Wake modifications in confined flows due to the presence of a downstream cylinder in staggered arrangement

In the present study, confined flows around two square cylinders in staggered arrangement were numerically investigated. Cross-flow and streamwise center-to-center spacings of one- and three-cylinder diameters, respectively, were considered. Simulations were carried out at Reynolds numbers Re = 50,100,150 and 180, where the resulting wakes are laminar and periodic. Results indicate that the presence of the downstream cylinder tends to reduce the Strouhal number, amplitude and the time-averaged lift coefficient of the upstream cylinder relative to the single cylinder cases. Furthermore, the time variations of upstream cylinder’s lift coefficient behave similar to that of a single cylinder

Quasi-two-dimensional MHD duct flow around a 180-degree sharp bend in a strong magnetic field

This study considers the quasi-two-dimensional flow of an electrically conducting fluid subjected to a strong out-of-plane magnetic field in a rectangular duct. The effect of Hartmann number on flow features such as the length of the downstream recirculation bubbles and the threshold Reynolds numbers between steady-state and unsteady flow regimes for values of the ratio between the throat of the bend and the duct height, β = 1 are identified. The simulations reveal that the primary recirculation bubble length decreases with increasing Hartmann number, and simultaneously the secondary recirculation bubble is significantly damped compared to the corresponding non-MHD case. The critical Reynolds number where the transitions from steady to unsteady flow occurs was found to increase with increasing of Hartman number. This study provides information that will be useful for refining the design of heat exchanger ducting in MHD systems to maximise the useful mass transport adjacent to the duct walls where heating is applied

Large Eddy simulation of low Reynolds number flow around a NACA0015 airfoil with modified trailing edges

The flow field of a low Reynolds number regime is three-dimensional and exceedingly complicated due to numerous forms of vortical phenomena, which has triggered the interest of many researchers. This study aims to investigate the influence of various trailing edge configurations on the aerodynamic characteristics and flow structure of airfoils. Specifically, five different configurations, namely baseline, serration, comb, and comb-serration are analyzed in detail. The study seeks to identify the configuration that provides optimal aerodynamic performance, which can then inform the design of more efficient airfoils for a range of applications, including unmanned aerial vehicle (UAV), wind energy, and automotive design. A Large-eddy simulation numerical model was developed to effectively evaluate unsteady pressure fluctuations and turbulence parameters at the source. The pressure coefficient and skin friction coefficient figures reveal that modifications result in an early negative pressure zone and uneven flow along the airfoil surfaces. This study presents numerical findings on the NACA0015 airfoil at a zero angle of attack. The pressure coefficient distribution along the airfoil surface exhibits a symmetrical pattern, with the highest pressure observed at the leading edge due to flow deceleration. Analysis of the skin friction coefficient confirms the absence of separation zones on the airfoil surface, except for the tip of the trailing edge. The velocity profile demonstrates a consistent and smooth flow, indicating stable and symmetrical conditions across the airfoil. Moreover, the velocity profiles of the baseline airfoil at zero angle of attack do not indicate any signs of flow separation. Notably, the serrated, combed and comb-serrated trailing edge configurations each yield distinctive effects on fluid flow. The serrated trailing edge promotes increased fluid velocity and pressure drop, while the combed configuration induces separation at the root. Meanwhile, the comb-serrated design sustains a continuous fluid flow over the airfoil surface. Overall, these results contribute to a comprehensive understanding of the aerodynamic behavior and flow characteristics influenced by various trailing edge configurations

Estimation of Mach numbers in supersonic jets using schlieren images

supersonic nozzles are commonly used in mechanical and aerospace engineering applications for decades. Therefore, it is essential to study their characteristics and discover techniques to measure relevant flow properties with minimal investment in terms of time, money, and effort. Supersonic jets are composed of shock waves and expansion waves, making the flowfield complex and difficult to probe and investigate. Some important parameters that are needed to understand the supersonic jet include the shock-cell orientation and the variation of the Mach number along the jet centerline. Expensive equipment and highly skilled manpower are needed to get this information both in the lab environment and in real applications. A simple yet effective approach is presented in the present work to get reasonable estimates of the Mach number from the schlieren images for a Mach 2.0 nozzle jet. Results are compared with the numerical simulations for the estimated Mach number from the experimental data

Experimental study of midplane jet evolution in multiple jets at Mach 2.0

The flowfield characteristics are experimentally studied in the inter-nozzle region of free jets from twin and triple supersonic nozzles. The nozzle is designed for Mach number 2.0, and the inter-nozzle spacing is twice the nozzle exit diameter. The impact of multiple jets on the flow characteristics such as the jet spread, supersonic jet core, and the shock wave structure is explored using pitot pressure readings and the schlieren technique. For Mach number 2.0 at nozzle pressure ratio (NPR) 2 and 8.5, pitot pressures are measured along the centerline, along the twin jet’s midplane, and the centroid of the triple jet. The crosswire tab is used as a passive control tool at the nozzle exit in two orientations to studying the effect of control. Schlieren images of Mach 2.0 twin jet at NPR 8.5 reveal that the supersonic jet core is different in a controlled jet than the uncontrolled jet

Study on flow structure behind multiple circular cylinders in a tandem arrangement under the effect of magnetic field

The fast-moving technologies and the increasing rate of growth population indicates that the demand for energy will continue to be spiking and prominent in the discussion of the upcoming future. Therefore, to cater to the need for sustainable and clean energy, the idea of nuclear fusion is proposed and studied. Because the nuclear fusion reaction happens at a high temperature, the concept of magnetic field is adapted to the nuclear or plasma fusion reaction. The energy will be harnessed inside a blanket module of the fusion reaction plant. However, the presence of the magnetic field affects the fluid flow inside the blanket module where it reduces the heat transfer efficiency in the channel. This research examines the flow structure behind multiple bluff bodies arranged in tandem in a channel under the influence of a magnetic field with the aim to increase the heat transfer efficiency inside the channel. The effect of gap ratio, G/h=[1-2.4] and Hartmann friction parameter, H=[0-800], were analysed to determine the critical Reynolds number and Nusselt number. It was found that the presence of the downstream cylinder with gap ratios, G/h= 1.2, 1.4 and 1.6, causes the flow to be unsteady at a lower Reynolds number compared to those of a single cylinder. The multiple cylinders proved to increase the Nusselt number. Increasing the Hartmann friction parameter increases the critical Reynolds number and decreases the Nusselt number

Effect of expansion level and relief to shear layer in a suddenly expanded flow: a CFD approach

Computational Fluid Dynamics analysis was used to study the effect of expansion level in a suddenly expanded flow for a converging-diverging nozzle expanded to the duct of larger diameter at supersonic Mach number. Parameters include the nozzle pressure ratio (NPR), L/D ratio, and area ratio. The model of the converging-diverging (C-D) nozzle suddenly expanding into the enlarged duct with the cavity was created using the Design Modeler of ANSYS Fluent. The Mach number of the study is 1.6. The area ratio varied from 2.25 to 5.29, and the L/D ranged from 1 to 10. The simulated nozzle pressure ratio (NPR) ranged from 2, 3, 4.25, and 6.375. The outcome demonstrated that the geometric alteration and NPR strongly affect the base pressure. The ambient pressure influences result in lower L/Ds. The cavity of aspect ratio 1 is most effective in raising the base pressure. Increasing the width does not yield any desirable results. However, the location of the cavity played a very significant role in base pressure regulation. The duct's wall pressure and the flow field remained identical with and without control

CFD modelling of wake-induced vibration at low Reynolds number

Flow-induced vibration is an enthralling phenomenon in the field of engineering. Numerous studies have been conducted on converting flow kinetic energy to electrical energy using the fundamental. Wake-induced vibration is one of the configurations used to optimise the generation of electricity. The results of the study on the effect of the gap between the multiple bluff bodies will provide insight into optimising the energy harvesting process. This study focuses on fluid behaviour and response behind two circular cylinders arranged in tandem when interacting with a fluid flow at low Reynolds numbers ranging from 200 to 1000. The study has been done on several gap lengths between the two cylinders, between 2D and 5D. The study was carried out numerically by using OpenFOAM. At Re = 1000, it is found that the gap length of 2.5D is optimal in terms of producing the highest lift force coefficient on the downstream circular cylinder

Study on Magnetohydrodynamic flow past two circular cylinders in staggered arrangement

The fusion reactor is anticipated to be a new source of clean energy. Magnetohydrodynamic flow in the fusion blanket is expected to cause the flow to be highly stable, causing the heat transfer to be poor. Passive vortex promoter such as bluff body is one of the methods found to be has a great potential in optimizing the heat transfer. In this study, two circular cylinders in a staggered arrangement are introduced to promote vortices to enhance heat convection from a heated wall using an electrically conducting fluid under a constant magnetic field. The effect of the Hartmann friction parameter and the height differential onto the Nusselt number were examined. Modified Navier—Stokes equations known as SM82 were used using OpenFOAM to simulate the confined, quasi-two-dimensional, incompressible and laminar MHD flow past the bluff bodies. It was found that the heat transfer is better when the height differential is small

Kinetic and thermodynamic characterization of amino acids generation via subcritical water reaction of microalgae Nannochloropsis sp. biomass

Emerging applications of amino acids in the development of biopharmaceuticals, functional foods and feeds, and biostimulants in sustainable agriculture have led to increasing interests in the development of commercially-viable technologies for amino acid production. Amongst the many technologies currently used, subcritical water reaction has the potential to offer a scalable and environmentally benign approach to amino acids synthesis. The present work investigates the kinetic and thermodynamic behaviour of amino acids synthesis from Nannochloropsis sp. biomass using subcritical water. Experiments were conducted in a batch reactor at temperatures between 250-280°C for a duration of 5-20 min using 1% (w/v) microalgal loading. The aqueous phase obtained from the reaction was directly analyzed for amino acid concentration. The highest amino acids yield of 0.0196 g AA / g biomass was obtained at 260°C for 20 min, representing 44% of amino acids extracted from the biomass. A single consecutive reaction model used for data validation showed a good agreement between the experimental and theoretical data generated. The results obtained from the kinetic study demonstrated that amino acids could be produced and decomposed rapidly from the subcritical water process. Thermodynamic analysis by transition-state theory showed that the subcritical water process as endothermic, while the Gibbs free energy showed the reaction as non-spontaneous, requiring constant external energy to support it