Computational Fluid Dynamics Program Research Articles

Research on the air-infiltration rate shelter coefficient of building complexes based on building parameter clustering

The configuration of a building complex can significantly influence the air-infiltration rate, which subsequently affects the energy consumption for heating and cooling. Given the diversity of parameters associated with a building complex, it is challenging to study all combinations. This study proposed the k-means clustering method to identify representative building clusters, thereby facilitating the derivation of correction coefficient for the air-infiltration rate within a complex. Initially, data pertaining to district characteristics, such as the complex density, height, and building aspect ratio, were collected and clustered to obtain several representative groups of building clusters. Subsequently, a validated computational fluid dynamics program with the renormalization group (RNG) k–ε turbulence model was employed to investigate the spatial characteristics of the pressure coefficient (Cp) on building surfaces across various groups within the complex. Finally, the shelter coefficient (SAIR), which represents the ratio of an individual building to those in different groups, was determined to correct for the air-infiltration rate in diverse district types. The results show that SAIR varies considerably (from 0.15 to 0.53) owing to the different densities, heights, and layouts between buildings. The applicability of SAIR was further demonstrated and verified in a case study of a building in Dalian, China. The research results can provide a method for predicting the air-infiltration rate of building complex.

Cohesive particle–fluid systems: An overview of their CFD simulation

AbstractSolid particles may experience different kinds of cohesive forces, which cause them to form agglomerates and affect their flow in multiphase systems. When such systems are simulated through computational fluid dynamics (CFD) programs, appropriate modelling tools must be included to reproduce this feature. In this review, these strategies are addressed for various systems and scales. After an introduction of the different forces (van der Waals, electrostatic, liquid bridge forces, etc.), the modelling approaches are categorized under three methodologies. For diluted slurries of very fine particles, many researchers succeeded with pseudo‐single phase approaches, employing a model for the non‐Newtonian rheology. This was especially popular for sludges in anaerobic digestions or certain types of soils. In other cases, continuum‐based approaches seem to be more adequate, including cohesiveness in the kinetic theory of granular flows or the restitution coefficient. Geldart‐A particles experiencing van der Waals forces are the primary focus of such studies. Finally, when each particle is modelled as a discrete element, the cohesive force can be directly specified; this is especially widespread for the wet fluidization case. For each of these approaches, a general overview of the main strategies, achievements, and limits is provided.

Validation of coupled ATHLET-OpenFOAM simulation on a large-scale single- and two-phase flow experiment

Abstract System thermal-hydraulics (STH) codes are successfully used in the last decades for design and analysis of the physical behavior of nuclear power plants (NPPs). These programs provide reliable results at comparatively low computational cost, but have limited capabilities to predict complex 3D flow phenomena, which is possible with Computational Fluid Dynamics (CFD) tools. In order to combine the advantages of STH and CFD codes, algorithms to couple these are developed. At GRS, a new OpenFOAM solver, based on the volume of fluid (VOF) method, was developed together with new coupling boundary conditions to couple the CFD program OpenFOAM with the system code ATHLET. In a next step, verification and validation activities were carried out. These included the analysis of a Pressurized Thermal Shock (PTS) scenario. For this purpose, data from the OECD/NEA ROSA V Test 1.1, carried out in the Japanese Large-Scale Test Facility (LSTF) was used. The experiment investigated the temperature stratification after emergency core cooling (ECC) injection under single- and two-phase natural circulation conditions in the primary cooling circuit of a pressurized water reactor (PWR). This paper discusses the results of the coupled simulations, compares the numerical results with experimental data, and identifies areas for future improvements.

Impacts of gaps below both door and partition walls of cubicles on odorous gas transport and respiratory infection in a public lavatory

Odorous gas transport and respiratory infection in a public lavatory are highly subject to the adopted ventilation system. The gaps below both the cubicle door and the partition walls can affect the ventilation performance. This study employed a validated computational fluid dynamics (CFD) program to investigate a public lavatory containing four cubicles with squat toilets. The airflow, concentrations of hydrogen sulfide and methyl mercaptan, and respiratory infection risk during use of the toilet were modeled. Odorous gases were released from the squat pan, while the pathogens resulting in respiratory infection were released by the exhalation of the toilet users. A total of seven different gap designs were considered, including designs without any gap, with a gap below only the cubicle door in three different gap heights, and gaps in three different heights below both the door and the partition walls. In addition, the use of a single central air exhaust and the use of multiple air exhausts were compared. The results revealed that the air from the gap below each cubicle door can effectively dilute the odorous gases released from the squat pan, whereas the gap below the partition walls was not shown to be favorable. The use of multiple air exhausts restrains the pollutant's spread and reduces the respiratory infection risk.

A Numerical Analysis on the Performance and Optimization of the Savonius Wind Turbine for Agricultural Use

Given the state of the world nowadays, renewable energy is becoming more and more essential rendering wind turbine electricity quite important. Its shape and the fact that the Savonius vertical axis wind turbine runs at relatively low wind speeds with high torque values makes it suitable for practical uses such as that of an irrigation system in agriculture industry. This paper utilizes numerical research with Computational Fluid Dynamics (CFD) to investigate the performance of a vertical-axis wind turbine. The ANSYS CFD program was engaged to construct the simulations during the pre- and post-processing stages. Wind speed remained constant while the angular velocity was altered to enable analysis of the flow through the wind turbine. Because of its mechanical simplicity, the primary profile of a semicircle has remained a typical option for turbines that generate high torque based on drag force. The effects of using elliptical curves and the fluctuation in thickness along the profile chord were both examined in this study. Equivalently, an attempt to optimize the rotor's design was made. After the performance of a numerical simulation, a geometry consisting of simple circle arcs was developed, with a 10.9% improvement in the power coefficient, analogous to prior optimizations with more complicated geometries. The numerical results derived include the torque coefficient evolution throughout a full rotation as well as the distribution of vorticity magnitude at different rotor points.

DEVELOPMENT OF NEW DESIGNS OF HORIZONTAL BULB HYDROTURBINES

The key aspects and methods of increasing the energy and operational efficiency of hydraulic turbine equipment at hydroelectric power plants areconsidered. A detailed analysis of directions for improving the main indicators characterizing the advantages of horizontal-type bladed hydraulicturbines has been carried out. Particular attention is paid to direct-flow rotary-blade hydraulic turbines with a horizontal axis of rotation for thehydraulic unit. These hydraulic turbines offer significant advantages over those using a spiral casing for water supply, including high throughput and awide range of operating pressures and flow rates. The focus of the article is on the advantages of direct-flow bulb hydraulic turbines and their potentialuse at high pressures. However, existing direct-flow hydraulic units operate at low heads of up to 25 m. Therefore, there is a need to develop newdesigns for these turbines to operate efficiently at higher heads up to 280 m, expanding the reliable operation zone. The paper examines new designsolutions for which Ukrainian patents have been received, aiming at the effective use of horizontal bulb hydraulic units. The text highlights theproblems of increasing the energy and operational performance of hydraulic turbine equipment at hydroelectric power plants, presenting importanttasks for researchers to optimize structures and improve efficiency. Recommendations for carrying out numerical modeling in CFD (ComputationalFluid Dynamics) programs are proposed to provide a detailed understanding of hydrodynamic processes in the flow parts of hydraulic turbines. Thepurpose of numerical modeling is to evaluate the efficiency and productivity of new hydroturbines in different operating modes. This includesanalyzing the pressure distribution, flow rate and other characteristics inside the turbine. The obtained data will allow to identify potential "weak"points and optimize the blading and other structural elements for maximum efficiency. This integrated research approach, including both experimentaland multiple methods, will contribute to the development of efficient and reliable hydroturbines in line with modern requirements for sustainableenergy development.

Study on coupled heat transfer model and enhanced heat transfer law of liquid metals and supercritical fluids

ABSTRACT The supercritical carbon dioxide Brayton cycle system is being considered for application in the power conversion system of advanced liquid metal fast reactors. One important research topic is the coupled heat transfer characteristics and enhanced heat transfer laws between liquid metals and supercritical fluids. However, the traditional Reynolds analogy hypothesis with a constant turbulent Prandtl number is difficult to satisfy the numerical conjugate heat transfer research of liquid metals and supercritical fluids. Therefore, based on the open-source computational fluid dynamics program OpenFOAM, a numerical method suitable for the coupled heat transfer calculation of liquid metals and supercritical fluids was developed, which can achieve precise conjugate heat transfer solutions by applying different turbulence models and heat flux models to liquid metals and supercritical fluids. Subsequently, based on this method, the coupled heat transfer behavior of liquid metals and supercritical fluids in the straight channel of a typically printed circuit heat exchanger was studied. The focus was investigating the conjugate heat transfer characteristics of liquid heavy metal lead-bismuth eutectic and liquid metal sodium with supercritical carbon dioxide. Some sensitive results, including the inlet temperature and Reynolds number of liquid metals and supercritical fluids, were qualitatively and quantitatively analyzed.

NUMERICAL SIMULATION OF TURBULENT FLOW IN A HEAT EXCHANGER EQUIPPED WITH FINS OF DIFFERENT MATERIALS AND GEOMETRIES

The miniaturization of electronic devices causes heat generation in the system. In this scenario, highly effective heat sinks are needed for the electronic devices. The present study focuses on enhancing heat transfer in heat sinks by using pin fins with different geometries (circular, elliptical, triangular, and square), various materials for pin fins (copper, aluminum, magnesium, tungsten, zinc, and steel), and Al<sub>2</sub>O<sub>3</sub>-EG nanofluid. The analysis is carried out by a commercial computational fluid dynamics (CFD) program called Ansys Fluent 14, which was used to numerically solve the governing equations and boundary conditions. The 3D model is subsequently discretized using the ICEM CFD meshing tool. From the analysis, it has been observed that 331.75 W of heat is lost by using copper material in a heat sink, and magnesium recorded 363.7 W of heat loss, whereas aluminum recorded 319.5 W. Moreover, copper is a great material for transferring heat. This means that heat moves quickly through copper and magnesium as they have good thermal conductivity. Elliptical materials conserve materials more than others when the space is limited to one direction. Elliptical shapes record 461.67 W heat loss.

Integration for coaxial irradiation of fiber laser, oxygen jet, and oxy-fuel gas

This study introduces a convergence approach named laser oxyfuel and oxy-flame hybrid (LOXAFH) cutting, integrating laser cutting and oxyfuel cutting techniques for cutting clad steel plates. The LOXAFH method combines laser, oxyflame, and oxygen jet in a coaxial manner, harnessing 1 kW power concentration. The LOXAFH cutting head was meticulously developed on the basis of a ray transfer matrix and estimated refractive index by incompressible flow with a computational fluid dynamics program and an optical design program. The LOXAFH cutting is validated through three experiments on 15 mm clad steel plates: oxyfuel cutting, laser-assisted oxygen cutting (LASOX), and LOXAFH cutting.

Experimental and Numerical Investigation of the Control of the Flow Structure on Surface Modified Airfoils

In this study, experimental and numerical flow analysis was performed on three different blade profiles with a chord length of 165 mm using passive flow control method. The first of the airfoil is the standard NACA 0018 profile. The second airfoil type has a NACA 0018 profile with a gap in the suction surface. The last airfoil is the NACA 0018 profile which is 66% of the trailing edge cut from the chord length. All airfoil profiles were analyzed at the Reynolds number, Re=2x104, and angles of attack α=0o, 5o, 10o, 12o and 14o in both experiment and numerical studies. The experiments were carried out using the Particle Image Velocimetry (PIV) method in a closed-loop open water channel, and the time-averaged velocity vectors, streamlines, and vorticity contours of the flow field were obtained. Subsequently, numerical analyses were performed using the ANSYS Fluent package program, one of the Computational Fluid Dynamics (CFD) programs used frequently in the literature. The streamlines and pressure contours of the airfoil profiles have been compared visually at the same Re and different angles of attack. In addition, according to the angle of attack of the airfoil profiles, lift coefficient CL, drag coefficient CD, and the ratio of lift coefficient to drag coefficient CL/CD graphs were presented. It has been shown that the gap on the airfoil at high attack angles caused changes in lift (up to 0.7) and drag (up to 0.15). These features can allow these models to be used for different purposes in the aerodynamics field.

Numerical Analysis of The Multilayer Structures Melting with Different Hole Network with Phase Change Material

Phase change materials (PCM) are used with different geometries to increase thermal performance. The thermal performance of the geometries on phase change materials have been investigated. For thermal energy storage systems (TES), porous structures are widely used to increase the thermal performance of the PCM. In addition, geometric parameters affect heat transfer, flow and melting solidification. In this work, the thermal performance of multilayer structures with different surface geometries and the control of the melt fraction of the PCM was investigated in terms of energy efficiency. The results were obtained by modeling the studies in the Computational Fluid Dynamics (CFD) program. The physical model was obtained by creating a multi-layer porous structure with different surface geometries in each layer thanks to the additive system. Modeling was carried out for natural convection depending on time. Paraffin was used as the PCM. The melting temperature of the paraffin used is 41 °C and the latent heat of fusion is 165 kJ/kg. In the present work, the distribution of melting isotherms gives more homogeneous results for the selected geometry. The results of PCM multilayer structure and other geometries were compared under the same conditions and it was seen that the multilayer structure improved the thermal performance. All melting graphs range from 0-1 (0: solid, 1: liquid). The results obtained for the selected geometry show that the melting value is between 0.8-0.9. In addition, the proposed physical model is a subject that can be encountered in engineering applications, thermal design engineering. In this respect, it is thought that the results obtained from the study, especially in the field of energy storage, will fill an important gap.

Burnup-control drum coupling characteristics investigation of lead–bismuth eutectic-cooled solid reactor

As an advanced research tool, neutronics and thermal-hydraulics coupling have a wide range of promising applications in the field of nuclear energy. This paper develops a burnup-control drum coupling code based on the Monte Carlo code RMC and the computational fluid dynamics (CFD) program STAR-CCM +. The dynamic adjustment of the control drums' position and more realistic prediction of reactor neutronics and thermal-hydraulics is achieved by updating the nuclide density, solving the control drum value function and updating the neutronics model in the process of burnup calculation. The core of a lead–bismuth-cooled solid reactor was also studied to investigate the neutronics and thermal-hydraulics properties of the solid core when the effective multiplication factor was kept at about 1.0, and the core's power and temperature variation patterns during the lifetime were obtained. The results of the study show that the simulation of the coupling code achieves the design purpose. In addition, the solid core's maximum fuel and cladding temperatures decrease with the deepening of the burnup.

Co-optimization of operating parameters, fuel composition, and piston bowl geometry of gasoline compression ignition (GCI) engine at high loads

Focusing on the gasoline compression ignition (GCI) combustion mode, the operating parameters, fuel composition, and piston bowl geometry were collaboratively optimized at high loads to improve engine performance. A meliorative genetic algorithm coupled with a three-dimensional computational fluid dynamics (CFD) program was adopted as the optimization tool. The optimal GCI combustion strategy is summarized based on the optimization results, and the key parameters affecting engine performance at high loads are further analyzed. The results show that the employment of the open-type piston bowl, high-reactivity fuel, and late start of injection (SOI) is desirable for GCI engines at high loads. Under this strategy, fuel burns in multiple stages, which can reduce the heat release rate and advance the combustion phase. The width of the piston bowl is the geometric parameter with the most notable impact on GCI combustion. Due to the weaker turbulent kinetic energy and the smaller surface area, the larger piston bowl width is conducive to diminishing the heat transfer losses of the engine and promoting the oxidation of unburned hydrocarbon (HC) emissions. Relative to the optimal case, the strategy with the open-type piston bowl, high-reactivity fuel, and early SOI can reduce fuel consumption but results in a higher in-cylinder pressure rise rate and increased ringing intensity (RI). On the contrary, the re-entrant type piston bowl, low-reactivity fuel, and late SOI can significantly reduce the pressure rise rate and RI while deteriorating thermal efficiency.

Enhancement of the performance of vertical axis wind rotors with straight blades

In this study, it has been aimed to improve the performance of vertical axis wind rotors with straight blades. For this purpose, an additional performance-enhancing setup has been used, placed in front of the vertical axis wind rotor with straight blades, in order to increase the performance. The effects on the rotor performance increase have been investigated numerically by keeping the dimensions of this performance-enhancing additional setup constant, by changing the number of blades of the straight bladed rotor and by changing the blade angles if the straight blades have been angled. Numerical analyzes performed in this study have been validated by experimental literature data. After creating the solid models required for the rotor performance analysis, the computational fluid dynamics (CFD) program ANSYS Fluent has been used. Here, studies have been carried out with two, three and four bladed rotors as the number of blades. As the blade angle, the effects of the angles between 180 and 120 have been examined. As a result of the study with the additional performance setup (APS), it has been determined that the optimum performance has been obtained with the vertical axis rotor with three blades and 150 blade angle. As a final result, it has been determined that the power coefficient obtained from the optimum vertical axis rotor with additional performance setup increased approximately 2.6 times compared to the optimum rotor without setup.

Experimental and numerical study on wave characteristics by a moving submerged body in a two-layer fluid

Waves induced by an immersed moving body in a two-layer fluid were studied experimentally and numerically. Unmixed fluids (water and cooking oil) were used as the two-layer fluid. A submerged body was manufactured to move with a wire loop system connected to the motor. The measured data were compared with numerical results and theoretical solutions. Numerical calculations were performed using the computational fluid dynamics (CFD) program. The characteristics of the generated waves, such as wave patterns and wavelengths, were qualitatively similar to the numerical results and theoretical values. Of the two wave propagation modes in a two-layer fluid, the baroclinic mode was dominant when the immersed body moved at a low speed. In contrast, the barotropic mode became more prominent as the body velocity increased. Based on these characteristics, transverse waves dominated when the velocity of the body was low, and divergent waves became more distinct as the velocity increased. In addition, the fluid depth and the location of a submerged body can affect the characteristics of the wave patterns.

Numerical analysis of the distribution of combustion products from methane explosions in a full-scale tunnel using all-speed CFD code GASFLOW-MPI

ABSTRACT Methane explosions are among the main hazards in coal mines. Shock waves from methane explosions can cause damage near the explosion site, and combustion products can spread along the tunnel to locations far from the explosion source and endanger the lives and health of personnel. Therefore, the study of the propagation patterns of methane explosion shock waves and the distribution of high-temperature combustion products in tunnels. has significance for emergency decision-making in the event of methane explosions in a mine. This study uses the 3D Computational Fluid Dynamics (CFD) program GASFLOW-MPI, which models the one-step methane combustion mechanism with the addition of a heat transfer model. The methane explosion process is simulated and reproduced at the Lake Lynn Experimental Mine (LLEM) to analyze the process of gas deflagration. The results reveal that the overpressure in the tunnel after the methane explosion oscillates and decays with time. Gaseous products of the explosion “expand and compress” and flow back and forth in accordance with the oscillation of overpressure. The maximum expansion ratio of the CO2 concentration isosurfaces of 0.5% in the heat transfer simulation is 6.21, whereas the volume expansion ratio is 3.78 once the flow field stabilizes. The distribution of combustion products along the alleyway exhibits a Gaussian decay trend. The range of gaseous product distribution and temperature fields in the adiabatic tunnel is significantly higher than that in the heat transfer simulations, thus indicating that heat loss significantly influences the temperature characteristics and distribution pattern of combustion products in the full-scale tunnel.

NNPred: Deploying neural networks in computational fluid dynamics codes to facilitate data-driven modeling studies

Data-driven modeling has contributed significantly to the field of computational fluid dynamics (CFD), but integrating machine-learning (ML) models into a CFD workflow still remains to be a challenging task. In this paper, we introduce an interface library for the deployment of ML models in CFD codes. The library supports multiple ML backends with binary interface compatibility and provides flexible data input/output (I/O) methods to match the type and layout of the data between ML models and CFD codes. For the convenience of CFD users, the library provides application programming interfaces for two widely used languages (i.e., C++ and Fortran), simplifying the deployment and prediction to only a few lines of code. Two data-driven modeling cases are demonstrated, along with the implementation details of the library in open-source CFD codes (i.e., OpenFOAM and CFL3D). The first case presents a simple heat-transfer problem with assumed experimental data of unknown emissivity, where the basic use of the library in OpenFOAM is demonstrated by solving a diffusive equation with the source term modeled by various ML algorithms. The second case discusses the modeling of turbulence in channel flow, and applies an ML-integrated closure model in both OpenFOAM and CFL3D. In both software, the ML-RANS model reproduces almost identical results to the reference data and favorable extrapolation performance is maintained. In addition, the parallel efficiency is compared with the traditional closure model under the same homogeneous parallel architecture, and only limited additional cost is imposed by running the ML prediction. This library could benefit CFD researchers in rapidly testing data-driven models in their CFD solvers. Program summaryProgram Title: NNPredCPC Library link to program files:https://doi.org/10.17632/v2jzcyjn8v.1Developer's repository link:https://github.com/Weishuo93/NN_PredLicensing provisions: MIT1, LGPL2, Apache-2.03Programming language: C++, FortranNature of problem: Coupling machine learning models with CFD programs with minimal modifications to facilitate the study of data-driven modeling methods (e.g., rapid modeling from experimental data, turbulence closure modeling, etc) with MPI supports.Solution method: First, an interfacing library is developed to bridge ML modeling and a CFD solver. The library supports different ML backends and provides flexible data I/O methods when interfacing with CFD codes. The API of this library can be accessed through C++ and Fortran, which are two most commonly used languages in the CFD community. Secondly, two data-driven modeling cases are demonstrated with the library's implementation details in OpenFOAM and CFL3D. The first case shows a semi-empirical modeling problem in heat transfer with assumed experimental data, whereas the second case reproduces the results of DNS with an ML-integrated turbulence model in two different CFD software (OpenFOAM and CFL3D). Finally, parallel computation is conducted using a homogeneous Message Passing Interface, which is adopted by most mainstream CFD programs. The extra costs are observed limited, and therefore users could validate their ideas on data-driven models with great convenience on parallel programs.Additional comments including restrictions and unusual features: Heterogeneous parallel strategy with GPU and associated applications need to be further developed.

Performance analysis of biofuel-ethanol blends in diesel engine and its validation with computational fluid dynamics.

The engine tests aimed to produce comparable data for fuel consumption, exhaust emissions, and thermal efficiency. The computational fluid dynamics (CFD) program FLUENT was used to simulate the combustion parameters of a direct injection diesel engine. In-cylinder turbulence is controlled using the RNG k-model. The model's conclusions are validated when the projected p-curve is compared to the observed p-curve. The thermal efficiency of the 50E50B blend (50% ethanol, 50% biofuel) is higher than the other blends as well as diesel. Diesel has lower brake thermal efficiency among the other fuel blends used. The 10E90B mix (10% ethanol, 90% biofuel) has a lower brake-specific fuel consumption (BSFC) than other blends but is slightly higher than diesel. The temperature of the exhaust gas rises for all mixtures as the brake power is increased. CO emissions from 50E50B are lower than diesel at low loads but slightly greater at heavy loads. According to the emission graphs, the 50E50B blend produces less HC than diesel. NOx emission rises with increasing load in the exhaust parameter for all mixes. A 50E50B biofuel-ethanol combination achieves the highest brake thermal efficiency, 33.59%. The BSFC for diesel is 0.254 kg/kW-hr at maximum load, while the BSFC for the 10E90B mix is 0.269 kg/kW-hr, higher than diesel. In comparison to diesel, BSFC has increased by 5.90%.

AI based temperature reduction effect model of fog cooling for human thermal comfort: Climate adaptation technology

This study developed a gradient-boosted regression tree-based artificial intelligence (AI) model––temperature reduction effect AI model (TREAM)––to determine the temperature reduction effect of fog cooling that varies with weather conditions. According to the trend of global warming, our society is suffering from serious damage from urban heat islands, especially negatively affecting human health and thermal comfort. Therefore, it is very important to develop and evaluate adaptive technology for providing pleasant thermal comfort to humans. This study select fog cooling as adaptive technology for human thermal comfort, and indoor and outdoor simulation were performed using STAR CCM+, a computational fluid dynamics(CFD) program. Moreover, transient analysis to validate the outdoor model of CFD and parametric study to identify the correlation between the environmental factors and fog cooling were performed. When initial temperature set as 45 °C at a relative humidity of 90% and wind speed of 1 m/s, a temperature reduction of 8.92% can be obtained. Regardless of the temperature and humidity conditions, the temperature reduction effect of fog cooling was ∼1% if the wind speed increased above 5 m/s. This study contributed to the quantitative analysis of the temperature reduction effect according to the change of environmental factors.

Performance enhancement of a galloping-based energy harvester with different groove depths on square bluff body

This paper focuses on the effects of a V-shaped groove depth on the performance of a galloping-based energy harvester. The study simulated air flow over cylindrical, square, and different depth grooved square bluff bodies using a computational fluid dynamics program with a user defined function added. An experiment using the particle-image velocimetry technique in a closed-loop wind tunnel was also conducted to validate and explain the results. The results show that the energy harvester and square bluff body with a ratio of 0.25 groove depth to the side generated the most power of 15.24 mW, which is 1.34 times higher than the power generated by the square bluff body at 9 m/s wind speed. This is because the groove on the windward side of the square bluff body increased the striking area of the fluid force and triggered the formation of a large vortex beside the bluff body. This results in a larger vibration amplitude and in an increased generation of electrical power. The discrepancy between the simulated and experimental results was also discovered to be due to a twist of the bluff body and hence a common used one-dimension oscillation assumption might be invalid.