work, a novel two-phase approach for multi-chamber model simulations of positive displacement compressors is presented. Initially, a quasi-isentropic reference process for vapour compression with internal liquid injection is introduced and efficiency ratings are derived. Furthermore, the simulation process is described in detail, and comprehensive thermodynamic simulations of a water-injected twin-screw steam compressor are carried out.

An Automated Geometric Analysis and Characterization of an Oil-Lubricated Twin-Screw Compressor for Predictive Modeling

Abstract Compressor manufacturing companies are showing a growing interest in the development of validated compressor simulation models capable of predicting the behaviour of the machine if subjected to appropriate modifications. A validated predictive model of the entire compressor is useful for analysing the influence of the variation of some fundamental parameters, such as the variation of volumes or new inlet and outlet sections, on the behaviour of the machine. To create these models, geometric parameters such as the variation in volumes, the variation in inlet and outlet sections and the presence of leakage or blowhole phenomena must be provided as input. The precision of these geometric parameters is of fundamental importance for the correct operation of the model and subsequent design analyses. In this work, the authors analysed the complete geometry of an oil-lubricated twin-screw compressor. In particular, an automated calculation methodology was developed using CAD software capable of defining the characteristic curves of the volumes and areas of the compressor: starting from the geometries of the rotors and the stator case, the fluid volumes delimited at the bottom by the rotors and at the top by the case were defined through a Boolean subtraction operation. Subsequently, the volumes that complete the compression phase together were isolated and, through an automatic kinematic analysis with steps of 5° of rotation, starting from the zero reference (null volumes), the characteristic curves of the volumes and inlet and outlet areas were defined through the use of special virtual sensors. The passage sections of the leakage and blowhole leaks were defined in the same way. Particular attention was paid to the analysis of leakage and blowhole phenomena, the presence of which determines a reverse flow of part of the mass flow rate of air during the compression phase, resulting in a decrease in volumetric efficiency. Knowledge of this data is of fundamental importance for the subsequent creation of the 1D/0D model.

New Data-Driven Models of Mass Flow Rate and Isentropic Efficiency of Dynamic Compressors

Dynamic compressors are widely used in many industrial sectors, such as air, land, and marine vehicle engines, aircraft environmental control systems (ECS), air-conditioning and refrigeration, gas turbines, gas compression and injection, etc. The data-driven formulas of mass flow rate and isentropic efficiency of dynamic compressors are required for the design, energy analysis, performance simulation, and control- and/or diagnosis-oriented dynamic simulation of such compressors and the related systems. This work develops data-driven models for predicting the performance of dynamic compressors, including empirical models for mass flow rate and isentropic efficiency, which have high prediction accuracy and broad application range. The performance maps of two multi-stage axial compressors of an aero engine and a centrifugal compressor of an aircraft ECS were chosen for evaluation of the existing empirical formulas and testing of the new models. There are 16 empirical models of mass flow rate and 14 empirical models of isentropic efficiency evaluated, and the results show that it is necessary to develop highly accurate empirical formulas both for mass flow rate and isentropic efficiency. With the data-driven method, two empirical models for mass flow rate and one for isentropic efficiency are developed. They are in general form, with some terms removable to make them simple while enhancing their applicability and prediction accuracy. The new models have much higher prediction accuracy than the best existing counterparts. The new mass flow rate models predict for the three compressors a mean absolute relative deviation (MAD) not greater than 1.3%, while the best existing models all have MAD > 2.0%. The new efficiency model predicts for the three compressors an MAD of 1.0%, 0.4%, and 1.9%, respectively, while the best existing model predicts for the three compressors an MAD of 1.8%, 0.8%, and 3.2%, respectively.

Computational Study on Compressor-Combustor Interactions for Improved Matching of a Micro Gas Turbine

ABSTRACT Understanding complex aerodynamics/combustion interactions across major components of aeroengines, including the compressor, combustor and turbine is demanded for the improved performance of advanced propulsion systems. This study employs high-fidelity CFD simulations to investigate the coupled compressor-combustor interactions for the improved performance of a micro gas turbine. In the prototype configuration, the deficient compressor/combustor matching causes insufficient air/fuel mixing and delayed combustion inside the combustor chamber. By reducing the flow area of the compressor and redistributing the air holes on the combustor chamber, a stable united recirculation structure is formed to promote air/fuel mixing and efficient combustion, achieving a over 50% decrease in OTDF and RTDF at the combustor exit and a total 20% decrease of pressure loss in the entire engine through-flow. Compared with the single-component combustor simulation, the coupled compressor-combustor results exhibit stronger turbulence mixing, increased temperature uniformity inside the combustor chamber. Compared with the single-component compressor simulation, the compressor in the multi-component simulation shows the reduced flow angle and Mach number at the compressor outlet, leading to increased stall critical angles and delayed flow separation at the compressor diffuser and vanes. This demonstrates that the added combustor endues the compressor with an expanded operating range and a lower mass-flow rate instability boundary. This work implies that 3D multi-component CFD simulation is necessary to understand the aerodynamic and combustion interactions and improve the multi-component matching in gas turbine engines.

Investigation on Rotation/Curvature Correction Methods of SST Turbulence Model in Numerical Simulation of Axial Compressor

Turbulence models which are widely used in engineering applications usually need correction in axial compressor CFD simulations due to the intense rotation of the system. In order to understand the applicability of rotation-curvature correction methods of turbulence models in numerical simulation of axial compressors, several correction methods were implemented based on SST turbulence model on an inhouse CFD solver ASPAC and numerical simulations were carried out on a transonic compressor Rotor37. The results shows that the rotation/curvature correction models mainly affect the corner separation on the suction surface of the blade. More specifically, SST-Helicity model reduces corner separation at the suction surface and performs well at conditions with relatively large mass flow rate. Results from SST-CC and SST-Hellsten model are close to but slightly worse than that of standard SST model in terms of agreement with experimental data. In summary, detailed assessment and discussions on different rotation/curvature corrections of turbulence models were carried out based on numerical results of a transonic compressor in this paper, which may contribute to the choice of turbulence models and investigation of turbulence modeling and model correction methods in axial compressor simulations in the future.

Research on Rotation/Curvature Correction Method of SA Turbulence Model for Numerical Simulation of Axial Compressor

The strong rotation effect exists in the flow of compressors, but it is rarely considered in the common turbulence models used in numerical simulation. In addition, when the widely used turbulence model is applied to the numerical simulation of compressor flow, it often needs to be modified. In order to evaluate the applicability of various turbulence model modification methods in axial compressor flow simulation, and explore suitable modification methods. Based on the numerical simulation software ASPAC for axial flow compressor developed by our research group, three turbulence model rotation/curvature correction methods were implemented based on SA turbulence model and applied to the flow simulation of Rotor 37. The results show that the modified models mainly affect the flow separation of the rotor suction surface. Specifically, the SA-Helicity model improves the prediction accuracy of the separation flow in the compressor. The total temperature and pressure calculated by SA-R and SA-RC models are on the small side. In this study, the applicability of rotation/curvature correction method of various SA turbulence models in compressor flow simulation is evaluated in detail based on transonic compressor, which provides a basis for the selection of turbulence models and the research of turbulence model and correction methods adapted to compressor simulations.

Computational procedure for simulating stall process of reciprocating compressors

This article presents in detail a computational procedure for simulating the stall process of reciprocating compressor. The focus of the work is the calculation of the compressor stall limits from the available torque curves of electrical motor. The procedure is composed by an algorithm to compute the compressor stall using a developed compressor simulation model. The compressor model considers the simulation of flow and mechanical interactions in the compressor components and was implemented in the GT-Power platform, a system simulation software. The compressor simulation results for steady state operation were compared with experimental data, indicating that the simulation model represented very well the overall compressor behavior, with a maximum relative error of 1.0% for the compressor global performance. The results for the compressor stall obtained by the proposed computational procedure agreed with the experimental stall tests, with a maximum average relative error of about 6.7%. The computed stall curve had similar trends in relation to experimental results. Performed parametric analyses considering statistical rank correlations indicated that the electric motor tension and motor temperature were the most influencing parameters on compressor stall. The obtained results show that the developed procedure could be an efficient tool for compressor design.

Assessment of a novel k–ω turbulence model for transonic centrifugal impeller simulations

Numerical simulation of high pressure ratio transonic centrifugal compressors is challenging for the existing turbulence models. A lagged k–ω model proposed by Olsen and Coakley for nonequilibrium effects was first applied to simulate the transonic centrifugal impeller SRV2-O. As comparative case studies, four other turbulence models ( k–ω model, RNG k–ε model, SST-CC model, and EARSM model) were also computed. The comparison showed that ( i) the selection of the turbulence model had a great influence on SRV2-O impeller simulations; ( ii) the lagged k–ω model had an advantage over other models in terms of overall pressure ratio and internal flow characteristics; and ( iii) the lagged model predicted a smaller blockage area caused by leakage vortex breakdown than other models, closer to the experimental result. The detailed parameter examination indicated that the nonequilibrium parameter a0 in the lagged model had little influence on the Mach number distribution and choking mass flow rate but a significant influence on the static pressure on the shroud casing. For a higher Mach number compressor, a smaller a0 is recommended for bettering the simulation accuracy.

A Computational Method of Rotating Stall and Surge Transients in Axial Compressor

The onset of rotating stall and surge in compressors limits the operating range of aero-engines. Accurately predicting the key features during these events is critical in the engine design process. In this paper, a three-dimensional computational model for transient simulation of multi-stage axial compressors during stall is proposed. The kinetic equations describing the dynamic process of the compression system are constructed, with a 3D through-flow model for the compression part and a 1D gas collector model for the outlet part. The calculation of the source term is performed using the developed body-force model, which realizes the correlation between the deviation angle and the loss coefficient with the inlet parameters in various flow regions. Validated on a single-stage compressor and a single-rotor fan, the results show that the method is capable of capturing the stall and surge features correctly and that the three-dimensional structure of the stall cell can be captured. In addition, this model could be used for the analysis of the surge load, which is significant for the structural integrity of the compressor.

Simulating the mechanically driven compressor of a marine diesel engine by CFD theory

This paper presents a flow analysis model through a mechanically driven compressor of the supercharger. The object was a centrifugal compressor directly driven from the engine crankshaft, which was used to increase the intake gas. The initial conditions for the compressor simulation were estimated based on the working relationship between the engine and its compressor, the geometry model was completed by CFturbo software, thereafter the fluid dynamic was simulated in the Ansys Workbench environment, which was based on CFD theory. The simulation results showed the relationships among the intake mass flow through the compressor and technical parameters such as the compressor efficiency and pressure ratio. The results can be applied to improve the efficiency of mechanically driven compressors in practical operation.

Simulating the mechanically driven compressor of a marine diesel engine by CFD theory

This paper presents a flow analysis model through a mechanically driven compressor of the supercharger. The object was a centrifugal compressor directly driven from the engine crankshaft, which was used to increase the intake gas. The initial conditions for the compressor simulation were estimated based on the working relationship between the engine and its compressor, the geometry model was completed by CFturbo software, thereafter the fluid dynamic was simulated in the Ansys Workbench environment, which was based on CFD theory. The simulation results showed the relationships among the intake mass flow through the compressor and technical parameters such as the compressor efficiency and pressure ratio. The results can be applied to improve the efficiency of mechanically driven compressors in practical operation.

Self-adapting anti-surge intelligence control and numerical simulation of centrifugal compressors based on RBF neural network

Anti-surge control of centrifugal compressors is an essential issue for the operation of long-distance natural gas pipeline systems. A suitable controller can make a centrifugal compressor runs smoothly and stably and improve the economy. This work presents a new intelligence control strategy with self-adapting ability. The strategy includes the proportional integral (PI) control self-tuned by radial basis function neural network (RBF-NN), recycle trip control, special derivative control, surge line correction, and asymmetric output of the controller. A hybrid numerical simulation platform is built to validate the anti-surge strategy, and a real centrifugal compressor is simulated. The results show that the strategy makes the anti-surge valve respond quickly, decreases the surge control line’s margin and backflow rate, and improves the economy. In the controller, the special derivative control can make the anti-surge valve open earlier and effectively reduce the fluctuating of inlet flow rate. Aiming at the problem that the gradient descent method is more sensitive to the initial value when solving RBF-NN, a hybrid algorithm of k-means, recursive least square, and gradient descent (KRG algorithm) is proposed. It is successfully applied in the anti-surge controller. Even if the given RBF-NN initial parameters are not good enough, the KRG algorithm illustrates good learning stability and increases the adaptive ability of RBF-NN.

Design optimization of external variable displacement compressor with R1234yf for vehicle air conditioning system

Due to the high global warming potential of the HFC-based R134a, it should be replaced by the HFO-based R1234yf as a working fluid for automotive air conditioning systems. In this study, for the external variable compressor whose stroke volume is controlled by the external signal used in the R134a air conditioning system, the optimization design of the compressor as the operating refrigerant changes from R134a to R1234yf is proposed. In order to analyze the working performance of the compressor a compressor simulation program was developed, and the drop-in test with R1234yf has been evaluated to replace R134a in the air conditioner system. From the drop-in test, both the cooling capacity and the coefficient of performance for the R1234yf decrease about 4 ~ 5% under the maximum stroke volume condition depending on the compressor operating speeds. And in the TEO5 control mode, where the lowest air temperature behind the evaporator is controlled at 5°C, it was found that there is only less than 4% reduction of the cooling capacity, while the coefficient of performance drops by up to 17% due to the increased compressor power. From the simulation result, we found that the reduced coefficient of performance of R1234yf might stem mainly from the increased losses by the suction and the discharge valves. By redesigning the suction and discharge valves within the designable range, as the results, the coefficient of performance is improved 1% at the MSV condition and 8% under the TEO5 control mode, respectively.

A fast approach for unsteady compressor performance simulation under boundary condition caused by pressure gain combustion

• Introduction of a coupled numerical scheme of 0D-plenum and 1D-pulsed detonation combustion tubes. • Compressor simulation with unsteady boundary condition caused by pressure gain combustion. • Unsteady 1D-Euler results match those computed by unsteady 3D-CFD. • 90% of the fluctuation’s amplitude is damped across four stages of the compressor. • Stability evaluation of a compressor exposed to pulsed detonation combustion. The constant pressure combustion of the Joule cycle is a dominant source of losses in gas turbines. One possible improvement is pressure gain combustion through pulse detonation combustion. However, the total pressure increase is the result of a transient periodic process that can adversely affect the performance of adjoining turbo components. The thermodynamic benefits of pressure gain combustion can thus be undermined by low efficiencies of compressor and turbine. In order to account for such unsteady effects early in the design process, suitable methods are essential. Given 3D-CFD simulations’ undue computational demands, an approach with low computation resources is required for first-order estimates. This paper introduces such an approach based on a 1D-Euler method and demonstrates its applicability. A compressor is simulated with 3D-CFD, which serves as a reference, as well as with the 1D-Euler code employing unsteady outlet boundary conditions that approximate those encountered with pulse detonation combustion. The findings suggest that the 1D-Euler code is able to accurately capture the transient compressor behaviour. Though the relative pressure amplitude at the compressor outlet of 3.6% is attenuated by 90% up to the compressor inlet, it still results in a compressor isentropic efficiency loss of 0.8 percentage points.

Force assisted discharge valve for piston compressors

Due to the enormous number of domestic refrigeration appliances worldwide and the associated high overall energy demand of the cooling sector, manufacturers are required to develop more efficient cooling devices. For this reason, variable speed compressors are increasingly being used in order to better match refrigeration demand and supplied cooling capacity. However, variable speed operation is associated with challenges concerning the valve dynamics. Valve oscillation as well as opening and closing delays reduce the energy efficiency (COP) of the compressor.The underlying study is about a simulation based potential analysis of a novel force assisted discharge valve to improve the valve dynamics of a small hermetic reciprocating compressor for domestic refrigeration. Discharge valve and valve support mechanism are modelled by a 1d-spring-damper-mass multi-body system and implemented in an existing in-house compressor simulation model.Systematic methods of statistical design of experiments (DOE) are applied not only to improve the COP but also to generate a robust valve behaviour which is largely independent of the operating conditions of the compressor. The findings of the force assisted discharge valve are basically transferable to any other piston compressor with flutter valves.

Development of a Throughflow-Based Simulation Tool for Preliminary Compressor Design Considering Blade Geometry in Gas Turbine Engine

Gas turbine engines are highly intricate machines, and every component of them is closely associated with one another. In the traditional engine developing process, vast experiment tests are needed. To reduce unnecessary trials, a whole gas turbine engine simulation is extremely needed. For this purpose, a compressor simulation tool is now developed. Considering the inherent drawbacks of 0D analysis and 3D CFD (Computational Fluid Dynamics) calculation, the 2D throughflow method is an indispensable tool. Based on the circumferential average method (CAM), 3D Navier–Stokes is transformed into a 2D method. One phenomenon arising is that the lack of description about circumferential motion leads to the need for the blade force modeling in compressor simulation. Previous models are based on the assumption that flow passes through the average stream surface without entropy increasing, which is not applicable in the CAM. An improved model is proposed based on the result analysis from CAM and NUMECA method in a linear cascade. Whereafter, the model is applied in a highly loaded and low-speed fan, which has been tested for its performance characteristics. Utilizing the new model, the error of the adiabatic efficiency between CAM and experiment decreases from 4.0% to 1.0% and the accuracy of the mass flow, and pressure ratio remains unchanged. The time involved in the CAM simulation is nearly 70 times faster than that of the 3D simulation.

Self-Adapting Anti-Surge Intelligence Control and Numerical Simulation of Centrifugal Compressors Based on RBF Neural Network

Self-Adapting Anti-Surge Intelligence Control and Numerical Simulation of Centrifugal Compressors Based on RBF Neural Network

An analytical method for simulation of centrifugal compressors

A pure analytical method for modeling and simulation of centrifugal compressors based on parametric analysis of governing equations is proposed. It will be shown that the main equations describing the compressor operation along with some new hypotheses allow to determine the most useful off-design characteristics of the machine for a given geometry and for given performances at design (nominal) regime. As example of application, a compressor map is determined along with other important features like surge and choke lines, optimal regimes line and constant efficiency curves (efficiency islands) without need of experimental data. The proposed method is intended for quick simulation of complex machines embedding centrifugal compressors, as an alternative of costly CFD analyses.

Numerical simulation of the non-uniform flow in a full-annulus multi-stage axial compressor with the harmonic balance method

To improve the understanding of unsteady flow in modern advanced axial compressor, unsteady simulations on full-annulus multi-stage axial compressor are carried out with the harmonic balance method. Since the internal flow in turbomachinery is naturally periodic, the harmonic balance method can be used to reduce the computational cost. In order to verify the accuracy of the harmonic balance method, the numerical results are first compared with the experimental results. The results show that the internal flow field and the operating characteristics of the multi-stage axial compressor obtained by the harmonic balance method coincide with the experimental results with the relative error in the range of 3%. Through the analysis of the internal flow field of the axial compressor, it can be found that the airflow in the clearance of adjacent blade rows gradually changes from axisymmetric to non-axisymmetric and then returns to almost completely axisymmetric distribution before the downstream blade inlet, with only a slight non-axisymmetric distribution, which can be ignored. Moreover, the slight non-axisymmetric distribution will continue to accumulate with the development of the flow and, finally, form a distinct circumferential non-uniform flow field in latter stages, which may be the reason why the traditional single-passage numerical method will cause certain errors in multi-stage axial compressor simulations.