Surrounding Fluid Flow Research Articles

Free movement of a near-wall particle in fluid of comparable density

The fundamental problem of nonlinear interaction between a freely moving particle and surrounding fluid flow is investigated for a density ratio of order unity, with potential applications to biomedical, environmental, and aerodynamic configurations. The interaction takes place near a fixed wall, with the particle being relatively thin. A mathematical model is presented, showing the fluid pressure forces to be dominant over the mass-acceleration effects in the particle motion (in contrast with previous analyses). The added mass due to the fluid motion, thus, greatly exceeds the body mass. Numerical simulations and asymptotic analysis reveal a range of possible particle motions. The main properties emerging are: (a) the distinction between collisions with the wall and fly-away responses; (b) the time scales involved in such behaviors; (c) the pressures and velocities induced at collision; (d) the occurrence of flow reversal in certain cases; and (e) the results being independent of the particle mass and moment of inertia as well as independent of the density ratio provided that the ratio is of order unity (0–7, say) or only slightly larger (8–30, say).

Conjugate heat transfer analysis of developing region of square ducts for isothermal and isoflux boundary conditions

Purpose This paper aims to present a comprehensive analysis of conjugate heat transfer phenomena occurring within the developing region of square ducts under both isothermal and isoflux boundary conditions. The study involves a rigorous numerical investigation, using advanced computational methods to simulate the complex heat exchange interactions between solid structures and surrounding fluid flows. The results of this analysis provide valuable insights into the heat transfer characteristics of such systems and contribute to a deeper understanding of fluid–thermal interactions in duct flows. Design/methodology/approach The manuscript outlines a detailed numerical methodology, combining computational fluid dynamics and finite element analysis, to accurately model the conjugate heat transfer process. This approach ensures both the thermal behaviour of the solid walls and the fluid flow dynamics are well captured. Findings The results presented in the manuscript reveal significant variations in heat transfer characteristics for isothermal and isoflux boundary conditions. These findings have implications for optimizing heat exchangers and enhancing thermal performance in various engineering applications. Practical implications The insights gained from this study have the potential to influence the design and optimization of heat exchange systems, contributing to advancements in energy efficiency and engineering practices. Originality/value The research introduces a novel approach to study conjugate heat transfer in square ducts, particularly focusing on the developing region. This unique perspective offers fresh insights into heat transfer mechanisms that were previously not thoroughly explored.

Mitigation of PWR fuel assembly vibrations using bio-inspired nozzles

Jet flows injected in a transverse flow need rapid and effective mixing for various applications ranging from medicine injection into bloodstreams to nuclear pressurized water reactors (PWRs). Inspired by marine organisms, spiral snails, and sharks, bio-inspired nozzles are proposed and experimentally investigated to explore their advantages in suppressing nuclear fuel assembly vibrations. It has been observed that a combination of axial flow and jet cross-flow causes vibrations of fuel rods and potential wear at spacer grid supports. Marine biomimetics is used to improve the mixing between the jet flow and surrounding fluid flows. Inspired by the structure of gastropod shells, a variable whorl spacing nozzle is proposed to induce a swirling jet flow to enhance the mixing rate with the flow inside the reactor cores. In addition, the smooth maneuverability of the sharks highlights the importance to include gill slits structure into nozzles. This work focuses on mitigating PWR fuel assembly vibrations using two biomimetic nozzles, a snail nozzle and a shark nozzle. These two nozzles are proposed to improve the mixing rate between the injected flow and the primary coolant flow, resulting in a reduced jet flow effect on fuel rods. A single-span mock-up PWR array is designed, fabricated, and instrumented to mimic the real nuclear fuel assembly. The array is experimentally tested under combined axial flow and jet cross-flow to investigate its dynamical behavior. Three different nozzles, a basic circular nozzle, a snail nozzle, and a shark nozzle, are tested. The research investigates the ability of the proposed marine biomimetic nozzles to suppress the vibration of the rod bundle by comparing the results from the three tested nozzles. The obtained results suggest that the proposed snail-inspired biomimetic nozzle is significantly better than the circular nozzle since it reduces rod bundle vibration by increasing flow mixing. A 50% reduction was achieved by implementing it instead of the circular nozzle. More importantly, the shark-inspired nozzle delays the critical jet flow rate, at which the unstable vibration occurs in the rod bundle, by 20%. In addition to delaying instability, a vibration amplitude reduction of 87.5% was obtained using the proposed shark-inspired nozzle compared to the circular nozzle. The results are promising for various applications including gas burners, combustion chambers, and chemical reactors for providing efficient and rapid mixing between two fluid streams.

Structural Stability Analysis of Multistory Building Structure under Wind Load Conditions

In the current research the effect of wind load on structural stability of building structure is evaluate using techniques of Computational Fluid Dynamics. The CFD analysis on building is conducted using ANSYS simulation package. The FSI simulations considered the complex interactions between the structural components and the surrounding fluid flow, providing valuable insights into the structural response and its vulnerability to external loading conditions. Through a combination of computational tools and numerical methods, the study was able to accurately predict the structural response, including deformations, stresses, and critical failure points.

Analytical simulation of vibration demeanor of robotic arm immersed in incompressible dynamic fluid

The use of underwater mechanical arms is extensively considered to be the most suitable tool for performing mechanical operations underwater. These mechanical arms can transport samples and patterns in water environments. A simulation of the fluid flow provoked vibrations in the arm of the robot is presented in this paper. Under the influence of the force generated through the surrounding fluid flow and considering the flexibility of the robotic arm, the governing forced vibration equations are derivative of the Rayleigh beam hypothesis. With the displacement couple pattern, the force from the surrounding fluid is tested for the arm. For analyzing the equations of movement, MATLAB software has been utilized to examine the influence of variables like the mechanical and geometric features and the liquid flow rate on the forced vibration the responding robot arm. Numerical simulations indicate that fluid inertial forces increase with increasing fluid velocity. Therefore, at higher levels of the fluid, the result of extra mass-produced by the fluid causes the range of oscillations to increase suddenly, which decreases the performance and accuracy of the arm. By identifying the lock-in area, the system parameters should be selected in such a way as to prevent the arm from entering the lock-in area.

High-performance computing in phononic materials with applications to nonlinearity and fluid–structure interaction

Phononic materials contain periodic and resonant substructures that enable novel acoustic and elastic wave behaviors, such as band gaps, topologically protected wave propagation, and negative refraction. Phononic materials preferentially take advantage of complex structures and intricate geometries, and even richer dynamics can occur in phononic materials that are nonlinear, multi-physics, or multi-phase. Certain phononic materials are often represented with reduced-order models such as lumped masses and springs, where the underlying physics can be revealed and systematically probed. However, high fidelity and/or performance simulations are critical to, e.g., interpret experimental validations, particularly with additively manufactured samples, analyze realistic structures and loadings, and for systematic optimizations. This talk presents two examples where high fidelity and high-performance computing enables the analysis of new behaviors of phononic materials and structures: (1) strongly nonlinear phononic materials that exploit history-dependent phenomena and effects of a continuum and (2) interactions between phononic materials and a surrounding fluid flow, where coupled nonlinear effects such as fluid–structure interaction are critical. Finally, opportunities for how high-performance computing that can advance phononic materials are discussed.

Moored motion prediction of a semi-submersible offshore platform in waves using an OpenFOAM and MoorDyn coupled solver

In this study, the motions of a moored buoy and its surrounding fluid flow are numerically studied. The solver is developed by coupling the computational fluid dynamics platform, OpenFOAM, with a lumped mass mooring line model, MoorDyn. The time marching interface to transfer the solution variables is developed for the robustness and accuracy of the solver. The developed coupled solver was validated against a moored cubic-shaped box model in waves. The different mesh configurations, mesh generation technique and mooring line discretization are considered in the numerical study. A cubic-shaped box attached with tensioned mooring lines in waves is simulated and the results are compared with the experimental results. Motion responses of a moored semi-submersible platform, which is designed by Korea Research Institute of Ship and Ocean Engineering (KRISO), in waves are predicted by the solver. The mooring line tensions acting on the body and anchor, the forces acting on the platform and the platform's motion performance are analyzed, and comparisons are made between simulation data and experimental data.

Magnetically Actuated Cell-Robot System: Precise Control, Manipulation, and Multimode Conversion.

Border-nearing microrobots with self-propelling and navigating capabilities have promising applications in micromanipulation and bioengineering, because they can stimulate the surrounding fluid flow for object transportation. However, ensuring the biosafety of microrobots is a concurrent challenge in bioengineering applications. Here, macrophage template-based microrobots (cell robots) that can be controlled individually or in chain-like swarms are proposed, which can transport various objects. The cell robots are constructed using the phagocytic ability of macrophages to load nanomagnetic particles while maintaining their viability. The robots exhibit high position control accuracy and generate a flow field that can be used to transport microspheres and sperm when exposed to an external magnetic field near a wall. The cell robots can also form chain-like swarms to transport a large object (more than 100 times the volume). This new insight into the manipulation of macrophage-based cell robots provides a new concept by converting other biological cells into microrobots for micromanipulation in biomedical applications.

Bio-inspired bistable piezoelectric energy harvester for powering animal telemetry tags: Conceptual design and preliminary experimental validation

This paper presents the conceptual design, preliminary experimental validation, and performance evaluation of a novel bio-inspired bi-stable piezoelectric energy harvester for self-powered animal telemetry tags. The overall conceptual design, which includes a bio-inspired attachment and a bi-stable piezoelectric energy harvester, is introduced firstly with a specific application example of marine fish tracking. The self-powered telemetry tag can be externally deployed on fish (dorsal fin) to monitor fish habitats, population, and underwater environment. Inspired by the Venus flytrap's rapid shape transition, a bi-stable piezoelectric energy harvester is developed to scavenge energy from fish maneuvering and the surrounding fluid flow for a sustainable power supply. The bistability of the harvester is characterized by the measured force-displacement curve and double potential wells. A bluff body is integrated to the free end of the bistable piezoelectric energy harvester to enhance the structure-fluid interaction for the large-amplitude snap-through vibrations and higher voltage output. Controlled laboratory experiments are conducted in a water tank on the bio-inspired bi-stable piezoelectric energy harvester using a servo motor system to simulate fish swing motion at various conditions to evaluate the power generation performance. The preliminary underwater experimental results demonstrated that the proposed bio-inspired bi-stable piezoelectric energy harvester could effectively convert fish swing motions into electricity. The device collected 17.25 mJ of energy over 130 s under a peak-to-peak swing angle of 30o at 1.5 Hz in the capacitor charging experiments.

Particle movement in a boundary layer

The study here is concerned with a thin solid body passing through a boundary layer or channel flow and interacting with the flow. Relevant new features from modelling, analysis and computation are presented along with comparisons. Three scenarios of such fluid-body interactive evolution in two-dimensional settings are considered in turn, namely a long body translating upstream or downstream, a long body with little or no translation and a short body with or without translation. The main progress and findings concern predictions of the time taken by the body to traverse the flow and impact upon the underlying wall, the delicate behaviour at the onset of impact, the dependence on parameters such as the initial conditions and the mass and shape of the body, and the influence of streamwise translation of the body in the surrounding fluid flow.

Flow field and drag characteristics of netting of cruciform structures with various sizes of knot structure using CFD models

The knowledge of drag characteristic and flow field around knotless and knotted cruciform patterns is very important for the design of successful netting structures. The effects of ratio between sphere (knot) and cylinder (twine) diameters (D/d) on the surrounding fluid flow and drag of cruciform structures with various attack angles was numerically investigated based on k-ω shear stress turbulent (SST) model in computational fluid dynamics (CFD) models. A finite volume method was used for solving Reynolds-averaged Navier-Stokes (RANS) equations. The results show that the effects of key parameters (attack angle, knot size) are significant on the flow pattern and drag coefficients. The drag coefficients of knotted cruciform are greater than those of knotless cruciform for one-cruciform and four-cruciform structures. The drag coefficients of one-cruciform and four-cruciform elements increased as attack angle increased. For the one-cruciform element, the knotless cruciform experienced a fewer substantial streamline detachment generating a lower drag, while knotted cruciform experienced a higher drag was because of the presence of a vortex and turbulence boundary layer flows that develops around the node causing large flow velocity reductions around it. For the four-cruciform structure, the knotted cruciform experienced a greater drag that can be attributed to a more significant development of dynamic vortex flow downstream each knot. The increase in attack angle increased the velocity reduction for four-cruciform structure, while that at downstream of one-cruciform decreased as the attack angle increased. In addition, the drag coefficient decreased as the D/d ratio increased for one-cruciform pattern, while for four-cruciform structure, it increased as the D/d ratio increased

FSI in Wind Turbines: A Review

This paper provides a brief overview of the research in the field of Fluid-structure interaction in Wind Turbines. Fluid-Structure Interaction (FSI) is the interplay of some movable or deformable structure with an internal or surrounding fluid flow. Flow brought about vibrations of two airfoils used in wind turbine blades are investigated by using a strong coupled fluid shape interplay approach. The approach is based totally on a regularly occurring Computational Fluid Dynamics (CFD) code that solves the Navier-Stokes equations defined in Arbitrary Lagrangian-Eulerian (ALE) coordinates by way of a finite extent method. The need for the FSI in the wind Turbine system is studied and comprehensively presented.

A fully 3D simulation of fluid-structure interaction with dynamic wetting and contact angle hysteresis

In this paper, we propose a three-dimensional diffuse-interface immersed-boundary (3D DIIB) method for the simulations of fluid-structure interaction (FSI) with dynamic wetting, complex geometry and contact angle hysteresis. In particular, the movement of rigid solid objects is allowed to have six degrees of freedom. In the method, the complex solid boundaries are represented by a set of Lagrangian patches that cover the whole surface of the solid objects, while the flows are solved on a staggered Cartesian grid. The couplings between the object movement and surrounding fluid flows are performed using an immersed boundary method. A simple model of contact angle hysteresis is used to ensure pinned contact lines if local contact angle is within the window of contact angle hysteresis. To relieve the stress singularity at moving contact lines, a characteristic moving contact line model [1] is adopted at 3D curved solid surfaces, after the geometrical information of interface is constructed in the vicinity of the contact line. For 3D simulations of FSI with dynamic wetting, it is crucial but difficult to estimate capillary force, of which the process consists of locating the moving contact line on complex solid surfaces, discretizing it into line segment, and determining the local tangent to the interface at the contact lines. Special consideration is given to the modeling of the capillary force and associated torque, in order to have accurate approximations. The performance of the 3D DIIB method is systematically examined through a series of numerical experiments, of which the results are either verified against theoretical predictions or compared with experimental data. Finally, we simulate the collision process of raindrops with 3D mosquito body, to show the potential of the 3D DIIB method in practical applications.

Multigear Bubble Propulsion of Transient Micromotors.

Transient, chemically powered micromotors are promising biocompatible engines for microrobots. We propose a framework to investigate in detail the dynamics and the underlying mechanisms of bubble propulsion for transient chemically powered micromotors. Our observations on the variations of the micromotor active material and geometry over its lifetime, from initial activation to the final inactive state, indicate different bubble growth and ejection mechanisms that occur stochastically, resulting in time-varying micromotor velocity. We identify three processes of bubble growth and ejection, and in analogy with macroscopic multigear machines, we call each process a gear. Gear 1 refers to bubbles that grow on the micromotor surface before detachment while in Gear 2 bubbles hop out of the micromotor. Gear 3 is similar in nature to Gear 2, but the bubbles are too small to contribute to micromotor motion. We study the characteristics of these gears in terms of bubble size and ejection time, and how they contribute to micromotor displacement. The ability to tailor the shell polarity and hence the bubble growth and ejection and the surrounding fluid flow is demonstrated. Such understanding of the complex multigear bubble propulsion of transient chemical micromotors should guide their future design principles and serve for fine tuning the performance of these micromotors.

An investigation of recast behavior in laser ablation of 4H-silicon carbide wafer

4H-silicon carbide (SiC) is a suitable semiconductor material for high-speed power devices but also a typical difficult-to-process and hard-brittle material. Laser ablation is an efficient approach to process SiC. However, recast layer is an inevitable thermal damage during laser ablation. The present study experimentally and numerically investigated the recast behavior in laser ablation of 4H–SiC. The recast humps are with height of 1.4–3.3 μm and width of 12–22 μm, consist of SiC, Si, and SiO2, where 15.08 wt% of oxygen is detected. Microcracks and pore clusters are observed on the recast humps under SEM. Recoil pressure and surface tension in the molten pool dominate the process of recast hump formation. The recoil pressure of Si vapor is 2.27 MPa at 5000 K, as high as 22 times of atmospheric pressure. The simulation results show that the fluid in the middle flows around while the surrounding fluid flows upwards. The upward flow is almost laminar while the flow at the bottom of the molten pool is turbulent entertaining air and forming bubbles. The vaporization-induced keyhole in the molten pool becomes deeper and the sidewall becomes more inclined over time, accompanying with the “growing” of the recast hump. There are mainly three reasons causing the increase of recast height and recast width with the increased average laser power: (a) increase of recoil pressure; (b) increase of temperature gradient in the molten pool, enhancing the Marangoni convection; and (c) enlarging the molten pool and leading to more materials melting. With the decrease of the laser scanning speed, more liquid molten material is evaporated in the molten pool instead of being ejected outward to form recast humps. The increase of the laser pulse frequency decreases the peak laser intensity and hence results in the decrease of the recoil pressure. Besides, it also leads to the weakening of the heating ability of laser and lessening of the liquid molten material that could be ejected.

Distributed optimal control applied to Fluid Structure Interaction problems

In this paper we focus on an optimal control problem based on Lagrangian multipliers and adjoint variables applied to the steady state Fluid-structure interaction problem. FSI systems consist of one or more solid structures that deform by interacting with a surrounding fluid flow. We consider the Fluid-structure interaction problem written in variational monolithic form in order to balance automatically solid and liquid forces at the interface. The objective of the control problem is the minimization of a velocity matching functional and it is obtained with a distributed force control that deforms the shape of the solid domain. This distributed control for Fluid-structure interaction systems can be easily used to control the shape of the solid domain and the flow effects of the fluid-solid interactions. The optimality system is derived from the first order optimality conditions by taking the Fréchet derivatives of the Lagrangian with respect to all the variables involved. The optimal solution is then obtained through a steepest descent algorithm applied to the optimality system. To support this approach we report a few numerical tests where the distributed force deforms the solid structure in order to match the desired velocity profile. The results obtained show the feasibility and robustness of this approach and its possible use in many industrial relevant applications.

Particle-scale computational approaches to model dry and saturated granular flows of non-Brownian, non-cohesive, and non-spherical rigid bodies

We discuss methods to compute the flow of non-Brownian, non-cohesive, and non-spherical rigid bodies immersed in a single homogeneous fluid. We address both the case of negligible effect of the surrounding fluid corresponding to dry granular flows in which the dynamics of rigid bodies is controlled by gravity and collisions only, and the case of non-negligible effect of the surrounding fluid in which rigid bodies not only exchange momentum by collisions but also by two-way coupling with the surrounding fluid flow. We review the common computational methods to compute rigid body collisions and the two-way interaction of rigid bodies with the surrounding fluid flow. We specifically discuss the extension or applicability of these methods to non-spherical rigid bodies.

Mass transfer towards a reactive particle in a fluid flow: Numerical simulations and modeling

We study mass transfer towards a solid spherical catalyst particle experiencing a first order irreversible reaction coupled to an external laminar flow. Internal chemical reaction and convective-diffusive mass transfer in the surrounding fluid flow are coupled by concentration and flux boundary conditions at the particle surface. Through this coupling, the mean particle surface and volume concentrations are predicted and the internal/external Sherwood numbers are obtained. We investigate the interplay between convection, diffusion, and reaction by computational fluid dynamics and establish a model for the mass transfer coefficient accounting for diffusion and internal first-order chemical reaction. We obtain a prediction of the mass transfer coefficient through mass balance or using the classical additivity rule. The model is numerically validated by fully resolved numerical simulations over a wide range of Reynolds number, Schmidt number and Thiele modulus which shows that assuming decoupled treatment of external and internal mass transfer gives very accurate predictions. Finally, we test the unsteady response of the model. The model predicts the evolution of the mean volume concentration for a particle placed in a steady convective-diffusive stream. Predictions of the unsteady model are in very good agreement with computed results.

A Light‐Driven Micromotor with Complex Motion Behaviors for Controlled Release

AbstractMicromotor that exhibits various movement behaviors has attracted more attention in recent years. However, most researchers focus on its motion behavior and few have studied the fluid flow surrounding it. In this work, a novel micromotor with both controlled motion behavior and surrounding fluid flow, which is driven by near‐infrared (NIR) light based on the unique Marangoni effect caused by the light irradiation of its constituent, i.e., polypyrrole (PPy), is reported. Interestingly, these motion behaviors and the surrounding fluid flow can be easily switched by adjusting the incident angle of the NIR laser. This unique property may have potentials in different fields. Among others, its application in remotely controlled targeted delivery and release is demonstrated.

Passive control of vortex-induced vibration by spanwise grooves

The objective of this numerical study is to investigate the effect of spanwise grooves on the suppression of vortex-induced vibration (VIV) and the reduction of drag force. For this purpose, we consider a standard configuration of the elastically mounted circular cylinder, which is free to vibrate in both streamwise and transverse directions with identical natural frequency. We introduce a novel staggered groove configuration whose geometry is especially designed by offsetting the cross-sectional portion of the cylinder continuously along the spanwise direction. We assess the characteristic VIV responses of the proposed staggered groove configuration against the helical surface grooves for the identical dimensions and physical conditions. The staggered and helical groove configurations differ only in their arrangement of cross-section geometry along the spanwise direction. Three-dimensional coupled fluid–structure simulations are conducted at low mass and damping values with moderate Reynolds number of Re=4800. The effective width and the depth of surface grooves are determined to characterize the size effects for the assessment of staggered and helical groove configurations. Results show that the staggered groove configuration is effective in suppressing VIV, wherein the net reductions of 37% in the peak transverse amplitude and about 25% in the mean drag coefficient are observed in comparison to the plain cylinder counterpart. Staggered groove configuration produces three dominant effects by introducing a continuous jump in the cross-sectional geometry along the spanwise direction: (i) reduction of the spanwise correlation, (ii) enhancement of the three-dimensional effects in the near-wake flow, and (iii) broadening of the frequency spectra of fluid forces. As a result of these physical effects, the transfer of energy from the surrounding fluid flow to the vibrating grooved-cylinder system is reduced as compared to its plain cylinder counterpart. Owing to the simplicity of mechanical design and the ease of installation, the proposed passive control concept has a potential application to deepwater marine risers and tall structures in a wind environment.