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Loureiro J.B.R.,Mechanical Engineering Program PEM COPPE UFRJ | Loureiro J.B.R.,Federal University of Rio de Janeiro | Freire A.P.S.,Mechanical Engineering Program PEM COPPE UFRJ
International Journal of Heat and Mass Transfer | Year: 2012

This paper investigates the influence of some governing parameters on the near wall characteristics of a circular impinging jet onto a smooth flat plate. Laser Doppler anemometry (LDA) is used to characterize the mean and turbulent fields including the wall shear stress. The experiments were conducted at one nozzle-to-plate space (H/D = 2) and Reynolds number of 47,100. The work makes a parametric analysis of impinging jets based on (i) conventional parameters that include the nozzle diameter, the nozzleto- plate distance and the bulk velocity of the jet and (ii) gross parameters like the jet momentum flux. Parametrization schemes based on conventional quantities are shown to be very sensitive to the particular choice of reference quantity, resulting in functional behaviours that can be represented through either power law or linear expressions. On the other hand, it is shown that the jet momentum flux and the kinematic viscosity suffice to determine the mean and fluctuating flow parameters, even in the initial region of wall jet development (1 < r/D < 5). With the latter choice, the streamwise variation of the maximum mean velocity and maximum Reynolds longitudinal stress are shown to decay according to power law expressions. A particular near wall parametrization scheme for the mean velocity profile that resorts to a scaling procedure based on the stream-wise evolution of the flow characterized by its maximum velocity is also presented. Higher-order moments of the velocity fluctuations are discussed. © 2012 Elsevier Ltd. All rights reserved.


Loureiro J.B.R.,Mechanical Engineering Program PEM COPPE UFRJ | Loureiro J.B.R.,Federal University of Rio de Janeiro | Silva Freire A.P.,Mechanical Engineering Program PEM COPPE UFRJ
Journal of Non-Newtonian Fluid Mechanics | Year: 2013

The asymptotic structure of turbulent boundary layers of purely viscous non-Newtonian systems is investigated through the intermediate variable technique. The cases of power-law and Carreau fluids are discussed in detail. Results show that a classical two-layered structure persists, with a viscous layer thickness that is dependent on the power-law index, n, and a logarithmic solution in the fully turbulent region. For Carreau fluids, in general, a three-layered structure emerges, with two nested viscous sub-layers. Experimental and numerical data from other authors are used to determine the functional behaviour of the linear coefficient of the log-law with n. © 2013 Elsevier B.V.


Loureiro J.B.R.,Mechanical Engineering Program PEM COPPE UFRJ | Loureiro J.B.R.,Federal University of Rio de Janeiro | Silva Freire A.P.,Mechanical Engineering Program PEM COPPE UFRJ
International Journal of Heat and Mass Transfer | Year: 2014

The transient heat transfer convection in a turbulent boundary layer is theoretically and experimentally studied when a time-periodical step-wise heat flux is imposed upon a rough surface. In particular, the behavior of the displacement height for the thermal boundary layer and the validity of the Reynolds analogy are analyzed. The local boundary layer characteristics, friction velocity, friction temperature and the displacement heights for the velocity and the temperature profiles, are evaluated through the graphical method of Perry and Joubert (1963) [3]. The results indicate that the displacement heights assume very different values and that the Reynolds analogy hypothesis is satisfied. © 2013 Elsevier Ltd. All rights reserved.


Marins L.P.M.,Petrobras | Duarte D.G.,Mechanical Engineering Program PEM COPPE UFRJ | Loureiro J.B.R.,Mechanical Engineering Program PEM COPPE UFRJ | Loureiro J.B.R.,National Institute of Metrology of Brazil | And 2 more authors.
Journal of Petroleum Science and Engineering | Year: 2010

The three-dimensional flow in a hydrocyclone especially developed for application in the petroleum industry has been investigated through the LDA and PIV techniques for one experimental condition. In the present physical simulation, the hydrocyclone is set to operate without an air-core. The tangential (Vθ) and axial (Vz) mean velocity profiles are analyzed through both measuring techniques. Radial (Vr) mean velocity profiles are only accounted for through PIV. The exponent n in the tangential velocity equation, Vθrn = C, was determined to be about 0.61. For the radial profile, Vrrm = - D, m was found to be 1.59. The rms-values of two-velocity components - tangential and axial - were evaluated via LDA. Turbulence in the axial direction is observed to be slightly higher than turbulence in the tangential direction. Approaching the axis of symmetry of the cyclone, however, this trend is reversed. The fluctuations in the tangential direction are found to be at least twice higher than the axial fluctuations. © 2009 Elsevier B.V. All rights reserved.


Loureiro J.B.R.,National Institute of Metrology of Brazil | Silva Freire A.P.,Mechanical Engineering Program PEM COPPE UFRJ
International Journal of Engineering Science | Year: 2011

The present work investigates the scaling of the turbulent boundary layer in regions of adverse pressure gradient flow. For the first time, direct numerical simulation and experimental data are applied to the theory presented in Cruz and Silva Freire [Cruz, D. O. A., & Silva Freire, A. P. (1998). On single limits and the asymptotic behaviour of separating turbulent boundary layers. International Journal of Heat and Mass Transfer, 41, 2097-2111] to explain how the classical two-layered asymptotic structure reduces to a new structure consistent with the local solutions of Goldstein and of Stratford at a point of zero wall shear stress. The work discusses in detail the behaviour of an adaptable characteristic velocity (uR) that can be used in regions of attached as well as separated flows. In particular, uR is compared to velocity scales based on the local wall shear stress and on the pressure gradient at the wall. This is also made here for the first time. A generalized law of the wall is compared with the numerical and experimental data, showing good agreement. This law is shown to reduce to the classical logarithmic solution and to the solution of Stratford under the relevant limiting conditions.. © 2010 Elsevier Ltd. All rights reserved.


Loureiro J.B.R.,National Institute of Metrology of Brazil | Sousa F.B.C.C.,Mechanical Engineering Program PEM COPPE UFRJ | Zotin J.L.Z.,National Institute of Metrology of Brazil | Silva Freire A.P.,Mechanical Engineering Program PEM COPPE UFRJ
International Journal of Heat and Fluid Flow | Year: 2010

In the present work, six different experimental techniques are used to characterize the non-equilibrium flow downstream of a rough-to-smooth step change in surface roughness. Over the rough surface, wall shear stress results obtained through the form drag and the Reynolds stress methods are shown to be mutually consistent. Over the smooth surface, reference wall shear stress data is obtained through two optical methods: linear velocity profiles obtained through laser-Doppler anemometry and a sensor surface, the diverging fringe Doppler sensor. The work shows that the two most commonly used methods to determine the wall shear stress, the log-law gradient method and the Reynolds shear stress method, are completely inappropriate in the developing flow region. Preston tubes, on the other hand, are shown to perform well in the region of a non-equilibrium flow. © 2010 Elsevier Inc.

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