Enhanced design methodology of a low power stall regulated wind turbine. BEMT and MRF-RANS combination and comparison with existing designs

[EN] Wind energy importance has increased over the past decades. Energy generation by small turbines installed near urban locations has experienced noticeable growth. This work is focused on the development of a design methodology for a low power blade well suited for all the wind operation conditions. First, a complete Design of Experiments will be presented using the low computational cost tool Blade Element Momentum Theory (BEMT) in order to discard those designs which are clearly not suited to the requirements of the system. Later, the remaining were analyzed using a Computational Fluid Dynamics (CFD) methodology in order to account for three dimensional effects. The value of the left slope of the non-dimensional power curve has been found to be a key parameter for the design. This methodology has been validated with experimental results available from NREL Phase VI wind turbine, allowing to conclude that BEMT is capable to provide with pre-design accurate results which, nevertheless, should corrected by CFD. The results of the proposed design are analyzed and compared to the CFD predictions of a commercial existing blade designed to comply with similar working. For the proposed design, predictions indicate better behavior in terms of maximum power and controllability.Torregrosa, AJ.; Gil, A.; Quintero-Igeño, P.; Tiseira, A. (2019). Enhanced design methodology of a low power stall regulated wind turbine. BEMT and MRF-RANS combination and comparison with existing designs. Journal of Wind Engineering and Industrial Aerodynamics. 190:230-244. https://doi.org/10.1016/j.jweia.2019.04.019S23024419

Fast 3-D heat transfer model for computing internal temperatures in the bearing housing of automotive turbochargers

[EN] Each of the elements that make up the turbocharger has been gradually improved. In order to ensure that the system does not experience any mechanical failures or loss of efficiency, it is important to study which engine operating conditions could produce the highest failing rate. Common failing conditions in turbochargers are mostly achieve due to oil contamination and high temperatures in the bearing system. Thermal management becomes increasingly important for the required engine performance. Therefore, it has become necessary to have accurate temperature and heat transfer models. Most thermal design and analysis codes need data for validation; often the data available falls outside the range of conditions the engine experiences in reality leading to the need to interpolate and extrapolate disproportionately. This paper presents a fast 3D heat transfer model for computing internal temperatures in the central housing for non-water cooled turbochargers and its direct validation with experimental data at different engine operating conditions of speed and load. The presented model allows a detailed study of the temperature rise of the central housing, lubrication channels, and maximum level of temperature at different points of the bearing system of an automotive turbocharger. It will let to evaluate thermal damage done to the system itself and influences on the working fluid temperatures, which leads oil coke formation that can affect the performance of the engine. Thermal heat transfer properties obtained from this model can be used for to feed and improve a radial lumped model of heat transfer that predicts only local internal temperatures[1]. Model validation is illustrated and finally the main results are discussed.The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: Authors want to acknowledge the Apoyo para la investigación y Desarrollo (PAID) grant for doctoral studies (FPI-2016-S2-1354).Gil, A.; Tiseira, A.; García-Cuevas González, LM.; Rodriguez-Usaquen, YT.; Mijotte, G. (2018). Fast 3-D heat transfer model for computing internal temperatures in the bearing housing of automotive turbochargers. International Journal of Engine Research. https://doi.org/10.1177/1468087418804949SKhalife, E., Tabatabaei, M., Demirbas, A., & Aghbashlo, M. (2017). Impacts of additives on performance and emission characteristics of diesel engines during steady state operation. Progress in Energy and Combustion Science, 59, 32-78. doi:10.1016/j.pecs.2016.10.001Payri, F., Olmeda, P., Martín, J., & Carreño, R. (2015). Experimental analysis of the global energy balance in a DI diesel engine. Applied Thermal Engineering, 89, 545-557. doi:10.1016/j.applthermaleng.2015.06.005Serrano, J. R., Tormos, B., Gargar, K. L., & Bouffaud, F. (2011). Study of the Effects on Turbocharger Performance Generated by the Presence of Foreign Objects at the Compressor Intake. Experimental Techniques, 37(2), 30-40. doi:10.1111/j.1747-1567.2011.00795.xGalindo, J., Serrano, J. R., Dolz, V., López, M. A., & Bouffaud, F. (2013). Behavior of an IC Engine Turbocharger in Critical Conditions of Lubrication. SAE International Journal of Engines, 6(2), 797-805. doi:10.4271/2013-01-0921Deligant, M., Podevin, P., & Descombes, G. (2011). CFD model for turbocharger journal bearing performances. Applied Thermal Engineering, 31(5), 811-819. doi:10.1016/j.applthermaleng.2010.10.030Sim, K., Lee, Y.-B., & Kim, T. H. (2013). Effects of Mechanical Preload and Bearing Clearance on Rotordynamic Performance of Lobed Gas Foil Bearings for Oil-Free Turbochargers. Tribology Transactions, 56(2), 224-235. doi:10.1080/10402004.2012.737502Drewczynski, M., & Rzadkowski, R. (2015). A stress analysis of a compressor blade in partially blocked inlet condition. Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering, 230(5), 934-952. doi:10.1177/0954410015601149Filsinger, D., Szwedowicz, J., & Scha¨fer, O. (2001). Approach to Unidirectional Coupled CFD–FEM Analysis of Axial Turbocharger Turbine Blades. Journal of Turbomachinery, 124(1), 125-131. doi:10.1115/1.1415035Romagnoli, A., & Martinez-Botas, R. (2012). Heat transfer analysis in a turbocharger turbine: An experimental and computational evaluation. Applied Thermal Engineering, 38, 58-77. doi:10.1016/j.applthermaleng.2011.12.022De Faoite, D., Browne, D. J., Chang-Díaz, F. R., & Stanton, K. T. (2011). A review of the processing, composition, and temperature-dependent mechanical and thermal properties of dielectric technical ceramics. Journal of Materials Science, 47(10), 4211-4235. doi:10.1007/s10853-011-6140-1Sachdev, A. K., Kulkarni, K., Fang, Z. Z., Yang, R., & Girshov, V. (2012). Titanium for Automotive Applications: Challenges and Opportunities in Materials and Processing. JOM, 64(5), 553-565. doi:10.1007/s11837-012-0310-8Tetsui, T. (2002). Development of a TiAl turbocharger for passenger vehicles. Materials Science and Engineering: A, 329-331, 582-588. doi:10.1016/s0921-5093(01)01584-2Wu, X. (2006). Review of alloy and process development of TiAl alloys. Intermetallics, 14(10-11), 1114-1122. doi:10.1016/j.intermet.2005.10.019Appel, F., Paul, J. D. H., & Oehring, M. (2011). Gamma Titanium Aluminide Alloys. doi:10.1002/978352763620

Analysis of the influence of different real flow effects on computational fluid dynamics boundary conditions based on the method of characteristics

Nowadays, turbocharged internal combustion engines (ICEs) are very common in automotive powerplants, monopolizing the Diesel sector and having a steadily increasing percentage in the gasoline one. In this frame, the interest in modeling the behavior of the turbomachinery components involved, with the ultimate goal of characterizing the performance of the turbocharged ICE, seems clear. A turbomachine can be simulated using 3D-CFD software, but its computational cost does not allow to reproduce the whole turbocharger test rig. Moreover, the existence of long ducts requires a considerable computational time until the pressure reflections at the boundaries dissipate in order to reach a periodic solution. The use of non-reflecting boundary conditions reduces the needed length of ducts without introducing spurious wave reflections. An anechoic boundary condition (BC) based on the Method of Characteristics has been previously developed, considering the case of an inviscid and adiabatic 1D flow of a perfect gas. However, real flows do not behave in such ideal manner. In this paper, the extension of the scope of the previous BC is sought. In this way, a methodology to evaluate the performance of the anechoic BC under these real flow situations is shown. The consideration of ideal gas instead of perfect gas, the flow viscosity and the non-homentropic flow makes it necessary to modify the Method of Characteristics, since the Riemann Invariants are not constant any more. In this frame they are referred to as Riemann Variables. An additional issue that has been considered is the effect of swirl flow, as the one in the turbine outlet, on the anechoic BC. Some improvements to be implemented in the BC are proposed in order to have a better performance in these real flow situations.Galindo, J.; Tiseira Izaguirre, AO.; Fajardo, P.; Navarro García, R. (2013). Analysis of the influence of different real flow effects on computational fluid dynamics boundary conditions based on the method of characteristics. Mathematical and Computer Modelling. 57(7-8):1957-1964. doi:10.1016/j.mcm.2012.01.016S19571964577-

Uncertainties in power computations in a turbocharger test bench

A specific study of the uncertainties of turbine power output measured in turbocharger test benches is presented using the law of uncertainty propagation and the influence of the different terms that contribute to it is shown. Then, non-linear mixed integer mathematical programming algorithms used with the turbine power uncertainty expression become an essential tool to overcome the problem of selection new sensors to improve an existing test rig or to contribute to a new one. A method of optimisation is presented for two different scenarios: first, where the maximum cost is a constraint; second where the maximum uncertainty is a constraint and the total cost is minimised. When using a large transducers database, computational efforts may be reduced by solving the relaxed non-integer problem by means of sequential quadratic programming and then probing the ceilings and floors of the parameters to get an optimum approximation with low costs. A comparison between the linear uncertainty propagation model and Monte Carlo simulations is also presented, only showing benefits of the later method when computing high order statistical moments of the turbine power output probability distribution.This work has been partially supported by the Spanish Ministerio de Ciencia e Innovacion through Grant No. DPI2010-20891-C02-02 and by the Spanish Ministerio de Economia y Competitividad through Grant No. TRA2012-36954.Olmeda González, PC.; Tiseira Izaguirre, AO.; Dolz Ruiz, V.; García-Cuevas González, LM. (2015). Uncertainties in power computations in a turbocharger test bench. Measurement. 59:363-371. https://doi.org/10.1016/j.measurement.2014.09.055S3633715

Development and validation of a radial variable geometry turbine model for transient pulsating flow applications

This paper presents the development and validation of a one-dimensional radial turbine model able to be used in automotive turbocharger simulations. The model has been validated using results from a numerical 3D CFD simulation of stationary and pulsating flow in a variable geometry radial turbine. As the CFD analysis showed, the main non-quasi-steady behavior of the turbine is due to the volute geometry, so special care was taken in order to properly model it while maintaining low computational costs. The flow in the volute has been decomposed in its radial and azimuthal direction. The azimuthal flow corresponds to the flow moving along the volute, while the radial flow is computed by coupling its flow with a stator model. Although the stator caused fewer accumulation effects than the volute, a small accumulation model has been used for it, which also allows to compute the evolution of the flow inside the turbine with lower costs. The flow in the moving rotor can be considered quasi-steady, so a zero-dimensional model for the rotor has been developed. Several losses models where implemented for both the stator and the rotor. The results show good agreement with the CFD computations. 2014 Elsevier Ltd. All rights reserved.The authors are indebted to the Spanish Ministerio de Economia y Competitividad through Project TRA 2010-16205.Galindo, J.; Tiseira Izaguirre, AO.; Fajardo, P.; García-Cuevas González, LM. (2014). Development and validation of a radial variable geometry turbine model for transient pulsating flow applications. Energy Conversion and Management. 85:190-203. https://doi.org/10.1016/j.enconman.2014.05.072S1902038

Influence of tip clearance on flow behavior and noise generation of centrifugal compressors in near-surge conditions

CFD has become an essential tool for researchers to analyze centrifugal compressors. Tip leakage flow is usually considered one of the main mechanisms that dictate compressor flow field and stability. However, it is a common practice to rely on CAD tip clearance, even though the gap between blades and shroud changes when compressor is running. In this paper, sensitivity of centrifugal compressor flow field and noise prediction to tip clearance ratio is investigated. 3D CFD simulations are performed with three different tip clearance ratios in accordance to expected operating values, extracted from shaft motion measurements and FEM predictions of temperature and rotational deformation. Near-surge operating conditions are simulated with URANS and DES. DES shows superior performance for acoustic predictions. Cases with reduced tip clearance present higher pressure ratio and isentropic efficiency, but no significant changes in compressor acoustic signature are found when varying clearance. In this working point, tip clearance is immersed in a region of strongly swirling backflow. Therefore, tip leakage cannot establish any coherent noise source mechanism.The equipment used in this work has been partially supported by FEDER project funds "Dotacion de infraestructuras cientifico tecnicas para el Centro Integral de Mejora Energetica y Medioambiental de Sistemas de Transporte (CiMeT), (FEDER-ICTS-2012-06)", framed in the operational program of unique scientific and technical infrastructure of the Ministry of Science and Innovation of Spain. The authors wish to thank Mr. Pau Raga for his worthy assistance during the meshing process.Galindo, J.; Tiseira Izaguirre, AO.; Navarro García, R.; López Hidalgo, MA. (2015). Influence of tip clearance on flow behavior and noise generation of centrifugal compressors in near-surge conditions. International Journal of Heat and Fluid Flow. 52:129-139. https://doi.org/10.1016/j.ijheatfluidflow.2014.12.004S1291395

Effect of the numerical scheme resolution on quasi-2D simulation of an automotive radial turbine under highly pulsating flow

Automotive turbocharger turbines usually work under pulsating flow because of the sequential nature of engine breathing. However, existing turbine models are typically based on quasi-steady assumptions. In this paper a model where the volute is calculated in a quasi-2D scheme is presented. The objective of this work is to quantify and analyse the effect of the numerical resolution scheme used in the volute model. The conditions imposed upstream are isentropic pressure pulsations with different amplitude and frequency. The volute is computed using a finite volume approach considering the tangential and radial velocity components. The stator and rotor are assumed to be quasi-steady. In this paper, different integration and spatial reconstruction schemes are explored. The spatial reconstruction is based on the MUSCL method with different slope limiters fulfilling the TVD criterion. The model results are assessed against 3D U-RANS calculations. The results show that under low frequency pressure pulses all the schemes lead to similar solutions. But, for high frequency pulsation the results can be very different depending upon the selected scheme. This may have an impact in noise emission predictions.The authors are indebted to the Spanish Ministerio de Economia y Competitividad through Project TRA 2012-36954. The authors also wish to thank Mr. Roberto Navarro for his invaluable work during CFD simulations.Galindo, J.; Climent, H.; Tiseira Izaguirre, AO.; García-Cuevas González, LM. (2016). Effect of the numerical scheme resolution on quasi-2D simulation of an automotive radial turbine under highly pulsating flow. Journal of Computational and Applied Mathematics. 291:112-126. https://doi.org/10.1016/j.cam.2015.02.025S11212629

Prediction of the non-linear aeroelastic behavior of a cantilever flat plate and equivalent 2D model

[EN] Reducing structure weigh is one of the main strategies for decreasing environmental and manufacturing costs of engineering solutions. The reduction in material is normally related with a higher impact of aeroelastic solicitations. For some industrial cases it is needed to account for non-linear aerodynamics and, therefore, the whole fully coupled set of equations needs to be simulated in order to predict its behavior. One possible way of reducing the high computational cost associated with this problem is the use of an equivalent 2D model, whose derivation is not straightforward. This article presents a methodology for reducing the order from a complete three dimensional arbitrary beam to its equivalent 2D characteristic section. The behavior of both systems is analyzed and it is shown how, when the methodology is applied, the resulting 2D system is capable to predict similar results with a computational cost which is reduced by orders of magnitude.This project was partially supported by the Spanish company "Axial Structural Solutions" in the benchmark of a collaboration project entitled "Analysis of solar plates stability". In addition, the manuscript has been partially funded by Spanish Ministry of Science, Innovation and University through the University Faculty Training (FPU) program with reference FPU19/02201.Gil, A.; Tiseira, A.; Quintero-Igeño, P.; Cremades-Botella, A. (2021). Prediction of the non-linear aeroelastic behavior of a cantilever flat plate and equivalent 2D model. Aerospace Science and Technology. 113:1-16. https://doi.org/10.1016/j.ast.2021.106685S11611