Stress-blended Eddy Simulation Research Articles

Numerical and experimental analysis of biomimetic tubercle for cavitation suppression in viscous oil flow around hydrofoil

This study explores the cavitation suppression mechanisms of biomimetic hydrofoils inspired by whale flipper tubercles, focusing on viscous oil flow around hydrofoils. A novel test system for viscous oil cavitation was developed, featuring a high-speed camera to capture transient cavitation phenomena. The study compared the cavitation behaviour of the flow around a basic blade (Base-blade) with that around a biomimetic blade (Bio-blade) designed with leading-edge tubercles. The visualization results demonstrated that the biomimetic structure significantly reduced the degree and unsteadiness of cavitation. The study also employed a three-dimensional CFD model using the Stress-Blended Eddy Simulation (SBES) method and the Zwart-Gerber-Belamri (ZGB) cavitation mass transfer model to reveal the flow mechanism. The Bio-blade reduced the vapour volume fraction by 9.67%, decreased the drag coefficient (Cd ) by 9.36%, and minimized the lift fluctuations compared to the Base-blade. The biomimetic design reduces the transient shedding cavitation scale, effectively suppressing severe cavitation events. The Bio-blade inhibited the formation of leading-edge separation vortices and reduced the scale of U-shaped vortices that enhance cavitation evolution. In summary, this study provides a comprehensive analysis of the cavitation suppression mechanisms of biomimetic hydrofoils in high-viscosity fluids, offering valuable insights for future research and engineering applications.

Intraventricular flow dynamics and thrombosis risk with a left ventricular assist device using accelerated thrombosis modeling and stress-blended eddy simulation

Intraventricular flow dynamics and thrombosis risk with a left ventricular assist device using accelerated thrombosis modeling and stress-blended eddy simulation

Evaluation of Film Cooling Adiabatic Effectiveness and Net Heat Flux Reduction on a Flat Plate Using Scale-Adaptive Simulation and Stress-Blended Eddy Simulation Approaches

Evaluation of Film Cooling Adiabatic Effectiveness and Net Heat Flux Reduction on a Flat Plate Using Scale-Adaptive Simulation and Stress-Blended Eddy Simulation Approaches

Numerical Analysis of Unsteady Phenomena in a Contra-Rotating Stage Based on the Reduction of Local Entropy Production

Abstract The primary purpose of this study is the reduction of local entropy production in a contra-rotating stage. As such, the unsteady flow phenomena and the impact of radial load distribution on these phenomena and local entropy production need to be clarified. In this study, the stress-blended eddy simulation (SBES) turbulence model is utilized to capture the vortices in the flow separation zone, and the γ-Reθ transition model is employed to predict the transition phenomenon within the boundary layer. Entropy production rate models suitable for different turbulence models are constructed separately to calculate local entropy production. Vortex visualization is achieved according to the λci criterion, and the relative vorticity change rate is used to analyze the components of the tip clearance vortices. The transition phenomenon is analyzed from the perspectives of both the Euler and the Lagrange descriptions. The primary findings can be summarized as follows: the transition begins earlier and progresses more rapidly in the rear rotor. Wake propagation, occurring at double the frequency, entropy production rate within the boundary layer changes in synchrony with the wall shear stress at the same frequency. Additionally, an investigation of the tip clearance vortices concludes that the main structure of the tip clearance vortices coincides with the flow pattern of the high entropy production rate region, and the flow structure related to the high divergence area is essential for considering subsequent optimization with the aim of reducing the entropy production rate.

Flow characterization of Maquet and Bio-Medicus multi-stage drainage cannulae during venoarterial extracorporeal membrane oxygenation

Background:Drainage cannulae extract blood from a patient during venoarterial extracorporeal membrane oxygenation (VA ECMO), a treatment that temporarily supports patients undergoing severe heart and/or lung dysfunction. Currently, the two most commonly used multi-stage drainage cannulae are manufactured by Maquet and Bio-Medicus, but their designs vary in many aspects which impacts the generated flow dynamics. Therefore, this study aimed to use computational fluid dynamics (CFD) to explore the flow characteristics of the aforementioned cannulae and their impact on complications such as thrombosis. Methods:The Maquet and Bio-Medicus cannulae were 3D modelled within a patient-specific geometry of the venous vasculature taken from a computed tomography scan of a patient undergoing VA ECMO. A drainage flow rate of 4 L/min was assigned to each cannula. Lastly, a stress blended eddy simulation turbulence model was employed to resolve bulk flow turbulence. Results:The proximal row of side holes in both cannulae generated high intensity counter-rotating vortices, thus generating supraphysiological shear. These proximal rows were also responsible for the majority of flow extraction in both cannulae (>1.6 L/min). Despite identical simulation settings, each cannulae had differing impacts on global flow dynamics. For instance, the Bio-Medicus model produced a total stagnant blood volume of 25.6 ml, compared to 17.8 ml the Maquet cannula, thereby increasing the risk of thrombosis. Conclusions:Overall, our results demonstrate that differences in design clearly impact flow dynamics and risk of complications. Therefore, further work in optimizing cannula design may be beneficial to prevent harmful flow characteristics.

Scale resolving simulations of the effect of glottis motion and the laryngeal jet on flow dynamics during respiration

Background and ObjectiveThe movement of the respiratory walls has a significant impact on airflow through the respiratory tract. The majority of computational fluid dynamics (CFD) studies assume a static geometry which may not provide a realistic flow field. Furthermore, many studies use Reynolds Averaged Navier-Stokes (RANS) turbulence models that do not resolve turbulence structure. Combining the application of advanced scale-resolving turbulence models with moving respiratory walls using CFD will provide detailed insights into respiratory flow structures. MethodsThis study simulated a complete breathing cycle involving inhalation and exhalation in a nasal cavity to trachea geometry that incorporated moving glottis walls. A second breathing cycle was simulated with static glottis walls for comparison. A recently developed hybrid RANS-LES turbulence model, the Stress-Blended Eddy Simulation (SBES), was incorporated to resolve turbulent flow structures in fine detail for both transient simulations. Transient results were compared with steady-state RANS simulations for the same respiratory geometry. ResultsGlottis motion caused substantial effects on flow structure through the complete breathing cycle. Significant flow structure and velocity variations were observed due to glottal motion, primarily in the larynx and trachea. Resolved turbulence structures using SBES showed an intense mixing section in the glottis region during inhalation and in the nasopharynx during expiration, which was not present in the RANS simulations. ConclusionTransient simulations of a realistic breathing cycle uncovered flow structures absent in simulations with a constant flow rate. Furthermore, the incorporation of glottis motion impacted airflow characteristics that suggest rigid respiratory walls do not accurately describe respiratory flow. Future research in respiratory airflow should be conducted using transient scale-resolving models in conjunction with moving respiratory walls to capture flow structures in detail.

NUMERICAL INVESTIGATION OF SUBMERGED HYBRID CAVITATION JET NOZZLE BASED ON STRESS-BLENDED EDDY SIMULATION MODEL

Cavitation jet technology is extensively applied in fields such as mechanical processing, rock fragmentation, and energy development. To further enhance the cavitation capability of the nozzle, first a submerged organ pipe-angular hybrid cavitation nozzle model is established using the software SOILDWORKS. Second, the stress blended eddy simulation (SBES) technology is applied, and the jet law of internal and external flow field of submerged cavitation nozzle is studied numerically using FLUENT. Finally, the periodic shedding of cavitation clouds and the velocity characteristics and vapor volume fraction are studied for different expansion or contraction angles. The study revealed that the cavitation first occurs in the expansion section. With the development of cavitation, the asymmetry of the cavitation cloud increases significantly. Under an inlet pressure of 20 MPa, the fluctuation part of velocity is more concentrated. As the pressure increases, the maximum jet distance and velocity also increase.

Stabilize cloud cavitation with an obstacle near hydrofoil's trailing edge and conduct local entropy production analysis

Cloud cavitation always causes severe damage to the efficiency and stability of the hydraulic machinery, resulting in extra energy losses in the system. We have observed an effective and simple way to prevent cloud cavitation formation by placing an obstacle near the hydrofoil's trailing edge. Cavitating flows around four different types of hydrofoils were simulated using the stress-blended eddy simulation turbulence model: the National Advisory Committee for Aeronautics (NACA) 66 hydrofoil and the NACA 66 hydrofoil with a 1 ×1 mm2 obstacle at 0.3c, 0.5c, or 0.7c. Sheet cavitation is the predominant mode of cavity flow when the obstruction is positioned at 0.7c. To find out why the cloud cavitation growth can be stopped when the obstruction is positioned at 0.7c, the velocity field, vorticity in the Z direction, and vortex structure of the Q-criterion were computed. To study the energy loss of the cavity flow and comprehend how obstacles affect it, the local entropy production rate was computed. It was discovered that the vorticity downstream of the obstacle, positioned at 0.7c, is restructured, which helps manage the flow separation upstream of the obstacle. Consequently, the hydrofoil's suction surface vorticity nearly rotates in the same direction as the obstacle at 0.7c, and the direction of Vx upstream of the obstacle is in the positive direction of the X axis, indicating that the reentrant flow has been controlled upstream of the 0.7c obstacle. Furthermore, cavitation shedding and the entropy production rate are strongly correlated, and regulating cloud cavitation growth is advantageous for energy conservation.

Flow-based stress-blended eddy simulation: A local RANS/LES turbulence model for urban flow CFD simulations

In the present article, we introduce a local hybrid RANS/LES turbulence model, the Flow-based Stress-Blended Eddy Simulation (Fb-SBES). The methodology is applied to urban flow simulations in atmospheric boundary layer. The blending from RANS to LES is performed on the fly with respect to a flow deviation parameter. This makes the model self-adaptive and requires no prior knowledge of the flow contrary to typical zonal LES models. The present methodology enables the RANS equations to be solved in the major part of the computational domain (e.g. on average 88% for a single building). The RANS zone is modelled with a comprehensive RANS turbulence model for ABL simulations that sustains the fully developed inlet conditions until the built environment. In general, Fb-SBES shows better agreement with experimental data on the building and in the wake compared to advanced RANS and DDES simulations.

Assessment of stress-blended eddy simulation on prediction of flow characteristics in a Rushton impeller stirred tank

Stressed-blended eddy simulation (SBES), a novel hybrid RANS-LES approach, offers enormous potential to improve the prediction of the scale-resolving flow. However, few studies have been carried out on complex flow in stirred tanks. In this study, the SBES model was used to investigate the flow characteristics in a Rushton turbine stirred tank. The quantitative predictions of phase-averaged and phase-resolved flow field, as well as turbulence characteristics were conducted to assess the comprehensive performance of SBES. The results were also compared with those obtained from the SAS-SST model and LES model, as well as experimental data. It is indicated that the SBES model offers excellent agreement with experimental data in velocity and turbulence quantities, especially for the prediction of radial, tangential velocity and turbulent kinetic energy. Moreover, SBES model can successfully capture the features of trailing vortices and resolve more turbulence structure than the SAS-SST model with moderate computational grids.

Forced-motion simulations of vortex-induced vibrations of wind turbine blades – a study of sensitivities

Abstract. Vortex-induced vibrations on wind turbine blades are a complex phenomenon not predictable by standard engineering models. For this reason, higher-fidelity computational fluid dynamics (CFD) methods are needed. However, the term CFD covers a broad range of fidelities, and this study investigates which choices have to be made when wanting to capture the vortex-induced vibration (VIV) phenomenon to a satisfying degree. The method studied is the so-called forced-motion (FM) approach, where the structural motion is imposed on the CFD blade surface through mode shape assumptions rather than fully coupled two-way fluid–structure interaction. In the study, two independent CFD solvers, EllipSys3D and Ansys CFX, are used and five different turbulence models of varying fidelities are tested. Varying flow scenarios are studied with low to high inclination angles, which determine the component of the flow in the spanwise direction. In all scenarios, the cross-sectional component of the flow is close to perpendicular to the chord of the blade. It is found that the low-inclination-angle and high-inclination-angle scenarios, despite having a difference equivalent to up to only a 30∘ azimuth, have quite different requirements of both grid resolution and turbulence models. For high inclination angles, where the flow has a large spanwise component from the tip towards the root, satisfying results are found from quite affordable grid sizes, and even with unsteady Reynolds-averaged Navier–Stokes (URANS) k–ω turbulence, the result is quite consistent with models resolving more of the turbulent scales. For low inclination, which has a high degree of natural vortex shedding, the picture is the opposite. Here, even for scale-resolving turbulence models, a much finer grid resolution is needed. This allows us to capture the many incoherent vortices, which have a large impact on the coherent vortices, which in turn inject power into the blade or extract power. It is found that a good consistency is seen using different variations of the higher-fidelity hybrid RANS–large eddy simulation (LES) turbulence models, like improved delayed detached eddy simulation (IDDES), stress-blended eddy simulation (SBES) and k–ω scale-adaptive simulation (SAS) models, which agree well for various flow conditions and imposed amplitudes. This study shows that extensive care and consideration are needed when modeling 3D VIVs using CFD, as the flow phenomena, and thereby solver requirements, rapidly change for different scenarios.

Experimental and numerical investigation of transverse combustion instability in a rectangle multi-injector rocket combustor

Rocket engines are prone to suffer from transverse combustion instabilities, manifesting as periodic oscillations in pressure and heat release rate. Self-excited transverse instabilities in a rectangle multi-injector rocket combustor powered by n-C12H26 and O2, are investigated experimentally and numerically in this paper. Transverse combustion instabilities are captured during repeatable experiments, while dynamic characteristics in the combustion chamber and driving mechanisms of instabilities are analyzed via numerical simulation based on stress-blended eddy simulation. Dynamic mode decomposition analysis reveals coupling behaviors between the transverse mode in the combustion chamber and longitudinal mode in the oxidizer post, resulting in propellant mass flow rate oscillations. Substantial evidence demonstrates that the intensities of heat release rate near the end walls are higher than that detected around the chamber center due to its intense coupling to the local first transverse (1W) acoustic mode. Flow field animations indicate strong deflection of oxygen posts and liquid particles by a transverse moving gas mixture leading to flame interactions and collision between adjacent share injectors. The propellant injected into the chamber does not burn immediately and is transported to the combustor end wall. Propellant mixing performance is significantly enhanced during interactions between acoustic pressure and end wall, causing a sudden heat release near 1W pressure anti-node, thereby strengthening pressure oscillations. Finally, a combustion instability driving mechanism associated with propellant mass flow rate oscillations, and interactions between unsteady acoustic pressure and heat release rate is proposed. The insights obtained from this work can aid comprehension of transverse combustion instabilities encountered by rocket engines.

Application of Stress Blended Eddy Simulation to the prediction of clarified layer depth and solids suspension in a draft tube reactor

Predictions of clarified layer depth and solids suspension in a draft tube reactor were investigated at a moderate solids loading of 16% v/v using both a RANS approach (k−ε) and a scale-resolving approach using Stress Blended Eddy Simulation (SBES). The multiphase flow was modelled using an Algebraic Slip model and the impact of drag law, turbulent particle diffusion and number of particle size classes was examined. The inclusion or exclusion of turbulent particle diffusion is found to dominate the RANS results, with resulting poor prediction of clarified layer depth and solids suspension under some conditions. In contrast, the SBES model is found to give good agreement with experimental data and the results show there is no need for a modelled turbulent dispersion force in this system if the large-scale turbulence structures responsible for particle transport are explicitly resolved.

Investigating the aerodynamic drag and noise characteristics of a standard squareback vehicle with inclined side-view mirror configurations using a hybrid computational aeroacoustics (CAA) approach

This study investigates the aerodynamic noise generated and radiated from a standard squareback body with various inclined side-view mirrors using a hybrid computational aeroacoustics method based on a stress-blended eddy simulation coupled with the Ffowcs-Williams and Hawkings acoustic analogy. The results indicate that in the absence of the side-view mirror, the idealized A-pillar is identified as the subsequent major contributor to the overall noise radiated from the vehicle body, and the coefficient of drag decreases by approximately 13.3% despite a minimal change in the projected frontal area. However, the behavior of the drag coefficient becomes nonlinear and highly dependent on the complex flow features, including the vortex shedding patterns and the interaction between the flow and side surface of the body, with increasing mirror inclination angle. In contrast, the radiated noise exhibits a constant decrease as the mirror inclination angle (θ) increases to 32°. Additionally, when the side-view mirror is considered as the sole source, the noise radiated is minimal for an inclination angle of 16°, and a further increase in inclination angle has no significant reduction on the noise radiated but alters the overall drag coefficient of the vehicle. These findings have practical implications for the design of side-view mirrors to reduce aerodynamic noise in automotive applications and highlight the complex tradeoffs between noise reduction and changes in the drag coefficient that must be considered in such designs.

Numerical investigation about the unsteady behavior of a free submerged cavitation jet using the SBES approach

Submerged cavitation jet has emerged as an efficient method for the removal of ship fouling. Due to the complicated revolution of cavitation cloud, it has attracted great research interest. Ascertaining the internal flow dynamics of cavitating jets is always a challenge. Thus, this paper investigates the unsteady behavior of a free submerged cavitating jet numerically in three dimensions. The turbulent cavitation flow is simulated utilizing the Stress-Blended Eddy Simulation (SBES) turbulent model combined with the Schnerr-Sauer cavitation model. The results are compared with the data from a famous experiment, and they exhibit good agreement in both time-averaged and unsteady characteristics. The cavitation life stages, i.e., the cavitation growth, shedding, contraction, and collapse are explored. In results, cavitation cloud forms around the jet core. Cavitation cloud shedding involves complex factors, including shear layer instability, complex pressure gradients, and re-entrant motion, and it may also be related to the potential core and jet core instability. Additionally, cavitation cloud development is closely related to the jet core and exhibits synchronous behavior. After the cavitation cloud collapse, a local high pressure is observed and then cavity rebound is generated, where the collapse can be either mild or intensive.

Hybrid LES/RANS simulations of a 90° pipe bend using different CFD solvers

In this study, the performance of several RANS and hybrid LES/RANS turbulence models along with different CFD solvers (ANSYS Fluent, OpenFOAM and RapidCFD) is tested in terms of their ability to reproduce the flow downstream of a 90° pipe bend. The focus is on the temporal mean profiles downstream of the bend up to approximately 31 times the pipe's diameter D. The turbulence models' accuracy is evaluated by means of performance indicators and flow profiles in comparison to LDA measurements. The results demonstrate that the use of RANS models is suitable as long as the location of interest is in the vicinity of the bend up to approximately 10 D downstream of the bend. With increasing distance, the accuracy of the RANS models decreases, and the use of hybrid LES/RANS models is recommended.Three hybrid LES/RANS models are tested: the stress-blended eddy simulation (SBES) model as well as the Spalart-Allmaras-based and the k-omega SST-based improved delayed detached eddy simulation (IDDES) models. All three models show enhanced results for a distance to the bend >10 D. Additionally, it is found that in this geometry configuration, the IDDES models require a transient inlet. The flow separation due to the redirection inside the bend is too weak to generate turbulent fluctuations and a fast transition to full LES mode in the separation region. Due to the turbulent excitation at the inlet, the RANS region downstream of the bend is distinctly reduced, resulting in an enhanced performance of the hybrid IDDES models.

Simulation and Validation of Cavitating Flow in a Torque Converter with Scale-Resolving Methods

The purpose of this paper is to study the mechanism and improve the prediction accuracy of transient torque converter cavitation flow by the application of scale-resolving simulation (SRS) methods with particular focus on cavitation vortex flow. Firstly, the numerical analysis of the entire internal flow field of the torque converter was carried out using different turbulence models, and the prediction accuracy of the hydraulic characteristics of the adopted models was analyzed and validated via test data. Secondly, the cavitation and turbulence behavior in the internal flow field were analyzed, and the blade surface pressure according to different turbulence models was compared and validated through test data. Finally, the transient cavitation characteristics of the flow field were studied based on the stress-blended eddy simulation (SBES) model. The prediction accuracy of the cavitation flow field simulation of the torque converter is significantly improved using the SRS model. The maximum error of capacity constant, torque ratio and efficiency are reduced to 3.1%, 2.3%, and 1.3% at stall, respectively. The stator is more prone to cavitation than pump and turbine. The SBES model has the highest prediction accuracy in multiple measurement points, and the maximum deviation can reach 13.32% under stall. Attached cavitation bubbles and periodic shedding cavitation can be found in the stator, and the evolution period is about 0.0036 s, i.e., 279 Hz. The prediction accuracy of different models was compared and analyzed, which has important guiding significance for the high-precision prediction and analysis of fluid machinery.

Numerical simulation of the flow field and radiation noise from a pump-jet propulsor under various stator pre-whirl angles

The effects of different stator pre-whirl angles on the hydrodynamic and noise performance of a pump-jet propulsor (PJP) are studied; these angles are the inlet, outlet, and stagger angles. The stress-blended eddy simulation (SBES) approach, used to describe flow details around a PJP, is combined with the variational Lighthill's analogy to perform the acoustic calculation. The discrete peaks of the unsteady thrust of a single rotor blade and of all of the rotor blades are located at the harmonics of the blade passage frequency for stator (BPFs) and the blade passage frequency for rotor (BPFr), respectively. The trend in the amplitude with the pre-whirl angle at various harmonics follows no systematic rule, but the excessive pre-whirl angle increases the amplitude in the whole spectrum. With increases in pre-whirl angle, the stator sheet vortex and root vortex are weakened and enhanced, respectively, leading to a reduction of the high turbulent kinetic energy (Tk) regime at the root. Further study of the PJP sound indicates that the discrete tonal noise is located at the BPFs, BPFr, and their harmonics; the pre-whirl angle does not affect these locations, except in the largest inlet angle case. The cases with the least pre-whirl angle have an extremely low noise level, particularly at the outlet angle, which has an obvious downstream directivity.

Self-adaptive turbulence eddy simulation of flow control for drag reduction around a square cylinder with an upstream rod

The use of an upstream circular rod to control the flow around a downstream square cylinder is found to efficiently reduce the drag of the square cylinder. The complex flow characteristics and mechanism of the rod-square system in tandem arrangement as a passive flow control method for various centre-to- centre gap ratios (L/D) are investigated by numerical simulation. Turbulence modelling of the rod-square cylinder system is challenging. To select a suitable turbulence modelling, the recently developed Self-Adaptive Turbulence Eddy Simulations (SATES), as well as IDDES (Improved Delayed Detached Eddy Simulation) and SBES (Stress Blended Eddy Simulation) are first assessed for single circular and single square cylinder flow test cases. The SATES method performs best among the three models for bluff body flow simulation and is thus used in the drag flow control study. For the rod-square flow control system, the Reynolds number is 34000 based on freestream velocity U0 and the edge length of the square cylinder D. The diameter of the control rod is kept constant at d/D = 0.18. The flow characteristics and mechanism are explored in detail, varying the rod and square cylinder distance of L/D = 1.5, 2.0, 2.5and 3.0. According to the absence or presence of vortex shedding from the upstream rod cylinder, two flow patterns (pattern I and pattern II) are observed. Large drag reduction is observed for all the simulation cases the maximum drag reduction is approximately 63% with L/D = 2.0, and the minimum drag reduction approximately 53% with L/D = 3.0. The secondary lock-frequency, which presents as pattern II, is caused by the excitation of upstream vortices. It is found that the side recirculation is associated with the wake recirculation length of the square cylinder, which is similar to the elongated cylinder in the flow pattern I. The flow mechanism of suppression of the vortices from the rod can be attributed to the effective diffusion of vorticity in the separating shear layer caused by the presence of the front wall of the square cylinder.

Numerical prediction nonlinear heat-driven acoustics behaviours in standing-wave thermoacoustic engines using stress-blended Eddy simulation method

The present work investigated a standing-wave heat-driven thermoacoustic engine (SWTAE) system by capturing its nonlinear thermoacoustic features with three-dimensional (3D) unsteady Reynolds-Averaged Navier-Stokes (URANS) and hybrid URANS/LES (large Eddy simulation) models such as detached-Eddy simulations (DES) and stress-blended Eddy simulation (SBES) models. The comparison studies show that the prediction of the acoustic power of SWTAE using URANS is about 21.0% lower than that using LES, while the results from SBES and DES are relatively in good agreement with LES. Comparative studies of nonlinear hydrodynamics in the flow fields show that the results from SBES are closer to LES than DES, which can be attributed to the SBES model providing a faster transition to an explicit LES model outside the wall boundary layer. Furthermore, the heat transfer characteristics are compared by analyzing heat leaks and transversal heat flux, and it is found that the URANS model over-estimates the heat transfer characteristics, while the results of the other three models are relatively smaller than those obtained by URANS. In conclusion, the SBES model has great potential to be applied in simulating thermoacoustic nonlinear, heat transfer and flow behaviors of heat-driven SWTAEs.