Reynolds-averaged Navier-Stokes Turbulence Models Research Articles

Influence Evaluation of Open Propellers with Boss Cap Fins: Case Studies on Types B4-70 and Ka4-70

Numerical analysis of fins effect on propeller performance was conducted, specifically using the B4-70 and Ka4-70 propellers. The study investigated different types of fins, including bare fins and PBCF (Propeller Boss Cap Fins) using computational fluid dynamics (CFD) simulations. The explicit algebraic stress model (EASM) based on Reynolds-Averaged Navier-Stokes (RANS) equations and turbulence modeling was employed to determine the optimal results. The main objective of this research was to enhance energy efficiency in ships by examining various open propeller configurations. The CFD simulation results for open propellers B4-70 and Ka4-70, with the addition of boss cap fins, revealed interesting phenomena. When the open propellers B4-70 and Ka4-70 were equipped with PBCF, they would experience an increase in efficiency (η0). This was because the performance of the fins functioned optimally when the advance ratio (J) is high, as evident from the high velocity values. Thus, with higher velocity and lower pressure in the boss cap region at high J values, there was an elevation in thrust force due to the reduction of hub vortex. In the case of open propeller B4-70 with added PBCF, there was an increase in the efficiency value (η0) ranging from 3% to 5% when J varied from 0 to 0.7. Similarly, for propeller Ka4-70 with the addition of PBCF, there was an increase in the efficiency value (η0) ranging from 1% to 3% when J varied from 0 to 0.7. Notably, the use of an Energy-Saving Device (ESD) in the form of PBCF can increase the efficiency of ship propeller, as reported in this paper. Consequently, these findings affirmed the reliability of the overall calculations using the CFD approach.

Impact of modelling assumptions in cavitating flow of simplified injector

Here, three-dimensional Reynolds-averaged Navier–Stokes (RANS) simulations are employed for in-nozzle flow modelling. The aim is to evaluate the capabilities and sensitivities of simulating in-nozzle flow phenomena by using homogeneous phase change models. Two commonly used homogeneous models are employed – (i) Homogeneous Equilibrium Model (HEM) and (ii) Homogeneous Relaxation Model (HRM) A simplified nozzle with reference experimental data is modelled in the developing, super cavitation, and hydraulic flip regimes using OpenFOAM. The influence of the inlet boundary condition and turbulence models are investigated. With HEM, three barotropic compressibility models are tested. The research seeks to understand the strengths and limitations of each approach by comparing different sub-models and their interactions with the flow fields and phase change phenomena. Ultimately, this study contributes to a better understanding of how different modelling choices can influence the accuracy and reliability of cavitation simulations using homogeneous phase change models. While the simulations demonstrated reliable predictions for low-order velocity statistics, substantial discrepancies were identified in the prediction of the cavitating region by both homogeneous models. Additionally, the relaxation model predicted only minor cavitation. In contrast, acceptable flow predictions were achieved using different barotropic compressibility models and inlet boundary condition types, as well as most RANS turbulence models, where the RNG k-ɛ model deviated more from the other turbulence models. Therefore, the added value of the present study is summarised as: (a) Four different cavitation regimes are simulated with HEM and HRM in a single study. (b) The more comprehensive HRM approach does not produce better velocity or cavitation predictions for a low-speed flow using the default relaxation time. (c) The choice of turbulence model can radically affect the cavitation prediction, in addition to velocity fields. (d) The HEM flow simulation has little sensitivity to the barotropic compressibility model.

Development of a Benchmark for Thermal Striping in Gas-Cooled Fast Reactors

This paper presents the development of a benchmark for predicting thermal striping through simulation. This work utilized large eddy simulation and will be used to benchmark future models. The testing domain was created using both the STRUCT and the Reynolds-averaged Navier-Stokes turbulence models and is based on an earlier design of the General Atomics Fast Modular Reactor upper plenum. The plenum features two adjacent, identical hexagonal bundles each with a center-placed axial rod drive, with a hot left coolant stream and a cold right coolant stream. The simulation solves the nondimensional Navier-Stokes equations, with temperature accounted as a passive scalar. First- and second-order flow statistics were obtained after 600 convective time units of averaging. The first-order statistics reveal that the hot jet is damped by a recirculatory flow from the near wall. At the same location, the second-order statistics show strong oscillations both in velocity and temperature. The power spectral density was utilized to determine that a low-frequency oscillation occurs here that is within the range of interest for thermal striping. Furthermore, proper orthogonal decomposition was used to identify coherent structures that confirm the oscillatory behavior, indicative of thermal striping. Overall, this benchmark can aid in the development of future models for predicting thermal striping in nuclear reactors, potentially leading to improved reactor safety and performance.

On the Fidelity of RANS-Based Turbulence Models in Modeling the Laminar Separation Bubble and Ice-Induced Separation Bubble at Low Reynolds Numbers on Unmanned Aerial Vehicle Airfoil

The operational regime of Unmanned Aerial Vehicles (UAVs) is distinguished by the dominance of laminar flow and the flow field is characterized by the appearance of Laminar Separation Bubbles (LSBs). Ice accretion on the leading side of the airfoil leads to the formation of an Ice-induced Separation Bubble (ISB). These separation bubbles have a considerable influence on the pressure, heat flux, and shear stress distribution on the surface of airfoils and can affect the prediction of aerodynamic coefficients. Therefore, it is necessary to capture these separation bubbles in the numerical simulations. Previous studies have shown that these bubbles can be modeled successfully using the Large Eddy Simulation (LES) and Direct Numerical Simulation (DNS) but are computationally costly. Also, for numerical modeling of ice accretion, the flow field needs to be recomputed at specific intervals, thus making LES and DNS unsuitable for ice accretion simulations. Thus, it is necessary to come up with a Reynolds-Averaged Navier–Stokes (RANS) equation-based model that can predict the LSBs and ISBs as accurately as possible. Numerical studies were performed to assess the fidelity of various RANS turbulence models in predicting LSBs and ISBs. The findings are compared with the experimental and LES data available in the literature. The structure of these bubbles is only studied from a pressure coefficient perspective, so an attempt is made in these studies to explain it using the skin friction coefficient distribution. The results indicate the importance of the use of transition-based models when dealing with low-Reynolds-number applications that involve LSB. ISB can be predicted by conventional RANS models but are subjected to high levels of uncertainty. Possible recommendations were made with respect to turbulence models when dealing with flows involving LSBs and ISBs, especially for ice accretion simulations.

Reynolds-average Navier-Stokes turbulence models assessment: A case study of CH4/H2/N2-air reacting jet

Computational Fluid Dynamics has become a very powerful tool for developing engineering combustion devices, such as burners and furnaces. However, there are a wide variety of turbulence models, and some of them have proven to be more effective for some turbulent flow configurations than others. A reacting turbulent jet is a common flow configuration found in combustion engineering devices like burners. The present work assesses Reynolds-Average Navier-Stokes turbulence models, being tested on a CH4/H2/N2-Air reacting jet. Eight two-equation eddy-viscosity and three five-equation turbulence models were tested in the studied turbulent flow. Computational results were compared against experimental measurements in terms of flow field variables, mean mixture fraction, temperature, and species mass fraction. The findings suggest a strong influence of the turbulence model perforce on the mean mixture fraction as well as on the turbulence-chemistry interaction model. The modified version of the standard k-ε model proves to be the more reliable choice for this reactive flow configurations. Specially, where the flow patterns of the jet dictate the general flow physics. Near the fuel nozzle, both the Reynolds stress model with stress baseline k-ω (RSM-SBSL) and the standard k-ω model exhibit better agreement with experimental data than the conventional modified k-ε model. Moreover, findings from the standard modified k-ε model indicate a significant underestimation of spreading rates for radial samples in regions where jet spreading intensifies.

Simulation of supersonic axisymmetric base flow with a data-driven turbulence model

Axisymmetric base flow involves massive flow separation which is challenging for a typical Reynolds-averaged Navier-Stokes (RANS) turbulence model. Furthermore, a supersonic condition imposes additional difficulties to a turbulence model in predicting strong compressibility effects associated with the flow separation phenomena. A data-driven approach is pursued here to improve a turbulence model. The Spalart-Allmaras model is corrected from an optimization process, and then the model correction is mapped to local flow features through a machine learning process. For the optimization-combined machine learning method, the field inversion and machine learning framework is adapted here with three major modifications. First, a zonal-field inversion method is suggested to avoid the undesired modification of attached flow in the optimization process for the model correction. Second, the RANS model is modified by adjusting a net balance between the production and destruction terms in the RANS equation. Third, the local Mach number is included in the machine learning process to incorporate compressibility effects of the supersonic flow. The current study indicates that the improved RANS model reduces the eddy viscosity in the separated region, compared to the baseline RANS model. The reduction of the eddy viscosity helps to predict the base expansion of the supersonic flow and the size of the recirculation region. Current computations are compared with relevant literature data including wake velocity profiles and the base pressure in the wide range of the supersonic Mach number.

Characteristics Investigations of Ducted Ka4-70 Series Propeller with Boss Cap Fins Using Numerical and Experimental Method

Unconventional system that are generally adopted for ship propulsion are Ducted Propellers. These devices have recently been studied with medium-fidelity computational fluid dynamics code (based on the potential flow hypothesis) with promising results. Numerical and experimental comparison of ducted propeller with PBCF, case studies with Propeller Ka4-70 used combination ducted and PBCF Divergent. The study was done numerically using computational fluid dynamics (CFD) approach. The solver is based on the Reynolds-Averaged Navier-Stokes (RANS) solutions and turbulence modelling explicit algebraic stress model (EASM). The test data was obtained from CFD simulations consisting of the open propeller and combination Nozzle plus PBCF, but the experiment was done to Nozzle and PBCF only. All measurements were carried out from J = 0 to J = 1.0 with speeds from 0 m/s to 2.445 m/s. The results of the comparative investigation cases between numerical and experiment analysis from Ka4-70 propellers with Nozzle 19A and PBCF Divergent appears that between CFD and experiments, several phenomena are seen. (i) the Ka4-70 propeller without Nozzle 19A and PBCF divergent experienced large pressure at low-speed J = 0.1 to high-speed J = 0.7, but Ka4-70 propeller with Nozzle and PBCF divergent reach highest pressure at J = 0.1 to J = 0.5; (ii) the Ka4-70 propeller without 19A nozzle and PBCF divergent increases the flow velocity at the boss cap fins but does not increase the axial induce velocity, while Ka4-70 propeller using nozzle and PBCF divergent increases the axial induce velocity of the blade, but does not increase the flow velocity of the boss cap fins; (iii) Ka4-70 propeller without Nozzle and PBCF value increase of propeller η0 to 12% when ESD added in the form of Nozzle and PBCF when J is high, from J = 0.7 to J = 1.0. ; (iv) Ka4-70 propellers with Nozzle 19A and PBCF Divergent has very similar η0 from J=0 to J=1.0. CFD approach are still appropriate to be relied upon for the overall simulation.

Numerical Investigations of Turbulent Flow Through A 90-Degree Pipe Bend And Honeycomb Straightener

Abstract Pipe bends are commonly used in piping systems in offshore and subsea installations. The present study explores the design considerations for the honeycomb straightener inserted downstream of a 90-degree pipe bend. The objective of the study is to evaluate the effectiveness of the honeycomb in suppressing the flow swirling for different distances from the bend outlet (Lb) and different values of the honeycomb thickness (t). The turbulent flow through the 90-degree circular pipe bend with the honeycomb straightener is investigated by carrying out numerical simulations using the Reynolds-Averaged Navier-Stokes (RANS) turbulence modeling approach. The Explicit Algebraic Reynolds Stress Model (EARSM) is adopted to resolve the Reynolds stresses. The honeycomb thickness to pipe diameter ratio (t/D) is varied between 0.1 and 1. The normalized distance from the bend outlet to the honeycomb straightener (Lb/D) is varied between 1 and 5. The disturbance in the velocity field is generated by the pipe bend with the curvature radius to pipe diameter ratio (Rc/D) of 2 and Reynolds number (Re) of 2×105. It is found that both the increase in Lb/D and t/D improves the performance of the device in removing the swirl behind the bend outlet. The best performance is observed for the honeycomb straightener with the distance Lb/D=5 and thickness t/D=0.5.

Effect of void space arrangement on wind power potential and pressure coefficient distributions for high-rise void buildings

High-rise void building complexes can augment the permeation of airflows over buildings, and thereby strengthen urban wind energy harvesting for realization of the sustainable development goals (SDGs). This paper considers the wind over a typical 2×2 compact high-rise building array with the openings to analyze the wind power potential at varying void sizes, locations of voids, and direction of incoming wind. The predicted mean wind speeds and turbulence intensities are compared against the measured data with 4 generic high-rise building models having voids in an atmospheric boundary layer wind tunnel for validation of the computational model. Based on the comparative results from four common Reynolds-averaged Navier-Stokes (RANS) turbulence models including the standard, realizable, renormalization group (RNG) k-ε, and shear-stress transport (SST) k-ω models as well as the Reynolds stress model (RSM), the RSM approach can provide the most accurate predictions of streamwise mean velocity and turbulence intensity. The present study then conducts CFD simulations to explore the effects of opening configuration and wind direction on the wind field around high-rise void buildings. Considering the variations of void sizes of 10 × 10 m2, 12.5 × 12.5 m2, 15 × 15 m2, void heights of z/H = 0.25, 0.5, 0.75 and wind directions of 0°, 45°, respectively, the simulated results indicate elevated wind power densities with acceptable turbulence intensities over the upstream gap passage and void channels to achieve prospective urban wind power harvest and mitigate wind load on structures of high-rise void buildings.

CFD modelling of initial stages of dam-break flow

Cases of dam failures are seen almost every year globally, and the propagation of rapidly varying unsteady flows resulting from those dam failures has significant environmental and economic consequences. A three-dimensional Computational Fluid Dynamics model was created to solve unsteady Reynolds-Averaged equations to investigate the generation and propagation of dam-break flows and reflected flood waves in the presence of a trapezoidal bottom obstacle. The dam-breaks were modelled using OpenFOAM based on the Volume of Fluid method employing the Finite Volume Method, and the performance of various Reynolds-Averaged Navier-Stokes turbulence models, including the realizable k − ε, SST k − ω (Shear Stress Transport k − ω), and v2 − f models, has been evaluated. To assess the capabilities of the different turbulence models, quantitative comparisons of numerical simulations with laboratory experiments were completed, and it was found that the SST k − ω model performed better in predicting the free surface profiles and negative bore propagation speeds than the realizable k − ε and v2 − f models.

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.

The performance of different unsteady Reynolds-averaged Navier-Stokes models mined by Fuzzy C-means algorithm with Fourier coefficient-based distance on the constructed vortex structures around a single building

ABSTRACT The Fuzzy C-means (FCM) method with Fourier coefficient-based distance was firstly used to construct the vortex features and analyze the large-scale unsteady flow pattern around the building by the transient ensemble velocity magnitude and Q criterion value. The performance of the unsteady Reynolds-averaged Navier-Stokes (URANS) turbulence models, including Standardmodel, Realizable, Renormalization Group (RNG) theoryand Shear-Stress Transport (SST) models on the flow structures around a high-rise building, was examined and compared by data analysis. The transient data was analyzed to identify the root of the different flow structures. The vortex structure was used to distinguish the different turbulence simulation performance directly. The result indicated that the RNGmodel shown the best simulation results on the mean velocity and total turbulent kinetic energy fields. The RNG model could simulate the modest scales of vortices which approximates the experiment data around the building, while the SSTmodel could simulate the abundant scales of vortices which led larger turbulence viscosity coefficient. In addition, the nature pressure difference ventilation partition method was proposed and verified in simulating the nature pressure difference around a single building.

Validation and application of pressure-driven RANS approach for wind parameter predictions in mountainous terrain

Computational Wind Engineering has undergone numerous developments over the past few decades and has been applied to solve a variety of wind engineering issues, but it cannot substitute wind tunnel testing and field measurements for accurately replicating wind characteristics in naturally hilly terrain. This paper is aimed at detecting the validity of the approach on numerical simulations by estimating wind flow behaviour at a bridge site in a Y-shaped valley and comparing the results from wind tunnel testing. Further, the terrain-induced effects on wind flow are investigated and the spatial distributions of wind parameters along the bridge structures are characterized. It is concluded that three Reynolds-Averaged Navier-Stokes (RANS) turbulence models, namely k-ε, k-ω and SST, make significant differences in the leeward regions and wind velocity, speed-up, and pitch angle profiles, with the k-model producing superior predictions within 20% error when compared to experimental results. The simulation results show that non-homogeneity of wind characteristics occurs frequently along bridge structures. One is significant rotations of the wind velocity profile up the height of both bridge towers, and then a practical equation for predicting wind deflection is proposed. The other is spanwise nonuniformities in mean wind speeds and pitch angles along the main girder, which necessitates the use of a modified terrain coefficient when securely predicting wind speed. The discussion of a few national bridge design codes reveals that most of them fall short of characterizing the wind load at the bridge site in mountainous areas.

Numerical simulation of the boundary layer development behind a single quarter elliptic-wedge spire

For decades wind tunnel has been utilized to generate a quasi-atmospheric boundary layer to observe the wake flow around objects submerged within the Atmospheric Boundary Layer. The quarter elliptic-wedge spire is the most commonly used as a vortex generator among other passive devices. However, despite numerous past studies that utilize rows of spires to generate deep quasi-ABL, only a few researchers targeted spires as the main subject of their investigation. Hence, the present work originally aims to investigate the wake flow structure behind a single quarter elliptic-wedge spire and its aerodynamic interaction with a smooth wall boundary layer. A computational fluid dynamics simulation predicting the wake flow structure behind a single quarter elliptic-wedge spire was conducted using the OpenFOAM® software. The computational domain consists a smooth flat plate, and a single quarter elliptic-wedge spire. A comparison of two Reynolds-Averaged Navier–Stokes turbulence models, namely the k-ɛ model and the SST k-ω model, was conducted. A SIMPLE algorithm was used as the solver in the simulation iteration and ParaFOAM® was used as the post-processing software. The development of the boundary layer height from streamwise x0=0.5S to downwind x0=20S was observed. The mean vertical velocity profiles predicted by both turbulence models are in good agreement with the previous wind tunnel experimental results. However, the results obtained with the k-ɛ model were overpredicted compared to the results of the SST k-ω model causing deviation of the boundary layer height from the wind tunnel experimental data. This anomaly might be caused by the velocity deficit recovery above the boundary layer height region where the turbulence is low.

Numerical simulation on the acoustic wave scattering and fluid perturbations inside confined orifice flow

Acoustic wave scattering and fluid perturbations produced by interactions between incident acoustic wave and confined orifice flow were investigated by a combined numerical solution containing nonlinear flow simulation and linearized acoustic simulation. In flow simulations, the mainstream Reynolds number was fixed at 10,000, which relates to the cooling pipe system of lithography. Turbulent flow fields corresponding to different orifice geometries were solved by an opensource finite volume solver OpenFOAM with Reynolds-averaged Navier–Stokes turbulence model. The turbulence database could efficiently improve the accuracy of subsequent linearized acoustic simulations as the viscosity dissipations were considered. In acoustic simulations, the linearized Navier-Stokes equations were solved by a finite element solver with transformation into frequency domain. The incident acoustic waves with varying frequencies from 500 Hz to 4000 Hz were arranged first at the inlet and then the outlet surfaces, enabling a two-port analysis on the transmission and reflection coefficients of acoustic waves. The numerical setup and the two-port model were well validated by results in literature. Generally, acoustic waves tend to gradually dissipate as their frequencies increase or the opening ratio of the ducted orifice decreases. However, the nonlinear variation in the transmission and reflection coefficients against the frequency variation of the incident acoustic waves could be investigated by increasing the thickness ratio. The acoustically induced fluid perturbations that were characterized by the Q-criterion could form a ring shape vortex structure in the vicinity of the orifice edge and then develop into disk-like packets. When the circumferential shape of the orifice was changed to a square, the attenuation of the incident acoustic waves corresponded to the intensity of the three-dimensionality of the acoustic-induced vortex structures, which indicated a greater energy transfer from the acoustic waves to the fluid perturbations.

Adding a simple production term to Reynolds-averaged Navier–Stokes turbulence models for flows over two-dimensional hills

We consider an additional production term for the k,ε turbulence model that is activated by curvature, for turbulent flow over two-dimensional hills of varying steepness. The new term depends on the difference between the strain rate, S, and the rotation, R, which we refer to as the “SR” modification. It is compared to the standard k,ε turbulence model, the Kato–Launder model, and the re-normalization group and realizable versions of the k,ε model. The Kato–Launder model showed the best overall predictions for mean velocity, turbulent kinetic energy, and Reynolds shear stress at most locations before, on, and after the crest of the hills. The SR model was slightly less accurate but uniquely predicted the flow separation in the lee of the steeper hill and was also correctly predicted the flow re-attachment point. This study demonstrates the importance of including a curvature production term in k–ε-based models for flows over hills.

Application of hydrogen mechanisms in combustion simulation of DLR scramjet combustor and their effect on combustion performance

In view of the promising application of hydrogen in scramjet combustor and the rapid development of hydrogen kinetic mechanisms, present work applies representative mechanisms with good kinetic performance to the combustion simulation of DLR scramjet combustor with a customized solver based on OpenFOAM platform. Different Reynolds-Averaged Navier Stokes (RANS) turbulence models including standard k-ε, SST k-ω and their corresponding modified versions for turbulent round jets, are utilized to simulate the non-reactive and reactive flow fields. Compared with the detailed experimental measurements of schlieren image, streamwise velocity, pressure etc., the modified k-ω SST turbulence model shows good performance and improves the simulation results near hydrogen jet. In combination with partially stirred reactor (PaSR) combustion model, three representative detailed hydrogen mechanisms (marked with Ó Conaire-2004, Varga-2015 and Konnov-2019) are adopted to evaluate their effect on combustion performance under scramjet combustion condition. And their effects on the combustion performance are quantified based on combustion efficiency, net thrust, total pressure loss, etc. All of them can well characterize the thermal combustion characteristics of hydrogen in the combustor. Among them, Ó Conaire-2004 slightly overestimates flame temperature, combustion efficiency and net thrust, and underestimates total pressure loss. Whereas Varga-2015 and Konnov-2019 provide nearly identical results on these performance parameters and give temperature profiles coinciding well with experimental data. Although the newly added excited states in Varga-2015 and Konnov-2019 deepen the understanding of hydrogen combustion processes and can served for optical combustion diagnostics, their effects on thermal combustion characteristics are negligible under present combustion condition, judging from their low content and the analysis on the performance parameters. Present work is conducive to the selection of hydrogen mechanisms for the combustion simulation of hydrogen-fueled scramjet combustor, and facilitates to obtain reliable simulation results for scramjet with turbulent round jets by employing the modified SST k-ω turbulence model.

Assessing the Structure-Based Turbulence Model Performance for Thermal Striping Applications Using Symmetric Jet Experiments

Turbulent mixing of coolant streams can result in an oscillatory mixing phenomenon called thermal striping. These fluctuations have the potential to lead to anticipated thermal fatigue failures in advanced nuclear reactors. To predict thermal striping, robust and computationally affordable modeling tools that are capable of accurately representing complex turbulence are needed. Hybrid turbulence approaches, such as detached-eddy simulation and scale-adaptive simulation, have shown some success in resolving complex unsteady turbulence for massively separated flows, however the applicability of these models to internal flows is limited. A STRUCTure-based (STRUCT) second-generation Unsteady Reynolds-Averaged Navier–Stokes turbulence model was recently proposed at the Massachusetts Institute of Technology to robustly extend the applicability of hybrid closures. In this work, the STRUCT model is evaluated using experimental data taken at the Reactor Cavity Cooling System separate-effects test facility at the University of Michigan. The experiments observed the interaction of parallel symmetric rectangular jets, and include measurements for mean profiles of velocity and Reynolds stresses. In the present work, the simulation results are assessed against mean profiles of velocity and Reynolds stresses, demonstrating the ability to reproduce the unsteadiness of the jets in close agreement with the measurements at considerably reduced computational cost.

Data-driven augmentation of a RANS turbulence model for transonic flow prediction

PurposeThis paper aims to improve Reynolds-averaged Navier Stokes (RANS) turbulence models using a data-driven approach based on machine learning (ML). A special focus is put on determining the optimal input features used for the ML model.Design/methodology/approachThe field inversion and machine learning (FIML) approach is applied to the negative Spalart-Allmaras turbulence model for transonic flows over an airfoil where shock-induced separation occurs.FindingsOptimal input features and an ML model are developed, which improve the existing negative Spalart-Allmaras turbulence model with respect to shock-induced flow separation.Originality/valueA comprehensive workflow is demonstrated that yields insights on which input features and which ML model should be used in the context of the FIML approach

Numerical investigation of the aerodynamic and wake characteristics of a floating twin-rotor wind turbine under surge motion

To elevate the power capacity of floating wind turbines and cut costs, development towards large-scale systems is underway. However, this requires solving the problem of fatigue loading on large, flexible blades, as well as corresponding improvements to production and installation technology. As an alternative to larger turbines, twin-rotor floating wind turbines have been proposed. The aerodynamic and wake interference characteristics of this twin-rotor are not yet well understood. In this study, we have investigated the power and wake characteristics of a twin-rotor floating wind turbine based on unsteady Reynolds-averaged Navier-Stokes turbulence model for a comprehensive analysis. Specifically, the power and wake recovery of a twin-rotor floating horizontal-axis wind turbine (FHAWT) under surge motion are compared in detail with those of a single floating wind turbine and bottom-fixed case, while both the effects of the three wind directions (β = 0°, 45°, 90°) and spacing ratios (S/D = 1.2, 1.375, 1.5) are considered. The results suggest that the mean power of the twin-rotor is enhanced by a maximum of 13% under surge motion compared to the single rotor, the small spacing ratio promotes the power gain. Surge motion plays a significant role in wake interaction between the twin-rotor and facilitates wake recovery. As compared to the baseline case, both power and wake recovery performance of the twin-rotor are boosted at β = 45°, with an increase in power of 12.7% as opposed to the single rotor. The modified Jensen wake model is proposed for the far-wake region and a modified Gaussian wake model is also suggested for different cases. This study can provide affiliated guidance for the application of the twin-rotor floating wind turbine.