Reynolds Number Research Articles

High-Fidelity CFD Simulation of Mixed Convection and Forced Convection in a Pebble Bed Test Reactor Core

The Hermes low-power [35-MW(thermal)] reactor will be built and operated by Kairos Power LLC (KP) to demonstrate its fluoride salt–cooled high-temperature reactor (FHR) technology. In the KP FHR, the reactor core is composed of randomly packed pebbles with TRISO fuel particles inside with FLiBe flow upward through the core acting as a coolant. Previous numerical and experimental studies have been limited to either a small-size bed or to a lack of detailed measurements for heat transfer. To address the lack of high-fidelity heat transfer data in a real-size FHR core, in this study, we simulated a pebble bed core with 34 374 pebbles randomly packed, similar to the Hermes reactor’s size. The core radius was 14 times that of the pebble diameter, while the core height was 45 times. In this work, we were particularly interested in a mixed convection regime, where buoyancy is important. Therefore, we performed several large-eddy simulations at different Reynolds numbers (160 to 1000) with gravitational force included. The spectral element computational fluid dynamics code NekRS with graphics processing unit acceleration was used for this study. The low-Mach number approximation was applied to address property changes in the FLiBe and to account for buoyancy. A pure hexahedral mesh with 60 million elements was generated by the Voronoi cell method. At the polynomial order of 5, the total degrees of freedom was 7.5 billion. The developed case in this work is the first of its kind in terms of size and complexity. The local numerical data across the domain were obtained and compared with empirical correlations. After examining the data, we found the following conclusions. For pressure drop, the Reger correlation predicted less than a 5% error. On the other hand, for heat transfer, the Wakao correlation outperformed the others. Based on our findings, we recommend the use of the Wakao correlation for the Nusselt number calculation, and for pressure drop, the KTA (Kerntechnischer Ausschuss) correclation, among the available experimental correlations. The Reger direct numerical simulation–driven correlation for pressure drops should also be considered, given its best agreement with our calculations.

Effects of Combined Utilization of Active Cooler/Heater and Blade-Shaped Nanoparticles in Base Fluid for Performance Improvement of Thermoelectric Generator Mounted in Between Vented Cavities

Abstract A wide range of technical applications, including solar power, waste heat recovery, electronics thermal management, and heat exchangers, employ thermoelectric generators. They can be mounted in between channels / cavities where hot and cold fluid streams exist. In this study, two novel methods of enhancing the power generation from thermoelectric generator device mounted in between vented cavities are proposed by combined utilization of active heater/cooler rectangular blocks and blade-shaped nanoparticles in base fluid. Finite element method investigation is conducted numerically for a range of hot and cold stream Reynolds numbers (250–1000), non-dimensional hot and cold block sizes (0.01 $$-$$ - 0.4), and heating/cooling increments (0–10), with nanoparticle loading limited to 0.03. Higher values of Reynolds number results in a rise in thermoelectric generator power. When comparing the cases of lowest and highest Reynolds number combinations, a 219 $$\%$$ % increase in power is achieved. The thermoelectric generator power will rise by around 27.5 $$\%$$ % when the object size reaches its maximum. However, for moderate object sizes, up to 31.6 $$\%$$ % reduction in power generation can be realized. Greater temperature differences result in a linearly rising power generation, with an achievable power increase of up to 22 $$\%$$ % . When nanoparticle loading in the base fluid for both cavities is raised to its maximum value, the resultant power increases by around $$30\%$$ 30 % . Thermoelectric generator power rises by 67.8 $$\%$$ % when an active heater/cooler with nanofluid is used in vented cavities, as opposed to the reference scenario of employing no object and only water. The thermoelectric generator device’s hot and cold interface temperatures are accurately estimated using the artificial neural network based method. The estimated temperature can be used as boundary condition for the solution of the governing equations in the thermoelectric generator device domain which will decrease the computational cost when dealing with very complex channel configurations.

Towards a standard application of the Reynolds number in studies of aquatic animal locomotion.

Nondimensional groups of measured quantities enable comparison between measurements of animals under different conditions and comparison between species. One of the most used such group is the Reynolds number, which compares inertial and viscous contributions to forces on swimming animals. This group includes two quantities that are chosen by the researcher: a typical length and speed. Choosing these parameters will affect the numerical value of the Reynolds number, defining the state of the fluid flow. For example: by choosing fish body length as opposed to propulsive fin chord, results may vary by an order of magnitude with consequences for analysis and hydrodynamic regimes. Here we suggest a standardized sets of lengths and speeds to be used for aquatic animal locomotion to enable confident utilization of data from different sources. This framework aims to improve comparative studies within the field.

Mathematical modeling of electroosmotic flow and thermal transport in stenotic tapered arteries using finite difference method

This study investigates the electroosmotic flow and thermal transport of nanofluids, specifically aluminum oxide and titanium dioxide, within tapered arteries with stenosis. Using the finite difference method (FDM), we modeled the flow dynamics and heat transfer mechanisms under the assumption of low Reynolds numbers and mild stenosis. The study focuses on the effects of nanoparticle volume fraction, heat absorption parameters, and electroosmotic forces on blood flow, velocity profiles, and temperature distribution. Results show that increasing nanoparticle concentration and heat absorption significantly reduce flow velocity, particularly in divergent artery geometries. Additionally, the inclusion of electroosmotic effects enhances heat transfer, while the Grashof number influences central velocity. These findings offer valuable insights into optimizing nanoparticle-based therapeutic interventions for cardiovascular treatments, providing a framework for enhancing drug delivery systems and improving the efficacy of heat-based therapies. The study’s outcomes could lead to improved diagnostic tools and therapeutic strategies for managing cardiovascular diseases.

Numerical and computational fluid dynamics experimental analysis of novel extended tetra-hybrid Tiwari and Das Sisko nanofluid passed a stenosed artery

The medical industry extensively uses nanoparticles for applications such as wound dressing, artificial organ components, drug delivery, tissue engineering, and cardiovascular disease treatment. The incorporation of nanoparticles into the base fluid enhances the rate of heat transmission and additionally decreases blood pressure. This study aims to examine the effects of a new tetra-hybrid nanofluid model, which includes nanoparticles, on the flow of blood through a stenosed artery with a circular shape. Model partial differential equations (PDEs) incorporate phenomena such as thermal radiation and viscous dissipation. Furthermore, we transform these modeled PDEs into dimensionless ordinary differential equations (ODEs) using self-similarity variables and numerically solve the proposed ODEs using the well-established Lobatto IIIa numerical technique. The impact of several dimensionless parameters on the heat transfer rate, skin friction, velocity, and temperature fields has been computed and analyzed using figures and tables. Moreover, we conducted a computational fluid dynamics (CFD) investigation on a tetra-hybrid nanofluid, using blood as the base fluid. The results indicate that heat transmission is higher in tetra-hybrid nanoparticles compared to tri-hybrid and di-hybrid nanofluids. The volume fraction of nanoparticles in the base fluid increases, resulting in a decrease in the surface drag coefficient and a decrease in the heat transport phenomenon. Amplification in the thermal radiation parameter improves heat transfer, helping to remove toxins and plaque from blood flowing through arteries. An increase in thermal radiation generates excess heat that dilates inflexible arteries, facilitating blood flow. From CFD analysis, it is observed that thermal conduction k and heat transfer coefficient h amplify by improving Reynolds number. Pressure at the outlet interface of the tube decreases from 3058 Pa to 2996 Pa for the case of a 10% volume fraction of nanoparticles. Velocity boundary layer thickness decreases from 1.46 to 1.37 with an increase in the volume fraction of nanoparticles from 1% to 10%. Heat deliverance rate amplifies in the case of tetrahybrid nanofluid 2.5394–2.6147 in contrast to trihybrid nanofluid 2.4008 to 2.4711 by amplifying Rd from 0.7 to 1.1. The surface drag coefficient amplifies by magnifying Re but the Nusselt number diminishes by improving the volume fraction of nanoparticles.

Features of Supersonic Flow Around a Blunt Body in the Area of Junction with a Flat Surface

This work studies the influence of a growing boundary layer on the process of supersonic flow around an aerodynamic body. The task is to select and implement in an experiment the parameters of a supersonic flow and to study the flow pattern near the surface of an aerodynamic body at different viscosity values for the incoming flow. Visualization of the shock wave configuration in front of the body and studying the change in the pressure field in the flow region under these conditions is the main goal of this work. The experiment was carried out on an experimental stand created on the basis of a shock tube. The aerodynamic body under study (a semi-cylinder pointed along a circle or an ellipse) was placed in a supersonic nozzle. The model was clamped by lateral transparent walls, which were simultaneously a source of boundary layer growth and the viewing windows for visualizing the flow. For selected modes with Reynolds numbers from 8200 to 45,000, schlieren flow patterns and pressure distribution fields near the surface of the streamlined models and the plate of the growing boundary layer were obtained. The data show a complex, unsteady flow pattern realized near the model which was caused by the viscous-inviscid interaction of the boundary layer with the bow shock wave near the wall.

Numerical Analysis on the Scale Effect of a Free-Running Ship’s Manoeuvring Characteristics

This study focuses on the manoeuvring characteristics of model- and full-scale ships. Various methods, including free-running model tests (FRMTs), computational fluid dynamics (CFD), and theoretical approaches, were employed to estimate ship manoeuvring performance. However, these methods are typically simulated at model-scale, which introduces discrepancies in the Reynolds number due to Froude scaling laws. Although numerous studies have investigated scale effects, most have concentrated on ship resistance, with limited research on manoeuvring performance. To address this gap, this study developed a free-running CFD simulation model for both a model-scale and full-scale ONRT. The study involved a detailed analysis of manoeuvring trajectories, forces, and moments. This analysis aimed to highlight differences in manoeuvring performance caused by Reynolds number discrepancies between model- and full-scale ships, providing a quantitative assessment of performance variations across scales and contributing to a more accurate understanding of manoeuvring characteristics at full scale.

Assessment of silica sand behavior around rotating square rod in cylindrical container via ultrasonic velocity profiling

Abstract This study aims to establish a test method for simultaneously evaluating material erosion and corrosion, and rotating-material wear tests were conducted using a slurry pot. The erosion and corrosion scars of specimens were assessed from photographic images, and wear condition diagrams organized by dimensionless particle size (d p /d) and Reynolds number (Re) were constructed. Furthermore, the flow structure and particle behaviour around each specimen were visualized via ultrasonic velocity profiling to confirm the mechanism of the ratio change between erosion and corrosion. Results showed that a vortex flow formed around the specimen near the bottom of the container, which caused erosion. The outward flow height due to the vortex varied at Reynolds numbers of 5 × 103 ≤ Re ≤ 1 × 104 and sand particle concentrations of 2.24 ≤ C v ≤ 40 vol%. It decreased with increasing Re and increased with C v , which was consistent with the trend in the surface wear images. The proposed wear condition diagram was supported by flow visualization, which showed that erosion- and corrosion-dominated regions could be distinguished from the amount of remaining rust. Graphical abstract

Experimental Investigation of the Dynamics of Methane-Oxygen Diffusion Flame Stabilized Over Swirl Coaxial Injector

ABSTRACT The combustion dynamics of methane-oxygen inverse diffusion flames stabilized over a swirl coaxial injector are investigated in detail. Mapping of different regimes of flame dynamics was carried out by classifying the flame into stable flames, oscillating flames, and unstable flames. The dominant frequency of the acoustics associated with different flame characteristics was determined from a free-field microphone measurement of combustion noise, and the respective flame morphology was studied by high-speed imaging of OH* chemiluminescence. Experiments were conducted for different oxidizer jet Reynolds numbers corresponding to each of the three different fuel jet Reynolds numbers. For all three power levels, flame transition from stable to unstable was observed as the oxidizer Reynolds number and equivalence ratio increased from fuel-rich to oxidizer-rich conditions. Strong acoustic-combustion heat release rate coupling was observed in the unstable flames. Modal decomposition techniques were employed to study the spatio-temporal evolution of the flame. The energetic coherent modes corresponding to the frequency of oscillation reveal two different modes of flame oscillation: longitudinal and transverse. All three fuel Reynolds numbers under investigation showed a predominant longitudinal mode of oscillation, while only the highest fuel flow conditions, corresponding to a fuel jet Reynolds number of 765 showed a transverse mode flame oscillation, as the oxidizer Reynolds number increased above 8000.

Optimizing thermal performance in a non-Darcy porous ventilated cavity with heated diagonal baffles of varied heights

This study investigates the convection effects of adding non-Darcy porous media to open enclosures with diagonally placed hot baffles near the open ports. The cold wall is fixed at the right side of the cavity. The remaining sidewalls are adiabatic. The fluid enters the enclosure from the inlet in the left vertical wall and leaves from an outlet at the right vertical wall. The finite difference method is employed to discretize the governing equations. The problem is analyzed for various parameters, Rayleigh number ([Formula: see text]), length of heating baffles ([Formula: see text]), porosity of the porous medium ([Formula: see text]), Reynolds number ([Formula: see text]) and Darcy number ([Formula: see text]) at alternate configured vented cavities and the results are illustrated graphically. The observation shows maximum heat transfer attained at BT open enclosure regardless of various parameters. For [Formula: see text] considerable increase in the heat transfer occurs at the right sidewall when the porosity of porous medium increases. The impact of configurations on heat transfer along the right wall is negligible at low Reynolds numbers but becomes significant at high Reynolds numbers.

Experimental Investigation on a Trailing Edge Morphing Airfoil (TEMA) with Zigzag Rib Structure at Low Speed

Camber-morphing wing technology enables adaptive adjustments to wing curvature by optimizing aerodynamic performance and efficiency for varying flight conditions. This study emphasizes the novel Trailing Edge Morphing Airfoil (TEMA) design and analysis, showcasing its noteworthy aerodynamic characteristics. The design uses the parabolic morphing method to obtain TEMA profiles for deflection angles. The different shapes of the TEMA and base airfoil were analyzed using the XFOIL solver with a linear-vorticity stream function formulation. TEMA with a flexible zigzag section was developed using a 3D printing technique with TPU material. The rectangular wing model was developed using TEMA and tested in a low-speed subsonic wind tunnel with Reynolds numbers of 1.19 ×105, 2.54 × 105 and 3.18 x 105 for different angles of attack. The test cases had a combination of different Reynolds numbers, deflection angles, and angles of attack. The aerodynamic characteristics were calculated by measuring the pressure coefficient around the TEMA using an advanced pressure scanner. The results show that TEMA with a moderate deflection angle has the potential to improve the lift-to-drag ratios by around 30%. It was concluded that TEMA with +5° and +10° deflection angles demonstrated superior aerodynamic efficiency at the Reynolds numbers mentioned compared to the conventional NACA 2412 airfoil.

Attenuation of shear-layer instabilities in steady and pulsatile axisymmetric shear-thinning flows

The current study characterizes the attenuation of instabilities in steady and unsteady shear layers by investigating shear-thinning flows downstream of a confined axisymmetric sudden expansion. Flow fields were captured using particle image velocimetry. Tested fluids exhibited approximate power-law indices of 1, 0.81, 0.61 and 0.47 and measurements were performed at mean throat-based Reynolds numbers of ${Re_m} = 4800$ and 14 400. Unsteady flows were tested at a Strouhal number and amplitude-to-mean velocity ratio of $St = 0.15$ and $\lambda = 0.95$ , respectively. For unsteady shear layers, shear-layer roll-up regardless of shear-thinning strength was evidenced by collapse of average circulation over time. For steady shear layers, consistent shear-layer behaviour regardless of shear-thinning strength was evidenced by similar shear-layer trajectories and by growth rates in vorticity thickness. However, vorticity fields of the unsteady and steady shear layers, standard deviations of shear-layer trajectory, thickness of steady shear layers and Reynolds shear-stress spectra of the steady shear layers reveal an attenuation of shear-layer instabilities not captured by Reynolds number. Specifically, shear-layer instabilities exhibit increased diffusion with increasing shear-thinning strength and, in the case of steady shear layers, shear-thinning strength is shown to promote shear-layer stabilization. Also, evidenced by vorticity fields and through Reynolds shear-stress spectra, instabilities frequently coalesce into large rollers, a result that would suggest the presence of an inverse eddy cascade. The behaviour of shear-thinning fluids is shown to stabilize shear layers through attenuating shear-layer instabilities, complementing observations from previous studies showing how shear-thinning fluids promote turbulence in the dominant flow direction.

New Nusselt Number Correlation and Turbulent Prandtl Number Model for Turbulent Convection with Liquid Metal Based on Quasi-DNS Results

Liquid metal is widely used as the primary coolant in many advanced nuclear energy systems. Prandtl number of liquid metal is much lower than that of the conventional coolant of water or gas. Based on the Reynolds analogy, the turbulent Prandtl number is assumed to be a constant around unity. For the turbulent convection of liquid metal, dissipations of half the temperature variance are larger than those of turbulent kinetic energies. The dissimilarity between the thermal and momentum fields increases as Pr decreases. The turbulent Prandtl number is larger than one for the liquid metal. In the current investigation, the turbulent convection of liquid metal in the channel is quasi-directly simulated with OpenFOAM-7. The turbulent statistics of the momentum and the thermal field are compared with the existing database to validate the numerical model. The power law for dimensionless temperature distribution with different Prandtl numbers is obtained by regression analysis of numerical results. A new Nusselt number correlation is derived based on the power law. The new Nusselt number correlation agrees well with the DNS results in the literature. The momentum mixing process between different layers in the cross section is compared with the thermal mixing process. The effects of the Prandtl number on the difference between the turbulence time scale and scalar time scale are analyzed. A new turbulent Prandtl number model with local parameters is obtained for turbulent convection with liquid metal. Combined with the k−ω model, the temperature distributions with the new turbulent Prandtl number model agree well with the DNS results in the literature. The new turbulent Prandtl number model can be used for turbulent convection with different Prandtl and different Reynolds numbers.

Dynamic wall shear stress measurement using event-based 3d particle tracking

We describe the implementation of a 3d Lagrangian particle tracking (LPT) system based on event-based vision (EBV) and demonstrate its application for the near-wall characterization of a turbulent boundary layer (TBL) in air. The viscous sublayer of the TBL is illuminated by a thin light sheet that grazes the surface of a thin glass window inserted into the wind tunnel wall. The data simultaneously captured by three synchronized event cameras are used to reconstruct the 3d particle tracks within 400μm of the wall on a field of view of 12.0mm×7.5mm. The velocity and position of particles within the viscous sublayer permit the estimation of the local vector of the unsteady wall shear stress (WSS) under the assumption of linearity between particle velocity and WSS. Thereby, time-evolving maps of the unsteady WSS and higher-order statistics are obtained that are in agreement with DNS data at matching Reynolds number. Near-wall particle acceleration provides the rate of change of the WSS which exhibits fully symmetric log-normal superstatistics. Two-point correlations of the randomly spaced WSS data are obtained by a bin-averaging approach and reveal information on the spacing of near-wall streaks. The employed compact EBV hardware coupled with suited LPT tracking algorithms provides data quality on par with currently used, considerably more expensive, high-speed framing cameras.

VENTILATION PERFORMANCE OF DIFFERENT TYPES OF MIXING VENTILATION SYSTEMS IN A GENERIC SCALED-DOWN EMPTY AIRCRAFT CABIN

The ventilation system of a commercial aircraft cabin plays an important role in ensuring passenger comfort and health during the flight. The commonly utilized ventilation system in aircraft cabin is mixing ventilation, where air is supplied either through the ceiling or sidewalls. However, ventilation efficiency can be affected by different types of mixing ventilation systems. Therefore, this study aims to evaluate airflow distribution and ventilation performance of various types of mixing ventilation systems, namely ceiling ventilation (CV), sidewall ventilation (SV), and the combination of ceiling and sidewall ventilation (CSV) of a generic scaled-down empty aircraft cabin. Computational Fluid Dynamics (CFD) with Launder-Sharma Low Reynold Number (L-S LRN) turbulence model using Open-source Field Operation and Manipulation (OpenFOAM) software was utilized in this simulation. For all simulated cases, two large circulation regions were observed on both sides of the aircraft cabin, with CV depicted a greater size of circulation compared to other ventilation approaches. The velocity profiles clearly showed the difference between the three ventilation systems, particularly in the merged jet area. Furthermore, different type of ventilation system affects the distribution of the age of the air in the aircraft cabin. The ceiling supplemented with the sidewall mixing system or CSV is able to reduce the age of the air, indicating that it has better ventilation efficiency.

Comparison Analysis on the Hydraulic Performance and Flow Characteristics on a Reactor Coolant Pump Under Rated Operating Condition Between Lead–Bismuth Eutectic and Water Mediums

Abstract Advanced Generation IV nuclear reactors aim to enhance the sustainability, passive safety, reliability, and economic efficiency of reactor operations. Within that, the reactor coolant pump is a critical component in the reactor's cooling system, due to the unique characteristics of the transported medium, posing challenges for engineering applications. This study focuses on a mixed-flow nuclear reactor coolant pump, indicating that significant differences in hydraulic performance and flow characteristics arise due to the varying flow Reynolds numbers under identical operating conditions for the two mediums. Research employing quantitative analysis of boundary layer friction losses and flow separation-induced flow blockage elucidates the origins of hydraulic performance differences. Subsequent studies focusing on the flow characteristics within the impeller reveal that, while the flow patterns inside the impeller show no fundamental differences, an increase in Reynolds number intensifies flow slippage phenomenon, partially diminishing the impeller's work capability. Analysis in static components indicates that the stronger centrifugal forces lead to increased nonuniformity in flow distribution within the guide vanes and an amplified wake phenomenon within the outlet pipe.

Numerical Study on Hydrodynamic Performance and Vortex Dynamics of Multiple Cylinders Under Forced Vibration at Low Reynolds Number

Flow around clustered cylinders is widely encountered in engineering applications such as wind energy systems, pipeline transport, and marine engineering. To investigate the hydrodynamic performance and vortex dynamics of multiple cylinders under forced vibration at low Reynolds numbers, with a focus on understanding the interference characteristics in various configurations, this study is based on a self-developed radial basis function iso-surface ghost cell computing platform, which improves the implicit iso-surface interface representation method to track the moving boundaries of multiple cylinders, and employs a self-constructed CPU/GPU heterogeneous parallel acceleration technique for efficient numerical simulations. This study systematically investigates the interference characteristics of multiple cylinder configurations across various parameter domains, including spacing ratios, geometric arrangements, and oscillation modes. A quantitative analysis of key parameters, such as aerodynamic coefficients, dimensionless frequency characteristics, and vorticity field evolution, is performed. This study reveals that, for a dual-cylinder system, there exists a critical gap ratio between X/D = 2.5 and 3, which leads to an increase in the lift and drag coefficients of both cylinders, a reduction in the vortex shedding periodicity, and a disruption of the wake structure. For a three-cylinder system, the lift and drag coefficients of the two upstream cylinders decrease with increasing spacing. On the other hand, this increased spacing results in a rise in the drag of the downstream cylinder. In the case of a four-cylinder system, the drag coefficients of the cylinders located on either side of the flow direction are relatively high. A significant increase in the lift coefficient occurs when the spacing ratio is less than 2.0, while the drag coefficient of the downstream cylinder is minimized. The findings establish a comprehensive theoretical framework for the optimal configuration design and structural optimization of multicylinder systems, while also providing practical guidelines for engineering applications.

The seepage flow state characteristics of SMA-13 asphalt mixture under triaxial fatigue load

Abstract The seepage flow state of water in asphalt pavement may not accordant with Darcy law due to the high hydrodynamic pressure generated under high-speed traffic load, In order to study the seepage flow state of water in asphalt pavement under high water pressure conditions and analyze the critical conditions for non Darcy flow to occur, the SMA-13 asphalt mixture with different compaction methods and different percent air voids were prepared, and triaxial fatigue tests and high water pressure seepage tests were conducted on the specimens, hydraulic gradient and critical Reynolds number were used to distinguish Darcy and non Darcy phenomena in the seepage process. The results indicate that the linear flow occurs at low flow velocity in the SMA-13 asphalt mixture with different compaction methods and different percent air voids, it shows obvious nonlinear flow at high flow velocity. The values of linear component coefficient a and nonlinear component coefficient b obtained by nonlinear fitting by using Forchheimer's law decrease with the increase of percent air voids, and the values of the coefficients of specimens formed by rotary compaction molding are larger than those formed by Marshall compaction molding. The critical flow velocity and critical Reynolds number increase with the increase of percent air voids before and after triaxial fatigue loading with different molding methods.

A Review of Experiment Methods, Simulation Approaches and Wake Characteristics of Floating Offshore Wind Turbines

With the urgent demand for net-zero emissions, renewable energy is taking the lead and wind power is becoming increasingly important. Among the most promising sources, offshore wind energy located in deep water has gained significant attention. This review focuses on the experimental methods, simulation approaches, and wake characteristics of floating offshore wind turbines (FOWTs). The hydrodynamics and aerodynamics of FOWTs are not isolated and they interact with each other. Under the environmental load and mooring force, the floating platform has six degrees of freedom motions, which bring the changes in the relative wind speed to the turbine rotor, and furthermore, to the turbine aerodynamics. Then, the platform’s movements lead to a complex FOWT wake evolution, including wake recovery acceleration, velocity deficit fluctuations, wake deformation and wake meandering. In scale FOWT tests, it is challenging to simultaneously satisfy Reynolds number and Froude number similarity, resulting in gaps between scale model experiments and field measurements. Recently, progress has been made in scale model experiments; furthermore, a “Hardware in the loop” technique has been developed as an effective solution to the above contradiction. In numerical simulations, the coupling of hydrodynamics and aerodynamics is the concern and a typical numerical simulation of multi-body and multi-physical coupling is reviewed in this paper. Furthermore, recent advancements have been made in the analysis of wake characteristics, such as the application of instability theory and modal decomposition techniques in the study of FOWT wake evolution. These studies have revealed the formation of vortex rings and leapfrogging behavior in adjacent helical vortices, which deepens the understanding of the FOWT wake. Overall, this paper provides a comprehensive review of recent research on FOWT wake dynamics.

Experimental investigation of the effects of different DBD plasma actuators on the aerodynamic performance of the NACA0012 airfoil

Abstract This study aims to investigate the flow control performance of linear and serpentine dielectric barrier discharge (DBD) plasma actuators mounted on the leading edge of a NACA0012 airfoil to control flow separation and improve aerodynamic performance. Experiments were conducted in a subsonic wind tunnel at Reynolds numbers of 87 × 103, 131 × 103, and 175 × 103. Velocity profiles in the wake and static pressure distributions over airfoil were measured using hot-wire anemometry and pressure sensors, respectively. All experiments conducted in the different plasma actuation parameters, including wave voltages (6, 8, 10 kV) and wave frequencies (6, 10 kHz), and the optimal combination of V pp = 10 kV and f AC = 10 kHz was identified. The results of several wind tunnel experiments showed that, a substantial increase in the lift coefficient of up to 26.58% and a delay in stall angle of attack up to 4º due to the implementation of DBD plasma actuators. Additionally, the serpentine actuator demonstrated a more significant impact on separation control compared to the linear actuator where the serpentine actuator has controlled the stall phenomenon more effectively in post-stall angles compared to the linear actuator due to generation of 3D structures.