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Made available in DSpace on 2022-04-28T19:42:09Z (GMT). No. of bitstreams: 0 Previous issue date: 2021-08-01 Fundação de Amparo à Pesquisa do Estado de Minas Gerais (FAPEMIG) A purely Lagrangian vortex method is employed to investigate turbulent flows past a rough circular cylinder under moving wall effect at large-gap regime, namely h*/d* = 0.45 and 0.80 (h* establishes the gap height between the moving wall base and the cylinder underside, and d* defines the outer cylinder diameter), yielding data in a transition regime, between the supercritical and transcritical regimes. In the large-gap regime, strong vortical structures are cyclically generated at the rear part of the cylinder. The numerical simulations utilize a two-dimensional model to simulate surface roughness effect. That model is inspired in a point set strategically located close to a body surface to inject momentum in its boundary layer and thus to capture a delay in the separation point of flow. Special attention is directed toward the relative roughness size variation, being that each test case always starts from an upper-subcritical Reynolds number of Re = 1.0 × 105. The present work contributes in the literature: (i) providing a detailed study of temporal evolution of pressure distribution, simultaneously computed with the integrated aerodynamic loads (drag and lift forces), Strouhal number and angle of boundary layer separation and (ii) examining the possibility of predicting suppression of vortex shedding. Such approach has been successfully applied within the study of bluff body aerodynamics at small-gap regime (i.e., h*/d* < 0.25), where the vortex shedding frequency completely disappears. Overall, the results reveal the sensitivity of the numerical technique to capture changes on the aerodynamic characteristics of a cylinder. For test with the rougher cylinder at h*/d* = 0.45, the big and small peaks on the drag curve are more influenced by increasing of noises because of surface roughness effect; consequently, the drag curve oscillates around small values reducing the mean drag coefficient. A drag reduction around 13% is identified as compared to a smooth cylinder. The lift force also reduces and still remains positive. The position of the separation points of the flow also changes, which characterizes boundary layer detachment with delay. The results are substantiated by a greater base pressure of the rougher cylinder; furthermore, only small differences are identified in the base pressure between both smooth and less rough cylinders, which explains the nearly constant level of drag force on them. Mechanical Engineering Institute Federal University of Itajubá (UNIFEI) School of Engineering São Paulo State University (UNESP) School of Engineering São Paulo State University (UNESP) FAPEMIG: APQ-02175-14

Made available in DSpace on 2022-04-29T08:35:47Z (GMT). No. of bitstreams: 0 Previous issue date: 2022-01-01 Rainwater harvesting systems (RWHS) can significantly contribute to the sustainability of cities and rural areas. In addition to their more obvious benefits (such as the ability to supply water in a decentralized manner, increasing local water security), several other benefits such as better stormwater management can be obtained through the use of these systems. This article summarizes the main benefits and barriers to the dissemination of RWHS, based on an extensive literature review. RWHS can reduce electricity use and greenhouse gas emissions when compared to public/centralized supply systems; however, the occurrence and magnitude of this reduction depend on the characteristics of both the public system and the RWHS, and should be analyzed locally. Stormwater runoff and associated problems can also be reduced by the used of RWHS, and the system tank/storage capacity is a key parameter to measure this benefit. Rainwater quality issues are influenced both by local characteristics and RWHS ones, including the roof type. Some of the main factors influencing the acceptance and dissemination of RWHS are economic (indicating the importance of financial incentives), lack of technical knowledge about the systems and a better perception of the real water availability in areas served by public water networks. School of Engineering Guaratinguetá. Avenida Dr. Ariberto Pereira da Cunha 333 São Paulo State University (Unesp) School of Engineering Department of Chemistry and Energy Guaratinguetá Avenida Dr. Ariberto Pereira da Cunha 333 São Paulo State University (Unesp) São José dos Campos Department of Environmental Engineering Avenida Engenheiro Francisco José Longo 777 São Paulo State University (Unesp) Institute of Science and Technology, Jardim São Dimas, CEP School of Engineering Guaratinguetá. Avenida Dr. Ariberto Pereira da Cunha 333 São Paulo State University (Unesp) School of Engineering Department of Chemistry and Energy Guaratinguetá Avenida Dr. Ariberto Pereira da Cunha 333 São Paulo State University (Unesp) São José dos Campos Department of Environmental Engineering Avenida Engenheiro Francisco José Longo 777 São Paulo State University (Unesp) Institute of Science and Technology, Jardim São Dimas, CEP

Made available in DSpace on 2020-12-12T01:15:34Z (GMT). No. of bitstreams: 0 Previous issue date: 2020-03-01 Fundação de Amparo à Pesquisa do Estado de Minas Gerais (FAPEMIG) Numerical tests at high Reynolds number flows were taken on circular cylinder placed near and parallel to a moving ground. A moving ground running at the same speed as the free stream eliminates the confusing effects of the boundary layer formed on the ground being, therefore, more effective to establish a better understanding of the relationship between complete vortex shedding suppression and surface roughness. A detailed quantitative measurement of the flow field around the cylinder using Lagrangian vortex method with roughness model was carried out. The effect of higher surface roughness heights is studied because it introduces greater instabilities in the boundary layer of bluff bodies. The purpose is to investigate supercritical flow patterns from subcritical Reynolds number flow simulations. The present results are compared against those measured for smooth cylinder under the same flow conditions. It is found that certain critical gap ratio between the rougher cylinder bottom and the moving wall significantly reduces the drag force. The lift force points away from the wall plane. The full vortex shedding suppression is successfully anticipated. In addition, the Strouhal number vanishes. The contribution of this research is to report that von Kámán-type vortex shedding totally ceases and instead two nearly parallel shear layers are formed behind the cylinder in moving ground when employing two-dimensional modeling of roughness. Previous numerical results for flow around smooth cylinder placed closer to the moving ground did not capture the behavior of Strouhal number equal to zero. Unfortunately, there is a lack of experimental results for rough cylinder near a moving wall, which motives the present study. Mechanical Engineering Institute Federal University of Itajubá (UNIFEI) São Paulo State University (UNESP) School of Engineering São Paulo State University (UNESP) School of Engineering FAPEMIG: 02175-14

Made available in DSpace on 2020-12-12T02:38:28Z (GMT). No. of bitstreams: 0 Previous issue date: 2020-01-01 Direct injection spark ignition engines aim at reducing specific fuel consumption and achieving the strict emission standards in state of the art internal combustion engines. This can be achieved by research comprising experimental methods, which are normally expensive and limited, and computational fluid dynamics methods, which are often more affordable and less restricted than their experimental counterpart. In the latter approach, the costs are mainly related to the acquisition, usage, and maintenance of computational resources, and the license cost when commercial computational fluid dynamics codes are used. Therefore, in order to make the research of direct injection spark ignition engines and their internal processes more accessible, this article proposes a novel open-source and free framework based on the OpenFOAM computational fluid dynamics library for the simulation of the internal flow in direct injection spark ignition engines using a large-eddy simulation closure for modeling the turbulence within the gas phase. Finally, this framework is tested by simulating the Darmstadt engine in motored operation, validating the results with experimental data compiled by the Darmstadt Engine Workshop. Smart Data Knowledge Services German Research Center for Artificial Intelligence (DFKI) São Paulo State University (UNESP) Department of Mechanical and Industrial Engineering University of Massachusetts Amherst São Paulo State University (UNESP)

Made available in DSpace on 2018-12-11T17:37:03Z (GMT). No. of bitstreams: 0 Previous issue date: 2018-05-01 Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Direct injection plays an important role in the efforts to increase efficiency of modern engines, and the correct evaluation of the velocity and fuel mixture fraction fields is crucial for modeling combustion in fuel sprays. Therefore, a computational study has been performed to assess the effect of different parameters on the mixture formation and flow field in the simulation of a single jet of the engine combustion network (ECN) “Spray G” evaporative gasoline injection test case. The Lagrangian particle tracking (LPT) approach was tested within both Reynolds-averaged Navier–Stokes (RANS) and large eddy simulation (LES) frameworks, and the varieties were compared. Additional parameters that were considered include mesh resolution (0.75, 0.50, and 0.25 mm) and droplet breakup (Reitz–Diwakar, Reitz–KHRT, and Pilch–Erdman), as well as stochastic turbulent dispersion (O’Rourke) and stochastic collision (O’Rourke) models. Experimental penetration length data from both liquid and vapor phases were used to validate the 54 simulations performed within this study. Then, a series of analyses were performed to weigh the effect of each isolated parameter on the outcome of the simulations. Finally, three additional simulations were conducted to study specific issues of LES in fuel spray modeling. In this way, this study was able to make a qualitative comparison of the evaporative spray cloud shapes and the evaluation of spray statistics in terms of the iso-octane mixture fraction and droplet/slip velocities. School of Engineering São Paulo State University (UNESP), Guaratinguetá Campus, Av. Dr. Ariberto Pereira da Cunha, 333 Portal das Colinas School of Engineering São Paulo State University (UNESP), Guaratinguetá Campus, Av. Dr. Ariberto Pereira da Cunha, 333 Portal das Colinas FAPESP: 2015/10299-9

Made available in DSpace on 2018-11-26T15:45:37Z (GMT). No. of bitstreams: 0 Previous issue date: 2017-11-01 Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) CENAPAD-SP Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) We present a novel fast algorithm for flow simulations using the discrete vortex method, DVM, for problems with periodic boundary conditions. In the DVM, the solution of the velocity field induced by interactions among N discrete vortex particles is governed by the Biot-Savart law and, therefore, leads to a computational cost proportional to O(). The proposed algorithm combines exponential and power series expansions implemented using a divide and conquer strategy to accelerate the calculation of the cotangent kernel that models periodic boundary conditions. The fast multipole method, FMM, is applied for the solution of singular terms appearing in the power series expansion and also for the exponential series expansion. Error and computational cost analyses are performed for the individual steps of the algorithm for double and quadruple machine precision. The current method presents more accurate solutions when compared to those obtained by periodic domain replication using the free-field FMM kernel. The novel algorithm provides computational savings of nearly 240 times for double-precision simulations with one million particles when compared to the direct calculation of the Biot-Savart law. Univ Estadual Campinas, BR-13083860 Campinas, SP, Brazil Sao Paulo State Univ, BR-12516410 Guaratingueta, SP, Brazil Sao Paulo State Univ, BR-12516410 Guaratingueta, SP, Brazil FAPESP: 2013/03413-4 FAPESP: 2013/07375-0 CNPq: 470695/2013-7 CNPq: 305277/2015-4 CENAPAD-SP: 551

Made available in DSpace on 2018-11-26T15:44:12Z (GMT). No. of bitstreams: 0 Previous issue date: 2017-10-01 Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) CENAPAD-SP Lagrangian simulations of unsteady vortical flows are accelerated by the multi-level fast multipole method, FMM. The combination of the FMM algorithm with a discrete vortex method, DVM, is discussed for free domain and periodic problems with focus on implementation details to reduce numerical dissipation and avoid spurious solutions in unsteady inviscid flows. An assessment of the FMM-DVM accuracy is presented through a comparison with the direct calculation of the Biot-Savart law for the simulation of the temporal evolution of an aircraft wake in the Trefftz plane. The role of several parameters such as time step restriction, truncation of the FMM series expansion, number of particles in the wake discretization and machine precision is investigated and we show how to avoid spurious instabilities. The FMM-DVM is also applied to compute the evolution of a temporal shear layer with periodic boundary conditions. A novel approach is proposed to achieve accurate solutions in the periodic FMM. This approach avoids a spurious precession of the periodic shear layer and solutions are shown to converge to the direct Biot-Savart calculation using a cotangent function. (C) 2017 Elsevier B.V. All rights reserved. Univ Estadual Campinas, BR-13083860 Campinas, SP, Brazil Sao Paulo State Univ, BR-12516410 Guaratingueta, SP, Brazil Sao Paulo State Univ, BR-12516410 Guaratingueta, SP, Brazil FAPESP: 2013/03413-4 FAPESP: 2013/07375-0 CNPq: 470695/2013-7 CNPq: 305277/2015-4 CENAPAD-SP: 551

Previous experimental observations suggest that a moving ground can be numerically simulated avoiding vorticity generation on it. In this research line the current paper presents a two-dimensional Lagrangian Vortex Method, which is able to analyze the vortex shedding suppression on a circular cylinder near a moving ground in a high Reynolds number flow of Re = 1 . 0 × 1 0 5 . The main purpose is to utilize numerical results to construct the instantaneous velocity and pressure fields for this kind of unsteady viscous flow. The analyses demonstrate that the physical mechanisms involved are associated with an additional circulation caused by the fluid viscosity and with the Venturi effect. Both of these effects are responsible for the increase in lift force as well as for the decrease in drag force acting on body surface.

The two-dimensional viscous incompressible fluid flow around a circular cylinder near a moving ground is numerically simulated. In a moving ground one eliminates the influence of the ground boundary layer, which is a crucial factor in the numerical simulation of the flow around a body moving in a close vicinity to a flat ground. A Lagrangian mesh-free vortex method is used to calculate global and local quantities of high Reynolds number flow of 1.0×105. This method is modified to take into account the sub-grid scale phenomena through a second-order velocity structure function model adapted to the Lagrangian scheme. In the present algorithm vortices with a Lamb core are generated only on the circular cylinder surface to ensure that the no-slip condition is satisfied and that the circulation is conserved. On the ground it is only sufficient to ensure the impermeability condition. Based on the experimental results available in the literature, the critical drag behaviour was found to be directly related to a global change in the near wake structure of the cylinder.

The objective of this paper is to study the vortex shedding from a circular cylinder near a moving ground; this is done using the Vortex Method. A moving ground has been widely used in the field of experimental vehicle aerodynamics, especially of high-performance racing cars, to properly consider the ground effect on the vehicles aerodynamic. In experimental work as well as in numerical simulations, the ground plane develops a boundary layer that interferes with the body viscous wake, leading to not so precise results. A ground moving with the incoming flow velocity, however, does not allow the development of a boundary layer. The results of our numerical simulations show that the critical drag behavior is directly related to a global change in the wake structure of the cylinder in the ground effect. Comparisons with experimental data are encouraging.