Reynolds Averaged Research Articles

Analysis of blade's chord length with NACA0015 profile for enhanced wave energy conversion of Wells turbine

This paper investigates the enhancement of Wells turbine blades by modifying the chord length design parameter. The Wells turbine, a promising device in wave energy conversion systems, faces a limited operating range due to flow separation, which restricts its efficiency at higher flow rates. Enhancing the performance of the Wells turbine is crucial for effective wave energy exploitation. The computational simulations in this study are conducted using ANSYS Fluent. Turbine performance is evaluated based on non-dimensional torque, pressure torque, and efficiency, derived from solving the steady 3D incompressible Reynolds Averaged Navier–Stokes equations. The results are validated against reliable references, showing good agreement. The numerical findings reveal that altering the turbine chord length significantly impacts efficiency. Optimizing the chord length enhances the Wells turbine's performance in wave energy conversion, making it a more viable option for renewable energy power generation.

Accuracy in evaluating convective heat transfer coefficient by RANS CFD simulations in a rectangular channel with high aspect ratio and V-shaped ribs

Abstract In the framework of heat transfer enhancement inside channels with ribbed surfaces, V-shaped ribs are placed as the most promising among the standard-shaped ribs. This works aims to present a numerical analysis of heat transfer characteristics for forced convection inside a rectangular channel with high aspect ratio 1:10 equipped with V-shaped ribs. CFD simulations are carried out by means of Reynolds Averaged Navier-Stokes (RANS) equations, working with an air flow inside a narrow rectangular channel 120 mm wide and 840 mm long. V-shaped ribs have square cross section and they have been tested both with the tip of the V pointing downwards both upwards with respect to the channel inlet. For each configuration three different values of dimensionless pitch (10, 20 and 40) have been analysed. Comparisons between numerical and experimental data on convective global heat transfer coefficient and pressure drops are presented, showing very good agreement. Finding a properly working CFD model is useful for authors because this work, together with previous studies on 90° and 60° ribs, aims to be exploited during parametric early design-phases of new heat exchangers.

Hidden field discovery of turbulent flow over porous media using physics-informed neural networks

This study utilizes physics-informed neural networks (PINNs) to analyze turbulent flow passing over fluid-saturated porous media. The fluid dynamics in this configuration encompass complex features, including leakage, channeling, and pulsation at the pore-scale, which pose challenges for detailed flow characterization using conventional modeling and experimental approaches. Our PINN model integrates (i) implementation of domain decomposition in regions exhibiting abrupt flow changes, (ii) parameterization of the Reynolds number in the PINN model, and (iii) Reynolds Averaged Navier–Stokes (RANS) k−ε turbulence model within the PINN framework. The domain decomposition method, distinguishing between non-porous and porous regions, enables turbulent flow reconstruction with a reduced training dataset dependency. Furthermore, Reynolds number parameterization in the PINN model facilitates the inference of hidden first and second-order statistics flow fields. The developed PINN approach tackles both the reconstruction of turbulent flow fields (forward problem) and the prediction of hidden turbulent flow fields (inverse problem). For training the PINN algorithm, computational fluid dynamics (CFD) data based on the RANS approach are deployed. The findings indicate that the parameterized domain-decomposed PINN model can accurately predict flow fields while requiring fewer internal training datasets. For the forward problem, when compared to the CFD results, the relative L2 norm errors in PINN predictions for streamwise velocity and turbulent kinetic energy are 5.44% and 18.90%, respectively. For the inverse problem, the predicted velocity magnitudes at the hidden low and high Reynolds numbers in the shear layer region show absolute relative differences of 8.55% and 4.39% compared to the CFD results, respectively.

Numerical analysis of turbulent natural convection in the presence of wire-induced non-uniform magnetic field inside a porous medium

Turbulent natural convection of Fe3O4-water ferrofluid with Reynolds Averaged Navier-Stokes (RANS) based turbulence model of k−ω in the presence of wire-induced non-uniform magnetic field inside a porous medium is simulated, numerically. To discretize and solve the related equations the FVM method and SIMPLE algorithm are implemented. For applying the non-uniform magnetic field, two wires carrying electric currents have been installed below and above the enclosure. Simulations are implemented for different Rayleigh numbers (106≤Ra≤108), porosity number of (η=0.5and0.9), volume fractions of nanoparticles 0≤ϕ≤4%, magnetic field numbers 0≤MFN≤109. According to the results, in low Rayleigh number and high MFN, at the high-volume fraction of nanoparticles, applying a magnetic field optimally influenced transfer and Nusselt number. At high porosity numbers, low Ra numbers and ϕ=4%, the heat transfer rate improved by up to 17 %. However, at high Ra numbers and highϕ, applying the magnetic field reduces the Nusselt number by almost 12 %.

Numerical simulation of turbulent airflow around a tall telecommunication tower model

In this study, wind flow around a telecommunication tower (Milad Tower) model was numerically simulated. Several computational fluid dynamics (CFD) simulations were performed using the Reynolds Averaged Navier–Stokes (RANS) and the Delayed Detached Eddy Simulation (DDES) models. Two cases resembling the tower head with different inlet turbulence intensity profiles were considered, and computational results for wind flow and pressure distributions on various sections around the tower head and structure were presented and compared with the available wind tunnel data. Good agreement of the simulated pressure coefficient distributions around the head section in the windward and leeward sides of the tower with the wind tunnel data was observed. The regions with positive and negative pressures on the tower surface were identified based on the pressure coefficient distributions. In addition, the airflow characteristics around a model of the entire Milad Tower were studied. The simulation results for the airflow and the drag and lift coefficients acting on the tower for the high and low-intensity winds were evaluated and discussed. It was demonstrated that the DDES model was preferred for the simulation of mean pressure coefficients over the tower; however, the RNG k–ε model results, which were obtained at lower computational costs, were also satisfactory. In addition, the DDES showed better performance in simulating the maximum and minimum pressure coefficients on different tower levels and predicting the mean aerodynamics drag and lift coefficients. The results of the DDES model illustrated the higher power spectral density of velocity fluctuations on the leeward side of the tower compared with the windward side.

Creation and research of numerical models of cyclones with inclined and horizontal inlets

The article considers the challenges of using cyclone devices for cleaning gas emissions from solid fuel combustion in power engineering and industry. With the increasing energy consumption and generation, including the use of coal, the requirements for the efficiency of cleaning emissions from small solid particles of classes PM10 and PM2.5 are also rising. One of the key tasks is to maintain high cleaning efficiency while minimizing energy costs, which is also important for reducing the environmental impact of generation and industrial production. The article considers the design features of currently used cyclones, as well as existing approaches to their classification. The main focus is on modern areas of research related to numerical modeling based on CFD (Computational fluid dynamics) aimed at optimizing the design of separators. It is shown that most studies are carried out for cyclone operating conditions in production cycles, rather than in emission cleaning systems that operate at low suspended matter loads. Using the example of creating numerical models of cyclones with inclined and horizontal inlet pipes (CN-11, SK-CN-34), the article discusses certain features of geometry creation in the SpaceClaim Direct Modeler (SCDM) environment, which ensure the correctness of grid generation and calculations in the future. The results of numerical modeling carried out using the ANSYS Fluent software are presented. The turbulence model (RANS, Reynolds Averaged Navier – Stokes), methods for closing the Navier – Stokes equations (k-ε model with near-wall functions), and methods for calculating the dispersed part of the flow (Euler – Lagrange, DPM) are selected based on the conditions relevant to the systems for cleaning emissions from coal generation. The results indicate that, with the same pressure drop, the efficiency of settling suspended matter with a concentration of 100 mg/m3 or less in an apparatus with an inlet angle of 11° to the horizontal can be higher than that of a cyclone with a horizontal inlet.

Whistling potential of throttling orifices and its connection to liquid rocket combustion instability

Orifice whistling is recently established as a cause of high frequency combustion instability in liquid rocket engines. The series of studies on the experimental thrust chamber, known as BKD, developed at the German Aerospace Center (DLR), were instrumental in identifying this phenomenon. BKD encountered an injector-driven thermo-acoustic instability caused by the self-excitation of the LOX injector. The throttle orifice in the LOX injector plays a vital role in the self-excitation through whistling. In this work, the impedance of the BKD throttling orifice is characterized with the motive to find its whistling range. The CFD approach based on solving the unsteady Reynolds Averaged Navier Stokes equations proposed by Lacombe et al. [1] is used for this characterization. We characterize the orifice at the weak and the strong coupling conditions reported in the literature. The orifice impedance is calculated in the range of 4 kHz to 15 kHz, covering the entire potential coupling range of LOX injector eigen modes. The impedance results show that the orifice character follows the whistling behavior of the “medium” orifices. The resistance turns negative in the Strouhal number range of St=0.89 - 1.2 for both the weak and strong operating conditions. When plotted against the frequency, the resistance at the strong coupling condition occurs close to the second longitudinal (2L) mode of the LOX injector, suggesting direct excitation of the injector through the orifice whistling. The coexistence of the 2L mode and the first transverse (1T) mode of the combustion chamber at the same frequency leads to combustion instability.

Computational fluid dynamics driven surrogate model to predict hydrodynamic and acoustic properties of propeller boss cap fins

A novel method is proposed to predict the hydrodynamic and acoustic properties of propeller boss cap fins (PBCF) based on computational fluid dynamics (CFD) and surrogate models. The propulsive performance and radiated noise of the B-series propeller equipped with PBCF under open-water and hull-propeller coupling conditions are predicted and analyzed. The transient calculations are performed to generate accurate sample data for the surrogate model based on the Unsteady Reynolds Averaged Navier–Stokes and Ffowcs Williams–Hawkings equations. The response surface, polynomial, and Kriging models are used to learn sample data and output predictions. The relationship between inputs and outputs can be established from local data, which enables to obtain arbitrary response results in the global range. The hydrodynamic performance and radiated noise are compared for configurations with and without PBCF. PBCF improves the open-water efficiency by more than 1.5% at medium to high advance velocities. For the self-propulsion efficiency, over 5% improvement is achieved under ideal working conditions. In addition, PBCF has a directional effect on the radial and axial radiated noise, with better noise reduction in the axial direction. The difference between the axial and radial spectrums is significant, especially near the first blade passing frequency.

Computational fluid dynamics based transient investigation of the penstock in a hydropower plant

Abstract Water hammer is a hydraulic transient phenomenon that occurs at hydropower plants (HPP) when the discharge is rapidly decreased or closed, which can damage the HPP components, mainly penstock. Sudden Pressure rise and collapse of water columns or cavity forms due to the low pressure may cause severe damage. Understanding transient flow behavior is necessary to prevent harmful pressure fluctuations and ensure power plant safety. The present 3D computational fluid dynamics (CFD) study is carried out to predict pressure fluctuations, the occurrence of any cavitation, and water column separation at critical locations in the water conductor system from the surge tank to the turbine inlet due to low pressure caused by the closing of the hydraulic turbine guide vane valve at downstream of the penstock. The hydraulic domain of the penstock, connecting the head race tunnel to the turbine inlet, is created as per the HPP UHL-III actual water conductor system elevations, bent bifurcations, and geometric sizes. Transient CFD simulations for different load rejection conditions were performed in the Ansys CFX by modifying the Unsteady Reynolds Average Navier’s Stoke equation (URANS), incorporating the elastic effect of penstock material, and considering the variable density of the water, taking the compressibility. Transient pressure in the penstock was recorded at various locations. Further, minimum pressure inside the flow domain that falls in the no-column separation zone was also obtained.

Numerical and geometric investigation of pool boiling heat transfer in cavities with isothermal rectangular corrugations

This numerical work presents a geometrical investigation of a corrugated isothermal surface placed in a two-dimensional cavity subjected to unsteady, turbulent pool boiling flows. The main purposes are maximizing the heat transfer rate between the isothermal surface and the surrounding water flow, and the volume of vapor generated into the cavity. The geometric investigation followed the constructal design method, being the ratio Hi/Li (i = 1, 2 or 3) of the corrugations varied for three different numbers of corrugations: N = 1, 2, and 3, keeping constant the corrugations area. The volume of fluid (VOF) and Lee's evaporation-condensation models are used to estimate the volume fractions of water vapor/liquid and interfacial mass transfer. The unsteady Reynolds Averaged Navier Stokes (URANS) continuity, momentum and conservation of energy equations, and volume fraction transport equation, are solved using the finite volume method (FVM) available in software Ansys FLUENT. For closure of turbulence, the k - ɛ model is adopted. For validation of the model, the heat flux and convection heat transfer coefficient obtained for a pool boiling bared surface case are compared with Rohsenow's correlations, and differences lower than 7.0 % are reached. Results indicated a strong influence of the ratio Hi/Li and number of corrugations (N) in the heat transfer rate per unit depth (qs) and dimensionless volume of vapor (Vdim) generated into the cavity. The highest intrusion of the corrugations led to the generation of few large and many small scales, benefiting the thermal performance, regardless of the performance indicator employed. The optimal configuration, N = 3 and H3/L3 = 2.0 improved 49 % and 188 % the Vdim and qs compared with the worst corrugated case, showing the importance of the geometry of the corrugation in this problem.

Unsteady Upwind Aerodynamics of a Sailing Yacht

_ Sail aerodynamics has been a researched topic since the start of competitive racing, such as the America's Cup and Whitbread Round the World Race. Recently, with restrictions on the use of wind tunnels and towing tanks in the America's Cup, there has been an increase in computational fluid dynamics (CFD) to study the aerodynamics and performance of yacht sails. These studies typically model steady-state conditions, but in contrast, this paper demonstrates the implementation of dynamic wind conditions in Reynolds Averaged Navier Stokes CFD and the effects it has on the aerodynamics of a yacht sailing upwind. A user-defined function was used to give a velocity profile and vary the wind direction with time to simulate a gust condition with a period of 10 s. In addition to the gusting model, steady models were run for the apparent wind angles (AWA) experienced in the gust to see if the dynamic wind conditions could be modelled by a series of steady state snapshots. The results show minor differences in the streamlines of two models and the pressure distributions show no significant difference. There is only a slight difference in sail forces at high AWAs. Although further research would be required this information could be valuable to anyone using CFD to test sail designs. Keywords CFD; transient; steady; upwind; UDF; RANS

Combined genetic algorithm and response surface methodology‐based bi‐optimization of a vertical‐axis wind turbine numerically simulated using CFD

AbstractIn this study, computational fluid dynamic (CFD) simulation of a vertical axis wind turbine (VAWT) geometry based on the Unsteady Reynolds–Averaged Navier–Stokes equations was investigated. In addition, the relationship between the geometric parameters of the VAWT and the two response variables, that is, moment and lift force, was determined using response surface methodology (RSM). Then, the Non‐Dominated Sorting Genetic Algorithm (NSGA‐II) was used to solve the multi‐objective optimization problem. The results obtained from the RSM showed that the lift force of the turbine is more sensitive to the change in the blade chord length, and the output moment of the turbine is more sensitive to the change in the rotor radius. Using the NSGA‐II multi‐objective optimization algorithm and the Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS) method, it was determined that among the optimal values of the independent variable, the most optimal response occurs in blade chord length = 0.18 m, rotor radius = 0.4 m, blade pitch angle = −3.27° and number of blades = 4. In these optimal values of the independent variables, the values of the dependent variables, which included the turbine's moment and the blades’ lift force, were obtained as 9.58 N m and 57.89 N, respectively.

Surface roughness effects in a transonic axial flow compressor operating at near-stall conditions

Surface roughness is a major contributor to performance degradation in gas turbine engines. The fan and the compressor, as the first components in the engine's air path, are especially vulnerable to the effects of surface roughness. Debris ingestion, accumulation of grime, dust, or insect remnants, typically at low atmospheric conditions, over several cycles of operation are some major causes of surface roughness over the blade surfaces. The flow in compressor rotors is inherently highly complex. From the perspective of the component designers, it is, thus, important to study the effect of surface roughness on the performance and flow physics, especially at near-stall conditions. In this study, we examine the effect of surface roughness on flow physics such as shock-boundary layer interactions, tip and hub flow separations, the formation and changes in the critical points, and tip leakage vortices among other phenomena. Steady and unsteady Reynolds Averaged Navier Stokes calculations are conducted at near-stall conditions for smooth and rough National Aeronautics and Space Administration rotor 67 blades. Surface streamlines, Q-criterion, and entropy contours aid in analyzing the flow physics qualitatively and quantitatively. It is observed that from the onset of stall, to fully stalled conditions, the blockage varies from 21.7% to 59.6% from 90% span to the tip in the smooth case, and from 40.5% to 75.2% in the rough case. This significant blockage, caused by vortex breakdown and chaotic flow structures, leads to the onset of full rotor stall.

Investigation of varying tip clearance gap and operating conditions on the fulfilment of low-speed axial flow fan

Abstract The present study aims to identify the suitable tip clearance and volumetric flow rates for low-speed axial flow fans. The performance of an axial fan depends on various parameters like fan speed, available tip clearance gap, volumetric flow rate, power consumption, and working fluid. Leakage flow occurring at a rotating component such as a blade and solid casing of a ducted axial fan is typically linked to losses and the potential emergence of a rotating stall. The numerical analysis for this study uses the Reynolds Averaged Navier–Stokes equations with the k-omega SST turbulence model to perform the steady-state simulations by varying tip gap and volumetric flow rate. The results proved that the optimum performance was obtained with a tip clearance gap of 1 mm, and maximum fan efficiency was achieved at a volumetric flow rate of 3.9–4.5 m3/s. The novelty of this proposed work is to enhance the efficiency of axial flow fans with circular arc-cambered aerofoils using optimum tip clearance and volumetric flow rate through steady-state simulations. This method can be used in turbomachinery to improve fan performance.

Three-dimensional finite element analysis of turbulent crude oil flow and solid particle deposition patterns in circular curved pipelines

This study presents a numerical investigation of turbulent crude oil flows in circular curved pipelines, with a focus on the deposition patterns of solid particles within the fluid. Simulations were conducted using the Reynolds–Averaged Navier–Stokes equations coupled with the k–ε turbulence model to examine the influence of structural characteristics, such as bend curvature angle and bend curvature radius, on flow dynamics and particle deposition. The results reveal that the complex flow patterns generated by these geometric features significantly affect pressure gradients and particle trajectories. Specifically, the study shows that turbulent flows within bends exhibit intricate behaviors, with deposition patterns being strongly influenced by the pipeline’s geometric parameters. Sand particles, commonly present in petroleum flows, are found to be more effectively transported in pipes with larger curvature angles, while they exhibit a higher propensity to settle at smaller curvature angles and larger bend curvature radii. Furthermore, the simulations indicate that the majority of deposited particles accumulate on the inner wall immediately downstream of the elbow entrance.

Quantifying the Wind‐Induced Bias of Rainfall Measurements for the Thies CLIMA Optical Disdrometer

AbstractThe wind‐induced bias of rainfall measurements obtained from non‐catching instruments is addressed in this work with reference to the Laser Precipitation Monitor (LPM) optical disdrometer manufactured by Thies CLIMA. A numerical simulation approach is adopted to quantify the expected bias, involving three different models with increasing complexity. Computational Fluid‐Dynamics simulation of the airflow field around the instrument with an embedded Lagrangian particle‐tracking module to obtain raindrop trajectories are performed by solving the Unsteady Reynolds Averaged Navier‐Stokes (URANS) equations and a Large Eddy Simulation (LES) model. URANS‐uncoupled, LES‐uncoupled, and LES‐coupled approaches are tested to assess the impact of modeling the airflow turbulent fluctuations in detail. Due to the non‐radially symmetric external shape of the instrument, various combinations of the wind speed and direction are considered. Catch ratios for monodisperse rain are obtained as a function of the particle Reynolds number and the wind direction and fitted to obtain site‐independent curves to support application of the simulation results. Based on literature expressions to link the drop size distribution of real rainfall events with the rainfall intensity (which instead depend on the local rainfall climatology at the measurement site), sample collection efficiency curves are obtained from the catch ratios of monodisperse rain. The resulting adjustment curves allow rainfall measurements to be corrected using either a real‐time or post‐processing approach. However, at high wind speed and assuming that the wind blows parallel to the instrument sensing area, the instrument may fail to report precipitation altogether.

Simplified Polynomial-asymptotic-distribution Actuator Disc (SPAD) method for wind turbine wake simulation based on k-[formula omitted]-[formula omitted] turbulence model

In large wind farms, wake effect has a negative impact on the annual production of wind turbines. As a result, wind turbine wake simulation is important for wind farm micro-sitting to minimize power loss and maximize energy production. Coupled with Reynolds Averaged Navier–Stokes turbulence model, Simplified Uniform-distribution Actuator Disc method is the most widely-used rotor model for wake simulation in engineering practice. The conventional simplified uniform-distribution actuator disc models suffer discrepancies of wake velocity prediction compared with the measurements in the near wake region. The novelty of the current research is to propose a Simplified Polynomial-asymptotic-distribution Actuator Disc method based on k−ϵ−fP turbulence model for cylindrical actuator disc cell region with finite thickness, which is simple for implementation and improves the accuracy of wake simulation compared with conventional method. The proposed method conforms to momentum conservation and is as simple as conventional method because of its polynomial formulation and no requirement for aerodynamics data in Generalized Actuator Disc model. From the verification and validation cases, it can be found that the proposed model has better agreement with both high-fidelity actuator line model and the field test measurements from Lillgrund wind farm compared with conventional model. The proposed actuator disc model has the potential to be applied to the micrositting of large offshore wind farms in the future.

An Investigation of the Effect of Varied Blade Shapes of the Trim Interceptor on the Resistance Characteristics of a Planing Vessel at Medium Speeds

The use of trim interceptors on fast boats to enhance performance still presents challenges in achieving optimal design across various parameters. The design of interceptor blades with conventional square cross-sections prompts consideration of whether altering the blade shape can affect its effectiveness in minimizing resistance on planing boats. This comprehensive study explores various permutations of interceptor blade shapes and their impact on the characteristics of resistance in planing botas. Computational Fluid Dynamics (CFD) using the Reynolds Averaging Navier-Stokes (RANS) method, verified and validated, is employed to conduct this investigation. The results indicate that the round shape consistently exhibits lower resistance compared to rectangular, ½ V, and full V shapes across a range of speeds (Froude number 0.76 – 0.99).

Flexible Vegetation Behavior under Varying Areal Densities and Effects on Flow Structures: Numerical Observations

This study carried out extensive numerical studies on a refined “One dimensional (1-D) Reynolds Averaging Navier-Stokes (RANS) Model” for vegetated open channel flow. In the 1-D RANS model, the Spalart Allmaras closure model was used to model the turbulence caused by eddies within the vegetation zone and the interface between the top of the vegetation and the clear water zone. In this work, numerical simulations using 1-D RANS model are carried out using dataset obtained from the laboratory under different hydraulic conditions of varying areal vegetation densities. Three classes of highly flexible vegetation densities were simulated: low, medium and highly dense vegetation. The model predictions in terms of mean vertical stream-wise velocity profile and Reynolds Shear Stresses were compared with the laboratory flume experimental results. The 1-D RANS model performances were satisfactory for low and medium densities. However, discrepancies were seen in the model prediction for highly dense vegetation. Hence, the hydraulic roughness parameters in the numerical model has been modified for model re-calibration to capture the position of zero-displacement of velocities. Using the modified parameters, the velocity profiles and the Reynolds Shear Stresses were predicted with very low uncertainty.

Probabilistic machine learning to improve generalisation of data-driven turbulence modelling

A probabilistic machine learning model is introduced to augment the k−ωSST turbulence model in order to improve the modelling of separated flows and the generalisability of learnt corrections. Increasingly, machine learning methods have been used to leverage experimental and high-fidelity simulation data, improving the accuracy of the Reynolds Averaged Navier–Stokes (RANS) turbulence models widely used in industry. A significant challenge for such methods is their ability to generalise to unseen geometries and flow conditions. Furthermore, heterogeneous datasets containing a mix of experimental and simulation data must be efficiently handled. In this work, field inversion and an ensemble of Gaussian Process Emulators (GPEs) is employed to address both of these challenges. The ensemble model is applied to a range of benchmark test cases, demonstrating improved turbulence modelling for cases involving separated flows with adverse pressure gradients, where RANS simulations are understood to be unreliable. Perhaps more significantly, the simulation reverted to the uncorrected model in regions of the flow exhibiting physics outside of the training data.