Theoretical and Computational Fluid Dynamics最新文献

{"title":"Exploring the instabilities of a three-dimensional viscoplastic Rayleigh-Bénard convection","authors":"Marco A. Ferrari,&nbsp;Paulo R. M. Santos,&nbsp;Luiz A. Hegele,&nbsp;Admilson T. Franco","doi":"10.1007/s00162-025-00771-z","DOIUrl":"10.1007/s00162-025-00771-z","url":null,"abstract":"<div><p>Rayleigh-Bénard convection is a canonical problem in fluid mechanics, where an adverse temperature gradient between the opposing boundaries induces instabilities that drive natural convection. For viscoplastic fluids, a minimal perturbation is required to initiate the flow. This study presents a numerical investigation of the three-dimensional Rayleigh-Bénard convection within a cubic cavity heated from below, with lateral walls subject to a linear temperature profile. The fluid behavior is modeled using the Bingham constitutive model. The moment-based Lattice Boltzmann Method was employed as the numerical method to solve the mass and momentum transport equations, with an extended formulation to incorporate the energy transport equation using a local diffusion coefficient approach. Simulations are performed for Rayleigh numbers between 10⁴ and 10⁷. Within this range, we observed a region of Yield numbers, between 0.004 and 0.007, that fluid plastifies. Increasing the Rayleigh number led to a transition from a stationary to a chaotic state, while larger Prandtl numbers damped the fluctuations in the velocity field. Notably, the imposition of a linear temperature profile on the lateral boundaries enhances flow instability, thereby amplifying plastic instabilities as the critical Yield number is approached.</p></div>","PeriodicalId":795,"journal":{"name":"Theoretical and Computational Fluid Dynamics","volume":"40 1","pages":""},"PeriodicalIF":2.8,"publicationDate":"2026-01-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145929837","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Modelling rectangular-jet screech via dimensional reduction","authors":"Grant Lu,&nbsp;Jayson Beekman,&nbsp;Soudeh Mazharmanesh,&nbsp;Daniel Edgington-Mitchell,&nbsp;Petrônio Nogueira","doi":"10.1007/s00162-025-00772-y","DOIUrl":"10.1007/s00162-025-00772-y","url":null,"abstract":"<div><p>This work presents a linear stability analysis of the waves involved in the screech resonance loop generated within a rectangular supersonic jet. Linear stability analysis of rectangular jets has often been performed using a planar-jet approximation, due to the significant reduction in complexity and computational cost. However, the impact of this simplification on the predictive power of the stability model has not been considered in detail thus far. In this work, the predictions of both a simplified planar model and a more representative two-dimensional model are compared for two waves of particular relevance to jet noise. These waves are the downstream-propagating Kelvin-Helmholtz (KH) instability, and the upstream-propagating guided-jet mode (GJM). Disparity in the predicted wavenumber for both waves is considered, as well as disparities in the KH growth rate, and the GJM band of existence. A parametric sweep through nozzle-pressure ratio is performed for rectangular jets with aspect ratios ranging from a square jet with <span>(textrm{AR}=1)</span> to an <span>(textrm{AR}=8)</span> rectangular jet. It is demonstrated that the KH wavenumber can be well approximated by a planar model for rectangular geometries with an aspect ratio as low as 2. The growth rate is more sensitive, but for <span>(textrm{AR} ge 4)</span> the differences between the two models are negligible. In contrast to the KH waves, the band of existence of the GJM, defined as the frequency range between the mode’s branch and saddle points, shows significant dependence on the modelling approach. For higher aspect ratios, the planar model can reasonably predict the saddle point of the GJM, but the predicted branch point of the GJM differs significantly from that predicted by the two-dimensional model. Performing the analysis about an experimentally derived mean-flow profile demonstrates that the predictions for the GJM are sensitive to small changes in the flow profile, with both branch and saddle points showing a strong dependence on the thickness of the shear layer. In all cases tested, the two-dimensional model predicts a much narrower band of frequencies over which the GJM is supported by the flow, as compared to the planar model. To verify the predictions made from the two models, screech frequency predictions are made using the modified weakest-link model and compared to experimental data. The planar model, though it overpredicts the band of existence of the GJM, still produces correct predictions of screech frequency. The two-dimensional model, when linearized about the experimental mean flow, also correctly predicts the screech tones, though performs no better than the planar model.</p></div>","PeriodicalId":795,"journal":{"name":"Theoretical and Computational Fluid Dynamics","volume":"40 1","pages":""},"PeriodicalIF":2.8,"publicationDate":"2025-12-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145772156","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Mathematical and computer models of the process of liquid filling a capillary in the system “experimental closed tank + capillary”","authors":"V. I. Trushlyakov,&nbsp;A. V. Panichkin,&nbsp;I. Y. Lesnyak","doi":"10.1007/s00162-025-00768-8","DOIUrl":"10.1007/s00162-025-00768-8","url":null,"abstract":"<div><p>A hypothesis is proposed about the process of liquid filling the experimental closed tank (ECT) with a capillary in its wall, the appearance of which may be of manufacturing defects in the ECT walls and welded seams. The hypothesis allows for the wettability properties of the ECT wall material, the capillary effect (CE), liquid evaporation and the pressure difference between the ECT volume and the environment, as well as the duration of the process. Three options for supplying liquid to the ECT volume are considered. They correspond to the technological operations in the ECT manufacture: washing, hydraulic testing, and calibration. A physical–mathematical model (PMM) of heat and mass transfer and liquid dynamics in the ECT and a capillary is developed on the basis of the Navier–Stokes equations. The obtained PMM is used to construct a corresponding computer model (CM). On the example of the ECT washing, a numerical simulation of the process of liquid filling the capillary is carried out. The changes in the capillary volume being filled with liquid are determined with respect to time, including temperature, pressure, mass flow rate of viscous incompressible liquid at the ECT entrance, wettability of the ECT walls and the exposure time interval. The capillary volume filling value is assessed for different duration of the washing process.</p></div>","PeriodicalId":795,"journal":{"name":"Theoretical and Computational Fluid Dynamics","volume":"39 6","pages":""},"PeriodicalIF":2.8,"publicationDate":"2025-12-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145778925","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Modal decomposition of flow behind a harmonically oscillating circular cylinder","authors":"Sudeep Menon,&nbsp;Xingeng Wu,&nbsp;Anupam Sharma","doi":"10.1007/s00162-025-00769-7","DOIUrl":"10.1007/s00162-025-00769-7","url":null,"abstract":"<div><p>We examine the flow behavior around a transversely oscillating circular cylinder using various dimensionality reduction techniques. Specifically, Fourier analysis, Proper Orthogonal Decomposition (POD), Dynamic Mode Decomposition (DMD), and multi-resolution DMD (mrDMD) are employed. Numerical simulations are performed at a cylinder-diameter-based Reynolds number of 500 for a range of oscillation displacement amplitudes. The flow field exhibits well-documented wake patterns, such as 2S, 2P, and P+S, as well as intermittent transitions between these patterns at varying amplitudes. Dimensionality reduction becomes particularly effective when the force spectrum exhibits a dominant tonal character. Under these circumstances, the selection of the modal decomposition technique has minimal impact–all approaches yield comparable mode shapes for the dominant modes. However, when the flow undergoes intermittent pattern switching (e.g., between 2P and 2S), only mrDMD is able to <i>automatically</i> distinguish them as distinct modes. Nonetheless, if the temporal windows over which mode switching occurs are specified a priori, POD, DMD, and DFT are also successful.</p></div>","PeriodicalId":795,"journal":{"name":"Theoretical and Computational Fluid Dynamics","volume":"39 6","pages":""},"PeriodicalIF":2.8,"publicationDate":"2025-12-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s00162-025-00769-7.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145729725","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Design and Dimensional Transfer of Reinforcement Learning-Based Closed-Loop Airfoil Flow Control","authors":"Qiong Liu,&nbsp;Luis Javier Trujillo Corona,&nbsp;David Espinoza,&nbsp;Fangjun Shu,&nbsp;Andreas Gross","doi":"10.1007/s00162-025-00770-0","DOIUrl":"10.1007/s00162-025-00770-0","url":null,"abstract":"<div><p>Reinforcement learning (RL)-based closed-loop flow control shows great potential for managing nonlinear and complex aerodynamic flows. In this study, we investigate RL-based flow control to enhance the lift-to-drag ratio of an NLF(1)-0115 airfoil at a chord-based Reynolds number of <span>( Re_c = 20{,}000 )</span> and an angle of attack <span>( alpha = 5^circ )</span>. Key control parameters, including the reward function, agent action time, observed state, and actuator placement, are systematically examined. Our results reveal that physics-informed tuning significantly improves control performance. An optimal agent action time of <span>( tau = 0.07 )</span>, corresponding to approximately 11% of the primary oscillation period, was identified. It broadens the induced forcing spectrum, enhancing interaction with a wider range of flow structures. This finding establishes a clear physical connection between the RL agent action time and the unsteady flow dynamics. However, excessively short agent action time reduce the forcing amplitude, limiting control authority. Adjusting the observed state from wake-region sensors to surface-mounted pressure sensors yields comparable improvements in lift-to-drag ratio, ranging from <span>( 34.1% )</span> to <span>( 35.5% )</span>, demonstrating the practical feasibility of using surface measurements. Forcing placement based on stability analysis significantly enhances control effectiveness. To improve data efficiency, the optimized 2D RL controller is transferred to a 3D CFD environment through prescribed spanwise wavenumber superposition. This lower-cost 3D controller effectively suppresses flow separation and significantly enhances aerodynamic performance. The results present a promising and practical alternative to direct 3D RL training for airfoil flow control.</p></div>","PeriodicalId":795,"journal":{"name":"Theoretical and Computational Fluid Dynamics","volume":"39 6","pages":""},"PeriodicalIF":2.8,"publicationDate":"2025-12-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145675123","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Variable density stratification of Kelvin–Helmholtz instability in a force field","authors":"Yaofeng Li,&nbsp;Chuandong Lin","doi":"10.1007/s00162-025-00767-9","DOIUrl":"10.1007/s00162-025-00767-9","url":null,"abstract":"<div><p>The Kelvin–Helmholtz (KH) instability in the gravitational field with various density stratifications is simulated using a two-component discrete Boltzmann method. The influence of Atwood numbers ranging from negative to positive is investigated through key aspects, including concentration gradients, mixing degree, amplitude, and vorticity dynamics. The results show that concentration fraction gradients and vorticity increase with higher Atwood numbers. Conversely, the mixing degree and amplitude initially decrease but later increase as the Atwood number rises. Furthermore, a detailed analysis of the vorticity equation terms reveals that the Atwood number significantly affects vorticity evolution. Interestingly, when the Atwood number is zero, the temporal accumulation of these terms is minimal. Physically, the KH instability enhances the growth of the interface and mixing degree, while diffusion broadens the transition layer. Additionally, the Rayleigh–Taylor (RT) instability extends the perturbed interface vertically and promotes the mixing of the two media if the upper medium is heavier than the lower one; otherwise, the RT stabilization suppresses these effects.</p></div>","PeriodicalId":795,"journal":{"name":"Theoretical and Computational Fluid Dynamics","volume":"39 6","pages":""},"PeriodicalIF":2.8,"publicationDate":"2025-11-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145561640","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Effect of density ratio on the stability of a Couette flow past viscoelastic compliant solid","authors":"Mandeep Deka,&nbsp;V. Kumaran","doi":"10.1007/s00162-025-00766-w","DOIUrl":"10.1007/s00162-025-00766-w","url":null,"abstract":"<p>In the stability analysis of flows past deformable surfaces, the critical Reynolds number is computed assuming the solid and fluid densities are equal. In real applications, the solid-to-fluid density ratio (<span>(rho _r)</span>) varies from <i>O</i>(1) for liquid flows to <span>(O(10^3))</span> for gas flows past deformable surfaces. The effect of <span>(rho _r)</span> on the linear stability of a Couette flow past a viscoelastic continuum solid is studied. An increase in the density ratio is found to have a significant destabilizing effect. The most unstable mode is an inviscid mode, which is an elastic wave of the solid that is destabilised due to a coupling with fluid fluctuations when the wave speed is smaller than the maximum of the flow velocity. As the density ratio is increased, the wave speed decreases and the flow becomes unstable at a lower flow speed or Reynolds number. From numerical results and theoretical reasoning, the critical Reynolds number (<span>(text{ Re}_c)</span>) is shown to scale as <span>(text{ Re}_c sim rho _r^{-1/2})</span>. At moderate to high Reynolds numbers, a small increase in density ratio can cause a relatively large decrease in the critical Reynolds number. Increasing solid-to-fluid viscosity ratio (<span>(mu _r)</span>) stabilises the system at all density ratios. For dissipative solids, the critical Reynolds numbers also decrease with an increase in the ratio of density to viscosity at all density ratios. This study shows that it is important to use the correct values of density ratio in computation of the stability boundaries.</p>","PeriodicalId":795,"journal":{"name":"Theoretical and Computational Fluid Dynamics","volume":"39 6","pages":""},"PeriodicalIF":2.8,"publicationDate":"2025-11-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145456187","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Free streamline detachment with surface tension: a conformal mapping-based numerical solution","authors":"Yuriy Semenov,&nbsp;Baoyu Ni,&nbsp;M. G. Blyth","doi":"10.1007/s00162-025-00765-x","DOIUrl":"10.1007/s00162-025-00765-x","url":null,"abstract":"<div><p>The problem of the detachment of a free streamline from a smoothly shaped body is considered taking into account the effect of surface tension. The fluid is assumed to be inviscid and incompressible, and the flow is assumed to be irrotational and stationary in the body-fixed frame. We employ the Brillouin-Villat criterion to determine the position of the free streamline detachment. Using the integral hodograph method, we derive expressions for the complex velocity and the derivative of the complex potential, both defined in an auxiliary parameter plane. A system of singular integral equations, formulated in terms of the velocity magnitude along the free surface and the slope of the body, is derived by applying the dynamic and kinematic boundary conditions. The numerical method is highly efficient, as it only requires the evaluation of these two nonsingular functions. Numerical results demonstrate the effect of surface tension on the free streamline detachment, the drag force and the free surface shape for a wide range of Weber numbers. It is shown that the surface tension generates capillary waves due to the distortion of the magnitude of the inflow velocity at the detachment point, which propagate along the free streamline in the freestream reference frame.</p></div>","PeriodicalId":795,"journal":{"name":"Theoretical and Computational Fluid Dynamics","volume":"39 6","pages":""},"PeriodicalIF":2.8,"publicationDate":"2025-10-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145406219","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Onset of convective instability in rotating double-diffusive fluids","authors":"Snehashish Sarkar,&nbsp;Santu Hansda,&nbsp;Pinaki Pal","doi":"10.1007/s00162-025-00763-z","DOIUrl":"10.1007/s00162-025-00763-z","url":null,"abstract":"<div><p>This study investigates the onset of convection in a uniformly rotating fluid layer by varying the Taylor number (<span>(textrm{Ta})</span>), solute Rayleigh number (<span>(mathrm {Ra_S})</span>), Prandtl number (<span>(textrm{Pr})</span>), Schmidt number (<span>(textrm{Sc})</span>), and boundary conditions. The control parameters are varied over the ranges <span>(textrm{Ta} in [0, 10^5])</span>, <span>(textrm{Pr} in (0, 10])</span>, <span>(textrm{Sc} in (0, 10^3])</span>, and <span>(mathrm {Ra_S} in [-3 times 10^3, 3 times 10^3])</span>. Using a staggered grid Chebyshev spectral collocation method, the analysis reveals that rotation brings stability to the system and reduces the cell size at the onset of convection. Rotation also suppresses zero critical wave number convection and concavity of stationary neutral stability curve towards the origin under the non-identical temperature and concentration boundary conditions, as discussed by D. A. Nield [“The thermohaline Rayleigh-Jeffreys problem,” <i>J. Fluid Mech.</i> 29(3):545-558, 1967] in the absence of rotation. It is observed that a positive solute Rayleigh number promotes stationary convection, whereas a negative solute Rayleigh number tends to favor an oscillatory onset, depending on the fluid properties. Under no-slip velocity boundaries, three transition regimes are identified: oscillatory-stationary (O-S), stationary (S), and stationary-oscillatory (S-O). In contrast, only stationary convection occurs at onset when water-ethanol is confined between two stress-free plates at fixed rotation rate and concentration gradients. Moreover, reversing the solute boundary conditions does not affect the onset threshold when both plates are perfectly thermally conducting.</p></div>","PeriodicalId":795,"journal":{"name":"Theoretical and Computational Fluid Dynamics","volume":"39 6","pages":""},"PeriodicalIF":2.8,"publicationDate":"2025-10-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145405719","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Dynamical response of a Newtonian fluid interface to mixed oscillatory deformations","authors":"Adrián García-Gutiérrez,&nbsp;Fernando Parra,&nbsp;José Antonio Mayo,&nbsp;Carlos Rubio","doi":"10.1007/s00162-025-00764-y","DOIUrl":"10.1007/s00162-025-00764-y","url":null,"abstract":"<div><p>This study presents a numerical investigation of the dynamic response of a Newtonian fluid interface subjected to mixed oscillatory deformations. A slender cylindrical probe, floating horizontally at a water–air interface and partially submerged by capillary forces, is driven sinusoidally in the direction perpendicular to its axis. The interface exhibits shear, dilatational, and extensional viscosities, and the system is modeled using the finite volume method within the OpenFOAM framework. The governing equations are nondimensionalized and solved for a wide range of Marangoni numbers (<span>(Ma in [1, 10^5])</span>) and dilatational-to-shear viscosity ratios (<span>(Theta in [1, 10^5])</span>). The simulations enable the decomposition of the total interfacial force into its constituent components, revealing distinct regimes dominated by Marangoni, dilatational, or extensional stresses. The results demonstrate the feasibility of isolating these contributions under specific conditions, offering insights into the design and interpretation of interfacial rheometry experiments. The influence of geometric parameters and oscillation characteristics is also explored, confirming the robustness of the observed force dynamics.</p></div>","PeriodicalId":795,"journal":{"name":"Theoretical and Computational Fluid Dynamics","volume":"39 6","pages":""},"PeriodicalIF":2.8,"publicationDate":"2025-10-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s00162-025-00764-y.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145327520","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}