Momentum Source Research Articles

Cross-code comparison of the edge codes SOLPS-ITER, SOLEDGE2D and UEDGE in modelling a high-power neon-seeded scenario in the DTT

Abstract In this work, we cross-compare the state-of-the-art edge plasma codes SOLPS-ITER, SOLEDGE2D, and UEDGE in a reactor-relevant neon-seeded Divertor Tokamak Test (DTT) scenario at nominal power, extending the simplified test-bed of Moscheni et al. (2022). Converged solutions targeting the same separatrix density and radiated power are obtained by adjusting the pumping albedo and the neon puffing rate. This higher-power scenario is generally characterised by substantial disagreement between the three codes, up to 78-178% in peak heat fluxes. Discrepancies found in Moscheni et al. (2022) are indeed exacerbated, and new ones arise. Underlying causes include the over-penetration of neutrals implied by the unified ion-neutral temperature of UEDGE (observed in Moscheni et al. (2022)), here resulting in a 38-114% over-estimation of core plasma densities. The particular set of EIRENE atomic-molecular reactions adopted is found to stiffly restrict the achievable code solutions, which results in the predicted effective charge Z eff changing from ∽5 to ∽8 at the outer mid-plane separatrix. The strong link between Z eff, main ion density and unified ion temperature emphasises the need of proper assessments of impurity cross-field transport, with its implications on core contamination and wall erosion. The advantages of extended plasma meshes are found to come with associated modelling intricacies, yet to be fully characterised but seemingly impacting on the activity around the secondary X-point of single-null magnetic topologies. An appreciable impurity particle imbalance, generated by the neon ion density floor, is noted—speculatively contributing to SOLEDGE2D's different radiation emission distribution, and expected to be even more deleterious for high-Z impurities in all the codes. Potential drivers of further discrepancies are the different Braginskii formulations of collision times and momentum sources in presence of impurities, and the SOLPS-ITER extra terms gaining importance around the detachment front. Outstanding questions unanswered in this work prompt further investigations.

Oscillatory responses of a spatially random seabed in the vicinity of structures: Validation and application of the integrated CFD-SFEM

A comprehensive examination of the wave-induced oscillatory response of seabeds around structures is of great significance for ensuring the safe operation of marine engineering projects and enhancing the efficiency of marine resource development. Soil properties in nature exhibit spatial variability due to various geological processes, which should be considered in seabed stability analysis. An integrated CFD-SFEM is proposed for spatially heterogeneous seabeds, incorporating multi-physical solvers for nonlinear wave motion and poroelastic seabed response within a unified framework through a one-way coupling procedure. The wave sub-model for nonlinear fluid flow is based on RANS equations, with an internal wave-maker and absorbing layers realized by employing a momentum source function and damping source terms. The spatially heterogeneous seabed sub-model is based on Biot’s poroelastic theory and the random field method. We have implemented the integrated model and automated the iterative algorithm for MCS using MATLAB codes, assisted by the LiveLink platform. The proposed method has been validated from various perspectives and applied to a study of soil response around a partially buried pipeline to demonstrate its practical utility. This study offers a novel framework and perspective for the probabilistic evaluation of oscillatory responses in spatially varied seabeds surrounding structures.

Effect of the radial temperature gradient on resonant oscillations of gas in a closed tube.

Resonant oscillations of gas in a closed tube with a heat source are studied. The amplitude-frequency characteristics and spatial distributions of pressure and velocity amplitudes in a tube with a radial temperature gradient are calculated. It is shown that a radial temperature gradient leads to the radial dependence of the oscillation velocity in the flow core and reduces the average value of the momentum source due to viscosity. Together with the temperature dependence of the viscosity, this leads to the amplification of resonant gas oscillations in a tube with a heat source. The influence of the heat source on the resonant gas oscillations is determined by the radial temperature gradient and the square of the reduced oscillation frequency.

The spiritual dimensions of new quality productive forces

The spiritual dimensions contained in New Quality Productive Forces are not only the core driving force for its vigorous development but also the key to leading it towards high-quality development. These spiritual dimensions include the scientific spirit of daring to innovate and continuous exploration, the fighting spirit of being unyielding and enterprising in the face of challenges, the collaborative spirit of being innovative and entrepreneurial in the face of challenges, and the spiritual spirit of being a good teacher. These spiritual dimensions include the scientific spirit of daring to innovate and continuous exploration, the fighting spirit of being unyielding and enterprising in the face of challenges, the collaborative spirit of advocating These spiritual dimensions include the scientific spirit of daring to innovate and continuous exploration, the fighting spirit of being unyielding and enterprising in the face of challenges, the collaborative spirit of advocating cross-disciplinary cooperation and open sharing, and the dedication of serving society and benefiting humanity. the concept of green development ensures that New Quality Productive Forces, while pursuing economic benefits, is also committed to achieving These spiritual dimensions are interwoven and complement each other, jointly constructing the spiritual core of New Quality Productive Forces. These spiritual dimensions are interwoven and complement each other, jointly constructing the spiritual core of New Quality Productive Forces and injecting it with profound moral depth and a continuous source of development momentum.

Enhanced modeling of vehicle-induced turbulence and pollutant dispersion in urban street canyon: Large-eddy simulation via dynamic overset mesh approach

This study presented a novel application of large-eddy simulation (LES) with a dynamic overset mesh approach to simulate vehicle-induced turbulence in a two-dimensional street canyon. The simulation incorporated moving vehicle entities to emulate two-way traffic, with each vehicle equipped with a pollutant source to simulate pollutant dispersion. Comprehensive long-term statistical analyses were conducted to compare the simulated turbulence with those produced by the conventional approach (where vehicle-induced momentum was not considered) and the quasi-steady method (where vehicle motion was simplified as momentum sources). The results revealed that the presence of moving vehicle entities significantly distorted the primary circulation within the canyon, altering the transport pathways of both lateral momentum and air pollutants. The motion of vehicle entities also induced a substantial amount of turbulence, resulting in different pollutant removal mechanisms at the top of the canyon. The ensemble-average analysis revealed a downwash followed by an upwash within a cycle of vehicle movement, which largely contributed to momentum and pollutant transport. These findings underscored the need for considering the moving entities in LES approaches to enhance vehicle-induced turbulence modeling. Other factors influencing the simulation were discussed, aiming to guide more accurate and reliable turbulence modeling in urban environments.

NTVTOK-ML: Fast surrogate model for neoclassical toroidal viscosity torque calculation in tokamaks based on machine learning methods

The Neoclassical Toroidal Viscosity (NTV) torque is a crucial source of toroidal momentum in tokamaks, exerting significant influence on plasma instability and performance. Accurate numerical modeling of NTV torque is essential for experimental design and operation, as well as for gaining insight into the relevant physical processes. However, the time-consuming nature of NTV torque calculation poses challenges for its practical application in experiment analysis and physical investigations. In this study, we have developed NTVTOK-ML, a surrogate model for NTV torque calculation that combines the expressive power and fast inference of machine learning methods to achieve simultaneous accuracy and time efficiency. To obtain datasets for NTV torque, extensive numerical calculations using NTVTOK and MARS-F codes were performed under various plasma conditions of Experimental Advanced Superconducting Tokamak (EAST), covering a wide range of experimentally relevant parameter regimes and incorporating rich physical effects such as pitch angle scattering, full toroidal geometry, resonances, etc. For fixed magnetic perturbation case, NTVTOK-ML employs Multi-Layer Perceptron (MLP) deep neural network and eXtreme Gradient Boosting (XGBoost) ensemble learning techniques respectively. Furthermore, when considering linear plasma response effect, Convolutional Neural Network (CNN) is utilized to process two-dimensional magnetic perturbation data. The prediction accuracy of NTVTOK-ML is evaluated based on statistical metrics including coefficient of determination (R2), mean squared error (MSE), and relative error; single sample prediction ability; and generalization ability - demonstrating its reliability in NTV torque prediction tasks. Importantly, the computational time required for predicting NTV torque using our proposed approach is significantly reduced compared to the original numerical code by several orders of magnitude. Additionally, the flexibility offered by the NTVTOK-ML framework allows users to optimize model performance under specific circumstances. Overall, our developed method provides an accessible solution for rapid yet accurate prediction of NTV torque while incorporating essential physical effects - thereby facilitating real-time or inter-shot analysis in experiments as well as comprehensive multi-scale nonlinear time evolution modeling. Program summaryProgram Title: NTVTOK-MLCPC Library link to program files:https://doi.org/10.17632/thcd9fbjd5.1Licensing provisions: Apache-2.0Programming language: PythonNature of problem: The traditional numerical calculation of NTV torque in tokamaks is time-consuming, which hinders real-time or inter-shot experimental analysis and multi-scale nonlinear time evolution modeling. Simplifications to physical models have been employed to accelerate the calculations; however, they often result in quantitative or qualitative deviations within certain parameter regimes. Therefore, achieving both accuracy and high time efficiency simultaneously for NTV modeling is essential for experiment design and operation, as well as a comprehensive understanding of relevant physical processes.Solution method: 1. Generate a comprehensive plasma parameter space that encompasses a wide range of experimentally relevant tokamak plasma conditions; 2. Conduct numerous NTVTOK and MARS-F calculations to construct NTV torque datasets that incorporate various physical effects, such as pitch angle scattering, full toroidal geometry, and resonances; 3. Pre-process the datasets using dimensionless methods and logarithm transformation. For two-dimensional magnetic perturbation data, employ CNN for pre-processing; 4. Develop and train machine learning models based on deep neural networks or ensemble learning methods; 5. Evaluate the model performance in terms of statistical metrics, single sample prediction capability, generalization ability, and computational efficiency. The results indicate that the NTVTOK-ML surrogate model can be applied to diverse physical tasks in future studies.

Development and Optimization of a Micro-Baffle for the Enhancement of Heat Transfer in Film Boiling

This study represents the development and optimization of a micro-baffle design to enhance heat transfer in film boiling. Numerical simulations are performed using an open-source computational fluid dynamics (CFD) model, which incorporates the Lee model for momentum source associated with the phase change, and the Volume of Fluid (VOF) method to capture bubble dynamics. A comparison of the numerical results with the previous numerical and experimental data confirmed the validity of the numerical model. The influence of key design parameters was systematically investigated. The results revealed that a vertical baffle provided the maximum performance. The optimal baffle design achieved a 57.4% improvement in the Nusselt number and a 66.4% increase in critical heat flux (CHF). Furthermore, the proposed design facilitated continuous bubble formation, even with a reduced temperature difference between the heated surface and the subcooled liquid, which is crucial for energy-efficient thermal management in engineering systems. Ultimately, this study demonstrates the potential of micro-baffle designs in controlling bubble dynamics and improving heat transfer in film boiling, thereby aiding the design of efficient thermal systems.

Simulation and modelling approach for bubblers effect into molten glass tank

The usage of air bubblers plays an important role in the glass-making industrial process because it enhances the global heat transfer efficiency and especially the uniformity and quality of the finished products. However, glass manufacturers rely on field practice to run their plants, due to the extreme difficulty of conducting experimental investigations in melting tanks. CFD analysis represents a powerful tool to optimize operating parameters and positioning of bubblers and other components, not only in existing plants, but also in the design of new furnaces.In the present paper, the behaviour of bubble columns in highly viscous liquids at high temperature was analysed using the Eulerian multiphase model. The macroscopic effect of the column on the surrounding fluid was translated in a locally momentum source term that was introduced in the single-phase CFD model developed in this study. This solution approximates the multiphase nature of the problem in a reliable way and it is of fast integration in comprehensive models of furnaces.A clear methodology to determine the diameter of the bubbles and the velocity of the bubble chain in the buoyancy source term calculus are presented and analysed in detail. In addition, a validation process based on the comparison with other theoretical and empirical studies on the subject was carried out in detail: it includes the evaluation of the bubble chains properties and effects by varying the liquid viscosity and the inlet gas flow, that is the real operational parameter in industry. Moreover, the effects of the variable height of the bubblers were investigated using the results of a single-phase model of a real industrial glass tank.The analysis of the obtained results shows that the model and the calculation methodologies followed in this work can be effectively applied in the dimensioning process of industrial glass tanks or to optimize existing plants.

A note on Taylor–Couette style flows with two parallel inner cylinders

The flow in the gap between an inner and outer cylinder presents a variety of regimes, which are well explored. In the present work, we attempt to explore a more complex flow, with two parallel co-rotating inner cylinders. The rationale behind this arrangement was the following: in terms of base two-dimensional flow, close to each inner cylinder, the base flow resembles a laminar Couette flow, and close to the outer cylinder, the flow may again resemble a Couette flow, with the two inner cylinders being seen as a single source of momentum, while in the middle point between the inner cylinder, there is stagnation saddle point with two incoming and two out coming streamlines, creating a zone with a high shear where interaction of Taylor–Couette style rolls is expected. The experiment allowed to identify six regimes: for Re<50, presence of the base two-dimensional flow; for 50<Re<70, the first regime of steady rolls, equivalent to Taylor vortices; for 70<Re<110, vortices become unsteady; for 110<Re<170, in the stretched zone, the flow is unsteady while the same fluid parcels are then stabilized when leaving the stagnation point region and slowed down toward the outer wall; when Re>170, there is the onset of turbulent rolls, with loss of spatial periodicity and apparition of turbulence; and finally a second type of steady rolls occurs for a sudden start of cylinders and 50<Re<60.

The Wave-Coherent Stress and Turbulent Structure over Swell Waves

Abstract The generation of ocean surface waves by wind has been studied for a century, giving rise to wave forecasting and other crucial applications. However, the reacting force of swell waves on the turbulence in the marine atmospheric boundary layer (ABL) remains unknown partly due to the unclear magnitude and profile of wave-coherent (WC) stress. In this study, the intersection frequency between the energy-containing range and inertial subrange range in the turbulent spectra is identified based on the attached eddy model (AEM), as the intersection modulated by swell wave could help to comprehend the physical process between the ocean surface wave and the marine ABL. Using observations from a fixed platform located in the South China Sea, this study shows that the intersection when the WC stress accounts for a lower proportion of the total wind stress (<10%) follows U/(2πz) given by AEM, where U is the wind speed and z is the height. While the intersection depends on the drag coefficient of WC stress for the case, WC stress accounts for a large part of the total wind stress (>10%). Considering the unclear magnitude and profile of WC stress, this study derives a new function to depict the WC stress. Significance Statement Turbulence located in the energy-containing range of the spectra is the primary source of momentum, heat, and water vapor fluxes between the ocean and marine atmospheric boundary layer (ABL). Thus, a better understanding of the turbulent structure within the wave boundary layer can help us accurately parameterize those fluxes. In addition to absorbing energy from the marine ABL, waves, especially swell waves, influence the turbulent structure. However, until now, the turbulent structure is unclear due to the unclear wave-coherent stress size and profile. In this study, a function that can depict the wave-coherent stress is proposed. We found that the wave-coherent stress can modulate the intersection between the energy-containing range and the inertial subrange range in the turbulent spectra.

Verification and validation of a numerical wave tank with momentum source wave generation

Verification and validation of a numerical wave tank with momentum source wave generation

CFD simulation of thermal stratification and mixing in a Nordic BWR pressure suppression pool

Boiling Water Reactor (BWR) employs the Pressure Suppression Pool (PSP) as a heat sink to prevent overpressure of the reactor vessel and containment. Steam can be injected into the PSP through spargers in normal and accident conditions and through blowdown pipes in case of a loss of coolant accident (LOCA). There is a safety limit on the maximum PSP temperature at which such steam injection might cause dynamic loads on the containment structures. The performance of the pool can be affected if thermal stratification is developed when temperature of the hot layer grows rapidly while cold layer remains inactive. Simulation of pool behavior during realistic accident scenarios requires validated models that can sufficiently address the interaction between phenomena, safety systems and operational procedures. Direct modeling of steam injection into a water pool in long-term transients is computationally expensive due to the need to resolve simultaneously the smallest space and time scales of individual steam bubbles and the scales of the whole PSP. To enable PSP analysis for practical purposes, Effective Heat source and Effective Momentum source (EHS/EMS) models have been proposed that avoid the need to resolve steam-water interface. This paper aims to implement mechanistic approaches previously developed by authors for the simulation of transient thermal stratification and mixing phenomena induced by steam injection through spargers in a Nordic BWR PSP. The latest version of the EHS/EMS models using the ‘Unit cell’ approach has been validated against integral effect pool tests and applied to plant simulations. Several scenarios with boundary conditions corresponding to postulated accident sequences were simulated to investigate the possibility of stratification development and the effects of activation of different systems (e.g., blowdown pipes, high momentum nozzle) on the pool behavior.

Momentum induced by steam injection into a subcooled pool

Boiling Water Reactors (BWR) and Advanced Pressurized Water Reactors (APWR) often use spargers to release steam from the primary coolant system into a pool with subcooled water to prevent containment overpressure. Direct contact Condensation (DCC) creates sources of mass, heat, and momentum determined by the condensation regimes in a subcooled pool. Thermal stratification can develop in the pool if buoyancy forces created by the heat source dominate the momentum source. Only part of the stratified pool volume can be used as the heat sink which is a safety concern. Modeling of steam injection and its effect on a large pool is computationally expensive due to the considerable spatial and temporal scale differences between the steam-water interface dynamics and global pool circulation. To enable the prediction of realistic plant transients, Effective Heat Source (EHS) and Effective Momentum Source (EMS) models were proposed. These models aim to calculate the time-averaged integral effects of the steam injection on the pool without resolving the dynamics of the interface and DCC phenomena.This work aims to develop the empirical correlations that predict the time-averaged effective momentum induced by steam injection into a subcooled pool. The experimental data were collected in a Separate Effect Facility (SEF-POOL) at LUT, Finland. The force acting on the injection pipe was measured in SEF-POOL to estimate the effective momentum rate created by steam injection. The condensation regime coefficient C, defined as the ratio of effective momentum rate to the theoretical momentum rate of injected steam, is presented as a function of Jakob and Mach numbers. We found that the pitch-to-diameter ratios (P/D) had a significant effect on both the effective (time averaged) momentum rate and instantaneous forces measured in the low Jakob number region, which might be attributed to the interactions between neighboring nozzles.

Quasi-three-dimensional high-lift wing design approach considering three-dimensional effects of slipstream for distributed electric propulsion aircraft

The efficient utilization of propeller slipstream energy is important for improving the ultra-short takeoff and landing capability of Distributed Electric Propulsion (DEP) aircraft. This paper presents a quasi-three-dimensional (2.5D) high-lift wing design approach considering the three-dimensional (3D) effects of slipstream for DEP aircraft, aiming at maximizing the comprehensive lift enhancement benefit of the airframe-propulsion coupling unit. A high-precision and efficient momentum source method is adopted to simulate the slipstream effects, and the distributed propellers are replaced by a rectangular actuator disk to reduce the difficulty of grid generation and improve the grid quality. A detailed comparison of the 2.5D and 3D configurations based on the X-57 Mod Ⅳ is performed in terms of flow characteristics and computational cost to demonstrate the rationality of the above design approach. The optimization results of the high-lift wing of the X-57 Mod Ⅳ show that the aerodynamic performance of the landing configuration is significantly improved, for instance, the lift coefficient increases by 0.094 at the angle of attack of 7°, and 0.097 at the angle of attack of 14°. This novel approach achieves efficient and effective design of high-lift wings under the influence of distributed slipstream, which has the potential to improve the design level of DEP aircraft.

Aerodynamic interference analysis and modeling of heterogeneous rotors

During closed-range rotorcraft missions, strong aerodynamic disturbances occur between multiple aircraft, thus affecting the stability and safety of cooperative flight processes. However, owing to the numerous control variables in rotor models, the cost and complexity of experiments and body-fitted grid simulation methods are high, thereby resulting in low analysis efficiency and difficulty in establishing a highly applicable aerodynamic-interference model. In this study, the effectiveness of a two-dimensional quasi-steady momentum source method for calculating the aerodynamic interference of heterogeneous rotors is validated using the sliding-mesh method. Using Latin sampling and momentum source methods to obtain aerodynamic-interference data points, a multiparameter-coupled heterogeneous-rotor aerodynamic-interference model is proposed and validated. The results indicate that the proposed aerodynamic-interference model provides clear physical significance and demonstrates high accuracy under different rotor configurations. In validation samples, the correlation coefficient between the predicted aerodynamic loss on the lower rotor and the computational fluid dynamics (CFD) calculation results is approximately 0.99, with the maximum errors in predicting thrust and moment losses are less than 7 % and 2 %. Meanwhile, the correlation coefficient between the predicted values on the upper rotor and the CFD calculation results is 0.82, with the maximum errors in predicting the dimensionless thrust and moment losses are less than 5.5 % and 1 %. The rapid aerodynamic-interference analysis model proposed herein can serve as a reference for the safe-flight strategy of rotorcraft during close-range cooperative missions.

Application of the fast 3D simplified simulation method for the large CAP1400 nuclear island evaporator based on the coupled source term method

As for the evaporator of the large CAP1400 nuclear power plant, it has a large volume with numerous tubes along with the complex flow heat transfer phenomenon. The traditional direct simulation method usually takes a lot of time and computing resources to obtain the flow heat transfer data. To solve the problem, a fast simulation method established on the porous medium source term was herein proposed. In this simplified simulation method, the complex evaporator model is replaced with the porous medium model, where the derived heat and momentum source terms are added into the governing equation to control the heat flows. Five kinds of simplified evaporator models with different numbers of pipes were set to be the research objects, the internal flows inside the evaporator were studied with the traditional direct simulation method and the newly proposed simplified simulation method. Via comparative analysis, it can be found that: 1) The newly proposed simplified simulation method accurately captures the distribution characteristics of pressure, temperature, and entropy production in the evaporator, serving as a viable alternative to traditional direct simulation methods. Specifically, the average simulation errors for inlet-outlet pressure difference and temperature difference are both less than 5 % and 7 %, respectively. 2) The newly proposed simplified simulation method can capture the mutual interference effects between the evaporator and the nuclear main pump. When the evaporator is connected in series with the main nuclear pump, the average head of the main pump increases by 0.34 m, while the efficiency decreases by an average of 0.34 %. The average simulation errors of the simplified simulation method are 0.06 m and 0.13 %, respectively. 3) The application of the simplified simulation method leads to a significant 85 % decrease in the average computational cost for evaporator calculations and a notable 36 % decrease for combined calculations of the evaporator and main pump. The study here is expected to provide technique support for the simulation and evaluation of the large nuclear island.

Theory of the momentum source method for synthetic turbulence

The interaction between turbulence and blade leading edges is known to have a significant impact on the aerodynamic and aeroacoustic performance of propellers. In addition to directly simulating turbulence, synthetic turbulence, such as the momentum source method, has been developed as a popular method for studying this interaction process in computational fluid dynamics and computational aeroacoustics. However, it is found that for non-periodic disturbances, although the induced velocity field is divergence-free, spurious noise may be generated in the source region and contaminate simulation results. To address this issue, the present work proposes adding a correction term so that the divergence-free condition is satisfied globally and the unwanted acoustic waves are suppressed, as an extension to our previous work for time-periodic gusts [H. Jiang, Phys. Fluids 35, 096115 (2023)]. The strength of the proposed approach lies in its simplicity, flexibility, and generality. First, it derives explicit source terms, which are straightforward for numerical implementations, to generate unsteady flow fluctuations. Second, the sources can be added inside the computational domain, saving computational costs for turbulence convection and being compatible with most existing boundary conditions. Third, the proposed method can obtain analytical expressions for the needed momentum source of the Navier–Stokes equation subject to any desired isotropic or anisotropic divergence-free turbulence fields. The method has been verified by examples of synthesizing harmonic gusts, Gaussian eddies, and random turbulence. The synthetic velocity results characterized by different spectral components are directly compared to target velocity fields, verifying the proposed approach and showing its capability. Parameters that influence the distribution of added sources are systematically investigated to identify an optimal combination for different scenarios. Finally, the model is employed to evaluate the aerodynamic interaction between an incoming turbulence and a thin airfoil. The obtained results exhibit good correspondence with analytical solutions.

Turbulence induced by a swarm of rising bubbles from coarse-grained simulations

We performed numerical simulations of a homogeneous swarm of bubbles rising at large Reynolds number, $Re=760$ , with volume fractions ranging from 1 % to 10 %. We consider a simplified model in which the interfaces are not resolved, but which allows us to simulate flows with a large number of bubbles and to emphasize the interactions between bubble wakes. The liquid phase is described by solving, on an Eulerian grid, the Navier–Stokes equations, including sources of momentum which model the effect of the bubbles. The dynamics of each bubble is determined within the Lagrangian framework by solving an equation of motion involving the hydrodynamic forces exerted by the fluid accounting for the correction of the fictitious self-interaction of a bubble with its own wake. The comparison with experiments shows that this coarse-grained simulations approach can reliably describe the dynamics of the resolved flow scales. We use conditional averaging to characterize the mean bubble wakes and obtain in particular the typical shear imposed by the rising bubbles. On the basis of the spectral decomposition of the energy budget, we observe that the flow is dominated by production at large scales and by dissipation at small scales and we rule out the presence of an intermediate range in which the production and dissipation are locally in balance. We propose that the $k^{-3}$ subrange of the energy spectra results from the mean shear rate imposed by the bubbles, which controls the rate of return to isotropy.

Numerical Simulation on Aerodynamic Characteristics of Transition Section of Tilt-Wing Aircraft

The tilt-wing aircraft has attracted widespread attention due to its excellent performance. However, its aerodynamic characteristics during the tilt transition section are characterized by unsteadiness, nonlinearity, and strong coupling, making it difficult to control. Using computational fluid dynamics (CFD) methods and moving overset grids to control the tilt-wing motion, the momentum source method is employed to replace actual propellers. The influence of the propeller on the aerodynamic characteristics of the tiltrotor at different tilt angles is investigated under incoming flow velocities of 8 m/s and 45 m/s in steady conditions. Additionally, the differences between steady and unsteady calculations of the tilt transition section are investigated at incoming flow velocities of 8 m/s, 15 m/s, 30 m/s, and 45 m/s in unsteady conditions. The research results indicate the following information: 1. the slipstream from the propellers significantly enhances the lift, drag, and stall angle of attack of the tilt-wing aircraft but reduces the lift-to-drag ratio; 2. there are noticeable differences in the forces acting on the tilt-wing aircraft between steady calculations with fixed tilt angles and unsteady calculations with continuous tilting.

A data–driven sensibility tool for flow control based on resolvent analysis

This study presents a novel application of data-driven resolvent analysis algorithm for flow control. The objective is to identify key coherent structures connected to regions of the flow that are highly sensitive to structural changes. Modifying such regions, i.e., including momentum source terms, flow stabilizers, or changing the shape of the body under study, we can control the appearance of flow instabilities. The method is tested in two different applications: the laminar flow behind a two-dimensional circular cylinder and a turbulent channel flow including heat transfer to the endwall. In the first test case, the flow unsteadiness is controlled by including two stabilizers (formed by two small cylinders) in the areas suggested by resolvent analysis. This is a benchmark problem in fluid dynamics that serves to validate the idea of using this tool for flow control. In the second test case, data-driven resolvent analysis is applied as a mean to control, enhance or reduce, convective heat transfer. Modifications in the geometry, in the form of cavities and ribs included in the areas pointed by resolvent analysis, show the possibility of enhancing heat transfer while reducing drag. The findings highlight the importance of resolvent analysis in understanding flow dynamics and designing effective flow control strategies.