Journal of fluids engineering. Transactions of ASME

Vol. 141, num. 7, p. 071108-1-071108-13

DOI: 10.1115/1.4042374

Date of publication: 2019-07

Abstract:

The present paper introduces a novel transient experimental method employed to determine the discharge coefficient of constant section nozzles of small diameters of 1 to 3 mm and with a length/diameter ratio of around one. Flow is considered to be real and compressible; the discharge process was analyzed at relatively high pressures, the fluid used was N2. Based on the experimental data, a generalized expression characterizing the discharge coefficient for nozzles of different diameters, lengths and fluid conditions was developed. In order to check the precision of the analytical equation presented, experimental upstream reservoir pressure decay was compared with the temporal pressure decay obtained using the new analytical equation. Good correlation was achieved for pressure differentials up to 7.6 MPa. Despite the fact that the procedure established can be extended to other gases and nozzle configurations, so far the equation presented to estimate the discharge coefficient, can only be applied to orifices with length to diameter ratios of around one.]]>

Journal of the Textile Institute

Vol. 110, num. 5, p. 652-659

DOI: 10.1080/00405000.2018.1532780

Date of publication: 2019-05

Abstract:

The vortices are generated at the conventional transfer channel, having adverse effects on fiber configuration. In a former research, a conventional transfer channel was modified via rounding the transfer channel inlet corner and adding a bypass channel. The simulation results obtained with the modified transfer channel showed that the vortices were eliminated and the inlet air velocity increased. We present the impact of this modification on the yarn properties and fiber straightness. Four groups of yarn samples were spun using the conventional and modified spinning system. Yarn properties and fiber straightness along the rotor groove were evaluated. Results revealed that tenacities of the yarns spun on the modified system, increased in comparison to that of the conventionally spun yarns. The number of nearly straight fibers is increased by 25.55% by using the modified system, which was mainly attributed to the decrease in the number of fibers with trailing and leading hooks.]]>

International Conference on Design and Production Engineering

p. 59-60

Presentation's date: 2018-12-04

num. CJA-D-18-00760

International Conference on Computational Fluid Dynamics

p. 1-13

Presentation's date: 2018-07-13

Abstract:

In the present paper, three-dimensional Fluid structures and wake characteristics are evaluated for a square cylinder with an upstream splitter plate. The splitter plate divides the incoming flow in two streams, the upper and lower one, existing between them a velocity ratio. Two different Reynolds numbers of 56 and 200 and three different velocity ratios are here considered. The effect of the mixing enhancement using a square cylinder located downstream of the splitter plate is evaluated. A Floquet analysis to compute the spanwise wavelengths of three dimensional disturbances appearing in the square cylinder wake with and without a splitter plate is performed. It is observed that the use of the detached splitter plate has a stabilizing effect at low velocity ratios. However, when the velocity ratio increases, the vortex shedding suffers a linear increase and the wake resembles that of a mixing layer. Vortex dislocations appear at ratios larger than 2, which points out the onset of a bifurcation to a more chaotic wake. The wavelength of this secondary instability has been measured by means of Floquet analysis and two-point correlations being in the order of 3.5D.]]>

International Conference on Computational Fluid Dynamics

p. 1-9

Presentation's date: 2018-07-12

Abstract:

Aerodynamic drag reduction plays a vital role in the reduction of automobiles fuel consumption. Boundary layer physics and its intricate mechanisms that result in flow separation are to be understood and manipulated using active or passive devices, in order to reduce drag. Active flow control has an advantage to be effective in wide range of flow conditions and is analysed in this research. Direct Numerical Simulation (DNS) is performed for computing the flow over ahmed body, which is a simflied car geometry for research activities. Two flow control techniques, steady blowing and steady suction, are implemented for a parametric set inspired from literature. Three simulations are computed i.e., a detailed Baseline flow simulation, then a simulation with steady suction and another with steady blowing. The Reynolds number (Re) based on ahmed body (1/4th scaled) height is 1.48 *10^4. Steady suction provided a 8.3% drag reduction followed by 3.9% increase with steady blowing, specific to the parametric set considered. The major contribution from this paper is an in-depth analysis of flow physics resulting in this performance and also clearly classifying the differences using suction and blowing actuation.]]>

Textile research journal

Vol. 88, num. 11, p. 1244-1262

DOI: 10.1177/0040517517698985

Date of publication: 2018-06-01

Abstract:

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.]]>

Date of publication: 2017-12-01

Abstract:

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.

Descripció del recurs: 27 de novembre de 2017]]>

International Conference on Computational and Mathematical Methods in Science and Engineering

p. 114-122

Presentation's date: 2017-07-08

Abstract:

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.]]>

International Conference on Computational and Mathematical Methods in Science and Engineering

p. 1954-1964

Presentation's date: 2017-07-07

Abstract:

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.]]>

International Conference on Computational and Mathematical Methods in Science and Engineering

p. 166-176

Presentation's date: 2017-07-07

Abstract:

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.]]>

International Conference on Computational and Mathematical Methods in Science and Engineering

p. 1712-1721

Presentation's date: 2017-07-07

Abstract:

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.]]>

Applied mathematical modelling

Vol. 42, p. 363-381

DOI: 10.1016/j.apm.2016.10.016

Date of publication: 2017-02

Abstract:

A lattice Boltzmann method (LBM) 9-bit model is presented to solve mathematical-physical equations, such as, Laplace equation, Poisson equation, Wave equation and Burgers equation. The 9-bit model has been verified by several test cases. Numerical simulations, including 1D and 2D cases, of each problem are shown respectively. Comparisons are made between numerical predictions and analytic solutions or available numerical results from previous researchers. It turned out that the 9-bit model is computationally effective and accurate for all different mathematical-physical equations studied. The main benefits of the new model proposed is that it is faster than the previous existing models and has a better accuracy.

© 2016. This version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/]]>