Open Source Field Research Articles

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.

NURTURING DOMESTIC OPEN-SOURCE TALENTS TO EMPOWER NEW-QUALITY PRODUCTIVITY: CONNOTATIVE CHARACTERISTICS AND DIRECTION OF PROMOTION

The domestic open source industry is showing a vigorous development trend, with many industrial-level open source projects springing up, injecting new vitality into China's independent innovation and industrial development. However, in the face of global competition, we must face up to the challenges we are currently facing. China's open source community is still in a disadvantageous position on the international stage. There is a significant gap between the performance of enterprises in the open source field and that of foreign countries, and there is also a serious shortage of open source talent reserves in domestic universities. In view of this, this article deeply analyzes the shortcomings in the development of open source industry talents, focuses on how to inject strong impetus into new productivity, and deeply explores the connotation characteristics and promotion path of open source talent cultivation, emphasizing the key role of open source talents in the formation of new productivity. Based on these analyses, this article proposes a series of countermeasures and suggestions, including supporting the development of open source communities, strengthening the construction of open source talent teams in enterprises, strengthening the cultivation and echelon construction of open source talents in universities, integrating talent elements and scientific and educational resources, and exerting the siphon effect of talents, aiming to help China achieve a leading position in the open source industry and promote the sustainable development of new productivity.

Phase-field formulated meshless simulation of axisymmetric Rayleigh-Taylor instability problem

A formulation of the immiscible Newtonian two-liquid system with different densities and influenced by gravity is based on the Phase-Field Method (PFM) approach. The solution of the related governing coupled Navier-Stokes (NS) and Cahn-Hillard (CH) equations is structured by the meshless Diffuse Approximate Method (DAM) and Pressure Implicit with Splitting of Operators (PISO). The variable density is involved in all the terms. The related moving boundary problem is handled through single-domain, irregular, fixed node arrangement in Cartesian and axisymmetric coordinates. The meshless DAM uses weighted least squares approximation on overlapping subdomains, polynomial shape functions of second-order and Gaussian weights. This solution procedure has improved stability compared to Chorin's pressure-velocity coupling, previously used in meshless solutions of related problems. The Rayleigh-Taylor instability problem simulations are performed for an Atwood number of 0.76. The DAM parameters (shape parameter of the Gaussian weight function and number of nodes in a local subdomain) are the same as in the authors’ previous studies on single-phase flows. The simulations did not need any upwinding in the range of the simulations. The results compare well with the mesh-based finite volume method studies performed with the open-source code Gerris, Open-source Field Operation and Manipulation (OpenFOAM®) code and previously existing results.

A finite volume model for maintaining stationarity and reducing spurious oscillations in simulations of sewer system filling and emptying

This paper introduces a model for simulating the unsteady dynamics of sewer systems filling and emptying, offering greater accuracy and stability. This article presents two novel contributions: first, the HLLS scheme (Harten–Lax–van Leer + Source term) is adapted to ensure the preservation of stationary conditions not only in free surface flows, as originally conceived, but also in pressurized flows and mixed flow scenarios. Second, a new method is proposed for the treatment of open channel flow cells near pressurization or adjacent to pressurized cells to minimize spurious oscillations when utilizing the two-component pressure approach (TPA) model. To verify the new model's effectiveness, it was tested for various conditions against the outcomes of the Open Source Field Operation and Manipulation (OpenFOAM) computational fluid dynamics (CFD) model. Furthermore, to demonstrate the model's potential for simulating real systems, the model was applied to three sewer systems that closely resemble real-world conditions, each of which had been intentionally modified for confidentiality purposes. The results show that the improved model successfully maintains stationary conditions within a sloped pipe across various flow conditions, while also preventing spurious oscillations at mixed flow interfaces even when using a pressure wave speed of 1000 m s − 1 .

Three-dimensional numerical investigation of vortex-induced vibration of a circular cylinder at low Reynolds number

Three-dimensional numerical investigations of vortex-induced vibration (VIV) of flexibly mounted rigid circular cylinder have been carried out using Open Source Field Operation And Manipulation (OpenFOAM). The cylinder is allowed to oscillate in both streamwise as well as cross-stream directions. The cylinder response and wake transition are studied by varying the mass damping parameter ( m∗ζ , 0.01 and 0.1) and Reynolds number (Re). The computations are conducted for a wide range of reduced velocities ( Ur ), ranging from 3 to 8, at a fixed value of Re equal to 350. Furthermore, the effect of Re, varied from 250 to 400, on VIV is illustrated for a fixed value of Ur = 4.5. The response of the cylinder in terms of streamwise and cross-stream displacements is examined in and outside the lock-in regime. The cylinder trajectories are found to be influenced by the change in Ur , m∗ζ and Re. The dynamic characteristics are also disclosed with the change in Ur , m∗ζ and Re. In order to capture the effect of Re on the wake transition of the circular cylinder undergoing VIV, the value of Re is varied from 250 to 400. Mode A instability is observed to be delayed due to VIV in comparison to that of the stationary cylinder.

An enhanced large-scale benthic reflectance retrieval model for the remote sensing of submerged ecosystems in optically shallow waters

Shallow water benthic habitats have been significantly degraded and seriously threatened by intensifying climate changes and anthropogenic stressors. Benthic reflectance (Rbλ) of optically shallow waters (OSWs) is a key parameter for remote sensing of benthic habitats’ composition and health status. The remote sensing reflectance (Rrsλ) just above the water surface contains the coupled spectral information of the water column and seabed in OSWs, which makes our effort challenging to separate the signals between seabed and water column properties. Due to too many unknowns of the water column and seabed optical properties, the current approaches are inaccurate or inadequate to retrieve benthic reflectance spectra over a large area from remotely sensed data. In this study, we proposed an enhanced large-scale benthic reflectance (LSBR) retrieval model from satellite data in OSWs with only input of Rrsλ. A new spectral library of benthic reflectance was built upon multi-source reflectance datasets obtained from several open-source field measurements. Then, the specific relationship between Rb443nm and Rb490nm was developed. By combining a semi-analytical benthic reflectance (SABR) model based on radiative transfer simulations and this relationship, water-column chlorophyll concentration (chl) was determined. Moreover, large-scale water depth was estimated by Rrsλ through satellite-derived bathymetry (SDB) technologies. Finally, benthic reflectance was retrieved with the inputs of the satellite-derived Rrsλ, chl, and water depth. In this way, the LSBR model fulfills the Rbλ retrieval with only input of satellite-derived Rrsλ. The new model was successfully applied to Sentinel-2/MSI data in the seagrass region of Xincun Bay and the coral region of Huaguang Reef and further verified by using field measurements and results of the along-track benthic reflectance (ATBR) retrieval model, which combined active lidar and passive high-resolution satellite images. Additionally, to gain insights into the long-term evolution of benthic communities, a typical application of the LSBR model for detecting benthic changes was conducted using eight years of Sentinel-2/MSI data in Heron Reef, depicting a similar consistency between the probable deterioration and restoration region and the sea surface temperature (SST) anomalies. The results demonstrated the robustness and accuracy of the LSBR model in retrieving benthic reflectance at large scales. The LSBR model should be helpful for further investigating benthic changes which can enhance the ability to monitor and assess the health status of submerged ecosystems in OSWs.

Open Meter Duo: Low-Cost Instrument for Fluorimetric Determination of Cholinesterase Activity.

Environmental screening is essential due to the increased occurrence of harmful substances in the environment. Open Meter Duo (OMD) is an open-source field photo/fluorimeter that uses an RGB diode that imitates a color according to the selected wavelength and uses a UV LED from the security kit diode as an excitation light source. The prepared PCB shield with a 3D-printed aperture was connected to Arduino UNO R4 WiFi. This system was used for the fluorescent detection of cholinesterase activity with the indoxyl acetate method. Carbofuran-a toxic pesticide-and donepezil-a drug used to treat Alzheimer's disease-were tested as model inhibitors of cholinesterase activity. The limit of detection of indoxyl acetate was 11.6 μmol/L, and the IC50 values of the inhibitors were evaluated. This system is optimized for wireless use in field analysis with added cloud support and power source. The time of analysis was 5 min for the fluorimetric assay and 20 min for the optional photometric assay. The time of field operation was approximately 4 h of continuous measurement. This system is ready to be used as a cheap and easy control platform for portable use in drug control and point-of-care testing.

High-Order Spectral Irregular Wave Generation Procedure in Experimental and Computational Fluid Dynamics Numerical Wave Tanks, with Application in a Physical Wave Tank and in Open-Source Field Operation and Manipulation

The accurate generation of a target sea state in numerical or experimental wave tanks is a fundamental line of research for the ocean engineering community. It guarantees the quality and relevance of wave–structure interaction tests. This study presents a reproducible irregular wave generation and qualification procedure, accounting for the nonlinear aspects of wave propagation. It can be used for both numerical simulation and experiments. The presented numerical and experimental results are obtained from the OpenFOAM solver and the Ecole Centrale Nantes wave tank facilities, respectively. The procedure comprises two steps: First, the wavemaker motion is calibrated numerically to generate the target wave spectrum at the position of interest. This is achieved with a wavemaker-equipped nonlinear potential flow solver. The open-source HOS-NWT solver, based on the high-order spectral method, was employed in this study. Then, the corrected wavemaker motion is used directly in the experimental wave tank. OpenFOAM simulations were performed to generate waves with the relaxation method, using wave elevation and velocity field data from HOS-NWT. The procedure was finally tested for mild and extreme breaking sea states. The waves generated by the HOS-NWT solver, the experiment, and the OpenFOAM simulation were compared from both stochastic and deterministic perspectives.

Direct numerical simulations on oscillating flow past surface-mounted finite-height circular cylinder

In this work, a surface-mounted circular cylinder with a fixed aspect ratio (ratio of height of the cylinder to its diameter) of 5 is subjected to a non-zero mean oscillating flow with a range of frequencies and amplitudes. Three-dimensional direct numerical simulations are then conducted on this finite-height cylinder. The mass and momentum equations are resolved using the finite volume-based Open Source Field Operation and Manipulation (OpenFOAM). A fixed Reynolds number Re=UoD/ν of 250 is used in this study, which is defined based on mean velocity at the inlet ( Uo ) and cylinder diameter (D). Here ν is the kinematic viscosity of the working fluid. Non-dimensional velocity oscillation amplitude ( A∗=a/Uo ) is varied from 0.1 to 0.3, while the non-dimensional oscillation frequency ( f∗=f/fo ) takes the values of 0.33, 0.5, 1, 2, and 3. Here a and f are the dimensional oscillation amplitude and frequency, respectively and fo is the vortex shedding frequency corresponding to a uniform flow at Re = 250. The three-dimensional vortex structures, presented with the help of iso-Q surfaces, show that the oscillating flow changes the size and shape of the hairpin-shaped vortices. Wake is found to be synchronized with the oscillation frequency at f* = 2 for each value of the A* and results in the maximum lift force on the cylinder. Hilbert Huang transformation analysis of the transverse velocity signals at a specific point in the wake reveals that the wake is more complex and aperiodic in nature for f* values of 0.33, 0.5, and 1, whereas it is periodic for f* = 2 and 3. In order to further disclose the nonlinearity associated with the oscillating flow, the degree of stationarity is discussed corresponding to each value of A* and f*. Dynamic mode decomposition is exploited to obtain information about the coherent vortical structures and their spatial and temporal behavior in the wake with a change in the value of f*. Effects of A* and f* on the dynamic characteristics are also investigated.

Wall effect on the wake characteristics of a transversely rotating sphere

In the present work, the flow over a transversely rotating sphere placed at varying separation from a plane wall at a Reynolds number Re=U∞Dν of 300 is numerically investigated using Open Source Field Operation and Manipulation, where Re is defined based on the free stream velocity (U∞) and the diameter (D) of the sphere. Three values of the non-dimensional rotational speed ω*=ωD2U∞, viz., −1, 0 and 1, have been chosen with ω being the dimensional rotation rate with anticlockwise rotation being positive. The non-dimensional separation gap G=gD between the sphere and the wall is varied from 0.25 to 3.0. Here, g is the dimensional gap between the sphere and the wall. At ω*=0 and G = 0.25, the wall completely suppresses vortex shedding from the sphere, whereas flow is found to be unsteady for other values of ω* and G. As compared to the case in the absence of the wall, the presence of the wall causes an increase in vortex shedding frequency for ω*=0 and 1 and decrease for ω*=−1. Hilbert spectrum reveals that the wake nonlinearity remains unchanged with an increase in G for ω*=0. On the other hand, it increases for ω*=−1 and decreases for ω*=1. Similar to the observation made for vortex shedding, the presence of wall increases drag force on the sphere for ω*=0 and 1 and decreases for ω*=−1. In order to reveal the spatial and temporal behavior of the coherent structures in the unsteady wake, dynamic mode decomposition (DMD) has been performed. For all the values of G, DMD mode 1 is found to be the primary vortex shedding mode.

Numerical Study of the Boundary Layer Separation of a Low‐Pressure Turbine Cascade at Different Incidence Angles

Modern low‐pressure turbine (LPT) pursues high blade loading to improve its efficiency while the possibility of boundary layer separation on the blades is still a challenging problem. The incidence angle is one of the main factors affecting the flow separation and laminar‐turbulent transition, which is of key importance for the design of LPT. In this work, based on the initial simulation results obtained using the Reynolds‐averaged Navier–Stokes (RANS) method, the flow past a single LPT cascade at three representative incident angles (i = −10°, 0°, +10°) is investigated using large‐eddy simulation (LES) method with approximately 26 million structured grids. The simulations are carried out with Open Source Field Operation and Manipulation (OpenFOAM) for an off‐design low Reynolds number condition Re = 40,000 and Ma = 0.5. The time‐averaged aerodynamic performances and three‐dimensional instantaneous flow characteristics of the LPT cascade are discussed in detail, and the results show that the blade loading and the transverse pressure gradient (TPG) from the pressure side to the suction side of leading edge (LE) increase with increasing incidence angle. At the incidence angle of +10°, the LPT cascade undergoes separation and reattachment from the LE to around 20% Cax on the suction surface, which weakens the separation phenomenon at the rear half of the suction surface and the total pressure loss downstream of the trailing edge (TE). It is worth noting that the RANS method underpredicts the blade boundary layer separation region compared with LES under these extreme conditions. These results may offer off‐design condition data for the future improvement of RANS models or experimental studies.

Implementation of a level-set-based volume penalization method for solving fluid flows around bluff bodies

A volume penalization-based immersed boundary technique is developed and thoroughly validated for fluid flow problems, specifically flow over bluff bodies. The proposed algorithm has been implemented in an open source field operation and manipulation (OpenFOAM), a computational fluid dynamics solver. The immersed boundary method offers the advantage of inserting a complex solid object inside a Cartesian grid system, and therefore, the governing equations can be applied to such a simpler grid arrangement. For capturing the fluid–solid interface more accurately, the grid is refined near the solid surface using topoSetDict and refineMeshDict utilities in OpenFOAM. In order to avoid any numerical oscillation and to compute the gradients accurately near the interface, the present volume penalization method (VPM) is integrated with a signed distance function, which is also referred to as a level-set function. Benchmark problems, such as flows around a cylinder and a sphere, are considered and thoroughly validated with the results available in the literature. For the flow over a stationary cylinder, the Reynolds number is varied so that it covers from a steady two-dimensional flow to an unsteady three-dimensional flow. The capability of the present solver has been further verified by considering the flow past a vibrating cylinder in the cross-stream direction. In addition, a flow over a sphere, which is inherently three-dimensional due to its geometrical shape, is validated in both steady and unsteady regimes. The results obtained by the present VPM show good agreement with those obtained by a body-fitted grid using the same numerical scheme as that of the VPM, and also with those reported in the literature. The present results indicate that the VPM-based immersed boundary technique can be widely applicable to scientific and engineering problems involving flow past stationary and moving bluff bodies of arbitrary geometry.

Hydrodynamic characteristics and particle tracking of 90° lateral intakes at an inclined river slope

Lateral intakes are common in rivers. The pump efficiency and sediment deposition are determined by the local hydrodynamic characteristics and mainstream division width. The hydraulic characteristics of lateral withdrawal from inclined river slopes at different intake elevations should be investigated. Meanwhile, the division width exhibits significant vertical non-uniformity at an inclined river slope, which should be clarified. Hence, a three-dimensional (3-D) hydrodynamic and particle-tracking model was developed with the Open Source Field Operation and Manipulation (OpenFOAM), and the model was validated with physical model tests for 90° lateral withdrawal from an inclined side bank. The flow fields, withdrawal sources, and division widths were investigated with different intake bottom elevations, withdrawal discharges, and main channel velocities. This study showed that under inclined side bank conditions, water entered the intake at an oblique angle, causing significant 3-D spiral flows in the intake rather than two-dimensional closed recirculation. A lower withdrawal discharge, a lower bottom elevation of the intake, or a higher main channel velocity could further strengthen this phenomenon. The average division width and turbulent kinetic energy were smaller under inclined side bank conditions than under vertical bank conditions. With a low intake bottom elevation, a low withdrawal discharge, or a high main channel velocity, the sources of lateral withdrawal were in similar ranges near the local inclined bank in the vertical direction. Under inclined slope conditions, sediment deposition near the intake entrance could be reduced, compared to that under vertical slope conditions. The results provide hydrodynamic and sediment references for engineering designs for natural rivers with inclined terrains.

CFD SIMULATION AND VALIDATION FOR MIXING VENTILATION SCALED-DOWN EMPTY AIRCRAFT CABIN USING OPENFOAM

An investigation into the spread of the COVID-19 virus within a confined space including an aircraft cabin is essential in order to find out the mechanism. However, this is time-consuming and limited in scope, so a computational fluid dynamics (CFD) simulation is used instead. Therefore, a prior study and an appropriate choice of turbulence model are required before the simulation. The main objective of this study is to validate and evaluate the results predicted by the Open Source Field Operation and Manipulation (OpenFOAM) software through comparison with the experimental data from the literature which was conducted using particle image velocimetry (PIV) measurement. Three different Reynolds-averaged Navier-Stokes turbulence models were selected; Re-normalisation Group k - ɛ (RNG), Realizable k - ɛ (RLZ) and Low Reynold Number (LRN) to simulate a mixing ventilation system of a scaled-down model of empty aircraft cabin. In the RNG and LRN model cases, a fairly large circulation flows were observed on the right and left sides of the model representing the passenger area. The results were also evaluated quantitatively using the factor of two of observations (FAC2) for the velocity components and turbulent kinetic energy (TKE) with root mean square error (RMSE) for the former and normalised mean square errors (NMSE) for the latter. The simulation results showed that RNG and LRN are capable of predicting the flow field well. However, for TKE prediction LRN performed better than RNG which concluded that LRN is the suitable turbulence model in simulating flow fields in investigated case.

NUMERICAL SIMULATION OF A FLUID FLOW IN THE CYLINDRICAL DUCT CONTAINING TWO DIAPHRAGMS WITH ORIFICES OF DIFFERENT DIAMETERS

The flow of a viscous incompressible fluid in a cylindrical duct with two serial diaphragms with orifices of different diameters was studied based on the numerical solution of the unsteady Navier-Stokes equations. The solution algorithm was based on the finite volume method using second-order accurate difference schemes in both space and time. The TVD (Total-Variation Diminishing) form of a central-difference scheme with a flux limiter was used for the interpolation of the convective terms. The combined evaluation of the velocity and pressure fields was carried out using the PISO (Pressure Implicit Split Operator) procedure. The problem was solved using OpenFOAM (Open-source Field Operation And Manipulation) open-source toolkit libraries using the computing power of the cluster supercomputer of the V.M. Glushkov Institute of Cybernetics of the National Academy of Sciences of Ukraine. It was shown that within a certain range of the diameter ratio of the orifices of the diaphragms, a circulation movement is established in the cavity between the diaphragms. The boundary layer breaks off from the surface of the first diaphragm and forms an annular shear layer. When approaching the second diaphragm, a sequence of ring vortices is formed in it, which interact with the surface of the diaphragm and lead to the emergence of tonal sound. When the ratio of the orifice diameter of the second diaphragm to the first decreases, the share of the jet’s kinetic energy, which participates in the circulation in the middle of the cavity between the diaphragms, increases. As a result, the amplitude of velocity fluctuations in the orifice of the second diaphragm decreases. When the ratio of the diameters of the orifices increases, the share of energy involved in the circulation decreases, and when a certain value of the ratio is reached, the interaction between the vortices in the shear layer and the surface of the diaphragm does not occur. As a result, the excitation of the tonal sound stops. The Strouhal number of self-oscillations practically does not change when the diameter ratio of the orifices changes. During the calculations, two different modes of self-oscillation were obtained, which is consistent with previous works.

Visualization and Parametric Study on Vortex Shedding Suppression of Cylindrical Structures in Offshore Engineering Using Large Eddy Simulation

Cylindrical structures are widely used in offshore and marine engineering, but they may suffer from vortex-induced vibration under the influence of ocean or wave currents, which can lead to severe fatigue damage. In this study, we applied the open-source software Open-Source Field Operation and Manipulation (OpenFOAM) to investigate the characteristics of fluid flow around offshore cylindrical structures, taking into account the effect of helical strake parameters, such as pitch and strake number. The aim of this study is to explore the possibility of suppressing vortex shedding with different helical strake parameters. Numerical simulation results demonstrated that attaching a helical strake to the bare cylinder destroyed vortex shedding in offshore cylindrical structures. The vortex visualization showed that the helical strake destroyed the three-dimensional vortex structures. Moreover, the lift coefficient data showed that the vibration frequency of the cylinder decreased after attaching the helical strake, indicating that the vortex-induced vibrations on the wake flow tended to fade. The results suggest that the helical strake is a promising option for suppressing the wake vortex shedding of cylindrical structures in offshore engineering.

Effect of size and spacing on the wake characteristics of two spheres placed in tandem

In the present study, the flow past two spheres placed in a tandem arrangement is investigated numerically using open source field operation and manipulation (OpenFOAM) at a fixed Reynolds number (Re) of 300, where the Reynolds number is defined based on the diameter (D) of the downstream sphere (DS) and the freestream velocity at the inlet. Keeping size of the DS constant, the diameter of the upstream sphere (US) has been varied, so that the diameter ratio, DR (ratio of the diameters upstream and downstream spheres), takes the values of 0.4, 0.6, 0.8, 1.0, and 1.5. The spacing between the spheres (S) is also varied from 1D to 5D. Iso-Q surfaces show that both upstream and downstream wakes undergo various transitions with changes in the values of DR and S. For US, transition from steady symmetric to planar symmetric occurs at DR = 0.6 and S = 1, which corresponds to a local Re of 180. For DR = 0.8, steady to unsteady transition occurs at S = 2, whereas for all other values of S, the wake remains steady. For DR > 0.8 and S > 1, both upstream and downstream wakes are found to be unsteady. Hilbert analysis revealed that unsteady wakes are periodic for DR values of 0.4, 0.8, and 1.0 and are aperiodic for DR = 1.5. In addition, the extent of wake nonlinearity has also been quantified in terms of degree of stationarity. The drag force on both the spheres increases with an increase in spacing between the spheres.

Numerical study of rotating convection with bi-directional temperature gradients

In this work, we report results from three-dimensional numerical simulations of convection in a rotating cylindrical annulus with mean temperature gradients present along the radial and vertical directions. The simulations have been performed in OpenFOAM (Open-source Field Operation And Manipulation). The bi-directional temperature gradient is achieved by imposing uniform heat flux in a thin circular strip at the outer periphery of the bottom surface, and a uniform temperature at the entire inner cylindrical surface. The study has been carried out for a particular Rayleigh number, Ra = 4.76×108, and a range of Taylor numbers, Ta = 6.5×108–2.7×109. The Ra value is chosen so that some qualitative comparison could be done with available experimental data. A laminar flow solver has been used to perform the computations in a rotating frame of reference. Complex empirical orthogonal function analysis has been carried out for the velocity and temperature fields. The contour maps of the radial velocity field in the r−θ plane clearly show the existence of mode 4 and 4 AV (amplitude vacillation) baroclinic waves at low values of Ta, which break down into eddies as Ta increases. The mean temperature field in the r–z plane supports the existence of Convective Columnar Plumes (CCP) on the outer edge, which interacts with the baroclinic waves, aiding in the transport of heat in the system. The fluctuations in CCP disintegrate into smaller-scale structures at the highest Ta. Quantification of turbulent fluxes shows the effectiveness of the heat transport at Ta∼O(108), as compared to Ta∼O(109). Our results clearly demonstrate the role of waves, plumes, and eddies on heat transport in the presence of bi-directional temperature gradients.

Actuator line model using simplified force calculation methods

Abstract. To simulate transient wind turbine wake interaction problems using limited wind turbine data, two new variants of the actuator line technique are proposed in which the rotor blade forces are computed locally using generic load data. The proposed models, which are extensions of the actuator disk force models proposed by Navarro Diaz et al. (2019a) and Sørensen et al. (2020), only demand thrust and power coefficients and the tip speed ratio as input parameters. In the paper the analogy between the actuator disk model (ADM) and the actuator line model (ALM) is shown, and from this a simple methodology to implement local forces in the ALM without the need for knowledge of blade geometry and local airfoil data is derived. Two simplified variants of ALMs are proposed, an analytical one based on Sørensen et al. (2020) and a numerical one based on Navarro Diaz et al. (2019a). The proposed models are compared to the ADM using analogous data, as well as to the classical ALM based on blade element theory, which provides more detailed force distributions by using airfoil data. To evaluate the local force calculation, the analysis of a partial-wake interaction case between two wind turbines is carried out for a uniform laminar inflow and for a turbulent neutral atmospheric boundary layer inflow. The computations are performed using the large eddy simulation facility in Open Source Field Operation and Manipulation (OpenFOAM), including Simulator for Wind Farm Applications (SOWFA) libraries and the reference National Renewable Energy Laboratory (NREL) 5 MW wind turbine as the test case. In the single-turbine case, computed normal and tangential force distributions along the blade showed a very good agreement between the employed models. The two new ALMs exhibited the same distribution as the ALM based on geometry and airfoil data, with minor differences due to the particular tip correction needed in the ALM. For the challenging partially impacted wake case, both the analytical and the numerical approaches manage to correctly capture the force distribution at the different regions of the rotor area, with, however, a consistent overestimation of the normal force outside the wake and an underestimation inside the wake. The analytical approach shows a slightly better performance in wake impact cases compared to the numerical one. As expected, the ALMs gave a much more detailed prediction of the higher-frequency power output fluctuations than the ADM. These promising findings open the possibility to simulate commercial wind farms in transient inflows using the ALM without having to get access to actual wind turbine and airfoil data, which in most cases are restricted due to confidentiality.

Open-source simulation of strongly-coupled fluid-structure interaction between non-conformal interfaces

Design code-based “life-safety” requirements for structural earthquake and tsunami design offer reasonable guidelines to construct buildings that will remain standing during a tsunami or seismic event. Much less consideration has been given to assessing structural resilience during sequential earthquake and tsunami multi-hazard events. Such events present a series of extreme loading scenarios, where damage sustained during the earthquake influences structural performance during the subsequent inundation. Similar difficulties exist with respect to damage sustained during tropical events, as wind and fluid loading may vary with structural response or accumulated damage. To help ensure critical structures meet a “life-safety” level of performance during such multi-hazard events, analysis software capable of simulating simultaneous structural and fluid dynamics must be developed. To address this gap in understanding of non-linear fluid-structure-interaction (FSI), an open-source tool (FOAMySees) was developed for simulation of tsunami and wave impact analysis of post-earthquake non-linear structural response of buildings. The tool is comprised of the Open-source Field Operation And Manipulation software package and OpenSeesPy, a Python 3 interpreter of OpenSees. The programs are coupled via preCICE, a coupling library for partitioned multi-physics simulation. FOAMySees has been written to work in a Linux OS environment with HPC clusters in mind. The FOAMySees program offers a partitioned conventional-serial-staggered coupling scheme, with optional implicit iteration techniques to ensure a strongly-coupled two-way FSI solution. While FOAMySees was developed specifically for tsunami-resilience analysis, it may be utilized for other FSI applications with ease. With this coupled Computational Fluid Dynamics (CFD) and Finite Element Analysis (FEA) program, tsunami and earthquake simulations may be run sequentially or simultaneously, allowing for the evaluation of non-linear structural response to multi-hazard excitation.