- Desenvolupar recerca a l'àmbit de les Enginyeries Mecànica i Aeroespacial, utilitzant tècniques numèriques (High Performance Computign) i experimentals. - Realitzar Transferència de Tecnologia amb les empreses del nostre entorn immediat i per extensió a tota la Unió Europea. - Incentivar la participació en projectes competitius nacionals i internacionals, com a part important de la recerca bàsica i aplicada necessària per assolir l'excel·lència a la recerca. - Projectar els resultats de la recerca a l'àmbit de la docència de Grau, Màster i als programes de Doctorat vinculats al Grup, contribuint d'aquesta manera a millorar-ne la qualitat.
Direct Steam Generation (DSG) is one of the most promising alternatives for parabolic trough solar plants to replace the synthetic oil and reduce the electricity cost. The focus of this work is to develop a comprehensive optical and thermo-hydraulic model for the performance prediction of DSG process under real operating conditions. Pressure drop and heat transfer characteristics are determined considering the effect of the non-uniform heat flux distribution due to the concentration of the sunlight. A numerical-geometrical method based on ray trace and finite volume method techniques is used to determine the solar flux distribution around the absorber tube with high accuracy. A heat transfer model based on energy balance is applied to predict the thermal performances of the different flow regimes in the DSG loop. The thermo-hydraulic behavior of the different DSG sections i.e. preheating, evaporation and superheating is investigated under different operating conditions. The validity of the model has been tested by being compared with experimental data from DISS test facility and other available models in the literature. The study also presents a comparative study of the effect of different parameters on the thermal gradient around the absorber tube. The analysis shows that the highest thermal gradient is occurring in the superheating section with a high risk of thermal bending and a potential damage risk. The model is also capable to evaluate the efficiency of a DSG loop for different conditions and help to take the appropriate control strategies to avoid flow instabilities in the DSG rows.
El presente libro es fruto de la experiencia adquirida durante toda una carrera universitaria. Esta obra está diseñada para presentar los principios básicos de la Mecánica de Fluidos de una manera clara y muy sencilla. Muchos de los problemas que se exponen fueron, en su momento, problemas de examen de la asignatura. Asimismo, pretende ser un libro de repaso para quienes, precisen fijar determinados conceptos sobre la materia. Finalmente, se desea que esta obra sirva de apoyo a todas las escuelas de los países de habla hispana que imparten las diversas Ingenierías. Espero y deseo que este libro sea un instrumento útil de repaso de la temática presentada.
Rodriguez, I.; Lehmkuhl, O.; Piomelli, U.; Chiva, J.; Borrell, R.; Oliva, A. Flow turbulence and combustion Vol. 99, num. 3-4, p. 729-763 DOI: 10.1007/s10494-017-9866-2 Data de publicació: 2017-10-27 Article en revista
This paper investigates the effects of surface roughness on the flow past a circular cylinder at subcritical to transcritical Reynolds numbers. Large eddy simulations of the flow for sand grain roughness of size k/D = 0.02 are performed (D is the cylinder diameter). Results show that surface roughness triggers the transition to turbulence in the boundary layer at all Reynolds numbers, thus leading to an early separation caused by the increased momentum deficit, especially at transcritical Reynolds numbers. Even at subcritical Reynolds numbers, boundary layer instabilities are triggered in the roughness sublayer and eventually lead to the transition to turbulence. The early separation at transcritical Reynolds numbers leads to a wake topology similar to that of the subcritical regime, resulting in an increased drag coefficient and lower Strouhal number. Turbulent statistics in the wake are also affected by roughness; the Reynolds stresses are larger due to the increased turbulent kinetic energy production in the boundary layer and separated shear layers close to the cylinder shoulders.
An, B.; Bergadà, J.M.; Mushyam, A. International Conference on Computational and Mathematical Methods in Science and Engineering p. 114-122 Data de presentació: 2017-07-08 Presentació treball a congrés
In the present paper it is presented the flow around a 2D square cylinder which is located downstream of a splitter plate and at a certain distance of it. The fluid velocity below and above the splitter plate is different, several velocity ratios are considered, it is interesting to see that the downstream vortex shedding frequency and amplitude highly depends on the velocity ratio defined upstream. So far, the Reynolds numbers evaluated fall into the laminar unsteady regime, yet the interaction between the upstream mixing layer and the wake generate fully different downstream vortex shedding for different upstream velocity ratios, lift, drag and Strouhal numbers are as well highly dependent on the velocity ratios. In the present paper, the comparison between the results obtained via CFD finite volumes and Lattice Boltzmann Method are being presented. For these initial cases studied the agreement is very good.
Prakash, B.; Mellibovsky, F.; Bergadà, J.M. International Conference on Computational and Mathematical Methods in Science and Engineering p. 1712-1721 Data de presentació: 2017-07-07 Presentació treball a congrés
Active Flow Control is implemented over NACA 2412 airfoil using Steady Suctionand Steady Blowing techniques. The pre-stall angle of attack (AOA) 12 0 is studied at a high Reynolds number (Re chord ) of 3.1*10 6 for two-dimensional, incompressible and steady flow conditions. A wide range of parametric value set is considered for Slot location (l s ), Velocity magnitude ratio (U j /U 0 ), slot width (w) and angle of perturbation (ß) using both steady suction and steady blowing independently. The numerical modeling is done using the corresponding solver in OpenFOAM, an open source CFD framework. The turbulence modeling is done using Reynolds Averaged Navier Stokes (RANS) equations, specifically k-k l -¿ model implementation in OpenFOAM. The impact of the parametric set on aerodynamic coefficients, lift (C l ) and drag( C d ), and flow separation is illustrated. Along with, the relevant boundary layer physics are explained.
Miro, A.; Soria, M.; Rodriguez, I.; Cajas, J. International Conference on Computational and Mathematical Methods in Science and Engineering p. 1492-1503 Data de presentació: 2017-07-07 Presentació treball a congrés
Synthetic jet actuators (SJA) consist of a cavity with a mechanically moving diaphragm, whose actuation causes external fluid to enter and leave through a small orifice resulting in a net jet able to transfer of kinetic energy and momentum to a fluid medium without the addition of external flow. They are expected to play a key role in active flow control (the application that motivates the present study), cooling and mixing.
This paper is focused on the interaction between the flow inside the actuator cavity and the external flow. Solving the coupling between the flow inside the actuator cavity and the external flow. Solving the coupling between the internal and external flows adds considerable complication and cost. It would be of interest to characterize the SJA outlet velocity and implement it as boundary condition. To invetigate the accuracy of this approach, an impinging jet, configuration has been implemented with three different models: cavity and moving surface, cavity and imposed velocity at the outlet. Time and phase averages of the external flows obtained with the different implementation are compared, and the effect of three different models is discussed.
Summ, T.; Prakash, B.; Bergadà, J.M.; Wierschem, A.; Mellibovsky, F. International Conference on Computational and Mathematical Methods in Science and Engineering p. 1954-1964 Data de presentació: 2017-07-07 Presentació treball a congrés
The NACA 2412 profile was numerically studied via employing 2D-DNS and implementing Active Flow Control (AFC), the Reynolds number considered was 6757, being the angle of attack of 8º. Initially, the basic flow without implementing AFC was considered, the point in which the boundary layer separates as well as the y+ value along the profile length were evaluated. A single groove location, just before the separation point, was considered, periodic forcing was employed to both modify the location of the separation point and change the separation area where vortices are present. This was undertaken resulting in a reduction of the drag coefficient while increasing the lift. Via studying a set of frequencies and amplitudes linked with the AFC periodic actuation, it was obtained the optimum set of parameters to minimize the drag while maximizing the lift.
Baghaei, M.; Bergadà, J.M.; Del Campo, D. International Conference on Computational and Mathematical Methods in Science and Engineering p. 166-176 Data de presentació: 2017-07-07 Presentació treball a congrés
When aimed to modify the downstream vortex shedding of a given bluff body, whether any road vehicle or wing profile, the use of Active Flow Control (AFC) appears to be an efficient technology. Among the different (AFC) methodologies the use of periodic forcing is ment to have better efficiency since it requires less energy to activate the shear layer, the reason behind this efficiency lies on the fact that periodic forcing interacts with the shear layer natural instabilites. In the present paper, one of the devices widely emloyed to generate pulsating flow, is carefully studied via 3D-CFD and using OpenFOAM. Initially the base flow is being determined and compared with previous experimental results, in a second step several internal dimensions of the fluidic actuator are being modified to characterize the output frequency and amplitude variations, among the conclusions obtained it is found that a given fluidic actuator is capable of generating several output frequencies and amplitudes when modifying some internal dimensions while maintaining a constant incoming flow Reynolds number.
The world airport network (WAN) is one of the networked infrastructures that shape today's economic and social activity, so its resilience against incidents affecting the WAN is an important problem. In this paper, the robustness of air route networks is extended by defining and testing several heuristics to define selection criteria to detect the critical nodes of the WAN. In addition to heuristics based on genetic algorithms and simulated annealing, custom heuristics based on node damage and node betweenness are defined. The most effective heuristic is a multi-attack heuristic combining both custom heuristics. Results obtained are of importance not only for advance in the understanding of the structure of complex networks, but also for critical node detection.
The turbulent flow around a circular cylinder has been investigated at Re=5000Re=5000 using direct numerical simulations. Low frequency behavior, vortex undulation, vortex splitting, vortex dislocations and three dimensional flow within the wake were found to happen at this flow regime. In order to successfully capture the wake three dimensionality, different span-wise lengths were considered. It was found that a length LZ=2pDLZ=2pD was enough to capture this behavior, correctly predicting different aspects of the flow such as drag coefficient, Strouhal number and pressure and velocity distributions when compared to experimental values. Two instability mechanisms were found to coexist in the present case study: a global type instability originating in the shear layer, which shows a characteristic frequency, and a convective type instability that seems to be constantly present in the near wake. Characteristics of both types of instabilities are identified and discussed in detail. As suggested by Norberg, a resonance-type effect takes place in the vortex formation region, as the coexistence of both instability mechanisms result in distorted vortex tubes. However, vortex coherence is never lost within the wake.
The conventional rotor spinning unit generates flow vortices in the transfer channel upstream region which affect the fiber configuration and consequently yarn properties. Geometry and spinning parameters such as transfer channel length, inlet width, rotor outlet pressure, opening roller speed, and diameter were found to be key parameters influencing airflow characteristics. To reduce the flow vortices in the upper stream region, modifications of the transfer channel were proposed, and their airflow fields were analyzed using computational fluid dynamics. Three designs were studied: a round transfer channel inlet, a bypass channel for extra air supply, and one with both the bypass and the round inlet. Analysis of airflow revealed that the design with both round transfer channel inlet and a bypass proved to be very effective in properly directing the flow and minimizing vortices. The design was also characterized by smoother velocity streamlines and maximum mass flow across the transfer channel. A conventional rotor spinning unit was modified in which a round transfer channel inlet corner and a bypass channel were utilized to conduct the experimental tests. Three sets of yarn samples were produced using the conventional and modified rotor spinning units under different rotor speed conditions. Yarn properties were tested. Properties such as tenacity, CVm%, and thin and thick places of the spun yarns produced by the new design improved compared to that of the conventional yarn.
Mellibovsky, F.; Bergadà, J.M.; Prat, J.; Prat-Farran,J.A. ; Prat, J.A.; Carbonell, M.; Soria, M.; Mas de les Valls, E.; Notti, E.; Del Campo, D.; Sala, A.; Avila-Cañellas, M. Projecte R+D+I competitiu