computational fluid dynamics (cfd)

The aerodynamic performance of wind turbines is significantly influenced by the design of their blades, which are engineered with advanced aerodynamic airfoils. However, the effectiveness of these designs is compromised by environmental factors such as dust, corrosion, sand, and insects, leading to alterations in blade shape and surface integrity over the turbine's operational period. These changes reduce the aerodynamic efficiency of the turbines. To assess these detrimental effects, this study utilizes a 3D Computational Fluid Dynamics (CFD) model based on the exact blade geometry. A modified version of the universal logarithmic wall function was implemented to quantify the influence of surface roughness. Comparative analyses between clean and rough blade surfaces under varying wind conditions showed that surface degradation significantly impacts the efficiency of wind turbines. Specifically, the findings indicate that surface roughness can lead to a substantial decrease in power output, with losses potentially reaching up to 35% under tested conditions. Notably, this roughness effect exhibits a critical value of  , beyond which the impact of roughness becomes negligible. Based on these results, an exponential correlation has been proposed. This study suggests that maintaining smooth blade surfaces or minimizing roughness is crucial for optimal turbine performance, especially under high wind conditions.

Turbulent impinging jet array is one of the most efficient and popular techniques for cooling gas turbine blades. In the present paper, we numerically investigated how the geometrical design parameters affect the cooling performance for jet array impinged to a curved target. The influence parameters, including jet spacing (2.5≤Pj≤10), jet angle (-45°≤θ≤+45°), and off-center distance (0≤Ej≤6) on average Nusselt number (Nu), air pressure drop (Δp), and heat transfer uniformity index (UI) were identified through a parametric study at a constant total mass flow rate. Results show, increasing jet spacing improved heat transfer but lowered uniformity and required more compression power. Tilting the jets generally decreases the average Nusselt number but boosts the uniformity. Also, increasing the inclination angle reduces the pressure drop. Moving the jets off-center consistently lowered pressure drop until Ej=4 and average Nusselt number till Ej=2 without affecting uniformity much up to until Ej=3, and beyond those values, increased them. best performance based on average Nusselt number is achieved for the case of Pj=10, θ=0°, and Ej=0. Also, the uniformity index is maximized and pressure drop is minimized at Pj=5, θ=+45°, and Ej=0.

The heat transfer improvement and the increase of heat exchangers’ efficiency represent a very important issue in the energy field. Many research projects have focused on the use of fluids with high thermal conductivity such as nanofluids. In this case, hybrid nanofluids, are a new class of nanofluids with good heat transfer characteristics. The present work falls within this framework and involves a numerical study to examine the influence of two oil-based hybrid nanofluids, Al2O3-MWCNT and MgO-MWCNT, with different volume concentrations and inlet flow rates. More to the point, the impact of different nanoparticle ratio and the location of hybrid nanofluid in a laminar flow of two-pipe counter-current heat exchanger have been investigated. In virtue of which, the results illustrate that increasing the volume concentration of nanoparticles and the flow rate of the hybrid nanofluid has a positive impact on improving the heat transfer rate. Therefore, the improvement in heat transfer rate reached 77.8% for Al2O3-MWCNT/oil hybrid nanofluid and 59.5% for MgO-MWCNT/oil hybrid nanofluid. Similarly, the study has also revealed that the preferred nanoparticles ratio for Al2O3-MWCNT/oil hybrid nanofluid is in the order of (25:75) and its circulation in the inner tube as a hot fluid makes it possible to improve the thermal performance of the considered two-tube heat exchanger to a greater advantage.

Imitating Dolphin fish-like movement is productive method for enhancing their hydrodynamic capabilities. This work aims to analyze and understand the oscillations of tail fluke of Dolphin, which can be used as a propulsive mechanism for underwater fish robots and vehicles. The objective of the work is to achieve the desired oscillating amplitude by simulating the NACA 0012 profile using computational models and Set up the swimming movement of the dolphin, imitating a fish like model. Computational techniques were employed to examine the propulsive capabilities of the oscillating hydrofoil, inspired by the dolphin's biological propulsion. The evolutionary of fluid pattern in the field surrounding both Dolphin fish model and the NACA0012 hydrofoil, from initial motion to cruising, was established, and the hydrodynamic impact was subsequently studied. An user-defined function (UDF) was developed to create a dynamic mesh interface with CFD code ANSYS FLUENT for establishing the oscillations of Dolphin tail across the flow field. Influencing hydrodynamic coefficients such as lift and drag coefficients at different frequencies were also obtained. The findings shown that when the acceleration of the Dolphin fish model increases, the time averaged drag force coefficient drops because The wake field's vortex disperses to have some beneficial effects and pressure of water surrounding the fish head intensifies to produce a large resistance force. Simulation results show a 98% agreement at lower frequency and speed levels but a 5% deviation at higher frequency and speed due to turbulence effects in both models. It was established that the vortex superposition enhances the Dolphin fish like model rather than lowering its positive impacts.  The Strouhal number, which is obtained by the fluid field's evolution rule, can be linked to the Kármán vortex street span with reverse.

In this article, an extracorporeal membrane oxygenator (ECMO) is simulated in 2D geometry using computational fluid dynamics (CFD). Momentum and mass transport equations were solved for the laminar flow regime (30 < Re < 130 for the blood channel) using the finite element method. In this study, the software COMSOL was used as the solver. To this end, the main problem of ECMO devices is the pressure drop and the risk of thrombus formation due to blood stagnation, so to solve this problem, the oxygen transfer rate to the blood should be increased. Therefore, in the present study, to optimize the oxygen transfer rate of the blood, three basic parameters were examined: blood flow velocity, oxygen velocity, and membrane thickness. Blood flow was considered at five different velocities (0.2, 0.4, 0.5, 0.6, and 0.8 mm/s). Results showed that increased blood flow velocity adversely affected oxygen permeability, increasing oxygen permeability from about 60% at 0.2 mm/s to about 24% at 0.9 mm/s. In addition, five different membrane thicknesses (0.04, 0.06, 0.08, 0.2, and 0.3 mm) were investigated, and, as expected, better oxygen exchange occurred as the membrane thickness decreased. We also found that the diffusion rate is about 40% for the 0.4 mm/s thin films and about 25% for the same inlet velocity and larger film thickness. Furthermore, the oxygen diffusivity increases from 28% to 38% as the oxygen gas velocity increases. However, oxygen velocities above 0.8 mm/s should not be used, as the range of oxygen diffusivity variation decreases with higher oxygen gas velocities.

Numerous studies have been conducted to investigate effect of blade geometry of vertical axis wind turbine performance. Most of the evaluations have focused on the airfoil series and airfoil geometry parameters such as thickness and camber of the airfoil. Few studies have examined the effect of other blade geometry parameters on the vertical axis wind turbine performance. In the present study, the effect of geometric change in leading-edge radius (LER) of a vertical axis wind turbine performance has been numerically studied. Hence, modified NACA 0021 airfoil profiles were created using the geometric method (CST). Then, the flow behavior around a Darrieus vertical axis wind turbine was simulated under the influence of the reduction and set-up coefficients of the leading-edge radius at a constant wind speed of 9 m/s and a tip speed ratio of 1.5 to 3.5 using the computational fluid dynamics. Additionally, the effects of the examined parameter (leading-edge radius) on fluid flow and aerodynamic performance coefficients, including the coefficients of power and torque, were investigated. The results indicated that the leading-edge radius affected the near wake flow of the turbine, and the optimization of leading-edge radius parameter controls the dynamic stall and reduces the formation of a vortex. Finally, the optimization of LER revealed that at 20% reduction in the LER the performance of the turbine at tip speed ratio of 1.5 was increased by more than 50%. This reinforces the self-starting capability of a Darrieus wind turbine.

Due to the vital role of motor-driven pumps in various industries such as oil and gas, manufacturing, chemical, etc., their continuous monitoring and implementing effective maintenance methods is of crucial importance. Periodic inspections and intermittent vibration data collection using accelerometers is among the most common methods. Electrical signature analysis is an alternative approach that only uses electrical measurements for the purpose of fault detection. Despite the unique advantages of this method, such as its non-intrusiveness and possibility of continuous monitoring of the equipment, there have been limited studies on its underlying theory with majority of the proposed ESA-based methods taking data-driven approach towards condition monitoring problem. Data-driven methods rely on the experimental data collected from the equipment to train the statistical models. This imposes a serious limitation on the application of electrical signature analysis and makes the generalization harder. In this paper the electromechanical coupling in a motor-driven centrifugal pump is studied in order to demonstrate the effects of different operating conditions of pump on motor electrical signals. Lumped parameter approach is employed to derive governing equations of the induction motor and computational fluid dynamics is utilized to analyze the interaction of the centrifugal pump blades and fluid. Such a modeling platform presents a physics-based approach towards electrical signature analysis based condition monitoring. A closed-loop hydraulic test rig is built to compare and verify the simulation results.

In this study, complex processes in a typical Electric Arc Furnace (EAF) such as combustion, radiation, heat, and mass transfer were solved and the optimum injector location was found using computational fluid dynamics (CFD). The main aim of the injection optimization was to improve the thermal performance and the metallurgical process by changing the injection angle, the central angle of the injector (CAI), and injector length. Fifteen parametric cases were predicted and analyzed for optimization study. To decrease each simulation solution time of each cases, a polyhedral mesh structure was used instead of tetrahedral mesh for the EAF geometry. Thus, the total element number of the model was decreased by 1/5 while providing faster and unchanging results compared to the case with a tetrahedral mesh structure. The response surface optimization method was used for the optimization study. As a result, the optimum injector positioning was obtained as injection angle: -45°, injector length 614 mm, and CAI: 60°.

In the present work, the effects of modifying the tongue geometry of a centrifugal pump on pressure pulsations under the design and off-design conditions are carried out numerically by the unsteady analysis of fluid flow. Numerical modeling based on the Re-Normalization Group (RNG) k-ε turbulence model using a Mosaic mesh structure, a technology which can easily, quickly and formally connects any type of mesh for complex geometries and flow regimes, is applied to simulate the flow within the modeled pump, which is validated with the available experimental results. The flow is simulated through a commercial Computational Fluid Dynamics (CFD) software that solved Reynolds-Averaged Navier-Stokes (RANS) equations for a three-dimensional unsteady flow. In addition to choosing Qd (the design flow rate), 0.4 Qd and 1.2Qd  are also taken into account as the inlet flow rates. Besides, pressures of 101KPa and 13KPa are considered as additional inlet conditions for this investigation. This unsteady simulation employing different inlet conditions is used to investigate the impacts of various volute tongue angles on the pressure coefficient (cp ). Results indicate that, overall, by changing the angle from 40° to 85°, the value of the pressure coefficient at the pump outlet grows by about 10% where it also causes a rise in the amplitude of pressure fluctuations. By the same token, a decrement to the inlet flow rate up to 40% of the nominal value brings about the amplitude of pressure fluctuations at the pump outlet to be increased significantly.

This paper investigates the flow structures on the near- and far-wake of a 1/8th scaled simplified heavy vehicle model called Ground Transportation System (GTS) model using a steady-state Reynolds-averaged Navier-Stokes (RANS) with k-ω Shear Stress Transport (SST) turbulence model at Reynolds number (Re) of 1.6 × 106 and yaw angles (Ψ) = 0o-14o. The current CFD results have been validated using experimental data from the literature. Two crosswind conditions based on the crosswind incidence angle (β) are adopted; β < 90o is called crosswind, and β = 90o (perpendicular to the GTS side surface) is called pure crosswind. Vortex detection scheme based on Ω method and total pressure coefficient (Cpt) contours is used to visualize the wake structure. With Ψ, vortices on the GTS roof take birth as a result of pressure differences between the windward and leeward sides. These vortices grow in size as they travel downstream. The growth in size is related to the Helmholtz theorem of vorticity and Kelvin’s Circulation Theorem. The vortices merged at Z/W > -4 (Z/W = 0 is the GTS rear surface) downstream of the GTS for Ψ = 7.5o and 14o. The merged vortex dissipates at Z/W > -6 and Z/W > -8 for Ψ = 7.5o and 14o, respectively. In the pure crosswind condition, the merged vortex attaches to the ground due to the velocity difference between the freestream and the moving computational ground used in the present simulation. At Ψ = 14o, surface streamlines on the GTS surface show the creation of two co-rotating vortices on the windward roof. For the present Ψ, similar flow structures between the two crosswind conditions are shown. Initial results show that the aerodynamic crosswind stability of a truck is related to the spanwise pressure difference between the windward and leeward surfaces of the truck.

Electrowinning is the process of depositing copper of the electrolyte solution inside the cell to the cathode. In the present study, the hydrodynamic simulation of the electrowinning cell of Miduk Copper Complex is studied using computational fluid dynamics. The Navier-Stokes and continuity equations are considered in the form of two phases of fluid and gas, turbulent, incompressible and steady state, and the equation for copper concentration in the electrolyte is solved with consideration of its specific boundary condition. The flow turbulence is modeled using 𝐾 − 𝜔 relationships. Due to large variations in the properties near cathode and anode, and also the large size of the electrowinning cell, to create a good grid, and increase the speed and accuracy of the results, global and local simulations are used together. The results of this simulation are the velocity vectors, the concentrations of acid and copper, turbulence Intensity, the amount of pressure, and the volume ratio of the oxygen phase in the entire electrowinning cell domain. For model validation, the model is compared with experiments conducted on actual cells in the industry. Results show high accuracy of this modeling technique. Then, the mass transfer coefficient values for the different electrode intervals are obtained by this modeling and the results are validated using the results of the experimental relations. In the next step, the electrolyte mixture containing different mass fractions of oxygen is sprayed into the electrowinning cell from the inlet of the simulated cell. Finally, effect of sparging different mass fraction of oxygen into electrowinning cell electrolyte, changing inlet temperature and flow rate of the electrolyte on the mass transfer coefficient is investigated by the obtained model.

Flows across an abrupt change in surface roughness lead to the development of an internal boundary layer (IBL). In this paper, the effect of surface discontinuity on the structure of flow and turbulence is unveiled by the Reynolds-averaged Navier-Stokes (RANS) turbulence model. Three configurations of smooth-to-rough transition, which are fabricated by sinusoidal wavy surfaces, are examined to contrast the flow adjustment. After the change in (increasing) surface roughness, the flows decelerate and the downward momentum flux ( u w'' '' ) increases to overcome the increasing drag. The changes in friction velocity (uτ,2/uτ,1) and roughness length (z0,2/z0,1) follow the conventional power law. The developments of roughness sublayer (RSL) and inertial sublayer (ISL), which characterize the flows adjustment, are clearly observed. The flow structure after the roughness transition is also defined quantitatively, through which the interaction among IBL, RSL and ISL is elucidated. The growth of IBL and ISL signifies that the influence from the upstream (smoother) surface is being weakened while the flows are developing in equilibrium with the downstream (rougher) surface. Finally, the winds over complex terrain (Hong Kong Island) are modelled to demonstrate the sea-land effect on atmospheric flows. The resultsshow that the flow dynamics and structure over natural topography are consistent with those over idealised surfaces.

The knowledge of pollutants dispersion in water bodies is a matter of concern in water quality control, especially when a new industrial development is installed e.g. near riverbanks. To predict pollutants dispersion in rivers, analytical, experimental and in-situ measurement can be performed. However, analytical estimation usually results in low accuracy, while experimental or in situ measurement are quite expensive in time and equipment. Hence, Computational Fluid Dynamics (CFD) approach is other alternative that can be used to obtain simple and accurate results for mass transport in rivers. In other words, it is a good alternative to analyse pollutants dispersion. As it is known, longitudinal diffusion coefficient (E) has strong influence on pollutants spreading into the water body. Therefore, the purpose of this paper is to analyse the effects of E on the mass transport of a conservative pollutant in rivers and channels via CFD. Contaminant dispersion is carried out by a scalar advection-diffusion transport equation that represents the conservation of mass. The velocity and pressure fields are calculated, considering an incompressible fluid, through the Navier-Stokes and the continuity equations. Numerical and analytical results, for one-dimensional (1D) flow, are compared in order to obtain the concentration field, over time and space, using different parametric equations. The concentration field showed significant differences of concentration peak and arrival time of the plume depending on the equation used to predict E. Numerical results, for two-dimensional (2D) flow, are compared with the experimental data from Modenesi et al. (2004). Such analyses are necessary to establish an appropriate correlation between simulated and real channel. The use of different parametric equations for the E in a 2D channel reveals significant differences of concentration peak and arrival time of the plume. As expected, the numerical results of the transport of pollutants show the dependence on the parameterization of the longitudinal dispersion coefficient. The one that best represents the distribution of pollutants is that proposed by Kashfipour & Falconer.

 Sudden expansion of flow in supersonic flow regime has gained relevance in the recent pasts for a wide run of applications. A number of kinematic as well as geometric parameters have been significantly found to impact the base pressure created within the suddenly expanded stream. The current research intends to create a predictive model for base pressure that is established in the abruptly extended stream. The artificial neural network (ANN) approach is being utilized for this purpose. The database utilized for training the network was assembled utilizing computational fluid dynamics (CFD). This was done by the design of experiments based L27 Orthogonal array. The three input parameters were Mach number (M), nozzle pressure ratio (NPR) and area ratio (AR) and base pressure was the output parameter. The CFD numerical demonstrate was approved by an experimental test rig that developed results for base pressure, and used a nozzle and sudden extended axis-symmetric duct to do so. The ANN architecture comprised of three layers with eight neurons in the hidden layer. The algorithm for optimization was Levenberg-Marquardt. The ANN was able to successfully predict the base pressure with a regression coefficient R2 of less than 0.99 and RMSE=0.0032. The importance of input parameters influencing base pressure was estimated by using the ANN weight coefficients. Mach number obtained a relative importance of 47.16% claiming to be the most dominating factor.