Papers by Keyword: Turbulent Flow

Abstract: Wire-net stainless steel (WS) is an alternative material used to enhance heat transfer in solar air heater (SAH) by inducing swirling or rotating airflow as air passes through its pores. In this study, WS with varying porosity—corresponding to pore per inch (PPI) of 16, 20, and 25—and a constant pitch distance (P) of 0.06 m was installed within the flow channel of the SAH, and air was used as the working fluid under turbulent flow. The results showed that WS significantly improved heat transfer performance, though accompanied by increased pressure drop. An increase in PPI resulted in a maximum of Nusselt number and friction factor by factors of 13.81 and 238.61, respectively, compared to SAH without WS. The highest thermal enhancement factor of 2.48 was observed at PPI=20.

Abstract: This study examines numerical modeling of concentrated leak erosion in cohesive soils under turbulent flow conditions using the Hole Erosion Test (HET). Internal erosion, where soil particles detach due to subsurface flow, significantly weakens structures like dams and dikes, potentially causing floods.The study made a model to show erosion using changing meshes at the spot where water meets soil. It uses rules based on key shear force and erosion numbers. The model was tested for pipe erosion in 2D with slow water. It was then checked against the HET model. Two different soils were tested successfully using this approach, followed by a study to see how erosion factors change erosion speed and channel size. This model was proved to work when looking at experiments and Bonelli's papers. It shows leak erosion well while giving helpful flow data to better know how erosion works.

Abstract: The paper deals with the influence of Al₂O₃ and TiO₂ nanoparticle admixtures to the water coolant on the heat exchange and the pumping power of its single-phase flow in the U-shaped vertical collector of the heat pump geothermal probe. The heat carrier is aqueous dispersions with TiO₂ and Al₂O₃ nanoparticles at volume concentrations of 0.1 %, 0.3 %, 0.6 %, 1.0 % and 1.3 %. Studies were performed for turbulent single-phase flow with a range of Reynolds numbers 11,500–67,000 and Euler numbers 48–75 and compared with similar results for a water coolant. The optimal volume fraction of nanoparticles in the coolant, at which nanofluids provide the lowest pumping capacity of the coolant compared to the base fluid, ensuring the required heat transfer coefficient at the level of 2230 W∙m^-2∙K^-1 is analyzed in the article.

Abstract: The thermophysical properties as well as the thermal performance of a nanofluid can be altered upon varying the nanoparticle type and/or nanoparticle volume concentration. Herein, the effects of variable nanoparticle concentration on water-based TiO₂, SiO₂, TiC, and SiC nanofluids have been studied analytically. The dispersion effects of 1-4% nanoparticle on the single-phase forced convection heat transfer performance of the nanofluids have been investigated. The effective thermophysical properties of the nanofluids are determined adopting the general correlations. The flow velocities of the nanofluids relative to their base fluids are assumed to be constant. Mouromtseff number has been employed as a convenient figure of merit to compare the nanofluids under fully developed internal laminar and turbulent flow conditions. The results indicate an increase in effective density, thermal conductivity, and dynamic viscosity of the nanofluids. Nanofluids containing carbide suspensions exhibit superior heat transfer properties compared to those having oxide suspensions.

Abstract: In this paper, the case of the steady two-dimensional flow in a two-sided lid-driven square cavity is numerically investigated by the finite volume method (FVM). The flow motion is due to the top and bottom horizontal walls sliding symmetrically in the opposite direction with equal velocities, U_T and U_B, obtained through three respective Reynolds numbers, Re_1,2=10000, 15000, and 20000. Due to the lack of availability of experimental results in this Reynolds number margin for this type of flow, the problem is first examined by considering that the flow is turbulent with the inclusion of four commonly used RANS turbulence models: Omega RSM, SST k-ω, RNG k-ε and Spalart-Allmaras (SA). Next, the regime is considered being laminar in the same range of Reynolds numbers. A systematic evaluation of the flow characteristics is performed in terms of stream-function contour, velocity profiles, and secondary vortices depth. Examination of the calculation results reveals the existence of a great similarity of the predicted flow structures between the Omega RSM model and those from the laminar flow assumption. On the other hand, the computed flow with the SST k-ω model, the RNG k-ε model, and the SA model reveals a remarkable under-prediction which appears clearly in the size and number of secondary vortices in the near-wall regions. Various benchmarking results are presented in this study.

Abstract: Numerical simulations have been performed to analyze the interaction of confined coaxial high-swirl jets in both cases: isothermal and reactive flows. Besides different setups of swirl injectors have been tested to study the influence of swirl in the flames for both stoichiometric and lean mixtures. The aim was to quantify the nitrogen oxide emissions as well as the flow pattern for different swirling annular air jet and non-swirling inner fuel jet. This simple setup is widely used in burners to promote stabilized flames of lean mixtures producing ultra low NOx emissions.

Abstract: In present study, a detailed investigation of an annular jet at high diameter ratio r = 0,905 has been reported numerically. The numerical simulation was performed by making use of the commercial CFD code which discretizes the solution domain into quadrilateral elements and use a numerical finite volume method coupled with a multigrid resolution scheme. In this research the applications of k-epsilon and k-omega models for prediction of a turbulent flow in annular jet are described. The flow governing equations are solved by using a performed coupled algorithm. The results of predicted axial velocity profiles are compared with the experimental data. The computations indicated that the results predicted by k-epsilon model are in good agreement with the experiment.

Abstract: A numerical study of a natural convection flow coupled with radiation was carried out in a double-skin façade. The solar radiation flux to which the double-skin façade is subjected has been chosen for a cold season month (φ = 66.9 W/m² ). The double-skin façade is installed on a building whose interior temperature is 293 K given that the temperature at the inlet in winter conditions is 255 K. This study focuses on 5 different widths of the double-skin façade (4, 6, 8, 10 and 12 cm). Three-dimensional numerical simulations have been carried out for a steady and turbulent flow. Transport equations of mass, momentum and energy are solved numerically using finite volume method. Velocity and temperature profiles show the differences between all the above mentioned 5 cases in order to highlight the optimal width of the double-skin façade.

Abstract: The computational fluid dynamics solver Eilmer has proven useful to The University of Queensland’s Centre for Hypersonics for its ability to simulate high-speed compressible flows. In Eilmer, turbulence is modelled using Wilcox’s 2006 k-ω model. While the turbulence model implementation has been validated for two-dimensional and axisymmetric flows, validation is required for three-dimensional flows. The present paper describes the progress of the validation of the k-ω turbulence model for two three-dimensional test cases. A case featuring Mach 4.5 air flow over a flat plate produced results that correlated with previous numerical results within 4%. A second case featuring the injection of Mach 1 air into a Mach 4 air cross-flow produced results indicating that the code successfully captured the main flow features.

Abstract: This work deals with the numerical simulation of unsteady compressible turbulent flow past a circular cylinder. Turbulent flow is modeled by two different methods. The first method is based on the system of URANS equations closed by the two equation TNT model or modified EARSM model. Second method is based on the X-LES model, which is a hybrid RANS-LES method. Numerical solution is obtained by the finite volume method. Presented results are for the sub-critical turbulent flow characterized by Re=3900.