Theoretical and Computational Fluid Dynamics最新文献

{"title":"Input–output study of mode-frequency characteristics in a low-speed axial compressor","authors":"Jiahao Hu,&nbsp;Ruize Xu,&nbsp;Dengke Xu,&nbsp;Xu Dong,&nbsp;Dakun Sun,&nbsp;Xiaofeng Sun","doi":"10.1007/s00162-024-00733-x","DOIUrl":"10.1007/s00162-024-00733-x","url":null,"abstract":"<p>The dynamic characteristics of mode behavior in a low-speed, single-stage axial compressor are crucial for studying linear stall inception. An input–output analysis framework has been established, enabling the introduction of forcing into the compressor system and identifying the most energetic mode. Both standard and compressed input–output analysis are conducted to explore sensitive forcing positions and flow variables, with opposition control employed to suppress energy gain. As throttling progresses, a shift in high energy gain distribution from high-order to first-order circumferential modes is observed, with two distinct branches emerging across the domain of circumferential mode numbers and forcing frequencies. Compressed input–output analysis shows that limiting the forcing range to the shroud, from the inlet to the rotor blade section, is sufficient to excite the energetic mode in the current cases. Subsequently, opposition control is applied at the shroud to suppress energy amplification and modulate stall propensity within these two distinct branches. The results reveal that axial velocity control reduces energy amplification and suppresses perturbation modes related to stall inception. A comprehensive assessment of componentwise energy amplification is conducted, considering various variable forcing. The predicted results indicate that velocity perturbations are the predominant factors influencing the resolvent mode distribution pattern. Moreover, opposition control significantly impacts the critical branch associated with stall inception.</p>","PeriodicalId":795,"journal":{"name":"Theoretical and Computational Fluid Dynamics","volume":"39 1","pages":""},"PeriodicalIF":2.2,"publicationDate":"2024-12-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142826153","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":"Fully convolutional networks for velocity-field predictions based on the wall heat flux in turbulent boundary layers","authors":"Luca Guastoni,&nbsp;Arivazhagan G. Balasubramanian,&nbsp;Firoozeh Foroozan,&nbsp;Alejandro Güemes,&nbsp;Andrea Ianiro,&nbsp;Stefano Discetti,&nbsp;Philipp Schlatter,&nbsp;Hossein Azizpour,&nbsp;Ricardo Vinuesa","doi":"10.1007/s00162-024-00732-y","DOIUrl":"10.1007/s00162-024-00732-y","url":null,"abstract":"<div><p>Fully-convolutional neural networks (FCN) were proven to be effective for predicting the instantaneous state of a fully-developed turbulent flow at different wall-normal locations using quantities measured at the wall. In Guastoni et al. (J Fluid Mech 928:A27, 2021. https://doi.org/10.1017/jfm.2021.812), we focused on wall-shear-stress distributions as input, which are difficult to measure in experiments. In order to overcome this limitation, we introduce a model that can take as input the heat-flux field at the wall from a passive scalar. Four different Prandtl numbers <span>(Pr = nu /alpha = (1,2,4,6))</span> are considered (where <span>(nu )</span> is the kinematic viscosity and <span>(alpha )</span> is the thermal diffusivity of the scalar quantity). A turbulent boundary layer is simulated since accurate heat-flux measurements can be performed in experimental settings: first we train the network on aptly-modified DNS data and then we fine-tune it on the experimental data. Finally, we test our network on experimental data sampled in a water tunnel. These predictions represent the first application of transfer learning on experimental data of neural networks trained on simulations. This paves the way for the implementation of a non-intrusive sensing approach for the flow in practical applications.</p></div>","PeriodicalId":795,"journal":{"name":"Theoretical and Computational Fluid Dynamics","volume":"39 1","pages":""},"PeriodicalIF":2.2,"publicationDate":"2024-12-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s00162-024-00732-y.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142845070","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":"Kinetic description of flow detachment at a smooth micro-step: the near-free-molecular regime","authors":"D. Ben-Adva,&nbsp;G. Tatsios,&nbsp;A. Manela","doi":"10.1007/s00162-024-00728-8","DOIUrl":"10.1007/s00162-024-00728-8","url":null,"abstract":"<div><p>We study the pressure-driven steady gas flow, imposed by temperature or density gradients, over a backward-facing step in a two-dimensional microchannel. Focusing on the near-free-molecular regime of high Knudsen (<span>(textrm{Kn})</span>) numbers, the problem is analyzed asymptotically based on the Bhatnagar, Gross and Krook kinetic model, and supported by numerical Discrete Velocity Method and Direct Simulation Monte Carlo calculations. The wall conditions are formulated using the Maxwell model, superposing specular and diffuse surface conditions. The asymptotic solution contains the leading-order free-molecular description and a first-order integral representation of the near-free-molecular correction. Our results indicate that flow separation at the step can occur at arbitrarily large (yet finite) Knudsen numbers in channels with specular surfaces (i.e., having an accommodation coefficient of <span>(alpha = 0)</span>), driven by temperature differences between the inlet and outlet reservoirs. It is then shown that detachment is significantly suppressed by density variations between reservoirs and partially diffuse surfaces (with <span>(alpha gtrsim 0.3)</span>). While the mass flow rate in a specular channel decreases with decreasing <span>(mathrm {Kngg 1})</span> in a density-driven setup (in line with the Knudsen Paradox), it increases in a temperature-driven flow. The results are obtained for arbitrary differences between the inlet and outlet reservoir equilibrium properties, and are rationalized using the linearized problem formulation.</p></div>","PeriodicalId":795,"journal":{"name":"Theoretical and Computational Fluid Dynamics","volume":"39 1","pages":""},"PeriodicalIF":2.2,"publicationDate":"2024-12-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s00162-024-00728-8.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142798254","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":"A systematic DNS approach to isolate wall-curvature effects in spatially developing boundary layers","authors":"Jason Appelbaum,&nbsp;Markus Kloker,&nbsp;Christoph Wenzel","doi":"10.1007/s00162-024-00729-7","DOIUrl":"10.1007/s00162-024-00729-7","url":null,"abstract":"<div><p>A methodology to numerically assess wall-curvature effects in boundary layers is introduced. Wall curvature, which directly induces streamline curvature, is associated with several changes in boundary-layer flow. By necessity, a local radial pressure gradient emerges to balance mean flow turning. Moreover, a streamwise (wall-tangential) pressure gradient can appear for configurations with non-constant wall curvature or a particular freestream condition; zero pressure gradient is a special case. In laminar concave flow, the Görtler instability and the associated Taylor-Görtler vortices destabilize the flow and promote laminar-turbulent transition, whereas in the fully turbulent regime, unsteady coherent structures formed by the centrifugal instability mechanism dramatically redistribute turbulent shear stress. One difficulty of assessing centrifugal effects on boundary layers is that they often appear simultaneously with other phenomena, such as a streamwise pressure gradient, making their individual evaluation often ambiguous. For numerical studies of transitional and turbulent boundary layers, it is therefore beneficial to understand the interactive nature of such coupled effects for generic configurations. A methodology to do so is presented, and is verified using the case of a subsonic, compressible turbulent boundary layer. Four direct numerical simulations have been computed, forming a <span>(2{times }2)</span> matrix of turbulent boundary-layer states; namely with and without concave wall curvature, each having a zero and a non-zero streamwise-pressure-gradient realization. The setup and accompanying procedures to determine appropriate boundary conditions are discussed, and the methodology is evaluated through analysis of the mean flow fields. Differences in mean flow properties such as wall shear stress and boundary-layer thickness due to either streamwise pressure gradient or wall curvature are shown to be remarkably independent of one another.\u0000</p></div>","PeriodicalId":795,"journal":{"name":"Theoretical and Computational Fluid Dynamics","volume":"39 1","pages":""},"PeriodicalIF":2.2,"publicationDate":"2024-12-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s00162-024-00729-7.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142798439","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":"Loosely coupled under-resolved LES/RANS simulation augmented by sparse near-wall measurement","authors":"Pasha Piroozmand,&nbsp;Oliver Brenner,&nbsp;Patrick Jenny","doi":"10.1007/s00162-024-00725-x","DOIUrl":"10.1007/s00162-024-00725-x","url":null,"abstract":"<p>We investigate scenarios, where only sparse wall shear stress measurements are available, while accurate wall shear stress and velocity profiles are sought. Applying discrete adjoint-based data assimilation, with only near-wall measurements, accurate wall shear stress profiles are achieved at the expense of unrealistic velocity profiles. We therefore add and employ internal reference data generated by performing a relatively cheap hybrid simulation. We modified the dual-mesh hybrid LES/RANS framework recently proposed by Xiao and Jenny (J Comput Phys 231(4):1848–1865, 2012, https://doi.org/10.1016/j.jcp.2011.11.009) by loosely coupling under-resolved LES in the interior with steady RANS near the walls. The framework was developed in OpenFOAM and tested for flow over periodic hills with Re = 10,595. Results show that the devised framework outperforms conventional dual-mesh hybrid LES/RANS and standalone sparse wall-data assimilated RANS models. <b>Graphical abstract</b> Horizontal mean velocity component <span>(U_{1})</span> (top plot) and wall shear stress (friction coefficient <span>(C_{f})</span>) profiles at the lower wall (bottom plot) obtained with S-RANS and assimilation of sparse wall shear stress data</p>","PeriodicalId":795,"journal":{"name":"Theoretical and Computational Fluid Dynamics","volume":"39 1","pages":""},"PeriodicalIF":2.2,"publicationDate":"2024-12-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s00162-024-00725-x.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142790313","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":"Shape diagram determination of a multiphase system in stratified configuration by CFD","authors":"Emma O. Erezuma-de-la-Hoz,&nbsp;Alejandro J. García-Cuéllar,&nbsp;José Luis López-Salinas","doi":"10.1007/s00162-024-00726-w","DOIUrl":"10.1007/s00162-024-00726-w","url":null,"abstract":"<p>Dynamics of a multiphase flow phenomenon involving water (at top), molten metal (at bottom), and vapor (between them), was numerically studied using volume of fluid method. Multiphase flow systems like this are present in a wide range of industrial applications and natural phenomena and are extensively investigated because of their potential to produce energy. This work pays special attention to the interface shape because of its influence on heat transfer rate. An approach, new for systems larger than drop scale, which consists in the construction of an interface shape diagram based on Reynolds (<i>Re</i>) and Bond (<i>Bo</i>) dimensionless numbers is proposed. The presented model demonstrated good capability to discern the governing forces such as viscous, inertial, and surface tension. The most favorable interface shapes for efficient premixing of phases involved were identified. The premixing significance lies in its determining role in steam explosion generation. Moreover, the effect of density ratio and triggering pressure is examined. In addition, Kelvin–Helmholtz and Rayleigh–Taylor fragmentation mechanisms were observed, and their preponderance was analyzed. The results obtained were validated with previous experimental data available in the literature finding good agreement. This proposal aims to provide useful information to enhance our understanding of this phenomenon from a fundamental perspective, applicable to further numerical and experimental studies in different research areas.</p>","PeriodicalId":795,"journal":{"name":"Theoretical and Computational Fluid Dynamics","volume":"39 1","pages":""},"PeriodicalIF":2.2,"publicationDate":"2024-12-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142789327","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":"Exact parallelized dynamic mode decomposition with Hankel matrix for large-scale flow data","authors":"Hiroyuki Asada,&nbsp;Soshi Kawai","doi":"10.1007/s00162-024-00730-0","DOIUrl":"10.1007/s00162-024-00730-0","url":null,"abstract":"<p>An exact parallel algorithm of dynamic mode decomposition (DMD) with Hankel matrices for large-scale flow data is proposed. The proposed algorithm enables the DMD and the Hankel DMD for large-scale data obtained by high-fidelity flow simulations, such as large-eddy simulations or direct numerical simulations using more than a billion grid points, on parallel computations without any approximations. The proposed algorithm completes the computations of the DMD by utilizing block matrices of <span>(X^TXin mathbb {R}^{ktimes k})</span> (where <span>(Xin mathbb {R}^{ntimes k})</span> is a large data matrix obtained by high-fidelity simulations, the number of snapshot data is <span>(n &gt; rsim 10^9)</span>, and the number of snapshots is <span>(klesssim O(10^3))</span>) without any approximations: for example, the singular value decomposition of <i>X</i> is replaced by the eigenvalue decomposition of <span>(X^TX)</span>. Then, the computation of <span>(X^TX)</span> is parallelized by utilizing the domain decomposition often used in flow simulations, which reduces the memory consumption for each parallel process and wall-clock time in the DMD by a factor approximately equal to the number of parallel processes. The parallel computation with communication is performed only for <span>(X^TX)</span>, allowing for high parallel efficiency under massively parallel computations. Furthermore, the proposed exact parallel algorithm is extended to the Hankel DMD without any additional parallel computations, realizing the Hankel DMD of large-scale data collected by over a billion grid points with comparable cost and memory to the DMD without Hankel matrices. Moreover, this study shows that the Hankel DMD, which has been employed to enrich information and augment rank, is advantageous for large-scale high-dimensional data collected by high-fidelity simulations in data reconstruction and predictions of future states (while prior studies have reported such advantages for low-dimensional data). Several numerical experiments using large-scale data, including laminar and turbulent flows around a cylinder and transonic buffeting flow around a full aircraft configuration, demonstrate that (i) the proposed exact parallel algorithm reproduces the existing non-parallelized Hankel DMD, (ii) the Hankel DMD for large-scale data consisting of over a billion grid points is feasible by using the proposed exact parallel algorithm with high parallel efficiency on more than 6 thousand CPU cores, and (iii) the Hankel DMD has advantages for high-dimensional data such as <span>(n &gt; rsim 10^9)</span>.</p>","PeriodicalId":795,"journal":{"name":"Theoretical and Computational Fluid Dynamics","volume":"39 1","pages":""},"PeriodicalIF":2.2,"publicationDate":"2024-12-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s00162-024-00730-0.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142789326","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":"An analytical study of micro-droplet generation in microfluidic double T-junction devices under effects of channel depth ratio using VOF method","authors":"Minh Duc Nguyen,&nbsp;The Khanh Lai,&nbsp;Ich Long Ngo","doi":"10.1007/s00162-024-00720-2","DOIUrl":"10.1007/s00162-024-00720-2","url":null,"abstract":"<p>This paper describes a numerical study on micro-droplet generation in a microfluidic double T-junction device under the effects of channel depth using the Volume-Of-Fluid method. The effects of various parameters such as capillary number (<i>Ca</i>), water fraction (<i>wf</i>), viscosity ratio <span>((beta ))</span>, and particularly the channel depth ratio <span>((varepsilon ))</span> were examined. Consequently, the numerical results match well with the experimental data obtained in the literature. Additionally, the micro-droplet size increases with increasing the channel depth ratio. A phase diagram with four main micro-droplet generation regimes is provided. Particularly, the alternating mode is narrowed in both <i>Ca</i> and <i>wf</i> ranges when increasing <span>(varepsilon )</span>. Moreover, four regimes of micro-droplet generation with the presence of channel depth were first discovered in the present study, and the stable micro-droplet generation regime can be gained within an effective range of both <span>(varepsilon )</span> and <span>(beta )</span>. These results are very useful and valuable for many applications in emulsion production, hydrogel particle generation, and drug delivery synthesis in biomedical treatment.</p>","PeriodicalId":795,"journal":{"name":"Theoretical and Computational Fluid Dynamics","volume":"39 1","pages":""},"PeriodicalIF":2.2,"publicationDate":"2024-11-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142736932","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":"An analysis of the effect of the jet initial conditions on the wavelet separated near-field acoustic pressure","authors":"Stefano Meloni,&nbsp;Roberto Camussi,&nbsp;Christophe Bogey","doi":"10.1007/s00162-024-00727-9","DOIUrl":"10.1007/s00162-024-00727-9","url":null,"abstract":"<div><p>This paper reports a parametric investigation of the effect of the nozzle exhaust initial conditions on the wavelet separated acoustic pressure generated by a single stream compressible jet in its near field from a database obtained by Large-Eddy Simulations of jet flows at M = 0.9 and Re = <span>(10^5)</span>. The nozzle–exit boundary–layer conditions consist of different turbulence intensities for fixed thickness and several thicknesses in laminar conditions. Pressure time series are extracted from virtual probes distributed in the near field of the jets and the acoustic components of the near field pressure are extracted using a wavelet-based procedure able to decontaminate the signals from the hydrodynamic contribution. The reconstructed acoustic time series are analyzed in the frequency domain and in terms of Overall Sound Pressure Level (OASPL). The results show that both the boundary-layer thickness and the turbulence level significantly affect the acoustic pressure in terms of both intensity and directivity. In the laminar case, strong sideline components are observed and strongly depend on the boundary layer thickness. These components clearly appearing in the energy spectra are associated with the Kelvin–Helmholtz instability waves. For large nozzle-exit turbulence intensities, the acoustic field is more uniform and less intense in the sideline direction. On the other hand, the streamwise directivity of the acoustic pressure appears to be strictly correlated to the length of the jet potential core which strongly varies with the initial conditions.</p></div>","PeriodicalId":795,"journal":{"name":"Theoretical and Computational Fluid Dynamics","volume":"39 1","pages":""},"PeriodicalIF":2.2,"publicationDate":"2024-11-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142679861","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":"Analyzing particulate behavior in high-speed, high-altitude conditions through an overlay-based computational approach","authors":"Akhil V. Marayikkottu,&nbsp;Nathaniel K. Myers,&nbsp;Irmak T. Karpuzcu,&nbsp;Deborah A. Levin,&nbsp;Qiong Liu","doi":"10.1007/s00162-024-00724-y","DOIUrl":"10.1007/s00162-024-00724-y","url":null,"abstract":"<div><p>This paper presents an overlay-based one-way coupled Eulerian–Lagrangian computational approach designed to investigate the dynamics of particulate phases in extreme high-speed, high-altitude flight conditions characterized by very low particulate mass loading. Utilizing the Direct Simulation Monte Carlo method to generate accurate gas flow fields, this study explores two canonical hypersonic flow systems. First we focus on the hypersonic flow over a sphere-cone, revealing the formation of dust-free zones for small particulate diameters and describing the particulate interaction with gas shocks. As particulate diameter and flight speed increase, the characteristics of the particulate phase evolve, leading to the emergence of distinctive features such as high particulate concentration bands or regions void of particulates. Subsequently, the investigation considers flow over a double-cone, emphasizing the behavior of particulate phases in separated vortex-dominated systems where particulate-inertia-driven interactions with vortices result in unique particulate-free zones in the vicinity of the primary and secondary vortices. Additionally, the paper addresses the importance of using realistic fractal-like particulate shapes and demonstrates that the shape effect tends to decelerate the fractal aggregates and trap them along the boundaries of the primary vortex. This research contributes to a deeper understanding of particulate phase dynamics in extreme flight conditions, offering insights relevant to aerospace and aerodynamic applications.</p></div>","PeriodicalId":795,"journal":{"name":"Theoretical and Computational Fluid Dynamics","volume":"39 1","pages":""},"PeriodicalIF":2.2,"publicationDate":"2024-11-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142672471","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}