Compressor Map Research Articles

A holistic methodology to correct heat transfer and bearing friction losses from hot turbocharger maps in order to obtain adiabatic efficiency of the turbomachinery

Turbocharger performance maps provided by manufacturers are usually far from the assumption of reproducing the isentropic performance. The reason being, those maps are usually measured using a hot gas stand. The definition of the effective turbocharger efficiency maps include the mechanical losses and heat transfer that has occurred during the gas stand test for the turbine maps and only the heat transfer for the compressor maps. Thus, a turbocharger engine model that uses these maps provides accurate results only when simulating turbocharger operative conditions similar to those at which the maps are recorded. However, for some critical situations such as Worldwide harmonized Light vehicles Test Cycles (WLTC) driving cycle or off-design conditions, it is difficult to ensure this assumption. In this article, an internal and external heat transfer model combined with mechanical losses model, both previously developed and calibrated, has been used as an original tool to ascertain a calculation procedure to obtain adiabatic maps from diabatic standard turbocharger maps. The turbocharger working operative conditions at the time of map measurements and geometrical information of the turbocharger are necessary to discount both effects precisely. However, the maps from turbocharger manufacturers do not include all required information. These create additional challenges to develop the procedure to obtain approximated adiabatic maps making some assumptions based on SAE standards for non-available data. A sensitivity study has been included in this article to check the validity of the hypothesis proposed by changing the values of parameters which are not included in the map data. The proposed procedure becomes a valuable tool either for Original Equipment Manufacturers (OEMs) to parameterize turbocharger performance accurately for benchmarking and turbocharged engine design or to turbocharger manufacturers to provide much-appreciated information of their performance maps.

МЕТОД РАСЧЁТА ТЕРМОГАЗОДИНАМИЧЕСКИХ ПАРАМЕТРОВ ТУРБОВАЛЬНОГО ГАЗОТУРБИННОГО ДВИГАТЕЛЯ НА ОСНОВЕ ПОВЕНЦОВОГО ОПИСАНИЯ ЛОПАТОЧНЫХ МАШИН. ЧАСТЬ II. ОПРЕДЕЛЕНИЕ ПАРАМЕТРОВ СТУПЕНЕЙ И МНОГОСТУПЕНЧАТЫХ КОМПРЕССОРОВ

Gas Turbine Engine (GTE) operating characteristics such as thrust (or power), specific fuel consumption and other cycle parameters on different regimes, can be determined by engine modeling and applying correspondent calculation method. Its accuracy is the function of the engine’s element maps definition precision. So these maps representations influence for engines investigation results significantly. Main points and equation system for engine performances calculation method were represented in Part I of this article. The method gives an opportunity for the flow path thermodynamical parameters and engine integral values analyzing by using multistage axial blade machines blade-to-blade descriptions. The compressor and gas turbine and parameters are getting by special program modules, adding to the engine operating characteristics investigation program complex. These modules use the flow path and cascade middle radius geometrical parameters as the data for calculation. The goal of this article is the representation of the method for axial stages and multistage compressors performances definition. The calculation technique is based on one-dimensional (1D) multistage axial compressor flow description. Proposed 1D flow analysis method allows to get the multistage axial compressor maps taking into account the blade-to-blade gaps flow bleeding and by-pass. The method including is founded on the thermal and gas dynamic equations and turbomachinery theoretical dependences and empirical functions for losses and deviation angles determination. Besides, the representing method allows to calculate gas dynamic parameters, velocity triangles, angles of attack, evaluate their deviations from optimal values, hydraulic losses. Also, it can show accordance of stages working on different regimes, find the stage, which is a reason for compressor instability, and stall margin. This method can be used in GTE mathematic simulation, founded on blade-to-blade description multistage blade machines or also in multistage compressor designing. The proposed method gives the opportunity to control the stator variable vanes stagger angles control and to analyze its influence for stage and multistage compressor gas dynamic parameters and maps.

Viscous flow and performance issues in a 6:1 supersonic mixed-flow compressor with a tandem diffuser

The advancement of multi-dimensional and viscous computational tools has eased the accessibility and overall effort for thorough analysis of complex turbomachinery designs. In this paper, we computationally evaluate a high-pressure ratio supersonic mixed-flow compressor stage designed using an in-house mean-line code. Objective is to include three dimensionalities, viscous flow and compressibility effects including the shock wave systems into account. As mixed-flow compressors are advantageous especially for small jet engine applications we choose mass flow rate, stage total pressure ratio and maximum diameter as the main design constraints. This computational analysis is the second paper of a two-part series explaining strategy for designing a high-pressure ratio mixed-flow compressor stage. The high-pressure ratio and small diameter requirements push this compressor for a highly-loaded supersonic ‘shock-in rotor’ design with supersonic stator/diffuser.The used RANS based computational fluid dynamics model is thoroughly assessed for its ability to predict compressor performance using existing well-established experimental data. NASA Rotor 37 and RWTH Aachen supersonic tandem stator are chosen as the test cases for exhibiting similar flow characteristics to present design. The computational approach helps to shed light upon the mixed-rotor and supersonic-stator 3D shock structures and viscous/secondary flow. Stage performance map, pressure and velocity distribution of this high-pressure ratio mixed-flow compressor is obtained. Areas of design optimization are highlighted to further improve performance and efficiency. The in-house mean-line design code predicted a pressure ratio of 6.0 with 75.5% efficiency for a mass flow rate of 3.5 kg/s. The mean-line code obviously lacked to fully represent three-dimensionality effects due to its inherent over-simplifying assumptions thus, inclusion of RANS based computations improves the fidelity of mixed-flow compressor design performance calculations at a great rate. Comprehensive computational analysis of the stage shows that our design goal is met with a stage total pressure ratio of ΠTT = 5.83 with an efficiency of ηIS = 77% for a mass flow rate of m˙ = 3.03 kg/s. A total pressure ratio of 6.12 at 75.5% efficiency is reached with a 3.5% increase in design rotational speed.

A new approach to generate turbine map data in the sub-idle operation regime of gas turbines

Gas turbines are likely to face critical situations such as compressor surge and stall in the sub-idle operation region. Thus, it is important to predict the operation characteristics of gas turbines accurately by using simulations in the sub-idle region. However, sufficient information about the component performance maps in the sub-idle region is generally not available, and extrapolation methods are usually used to generate data. However, extrapolation methods tend to generate physically invalid data points in very low-speed regimes, which sometimes cause critical numerical problems in simulations of engine performance. This study proposes a new method to generate performance data in the sub-idle region of turbine performance maps through interpolation. A zero point is introduced where the pressure ratio is one and the mass flow rate is zero. Performance data were generated between the existing performance curve and the zero point using the interpolation. To validate the proposed method, it was applied to publicly available turbine performance maps. It was confirmed that the proposed method improves the numerical matching between the compressor and turbine maps and thus expands the predictable operating regime by as much as 23.3% compared to a conventional extrapolation method.

Numerical analysis of a turbocharger compressor

The automotive industry is under obligation to meet regulations for emission control that has resulted in further use of turbochargers in passenger cars to enable downsizing and increase engine power density. In this study, a set of numerical simulations are conducted along two turbocharger compressor speed lines of 150,000 rpm and 80,000 rpm to analyse and validate the results against experimental data. The domain includes the full compressor stage comprising intake, impeller as a Multiple Reference Frame, diffuser and outlet. The k-omega SST turbulence model with three different mesh sizes is used tosolve the compressible flow using ANSYS Fluent software. Three points on each speed-line are selected:one point each in regions close to surge and choke and a point in the stable zone of the compressor map. The simulations predict compressor performance in terms of the total–to–total pressure ratioand total–to–total efficiency. Results reveal the predicted pressure ratio error is in the range of 1-6%. At 150,000 rpm the pressure ratio is underpredicted for the point close to the surgebut overpredicted for the point close to the choke. However, the pressure ratio results are within 1% difference for 80,000 rpm. In all cases, the predicted efficiency increased when a finer mesh is used.While results are close to the experimental data in both the surge and stable areas of the map, the efficiency wasoverpredicted up to 20% in the region close to the choke. In conclusion, the finer mesh leads to higher pressure ratio and efficiency values that overpredict the performance, especially for the pointclose to choke.

Optimum design and performance of a solar dish microturbine using tailored component characteristics

The aim of the paper is to find the optimum design and performance of solar microturbines powered by parabolic dish collectors using an innovative methodology which integrates the design and off-design models of the total system. In contrast to the common practice of assigning an estimated efficiency to the engine turbomachinery (generalized performance maps), the procedure hereinafter produces the specific geometry and the characteristic maps of compressor and turbine, according to their inlet/outlet thermodynamic states and working cycle boundary conditions.With this global approach, a sensitivity analysis is performed to search for the pressure ratio that maximizes the solar-to-electric efficiency at design point for a constant air mass flow rate and turbine inlet temperature. Maximum values in the range 18.0–21.7% are obtained for a pressure ratio of 3.2 when the turbine inlet temperature changes between 800 °C (base-case system) and 900 °C.The methodology allows also to simulate the performance of the system when different design DNIs are considered with the aim to maximize the annual yield of the system. Simulations performed for Beijing, Seville and San Diego showed that quite different DNIs (610–815 W/m2) are to be chosen to get the maximum annual (average) efficiency: 11–16% for the base-case system and 14–19% for a more advanced design.

Measuring turbocharger compressor inlet backflow through particle image velocimetry

An experimental measurement campaign is presented where particle image velocimetry (PIV) was used in an effort to characterize the velocity field in a turbocharger compressor when unstable operating conditions lead to flow reversing from the diffuser into the inlet pipe. Previous studies have successfully used this and similar techniques, but the most relevant results have been obtained in an open compressor where the backflow can diffuse into the ambient. In this work a glass pipe long enough to confine the full extent of the backflow has been used. Advantage was taken from the fact that this backflow is at higher temperature due to the compression process, enabling a preliminary work where a thermocouple array was used to estimate its maximum length across the compressor map. Using these results as a reference both axial and transversal velocity fields were measured. Issues associated with each one are described, along with relevant results that show how the technique correctly identifies the reversed flow, a conclusion that is supported by the comparison of the velocity average and standard deviation profiles with those of measured temperature.

Compressor map regression modelling based on partial least squares.

In this work, two kinds of partial least squares modelling methods are applied to predict a compressor map: one uses a power function polynomial as the basis function (PLSO), and the other uses a trigonometric function polynomial (PLSN). To demonstrate the potential capabilities of PLSO and PLSN for a typical interpolated prediction and an extrapolated prediction, they are compared with two other classical data-driven modelling methods, namely the look-up table and artificial neural network (ANN). PLSO and PLSN are also compared with each other. The results show that PLSO and PLSN have a better prediction performance than the look-up table and the ANN, especially for the extrapolated prediction. The computational time is also decreased sharply. Compared with PLSO, PLSN is characterized by a higher prediction accuracy and shorter computational time than PLSO. It is expected that PLSN could save computational time and also improve the accuracy of a thermodynamic model of a diesel engine.

Experimental Evaluation of Turbo-Matching Appropriateness of B60J67, B60J68, A58N70 and A58N72 Turbo-Chargers for a Commercial Vehicle Engine

The Turbocharger is a charge booster for internal combustion engines to ensure best engine performance at all speeds and road conditions especially at the higher load. Random selection of turbocharger may lead to negative effects like surge and choke in the breathing of the engine. Appropriate selection or match of the turbocharger (Turbomatching) is a tedious task and expensive. But perfect match gives many distinguished advantages and it is a one time task per the engine kind. This study focuses to match the turbocharger to desired engine by simulation and on road test. The objective of work is to find the appropriateness of matching of turbochargers with trim 67 (B60J67), trim 68 (B60J68), trim 70 (A58N70) and trim 72 (A58N72) for the TATA 497 TCIC -BS III engine. In the road-test (data-logger method) the road routes like highway and slope up were considered for evaluation. The operating conditions with respect various speeds, routes and simulated outputs were compared with the help of compressor map.

A physics-based zero-dimensional model for the mass flow rate of a turbocharger compressor with uniform/distorted inlet condition

Turbocharger compressor, when fitted to a vehicle, usually operates with a curved inlet pipe which leads to distorted inlet flow field, hence deteriorating compressor flow capability. During the measurement of compressor performance, turbocharger-engine matching and controller design, the inlet flow field is, however, assumed to be uniform, which deviates from the real-world conditions. Consequently, the overall system performance could be compromised if the inlet distortion effect is ignored. To address this issue, in this article, a turbomachinery physics-based zero-dimensional model was proposed for the mass flow rate of a compressor with distorted inlet flow field due to 90° and 180° bent inlet pipe. The non-uniform flow is approximated as two-zone flow field, similar to parallel compressors, with the total pressure deviation between two zones modeled as a function of the flow velocity and pipe geometry. For each flow zone, the corresponding mass flow rate is estimated by approximating each sub-compressor as an adiabatic nozzle, where the fluid is driven by external work delivered by a compressor wheel governed by Euler’s turbomachinery equation. By including turbomachinery physics and compressor geometry information into the modeling, the model achieves high fidelity in compressor map interpretation and extrapolation, which is validated in experiments and the three-dimensional computational fluid dynamic simulation.

Experimentally validated modeling of a turbo-compression cooling system for power plant waste heat recovery

Waste heat recovery systems utilize exhaust heat from power generation systems to produce mechanical work, provide cooling, or create high temperature thermal energy. One system that provides a cooling effect is the turbo-compression cooling system, which operates by using low-grade waste heat to vaporize a fluid and spin a turbine in a recuperative Rankine cycle. The turbine power is used to directly drive a compressor in a traditional vapor-compression cycle. This study presents a theoretical modeling approach that uses compressor and turbine efficiency maps and a heat exchanger UA scaling methodology to make performance predictions over a range of ambient temperatures and cooling loads. The results of experimental testing for a 250 kWth TCCS showed good correlation (maximum error of 2.0%) for power and cooling cycle mass flow ranges of 0.35 kg s−1–0.5 kg s−1 and 0.65–0.85 kg s−1, respectively. The validated modeling approach was used to predict system performance for a Natural Gas Combined Cycle power plant application.

Three-dimensional through-flow modelling of axial flow compressor rotating stall and surge

This paper presents a three-dimensional through-flow approach based on the cylindrical Euler equations incorporating a body force method. Blade performance is captured through a mixture of empirical correlations and a novel reverse flow treatment. The code is the first application of a physically correct Godunov solver to three-dimensional rotating stall and surge modelling. This solver ensures the accurate calculation of inter-cell fluxes unlike in typical modern CFD codes in which the non-linear convective terms are linearised. Validation consists of modelling a low speed three-stage axial compressor in all operating regions, recreating the reverse flow, rotating stall and forward flow characteristics with good agreement to experimental data. Additional comparisons are made against rotating stall cell size and speed, to which good agreement is also shown. The paper ends with some full surge cycle simulations modifying both the tank volume after the compressor and the level of inlet distortion applied. Both tank volume and level of distortion have been found to affect the type of instability developed. The development of this code is a step forward in compressor rotating stall and reverse flow modelling and allows recreation of a full compressor map at a significantly low computational cost when compared to commercially available 3D CFD codes.

A Reduced Complexity Model for the Compressor Power of an Automotive Turbocharger

Control-oriented models for automotive turbocharger (TC) compressors typically describe the compressor power assuming an isentropic thermodynamic process with fixed isentropic and mechanical efficiencies for power transmission between the turbine and the compressor. Although these simplifications make the control-oriented model tractable, they also introduce additional errors due to unmodeled dynamics. This is especially true for map-based approaches since the manufacture-provided maps tend to be sparse and often incomplete at the operational boundaries, especially at operational conditions with low mass flow rate and low speed. Extrapolation scheme is often used when the compressor is operated outside the mapped regions, which introduces additional errors. Furthermore, the manufacture-provided compressor maps, based on steady-flow bench tests, could be quite different from those under pulsating engine flow. In this paper, a physics-based model of compressor power is developed using Euler equations for turbomachinery, where the mass flow rate and the compressor rotational speed are used as model inputs. Two new coefficients, speed and power coefficients, are defined. As a result, this makes it possible to directly estimate the compressor power over the entire compressor operational range based on a single analytic relationship. The proposed modeling approach is validated against test data from standard TC flow bench tests, standard supercharger tests, steady-state, and certain transient engine dynamometer tests. Model validation results show that the proposed model has acceptable accuracy for model-based control design and also reduces the dimension of the parameter space typically needed to model compressor dynamics.

Effect of bleed slots on turbocharger centrifugal compressor stability

Bleed slots located in the inducer region of centrifugal compressors have been demonstrated to extend the surge margin with minimal negative impact on performance. This paper describes the impact of bleed slots on surge margin enhancement in a turbocharger centrifugal compressor used for heavy duty diesel engines. The study included evaluation of pressure instabilities throughout the compressor map, characterization of dynamic phenomena occurring at low mass flow rates (mfr), and elucidation of the impacts of bleed slots on the compressor stability and surge line.A comparison of the compressor performance was performed between open and blocked bleed slots. Pressure instability levels were measured throughout the accessible compressor map using a high frequency response pressure transducer at the compressor outlet for the two cases. Static and dynamic pressure measurements were acquired within the diffuser using pressure taps and high frequency response pressure transducers.The compressor with open bleed slot showed lower instability levels at low mfr when not experiencing deep surge. Spectral analysis at low mfr showed that the bleed slot suppresses broadband frequencies linked to piping resonance and below the rpm frequency, thus improving the overall stability. When excited, these frequencies create periodic flow disturbances that originate from the low pressure region below the tongue, at low mfr. The low pressure perturbations are then convected by the flow and propagate around part of or the entire perimeter, depending on the compressor speed.

Adaptation Method for Overall and Local Performances of Gas Turbine Engine Model

An adaptation method was proposed to improve the modeling accuracy of overall and local performances of gas turbine engine. The adaptation method was divided into two steps. First, the overall performance parameters such as engine thrust, thermal efficiency, and pressure ratio were adapted by calibrating compressor maps, and second, the local performance parameters such as temperature of component intersection and shaft speed were adjusted by additional adaptation factors. An optimization technique was used to find the correlation equation of adaptation factors for compressor performance maps. The multi-island genetic algorithm (MIGA) was employed in the present optimization. The correlations of local adaptation factors were generated based on the difference between the first adapted engine model and performance test data. The proposed adaptation method applied to a low-bypass ratio turbofan engine of 12,000 lb thrust. The gas turbine engine model was generated and validated based on the performance test data in the sea-level static condition. In flight condition at 20,000 ft and 0.9 Mach number, the result of adapted engine model showed improved prediction in engine thrust (overall performance parameter) by reducing the difference from 14.5 to 3.3%. Moreover, there was further improvement in the comparison of low-pressure turbine exit temperature (local performance parameter) as the difference is reduced from 3.2 to 0.4%.

Analysis of the Effect of Multirow and Multipassage Aerodynamic Interaction on the Forced Response Variation in a Compressor Configuration—Part I: Aerodynamic Excitation

The aeroelastic prediction of blade forcing is still a very important topic in turbomachinery design. Usually, the wake from an upstream airfoil and the potential field from a downstream airfoil are considered as the main disturbances. In recent years, it became evident that in addition to those two mechanisms, Tyler–Sofrin modes, also called scattered or spinning modes, may have a significant impact on blade forcing. It was recently shown in literature that in multirow configurations, not only the next but also the next but one blade row is very important as it may create a large circumferential forcing variation, which is fixed in the rotating frame of reference. In the present paper, a study of these effects is performed on the basis of a quasi three-dimensional (3D) multirow and multipassage compressor configuration. For the analysis, a harmonic balancing code, which was developed by DLR Cologne, is used for various setups and the results are compared to full-annulus unsteady calculations. It is shown that the effect of the circumferentially different blade excitation is mainly contributed by the Tyler–Sofrin modes and not to blade-to-blade variation in the steady flow field. The influence of various clocking positions, coupling schemes and number of harmonics onto the forcing is investigated. It is also shown that along a speed-line in the compressor map, the blade-to-blade forcing variation may change significantly. In addition, multirow flutter calculations are performed, showing the influence of the upstream and downstream blade row onto aerodynamic damping. The effect of these forcing variations onto random mistuning effects is investigated in the second part of the paper.

A multi-variable multi-objective methodology for experimental data and thermodynamic analysis validation: An application to micro gas turbines

A methodology aimed at defining thermodynamic model parameters and validating experimental data has been proposed. The methodology consists of a thermodynamic model of a micro gas turbine coupled with a multi-variable multi-objective genetic optimization algorithm, in which decision variables and objectives are set depending on available experimental data. To validate both the thermodynamic model and the collected experimental data, the methodology has been applied to two micro gas turbine plants: the Capstone C30 and the Turbec T100. Validations of the thermodynamic model and the collected experimental data for the two plants have been performed by evaluating the match between input and output physical parameters. The optimal results of the optimization algorithm have plausible thermodynamic parameters and constitute the Pareto front; between these results, the one with the minimum difference between experimental data and calculated values is chosen as preferred. The two studied cases highlight the effect of measurement chain errors on experimental data reliability: the greater is the overall variance of the objectives, the lower is the accuracy of the experimental data. The effectiveness of proposed methodology has been verified for the Capstone C30 through the congruence of the design operating conditions on both the compressor and turbine maps.

Model-based performance diagnostics of heavy-duty gas turbines using compressor map adaptation

The major cause of the performance degradation of industrial gas turbines is compressor fouling due to airborne contaminants. Performance diagnostics is required to evaluate degradation precisely. In general, the measured performance in the fully opened inlet guide vane (IGV) condition is regarded as full-load performance and used for diagnostics. A new diagnostic method is proposed in this study. A scheme to determine whether the measured performance is at full-load operation is suggested. If operation is not at full-load, a virtual gas turbine state corresponding to the measured data is modeled using adaptive modeling. Then, the virtual full-load performance and the corrected performance are predicted using a reference firing temperature. This calculation methodology is applied to almost two-years of data of a 150 MW class gas turbine. The analysis revealed that the maximum reduction of power output and efficiency are 14.8 MW and 0.8 percentage points compared with the rated performance. In addition, it was shown that if the measured performance is used directly, the maximum deviation in the predicted power degradation was as much as 4.9 MW (2.8%) compared with the rated performance. This paper demonstrates the necessity of a model-based analysis for enhancing the accuracy of performance diagnostics.

Simulation of a centrifugal compressor to obtain the characteristic map through computational effort

The association of turbochargers with piston engines is widespread since both the efficiency and the power output of an engine could be improved. However, a piston engine operational range is wide and highly variable. This characteristic imposes challenges for the project and application of a turbocharger that should perform properly within the operational range. An important tool used to evaluate the performance of both turbine and compressor, which compose a turbocharger, is the characteristic map. The map condenses the main performance parameters into a single graphic that allow the evaluation of the machine characteristics, such as the operational width. A typical characteristic map relates the pressure ratio, mass flow rate, rotation and efficiency for each operational condition. The present work provides a technique to obtain the characteristic map of a turbocharger centrifugal compressor with reduced time consumption through steady state simulation using a fully unstructured mesh. Evaluation of the results indicated good accuracy for the predicted mass flow rate and pressure ratio. However, the resulting efficiency presented considerable discrepancy, which was aggravated when simulating extreme operational conditions or when the mass flow was used as a boundary condition. At last, the porter shroud and volute were evaluated within the entire range to provide an insight into the compressor operation.

Thermodynamic performance evaluation of HFC refrigerants for the chiller system simulated by hot gas bypass cycle

The competitive of the building air-conditioning equipment pushes manufactures to develop and improve the performance and efficiency of their products. This process is cost and time consuming for testing the whole units. In this study, for the first time a modified proposed test block with hot gas bypass cycle (HGBP), based on the experimental compressor map, has been used as a model to investigate the theoretical performance of the chiller system. The model assumes one dimensional steady state conditions and uses an experimental compressor map to predict the thermodynamic performance of the system. A computational model, using the software program EES (EES-V8.4), in a single stage of the chiller system with HGBP cycle based on the first and second law analyses are presented for the prediction of the effects of the pressure ratio, degree of superheating and sub-cooling, condenser temperature, outdoor air temperature and humidity ratio on the exergy destruction, exergetic efficiency, gas power and coefficient of performance (COP) of the chiller system. The performance of the implemented model with various hydrofluorocarbon (HFC) refrigerants such as R134a, R152a and R423a are compared . The results, firstly, indicates that the modified model with applying the energy and exergy analysis works for all kind of working refrigerants including HFC refrigerants. Secondly, the performance of the compression refrigeration system based on the experimental compressor map data to choose the right compressor can help engineers to design a high quality unit before going to design the system practically. The results indicate that R423a has a higher coefficient of performance as compared to the rest of the refrigerants. The developed simulation model helped to establish the strong dependence between system performances and the compressor map.