Modelling the squeeze flow in a deformed rectangular microchannel

Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech.Rheinforce cork composites, previously named elsewhere as CorkSTFluidics [1], are sandwiches consis?ng of two microagglomerated cork pads embedding microfluidic paCerns that are filled with a shear thickening fluid (see Figure 1 (a)), whose mechanical performance under impact loads is determined by the microfluidic paCern and the rheological proper?es of the fluid [2]. From the experimental results it is impossible to decouple the fluid contribu?on from the solid contribu?on to the force?me response of the composite. In this work, we have developed a simple model of the fluid-flow dynamics that it is able to predict the fluid contribu?on in the energy dissipa?on of the Rheinforce cork composites under impact loads. To that end, we model the viscous flow inside a microchannel for a known displacement of the upper lid h(t, x), calcula?ng as a result the needed force to create that movement

Transition to turbulence in the bottom boundary layer under a solitary wave.

Se estudia la transición a la turbulencia en una capa límite oscilatoria.Se estudia la transición a la turbulencia en una capa límite oscilatoria.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Theoretical parameters of trailing vortices versus aspect ratio of wing models

We perform 2D-PIV measurements to characterize trailing vortices in NACA0012 wing models for aspect ratios ranging between 1 and 2.5, and for chord-based Reynolds numbers from 7000 to 40000. Firstly, and regarding the influence of the Reynolds number, the increase of this dimensionless parameter generates a more concentrated and intense vortex, presenting, therefore, an increase in all its characteristic magnitudes: maximum azimuthal velocity and vorticity. Secondly, the greater the aspect ratio, the greater the vortex strength is observed. Thirdly, the radial location of the peak of the azimuthal velocity has a strong decay as the aspect ratio increases for Re=7000, but it changes its trend for Re=40000.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech.. Ministerio de Economía y Competitividad (Spain) Grant No. DPI2013-40479-P and DPI2016-76151-C2-1-R and Junta de Andalucía Grant No. P11-TEP-7776

Stability analysis of flow structures in hovering using robotic experiments and flow visualizations

We investigate the kinematics and stability of hovering flight making use of a robotic experimental device that simulate the movement of insects or birds. We carried out this analysis based on the characterization of this movement with flow visualizations and particle image velocimetry -PIV-. First, we characterized the kinematics of the robotic device inside water. Therefore, it has been verified that the robotic experiments follow the desired input signal precisely. Second, we give qualitative and quantitative information from the experimental tests as a function of frequency and angular amplitude. The kinematics of the hovering flight produces vortices that are stable or unstable around the rigid flat plate, as well as one transient regime that has been also found between these two latter states. Finally, dimensional velocity field plus associated vorticity have been characterized in these flow regimes through PIV measurements, and we also validated the reproducibility of experiment finding excellent agreement between different set of experiments.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tec

Nonlinear evolution of harmonically forced perturbations on a wingtip vortex

Wingtip vortices are created by flying airplanes due to lift generation. The vortex interaction with the trailing aircraft has sparked researchers’ interest to develop an efficient technique to destroy these vortices. Different models have been used to describe the vortex dynamics and they all show that, under real flight conditions, the most unstable modes produce a very weak amplification. Another linear instability mechanism that can produce high energy gains in short times is due to the non-normality of the system. Recently, it has been shown that these non-normal perturbations also produce this energy growth when they are excited with harmonic forcing functions. In this study, we analyze numerically the nonlinear evolution of a spatially, pointwise and temporally forced perturbation, generated by a synthetic jet at a given radial distance from the vortex core. This type of perturbation is able to produce high energy gains in the perturbed base flow (10^3), and is also a suitable candidate for use in engineering applications. The flow field is solved for using fully nonlinear three-dimensional direct numerical simulation with a spectral multidomain penalty method model. Our novel results show that the nonlinear effects are able to produce locally small bursts of instability that reduce the intensity of the primary vortex.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Modeling the external flow of a novel HorseShoe receiver and the evaluation of thermal performance

The linear receiver of a Parabolic Trough Collector is the most critical element in the entire system. The Universal Vacuum Air Collector concept is the most extended type of receiver in both experimental and industrial facilities. Besides their considerable cost, their efficiency usually drops as operation time passes. This is mainly due to a partial loss of vacuum in the evacuated annulus between the absorber and the glass cover. An alternative design called HorseShoe receiver is proposed in this work, whose main goal is to maintain the thermal performance throughout its entire lifespan. This innovative receiver is indicated for low-to-medium temperature ranges, which is particularly suitable for solar heat for industrial processes. It consists of a horseshoe-like cavity absorber having its upper border insulated. In addition, two main advantages can be taken by using two symmetric lenses as glass cover: reconcentrate solar radiation into the cavity (improvement of the intercept factor) and protect stratification conditions (reduction of thermal losses). A transient numerical model with customized boundary conditions has been implemented to evaluate both thermal performance and temperature difference in the absorber domain, which is critical for the thermal stress conditions. For that purpose and as a key contribution, not only the Heat Transfer Fluid (HTF) temperature but also the heat transfer coefficient in the duct are set. In particular, HTF temperature ranges from 80 °C to 220 °C and the inner heat transfer coefficient from 600 W/(mK) to 1800 W/(mK). Results show that numerical thermal performance is above 96%, which is mainly due to the reduction of thermal radiation losses, where the absorber active surface emittance is . (...)Second (corresponding) author J.J. Serrano-Aguilera acknowledges the support provided by Junta de Andalucía (Government of Andalusia) and Universidad de Málaga for the source of funding for the HERTERSOL project (UMA18-FEDERJA-195), as well as to Ministerio de Ciencia, Innovación Universidades (Spain) by means of the postdoc position: Ref No. FJCI-2017-32403 (Juan de la Cierva-Formación Postdoc Grant). Third author acknowledges the support of Universidad de Málaga, Spain through the Project WALICON, 2021. Authors also acknowledge funding for open access charge: Universidad de Málaga / CBUA

Wingtip vortex in a NACA0012 airfoil and its active control

Contribución mediante sesión pósterWe conduct experiments in a towing-tank to analyse the flow patterns of wingtip vortices in a NACA 0012 airfoil. In this experimental research, we provide PIV measurements and flow visualisations. Without active control, several parameters are given experimentally as function of the Reynolds number, so we compare these data with the theoretical models of Batchelor, and Moore and Saffman together with DNS. Secondly, we analyse the effect of a continuous injection in the spanwise direction. The continuous jet has a strong influence on the wing-tip vortex formation. We explore this effect at low chord based Reynolds number ranging from 7000 up to 20000. We change the aspect ratio of the injection, R, defined as the ratio of the velocities between the jet (Uj) and free-stream (U). For R=1, we find that the jet strongly affects the wingtip vortex formation with a sudden decrement of the axial vorticity and the azimuthal velocity. This technique is a challenge and a promising tool to reduce the intensity of the vortex core.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

On the effect of low blowing ratio continuous jets on wingtip vortex characteristics

Vortices are an unavoidable effect of flight, which appear behind the wing with a bounded length. The strength of these vortices, which are extremely stable, is due to the lift force [1]. That is the reason why this phenomenon is especially relevant during take-off and landing operations. In these situations, when aircraft are departing from or arriving to the airport runways, the following aircraft might feel two counter-rotating vortices which remain long time under normal environmental conditions. Unfortunately, this huge rotation of airflow patterns always destabilizes the following aircraft. Consequently, trailing vortices have a mighty influence on the air traffic control of airport runways, and they have justified the research interest in this topic since the 1960's [2]. However, aeronautical engineers are still searching for different technological strategies to breakdown these wingtip vortices.Short-Term Postdoctoral Stay of Talent Attraction Plan of Andalucía TECH ICE. Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tec

Effect of the axial jet on the optimal response in Batchelor vortex

En este póster se estudia la respuesta óptima del torbellino de Batchelor para distintos números de onda. Se demuestra que incluso teniendo la velocidad axial, un torbellino es capaz de tener grandes amplificaciones de energía.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech