Publications Scientifiques

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    Comparative analysis on heat transfer, between a steady and oscillating jet in a cavity
    (Inderscience Publishers, 2024) Iachachene, Farida; Mataoui, Amina
    This paper numerically investigates the cooling of a heated rectangular cavity by a cold slot jet. The study aims to examine the effect of the jet location inside the cavity (Lf and Lh) and Reynolds number on heat transfer, using URANS turbulence modelling. Different flow behaviours, including oscillatory and steady flows, are generated depending on the jet location inside the cavity. The study identifies and discusses the optimal jet locations for achieving optimal cavity cooling. The results indicate that the lateral placement of the jet has a negligible effect on heat transfer across all cavity walls. Additionally, oscillatory flow consistently expands the heat exchange zone along all three walls, resulting in a wider effective exchange area compared to steady flow conditions. The study proposes optimised jet positions within the cavity for specific wall cooling requirements. By considering the optimal combination of jet height and impinging distance, the cooling performance can be optimised.
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    Comparative Assessment of Non-newtonian Single-Phase and Two-Phase Approaches for Numerical Studies of Centrifugal Pumps Handling Emulsion
    (Springer Nature, 2024) Achour, Lila; Specklin, Mathieu; Asuaje, Miguel; Kouidri, Smaine; Belaidi, Idir
    Computational Fluid Dynamics is commonly employed to assess the effect of oil-water emulsions on pump performance, usually using two-phase models. However, these models often neglect the emulsion’s non-Newtonian behavior, despite its known experimental significance in enhancing pump performance. This study attempts to evaluate both single-phase non-Newtonian and two-phase approaches to model emulsion flow within centrifugal pumps. The non-Newtonian single-phase and several two-phase models are evaluated by comparing the predicted pump heads with experimental data of a multistage pump from the literature. The findings show that the non-Newtonian single-phase model generally provides better agreement with experimental measurements, particularly for emulsions with low dispersed phase fractions. Nevertheless, for emulsions with a high dispersed phase fraction (≈ 50%), the difference between the two approaches is insignificant. Thus, due to the lack of a universal multiphase model for emulsion simulation, the non-Newtonian single-phase model can serve as a viable alternative, overcoming the limitations of two-phase approaches in simulating complex multiphase fluid systems.
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    Modeling surge pressures during tripping operations in eccentric annuli
    (Elsevier, 2021) Belimane, Zakarya; Hadjadj, Ahmed; Ferroudji, Hicham; Rahman, Mohammad Azizur; Qureshi, M. Fahed
    The aim of this paper is to present a new numerical model to study the drilling fluid flow through eccentric annulus during tripping operations and to investigate the effect of the eccentricity on the annular velocity and apparent viscosity profiles. Many published works studied surge and swab phenomenon using simplified numerical models that do not consider the azimuthal variation of the shear stress in the eccentric annuli. In this paper, the developed numerical model takes into consideration this variation. Non-orthogonal, curvilinear coordinates were used to generate a body-fitted elliptic mesh that maps the irregular complicated eccentric annulus into a simple rectangle where flow equations can be discretized using the finite difference method then solved numerically. Besides, a commercial software (ANSYS Fluent 19R3) was used to support the findings of the numerical model. Results of these models were validated against the experimental data from literature where good agreement was observed with an average relative error of 2.6%, 3.8%, and 6.8% for the three Herschel-Bulkley fluids studied in the eccentric case. The profiles of velocity and viscosity were plotted, the contours showed that we cannot use an average velocity or a single value for the apparent viscosity to describe the drilling fluid flowing through an eccentric annulus, but, the whole profile should be used, instead. The developed numerical model was used in a parametric study to investigate the effect of eccentricity on the relationship between surge pressure and the relevant drilling parameters namely tripping velocity, annular geometry, and fluid rheological properties. The results showed that the eccentricity decreases the surge pressure independently of the previous parameters and that the rate of decrease varies from one parameter to another. The outcome of this parametric study was used to construct a surrogate model using Random Forest Regressor. Predictions from the surrogate model fit the numerical data very well with R-squared of 0.99 and 0.97 for training and test data, respectively
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    The effect of orbital motion and eccentricity of drill pipe on pressure gradient in eccentric annulus flow with Newtonian and non-Newtonian fluids
    (Inderscience, 2020) Ferroudji, Hicham; Hadjadj, Ahmed; Ntow Ofei, Titus; Rahman, Mohammad Azizur
    The correct prediction of the pressure gradient is the fundamental parameter to establish an effective hydraulics program, which enables an optimised drilling process. In the present work, the effect of the orbital motion of the drill pipe on the pressure drop in an eccentric annulus flow with Newtonian and non-Newtonian fluids is studied numerically for both laminar and turbulent regimes using finite volume method (FVM). Furthermore, the effect of eccentricity when the inner pipe makes an orbital motion is evaluated. Different behaviours are observed in laminar and turbulent regimes. In the laminar regime, the simulation results showed that an increase of the orbital motion speed causes a considerable increment of the pressure gradient for the Newtonian fluid. For the power-law, non-Newtonian fluid in the laminar regime, on the contrary, a decrease of the pressure gradient is observed due to the shear-thinning effect. In the turbulent regime the mentioned trends are predicted to be much weaker. As eccentricity increases, the pressure drop of the non-Newtonian fluid decreases with a more pronounced diminish in pressure drop when the drill pipe is in orbital motion for both laminar and turbulent flow regimes.
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    3D-Numerical simulation of the effect of radial gap on the stability of taylor-couette flow
    (2015) Daimallah, Ahmed; Lebbi, M.; Bouabdallah, A.
    We study numerically the effect of the radial gap on the onset of Taylor vortices in Taylor-Couette flow system. The inner cylinder is rotating and the outer is at rest. We interested in the appearance of Taylor vortices for a varied radius of the inner and the outer cylinders while making sure to keep a constant annulus between the cylinders in the aim to examine the influence of centrifugal force on the stability of the flow. The obtained results indicate that the onset of Taylor vortices is delayed when the radial gap is increasing.