Analysis of bifurcations in a Bénard-Marangoni problem: Gravitational effects

This article studies the linear stability of a thermoconvective problem in an annular domain for different Bond (capillarity or buoyancy effects) and Biot (heat transfer) numbers for two set of Prandtl numbers (viscosity effects). The flow is heated from below, with a linear decreasing horizontal temperature profile from the inner to the outer wall. The top surface of the domain is open to the atmosphere and the two lateral walls are adiabatic. Different kind of competing solutions appear on localized zones of the Bond-Biot plane. The boundaries of these zones are made up of co-dimension two points. A co-dimension four point has been found for the first time. The main result found in this work is that in the range of low Prandtl number studied and in low-gravity conditions, capillarity forces control the instabilities of the flow, independently of the Prandtl number. (C) 2014 Elsevier Ltd. All rights reserved.Hoyas Calvo, S.; Fajardo Peña, P.; Gil Megías, A.; Pérez Quiles, MJ. (2014). Analysis of bifurcations in a Bénard-Marangoni problem: Gravitational effects. International Journal of Heat and Mass Transfer. 73:33-41. doi:10.1016/j.ijheatmasstransfer.2014.01.061S33417

DNS of a turbulent Couette flow at constant wall transpiration up to Re-tau=1000

[EN] We present a new set of direct numerical simulation data of a turbulent plane Couette flow with constant wall-normal transpiration velocity V-0, i.e. permeable boundary conditions, such that there is blowing on the lower side and suction on the upper side. Hence, there is no net change in flux to preserve periodic boundary conditions in the streamwise direction. Simulations were performed at Re-tau = 250; 500; 1000 with varying transpiration rates in the range V-0(+) approximate to 0.03 to 0.085. Additionally, a classical Couette flow case at Re-tau = 1000 is presented for comparison. As a first key result we found a considerably extended logarithmic region of the mean velocity profile, with constant indicator function kappa = 0.77 as transpiration increases. Further, turbulent intensities are observed to decrease with increasing transpiration rate. Mean velocities and intensities collapse only in the cases where the transpiration rate is kept constant, while they are largely insensitive to friction Reynolds number variations. The long and wide characteristic stationary rolls of classical turbulent Couette flow are still present for all present DNS runs. The rolls are affected by wall transpiration, but they are not destroyed even for the largest transpiration velocity case. Spectral information indicates the prevalence of the rolls and the existence of wide structures near the blowing wall. The statistics of all simulations can be downloaded from the webpage of the Chair of Fluid Dynamics.This work was supported by the German Science Foundation (DFG) under grant number OB96/39-1. S.H. was partially supported by project ENE2015-71333-R. The work of S.K. is partially supported by the 'Excellence Initiative' of the German Federal and State Governments under the umbrella of the Graduate School of Computational Engineering at TU Darmstadt. The computations of the new simulations were made possible by a generous grant of computing time from the SuperMUC Petascale System at the Leibniz Supercomputing Centre (LRZ) under project-ID pr92la.Kraheberger, S.; Hoyas, S.; Oberlack, M. (2018). DNS of a turbulent Couette flow at constant wall transpiration up to Re-tau=1000. Journal of Fluid Mechanics. 835:421-443. https://doi.org/10.1017/jfm.2017.757S421443835Komminaho, J., Lundbladh, A., & Johansson, A. V. (1996). Very large structures in plane turbulent Couette flow. Journal of Fluid Mechanics, 320(-1), 259. doi:10.1017/s0022112096007537Avsarkisov, V., Oberlack, M., & Hoyas, S. (2014). New scaling laws for turbulent Poiseuille flow with wall transpiration. Journal of Fluid Mechanics, 746, 99-122. doi:10.1017/jfm.2014.98Hamilton, J. M., Kim, J., & Waleffe, F. (1995). Regeneration mechanisms of near-wall turbulence structures. Journal of Fluid Mechanics, 287, 317-348. doi:10.1017/s0022112095000978Pope, S. B. (2000). Turbulent Flows. doi:10.1017/cbo9780511840531Kametani, Y., Fukagata, K., Örlü, R., & Schlatter, P. (2015). Effect of uniform blowing/suction in a turbulent boundary layer at moderate Reynolds number. International Journal of Heat and Fluid Flow, 55, 132-142. doi:10.1016/j.ijheatfluidflow.2015.05.019Hoyas, S., & Jiménez, J. (2006). Scaling of the velocity fluctuations in turbulent channels up to Reτ=2003. Physics of Fluids, 18(1), 011702. doi:10.1063/1.2162185Schlatter, P., & Örlü, R. (2011). Turbulent asymptotic suction boundary layers studied by simulation. Journal of Physics: Conference Series, 318(2), 022020. doi:10.1088/1742-6596/318/2/022020Moser, R. D., Kim, J., & Mansour, N. N. (1999). Direct numerical simulation of turbulent channel flow up to Reτ=590. Physics of Fluids, 11(4), 943-945. doi:10.1063/1.869966Avsarkisov, V., Hoyas, S., Oberlack, M., & García-Galache, J. P. (2014). Turbulent plane Couette flow at moderately high Reynolds number. Journal of Fluid Mechanics, 751. doi:10.1017/jfm.2014.323Kim, J., Moin, P., & Moser, R. (1987). Turbulence statistics in fully developed channel flow at low Reynolds number. Journal of Fluid Mechanics, 177, 133-166. doi:10.1017/s0022112087000892Bech, K. H., Tillmark, N., Alfredsson, P. H., & Andersson, H. I. (1995). An investigation of turbulent plane Couette flow at low Reynolds numbers. Journal of Fluid Mechanics, 286, 291-325. doi:10.1017/s0022112095000747Lam, K., & Banerjee, S. (1992). On the condition of streak formation in a bounded turbulent flow. Physics of Fluids A: Fluid Dynamics, 4(2), 306-320. doi:10.1063/1.858306Bobke, A., Örlü, R., & Schlatter, P. (2015). Simulations of turbulent asymptotic suction boundary layers. Journal of Turbulence, 17(2), 157-180. doi:10.1080/14685248.2015.1083574CHAKRABORTY, P., BALACHANDAR, S., & ADRIAN, R. J. (2005). On the relationships between local vortex identification schemes. Journal of Fluid Mechanics, 535, 189-214. doi:10.1017/s0022112005004726Hoyas, S., & Jiménez, J. (2008). Reynolds number effects on the Reynolds-stress budgets in turbulent channels. Physics of Fluids, 20(10), 101511. doi:10.1063/1.3005862Hutchins, N., & Marusic, I. (2007). Large-scale influences in near-wall turbulence. Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, 365(1852), 647-664. doi:10.1098/rsta.2006.1942Jeong, J., & Hussain, F. (1995). On the identification of a vortex. Journal of Fluid Mechanics, 285(-1), 69. doi:10.1017/s0022112095000462JIMÉNEZ, J., UHLMANN, M., PINELLI, A., & KAWAHARA, G. (2001). Turbulent shear flow over active and passive porous surfaces. Journal of Fluid Mechanics, 442, 89-117. doi:10.1017/s0022112001004888KITOH, O., NAKABYASHI, K., & NISHIMURA, F. (2005). Experimental study on mean velocity and turbulence characteristics of plane Couette flow: low-Reynolds-number effects and large longitudinal vortical structure. Journal of Fluid Mechanics, 539(-1), 199. doi:10.1017/s0022112005005641Lee, M., & Moser, R. D. (2015). Direct numerical simulation of turbulent channel flow up to. Journal of Fluid Mechanics, 774, 395-415. doi:10.1017/jfm.2015.268Lele, S. K. (1992). Compact finite difference schemes with spectral-like resolution. Journal of Computational Physics, 103(1), 16-42. doi:10.1016/0021-9991(92)90324-rPIROZZOLI, S., BERNARDINI, M., & ORLANDI, P. (2011). Large-scale motions and inner/outer layer interactions in turbulent Couette–Poiseuille flows. Journal of Fluid Mechanics, 680, 534-563. doi:10.1017/jfm.2011.186Spalart, P. R., Moser, R. D., & Rogers, M. M. (1991). Spectral methods for the Navier-Stokes equations with one infinite and two periodic directions. Journal of Computational Physics, 96(2), 297-324. doi:10.1016/0021-9991(91)90238-gTsukahara, T., Kawamura, H., & Shingai, K. (2006). DNS of turbulent Couette flow with emphasis on the large-scale structure in the core region. Journal of Turbulence, 7, N19. doi:10.1080/14685240600609866Zhapbasbaev, U. K., & Isakhanova, G. Z. (1998). Developed turbulent flow in a plane channel with simultaneous injection through one porous wall and suction through the other. Journal of Applied Mechanics and Technical Physics, 39(1), 53-59. doi:10.1007/bf02467997DEL LAMO, J. C., JIMNEZ, J., ZANDONADE, P., & MOSER, R. D. (2004). Scaling of the energy spectra of turbulent channels. Journal of Fluid Mechanics, 500, 135-144. doi:10.1017/s002211200300733xKitoh, O., & Umeki, M. (2008). Experimental study on large-scale streak structure in the core region of turbulent plane Couette flow. Physics of Fluids, 20(2), 025107. doi:10.1063/1.2844476Del ÁLAMO, J. C., JIMÉNEZ, J., ZANDONADE, P., & MOSER, R. D. (2006). Self-similar vortex clusters in the turbulent logarithmic region. Journal of Fluid Mechanics, 561, 329. doi:10.1017/s0022112006000814Sumitani, Y., & Kasagi, N. (1995). Direct numerical simulation of turbulent transport with uniform wall injection and suction. AIAA Journal, 33(7), 1220-1228. doi:10.2514/3.12363Tillmark, N. 1995 Experiments on transition and turbulence in plane Couette flow. PhD thesis, KTH, Royal Institute of Technology.Pirozzoli, S., Bernardini, M., & Orlandi, P. (2014). Turbulence statistics in Couette flow at high Reynolds number. Journal of Fluid Mechanics, 758, 327-343. doi:10.1017/jfm.2014.52

Effect of the horizontal aspect ratio on thermocapillary convection stability in annular pool with surface heat dissipation

[EN] A linear stability analysis of the thermoconvective problem of a thin liquid film contained in an annular domain has been conducted. The influence of the horizontal aspect ratio on the solution has been considered by keeping a fixed external wall while the internal radius of the annular domain was modified. The parameter used in the study, Gamma(h), has been defined as the ratio of the internal radius to the domain depth. The other control parameter of the study is the Prandtl number ranging from 0.7 to 50, i.e. characteristic of fluids as air to n-butanol. The study has been performed for different Bond (Bo) regimes ranging from 0.0 for surface tension dominated flows to 67 for buoyancy dominated ones. Three different kind of bifurcations are found in the Gamma(h) - Pr plane for large Bonds, while for low Bonds only two of them appear. In the case of pure buoyancy or surface tension flows, for every Gamma(h) there exists a Prandtl number such that oscillatory and stationary coexist in a co-dimension two bifurcation point. These transitions show a strong dependency with the Bond number. Indeed, the lower transition disappears for low Bo and the upper one disappears with intermediate Bo values. Furthermore, there is a non-linear dependency of the number of structures of the growing bifurcation with Gamma(h). These co-dimension two lines show a strong dependency with Bo. Firstly, looking at the frontier between HWI and LR regions, for large Bo numbers, Pr increases with Gamma(h), while for low Bo the trend is reversed. Additionally, this transition only appears in the extreme Bo cases, for the central values of the considered, no transition is found. Similarly, the second transition found only appears for Bo larger than 30.SH and MJPQ work have been supported by project RTI2018-102256-B-I00 of Mineco/FEDER. PF work has been partially supported by the Spain's National Research and Development Plan (Project ESP2016-75887) and by the CHEOPS project (Grant Agreement 730135). This work was supported by a generous grant of computer time from the supercomputing center of the UPV.López-Núñez, E.; Pérez Quiles, MJ.; Fajardo, P.; Hoyas, S. (2020). Effect of the horizontal aspect ratio on thermocapillary convection stability in annular pool with surface heat dissipation. International Journal of Heat and Mass Transfer. 148:1-8. https://doi.org/10.1016/j.ijheatmasstransfer.2019.119140S1814

CFD Simulation of a Hyperloop Capsule Inside a Low-Pressure Environment Using an Aerodynamic Compressor as Propulsion and Drag Reduction Method

[EN] One of the most restrictive conditions in ground transportation at high speeds is aerodynamic drag. This is even more problematic when running inside a tunnel, where compressible phenomena such as wave propagation, shock waves, or flow blocking can happen. Considering Evacuated-Tube Trains (ETTs) or hyperloops, these effects appear during the whole route, as they always operate in a closed environment. Then, one of the concerns is the size of the tunnel, as it directly affects the cost of the infrastructure. When the tube size decreases with a constant section of the vehicle, the power consumption increases exponentially, as the Kantrowitz limit is surpassed. This can be mitigated when adding a compressor to the vehicle as a means of propulsion. The turbomachinery increases the pressure of part of the air faced by the vehicle, thus delaying the critical conditions on surrounding flow. With tunnels using a blockage ratio of 0.5 or higher, the reported reduction in the power consumption is 70%. Additionally, the induced pressure in front of the capsule became a negligible effect. The analysis of the flow shows that the compressor can remove the shock waves downstream and thus allows operation above the Kantrowitz limit. Actually, for a vehicle speed of 700 km/h, the case without a compressor reaches critical conditions at a blockage ratio of 0.18, which is a tunnel even smaller than those used for High-Speed Rails (0.23). When aerodynamic propulsion is used, sonic Mach numbers are reached above a blockage ratio of 0.5. A direct effect is that cases with turbomachinery can operate in tunnels with blockage ratios even 2.8 times higher than the non-compressor cases, enabling a considerable reduction in the size of the tunnel without affecting the performance. This work, after conducting bibliographic research, presents the geometry, mesh, and setup. Later, results for the flow without compressor are shown. Finally, it is discussed how the addition of the compressor improves the flow behavior and power consumption of the case.This research was funded by Mineco/FEDER grant number RTI2018-102256-B-I00 and the author Federico Lluesma-Rodriguez was partially funded by Ministerio de Ciencia, Innovacion y Universidades under the grant "Doctorandos Industriales" number DI-17-09616.Lluesma-Rodríguez, F.; Gonzalez, T.; Hoyas, S. (2021). CFD Simulation of a Hyperloop Capsule Inside a Low-Pressure Environment Using an Aerodynamic Compressor as Propulsion and Drag Reduction Method. Applied Sciences. 11(9):1-21. https://doi.org/10.3390/app11093934S12111

CFD simulation of a hyperloop capsule inside a closed environment

[EN] One of the most restrictive conditions in ground transportation is traveling through a tunnel at high speed. In those conditions waves are propagated, increasing the pressure upstream the object, and so, the drag compared to the open flow case. Although this drawback is mitigated with larger tunnels, another proposed solution is to decrease the pressure inside the tunnel. In this paper it is demonstrated that the drag coefficient is almost invariant with the pressure conditions. This effect allows, not only to have smaller tunnels with respect to the existing for standard trains, but also to enhance the speed of the train without increasing its aerodynamic losses.SH and FLR work have been supported by project RTI2018-102256-B-I00 of Mineco/FEDER. FLR is partially funded buy MCIU under grant DI-17-09616.Lluesma-Rodríguez, F.; González, T.; Hoyas, S. (2021). CFD simulation of a hyperloop capsule inside a closed environment. Results in Engineering. 9:1-3. https://doi.org/10.1016/j.rineng.2020.10019613

Evidences of persisting thermal structures in Couette flows

[EN] DNS of passive thermal turbulent Couette flow at several friction Reynolds numbers (180, 250, and 500), and the Prandtl number of air are presented. The time averaged thermal flow shows the existence of long and wide thermal structures never described before in Couette flows. These thermal structures, named CTFS (Couette Thermal Flow Superstructures), are defined as coherent regions of hot and cold temperature fluctuations. They are intrinsically linked to the velocity structures present in Couette flows. Two different 2D symmetries can be recognized, which get stronger with the Reynolds number. These structures do not affect the mean flow or mean quantities as the Nusselt number. However, turbulent intensities and thermal fluxes depend on the width of the structures, mainly far from the walls. Since the width of the structures is related to the channel width, the statistics of thermal Couette flow are to some point box-dependent.This work was supported by the MINECO/FEDER, under project ENE2015-71333-R. The computations of the new simulations were made possible by a generous grant of computing time from the Barcelona Supercomputing Centre, reference FI-2018-1-0037. FAA is partially funded by GVA/FEDER project ACIF2018. We are very grateful for the advices and revision provided by one of the referees of the article, as it has helped to enrich its content.Alcántara-Ávila, F.; Gandía-Barberá, S.; Hoyas, S. (2019). Evidences of persisting thermal structures in Couette flows. International Journal of Heat and Fluid Flow. 76:287-295. https://doi.org/10.1016/j.ijheatfluidflow.2019.03.001S2872957

A moving mesh generation strategy for solving an injector internal flow problem

[EN] The ability to handle complex geometries is an important part of transient calculations; therefore, the need for fully automatic mesh generation capable of dealing with such geometries is quite demanded. In this paper a specific approach to fully automatic three-dimensional mesh generation is presented. An approach to moving the generated mesh is also outlined. In particular, the simulation of a diesel injector needle movement is sought. The movement of the needle was calculated on the basis of injection rate experimental data and injection rate predicted data with steady state boundaries and geometry. The simulation was performed using the commercial code STAR-CD version 4.06. (C) 2010 Elsevier Ltd. All rights reserved.This research was funded by the Spanish Government in the framework of the Project "Caracterizacion experimental de la cavitacion en el flujo interno e influencia sobre modelos de chorro Diesel'', Reference TRA2007-68006-C02-01. SH and PF were partially supported by the Universidad Politecnica de Valencia under the program "Primeros Proyectos de investigacion'', in the framework of the project "Simulacion CFD de chorros Diesel en inyeccion directa: la atomizacion primaria'', Reference PAID-2759.Margot, X.; Hoyas, S.; Fajardo, P.; Patouna, S. (2010). A moving mesh generation strategy for solving an injector internal flow problem. Mathematical and Computer Modelling. 52:1143-1150. doi:10.1016/j.mcm.2010.03.018S114311505

URANS Analysis of a Launch Vehicle Aero-Acoustic Environment

[EN] Predicting and mitigating acoustic levels become critical because of the harsh acoustic environment during space vehicle lift-off. This paper aimed to study the aero-acoustic environment during a rocket lift-off. The sound propagation within a launch event was studied using dedicated computational fluid dynamics (CFD). The resolution of all the phenomena that occur is unfeasible. We discuss the turbulence simplification and propose a feasible simulation through an unsteady Reynolds-averaged Navier¿Stokes (URANS) model. The results were validated with experimental data showing a good correlation near the fairing surface and an improvable accuracy in the far field. To assess noise generation, the main shock waves were identified, and the evolution of the generated sound pressure was assessed. Moreover, vertical directivity was revealed by data analysis of the pressure field surrounding the fairing.This research was funded by the European Space Agency of Project REDLAUCH: Launch Sound Level Reduction under contract 4000126316/19/NL/LvH. The work was supported by the MICINN (grants: DIN2019-010877 and RTI2018-102256-B-100) and by the Barcelona Supercomputing Center under Project IM-2021-2-0017 Rocket launch aeroacoustics.Escartí-Guillem, MS.; García-Raffi, LM.; Hoyas, S. (2022). URANS Analysis of a Launch Vehicle Aero-Acoustic Environment. Applied Sciences. 12(7):1-9. https://doi.org/10.3390/app120733561912

Influence of geometrical parameters on the linear stability of a Benard-Marangoni problem

[EN] A linear stability analysis of a thin liquid film flowing over a plate is performed. The analysis is performed in an annular domain when momentum diffusivity and thermal diffusivity are comparable (relatively low Prandtl number, Pr = 1.2). The influence of the aspect ratio (Gamma) and gravity, through the Bond number (Bo), in the linear stability of the flow are analyzed together. Two different regions in the Gamma-Bo plane have been identified. In the first one the basic state presents a linear regime (in which the temperature gradient does not change sign with r). In the second one, the flow presents a nonlinear regime, also called return flow. A great diversity of bifurcations have been found just by changing the domain depth d. The results obtained in this work are in agreement with some reported experiments, and give a deeper insight into the effect of physical parameters on bifurcations.The computations shown in this work were made possible by a generous grant of computer time from the supercomputation center of the Universitat Politecnica de Valencia.Hoyas, S.; Fajardo, P.; Pérez Quiles, MJ. (2016). Influence of geometrical parameters on the linear stability of a Benard-Marangoni problem. Physical Review E. 93(4). https://doi.org/10.1103/PhysRevE.93.043105S934Bénard, H. (1901). Les tourbillons cellulaires dans une nappe liquide. - Méthodes optiques d’observation et d’enregistrement. Journal de Physique Théorique et Appliquée, 10(1), 254-266. doi:10.1051/jphystap:0190100100025400Smith, M. K., & Davis, S. H. (1983). Instabilities of dynamic thermocapillary liquid layers. Part 1. Convective instabilities. Journal of Fluid Mechanics, 132, 119-144. doi:10.1017/s0022112083001512Garnier, N., & Chiffaudel, A. (2001). Two dimensional hydrothermal waves in an extended cylindrical vessel. The European Physical Journal B, 19(1), 87-95. doi:10.1007/s100510170352Hoyas, S., Herrero, H., & Mancho, A. M. (2002). Bifurcation diversity of dynamic thermocapillary liquid layers. Physical Review E, 66(5). doi:10.1103/physreve.66.057301Hoyas, S., Herrero, H., & Mancho, A. M. (2002). Thermal convection in a cylindrical annulus heated laterally. Journal of Physics A: Mathematical and General, 35(18), 4067-4083. doi:10.1088/0305-4470/35/18/306Hoyas, S., Mancho, A. M., Herrero, H., Garnier, N., & Chiffaudel, A. (2005). Bénard–Marangoni convection in a differentially heated cylindrical cavity. Physics of Fluids, 17(5), 054104. doi:10.1063/1.1876892Herrero, H., & Mancho, A. M. (1998). Influence of aspect ratio in convection due to nonuniform heating. Physical Review E, 57(6), 7336-7339. doi:10.1103/physreve.57.7336Mancho, A., Herrero, H., & Burguete, J. (1997). Primary instabilities in convective cells due to nonuniform heating. Physical Review E, 56(3), 2916-2923. doi:10.1103/physreve.56.2916Ezersky, A. B., Garcimartín, A., Burguete, J., Mancini, H. L., & Pérez-García, C. (1993). Hydrothermal waves in Marangoni convection in a cylindrical container. Physical Review E, 47(2), 1126-1131. doi:10.1103/physreve.47.1126Hoyas, S., Gil, A., Fajardo, P., & Pérez-Quiles, M. J. (2013). Codimension-three bifurcations in a Bénard-Marangoni problem. Physical Review E, 88(1). doi:10.1103/physreve.88.015001Peng, L., Li, Y.-R., Shi, W.-Y., & Imaishi, N. (2007). Three-dimensional thermocapillary–buoyancy flow of silicone oil in a differentially heated annular pool. International Journal of Heat and Mass Transfer, 50(5-6), 872-880. doi:10.1016/j.ijheatmasstransfer.2006.08.015Shi, W., Liu, X., Li, G., Li, Y.-R., Peng, L., Ermakov, M. K., & Imaishi, N. (2010). Thermocapillary Convection Instability in Shallow Annular Pools by Linear Stability Analysis. Journal of Superconductivity and Novel Magnetism, 23(6), 1185-1188. doi:10.1007/s10948-010-0661-8Torregrosa, A. J., Hoyas, S., Pérez-Quiles, M. J., & Mompó-Laborda, J. M. (2013). Bifurcation Diversity in an Annular Pool Heated from Below: Prandtl and Biot Numbers Effects. Communications in Computational Physics, 13(2), 428-441. doi:10.4208/cicp.090611.170212aEckert, E. R. G., Goldstein, R. J., Ibele, W. E., Patankar, S. V., Simon, T. W., Kuehn, T. H., … Garrick, S. (2000). Heat transfer — a review of 1997 literature. International Journal of Heat and Mass Transfer, 43(14), 2431-2528. doi:10.1016/s0017-9310(99)00196-9Hoyas, S., Fajardo, P., Gil, A., & Perez-Quiles, M. J. (2014). Analysis of bifurcations in a Bénard–Marangoni problem: Gravitational effects. International Journal of Heat and Mass Transfer, 73, 33-41. doi:10.1016/j.ijheatmasstransfer.2014.01.061O’Shaughnessy, S. M., & Robinson, A. J. (2013). Heat transfer near an isolated hemispherical gas bubble: The combined influence of thermocapillarity and buoyancy. International Journal of Heat and Mass Transfer, 62, 422-434. doi:10.1016/j.ijheatmasstransfer.2013.02.064Celli, M., Barletta, A., & Alves, L. S. de B. (2015). Marangoni instability of a liquid film flow with viscous dissipation. Physical Review E, 91(2). doi:10.1103/physreve.91.023006Orszag, S. A. (1972). Comparison of Pseudospectral and Spectral Approximation. Studies in Applied Mathematics, 51(3), 253-259. doi:10.1002/sapm1972513253Canuto, C., Hussaini, M. Y., Quarteroni, A., & Zang, T. A. (1988). Spectral Methods in Fluid Dynamics. doi:10.1007/978-3-642-84108-8JIMÉNEZ, J., & HOYAS, S. (2008). Turbulent fluctuations above the buffer layer of wall-bounded flows. Journal of Fluid Mechanics, 611, 215-236. doi:10.1017/s0022112008002747Mancho, A. M., & Herrero, H. (2000). Instabilities in a laterally heated liquid layer. Physics of Fluids, 12(5), 1044-1051. doi:10.1063/1.870359Favre, E., Blumenfeld, L., & Daviaud, F. (1997). Instabilities of a liquid layer locally heated on its free surface. Physics of Fluids, 9(5), 1473-1475. doi:10.1063/1.869470Burguete, J., Mukolobwiez, N., Daviaud, F., Garnier, N., & Chiffaudel, A. (2001). Buoyant-thermocapillary instabilities in extended liquid layers subjected to a horizontal temperature gradient. Physics of Fluids, 13(10), 2773-2787. doi:10.1063/1.1398536Daviaud, F., & Vince, J. M. (1993). Traveling waves in a fluid layer subjected to a horizontal temperature gradient. Physical Review E, 48(6), 4432-4436. doi:10.1103/physreve.48.4432RILEY, R. J., & NEITZEL, G. P. (1998). Instability of thermocapillary–buoyancy convection in shallow layers. Part 1. Characterization of steady and oscillatory instabilities. Journal of Fluid Mechanics, 359, 143-164. doi:10.1017/s0022112097008343Mercier, J. F., & Normand, C. (1996). Buoyant‐thermocapillary instabilities of differentially heated liquid layers. Physics of Fluids, 8(6), 1433-1445. doi:10.1063/1.868920Yu, J.-J., Ruan, D.-F., Li, Y.-R., & Chen, J.-C. (2015). Experimental study on thermocapillary convection of binary mixture in a shallow annular pool with radial temperature gradient. Experimental Thermal and Fluid Science, 61, 79-86. doi:10.1016/j.expthermflusci.2014.10.01

Set-up analysis and Optimization of CFD Simulations for Radial Turbines

[EN] This paper proposes a CFD method for simulating radial turbocharger turbine flows. A review is presented of the computational model in terms of meshing, mesh movement strategy, and computational algorithm in turbomachinery CFD simulations. A novel local mesh independence analysis is developed for this purpose. This procedure is aimed at distributing the cells more efficiently by selecting suitable cell sizes for the different regions of the domain to optimize the use of the available computational resources. Pressure- and density-based solvers are compared. The influence of the moving-mesh strategy was analyzed, and small differences were observed in the region near the maximum efficiency point, while these differences increased when off-design conditions were considered. Finally, a comparison of the results with data from an experimental test bench shows that the proposed computational methodology can be used to characterize radial turbomachinery. The objective of the analysis and the optimization of the case configuration was to establish some general guidelines for CFD turbomachinery simulations.The authors are indebted to the Spanish Ministerio de Econom a y Competitividad through Project TRA 2010-16205.Galindo, J.; Hoyas, S.; Fajardo, P.; Navarro, R. (2013). Set-up analysis and Optimization of CFD Simulations for Radial Turbines. Engineering Applications of Computational Fluid Mechanics. 7(4):441-460. doi:10.1080/19942060.2013.11015484S44146074ANSYS (2009).Ansys Fluent 12.0 User’s Guide. Canonsburg, PA: ANSYS Inc.ANSYS (2011).ANSYS FLUENT Theory Guide. ANSYS Inc.Aymanns R, Scharf J, Uhlmann T, Lückmann D (2011). A revision of quasi steady modelling of turbocharger turbines in the simulation of pulse charged engines.16th Supercharging Conference.Hellström F (2010).Numerical Computations of the Unsteady Flow in Turbochargers. PhD thesis, Royal Institute of Technology KTH Fluid Physics.Hiereth H, Prenninger P (2007).Charging the Internal Combustion Engine. Springer Verlag.Japikse D, Baines NC (1997).Introduction to Turbomachinery. Oxford University Press.Liu Z, Hill DL (2000). Issues surrounding multiple frames of reference models for turbo compressor applications.Fifteenth International Compressor Engineering Conference, Purdue University, USA